How To...

Engineering Guide

1219'
6' 3' 6'
6' 3' 8'
3'
21.4'

5' 3'

40' 15' 12'

13'

64'
20' 20'

25'

3'
3'
40'

63'

40'
120'

85'
3'
40'

40'

32' 50' 23'

40'

60' 60' 60' 60' 30' 32' 23'

40'

78.5' 13' 3' 331'

75'

19'
40'

40'
120'
125'
40'

40'
587'

75'

20' 20'
222'
40'

11'
29'
45'

60'

12'
40'

80' 80' 80' 80'

3' 6'
97'

45'

16' 30'
40'

68'
3'
24'

9'
40'

17'

18' 25' 3' 6' 10' 10' 10' 10'

31'

50'

86.5' 3' 81.5'

70'
10'10'
42'

6' 3' UNLOADING

ZONE
50'

98.5'
3' 58' 24'
3'
3' 6'

251' 435' 245' 146'

27' 110' 32'

All Grid Conductors Existing Grid Conductors

60’ Metallic Chain-Link Fence
Scale LEGEND and Ground Rods
Buried at 1.5’
Existing Fence Ground Conductor (below/near fence)
New Fence Ground Conductor (below/near fence)
New 4/0 AWG Stranded
Hard-Drawn Copper Conductors
10’ Copper-Clad Steel
Ground Rods (5/8“ diameter) Existing Ground Rods
Gas Pipes

New Grounding System of Substation

This page is intentionally left blank
 HOW TO… Engineering Guide

Large Suburban Substation

Grounding System Analysis:
Measurements & Computer Modeling

2017 Release
 REVISION RECORD

Date Version Number Revision Level

October 1997 1 0

January 1999 7 0

January 2000 8 0

November 2002 10 0

June 2004 11 0

December 2006 13 0

January 2012 14 0

June 2017 16 0

Page iv
 SPECIAL NOTE

As SES software is constantly evolving, with frequently created updates, minor

discrepancies may appear between this How To manual illustrations of the software
interface and the present software version interface. These differences are cosmetic in
nature and do not impact the validity of the guidance and procedures provided herein.
Furthermore, small differences in the reported and plotted numerical values may exist
due to continuous enhancements of the computation algorithms.

Address comments concerning this manual to:

Safe Engineering Services & technologies ltd.

___________________________________________
3055 Blvd. Des Oiseaux, Laval, Québec, Canada, H7L 6E8
Tel.: (450)622-5000 FAX: (450)622-5053
Email: support@sestech.com
Web Site: www.sestech.com

Copyright  1995-2017 Safe Engineering Services & technologies ltd. All rights reserved.
 SUMMARY
Introduction
This study was undertaken in order to evaluate the adequacy of the existing grounding system of
Lakeshore Substation and to provide any new grid designs and other mitigation techniques required
for the substation area (particularly the areas for the new 230 kV/115 kV transformer and the gas
substations). The final design was to limit touch and step voltages to safe levels for personnel within
the substation area, based on up-to-date system data, appropriate measurement techniques and
instrumentation, and state-of-the-art computer modeling methods.
The adequacy of the Lakeshore Substation grounding system during fault conditions has been
studied from an electrical safety point of view, in terms of touch voltages, step voltages and GPR
(ground potential rise) differentials between different parts of the grounding system; an upgrade to
the existing grounding system has been designed to accommodate the presently anticipated fault
current levels and new equipment. This study and subsequent SES measurements revealed that the
electric substation is electrically continuous with the adjacent gas substations and with the nearby
water mains (e.g., via the distribution system neutral). The influences of these structures have been
accounted for in the detailed computer modeling of the grounding system and associated 115 kV
transmission lines performed with the CDEGS software package. Comprehensive field
measurements were made to supply data upon which the computer models are based and to verify
key results.
Soil Resistivity Measurements
Soil resistivity measurements have been made at 3 locations in and around the substation, using
special procedures and equipment to eliminate power system noise and interlead inductive coupling.
Measurements have been made up to 2000 ft spacing between current injection probes, in order to
determine the resistivities of the deeper soil layers which can have a significant influence on the
ground impedance of a grounding system as large as that of Lakeshore Substation. It was found that
on a large scale, a vertically layered soil, with a resistivity of 753 ohm-m to the south-east of the
substation and 200 ohm-m in the vicinity of the substation resulted in an excellent match with
measured apparent ground impedances. On a smaller scale, which is most important for the
computation of touch and step voltages near the substation, measurements suggested horizontally
layered soils, with low resistivities near the surface (on the order of 107 to 209 ohm-m) and higher
resistivities at greater depths (on the order of 317 to 753 ohm-m).
Grounding System Impedance Measurements
The low frequency grounding system impedance of the substation (including all other associated
grounding structures such as transmission line towers, gas substations, water pipes), was determined
to be 0.181 , by measurements made according to the Fall-of-Potential method and subsequent
processing with the CDEGS software; the software indicates the location at which the measurements
best reflect the true ground impedance, based on the soil structure, grounding grid configuration,
positions of surrounding poles and towers, residential water pipes, and position of the test current
return electrode. The 60 Hz grounding system impedance is 0.315  according to the computer
model. Agreement between measured and computed impedances is excellent: the computed low
frequency ground impedance is within 7% of the measured value. This computer modeling showed
that the low measured value must result from interconnections with other structures which were

Page vi
 Summary

initially believed to be isolated from the substation (such as the adjacent gas substations) or simply
not accounted for (such as the nearby water pipes). Prompting by SES resulted in further
measurements which confirmed the existence of such interconnections.
Touch and Step Voltage Measurements
Touch and step voltages were measured at 10 locations within and around the perimeter fence of the
existing part of the electric substation. After extrapolation to worst case fault conditions, the
maximum step voltage during fault conditions was estimated to be 215 V; maximum touch voltages
exceeding 500 V were estimated, particularly near the perimeter fence. Similar values were obtained
from the detailed computer model. While the step voltage is not excessive, the touch voltage exceeds
the safety limit of 381 V by a significant margin with the existing grid design.
Detailed Computer Modeling
The main analysis consisted of computer simulations of a single phase-to-ground fault at one of the
115 kV busses of the substation. The computer models accounted for currents flowing out of the grid
into the static wires of each transmission line and into the nearby water pipes and gas substations,
voltage drops in the grid due to circulating currents, and the effects of soil layering. The static wire
currents were computed from detailed circuit models of the transmission lines, accounting for
inductive coupling between phase conductors and static wires. The grid performance was studied
based on the more conservative soil model derived from the measurements made inside the
substation. Touch voltages, step voltages, longitudinal currents flowing in conductors and ground
potential rise differentials were computed throughout the substation.
Results are presented in graphical form. In particular, touch voltages are represented as shaded areas
of varying intensity on plan view plots of the grounding system.
Overview of Computer Simulation Results
The principal results from the main study are as follows:
 Existing grounding mat impedance, without static wires and water pipes connected (60 Hz):
0.61   3.8
 New grounding mat impedance, without static wires and water pipes connected (60 Hz):
0.51   1.9
 Maximum ground potential rise (for worst case fault scenario): 7.8 kV
 Maximum net fault current injected into earth by grid: 23.7 kA
 Maximum net fault current flowing into substation: 35.0 kA
 Fault current split (static and neutral wires/grid): 17%/84%
 Maximum potential difference between remote parts of new grid: on the order of 1 kV or
higher
 Maximum ANSI/IEEE Std. 80-1986 tolerable touch and step voltages are as follows for the
parameters used in this study (i.e., 0.5-second fault clearing time, 50 kg body weight, X/R
ratio of 20, 3” crushed rock thickness, 107 -m native earth resistivity):
 Maximum safe touch voltage: 191 V (native soil only), 381 V (2,000 -m crushed rock
layer).
 Maximum safe step voltages: 274 V (native soil only), 1033 V (2,000 -m crushed rock
layer).

Page vii
 Summary

 Highest local touch voltage computed anywhere within or immediately outside (within
3.3 feet of the fence) the substation: less than 374 V (for the final grounding system
design).
 The maximum computed step voltage is approximately 156 V, less than the 274 V limit for a
107 -m native earth surface.
Grounding System Design Upgrade
The grounding system in the existing electric substation area has been reinforced and expanded into
the new 230 kV/115 kV transformer area as part of the grounding system design upgrade.
Furthermore, additional conductors have been included in the two gas substations and in the new
unloading zone.
Computer modeling of fault conditions has shown that touch and step voltages throughout the
Lakeshore Substation site, including the two neighboring gas substations and unloading zone,
comply with the applicable ANSI/IEEE Standard 80-1986 limits with this new design, which is
described in Chapter 6 of this report (see Figure 6.7). The design includes a 3” (minimum) thick
layer of crushed rock, with a minimum wet resistivity of 2,000 ohm-m, which must be present
throughout the site, up to a distance of 3.3 ft beyond the perimeter fence.
Recommendations
1. Grounding System Upgrade. It is recommended that the new grounding system design
described in Chapter 6 of this report be implemented. This design includes not only the new
grounding grid conductors and vertical rods shown in Appendix F, but also at least 1 new bare
buried 4/0 copper connection from each piece of equipment and structure to the grounding grid,
within the existing part of the electric substation. The design also includes a 3” thick (minimum)
layer of crushed rock, with a wet resistivity of 2,000 ohm-m (minimum), throughout the site; the
site comprises the electric substation, the two adjacent gas substations on the north and south
sides, and the gas unloading zone on the east side. The crushed rock must extend up to 1 m (i.e.,
3.3 feet) beyond the perimeter fence bounding this site such that a person touching any metallic
structure associated with any of the gas or electric facilities must necessarily be standing on
crushed rock.
This crushed rock layer must be maintained over time. The thinning of the layer and
contamination with sand, earth, grass and other such matter which fills the voids between the
stones with low resistivity material result in a significant lowering of the level of protection
provided by the crushed rock.
2. Perimeter Fence Gates. The presently proposed grounding system design is based on a
maximum reach distance of 1 m (3.28 feet) from the fence line, in order to minimize the extent to
which additional grid conductors must be installed far outside the fence. At some locations, this
will avoid placing grid conductors over gas pipes. To maintain compatibility with this grounding
design, it is important therefore that all gates open inward, rather than outward, except in areas
identifiable in Figure 6.10 where touch voltages are satisfactory throughout the swing region of a
gate opening outward. If it is not possible to ensure inward opening gates everywhere, then the
grounding system and crushed rock layer must be extended outward at these locations.
3. Gas Pipelines Since the various gas station and gas pipeline grounds are solidly connected to the
substation ground, it is recommended that several (at least two) 4/0 insulated copper bonds be
added between the gas station and electric substation grounds to avoid the dependence on the

Page viii
 Summary

existing inadvertent bonds. No potential problems for the cathodic protection systems are
perceived since the existing interconnections between the ground eliminate dangerous potential
differences in this way and no detrimental effects have been reported to SES.
4. Protection of Equipment and Low Voltage Conductors. Based on one 115 kV fault scenario,
it has been determined that potential differences on the order of 1 kV or higher can occur
between remote parts of the grounding grid as a result of circulating currents in the substation’s
grounding system. Equipment connected to insulated (or isolated) low voltage conductors which
are connected to remote parts of the substation may be subjected to high stress voltages as a
result and may cause excessive potential differences if not grounded locally. Additional fault
simulations at representative locations throughout the substation area should be performed in
order to determine the extent of this GPR differential problem so that appropriate protection
levels can be defined for the low voltage equipment and appropriate mitigation designed for
stress voltages as well.
5. Protection of Communications Equipment Connected to Lines Leaving Substation. The
maximum ground potential rise of the substation is estimated to be 7.8 kV. Protection systems
for any communications equipment connected to lines leaving the substation should be rated
above this voltage level. Note that in calculating the required minimum protection level, induced
voltages from power lines running parallel or nearly parallel to communications lines must also
be considered. However, this maximum ground potential rise is only possible if the far end of the
connected equipment is at remote distance. In general however, the communications centre is
relatively close to the substation ( a mile of two) and only a fraction of the full 7. 8 kV GPR is
applicable.
6. Step Voltages Outside the Substation. Step voltages immediately outside the corners of the
grounding system (within a maximum distance of about 7 ft from the grid perimeter, where
surface crushed rock may not be present) slightly exceed the safety limit suggested by
ANSI/IEEE Standard 80. Note, however, that the standard refers to test results indicating that 25
times as much current is required in the foot-to-foot circuit than in the hand-to-foot circuit to
produce the same current in the heart region, suggesting that step voltages must be several times
higher than the ANSI/IEEE Standard 80 limit in order to produce ventricular fibrillation.
If it is desired to strictly comply with the ANSI/IEEE Standard 80 limit, then surface crushed
rock should be extended to partially cover the applicable areas up to a distance of 1m (3.3 feet)
from the outer edge of each area. Specified in more simple terms, this would be achieved by
extending the crushed rock layer an additional 1.2 m from the perimeter fence, for a total width
of 2.2 m from the perimeter fence. Alternative solutions are more intrusive and difficult to
achieve: for example, gradient control wires covering the seven-foot area could be buried at
progressively increasing depths (to be determined); inclined ground rods could also be driven to
accomplish the same result.
7. Transfer Potentials Outside the Substation. The substation grounding system appears to be
electrically interconnected to gas pipelines and to water pipes that serve the local area. These
should be examined to determine the level of transfer voltages to nearby users of these utilities
and to evaluate the need for mitigative measures if any. Such a task requires knowledge of the
structures and conductors buried in the local area.

Page ix
This page is intentionally left blank

Page x
 TABLE OF CONTENTS

Page

CHAPTER 1
INTRODUCTION ................................................................................................................. 1-1
1.1 OBJECTIVE ............................................................................................................................................... 1-1
1.2 SPECIAL PROJECT REQUIREMENTS ................................................................................................... 1-1
1.3 COMPUTER MODELING TOOL ............................................................................................................... 1-2
1.4 ORGANIZATION OF THE MANUAL ........................................................................................................ 1-2
1.5 SOFTWARE NOTE.................................................................................................................................... 1-3
1.6 FILE NAMING CONVENTIONS ................................................................................................................ 1-3
1.7 DEMO EVALUATION ................................................................................................................................ 1-5
1.8 WORKING DIRECTORY ........................................................................................................................... 1-5
1.9 INPUT AND OUTPUT FILES USED IN TUTORIAL ................................................................................. 1-5
CHAPTER 2
SOIL RESISTIVITY MEASUREMENTS & INTERPRETATION.......................................... 2-1
2.1 INTRODUCTION........................................................................................................................................ 2-1
2.2 SOIL RESISTIVITY MEASUREMENT LOCATIONS ................................................................................ 2-2
2.3 MEASUREMENT METHODOLOGY ......................................................................................................... 2-2
2.4 MEASURED RESISTIVITIES .................................................................................................................... 2-5
2.5 INTERPRETATION OF SOIL RESISTIVITY MEASUREMENTS FROM TRAVERSES 1 ....................... 2-5
2.5.1 PREPARATION OF THE RESISTIVITY INPUT FILE .................................................................. 2-7
2.5.1.1 START UP PROCEDURES ........................................................................................... 2-8
2.5.1.2 DATA ENTRY ............................................................................................................... 2-15
2.5.1.3 HOW TO PRODUCE THE RESAP INPUT FILE.......................................................... 2-17
2.5.2 SUBMISSION OF THE RESAP RUN ......................................................................................... 2-17
2.5.3 EXTRACTION OF THE RESULTS FROM RESAP COMPUTATION RESULTS FILES ........... 2-18
2.6 REFINEMENTS OF SOIL MODELS FROM TRAVERSES 1.................................................................. 2-19
2.6.1 FIRST RESAP RUN: FIVE-LAYER SOIL MODEL ..................................................................... 2-20
2.6.1.1 PREPARATION OF RESAP INPUT FILE .................................................................... 2-20
2.6.1.2 SUBMISSION OF RESAP RUN AND EXTRACTION OF RESULTS USING
TOOLBOX .................................................................................................................... 2-21
2.6.2 SECOND RESAP RUN: TWO-LAYER SOIL MODEL ................................................................ 2-21
2.6.2.1 PREPARATION OF RESAP INPUT FILE .................................................................... 2-21
2.6.2.2 SUBMISSION OF RESAP RUN AND EXTRACTION OF RESULTS .......................... 2-22
2.6.3 THIRD RESAP RUN: FOUR-LAYER SOIL MODEL ................................................................... 2-22
2.6.3.1 PREPARATION OF RESAP INPUT FILE .................................................................... 2-22
2.6.3.2 SUBMISSION OF RESAP RUN AND EXTRACTION OF RESULTS .......................... 2-23
2.6.4 FOURTH RESAP RUN: ADJUSTED TWO-LAYER SOIL MODEL ............................................ 2-24

Page xi
 TABLE OF CONTENTS (CONT’D)

Page

2.7 INTERPRETATION OF SOIL RESISTIVITY MEASUREMENTS FROM TRAVERSES 2 & 3 .............. 2-25
CHAPTER 3
GROUND IMPEDANCE MEASUREMENTS & INTERPRETATION .................................. 3-1
3.1 INTRODUCTION ....................................................................................................................................... 3-1
3.2 MEASUREMENT METHODOLOGY ......................................................................................................... 3-1
3.3 MEASURED VALUES .............................................................................................................................. 3-3
3.4 INTERPRETATION OF FALL-OF-POTENTIAL IMPEDANCE MEASUREMENTS ................................ 3-4
3.4.1 PREPARATION OF THE MALZ INPUT FILE .............................................................................. 3-5
3.4.1.1 START UP PROCEDURES ........................................................................................... 3-5
3.4.1.2 DATA ENTRY ................................................................................................................ 3-7
3.4.2 SUBMISSION OF THE MALZ RUN ........................................................................................... 3-18
3.4.2.1 SUBMIT COMPUTATION PROGRAM USING SESCAD ............................................ 3-18
3.4.2.2 SUBMIT COMPUTATION PROGRAM USING CDEGS.............................................. 3-19
3.4.3 EXTRACTION OF THE RESULTS FROM MALZ COMPUTATION RESULTS FILES .............. 3-19
CHAPTER 4
TOUCH VOLTAGE MEASUREMENTS & INTERPRETATION ......................................... 4-1
4.1 INTRODUCTION ....................................................................................................................................... 4-1
4.2 METHODOLOGY ...................................................................................................................................... 4-2
4.3 MEASUREMENT RESULTS ..................................................................................................................... 4-2
CHAPTER 5
GROUND CURRENT DISTRIBUTION ANALYSIS ............................................................ 5-1
5.1 INTRODUCTION ....................................................................................................................................... 5-1
5.2 COMPUTATION OF THE LINE PARAMETERS ...................................................................................... 5-1
5.2.1 PREPARATION OF THE TRALIN INPUT FILE ........................................................................... 5-4
5.2.1.1 START UP PROCEDURES ........................................................................................... 5-4
5.2.1.2 DATA ENTRY ................................................................................................................ 5-5
5.2.1.3 HOW TO PRODUCE THE TRALIN INPUT FILE .......................................................... 5-8
5.2.2 SUBMISSION OF THE TRALIN RUN .......................................................................................... 5-9
5.3 COMPUTATION OF THE FAULT CURRENT DISTRIBUTION ............................................................. 5-10
5.3.1 PREPARATION OF THE SPLITS INPUT FILE.......................................................................... 5-11
5.3.1.1 START UP PROCEDURES ......................................................................................... 5-11
5.3.1.2 DATA ENTRY .............................................................................................................. 5-13
5.3.1.3 HOW TO PRODUCE THE SPLITS INPUT FILE ......................................................... 5-23
5.3.2 SUBMISSION OF THE SPLITS RUN ........................................................................................ 5-24
5.3.3 EXTRACTION OF THE RESULTS FROM SPLITS COMPUTATION RESULTS
FILES .......................................................................................................................................... 5-24

Page xii
 TABLE OF CONTENTS (CONT’D)

Page

CHAPTER 6
PERFORMANCE EVALUATION OF LAKESHORE SUBSTATION .................................. 6-1
6.1 SAFETY CRITERIA ................................................................................................................................... 6-1
6.1.1 TOUCH VOLTAGES ..................................................................................................................... 6-1
6.1.2 STEP VOLTAGES ........................................................................................................................ 6-2
6.1.3 GPR DIFFERENTIALS ................................................................................................................. 6-2
6.1.4 DETERMINING SAFE TOUCH AND STEP VOLTAGES CRITERIA USING CDEGS ................. 6-2
6.1.4.1 START UP PROCEDURES ........................................................................................... 6-3
6.2 COMPUTER MODEL................................................................................................................................. 6-5
6.2.1 MODELING OF THE LAKESHORE SUBSTATION GROUNDING SYSTEM .............................. 6-5
6.2.2 MALZ INPUT FILES ...................................................................................................................... 6-6
6.2.3 COMPUTATION OF TOUCH AND STEP VOLTAGES AT LAKESHORE
SUBSTATION ............................................................................................................................... 6-7
6.2.4 GROUNDING SYSTEM UPGRADE ............................................................................................. 6-9
6.2.5 PREPARATION OF MALZ INPUT FILES ................................................................................... 6-11
6.2.6 SUBMISSION OF MALZ RUNS .................................................................................................. 6-12
6.3 COMPUTATION RESULTS .................................................................................................................... 6-12
6.3.1 EXTRACTING TOUCH AND STEP VOLTAGES USING THE CDEGS OUTPUT
PROCESSOR ............................................................................................................................. 6-12
6.3.1.1 START UP PROCEDURES ......................................................................................... 6-12
6.3.2 TOUCH AND STEP VOLTAGES ................................................................................................ 6-15
6.3.3 GROUND POTENTIAL RISE ...................................................................................................... 6-20
6.3.4 TOUCH VOLTAGES USING A FOUR-LAYER SOIL MODEL ................................................... 6-21
CHAPTER 7
CONCLUSIONS AND RECOMMENDATIONS................................................................... 7-1
7.1 CONCLUSIONS ......................................................................................................................................... 7-1
7.2 RECOMMENDATIONS.............................................................................................................................. 7-3
APPENDIX A
SOIL RESISTIVITY MEASUREMENTS: TABULATED DATA.......................................... A-1
APPENDIX B
FALL-OF-POTENTIAL IMPEDANCE MEASUREMENTS: TABULATED DATA.............. B-1
APPENDIX C
TOUCH, STEP AND LONG REACH VOLTAGE MEASUREMENTS:
TABULATED DATA .......................................................................................................... C-1
APPENDIX D
FAULT CURRENT CONTRIBUTIONS FOR 115 KV BUS FAULT (SINGLE
PHASE TO GROUND) ....................................................................................................... D-1

Page xiii
 TABLE OF CONTENTS (CONT’D)

Page

APPENDIX E
GROUND POTENTIAL RISE, LONGITUDINAL CURRENTS AND TOUCH
VOLTAGES THROUGHOUT LAKESHORE SUBSTATION GROUNDING
SYSTEM DURING 115 KV FAULT WITH CIRCULATING CURRENTS
MODELED.......................................................................................................................... E-1
APPENDIX F
FINAL UPGRADED GROUNDING DESIGN...................................................................... F-1
APPENDIX G
COMMAND INPUT MODE ................................................................................................. G-1

Page xiv
 Chapter 1. Introduction

CHAPTER 1
INTRODUCTION
1.1 OBJECTIVE
This study was undertaken in order to evaluate the adequacy of the existing grounding system of
Lakeshore Substation and to provide any new grid designs and other mitigation techniques required
for the substation area (particularly the areas for the new 230 kV/115 kV transformer and the gas
substations). The final design was to limit touch and step voltages to safe levels for personnel within
the substation area, based on up-to-date system data, appropriate measurement techniques and
instrumentation, and state-of-the-art computer modeling methods.

1.2 SPECIAL PROJECT REQUIREMENTS

Because of the large dimensions of Lakeshore Substation and its proximity to residential areas, it
was recognized that studying the performance of the relatively large grounding system of Lakeshore
Substation adequately would require special techniques, not only for the design calculations, but also
for the field measurements required for the calculations. Note that the grounding grid has dimensions
on the order of 500 ft x 1000 ft. For example:
 In order to obtain soil resistivity data down to the considerable depths which influence the
performance of this large grounding system, it was necessary to inject currents into the earth via
probes spaced over 600 ft apart; this necessitated the use of frequency-selective equipment to
eliminate power frequency noise, with sufficiently powerful sources to generate a measurable
signal. Very low frequency injection currents were used to avoid interlead coupling problems,
which can occur for such large electrode spacings.
 In order to measure the ground impedance of the substation, it was necessary not only to employ
the frequency-selective equipment used for the resistivity measurements, but also to model the
grounding system (including adjacent water pipes determined to be electrically continuous with
the substation and nearby transmission line poles and towers) in a hybrid layered soil structure
obtained from the soil resistivity measurements in order to determine the location at which the
apparent impedance reading represented the true grounding system impedance.
 Conventional modeling methods assume that the grounding grid constitutes an equipotential
structure. For a grounding grid the size of Lakeshore Substation, this assumption is no longer
valid. Indeed potential differences in excess of 10% of the ground potential rise of the grid can
be observed between parts of the electric and gas substation grids. With the water pipes modeled,
these effects become even more pronounced. It was therefore important in this study to use a
modeling tool that could represent these potential differences properly.
 Lakeshore Substation is connected to numerous transmission and distribution lines, some of
whose static/neutral wires are connected to the substation grounding grid. It was important in this
study to use a modeling tool that could accurately compute the current distribution during fault
conditions, rather than making potentially costly conservative assumptions regarding the
percentage of fault current actually injected into the grid. In fact, the software used for this study

Page 1-1
 Chapter 1. Introduction

models in detail each transmission and distribution line whose static/neutral wires are connected
to the substation grounding grid, conductor by conductor, span by span, accounting for magnetic
and capacitive coupling between all phases and static or neutral wires, the ground resistances of
all poles and towers, and the electrical characteristics of all conductors.

1.3 COMPUTER MODELING TOOL

SES’s proprietary CDEGS software package was used for the computer modeling throughout this
project in order to meet the demanding requirements described above. CDEGS was used to model
the field measurements (i.e., soil resistivities, grounding system impedance, and touch voltages) and
interpret the measured data, to compute the distribution of fault current between the transmission
line static wires, distribution line neutral wires, and the substation grounding grid, and to simulate a
representative phase-to-ground fault in the substation in order to compute touch voltages, grid
potentials, and grounding cable current flows throughout the substation.

1.4 ORGANIZATION OF THE MANUAL

In this manual, we will show how to use the RESAP computation module to analyze the soil
resistivity data based on the measurements taken at Lakeshore substation, how to use the TRALIN
and SPLITS modules to compute line parameters and fault current distribution between soil and
other metallic conductor paths and how to use the MALZ module to conduct the grounding analysis
at Lakeshore substation. This manual also illustrates the use of SES’s input and output processors.
Chapter 2 to 4 of this manual describe the field measurements: how they were conducted, the
measured data, the interpreted results, and a discussion of the results. Measurements made were:
 Soil resistivity measurements: one longer traverse to the south-east side of the substation for
detailed information about the soil’s electrical characteristics down to great depths and two
shorter traverses in and around the substation to determine the degree of variation of surface soil
resistivities throughout the area. This key task provided the soil structure constituting the basis
for the remainder of the study (Chapter 2).
 Grounding system impedance measurements using the Fall-of-Potential method. These
measurements provided a means of verifying the precision of the computer model (Chapter 3).
 Touch, step and mesh voltage measurements at 10 locations throughout the substation for
comparison with values obtained from the computer model (Chapter 4).

The interpretations of the measurements in these chapters include how to use RESAP to analyze the
soil resistivity data and how to use MALZ to emulate the Fall-of-Potential measurements and the
touch, step and mesh voltage measurements.

Chapter 5 of this manual describes how to use the TRALIN and SPLITS modules to determine the
fault current distribution (for the fault current simulations) between the transmission line static wires,
distribution line neutral wires, and the substation grounding grid.

Chapter 6 presents the ANSI/IEEE safety criteria applicable to substation grounding, describes the
detailed computer model of the Lakeshore substation grounding grid, presents the fault simulation

Page 1-2
 Chapter 1. Introduction

results in graphical and tabular form and discusses them. Grid potentials, touch voltages, and grid
conductor longitudinal currents are provided in detail. Step-by-step instructions about how to obtain
these results will be illustrated.

In Chapter 7, the conclusions of this study are summarized and the recommendations are presented.

The appendices provide detailed data in graphical and tabular form from the measurements,
measurement interpretation, and fault simulations. Key data provided to SES for this study are also
included.

1.5 SOFTWARE NOTE

This tutorial assumes that the reader is using the Windows version of CDEGS.

1.6 FILE NAMING CONVENTIONS

It is important to know which input and output files are created by the CDEGS software. All CDEGS
input and output files have the following naming convention:

XY_JobID.Fnn

where XY is a two-letter abbreviation corresponding to the name of the program which created the
file or which will read the file as input. The JobID consists of string of characters and numbers that
is used to label all the files produced during a given CDEGS run. This helps identify the
corresponding input, computation, results and plot files. The nn are two digits used in the extension
to indicate the type of file.

The abbreviations used for the various CDEGS modules are as follows:

Application Abbreviation Application Abbreviation

RESAP RS FCDIST FC
MALT MT HIFREQ HI
MALZ MZ FFTSES FT
TRALIN TR SESEnviroPlus TR
SPLITS SP SESShield-3D SD
SESTLC TC ROWCAD RC
SESShield LS SESeBundle BE
GRSPLITS-3D SP CorrCAD CC
AutoGroundDesign AD SESThreshold TH
SESAmpacity AP SESCrossSection XS
SESImpedance FM CSIRPS* CS

* The CSIRPS module is used internally by the graphics and report generating interfaces.

The following four types of files are often used and discussed when a user requests technical support
for the software:

Page 1-3
 Chapter 1. Introduction

The following four types of files are often used and discussed when a user requests technical support
for the software:

 .F05 Command input file (for computation applications programs). This is a text file that can
be opened by any text editor (WordPad or Notepad) and can be modified manually by
experienced users.

 .F09 Computation results file (for computation applications programs). This is a text file that
can be opened by any text editor (WordPad or Notepad).

 .F21 Computation database file (for computation applications programs). This is a binary file
that can only be loaded by the CDEGS software for reports and graphics display.

 .F33 Computation database file (for computation applications programs MALZ and HIFREQ
only). This is a binary file that stores the current distribution to recover.

For further details on CDEGS file naming conventions and JobID, please consult CDEGS Help
under Help | Contents | File Naming Conventions.

Page 1-4
 Chapter 1. Introduction

1.7 DEMO EVALUATION

In order to be able to evaluate SES Software without a license, you should install the software as a
demo. This will give you access to the computed results without extra effort.

In the demo environment, the input and output files of the case studies in this tutorial are already
installed under the SES Software documents subfolder, HowTo; e.g.,
“C:\Users\Public\Documents\SES Software\<version>\HowTo\CDEGS\SUBURBAN”, where
<version> is the version number of SES Software. You must use this default location as the working
directory when the software is installed as a demo.

1.8 WORKING DIRECTORY

A Working Directory is a folder where all input and output files of case studies are stored and
created. If you are doing a demo evaluation, the working directory for this tutorial is already set up
by the installation. If you have a valid SES Software license to use the programs that are covered by
this tutorial, we recommend using the following working directory to follow the tutorial.

<drive>\CDEGS HowTo\Suburban

e.g., C:\CDEGS HowTo\Suburban

1.9 INPUT AND OUTPUT FILES USED IN TUTORIAL

All input and output files used in this tutorial are supplied from the SES Software distribution. When
the software is installed as a demo, the full set of distribution files are available under the default
SES Software documents subfolder, Setup.Z, where “Z” is part of the version number of the
software. Note that the package file, SESXY.EXE, may be unpacked at any time (“X” and “Y” are
part of the version number of the software) if the tutorial is being followed without a demo
installation.

The original files of this tutorial can be found in the distribution under the following subfolders:

Input Files: Examples\Official\HowTo\CDEGS\SUBURBAN\inputs

Output Files: Examples\Official\HowTo\CDEGS\SUBURBAN\outputs

If you prefer to load the input files into the software and simply follow the tutorial, copy all the files
from the inputs subfolder in the distribution to your working directory. The outputs subfolder
contains the precomputed results that can be used if you do not have a valid license. The above
locations can also be used to refresh files in the working directory if you feel the need to do so. Note
that the files found in both the inputs and the outputs subfolders should be copied directly into the
working directory, not into subdirectories.

After the tutorial has been completed, you may wish to explore the other how-to engineering
manuals; they can be accessed from the program shortcut, SES Software X.Y > Documentation >
Manuals. The same manuals can also be retrieved from the SES Software distribution under the
subfolder, PDF\HowTo Manuals.

Page 1-5
This page is intentionally left blank
 Chapter 2. Soil Resistivity Measurements & Interpretation

CHAPTER 2
SOIL RESISTIVITY MEASUREMENTS &
INTERPRETATION
2.1 INTRODUCTION
Soil resistivity measurements constitute the most important step and the basis of any grounding
study. In a study such as this one, involving a large substation grounding system connected to an
extensive system of multigrounded transmission line static wires and residential water pipes, soil
resistivity measurements are required to establish the following:

1. The ground impedance of the substation grounding system.

2. The location where the system ground impedance (including the grounding provided by the
transmission line static wires and residential water pipes) can be measured, using the Fall-
of-Potential method, as will be seen in Chapter 3.
3. Touch and step voltages throughout the substation during various fault scenarios.
4. Transmission line and grounding conductor impedances for current distribution calculations
associated with the interpretation of Fall-of-Potential and touch voltage measurements and
for the modeling of faults.
Soil resistivity measurements are made by injecting current into the earth between two outer
electrodes and measuring the resulting voltage between two potential probes placed between the
current-injection electrodes. When the electrodes are close together, the measured soil resistivity is
indicative of local surface soil characteristics. When the electrodes are far apart, the measured soil
resistivity is indicative of average deep soil characteristics throughout a much larger area. Details on
the measurement procedure are provided later in this chapter.

For a substation the size of Lakeshore, soil resistivities must be measured to great depths in order to
properly characterize the performance of the grounding system. One series of soil resistivity
measurements was therefore made along a long traverse extending up to 1980 ft between current-
injection electrodes (i.e., 660 ft between potential probes), in order to ascertain average soil
resistivities down to depths on the order of 1000 ft, throughout a large area in close proximity to the
substation. Note that this traverse could not be located within the substation due to the distortions in
the measurements that would have been introduced by the grounding grid as soon as the current-
injection electrodes spanned more than one mesh or approached any grid conductor.

In addition, in order to characterize soil resistivities closer to the surface throughout the substation,
soil resistivities were measured along short traverses reaching 405 and 675 ft between current-
injection electrodes, at two sites closer to the substation: one within the substation and the other
outside. In the former case, distortions from the grid were minimized by locating the measurement

Page 2-1
 Chapter 2. Soil Resistivity Measurements & Interpretation

traverse in the soon to be constructed 230 kV/115 kV transformer area, far from any known, bare,
existing buried conductors.

2.2 SOIL RESISTIVITY MEASUREMENT LOCATIONS

Soil resistivity measurements were made at 3 locations in and around the substation, as indicated in
Figure 2.1. Traverse 1 is a long traverse (1980 ft between current probes), which is located in a
cemetery area to the southeast of the substation. Traverses 2 and 3 were chosen in and around the
substation. Traverse 2 is located in the area where the future 230 kV/115 kV transformer will be
installed: the only known conductors near it are coated gas pipelines. Traverse 3 is about 90 ft away
from the substation along a railway track.

Figure 2.1 Traverses of Soil Resistivity Measurements.

2.3 MEASUREMENT METHODOLOGY

All measurements were conducted based on the Wenner 4-pin method, whereby the distances
between all adjacent electrodes are the same.

Special Precautions

Due to the great proximity of the measurement sites to the substation, substantial noise levels at 60
Hz and its harmonics were expected in the measurements, particularly for the large electrode
spacings required for the long traverse. Conventional measurement methods can confound this noise
with the measurement signal, resulting in apparent soil resistivity readings that can be an order of
magnitude or more in excess of the true values.

In order to overcome this problem, SES has designed a measurement methodology that uses
frequency-selective equipment to inject a signal at an adjustable frequency other than 60 Hz into the
earth and then measure only this signal, by filtering out the 60 Hz noise and other frequencies not
associated with the signal. This measurement methodology is described below. With minor
modifications, it is applicable as well to measuring grounding system impedances using the Fall-of-
Potential method, as described in Chapter 3.

Page 2-2
 Chapter 2. Soil Resistivity Measurements & Interpretation

For the present study, a second methodology was also used for the soil resistivity and Fall-of-
Potential measurements, and indeed retained as the primary measurement methodology due to its
superior performance in the Lakeshore Substation environment. This methodology has the
advantages of requiring fewer pieces of equipment (1 instead of 5), thus minimizing set-up time and
chances of equipment failure, and experiencing negligible loss of accuracy at large electrode
spacings due to interlead coupling (i.e., magnetic coupling between the leads injecting current into
the outer electrodes and the leads measuring the voltage between the inner electrodes). This
immunity to interlead coupling results from the low frequency of operation (0.25-1.0 Hz as opposed
to 80 Hz or so for the other equipment). This methodology, however, is less tolerant of high noise
levels (6 V maximum ac noise), which can, however, be mitigated through the use of a voltage
divider circuit. Furthermore, this methodology cannot be used in environments where there is
significant noise in the range of 0.25 to 1.0 Hz.

Methodology 1: Independent Signal Generator and Frequency-Selective Voltmeter

Figure 2.2 and Figure 2.3 show the equipment set-up. Figure 2.2 is a functional block diagram of the
equipment used for the soil resistivity measurements. A variable frequency generator and a
frequency-selective voltmeter (i.e., wave analyzer) tuned to 80 Hz are used to discriminate against
60 Hz noise from the substation.

Figure 2.3 shows the equipment set-up in more detail. It consists of a portable AC power generator
(1-5 kVA, 110/220 V), a variable-frequency power source (250 VA to 1000 VA) powered by the
portable AC generator and capable of generating 80 Hz and 500 Hz signals at voltages on the order
of 140 - 260 V, a battery-powered frequency-selective voltmeter (with a bandwidth resolution of at
least  3 Hz) or spectrum analyzer with FFT display capabilities (i.e., Hewlett-Packard Model
3560A Dynamic Signal Analyzer) and two precision multimeters.

Measurements are made at both 80 Hz and 500 Hz. Differences between these readings indicate the
extent to which inductive coupling of some form is present between the current injection and
potential measurement circuits.

The broadband voltmeter is used to validate the readings from the frequency-selective voltmeter or
digital spectrum analyzer. At short electrode spacings, the readings from the two sets of instruments
should match. At larger electrode spacings, the broadband voltmeter reading should be larger than
that of the frequency-selective voltmeter to the extent that there is noise present.

Methodology 2: SYSCAL Junior Soil Resistivity Tester

The SYSCAL Junior Soil Resistivity Tester has four terminals, two of which are connected to the
outer current-injection electrodes, and two of which are connected to the inner potential probes. The
operator can vary the output voltage of the current-injecting terminals from 50 V to 400 V, as
required, in order to obtain a sufficiently strong signal. The operator can also select one of 3 square-
wave current waveform frequencies (i.e., 0.25 Hz, 0.5 Hz or 1.0 Hz) and any number of
measurement cycles over which apparent resistivities are computed and then averaged. A frequency
of 0.25 Hz is the recommended setting. This was the frequency used for the measurements
conducted at Lakeshore Substation, with a minimum of 7 measurement cycles run for each
resistivity reading taken.

Page 2-3
 Chapter 2. Soil Resistivity Measurements & Interpretation

The instrument measures not only the injected current and resulting voltage between potential
probes, but also the following:
 the self potential (or background noise) SP before the start of the each series of measurements,
which is subtracted from each voltage measured during a given series of measurements;
 the standard deviation Q of the resistivities measured during a series of measurements, as an
indication of the quality of the reading.

Methodology 1: Variable Frequency Power Source and Wave Analyzer

Figure 2.2 Simple Block Diagram of Equipment Used for Soil Resistivity Measurements -
Methodology 1.

Page 2-4
 Chapter 2. Soil Resistivity Measurements & Interpretation

Figure 2.3 Detailed Block Diagram of Equipment Used for Soil Resistivity Measurements -
Methodology 1.

2.4 MEASURED RESISTIVITIES

The measured soil resistivity data is tabulated in Appendix A. Table A.1 presents the data measured
along Traverse 1 to the southeast of the substation. Table A.2 and Table A.3 present data measured
along Traverses 2 and 3, respectively. All the data were measured using Methodology 2.
Methodology 1 was used to verify the measurements made using Methodology 2 at a number of
points, during the measurement process. Since there was excellent agreement between the two sets
of measurements at short to moderate spacings, Methodology 2 was used throughout the
measurements, since Methodology 2 is more rapid and the noise due to interlead coupling at large
spacings is minimized due to the low measurement frequency (0.25 Hz).

As shown in the tables, apparent resistivities were measured using the Wenner arrangement (i.e., the
distances between adjacent electrodes are equal) starting at 1 ft and increasing exponentially to the
maximum electrode spacing, in order to span each traverse efficiently.

2.5 INTERPRETATION OF SOIL RESISTIVITY

MEASUREMENTS FROM TRAVERSES 1
The following data values were entered as input to the RESAP soil resistivity analysis module of the
CDEGS software package:
 Vsignal /Iinject. This represents the apparent resistance measured at each probe spacing.

Page 2-5
 Chapter 2. Soil Resistivity Measurements & Interpretation

 Cpin Depth. This is the depth to which the current injection electrodes were driven into
the earth. This value influences the interpretation of soil resistivities at short electrode
spacings.
 Ppin Depth. This is the depth to which the potential probes were driven into the earth.
This value also influences the interpretation of soil resistivities at short electrode
spacings.
 Pin Spacing. This is the distance between adjacent measurement probes (Wenner
Configuration).

The soil resistivity interpretation module RESAP was used to determine equivalent horizontally
layered soils for the three measurement sites. The characteristics of the equivalent soil structures are
shown in Table 2.1 along with grounding system impedances as computed by the frequency-
dependent grounding module MALZ (see the next chapter). Note that the impedances shown here
were computed for the grounding system of Lakeshore Substation alone (see Figure 2.1), excluding
the grounding systems of the gas substations and pipes, which were not connected to Lakeshore
Substation, according to initially supplied data.

The “RMS Error” in Column 5 of Table 2.1 (computed by RESAP as described in this section)
provides a quantitative indication of the agreement between the measurements and the proposed soil
models. Note that the table shows two equivalent soil structures for each measurement site, namely a
multilayer structure and a two-layer structure. Although the fit of computed to measured soil
resistivities is considerably better when a four-layer soil model is used, the computed grid
impedances corresponding to the two-layer and four-layer soil models are similar (Traverses 1 and
2) or more conservative (Traverse 3). The two-layer soil models in Table 2.1 were therefore used to
perform the analysis of the Fall-of-Potential (FOP) measurements and for the grid design update
modeling. Note that several different soil structures could have been used in this study, including
multilayer structures such as those presented in Table 2.1, which include layers with highly
contrasting resistivities and thicknesses of 1-2 feet. It is unlikely, however, that such sharp
boundaries occur in this way throughout the substation site, particularly after disturbing of the soil
and addition of any backfill by construction, so equivalent two layer soils with uniform soil
resistivities near the surface were used. It was therefore not attempted to perform the study with the
multilayer soil structures. Such an analysis would require performing the entire grounding study with
several different soil structures in order to determine the most appropriate worst-case soil model. As
shown in Table 2.1, depending on the soil models used, the grid impedance varies significantly. This
variation ranges from 0.9  for Traverse 2 to 2.4  for Traverse 1. The Fall-of-Potential impedance
measurement made at Lakeshore Substation was extremely valuable if not essential to help
determine the most appropriate soil model to use to compute the ground impedance required for the
design of the recommended substation grounding and bonding system. Note that both the soil
resistivity and Fall-of-Potential (FOP) measurements were carried out at a low frequency (i.e., 2000
ms pulses or 0.25 Hz).

Page 2-6
 Chapter 2. Soil Resistivity Measurements & Interpretation

Soil Model
Site Layer Resistivity Thickness RMS Error Grid Impedance
(-m) (ft) (%) Magnitude
()Angle
Traverse 1 Top 236.0 4
2nd 3800.0 16
3rd 106.0 32 4.0 2.4361.94
Bottom 1432.0 
Top 208.5 1.82
Bottom 753  20.5 2.4491.38
Traverse 2 Top 75.0 1.12
2nd 640.0 1.12
3rd 14.0 2.24 13.2 0.9113.54
Bottom 309.0 
Top 106.8 23.54
Bottom 317.04  18.3 0.8583.95
Traverse 3 Top 167.0 5
2nd 28.0 2
3rd 5015.0 8 4.6 1.1093.36
Bottom 294.0 
Top 151 11.5
Bottom 487  13.9 1.4062.45

Table 2.1 Horizontally Layered Soil Models at Lakeshore Substation and Corresponding
Grid Impedances.

The following describes the steps to achieve the soil models in Table 2.1. We choose Traverse 1 as
an example to illustrate how to use RESAP to obtain the soil models in Table 2.1.

2.5.1 Preparation of the Resistivity Input File

The soil resistivity interpretation input file can be prepared using one of the two input interface
modules or with a standard text editor such as the one provided with CDEGS. See Appendix G for a
short description of the various input interface modules and the resulting input files and their
structures.

This section describes the Windows CDEGS input session, which is used to generate the SICL (SES
Input Command Language) Command mode compatible input files, (.F05 file extension) described
in Appendix G both of which can be reloaded during subsequent sessions. The most important
features in preparing the data are explained in Section 2.5.1.2, which also contains some hints on
how to avoid common problems with RESAP. The instructions describing how to produce the
Command Mode compatible RESAP input file once the data is entered are given in Section 2.5.1.3.

Page 2-7
 Chapter 2. Soil Resistivity Measurements & Interpretation

2.5.1.1 Start Up Procedures

In the SES Software <Version#> group folder, where <Version#> is the version number of the
software, you should see the icons representing Autogrid Pro, AutoGroundDesign, CDEGS,
Right-of-Way, SESEnviroPlus, SESShield-3D and SESTLC software packages, as well as four
folders. The Documentation folder contains help documents for various utilities and software
packages. The Program Folders provides shortcuts to programs, installation and projects folders.
The System folder allows you to conveniently set up security keys. Various utilities can be found in
the Tools folder. The main function of each software package and utility is described hereafter.

Page 2-8
 Chapter 2. Soil Resistivity Measurements & Interpretation

SOFTWARE PACKAGES

 Autogrid Pro provides a simple, integrated environment for carrying out detailed grounding
studies. This package combines the computational powers of the computation modules RESAP,
MALT and FCDIST with a simple, largely automated interface.

 AutoGroundDesign offers powerful and intelligent functions that help electrical engineers
design safe grounding installations quickly and efficiently. The time devoted to design a safe and
also cost-effective grounding grid is minimized by the use of automation techniques and
appropriate databases. This module can help reduce considerably the time needed to complete a
grounding design.

 CorrCAD tackles a large variety of cathodic protection design tasks and related issues, onshore
and offshore, and can also predict the degree of corrosion control provided by a system. A
typical application for corrosion control includes Impressed Cathodic Current Protection systems
(ICCP) and use of sacrificial anodes in anodic protection systems, where anodic current is
impressed on corroding material to enforce passivation. Another application is to estimate the
effect of stray currents such as those produced by HVDC electrodes or dc rail traction systems on
the corrosion of buried metallic structures. CorrCAD can evaluate the corrosion status of the
structure and help optimize the location and characteristics of the corrosion protective system
(such as ICCP) to minimize stray current interference effects on protected structures such as
pipelines.

 Right-of-Way is a powerful integrated software package for the analysis of electromagnetic

interference between electric power lines and adjacent installations such as pipelines and
communication lines. It is especially designed to simplify and to automate the modeling of
complex right-of-way configurations. The Right-of-Way interface runs the TRALIN and SPLITS
computation modules and several other related components in the background.

 SESEnviroPlus is a sophisticated program that evaluates the environmental impact (radio

interference, audible-noise, corona losses, and electromagnetic fields) of AC, DC or mixed
transmission line systems.

 SESShield-3D is a powerful graphical program for the design and analysis of protective
measures against lightning for substations and electrical networks. Its 3D graphical environment
can be used to model accurately systems with complex geometries.

 SESTLC is a simplified analysis tool useful to quickly estimate the inductive and conductive
electromagnetic interference levels on metallic utility paths such as pipelines and railways
located close to electric lines (and not necessary parallel to them), as well as the magnetic and
electric fields of arbitrary configurations of parallel transmission and distribution lines. It can
also compute line parameters.

 CDEGS is a powerful set of integrated software tools designed to accurately analyze problems
involving grounding, electromagnetic fields, electromagnetic interference including AC/DC
interference mitigation studies and various aspects of cathodic protection and anode bed analysis
with a global perspective, starting literally from the ground up. It consists of eight computation
modules: RESAP, MALT, MALZ, SPLITS, TRALIN, HIFREQ, FCDIST and FFTSES. This is

Page 2-9
 Chapter 2. Soil Resistivity Measurements & Interpretation

the primary interface used to enter data, run computations, and examine results for all software
packages other than Right-of-Way, Autogrid Pro, AutoGroundDesign, SESTLC, SESShield-3D
and SESEnviroPlus. This interface also provides access to the utilities listed below.

CDEGS is accessible via a modern, user-friendly and flexible main interface. A legacy interface,
called CDEGS-Legacy, is also available.

TOOLS

 AutoTransient automates the process required to carry out a transient analysis with the HIFREQ
and FFTSES modules

 CETU simplifies the transfer of Right-of-Way and SPLITS output data to MALZ or HIFREQ. A
typical application is the calculation of conductive interference levels in an AC interference
study.

 F05TextEditor is an enhanced text editor that recognizes the command structure of the module
indicated by the file prefix. The program provides syntax highlighting and a command parameter
identification tooltip to greatly simplify manual editing of an .f05 file.

 FFT21Data extracts data directly from FFTSES’ output database files (file 21) in a spreadsheet-
compatible format or in a format recognized by the SESPLOT utility.

 GraRep is a program that displays and prints graphics or text files. For more information on
GraRep see Chapter 6 of the Utilities Manual or invoke the Windows Help item from the menu
bar.

 GRServer is an advanced output processor which displays, plots, prints, and modifies
configuration and computation results obtained during previous and current CDEGS sessions.

 GRSplits plots the circuit models entered in SPLITS or FCDIST input files. This program
greatly simplifies the task of manipulating, visualizing and checking the components of a
SPLITS or FCDIST circuit.

 GRSplits-3D is a powerful interactive 3D graphical environment that allows you to view and
edit the circuit data contained in SPLITS input files and to simultaneously visualize the
computation results.

 RowCAD is a graphical user interface for the visualization and specification of the geometrical
data of Right-of-Way projects. Its 3D graphical environment can be used to visualize, specify
and edit the path data of Right-of-Way, and to define the electrical properties of those paths.

 SESAmpacity computes the ampacity, the temperature rise or the minimum size of a bare buried
conductor during a fault. It also computes the temperature of bare overhead conductors for a
given current or the current corresponding to a given temperature, accounting for environmental
conditions.

Page 2-10
 Chapter 2. Soil Resistivity Measurements & Interpretation

 SESBat is a utility that allows you to submit several CDEGS computation module runs at once.
The programs can be run with different JobIDs and from different Working Directories.

 SESCAD is a CAD program which allows you to create, modify, and view complex grounding
networks and aboveground metallic structures, in these dimensions. It is a graphical utility for
the development of conductor networks in MALT, MALZ and HIFREQ.

 SESConductorDatabase gives access to the SES Conductor Database. It allows you to view the
electrical properties of conductors in the database, and to add new conductors to the database or
modify their properties.

 SESConverter is a DXF-DWG Converter tool that can be used to import CAD based files to
various SES software package compatible input files or export various SES software package
input command files to CAD files compatible with the DXF or DWG format. The program
allows filtering of data to be imported aided by a 2D viewer of selected data, to avoid excessive
conductor creation in the SES software package compatible files.

 SESCrossSection provides an interactive interface with direct visual system representation for
the specification of conductor characteristics and locations within a conductor path cross-section.
The program allows data specification for eventual use in CorrCAD, Right-of-Way, Cable and
Conductor modes of SESLibrary, SESeBundle, and Circuit, Group and Single modes of the
TRALIN module.

 SESCurveFit is a general curve fitting tool with a special focus on "Polarization curves" used in
CorrCAD. It incorporates a curve digitizer utility as well.

 SESeBundle finds the characteristics of an equivalent single conductor accurately representing a

bundle of conductors, as far as their series impedance is concerned. This utility is particularly
useful to simplify models in modules, such as HIFREQ, where reducing the number of
conductors is important to keep the computational time low.

 SESEnviroPlot is an intuitive Windows application that dynamically displays computation data

produced by the SESEnviroPlus software module.

 SESFcdist is an interactive and flexible interface to prepare and run input files, and view results
from, the FCDIST computation module.

 SESFFT is a Fast Fourier Transform computation module designed to help you automate time
domain (lightning and switching surges) analyses based on frequency domain results obtained
from CDEGS computation modules such as SPLITS, MALZ, and HIFREQ. The forward and
inverse Fast Fourier transformations, the sample selection of the frequency spectrum, and
related reporting and plotting functions have been automated in SESFFT.

 SESGSE rapidly computes the ground resistances of simple grounding systems, such as ground
rods, horizontal wires, plates, rings, etc., in uniform soils. SESGSE also estimates the required
size of such grounding systems to achieve a given ground resistance.

Page 2-11
 Chapter 2. Soil Resistivity Measurements & Interpretation

 SESImpedance computes the internal impedance per unit length of long conductors of arbitrary
geometry and composition, and whose cross-section does not vary over the length of the
conductor. The program uses the Finite Element Method (FEM) for calculating the electrical
characteristics of conductors and is capable of handling conductors of arbitrary shapes and
realistic material properties. The calculations fully account for skin effect, and can be carried out
at low or high frequency.

 SESLibrary allows you to inspect the properties of a large number of components that can be
part of models for many SES Software computation modules. It currently includes a
comprehensive database of conductors as well as several power cables.

 SESPlot provides simple plots from data read from a text file.

 SESPlotViewer is a tool used by SESEnviroPlus for plot rendering.

 SESResap is an interactive and flexible interface to prepare and run input files and view results
from the RESAP computation module.

 SESResultsViewer processes the computation data and results of all computation modules in
CDEGS, offering a complete solution for displaying the plots and reports in an integrated viewer.
It presents a light layout with intuitive organization of its settings that use sensible defaults that,
in turn, allow for a fast configuration of the settings in order to achieve the desired output results.

 SESScript is a script interpreter that adds programming capabilities to SES input files.
SESScript can systematically generate hundreds of files from a single input file containing a
mixture of the SICL command language and scripting code and user-defined parameter ranges
and increments.

 SESShield provides optimum solutions for the protection of transmission lines and substations
against direct lightning strikes and optimizes the location and configuration of shield wires and
masts in order to prevent the exposure of energized conductors, busses and equipment. It can
also perform risk assessment calculations associated with lightning strikes on various structures.

 SESSystemViewer is a powerful 3D graphics rendition software that allows you to visualize the
complete system including the entire network and surrounding soil structure. Furthermore,
computation results are displayed right on the system components.

 SESThreshold is an application for computing threshold limits, as recommended by industry

standards, for touch and step voltages. It is coupled with the Zone Editor application, allowing
zones where different threshold limits are applicable to be defined.

 SESTralin is an interactive and flexible interface to prepare and run input files, and view results
from, the TRALIN computation module.

 SoilModelEditor is a standalone module with an interactive graphical interface that assists in the
creation of soils models for all relevant target SES modules.

Page 2-12
 Chapter 2. Soil Resistivity Measurements & Interpretation

 SoilModelManager is a software tool that automates the selection of soil model structures that
apply during various seasons.

 SoilTransfer utility allows you to transfer the soil model found in several SES files into several
MALT, MALZ or HIFREQ input (F05) files.

 TransposIT is a tool for the analysis of line transpositions on coupled electric power line
circuits. To ensure that voltage unbalance is kept within predefined limits, it allows the user to
determine the optimal number of power line transpositions and their required locations.

 WMFPrint displays and prints WMF files (Windows Metafiles) generated by CDEGS or any
other software.

During this tutorial, for simplicity, we will be using the CDEGS icon to carry out most of the input
and output tasks. We will refer to the other utility modules when appropriate.

In the SES Software group folder, double-click the CDEGS icon to start the CDEGS program. You
will be prompted for a Working Directory and a Current Job ID. Enter the complete path of your
working directory in the Working Directory box (or use the Browse button to find the directory).
Any character string can be used for the Current Job ID – LAK1T is recommended for this part of
this tutorial.

 If the model has not been created for the selected module, the two color bars under the
module icon are red, as shown below.

 If the model for the selected module is only created (a valid F05 file can be found), the left
color bar changes to green (the right color bar still keeps red). You can click Specify icon to
modify the model or click Compute icon to launch the computation. For instance, a MALT
model is created as in the selected one in the JobID list, the color bars and the available
options are shown below.

Page 2-13
 Chapter 2. Soil Resistivity Measurements & Interpretation

 After the model for the selected module is computed (a valid F21 file can be accessed), then
both color bars are green. You can click Specify icon to modify the model, click Compute
icon to relaunch the computation or click Examine icon to view/plot the results. For instance,
both the F05 file and F09 file exist for the selected MALT module in the JobID list, the color
bars and the available options are shown below.

Click the RESAP button located within the CDEGS

toolbar and choose the Specify session mode: the
RESAP screen will appear as shown on the right (but
without the text) and you are now able to input data.

In the following section, it is assumed that the reader is

entering the data as indicated in the instructions. Note
that it is advisable to save your work regularly with the
use of the Save button. The entered data will be saved in
an editable (text) file called RS_LAK1T.F05. Each file can be retrieved at any time with the use of
the Open function located in the application backstage. The same method can be used if a data entry
session has to be interrupted. (Close all active windows to exit the program after saving your data).

Page 2-14
 Chapter 2. Soil Resistivity Measurements & Interpretation

If you intend to enter the data manually, proceed directly to Section 2.5.1.2, otherwise you can
directly open the file “RS_LAK08.F05” copied to the working directory as described in Section 1.9.

2.5.1.2 Data Entry

As shown in Figure G.1 in Appendix G, the RESAP commands are grouped into modules, reflecting
the hierarchical nature of the SES Input Command Language. Each module of Figure G.1 (with the
exception of the OPTION module) is associated to a button in the RESAP screen. The OPTION
module is actually part of the RESAP main screen.

The Help Key (F1) can be used to obtain relevant context-sensitive information when any CDEGS
Input or Output text field is selected.

The data entry field in the Module Description tab allows you to enter comments that will be used
to describe the case to be analyzed in the RESAP module. They are shown in the RESAP output.

If you place your mouse cursor on any comment line and click on it (i.e., focus on the comment line)
then hit the F1 (Help Key) display help text relevant to the Comments text input area will be
displayed.

A run-id LAK1T is entered in the Run-Identification box and the Metric System of Units is
chosen. Focusing on the Run-Identification field and then hitting the F1 key will bring a help text
related to that field.

Go the Measurements panel to enter

the measured apparent resistivities from
Traverse 1. A quick way to enter the
same data, such as probe depth, into
several data fields is to select these
fields first, then type in the data. This
screen also allows you to specify the
method used to gather the data, the type
of measurements, and the results
obtained. Furthermore, it allows you to
immediately plot the results in a
linear/linear or log/linear fashion to
determine the shape of the curve or the
presence of noise in the measurements.
By default, RESAP selects Wenner Method and also selects Account for Probe Depth. The data
are entered into Traverse parameters. The results are automatically plot in the Plots panel.

To start, we will choose a two-layer soil. Click the Computations tab to access the appropriate
screen. Select Horizontal Layers soil type. Select 2 layers for the Number of Soil Layers. By
entering a 0 or blank value in all the applicable fields under Initial Estimates for horizontal soil
model parameters as shown in the Computations screen, you are requesting that the RESAP
program determines suitable initial values to the requested soil characteristics. If for any reason you

Page 2-15
 Chapter 2. Soil Resistivity Measurements & Interpretation

prefer to specify your own values, you should enter valid initial guesses in all the required fields,
otherwise the program assumes its own
choices.
The Computations options allows you
to Lock and/or Unlock the resistivity
and the depth of each layer and to
define the extent of the Computed
Resistivity Traverse. This Computed
Resistivity Traverse option specifies a
traverse along which apparent earth
resistivities are to be computed based
on the equivalent earth model
determined by RESAP. Two values are
to be entered:

1. The number of consecutive electrode spacings for which the computation of apparent resistivity
is to be carried out. Note that the total number of computed points and field measurement points
must not exceed 10,000 and that the default number of computed points is set at 100.

2. The incremental value of the outer-electrode spacing used for the apparent earth resistivity
computations (meters or feet). This value represents the outer-electrode spacing increase between
two consecutive computed points and is normally set at 1.

Please note that the calculations start with a very short electrode spacing. The ratio of the outer-inner
electrode spacing to the inner-inner electrode spacing will be based on the average ratio as
determined from the field measurement data.

The Computations options

allows you to specify the
minimization algorithms and
to control the iterative
minimization process. In this
study, we use the Levenberg-
Marquardt method. There are
only three parameters you should modify when the RMS error between the computed data and
measured data is not satisfied. They are

 Accuracy: This parameter sets the desired RMS error (default value is 0.025).

 Iterations: This parameter sets the total number of iterations (default value is 500).

 Step Size: This parameter specifies the minimum change of RMS error below which the
optimization process will stop. The program will conduct a convergence test by computing the
average RMS error change over the past 25 iterations. The minimization will stop if the averaged
RMS error change is less than the value specified by Step Size command. Decreasing the Step
Size usually improves the fit of the computed soil model to the measured data, but increases the
computation time. The default value of Step Size is 0.0001 (0.01%).

Page 2-16
 Chapter 2. Soil Resistivity Measurements & Interpretation

By clicking on the Advanced options, it

allows you to choose or generate different
filters. By default, RESAP chooses
Standard Filter, which is sufficient for
most practical cases. The High Precision
Filter is sometimes needed when extreme
soil conditions (very large soil resistivity
contrast ratio) encountered and it will greatly increase the computation time. Generating new filters
is seldom needed unless RESAP encounters a missing or corrupted filter database file.

RESAP will terminate the iterative minimization process whenever the desired Accuracy is reached,
or the minimization Step Size is smaller than the threshold value, or the total number of Iterations is
reached.

2.5.1.3 How to Produce the RESAP Input File

At this point, you have completed the preparation of the data using CDEGS: it is ready to be
submitted to the RESAP computation module in the next section.
If you are a licensee of the CDEGS software you will now be able to proceed to Section 2.5.2. Users
of the demo software are not able to process the input file, but are able to peruse all output files
which are already available. Therefore read Section 2.5.2 for reference only. Any attempt to start the
computation modules will result in a message stating that the Computation module is not active.

2.5.2 Submission of the RESAP Run

Click the Compute button to submit and run the model. This does two things:

1. It saves a file under the name RS_LAK1T.F05. Each file can be reread from the Toolbox
using the Open option located in the application backstage. Furthermore, the *.F05 files are
ASCII files you can edit and view at any time.

2. It starts the RESAP computation program.

The RESAP computation module will start and will carry out all requested computations. At
completion, the program will produce two important files: an OUTPUT file (RS_LAK1T.F09) and a
DATABASE file (RS_LAK1T.F21).
The OUTPUT file is an ASCII file, while the DATABASE file is a binary file. Any ERROR or
WARNING messages generated during the RESAP run will appear in the OUTPUT file. You can
view the OUTPUT file by clicking the File Viewer ( ) button in the Output section of the
CDEGS toolbar. You can also use the GraRep utility (See Section 2.5.1.1) to view and edit any
ASCII output files.

The next section examines the computation results using the Examine (Output) Mode of CDEGS.

Depending on your settings, the program may automatically start the output session the moment the
computation program terminates. This is controlled by the option View the output session after

Page 2-17
 Chapter 2. Soil Resistivity Measurements & Interpretation

engineering computations in the “System Settings” window (accessible from the Settings | System
menu item).

2.5.3 Extraction of the Results from RESAP Computation Results

Files
The OUTPUT file contains all the input information and
computation results from your RESAP run.
The DATABASE file is normally used by the CDEGS
Output Session and the SES Interactive Report & Plot
Software processors (such as GraRep) to display the
computation results. In the following, we will give an
example to show how to use the Windows Toolbox
interface to produce the corresponding graphs.
If you have followed the instructions up to this point, the
active JobID should be "LAK1T". We will therefore
extract the results and display the plot on screen. If the
CDEGS-Examine-RESAP screen is not already
visible, click on the (Examine) button in Resap: the
CDEGS-Examine-RESAP screen will appear and you
are now ready to make plots.
Enter a Plot Title (TRAVERSE 1) in order to identify
the plot, select the British radio button from the X-Axis
Units option, and click the Plot/Draw button to obtain a plot of the computed results, as shown in
Figure 2.4. As you may have noticed, the fit between measured and computed results is very poor
suggesting that perhaps a five-layer soil model would be a more adequate choice. The refinement of
the soil model will be discussed in the next section.

Page 2-18
 Chapter 2. Soil Resistivity Measurements & Interpretation

Figure 2.4 Result of Trial RESAP Run Using All of Data Points: Two-Layer Soil Model.

Click the Report button to review

numerical highlights of the results.

You can also send the plot and report to

a file for processing.

Once you are done examining the

results, you can close the CDEGS
Examine window to go back to the
CDEGS startup screen.

2.6 REFINEMENTS OF SOIL MODELS FROM TRAVERSES 1

As shown in Figure 2.4 in the preceding section, the agreement between the measured and computed
apparent resistivity is very poor due to three divergent measurement data points at 30 ft, 100 ft and
660 ft. By examining the shape of the curve, i.e., by following the number of inflection points, we
realize that a five-layer soil model should provide an appropriate fit provided that the three
(possibly) bad data points are removed. This leads to our first RESAP run using a five-layer soil
model.

Page 2-19
 Chapter 2. Soil Resistivity Measurements & Interpretation

2.6.1 First RESAP Run: Five-Layer Soil Model

2.6.1.1 Preparation of RESAP Input File
We first need to choose a Job ID for the first
RESAP run. In this tutorial, we choose LAK1A as
the Job ID. See the following screen:

Click the RESAP button located in the toolbar,

and select Specify in the Session Mode list to
load the RESAP screen.

In the RESAP backstage, click the Open button

and load the file RS_LAKlT.F05 as described in
Section 2.5.1.1. The RESAP screen shown in
Section 2.5.1.1 should appear and you are now
ready to modify RS_LAK1T.F05 to create
RS_LAK1A.F05.

First, change the comments and Run-

Identification according to the following
screen. Click the Measurements tab and
delete the data lines corresponding to 30
ft, 100 ft and 660 ft. Now, click the
Computations tab. Under Number
Layers, enter 5 in the label, as shown on
the screen below.

Page 2-20
 Chapter 2. Soil Resistivity Measurements & Interpretation

You can now return to the RESAP main screen by clicking OK and you have completed the
modification of the data.

2.6.1.2 Submission of RESAP Run and Extraction of Results Using Toolbox

Click the Compute button to exit the RESAP screen and start the RESAP computation module.
A RESAP input file RS_LAK1A.F05 is generated. Printout G.2 shows this file.

After completion of the RESAP run, the results can be extracted by repeating the instruction
described in Section 2.5.3. The following shows the best fit of soil resistivity data using the five-
layer soil model. As shown in Figure 2.5 below, the computed curve fit the measured data very well.
The data in the REPORT screen indicates the resistivities and thicknesses of all layers. The “RMS
Error” in the screen provides a quantitative measure of the agreement between the measurements and
the proposed soil models.

Figure 2.5 Computed Versus Measured Resistivities for Traverse 1: Five-Layer Soil
Model.

2.6.2 Second RESAP Run: Two-Layer Soil Model

2.6.2.1 Preparation of RESAP Input File
The goal of the second RESAP run is to find the best two-layer soil model. Note that it is always a
good idea to find the simplest soil model possible since this will later reduce the computation time
for the grounding analysis. In this tutorial, we choose LAK1B as the Job ID.

Page 2-21
 Chapter 2. Soil Resistivity Measurements & Interpretation

The steps to generate new RS_LAK1B.F05 file from RS_LAK1A.F05 are very similar to those used
to create the RS_LAK1A.F05 file from RS_LAK1T.F05, which are described in the preceding
section. As shown in Printout G.3, the only difference between RS_LAK1B.F05 and
RS_LAK1A.F05 is the number of layers in the SOIL-TYPE module.

2.6.2.2 Submission of RESAP Run and Extraction of Results

Start the RESAP computation module by clicking the Compute button in the RESAP screen.
After completion of the RESAP run, the results can be extracted by repeating the instruction
described in Section 2.5.3. The following results compare the measured resistivities with those
computed from a two-layer soil structures. Figure 2.6 shows that the agreement between the
computed curves and the measured data is good for short spacings and constitutes an averaging of
the larger spacing readings. The REPORT file screen lists the attributes of each layer.

Figure 2.6 Computed Versus Measured Resistivities for Traverse 1: Two-Layer Soil
Model.

2.6.3 Third RESAP Run: Four-Layer Soil Model

2.6.3.1 Preparation of RESAP Input File
The five-layer soil model and two-layer model are obtained by simply specifying the number of
layers in the RESAP runs. From the table in Table 2.1, we can create the four-layer soil defined in
Table 2.2 by eliminating the very thin third layer defined by the five-layer soil model and expect that
the RMS Error will not change too much.

Page 2-22
 Chapter 2. Soil Resistivity Measurements & Interpretation

Four-Layer Soil Model

Layer Resistivity (-m) Thickness (ft)
Top 236.0 4.0
2nd 3800.0 16.0
3rd 106.0 32.0
Bottom 1432.0 

Table 2.2 A Four-Layer Soil Model Deduced From the Five-Layer Soil Model after the
First RESAP Run.

The resistivity of the second layer was reduced to compensate for the low resistivity of the third
layer that was eliminated. The thickness of each layer is also adjusted such that their thicknesses are
multiples of a base thickness, which is 4’ in this case. A reduction in the number of layers along the
thickness adjustment will accelerate the computation for the grounding analysis that will be
conducted next using the MALZ module of the CDEGS software package.

For a known soil model, the agreement between the measured and computed resistivity can be
checked quickly using the LOCK feature available in RESAP. With the LOCK function in RESAP,
you can specify which layers’ parameters are fixed, and which are optimized.

In this tutorial, LAK1C is chosen as the Job ID. By following the instructions given in Section 2.5.1,
we can create RS_LAK1C.F05 from RS_LAK1A.F05. The soil model in Table 2.1 is entered in the
SOIL-TYPE module. This soil model is locked by selecting the Lock All option button in the
RESAP (Computation) screen. The input file RS_LAK1C.F05 is shown in Printout G.4.

2.6.3.2 Submission of RESAP Run and Extraction of Results

Start the RESAP computation module by clicking the Compute in the RESAP screen. After
completion of the RESAP run, the results can be extracted by repeating the instruction described in
Section 2.5.3. Figure 2.7 indicates that the computed curve still fits the measured data very well. The
RMS error is only increased slightly from 3.7 % to 4.0%.

Page 2-23
 Chapter 2. Soil Resistivity Measurements & Interpretation

Figure 2.7 Computed Versus Measured Resistivities for Traverse 1: Four-Layer Soil
Model.

2.6.4 Fourth RESAP Run: Adjusted Two-Layer Soil Model

The two-layer soil model shown below is constructed from the four-layer soil model in Table 2.2
and the two-layer soil model obtained in Section 2.6.2 by a grid impedance matching method
described as follows. Assume the grid impedance using the four-layer soil model is Z; we want to
construct a two-layer soil model that will give the same grid impedance Z. If the grid impedance
using the two-layer soil model in Section 2.6.2 is Z and if we assume that Z is mainly influenced by
the bottom layer, then the soil resistivity of the bottom layer of the new two-layer soil model will be
Z 2.439
874 .764   874 .764   753 (-m)
Z 2.833
The computed grid impedance using the new two-layer soil model is 2.439 , as shown in Table 2.1.

Two-Layer Soil Model

Layer Resistivity (-m) Thickness (ft)
Top 208.5 1.82
Bottom 753.0 

Table 2.3 A Two-Layer Soil Model Constructed by Matching Grid Impedance.

Page 2-24
 Chapter 2. Soil Resistivity Measurements & Interpretation

Figure 2.8 Computed Versus Measured Resistivities for Traverse 1: Adjusted Two-
Layer Soil Model.

2.7 INTERPRETATION OF SOIL RESISTIVITY

MEASUREMENTS FROM TRAVERSES 2 & 3
The interpretation of the soil resistivity measurements for Traverses 2 and 3 can be done similarly.
We first simply specify the number of layers for the RESAP runs to obtain the best fit. Next, the best
fit soil models are simplified manually without increasing the RMS Error significantly to create soil
models which will accelerate the MALZ runs for the grounding analysis (by insuring that the
thicknesses of all layers are exact multiples of a base value). No data points were discarded for
Traverses 2 and 3. For Traverse 2, the four-layer soil model in Figure 2.11 is similar to the best-fit
soil model in Figure 2.9 except that 1.12 m is used as a base layer thickness. A similar approach is
used for the four-layer soil model in Figure 2.14 for Traverse 3. The soil resistivity of the bottom
layer in the two-layer soil model of Figure 2.15 is lowered to 487 -m, which corresponds to the
measured resistivity at 100 ft spacing. The input files for Figure 2.9 to Figure 2.11 are
RS_LAK2A.F05, RS_LAK2B.F05 and RS_LAK2C.F05, respectively. The input files for Figure
2.12 to Figure 2.15 are RS_LAK3A.F05, RS_LAK3B.F05, RS_LAK3C.F05 and RS_LAK3D.F05.

Page 2-25
 Chapter 2. Soil Resistivity Measurements & Interpretation

Figure 2.9 Computed Versus Measured Resistivities for Traverse 2: Four-Layer Soil
Model (RS_LAK2A.F05).

Figure 2.10 Computed Versus Measured Resistivities for Traverse 2: Two-Layer Soil
Model (RS_LAK2B.F05).

Page 2-26
 Chapter 2. Soil Resistivity Measurements & Interpretation

Figure 2.11 Computed Versus Measured Resistivities for Traverse 2: Improved Four-Layer
Soil Model (RS_LAK2C.F05).

Figure 2.12 Computed Versus Measured Resistivities for Traverse 3: Four-Layer Soil
Model (RS_LAK3A.F05).

Page 2-27
 Chapter 2. Soil Resistivity Measurements & Interpretation

Figure 2.13 Computed Versus Measured Resistivities for Traverse 3: Two-Layer Soil
Model (RS_LAK3B.F05).

Figure 2.14 Computed Versus Measured Resistivities for Traverse 3: Adjusted Four-Layer
Soil Model (RS_LAK3C.F05).

Page 2-28
 Chapter 2. Soil Resistivity Measurements & Interpretation

Figure 2.15 Computed Versus Measured Resistivities for Traverse 3: Final Two-Layer Soil
Model (RS_LAK3D.F05).

Page 2-29
 Chapter 3. Ground Impedance Measurements & Interpretation

CHAPTER 3
GROUND IMPEDANCE MEASUREMENTS &
INTERPRETATION
3.1 INTRODUCTION
The Lakeshore Substation grounding system ground impedance was measured using the Fall-of-
Potential method. This measurement provides a means of assessing the accuracy of the computer
model of the system.

Note that the computer model of the grounding system consists of three principal components:
 Substation Grounding Grid. The most approximate part of this component (or any typical
grounding grid model) is the soil structure;
 Multigrounded Network of Transmission Line Static Wires. The most approximate part
of this component is the estimated tower and pole ground resistances.
 Nearby Residential Water Pipes. The most approximate part of this model is the total
length of water pipes to be modeled.

All of these elements provide low impedance paths to ground for fault current (or test currents
injected into the substation’s grounding grid) and must therefore be considered in order to correctly
estimate the effective impedance to ground of the substation’s grid.

3.2 MEASUREMENT METHODOLOGY

The Fall-of-Potential method was used to measure the impedance of the grounding system of
Lakeshore Substation. This method is similar to the Wenner method used to make the soil resistivity
measurements; the same frequency-selective equipment is required to mitigate the effects of power
system noise, which can otherwise quickly drown out the sought-after signal.

Figure 3.1 and Figure 3.2 show the equipment setup used for the Fall-of-Potential measurement.
Equipment in both Methodologies 1 and 2 were used for the measurement. The measurement
principle for both circuits is the same: only the instruments (voltage source, voltmeter and ammeter)
are different.

Page 3-1
 Chapter 3. Ground Impedance Measurements & Interpretation

Figure 3.1 Detailed Block Diagram of Equipment (Methodology 1) Used for the Fall-of-
Potential Measurements

Figure 3.2 Detailed Block Diagram of Equipment (Methodology 2) Used for Fall-of-Potential
Measurements

Page 3-2
 Chapter 3. Ground Impedance Measurements & Interpretation

As shown in Figure 3.1 and Figure 3.2, a current is injected from an independent variable-frequency
sinusoidal power source (Methodology 1) or the low frequency, square wave voltage source within
the SYSCAL Junior Resistivity Tester (Methodology 2), between the substation’s grounding grid
and a remote return electrode. In Methodology 1, a frequency-selective voltmeter tuned to the same
frequency as the power source or a dynamic signal analyzer measures the potential difference
between the grounding grid and a potential probe; the latter is placed at a series of locations,
beginning close to the grid and ending near the return electrode, moving along a set of 10 points
marked in Figure 3.1 and Figure 3.2 (these locations are shown to scale in Figure 3.3). In
Methodology 2, the voltage is measured by the voltmeter built in the SYSCAL Junior Soil
Resistivity Tester. Since the SYSCAL Junior Soil Resistivity Tester cannot measure voltages
exceeding 6 Volts, a voltage divider, as shown in Figure 3.2, was used for the last 5 locations (near
the return electrode), during which background noise levels were large. A multiplier of 11.13
 1.04  0.1027 
  is used to scale these voltages.
 0.1027 

The voltage read by the voltmeter VAC divided by the current injected into the grid (as read by the
VAB
ammeter in Methodology 1 or obtained by in Methodology 2) is the so-called “apparent
1.01
resistance”, which can be plotted versus distance of the potential probe from the grid. If the return
electrode is sufficiently distant from the grid, then a plateau is obtained on the graph, representing
the impedance of the grounding system. In theory, a plateau or horizontal line will never occur and
the Fall-of-Potential line has an upward slope. In practice, however, if the probe is placed far enough
from the grounding grid and the return probe, the rate of change on the Fall-of-Potential curve is
very small. Furthermore, by modeling the grounding system and associated transmission line static
wire system in the soil structure determined from the soil resistivity measurements, it is possible to
determine the probe position at which the measured apparent impedance will represent the actual
grounding system impedance. In this way, even if no plateau is obtained (as often occurs in
practice), the grounding system impedance can be determined from the measurements.

As Figure 3.1 and Figure 3.2 show, the remote return electrode was placed at a distance of 3349 ft
from the corner of the grounding grid where one of the current injection leads was connected. The
potential probe was successively placed at the 10 locations indicated in Figure 3.3.

3.3 MEASURED VALUES

Table B.1 in Appendix B presents the results of the Fall-of-Potential measurements made using the
SYSCAL Junior Soil Resistivity Tester. Apparent impedances were measured at 0.25 Hz, yielding
essentially the DC resistance of the substation grounding grid and other associated grounding. The
computer modeling of the grid was performed initially at low frequencies for validation with this
value; 60 Hz was subsequently used to compute the grid’s AC impedance. An attempt was also
made to measure the AC impedance directly (at a frequency of 80 Hz, which is representative of
power system frequency) using Methodology 1. Because of the obstacles along the first 2000 ft of
the traverse, however, the leads connected to the voltmeter could not be laid systematically at a large
constant distance from the current injection leads (within the period allotted for the measurements);
as a result, interlead coupling rendered the 80 Hz values measured by this method too noisy to be

Page 3-3
 Chapter 3. Ground Impedance Measurements & Interpretation

used. The Fall-of-Potential impedance measurements were therefore completed solely at 0.25 Hz
using the SYSCAL Junior Soil Resistivity Tester, which yielded excellent results.

3.4 INTERPRETATION OF FALL-OF-POTENTIAL IMPEDANCE

MEASUREMENTS
At the beginning of the project, SES was told that the gas and water supply grounding systems were
isolated from the electric substation grounding systems. Early during the conductor modeling phase,
it became clear that the computed results were differing from the measured ones because of wrong
information concerning interconnected grounds. It was therefore suspected that the grounding
system of the gas substations, gas pipes and water pipes, including those of the adjacent residential
areas were all interconnected to the electrical substation ground, directly or via the distribution line
neutrals. This was confirmed later by measurements conducted at the Lakeshore Substation.

The computed 60 Hz grounding system impedance (including structures connected to the static wires
and nearby residential water pipes), as seen from a current injection point at the center of Lakeshore
Substation, was determined to be 0.282 + j0.140  (0.315  26.4). The following describes the
steps that led to this value.

Figure 3.3 shows the measurement traverse that consists of 10 points.

Figure 3.3 Traverse of Fall-of-Potential Measurements

The FOP measurements were simulated using the MALZ program. The two-layer soil models in
Table 2.1 were initially used to conduct the simulations. The computed grounding impedances were
obtained by injecting a current at a location close to the center of Lakeshore Substation. We first
assumed the grounding system to consist of the grounding system of Lakeshore (electrical)

Page 3-4
 Chapter 3. Ground Impedance Measurements & Interpretation

Substation, with the grounding systems of the nearby gas substations included in the computer
model, but not connected to Lakeshore. The gas pipes at the west and east sides of the electric
substation were also modeled, but assumed not connected electrically to the gas substation grids.
Detailed descriptions of the grounding system modeling of Lakeshore Substation, the gas substations
and nearby pipes will be given in Chapter 6.

3.4.1 Preparation of the MALZ Input File

This section describes in detail how to prepare the MALZ input file (.F05 extension) using the
SESCAD program. The SESCAD program allows you to create, modify, and view complex
grounding networks and aboveground metallic structures visually, in three dimensions.

Note that MALZ input files can also be prepared using the Command Input Mode (see Appendix
G).

The required MALZ input file MZ_FGD1D.F05 corresponds to the initial grounding system of
Lakeshore substation. The two-layer soil model from Traverse 1 is used. The following provide step-
by-step instructions on how to create this input file, how to submit the MALZ run and how to obtain
the computed Fall-of-Potential curve.

The most important features in preparing the data in SESCAD are explained in Section 3.4.1.2,
which also describes some tricks on how to avoid common input problems.

3.4.1.1 Start Up Procedures

This step is identical to the one already described in Section 2.5.1.1. In the SES Software group
folder, double-click the CDEGS icon to start the CDEGS program. You will be prompted for a
Working Directory and a Current Job ID. Enter the complete path of your working directory in
the Working Directory field (or use the Browse button to find the directory). Any character string
can be used for the Current Job ID – FGD1D is recommended for this part of this tutorial.

Page 3-5
 Chapter 3. Ground Impedance Measurements & Interpretation

Click on the MALZ icon and select the Specify mode.

Select the SESCAD icon, and the following SESCAD
screen will appear.

As illustrated in Section 1.6, the abbreviation “MZ” means

that this is a MALZ input file.

In the following section, it is assumed that the reader is

entering the data as indicated in the instructions. Note that
it is advisable to save your work regularly with the use of
the Save Document button. This file can be retrieved at
any time by selecting Open Document… under the File
menu.
Click here to
If you intend to enter the data manually, proceed directly start SESCAD.
to Section 3.4.1.2, otherwise, you can directly open the file
“MZ_FZG1D.F05” copied to the working directory as
described in Section 1.9.

Page 3-6
 Chapter 3. Ground Impedance Measurements & Interpretation

3.4.1.2 Data Entry

Step 1. Define a Run ID and System of Units: Under the
Define | Units and Other Settings… menu in the
SESCAD window. In the Case Description block of
this window, you can enter comment lines that are used
to describe the case. These are echoed in the MALZ
output (.F09 file). In this tutorial,
“FOP_LAK1D_GRID_ALONE” is entered under the
Specify option of Run ID, and the British Systems of
Units is chosen. Note that a Run ID is different from
the Job ID. The run-id is a string that is used to
identify plots, whereas the JobID is simply part of the
file names.

Step 2. Define Test Frequency: The test frequency in this

study is 0.25 Hz. In order to define
this value, select the Define |
Computation Settings… menu item
and enter the values as shown in the
above screen.

Step 3. Define Soil Model: Under the Define

menu in the SESCAD window,
select Soil Model to call the soil
structure dialog. MALZ supports
a number of soil models. The soil
type is defined by selecting
Horizontal – 2 Layer with
Multi-Layer Method. The data
entry fields in the Soil
Characteristics block allow you
to define the properties of the air
and earth. In this example, a two-
layer soil model from Traverse 1
(see Table 2.1) is entered as in the
screen. Click OK to return to the
SESCAD main screen.

Page 3-7
 Chapter 3. Ground Impedance Measurements & Interpretation

We will now proceed with the description of an initial model of the grounding system (see Figure
3.4 (a)) in the area defined by the property line of the Lakeshore substation. As described earlier, the
initial model includes the grounding system of the Lakeshore (electrical) substation and gas
substation without nearby overhead static wires. The Lakeshore substation and gas substation were
assumed not connected.

Figure 3.4 (a) Grounding System of Lakeshore Substation. (b) Final Modeling of Grounding
System of Lakeshore Substation (Including Water Pipes).

Page 3-8
 Chapter 3. Ground Impedance Measurements & Interpretation

Step 4. Define Conductor Types: The grounding system and its energization are defined in
the Define menu. Five types of conductors are encountered in this study. Conductor
Type No. 0 is a default conductor that is pure copper (if not specified otherwise).
Conductor types No. 2, 3 and 4 define the 4, 12 and 10 gas pipes, respectively,
while Conductor Type No. 5 defines the 3 (assumed) water pipes. These five
conductor types are specified by clicking on the Define | Conductor Types menu
item and entering the data, which includes the resistivity, permeability and internal
radius of the conductor as shown in the Conductor Types screen.

Step 5. Define Coating Types: The coating type for the gas pipe conductors is specified in
the Define | Coating Types menu. In this study, a “perfect” coating (i.e., a Coating
Type of -1) is applied to the pipeline. This coating corresponds to 0.003 ft of a very
high resistivity material. Its properties cannot be redefined. Now that the properties of
the conductors and their coating have been defined, click OK to return to the
SESCAD screen.

Step 6. Define Energizations: Two

different energizations are used. A
nominal current of 1000 A is used
as the test current discharged into
the grid during the Fall-of-
Potential measurements. This
current is collected by a return
electrode. The magnitude of the
current 1000 A is chosen arbitrarily

Page 3-9
 Chapter 3. Ground Impedance Measurements & Interpretation

since we are computing the apparent resistance (a value of 1 A could have been
selected as well). The energizations are defined by clicking on the Define |
Energization Types menu item. The real and imaginary parts of the currents are
entered in the data entry field in the above screen. Although you can select any of the
specified buses as a reference, it is usually a good idea to choose the Last Bus as the
Reference Bus to keep the one-to-one correspondence between the bus number and
bus name. Note that Source SES 2 is specifically entered as the last bus. By default
the last bus specified in the energization grid becomes the Reference Bus whose GPR
serves as a reference value in the output (see Section 3.4.3 next). Once the data is
entered, click OK to return to the SESCAD screen.

With the conductor type, coating type and energization type specified, the conductor networks and
current energization can now be defined by selecting the Edit | Create Object menu item.

For example, a 478’ long conductor, which extends from Xs=3’ to Xp=481’ and is at 1.5’ below
earth surface, can be defined in the following screen by selecting the Edit | Create Object | Single
Conductor menu item. The coordinates (Xs,Ys,Zs) specify the origin of the conductor and
(Xp,Yp,Zp) specify its end. The characteristics of conductors and their energizations are assigned by
clicking on Characteristics. The radius for 4/0 conductor is 0.02’. The desired number of segment
subdivision is defined in Subdivision (a 0 or 1 indicate that no further subdivision of the conductor
is required). The negative number (pointer) -1 under Lead Type indicates that this conductor is not
energized directly by a current source. The Conductor Type 0 selects the default material type for
this conductor, i.e., a bare copper. The Coating Type 0 selects the first coating type, i.e., no coating.
The Energization 0 means that this conductor is not connected to a current energization bus. Do not
click Apply at this stage; as we will import the conductor data from .DXF files later. Click Cancel
and Close to return to SESCAD.

By using the same method, we can create the conductors which form the conductor loop 3’ inside the
fence perimeter of the existing Lakeshore substation. In this study, there are 257 conductors in the
initial design, so it requires a lot of work to create the conductors one by one. However, in practice,
once the origin of the coordinate system has been defined, the coordinates of all the conductors in
the grounding system can be determined from the drawing provided to SES (note that the origin of
the coordinates system is set at one corner of the fence). At this stage, it is possible to directly obtain
the grid configuration from a DXF compatible CAD drawing system. However, users need to pay

Page 3-10
 Chapter 3. Ground Impedance Measurements & Interpretation

attention to the discrepancies between SESCAD and AutoCAD. Firstly, when importing a DXF file
into SESCAD, a default conductor radius will be assigned to all conductors, so all the conductors
will have the same radius. Secondly, AutoCAD only has the geometric information; it does not have
the characteristics of the conductors (e.g., conductor type, coating type, and subdivision). And
thirdly, the current version of SESCAD does not recognize the group information generated from
AutoCAD. As a result, after importing a drawing from a DXF file, you will still need to modify the
conductors one by one, and this requires a lot of extra work if the grounding system is complicated.

One way to resolve this issue is to use the Color/Radius Mapping feature in SESCAD; namely, we
can use the mapping between colors in AutoCAD and radii in SESCAD. (An alternative solution,
which imports the drawing group by group, will be presented later.) Specifically, when a drawing is
created in AutoCAD, the user can assign each conductor group (which is distinguished by its radius)
with a color. In this initial study, an AutoCAD drawing file MZ_FGD1D.DWG is provided as an
example; this drawing has six colors (six different radii), as shown in the following table.

Conductor Group Number of Conductors Radius (ft) Color Index Color

Grid 142 0.02 1 Red

Rod 92 0.026 2 Yellow
Tower 16 0.0417 3 Green
4” Pipe 4 0.1845 4 Cyan
12” Pipe 1 0.53125 5 Blue
10” Pipe 1 0.4479 6 Magenta

Table 3.1 Color/Radius Mapping.

After assigning each conductor group with a color in AutoCAD, we can export it as a DXF file. This
DXF file (MZ_FGD1D.DXF) is ready to be imported into SESCAD.

Step 7. Import DXF File Representing Grounding System and Assigning Conductor
Radius: In SESCAD, select the File | Import menu and choose the file
MZ_FGD1D.DXF. Note that you can click the Options button to ensure that the
Show the DXF Import Options dialog option is checked.

Page 3-11
 Chapter 3. Ground Impedance Measurements & Interpretation

Click OK and the DXF Import Filter window will appear. Click on the
Color/Radius Mapping button, a Color To Radius Map window will appear. Here
we input the color index and its corresponding radius, as shown below.

Note that the color index numbering here must correspond to the same color index
number in AutoCAD. Click the OK button and you will see a brief report of the
number of the conductors being imported.

All the conductors are imported as one group (Make sure that Edit | Use Group
Information is checked). All properties have the default values, except for the radii
which have been specified through color/radius mapping when we import the data. In
the following, we will define other properties of these conductors.

Page 3-12
 Chapter 3. Ground Impedance Measurements & Interpretation

Step 8. Define Grounding Grid Conductors: With

the conductors still selected, select the Edit |
Ungroup menu item. This ungroups all
conductors. Next we will re-group conductors
creating one group per radius. In order to select
the conductors with a specific radius, we need
to use filter. Select Display | Filter | Radius or
click on the Filter by Radius button at the
bottom of the SESCAD window, and the
following filter legend will appear. (If it does
not appear, select Display | Filter | Show Legend or click on the Show Legend
button at the bottom.)

This legend distinguishes the conductors by their radius

(Value) and shows the numbers of the conductors (Count).
With the 0.02” conductors selected (as shown in the above
filter legend), select Display | Filter | Select Filtered
Objects or click on the Selected Filtered Objects button
at the bottom of the SESCAD window.

This procedure will select all the conductors with a 0.02”

radius, i.e., the conductors of the grounding grid of the
substation. Right click on the selected objects and select
Group to group.

With the grounding grid still selected, press the F9 function key (or select Set As
Active Object under the Advanced menu). This will enable you to edit conductors
inside a grouped object without ungrouping the object. We are now ready to define
the characteristics of the grounding grid conductors.

Firstly, we define the injecting current. A current of 1000 A is injected into the
middle point of the first segment of the conductor locates at XS = 3’ to XP = 580’; this
conductor is the part of the conductor loop 3’ inside the fence perimeter of the
existing Lakeshore substation (see Figure 3.3). Right click on it to bring up the
characteristics window. Select Lead Type 0 to indicate that the conductor is
energized; also select Source-SES 2, which is defined to be a bus with an
energization current 1000 A.

Page 3-13
 Chapter 3. Ground Impedance Measurements & Interpretation

Note that if the X coordinates of the origin and end of above conductor are
interchanged, a different segment will be injecting the 1000 A into the grid. This
occurs because the subdivision process which must occur when two conductors
intersect at a node will create segment No. 1 which is now close to the other end XP =
580’. This will no longer correspond to the actual location used during the Fall-of-
Potential measurements.

Secondly, in order to improve the accuracy of the calculations, long conductors need
to be subdivided into segments. Conductors intersecting with other conductors will be
subdivided automatically. But for the grounding grids of the gas substations, we need
to subdivide them manually. Select the gas substation grounding grids on the left and
on the right, enter the subdivision number according to the following table.

Gas Substation (Left) Gas Substation (Right)

(Xs,Ys) (-88.5,-51) (-88.5,380) (-10,380) (905,92) (905,387) (1005,387) (1005,92)
(XP,YP) (-88.5,380) (-10,380) (-10,-51) (905,387) (1005,387) (1005,92) (905,92)
Subdivision 10 3 10 7 3 7 3

Table 3.2 Subdivision of Conductors for Gas Substations

We have completed the work for the grounding grid, press the Shift + F9 function
key (or select Set Parent As Active Object under the Advanced menu) to exit the
grouped grounding grid conductors.

We will now repeat the above procedure to select, group, and specify characteristics
to the remaining conductors.

Page 3-14
 Chapter 3. Ground Impedance Measurements & Interpretation

Step 9. Define Ground Rods: In the Filter Legend, select the conductors with 0.026”
radius; this will highlight all grounding rods. It is easier to view the grounding rods
under the Orthogonal Projection View (click the button or select Display |
Orthogonal Projection View) in X-Z View , as shown in the following screen.
Click on the Selected Filtered Objects button at the bottom of the SESCAD
window to select all ground rods. Right click and select Group to group them.

Step 10. Define Towers: We repeat Step 9 to define the towers. The radius is 0.0147 ft and
there are 16 conductors. Make sure to group them.

Page 3-15
 Chapter 3. Ground Impedance Measurements & Interpretation

Step 11. Define Pipes: The last step is to specify the characteristics for the pipes. This can be
done by repeating the previous step, but changing the characteristics of conductors.
In the Filter Legend, select the 4”, 12”, and 10” pipes respectively, and specify their
characteristics according to the following table. Note that we only need to group the
4” pipe.

4 Gas Pipe 12 Gas Pipe 10 Gas Pipe

Radius (ft) 0.1875 0.53125 0.4479

Conductor Type 2 3 4
Coating Type -1 - Insulated

Table 3.3 Conductor Types and Coating Types for Gas Pipes

Steps 7 to 11 show how to use the Color/Radius Mapping to define the conductors. Alternatively,
one can import the conductors group by group and assign their characteristics group by group. The
following illustrates briefly the main steps.

 First, assume that an AutoCAD drawing has been prepared such that it consists of four
conductor groups shown in Table 3.4. In AutoCAD, one can then save each group as a
separate DXF file, one for each group.

Group File Name Number of Conductors Radius (ft) Conductor Type

Grid MZ_FGD1D_Grid.DXF 142 0.02 0

Rod MZ_FGD1D_Rod.DXF 92 0.026 0

Tower MZ_FGD1D_Tower.DXF 16 0.0417 0

Pipe MZ_FGD1D_Pipe.DXF 6 See Table 3.1

See Table 3.3

Table 3.4 Four DXF Files to Model Grounding System

 We can then define the properties of each conductor group by repeating Steps 8-11. For
example, when importing the grounding grid, enter 0.02 (ft) as the default conductor radius.
The grounding grid will be imported as a single group. One can then modify their
characteristics (i.e., Conductor Types, Coating Types, Energization types, and subdivisions)
by repeating Step 8.

Step 12. Define Return Electrode: The last step to finalize our grounding system is to define
the return electrode for fall-of-potential measurement, which is located at (-3061’,-
1357’) and collects the 1000 A test current discharged into the Lakeshore substation.
The return electrode can be created by selecting the Edit | Create Object | Single
Conductor menu item and by inputting the coordinates and the characteristics as in
the follow screens.

Page 3-16
 Chapter 3. Ground Impedance Measurements & Interpretation

The Lead Type 0 is not negative to indicate that the conductor is energized. The
conductor is connected to Source-SES 1 that collects a current of 1000 A from the
earth (i.e., a current injection of -1000 A). Also enter 0.03 (ft) as the radius and 2 as
the number of subdivision.

Step 13. Define Observation Points: We now define

the location of the observation points. In this
study, the electric scalar potentials are
computed at 10 observations points
corresponding to the measurement points (as
shown in Figure 3.3). These points are
entered, as shown in the following table, by
selecting the Define | Observation Points
menu item.

Points Profile X Y Z
Number (Feet) (Feet) (Feet)
1 1 -356 560 0.0
2 1 -705 695 0.0
3 1 -1020 622 0.0
4 1 -1326 432 0.0
5 1 -1615 226 0.0
6 1 -1772 -98 0.0
7 1 -2030 -350 0.0
8 1 -2288 -602 0.0
9 1 -2546 -854 0.0
10 1 -2804 -1106 0.0
Table 3.5 Observation Points in Fall-of-Potential Measurements.

We have now completed the preparation of the data using SESCAD. Under the File menu, select
Save Document and then click Close Document to close this file in SESCAD. This creates the
MZ_FGD1D.F05 file. The *.F05 is an ASCII files you can edit and view at any time. This file is
ready to be submitted to the MALZ computation module in the next section.

Page 3-17
 Chapter 3. Ground Impedance Measurements & Interpretation

If you are a licensee of the CDEGS software you will now be able to proceed to Section 3.4.2. Users
of the demo software are not able to process the input file, but are able to peruse all output files
which are already available. Therefore read Section 3.4.2 for reference only. Any attempt to start the
computation modules will result in a message stating that the Computation module is not active.

3.4.2 Submission of the MALZ Run

There are two ways to submit the MALZ runs

3.4.2.1 Submit Computation Program Using SESCAD

You can submit the computation run directly from SESCAD, by selecting the Run/Reports | Save
& Run menu item. This will start the SESBatch program and automatically run the computation
module. Note that for illustration purposes, the generic grounding grid shown in the following screen
shot has been used instead of the specific case discussed in this How To manual.

Once the run is complete, a window will pop up to inform you that a log file has been generated.
Click the OK button to close the message window. SESBatch allows you to conveniently access
some of the important files that it generates. For example, from the Tools | View Run Log File…
menu item you can view the log file generated during the computations. From the Tools | View
Output File… menu item you can view the output file, which may contain ERROR or WARNING
messages requiring your attention. Finally, you can launch Output Toolbox directly from the Tools |
View Results with Output Toolbox… menu item.

Page 3-18
 Chapter 3. Ground Impedance Measurements & Interpretation

3.4.2.2 Submit Computation Program Using CDEGS

You can also submit the input file prepared in Section 3.4.1.2 to MALZ using CDEGS. Make sure
the Working Directory is \CDEGS Howto\Suburban and the JobID is FGD1D. Select the MALZ
button in the top menu and select Compute in the Session Mode list to submit the MALZ
Computation run

The MALZ computation module will start and will carry out all requested computations. The run
should be quite fast. At completion, the program will produce three important files: an OUTPUT file
(MZ_FGD1D.F09), a REPORT file (MZ_FGD1D.F17) and a DATABASE file (MZ_FGD1D.F21).

The OUTPUT and REPORT files are ASCII files, while the DATABASE file is a binary file. Any
ERROR or WARNING messages generated during the MALZ run will appear in the OUTPUT file.
You can view the OUTPUT file by clicking the File Viewer ( ) button in the CDEGS Tools
section of the toolbar. If prompted, select the Frequency Domain Grounding option, and click OK.

3.4.3 Extraction of the Results from MALZ Computation Results Files

Unlike the MALT program, which can analyze the Fall-of-Potential data automatically, the
computed Fall of Potential curve from MALZ has to be obtained by manually extracting the
appropriate data from the MALZ output file. The apparent resistances at each observation point can
be computed by calculating the potential differences between the potential at each observation point
and the GPR of the Reference Source Bus divided by the injection current of 1000 A. The GPR of
the Reference Source Bus was obtained by searching for the string “GPR” in the MALZ output file
MZ_FGD1D.F09. The results are shown below.
GROUND POTENTIAL RISE (GPR) OF REFERENCE SOURCE BUS (BUS # 2)

--------------------------------------------------------------
........................VOLTS....................... DEGREES
REAL PART IMAGINARY PART MODULUS ANGLE
============== ============== =============== ========
2200.1792 0.1701 2200.1792 0.00

BUS *--------GROUND POTENTIAL RISE (GPR)---------*

SOURCE .....................VOLTS..................... DEGREES
NUMBER REAL PART IMAGINARY PART MODULUS ANGLE
====== ============== ============== ============== =======
1 -330728.0593 -0.0002 330728.0625 180.00
The scalar potential at the observation points can be found at the end of the MALZ output file
MZ_FGD1D.F09:
EARTH POTENTIALS FOR PROFILE 1
==================================

OBSER
VATION *-----COORDINATES OF POINT-----* *---------------------------POTENTIAL----------------------------*
POINT ............ feet ............ ....................VOLTS.................... DEGREES IN % OF
NUMBER ----X----- ----Y----- ----Z----- REAL PART IMAGINARY PART MODULUS ANGLE REFER. GPR
====== ========== ========== ========== ============= ============== ============== ======= ==========
1 -356.000 560.000 0.000 454.6906 0.0051 454.6906 0.00 20.7
2 -705.000 695.000 0.000 245.2122 0.0000 245.2122 0.00 11.1
3 -1020.000 622.000 0.000 159.9145 0.0000 159.9145 0.00 7.27
4 -1326.000 432.000 0.000 92.9259 0.0000 92.9259 0.00 4.22
5 -1615.000 226.000 0.000 30.6072 0.0003 30.6072 0.00 1.39
6 -1772.000 -98.000 0.000 -22.7975 0.0000 22.7975 180.00 1.04
7 -2030.000 -350.000 0.000 -102.6573 0.0000 102.6573 180.00 4.67
8 -2288.000 -602.000 0.000 -213.8587 0.0000 213.8587 180.00 9.72
9 -2546.000 -854.000 0.000 -412.0677 0.0000 412.0677 180.00 18.7
10 -2804.000 -1106.000 0.000 -971.9191 0.0000 971.9191 180.00 44.2

Page 3-19
 Chapter 3. Ground Impedance Measurements & Interpretation

A simple procedure can be written to extract from the MALZ output file the apparent resistances
versus the distance for each observation point including the current injection location (3’, 407’). Of
course, this can be also done manually since we only have 10 points to examine.

An alternative way to obtain the apparent resistances is to

plot the touch voltages. In the SESResultsViewer
screen, choose the Computations radio button; under
Reference GPR, choose User Defined. Then the
Energization Scaling Factor checkbox should be
checked and apply a value of 0.001. (Since the injecting
current is 1000 A, to obtain the apparent resistance we
need to divide the touch voltage by 1000.) Now, you
should have the screen on the right.

Click Plot/Draw, you will obtain a curve which is the

same as the Traverse 1 curve in Figure 3.5.

To extract the data, click Report, and click on Proceed

in the Export Raw Data to file window. This will bring a
Save As window for which the csv file can be saved in
the chosen directory. By opening this file with an edition
tool, the touch voltages (which have been divided by
1000) are the same as the apparent resistances shown in
Table 3.6.

Page 3-20
 Chapter 3. Ground Impedance Measurements & Interpretation

Scalar Potentials/Touch Voltages/Worst Spherical

|--Profile---|----- Coordinates ( feet )------| Touch Voltage (Volts)
Pr.No Point X Y Z Magnitude Ang.(deg) Real Part Imag. Part
====== ====== ====== ====== ====== ====== ====== ====== ======
1, 1, -356.0000 , 560.0000 , 0.000000 , 0.1746173 , 0.3617310 , 0.1746139 , 0.001102421
1, 2, -1020.000 , 622.0000 , 0.000000 , 0.2210775 , 0.3612984 , 0.2210731 , 0.001394071
1, 3, -1326.000 , 432.0000 , 0.000000 , 0.2249632 , 0.3579124 , 0.2249588 , 0.001405280
1, 4, -1615.000 , 226.0000 , 0.000000 , 0.2291838 , 0.3636223 , 0.2291792 , 0.001454484
1, 5, -1772.000 , -98.00000 , 0.000000 , 0.2265228 , 0.3748133 , 0.2265180 , 0.001481840
1, 6, -2030.000 , -350.0000 , 0.000000 , 0.1686753 , 0.1439158 , 0.1686747 , 0.004236789
1, 7, -2288.000 , -602.0000 , 0.000000 , 0.1708733 , 0.1569096 , 0.1708727 , 0.004679513
1, 8, -2546.000 , -854.0000 , 0.000000 , 0.1723665 , 0.1703659 , 0.1723657 , 0.005125216
1, 9, -2804.000 , -1106.000 , 0.000000 , 0.08443001 , -0.3776605 , 0.08442818 , -0.00556509

In order to find out the exact potential probe location as a percentage of the traverse length in the
FOP measurement, we need to know the grid impedance of the grounding system in the absence of
the return current electrode. Therefore, four minor changes were applied to the input file
MZ_FGD1D.F05 to create a new input file named MZ_ZGD1D.F05. In SESCAD, select File | Save
As… to save the MZ_FGD1D.F05 as the MZ_ZGD1D.F05. The four minor changes are described
as follows:

(a) The first change was to remove the return current electrode. This is done by simply deleting
the return electrode;
(b) The second change was to move the current injection site towards the center of the Lakeshore
substation so that the grid impedance is computed for a typical phase-to-ground fault
occurring somewhere in the middle of the substation. Select the View | Labeling | Show
Conductor Numbers menu item to show all conductor numbers. Press the Function Key F9
to modify the grounding grid conductors individually. Select Conductor #3 (see Step 8).
Right-click and select the Characteristics…. This conductor at (Xs,Ys) = (3,407) will be de-
energized by changing the Energization from “2” to “0”;
(c) The third change is to energize the middle of the grounding grid. Select Conductor #80 which
is defined as from (Xs,Ys) = (312,251) to (Xp,Yp) = (556,251). Right-click and select the
Characteristics…. This conductor will be energized by changing the Energization from “0”
to “1”; Note that by default, the energization is automatically applied to the beginning of a
conductor, i.e. (Xs,Ys) = (312,251). Therefore, the center of the grid is energized;
(d) The fourth change is to remove the Energization Type for the return electrode. Select the
Define | Energization Types… menu item, delete “Source-SES2” and change the “Source-
SES1” Current from -1000 A to 1000 A.

Page 3-21
 Chapter 3. Ground Impedance Measurements & Interpretation

After completing this new MALZ run, the grid impedance is obtained by dividing the GPR of the
Reference Source Bus by the injection current of 1000 A. From the MALZ output file
MZ_ZGD1D.F09, the grid impedance is 2.307  0.00.
GROUND POTENTIAL RISE (GPR) OF REFERENCE SOURCE BUS (BUS # 1)
--------------------------------------------------------------
........................VOLTS....................... DEGREES
REAL PART IMAGINARY PART MODULUS ANGLE
============== ============== =============== ========
2306.6583 0.1267 2306.6582 0.00

The computed Fall-of-Potential curves for the two-layer soil models corresponding to Traverses 2
and 3 can be obtained similarly. The MALZ input files (MZ_FGD2B.F05 and MZ_ZGD2B.F05 for
Traverse 2, and MZ_FGD3D.F05 and MZ_ZGD3D.F05 for Traverse 3) are provided for reference.
These files were created easily by simply replacing the soil models in MZ_FGD1D.F05 and
MZ_ZGD1D.F05.

Page 3-22
 Chapter 3. Ground Impedance Measurements & Interpretation

Table 3.6 lists the measured and computed apparent resistances for the three soil models.

Distance From
(3.0, 407.0,0) Measured Computed Apparent
Measurements Point to Apparent Resistance ()
Potential Probe Resistance ()
(feet)
Traverse 1 Traverse 2 Traverse 3
R1 390.24 0.047 1.745 0.566 0.954
R2 764.34 0.054 1.955 0.652 1.088
R3 1045.35 0.062 2.040 0.688 1.143
R4 1329.24 0.103 2.107 0.716 1.187
R5 1628.09 0.156 2.170 0.742 1.227
R6 1845.44 0.209 2.223 0.764 1.262
R7 2169.36 0.315 2.303 0.798 1.313
R8 2503.35 0.487 2.414 0.845 1.385
R9 2843.86 0.808 2.612 0.927 1.513
R10 3188.80 1.042 3.172 1.153 1.871

Table 3.6 Measured and Computed Apparent Resistance Values Using the Fall-of-Potential
Method. Initial Modeling of Grounding System of Lakeshore Substation.

Figure 3.5 displays the computed and measured Fall-of-Potential (FOP) curves. It is clear from
Figure 3.5 that the computed apparent ground impedances using the two-layer soil models from the
three traverses are all much higher than the measured values.

From the MALZ output files MZ_ZGD1D.F09, MZ_ZGD2B.F09 and MZ_ZGD3D.F09, the grid
impedances corresponding to these soil structures are as follows:

Traverse 1: Zgrid = 2.307  0.00

Traverse 2: Zgrid = 0.799  0.01
Traverse 3: Zgrid = 1.316  0.01.
Clearly, from Figure 3.5, the assumptions made to build the computer model do not reflect the actual
situation. One important factor which accounts for the difference between computed and measured
results is the true extent of the grounding system, which is greater that initially modeled.

Page 3-23
 Chapter 3. Ground Impedance Measurements & Interpretation

3.5
Measured
Computed using 2-layer
3 soil from Traverse 1
Computed using 2-layer
soil from Traverse 2
Computed using 2-layer
Apparent Resistance (Ohms)

2.5
soil from Traverse 3

1.5

0.5

0
0 500 1000 1500 2000 2500 3000 3500
Distance: Potential Probe From Grid (ft)
Figure 3.5. Measured vs Computed Apparent Resistance in FOP. Initial Modeling of
Grounding System of Lakeshore Substation.

In a first attempt to get a better match between the measured and computed grounding system
impedances, we extended the grounding system to include nearby 115 kV transmission and 23
kV/33 kV distribution line structure grounds connected to the substation via the overhead ground
wires and neutral wires. As shown in Figure 3.4 (b), structure grounds as far as 2000 ft (see Figure
6.1 and Figure 6.2) from the substation were modeled. The input files MZ_ZSK1D.F05,
MZ_ZSK2B.F05 and MZ_ZSK3D.F05 were created from the MZ_ZGD1D.F05, MZ_ZGD2B.F05
and MZ_ZGD3D.F05 files by adding the conductors corresponding to nearby 115 kV transmission
and 23 kV/33 kV distribution line structure grounds connected to the substation via the overhead
ground wires and neutral wires. These conductors are identified in the input files by appropriate
comments. Note that the overhead ground wires and neutral wires are insulated (by specifying a
coating type of -1) to account for the fact that they are not in direct contact with soil. The grid
impedances can be obtained from the output files MZ_ZSK1D.F09, MZ_ZSK2B.F09 and
MZ_ZSK3D.F09. They decreased by about 40% to:

Traverse 1: Zgrid = 1.617  0.01

Traverse 2: Zgrid = 0.489  0.05
Traverse 3: Zgrid = 0.800  0.03.

Page 3-24
 Chapter 3. Ground Impedance Measurements & Interpretation

The impedances are still too high compared to the measured ones. We then added connections
between the gas pipes and the gas substation grids to form the input files MZ_ZGC1D.F05,
MZ_ZGC2B.F05 and MZ_ZGC3D.F05. The grounding grids of the gas substations were also
assumed to be connected to the Lakeshore Substation grid. The grid impedances decreased by
another 12-15% to reach the following values:
Traverse 1: Zgrid = 1.342  0.01
Traverse 2: Zgrid = 0.430  0.05
Traverse 3: Zgrid = 0.697  0.03.
To lower the grid impedances even further, a portion of the water pipes (“Residential Area 1” in
Figure 3.4) located in one residential area near the substation was added to the model, but not
connected to the substation’s grounding system. The water pipes are assumed to be 3 steel pipes
and are represented by Conductor Type No. 5. Based on the drawing provided to SES, the conductor
network of water pipes was determined by following the streets near the Lakeshore substation. Note
that these water pipes were all assumed to be connected to one another. The input files are
MZ_ZWN1D.F05, MZ_ZWN2B.F05 and MZ_ZWN3D.F05. The grid impedances were reduced
slightly:
Traverse 1: Zgrid = 1.297  0.01
Traverse 2: Zgrid = 0.397  0.06
Traverse 3: Zgrid = 0.647  0.04.
When the water pipes are assumed to be connected to the nearest gas substation grid to create the
input files MZ_ZWC1D.F05, MZ_ZWC2B.F05 and MZ_ZWC3D.F05, the grid impedances
decrease substantially to:
Traverse 1: Zgrid = 0.450  0.18
Traverse 2: Zgrid = 0.201  0.31
Traverse 3: Zgrid = 0.286  0.25.
Finally, when a subset of the water pipes associated with another residential area (“Residential Area
2” in Figure 3.4) located in the vicinity of Lakeshore Substation are added to the final grounding
system as shown in Figure 3.4, the computed grid impedances become:
Traverse 1: Zgrid = 0.367  0.30
Traverse 2: Zgrid = 0.185  0.40
Traverse 3: Zgrid = 0.250  0.37.
The input files MZ_FZG1D.F05, MZ_FZG2B.F05 and MZ_FZG3D.F05 (no return current
electrode) were used to compute the grid impedance. The input files MZ_FAL1D.F05,
MZ_FAL2B.F05 and MZ_FAL3D.F05 were used to compute the Fall-of-Potential curves. Table 3.7
lists the measured and computed apparent resistances for the three soil models.

Page 3-25
 Chapter 3. Ground Impedance Measurements & Interpretation

Distance From Computed Apparent

(3.0, 407.0,0) Measured Resistance ()
Measurements Point to Apparent
Potential Probe Resistance () Traverse 1 Traverse 2 Traverse 3
(feet)
R1 390.24 0.047 0.174 0.083 0.111
R2 764.34 0.054 0.213 0.105 0.139
R3 1045.35 0.062 0.235 0.117 0.156
R4 1329.24 0.103 0.258 0.129 0.172
R5 1628.09 0.156 0.285 0.142 0.190
R6 1845.44 0.209 0.315 0.154 0.209
R7 2169.36 0.315 0.369 0.178 0.245
R8 2503.35 0.487 0.458 0.217 0.304
R9 2843.86 0.808 0.637 0.292 0.419
R10 3188.80 1.042 1.177 0.510 0.764

Table 3.7 Measured and Computed Apparent Resistance Values Using the Fall-of-
Potential Method. Final Modeling of Grounding System of Lakeshore
Substation (including water pipes).

This results in a better fit between the computed and measured FOP curves, as shown in Figure 3.6.
It is seen here that the measured values are closest to Traverse 1 curve near the return electrode, far
from the substation grid, whereas they are closer to Traverses 2 and 3 near the substation grid.
1.2
Measured
Computed using 2-layer
soil from Traverse 1
1
Computed using 2-layer
soil from Traverse 2
Apparent Resistance (Ohms)

Computed using 2-layer

soil from Traverse 3
0.8

0.6

0.4

0.2

0
0 500 1000 1500 2000 2500 3000 3500
Distance: Potential Probe From Grid (ft)

Figure 3.6 Measured vs Computed Apparent Resistance from FOP Profiles. Final Modeling
of Grounding System of Lakeshore Substation (including water pipes).

Page 3-26
 Chapter 3. Ground Impedance Measurements & Interpretation

This suggests a hybrid soil model consisting of two distinct soil resistivity regions. The following
vertically layered soil model is a good candidate: a low resistivity of 200 -m near Lakeshore
Substation and a high resistivity soil of 753 -m in the cemetery area located 1200 ft away from
Lakeshore Substation. The input file MZ_FALVE.F05 was created from the input file
MZ_FAL1D.F05 by replacing the horizontally two-layered soil model with the vertically layered
soil model described before. The vertically layered soil model is defined by the following command:
SOIL-TYPE
VERTICAL
LAYER,LEFT,753.0
LAYER,RIGHT,200.0
TRACE-POINT,LEFT,-1200.0,0.0
ANGLE, 90.0

It can also be defined using the following screen in SESCAD:

The computed grid impedance at 0.25 Hz using input file MZ_FZGVE.F05 based on this soil
structure becomes
Zgrid = 0.181  0.38 (i.e., 0.181 + j0.001 )
and the corresponding computed FOP profile is shown in Figure 3.7. A very good match is obtained
between the computed and measured values. Table 3.8 lists the measured and computed apparent
resistances for this soil model.

Page 3-27
 Chapter 3. Ground Impedance Measurements & Interpretation

Distance From
(3.0, 407.0,0) Measured Computed
Measurements Point to Apparent Apparent
Potential Probe Resistance () Resistance ()
(ft)
Vertically Layered
Soil Model
R1 390.24 0.047 0.090
R2 764.34 0.054 0.106
R3 1045.35 0.062 0.113
R4 1329.24 0.103 0.128
R5 1628.09 0.156 0.159
R6 1845.44 0.209 0.190
R7 2169.36 0.315 0.248
R8 2503.35 0.487 0.343
R9 2843.86 0.808 0.526
R10 3188.80 1.042 1.073

Table 3.8 Measured and Computed Apparent Resistance Values Using the Fall-of-
Potential Method. Final Modeling of Grounding System of Lakeshore
Substation (including water pipes).
1.2
Measured
Computed using vertically
layered soil model
1
Apparent Resistance (Ohms)

0.8

0.6

0.4

1782 ft

0.2

0
0 500 1000 1500 2000 2500 3000 3500
Distance: Potential Probe From Grid (ft)

Figure 3.7 Measured vs Computed Apparent Resistance in FOP. A Vertical Two-Layer Soil
Model is Used.

Page 3-28
 Chapter 3. Ground Impedance Measurements & Interpretation

The computed grounding system impedance of 0.181  occurs at the potential probe position 1782’
from the grounding grid. At this location, the measurements indicate a grounding system impedance
of 0.195  (@0.25 Hz). At this position the difference between measured and computed values is
approximately 7%.
Now that we have achieved a good fit between measured and computed results, the selected soil
model is used to determine the grid impedance of the substation at 60 Hz (under fault conditions).
The input file MZ_F60VE.F05 is therefore created from file MZ_FZGVE.F05 by replacing the
computation frequency of 0.25 Hz with the computation frequency of 60 Hz. The resulting grid
impedance is:
Zgrid = 0.315  26.4 (i.e., 0.282 + j0.140 )
A value similar to this will be used for the fault current distribution computation described in
Chapter 5. Note that the 115 kV overhead ground wires associated with transmission lines feeding
the modeled faults will be removed when computing the grid impedance at 60 Hz for the fault
current distribution, since these overhead ground wires and their grounds will be modeled separately.

It is important to note here that the vertical soil model selected reflects the low resistivity nature of
the soil near Lakeshore substation (possibly backfill) and the high resistivity soil further away from
the substation.

Page 3-29
This page is intentionally left blank
 Chapter 4. Touch Voltage Measurements & Interpretation

CHAPTER 4
TOUCH VOLTAGE MEASUREMENTS &
INTERPRETATION
4.1 INTRODUCTION
Touch and step voltage measurements were made at 10 representative locations throughout
Lakeshore Substation as a complement to the computer simulations of the grounding system’s
performance discussed in Chapter 6. Figure 4.1 shows the measurement sites on a plan view of the
substation’s grounding system.

As can be seen from this figure, the preferred locations were sites along edges or corners of the
substation, where touch and step voltages are typically the highest:

Figure 4.1 Touch Voltage Measurement Sites (marked on plan of grounding grid).

Page 4-1
 Chapter 4. Touch Voltage Measurements & Interpretation

4.2 METHODOLOGY
At each measurement location, the following basic measurements were made:
 Long reach voltage. This is the difference in potential between an exposed metallic
structure (such as a fence, a transmission line pole, or a bus supporting structure) or its
associated grounding cable and a point in the earth located a distance of 6-52 ft away.
These values were measured primarily for comparison with computed values. The
starting points of the dotted lines in Figure 4.1 indicate the approximate locations of the
connection points to the exposed metallic structures on which long reach and touch
voltages were measured. The arrows indicate the direction in which the potential probe
was moved away from the structure connection point in order to measure the earth
potential for the long reach voltage and the distance between the probe and the structure
is shown as well.
 Touch voltage. This is the difference in potential between an exposed metallic structure
(such as a fence, a transmission line pole, or a bus supporting structure) or its associated
grounding cable and a point in the earth 1 m (i.e., 3.3 ft) away. Let us designate this point
in the earth as “Point A” for the step voltage definition below. The starting points of the
dotted lines in Figure 4.1 again indicate the approximate locations of the connection
points to the exposed metallic structures on which touch voltages were measured. The
arrows indicate for most sites the direction in which the potential probe was moved away
from the structure connection point in order to measure the earth potential.
 Step voltage. This is the difference in potential between two points in the earth spaced 1
m apart. At each measurement site, the step voltage was measured between Point A (as
defined above) and another point located 1 m further away from the structure on which
the touch voltage was measured.

The same equipment was used here as for the Methodology 1 soil resistivity measurements and the
set-up was similar. The variable frequency power source, powered by an AC power generator
injected an 80 Hz signal into the grounding grid at the south corner of the substation (same location
as for the Fall-of-Potential impedance measurements), with current returning from a remote
electrode placed 3350 ft southeast of the grid (as for the Fall-of-Potential measurements). A
broadband ammeter in the signal injection circuit monitored the magnitude of the injection current.

Touch, step and long reach voltages were measured by the HP dynamic signal analyzer which was
transported to each measurement site, independently of the signal-generating equipment described in
the previous paragraph.

4.3 MEASUREMENT RESULTS

Appendix C presents the tabulated measured data. As indicated in Table C.1, the measured voltages
are based on grid injection currents of about 500 mA. In order to convert these values into estimates
of voltages arising during fault conditions, the following factors must be considered:

 Frequency. During fault conditions, the current injected into the grounding system of the
substation is primarily a 60 Hz waveform. On the other hand, the primary tests were conducted at

Page 4-2
 Chapter 4. Touch Voltage Measurements & Interpretation

a frequency of 80 Hz (in order to allow 60 Hz noise to be filtered out during the measurements).
This higher test current frequency would tend to increase the apparent impedance of the
grounding system, due to the increased reactance of all grounding grid conductors and static
wires, resulting, in general, in increased touch, step and long reach voltages. Thus, the
measurements provide conservative touch, step and long reach voltage values.
Note that the degree of conservatism due to this frequency factor would be relatively small,
however, given the small difference between the 80 Hz primary test frequency and 60 Hz fault
frequency and the predominant grounding system resistance compared to its reactance (i.e., the
angle of the impedance is approximately 27, as seen in Section 3.4 of Chapter 3).

 Magnetic Induction between Faulted Phase and Static Wires. During phase-to-ground fault
conditions, magnetic induction between the faulted phase of each transmission line and its static
wires increases the proportion of the fault current which flows into the static wires instead of the
substation’s grounding grid. During the touch, step and long reach voltage tests, no such
induction was present, resulting in a greater proportion of the total test injection current flowing
into the substation’s grounding grid and therefore in higher touch, step and long reach voltages
per unit injection current than would occur during fault conditions, per unit fault current. In this
sense, the measurements are conservative.

 Influence of Test Current Return Electrode. The presence of the current return electrode required
for the measurements tends to increase touch voltages when the potential probe is to the
southeast of the measured structure (i.e., closer to the return electrode than the structure) and
decrease them when the potential probe is to the northwest of the measured structure. This effect
is most pronounced on the long reach voltages, which involve measurement of an earth potential
that is relatively far from a grounding grid conductor. For these latter, the current return
electrode can modify the measured voltage by as much as 5% in this type of soil.

 Grid Circulating Currents during Fault Conditions. During fault conditions, considerable
circulating currents can flow in the substation’s grounding grid between the ground connections
of the transformers, the ground connections of the faulted structure and the static wire
connections to the grid. The effects of these currents, which vary with the location of the fault
within the substation, are not accounted for by the measurements, yet may result in significant
earth gradients within the substation. The test voltages are therefore most pertinent at locations in
the substation least influenced by these circulating currents (e.g., near the perimeter where there
are no nearby static wire connections) and for fault scenarios with the circulating currents of
least extent (e.g., faults near the transformers injecting the most current into the grounding grid).

Page 4-3
 Chapter 4. Touch Voltage Measurements & Interpretation

Site Description Estimated Voltages During 115 kV Fault (V)

Site No. Mesh Voltage Touch Step Voltage Long Reach
Distance (ft)1 Voltage Voltage
1 51.8 1485 215 3094
2 51.8 224 68 1160
3 51.8 521 98 1274
4 51.8 18 1 18
5 33.5 568 125 947
6 9.4 60 32 124
7 16.6 260 89 403
8 6 162 67 230
9 6 30 2 32
10 24 7 16 78
Table 4.1 Measured Touch, Step, and Long Reach Voltages at Lakeshore Substation,
Scaled to Provide Estimated Values During a 115 kV Fault.

Site Description Estimated Voltages During 115 kV Fault (V)

Site No. Mesh Voltage Touch Step Voltage Long Reach
Distance (ft) Voltage Voltage
1 51.8 682 192 2193
2 51.8 872 157 2361
3 51.8 585 111 1551
4 51.8 436 82 1062
5 33.5 363 102 666
6 9.4 442 7 427
7 16.6 366 20 395
8 6 528 6 533
9 6 340 18 322
10 24 979 36 1204
Table 4.2 Computed Touch, Step, and Long Reach Voltages at Lakeshore Substation
for 115 kV Fault

Keeping in mind the above, the measurements can nevertheless be used to provide an indication of
expected touch, step and long reach voltage levels during fault conditions. In Table 4.2, the 80 Hz

1
Distance from structure to potential probe.

Page 4-4
 Chapter 4. Touch Voltage Measurements & Interpretation

measurements have been increased in proportion to the ratio of the worst-case-fault current to the
injection current used for the tests. By “worst-case-fault current”, it is meant the total current leaving
the substation by means of the transmission line static wires and by means of injection into the earth
by the grounding system of the substation, for the phase-to-ground fault scenario which maximizes
this value. The total earth/static wire current is as follows for phase-to-ground faults within the
substation at the 115 kV voltage level:
35 kA
The measured and computed touch, step, and long reach voltages are shown in the table that follows.
The two-layer soil model from Traverse 2 (see Table 2.1) is used for the computation, as this is the
soil model derived from measurements made closest to the substation.

As Table 4.1 shows, measured touch voltages at the sites within the substation fence (Sites 5-10)
range from 7 V to 568 V, while step voltages range from 2 V to 125 V. Long reach voltages range
from 32 V to 947 V.

Outside the substation fence (Sites 1-4), touch and step voltages are considerably higher. Touch
voltages range from 18 V to 1485 V around the main substation fence; step voltages range from 1 V
to 215 V. Note that touch, step and long reach touch voltages measured at Site 4 are much lower
than the corresponding values at Sites 1-3, which probably indicates the presence of buried ground
conductors.

If these values are compared with the computed values in Table 4.2, good agreement is obtained
between the maximum values. The maximum computed step voltage is on the order of 192 V versus
the measured maximum of 215 V. The maximum computed long reach / touch voltage is 2361 V
versus the measured maximum of 3094 V. As Table 4.1 and Table 4.2 show, the computation results
match the measured values fairly well at some locations (mostly where unsuspected ground
conductors are not likely to exist), while poor matches were encountered at other locations (most
probably due to the presence of buried ground conductors which have not been accounted for due to
insufficient documentation).

The touch, step, and long reach voltages at Lakeshore Substation in Table 4.2 were computed using
the MALZ program. The input file MZ_MEA2B.F05 corresponding to the two-layer soil model
from Traverse 2 was prepared based on the input file MZ_FAL2B.F05. The following modifications
were applied to MZ_FAL2B.F05 to create the file MZ_MEA2B.F05:

(a) A number of additional conductors were added to the grounding grid of the Lakeshore
substation. These conductors are identified by the appropriate comments in MZ_MEA2B.F05.
(b) The computation frequency of 0.25 Hz was replaced with 80 Hz.
(c) The 10 observation points in the Fall-of-Potential measurements were replaced by 10 profiles
that define the 10 locations indicated in Figure 4.1.
The observation points within each profile are defined in such a way so that the touch, step and long
reach voltages can be easily obtained (see Table 4.1 for the long reach distances). The touch and
long reach voltages are computed as the potential difference between the scalar potential at the
measurement location and the GPR of the conductor segment which is the nearest one to the
measurement location. The step voltages are computed as the potential difference between two

Page 4-5
 Chapter 4. Touch Voltage Measurements & Interpretation

observation points which are 1m (3.28 ft) apart. The scalar potentials at the second and the last
observation points in each profile are used to compute the touch and long reach touch voltages,
respectively. The scalar potentials at the second and the third observation points in each profile are
used to compute the step voltages. The computed values (modulus) are then multiplied by 35 to
obtain the touch and step voltages corresponding to the total fault current of 35 kA.

To obtain the above touch voltage and long reach voltage values using CDEGS-Examine-MALZ
via SESResultsViewer:

1. Enter an Energization Scaling Factor of 35 (click on Define under Energization Scaling

Factor, then check Apply Scaling Factor, type 35 in the Factor Value box and click OK).
This will scale all computed values by 35, as required.

2. Select Scalar Potentials in the Category List and Touch Voltages in the Result Selection
list and Nearest Conductor Segment in the Reference GPR list.

3. Export and Proceed and save as csv file.

This generates a report and displays it on screen. The touch voltage values are listed for Point # 2 of
each profile; the long reach voltage values are listed for the last point of each profile. Click OK to
return to the CDEGS-Examine-MALZ screen.
Scalar Potentials/Touch Voltages/Nearest Conductor Segment

Pr.No Point X Y Z Magnitude Ang.(deg) Real Part Imag. Part

====== ====== ====== ====== ====== ====== ====== ====== ======

1, 1, 29.5 410 0.000000 489.175 -10.9961 480.1939 -93.3059

1, 2, 29.5 413 0.000000 681.5814 4.176424 679.7714 49.63808

1, 3, 29.5 416 0.000000 851.2762 10.1989 837.8253 150.7319

1, 4, 29.5 461.8 0.000000 2193.266 27.90239 1938.29 1026.375

2, 1, 481.8 410 0.000000 678.4444 42.74873 498.2072 460.5175

2, 2, 481.8 413 0.000000 872.3273 38.95523 678.3543 548.4435

2, 3, 481.8 416 0.000000 1020.601 36.49398 820.4807 606.9904

2, 4, 481.8 461.8 0.000000 2361.39 30.45769 2035.527 1196.993

3, 1, 421 0 0.000000 440.6534 20.11945 413.7636 151.5753

3, 2, 421 -3 0.000000 585.3663 20.32784 548.9098 203.3512

3, 3, 421 -6 0.000000 696.57 20.51252 652.4044 244.0865

3, 4, 421 -51.8 0.000000 1550.589 21.9673 1438.012 580.0403

4, 1, 241 0 0.000000 328.1697 20.77029 306.8419 116.3762

4, 2, 241 -3 0.000000 436.0394 21.80369 404.846 161.9571

Page 4-6
 Chapter 4. Touch Voltage Measurements & Interpretation

4, 3, 241 -6 0.000000 517.9982 22.44254 478.7665 197.7493

4, 4, 241 -51.8 0.000000 1061.68 17.12746 1014.596 312.6631

5, 1, 91.7 410 0.000000 483.4356 9.436523 476.8937 79.2616

5, 2, 92.64 407.2 0.000000 362.5273 35.86126 293.8058 212.3774

5, 3, 93.58 404.3 0.000000 464.6729 36.05687 375.6569 273.5009

5, 4, 102.2 378.2 0.000000 665.5237 39.76903 511.5411 425.7318

6, 1, 85 315 0.000000 445.3115 43.77571 321.5387 308.083

6, 2, 85 312 0.000000 441.5339 44.38647 315.5369 308.8506

6, 3, 85 309 0.000000 436.0264 45.05653 308.0129 308.6213

6, 4, 85 305.6 0.000000 427.2719 45.89811 297.3541 306.8253

7, 1, 10.9 356.2 0.000000 296.7332 28.0566 261.8622 139.5666

7, 2, 10.9 359.2 0.000000 366.0333 33.88651 303.8602 204.0817

7, 3, 10.9 362.2 0.000000 385.0977 33.10248 322.5944 210.3166

7, 4, 10.9 372.8 0.000000 395.1897 30.32711 341.1107 199.5455

8, 1, 265.1 378.2 0.000000 518.9191 31.4239 442.811 270.5466

8, 2, 265.1 381.2 0.000000 527.8597 31.09789 451.9989 272.6405

8, 3, 265.1 384.2 0.000000 532.8672 30.81462 457.6419 272.9676

8, 4, 528.3 257 0.000000 354.0974 27.75411 313.36 164.8954

9, 1, 525.3 257 0.000000 339.9488 27.71058 300.9594 158.0781

9, 2, 522.3 257 0.000000 321.9795 27.66607 285.1672 149.5008

9, 3, 445 136 0.000000 942.3232 31.26175 805.5031 489.0172

9, 4, 445 133 0.000000 978.5817 31.37072 835.5297 509.4236

10, 1, 445 130 0.000000 1014.388 31.4807 865.0862 529.7248

10, 2, 445 112 0.000000 1204.029 32.17846 1019.082 641.2153

10, 3, 29.5 410 0.000000 489.175 -10.9961 480.1939 -93.3059

10, 4, 29.5 413 0.000000 681.5814 4.176424 679.7714 49.63808

To obtain the above step voltage values using CDEGS-Examine-MALZ:

1. Select Scalar Potentials in the Category List and Step Voltages (Spherical) in the Result
Selection list and Worst Spherical in the Reference GPR list.

2. Export and Proceed and save as csv file.

Page 4-7
 Chapter 4. Touch Voltage Measurements & Interpretation

This generates a report of the scalar potentials and displays it on screen. The step voltage is the
difference of the values listed for Point #2 and Point #3 for all profiles. (Note that you must account
for the phase angle when computing the difference).
Scalar Potentials/ Scalar Potentials

Pr.No Point X Y Z Magnitude Ang.(deg) Real Part Imag. Part

====== ====== ====== ====== ====== ====== ====== ====== ======

1, 1, 29.5 410 0.000000 9664.074 27.09402 8603.542 4401.521

1, 2, 29.5 413 0.000000 9421.364 26.8729 8403.965 4258.578

1, 3, 29.5 416 0.000000 9231.185 26.69717 8247.081 4147.339

1, 4, 29.5 461.8 0.000000 7724.942 25.45642 6974.946 3320.369

2, 1, 481.8 410 0.000000 9408.299 24.14006 8585.529 3847.698

2, 2, 481.8 413 0.000000 9207.949 24.09922 8405.382 3759.772

2, 3, 481.8 416 0.000000 9051.232 24.06663 8264.426 3691.081

2, 4, 481.8 461.8 0.000000 7701.327 23.74507 7049.38 3101.078

3, 1, 421 0 0.000000 9098.221 21.55498 8461.94 3342.63

3, 2, 421 -3 0.000000 8953.504 21.56456 8326.795 3290.854

3, 3, 421 -6 0.000000 8842.281 21.56556 8223.3 3250.119

3, 4, 421 -51.8 0.000000 7987.899 21.37019 7438.696 2910.729

4, 1, 241 0 0.000000 9244.896 22.45794 8543.766 3531.598

4, 2, 241 -3 0.000000 9136.914 22.42855 8445.762 3486.017

4, 3, 241 -6 0.000000 9054.931 22.39767 8371.841 3450.225

4, 4, 241 -51.8 0.000000 8345.869 21.9168 7742.687 3115.178

5, 1, 91.7 410 0.000000 9589.671 26.1671 8606.843 4228.954

5, 2, 92.64 407.2 0.000000 9806.99 26.28684 8792.831 4343.176

5, 3, 93.58 404.3 0.000000 9706.552 26.17733 8710.98 4282.053

5, 4, 102.2 378.2 0.000000 9517.757 25.71577 8575.096 4129.822

6, 1, 85 315 0.000000 9679.185 25.66003 8724.617 4191.381

6, 2, 85 312 0.000000 9684.263 25.64056 8730.619 4190.613

6, 3, 85 309 0.000000 9691.146 25.62253 8738.143 4190.843

6, 4, 85 305.6 0.000000 9701.533 25.60488 8748.802 4192.639

7, 1, 10.9 356.2 0.000000 9806.201 26.4231 8781.771 4363.722

7, 2, 10.9 359.2 0.000000 9774.869 26.43192 8753.042 4351.128

Page 4-8
 Chapter 4. Touch Voltage Measurements & Interpretation

7, 3, 10.9 362.2 0.000000 9755.318 26.44811 8734.308 4344.894

7, 4, 10.9 372.8 0.000000 9743.554 26.55332 8715.792 4355.665

8, 1, 265.1 378.2 0.000000 9438.965 24.56613 8584.568 3924.186

8, 2, 265.1 381.2 0.000000 9429.738 24.57777 8575.381 3922.092

8, 3, 265.1 384.2 0.000000 9424.471 24.59023 8569.737 3921.765

8, 4, 528.3 257 0.000000 9524.833 24.04887 8698.061 3881.519

9, 1, 525.3 257 0.000000 9538.936 24.05591 8710.461 3888.336

9, 2, 522.3 257 0.000000 9556.853 24.06427 8726.253 3896.913

9, 3, 445 136 0.000000 8940.633 23.40293 8205.125 3551.173

9, 4, 445 133 0.000000 8904.974 23.35917 8175.099 3530.767

10, 1, 445 130 0.000000 8869.793 23.31448 8145.542 3510.466

10, 2, 445 112 0.000000 8684.345 23.04108 7991.546 3398.975

10, 3, 29.5 410 0.000000 9664.074 27.09402 8603.542 4401.521

10, 4, 29.5 413 0.000000 9421.364 26.8729 8403.965 4258.578

Note that in comparing measured with computed results, one should keep in mind the 4 factors
described in bullet form above, which cause test conditions to return different touch, step and mesh
voltages per unit injection current than fault conditions. Furthermore, variations in local soil
resistivities can cause measured results to differ from computed results. At locations where a low
resistivity surface layer exists (i.e., lower in resistivity than that used in the computer model) earth
surface potential gradients, touch voltages and step voltages will tend to be lower than computed.

Page 4-9
This page is intentionally left blank
 Chapter 5. Ground Current Distribution Analysis

CHAPTER 5
GROUND CURRENT DISTRIBUTION
ANALYSIS
5.1 INTRODUCTION
The touch and step voltages associated with the grounding network are directly proportional to the
magnitude of the fault current component discharged directly into the soil by the grounding network.
It is therefore important to determine how much of the fault current returns to remote sources via the
skywires and neutral wires of the transmission lines and distribution lines connected to Lakeshore
Substation. In order to be able to determine the actual fault current split, a model of the overhead
transmission line network must be built. Before this, however, it is necessary to calculate
transmission and distribution line parameters such as self and mutual inductive and capacitive
impedances, at representative locations.

This work is described in the present chapter. The line parameters were computed using the
TRALIN module of the CDEGS software package. The resulting parameters were used by the
SPLITS module of the CDEGS software package to compute the fault current distribution.

In Chapter 4, measured touch and step voltages were converted to actual values during fault
conditions by assuming that the current discharged into the Lakeshore Substation grounding system
is the maximum available fault current for a single-phase-to-ground fault at Lakeshore Substation. In
reality, the current discharged into the Lakeshore substation grounding system is smaller than the
maximum available fault current, because a portion of the fault current returns via the skywires and
neutral wires of the power lines connected to Lakeshore Substation.

5.2 COMPUTATION OF THE LINE PARAMETERS

A simple schematic of the 115 kV transmission lines connected to Lakeshore Substation is shown in
Figure 5.1. Typical transmission line cross sections, as provided to SES, were chosen for the
transmission lines between Lakeshore Substation and the other substations and plants. Tower T-1
(Figure 5.2) is the representative structure used to represent the lines connected to Alexander and
Appleby Substations. Tower HF (Figure 5.3) is a typical structure for the line to Willow Substation.
It should be noted that the heights of the conductors shown in the figures are average values (sag is
taken into account). The phase conductors are 477 MCM ACSR 26/7 Hawk and the overhead ground
wires are 3/8" steel.

The computed fault currents flowing in all circuits, as supplied to SES, are listed in Appendix D. As
shown in Figure 5.1, eleven 115 kV transmission line circuits were accounted for in the computer
model. The 11 circuits have been reduced to the four-terminal circuit model shown in Figure 5.4.
Three terminals (Terminals Willow, Alexander and Appleby) contribute fault current and have
continuous overhead ground wires near the substation. Terminal “Others” represents the other
circuits that do not have continuous overhead ground wires connected to Lakeshore (or have no fault

Page 5-1
 Chapter 5. Ground Current Distribution Analysis

current contributions as is the case for Louisville and Beach). Further discussion about how to setup
SPLITS input file corresponding to the circuit shown in Figure 5.4 will be given in the next section.

The TRALIN program was used to calculate the required transmission line parameters, such as self
and mutual impedances between the various conductors. These parameters were used to build the
circuit model used by the SPLITS program to compute the fault current distribution. A single-phase-
to-ground fault was simulated at one of the 115 kV busses of the substation (115 kV faults constitute
the worst cases from a grounding performance perspective).

Based on the circuit shown in Figure 5.4, it is only necessary to compute the transmission line
parameters for the circuits from Lakeshore Substation to Terminals Willow, Appleby, Alexander and
Others. The transmission line cross sections to Terminals Willow, Appleby and Alexander are
shown in Figure 5.2 and Figure 5.3. The transmission line cross section to Terminal Others consists
of only a single phase conductor at an average height of 60 ft.

Figure 5.1 Schematic Diagram of Sources Connected to Lakeshore Substation.

Page 5-2
 Chapter 5. Ground Current Distribution Analysis

Figure 5.2 Tower T-1: Representative Structure Modeled for Alexander and Appleby 115 kV
Lines.

Figure 5.3 Tower HF: Representative Structure Modeled for Willow Line.

Page 5-3
 Chapter 5. Ground Current Distribution Analysis

5.2.1 Preparation of the TRALIN Input File

In the following, we will describe in detail how to setup the TRALIN input file for Substation
(Terminal) Willow. The TRALIN input files for Terminals Alexander, or Appleby and Others can be
setup in a very similar way. Therefore, we will only discuss the differences among them.

In this example, we have decided to ignore the presence of the other non-faulted phase conductors
although it is very likely that they are carrying a non-zero load current at the time the fault occurred.
Furthermore, the fault current carried out by the faulted phase conductor will induce currents on the
other phases. Consequently, the fault current distribution results are approximate values. Obviously,
it is relatively easy to include the other phases and repeat the computations to assess the extent of the
approximation. The reader is encouraged to perform this additional comparison run.

Finally, the selected faulted conductor is the one that is farthest from the overhead ground (shield)
wires resulting in the largest fault current magnitude. Phase Number 1 was assigned to the
conductor. The two ground wires were assigned 2 as their phase number. This implies that they will
be reduced to one equivalent conductor since bundle reduction is required by default.

As with the RESAP and MALZ input files, you can prepare the TRALIN input file using either of
the input interface module provided, or with a standard text editor. The following section describes
the Windows-compatible input session. The most important features in preparing the data are
explained in Section 5.2.1.2, which also describes some tricks on how to avoid common input
problems.

5.2.1.1 Start Up Procedures

In the SES Software group folder, double-click the SESCDEGS icon to start the CDEGS program
interface (if not already started). You will be prompted for the Working Directory and a Current
Job ID. Enter the complete path of your working directory in the Working Directory box. Enter
WILLO as the Current Job ID (any other string could be used).

Click the TRALIN button located in the toolbar and the Specify mode in the dropdown menu. The
SESTRALIN screen will appear (without the text) and you are now ready to input your data.

Page 5-4
 Chapter 5. Ground Current Distribution Analysis

In the following section, it will be assumed that

the reader is entering the data as indicated in the
instructions. Note that it is advisable to save
your work regularly by clicking the Save button
and following the instructions in the dialog box.
The data entered up to that point will be saved
in a file under the name TR_WILLO.F05. Each
file can be retrieved at any time by clicking on

the Open button in the backstage and following

the instructions in the dialog box. The same
considerations apply if a data entry session has to
be interrupted. Close all active windows to exit
the program after saving your data.

If you intend to enter the data manually, proceed

directly to Section 5.2.1.2, otherwise, you can
directly open the file “TR_WIL08.F05” copied to
the working directory as described in Section 1.9.

5.2.1.2 Data Entry

As shown in Figure G.3 in Appendix G, the TRALIN commands are grouped into modules,
reflecting the hierarchical nature of the SES Input Command Language. Each module of Figure G.3
(with the exception of the OPTION module) is associated to a button in the TRALIN screen. The
OPTION module is actually part of the TRALIN main screen.

Again, the data entry field in the Module Description tab under the Case Description block allows
you to type comment lines that
are used to describe the case to
be analyzed in the TRALIN
module. They are echoed in the
TRALIN output file. A Run-ID
WILLOW is entered in the Run-
Identification data entry field.
Note that a default value of 60
HZ is used for the computations.

We will first define the soil

model by clicking the Soil
Characteristics button. A two-
layer soil model based on the
resistivity measurement along
Traverse 3 is used since this soil
model represents more closely

Page 5-5
 Chapter 5. Ground Current Distribution Analysis

the soil structure around the Lakeshore substation. The two-layer soil model is defined by the
following screen. Note that the Horizontal 2-Layer or Horizontal 3-layer soil type are only available
if Single Mode (see next screen) under Cross Section Specification Options is selected in the
Project Info screen.

Now we are ready to specify the overhead transmission line system. Click on the Project tab to
display the application backstage. The Project Info screen is displayed.

There are three modes to enter conductors in the

transmission line system. The Group Mode should be
used if the system contains underground, insulated,
pipe-enclosed or cable-type conductors. In the group
mode, no more than one earth layer (and one air layer)
may be described in the soil model. The Single Mode is used for systems consisting entirely of
aboveground, uninsulated conductors. The conductors are described one at a time. The Circuit
Mode is used for systems consisting entirely of aboveground, uninsulated bundled conductors. The
conductors are described circuit by circuit. Due to several restrictions concerning circuit selection
and identification of ground wires, we recommend the use of the single mode whenever possible.
The Single Mode is selected in this case. The soil model used in both Single Mode and Circuit
Mode allows the specification of up to three earth layers in addition to the air layer.

The location, size, and characteristics of

conductors are entered by clicking on the
Cross-section tab. The following text and
screens describe the steps required to
define the transmission line conductors
modeled between Lakeshore Substation
and Terminal Willow.

The data in Phase/Line Number specifies

the phase number of the conductor. The
phase number is used to indicate which
conductors share the same energization
sources (points) and are to be reduced to
an equivalent single conductor when the
Bundle Reduction option (in the Home
tab) is in effect. The phase number of the
phase conductor is set to 1. The phase number of the overhead ground wires is set to 2. Note that the
phase number assigned to a conductor or a group of conductors should be the same as the
energization bus number to be used in the corresponding SPLITS input file. The Y Coordinate and
Z Coordinate define the location of these conductors, as specified in Figure 5.3.

The characteristics of the phase conductor and overhead ground wires are defined by clicking on the
Component Type (i.e., C1, C2, C3, etc.).

Page 5-6
 Chapter 5. Ground Current Distribution Analysis

We first define the faulted phase conductor C1 by selecting the

From database option when the following screen appears. Select
ACSR from the Conductor Class list. Scroll down the screen to
find the Hawk conductor and click the Import button. The phase
conductor C1 is now defined.

The two overhead ground wires C2 and C3 can be defined similarly. Click the C2 button from
Component Type, select Import from database and select Steel from the Conductor Class list.
Choose the 3/8 HS-AG conductor and click the Import button.

Page 5-7
 Chapter 5. Ground Current Distribution Analysis

The overhead ground conductor C3 can be defined by simply repeating the steps above since it has
the same property as conductor C2. Click Close to return to the TRALIN-Single Conductor Input
Mode screen.

5.2.1.3 How to Produce the TRALIN Input File

You can now return to the TRALIN screen by clicking OK. At this point, you have completed the
preparation of the input data: it is ready to be submitted to the TRALIN computation module in the
next section.

By following the steps described above for Terminal Willow, the TRALIN input files for Terminals
Alexander, Appleby and Others can be easily obtained. These files, named TR_ALE08.F05 and
TR_OTH08.F05, have already been created so that they can readily be loaded. The only differences
between TR_WIL08.F05, TR_ALE08.F05 and TR_OTH08.F05 are the conductor configurations of
the transmission line system. The transmission line cross-section from Lakeshore Substation to
Terminals Alexander and Appleby is defined in the following screen.

The transmission line cross-section from Lakeshore Substation to Terminal Other is defined in the
following screen. Note that no overhead ground wires exist along the equivalent Terminal Others as
explained before.

Page 5-8
 Chapter 5. Ground Current Distribution Analysis

If you are a licensee of the CDEGS software you will now be able to proceed to Section 5.2.2. Users
of the demo software are not able to process the input file, but are able to peruse all output files
which are already available. Therefore read Section 5.2.2 for reference only. Any attempt to start the
computation modules will result in a message stating that the Computation module is not active.

5.2.2 Submission of the TRALIN Run

Click the Compute button to submit and run the model. This does two things:

1. It saves file under the name TR_WILLO.F05. Each file can be reread from the Toolbox using
the Open button located in the backstage. Furthermore, the *.F05 files are ASCII files you
can edit and view at any time.

2. It starts the TRALIN computation program.

The TRALIN computation module will start and will carry out all requested computations. The run
should be quite fast (within a minute). At completion, the program will produce two important files:
an OUTPUT file (TR_WILLO.F09) and a REPORT file (TR_WILLO.F27).

Both the OUTPUT and REPORT files are ASCII files. Any ERROR or WARNING messages
generated during the TRALIN run will appear in the OUTPUT file. You can view the OUTPUT file
by clicking the File Viewer ( ) button in the Output section of the toolbar. If prompted, select the
TRALIN: Line Parameters option, and click OK.

The REPORT file contains a portion of the structured input data needed to build the SPLITS input
file. This data describes the self impedances per unit length (here per mile) of all the conductors and
the mutual impedances between all pairs of conductors of our electrical model. This data can be
imported into the SPLITS input file.

Page 5-9
 Chapter 5. Ground Current Distribution Analysis

The input files TR_ALE08.F05 and TR_OTH08.F05 can be similarly submitted using the
recommended Job IDs ALEXA and OTHER, respectively.

5.3 COMPUTATION OF THE FAULT CURRENT

DISTRIBUTION
After TRALIN produced the required line parameters, a circuit model of the overhead transmission
lines was built, as illustrated in Figure 5.4. The computed fault currents flowing in all circuits, as
supplied to SES, were used to determine the equivalent source impedances at the corresponding
terminals. The equivalent ground impedances (which include the substation ground system and all
parallel neutral outgoing connections) of the substation terminals were assumed to be 0.01  which
is a low value (conservative assumption). As mentioned earlier, the 11 circuits have been reduced to
the four-terminal circuit model shown in Figure 5.4.

Figure 5.4 Transmission Line Circuit Model.

Since a single-phase fault was simulated, only one phase conductor and the neutral wire were needed
in the model. The average span length is 400 feet from Lakeshore Substation to Willow Substation
and 500 feet from Lakeshore Substation to Alexander and Appleby Substations, according to data
provided to SES. Based on the average span length and transmission line lengths between these
substations, there are 26 spans from Lakeshore Substation to Willow Substation, 89 spans from
Lakeshore to Alexander, and 486 spans from Lakeshore to Appleby. The tower ground resistances
are assumed to be 68  on the Willow line and 76  on the Alexander and Appleby lines, which are
conservative values based on the tower structure grounding system dimensions and the type of soil
structure found around Lakeshore Substation. The central site ground impedance (i.e., Lakeshore
substation ground impedance) is 0.2932 + j 0.1496 , which is the 60 Hz grounding grid impedance
computed by MALZ as described in Chapter 3, but with the grounding provided by the Willow,
Appleby and Alexander transmission lines towers removed from the model (since these towers are

Page 5-10
 Chapter 5. Ground Current Distribution Analysis

represented separately in the circuit model). The MALZ input file MZ_FZGSP.F05 is used for
computing the impedance.

The single-phase-to-ground fault currents, provided to SES, are:

Willow Substation: 5828.9A  -79.81
Alexander Substation: 2405.4A  -83.36
Appleby Substation: 1329.6A  -78.63
Others Remote Sources: 18694.7A  -79.5
The SPLITS program was used to compute the fault current distribution. The total fault current
injected into the Lakeshore substation grounding system was obtained as well as the currents
discharged into the grounding system of each terminal and each transmission tower.

The following describes the steps required to build the SPLITS input file and to obtain the fault
current distribution.

5.3.1 Preparation of the SPLITS Input File

As with the RESAP, MALT and TRALIN input files, you can prepare the SPLITS input file using
either of the two input interface modules provided, or with a standard text editor. The following
section describes the Windows-compatible input session. This section describes in detail how to
prepare the SPLITS input data using the CDEGS Input Mode. The most important features in
preparing the data are explained in Section 5.3.1.2.

5.3.1.1 Start Up Procedures

In the SES Software group folder, double-click the CDEGS icon to start the CDEGS program
interface (if not already started). You will be prompted for a Working Directory and a Current Job
ID. Enter the complete path of your working directory and CULAK for the Current Job ID.

Page 5-11
 Chapter 5. Ground Current Distribution Analysis

Select the SPLITS button located in the toolbar and click on Specify in the Session Mode list. The
CDEGS-Specify-SPLITS screen will appear (without the text) and you are now ready to input your
data.

In the following section, it will be assumed that the reader is entering the data as indicated in the
instructions. Note that it is advisable to save your work regularly by clicking the Save button and
following the instructions in the dialog box. The data entered up to that point will be saved in a file
under the name SP_CULAK.F05. Each file can be retrieved at any time by clicking on the Open
button located in the backstage and following the instructions in the dialog box. The same
considerations apply if a data entry session has to be interrupted. Close all active windows to exit the
program after saving your data.

If you intend to enter the data manually, proceed directly to Section 5.3.1.2. If you do not wish to do
so, you can import all the data by proceeding as follows.

Importing DATA
Click the Open button located in the Project tab. Change the File Name in the dialog box to
SP_LAK08.F05 then click the Load button in the dialog box. Click OK in the resulting message
dialog box. The data described in the next section will be loaded and you will not have to enter it.

Page 5-12
 Chapter 5. Ground Current Distribution Analysis

5.3.1.2 Data Entry

As shown in Figure G.4, the SPLITS commands are grouped into modules, reflecting the
hierarchical nature of the SES Input Command Language. Each module of Figure G.4 (with the
exception of the OPTION module) is associated to a button in the SPLITS screen. The OPTION
module is actually part of the SPLITS main screen.

The data entry field in the Module Description block allows you to type comment lines that are
used to describe the case being analyzed. They are echoed in the SPLITS output file. A Run-ID
CURR_LAKESHORE is entered in the Run-Identification box (click Specify to define this value).
The Run-ID is useful in identifying all the plots which will be made later in Section 5.3.3. Note that
the source voltage is set to the phase-to-neutral voltage (by default, the source voltage is the phase-
to-phase voltage).

We first define the span scaling options by clicking

on the Span Scaling button. The Span Scaling
Factor in the following screen defines a constant
which can be used to scale series, mutual, shunt and
connection impedances, as well as terminal source
impedances. The selection of option buttons control
whether or not the Scaling Factor and Span Length
are actually applied to series, mutual, shunt,
connection, and source impedances. When enabled,
Scaling Factor and Span Length multiplies series,
mutual and source impedances and divides
connection impedances and the real and imaginary
parts of shunt impedances. The main utility of this constant is to permit simple conversion of input
data specified in ohms per unit of a base length (i.e., km, mile etc.) to actual ohms for the specified
section (span) length. Note that in this input file the impedances are specified in ohms per mile
except for the Terminal Source Impedances and Resistive Component of Shunt Impedances which
are in ohms and will not be scaled. This is
the most frequent case.
We will now specify the circuit according
to Figure 5.4. Click the System button. The
SPLITS (System) screen is displayed.

The screen above defines the Central Site,

i.e., Lakeshore Substation, where a fault is
often modeled (see Figure 5.4). The ground
impedance of the ground network at the
Lakeshore substation is equal to 0.2932 +
j0.1496 . The data fields in the Central
Site Busses tab allow you to label the
busses at the central station and specify the
equipment impedances through which
these busses are connected to the ground
network. In this case, Bus No. 1 is the

Page 5-13
 Chapter 5. Ground Current Distribution Analysis

faulted phase conductor that is

supposed to be connected to the
ground grid of the Lakeshore
substation through an electric
arc or metallic short with zero
impedance. Bus No. 2 is the
overhead ground wire that is
normally connected to the
Lakeshore substation with a
very small impedance assumed
to be 0.00001 .

We will now define the four

terminals: Willow, Appleby,
Alexander and Others. Click the
Terminals tab under Define,
and enter Willow under
Terminal Name.

Then click the Define Data button. The source at Terminal Willow is defined as shown in the
following screen.

As shown in Figure 5.4, the fault current contribution from Terminal Willow was estimated to be
5828.9-79.8 A. This fault current could be directly assigned as the energization for this bus.
However, for this tutorial a voltage-driven energization bus is used instead; the required fault current

Page 5-14
 Chapter 5. Ground Current Distribution Analysis

is forced by assigning a terminal source voltage of 5828.9-79.8 kV (in Polar form) and a large
source impedance of 1 k. A source voltage such as this one is, in fact, equivalent to a current
source. Taking into account the total impedance of the phase conductor from Terminal Willow to
Lakeshore Substation, the Equivalent Source Impedance in  is therefore given approximately as:

1000 − 𝑍line = 1000 − 𝑁span × 𝐿span × 𝑍span

= 1000 − 26 × 0.07576 × (0.29194 + 𝑗 1.4842)
= 999.4249 − 𝑗 2.9235

where Zline represents the impedance as seen by the phase conductor from Terminal Willow to
Lakeshore Substation. Nspan is the total number of spans (sections) and Lspan is the average span
length, i.e., about 400 feet or 0.07576 mile. Zspan represents the series impedance of one span. Zspan
(in ohm/mile) was computed by TRALIN previously and can be found in the TRALIN output file
TR_WILLO.F27. Note that Zline is usually small compared to the source impedance and can usually
be ignored.

The source voltage applied to the overhead ground conductor Bus No. 2 is of course, zero and the
equivalent source impedance is also essentially zero. The equivalent ground impedance of the
terminal including its grounding system is assumed to be a low value of 0.01 . Note that it is
possible to have different or identical source voltages applied to several buses (or lines). Program
SPLITS assumes that between the central station and any terminal there is the same number of lines
and, moreover, the program assumes that the lines are all connected to their associated busses (i.e.
line 3 to bus 3). In order to specify non-existing lines one can declare a line as “Dummy”. If on the
other hand some sections or spans are absent then the user can specify “Dummy Sections”.

We will now define the sections

between Terminal Willow and
Lakeshore Substation by clicking the
Sections option button. As shown in
Figure 5.4, there are 26 sections
corresponding to 26 spans from
Lakeshore Substation to Willow
Substation. The average span length is
400 feet, which is 0.07576 mile. These
data are entered in the following
screen. We specify the span length in
mile because during the computations
this span length will be used to scale
the series, shunt, mutual and
connection impedances which, as you may recall, are in /mile (see TR_WILLO.F27). The sections
are numbered as follows: the section next to the central station is Section 1; section numbers then
increase as we move away from the central station. Note that the very last section or "Terminal
section" was already defined. Its series impedance is the equivalent source impedance.

The series and shunt impedances of each section and the mutual impedances between sections were
already computed by TRALIN and can be conveniently imported into SPLITS simply by clicking
the Import Data button.

Page 5-15
 Chapter 5. Ground Current Distribution Analysis

Select the file TR_WILLO.F27. Click the Open button. These impedances have been imported as
shown in the following two screens.

Page 5-16
 Chapter 5. Ground Current Distribution Analysis

The shunt impedance is usually the tower ground resistance when the line is an overhead ground
wire or the line capacitance (actually, capacitive reactance) when the line is a phase conductor.
Shunt reactors or capacitors can also be modeled. The series impedance of the phase conductor
computed by TRALIN was already used to compute the equivalent source impedance. To specify a
tower ground resistance of 68  (see Figure 5.4), the shunt impedances of the overhead ground wire
(Line 2) as compute by TRALIN, i.e., 0.0- j0.20656E+06  was simply replaced by 68 + j0.0 
manually.

The status of both lines is set to Active. When the Dummy status is specified, the lines are modeled
as open circuits: i.e., they are assumed to have an infinite series impedance. The series impedances
should therefore not be entered in this case. On the other hand, a shunt impedance can be entered if
desired: this usually specifies a terminating ground impedance at one end of a conductor. The
DUMMY option is useful, for example, to model the endpoint of a pipeline or long counterpoise
which ends abruptly between a terminal and the central station.

The Mutual Impedance and Interconnection Impedance defines the inductive coupling and
capacitive coupling, respectively, between one group of lines and another group of lines in the last
specified range of sections. SPLITS automatically ignores any mutual impedances between a section
and itself. A short circuit between two or more lines can be modeled by specifying a small value for
the Interconnection Impedance between the lines involved.

The Zero/Infinite status is meaningful only when the interconnection impedance is zero (both real
and imaginary parts are zero) or is not specified. The Infinite qualifier means that if the
interconnection impedance is zero, an infinite value is assigned instead; the Zero qualifier means that
if the interconnection impedance is zero, a zero value is effectively assigned. The Infinite qualifier is
the default setting. When the interconnection impedance is not zero, the specified values are used by
the program, no matter what status is specified.

This completes the definition of Terminal Willow. Click the OK button to return to the SPLITS
(System) screen. The remaining three terminals can be entered similarly. The TRALIN output files

Page 5-17
 Chapter 5. Ground Current Distribution Analysis

which contain the transmission line parameters are TR_ALEXA.F27 for Terminals Appleby and
Alexander, and TR_OTHER.F27 for Terminal Others. The SPLITS (System) screen is shown
below after all four terminals being defined. As shown in Figure 5.4, the tower ground resistances
are set to 76 ohms for both Terminals Alexander and Others.

The following screens define Terminal Appleby:

Page 5-18
 Chapter 5. Ground Current Distribution Analysis

Page 5-19
 Chapter 5. Ground Current Distribution Analysis

The following screens define Terminal Alexander:

Page 5-20
 Chapter 5. Ground Current Distribution Analysis

Page 5-21
 Chapter 5. Ground Current Distribution Analysis

The following screens define Terminal Others:

Page 5-22
 Chapter 5. Ground Current Distribution Analysis

5.3.1.3 How to produce the SPLITS Input File

You can now return to the SPLITS main screen by clicking OK. At this point, you have completed
the preparation of the input data: it is ready to be submitted to the SPLITS computation module in
the next section.

If you are a licensee of the CDEGS software you will now be able to proceed to Section 5.3.2. Users
of the demo software are not able to process the input file, but are able to peruse all output files
which are already available. Therefore read Section 5.3.2 for reference only. Any attempt to start the
computation modules will result in a message stating that the Computation module is not active.

Page 5-23
 Chapter 5. Ground Current Distribution Analysis

5.3.2 Submission of the SPLITS Run

Click the Compute / Submit button to submit and run the model. This does two things:

1. It saves a file under the name SP_CULAK.F05. Each file can be reread from the Toolbox
using the Import/Load button. Furthermore, the *.F05 files are ASCII files you can edit and
view at any time.

2. It starts the SPLITS computation program.

The SPLITS computation module will start and will carry out all requested computations. The run
should be quite fast (a few minutes). At completion, the program will produce two important files:
an OUTPUT file (SP_CULAK.F09) and a DATABASE file (SP_CULAK.F21).

The OUTPUT file is an ASCII file, while the DATABASE file is a binary file. Any ERROR or
WARNING messages generated during the SPLITS run will appear in the OUTPUT file. You can
view the OUTPUT file by clicking the clicking the File Viewer ( ) button in the Output section
of the toolbar, selecting the SPLITS: Current Distribution and Interference option, and clicking
the OK button.

5.3.3 Extraction of the Results from SPLITS Computation Results

Files
The OUTPUT file contains all the input information and computation results from your SPLITS run.

The DATABASE file is normally used by the CDEGS Output Session and the SES Interactive
Report & Plot Software processors (such as GraRep) to display the computation results. In the
following, we will give an example to show how to use the GRSPLITS-3D interface to produce the
corresponding graphs.

We will extract the results and

display the plot on the screen. If
the GRSPLITS-3D screen is not
already visible, click on the
(Examine) button on the toolbar:
the GRSPLITS-3D screen will
appear and you are now ready to
make plots.

From the output file SP_CULAK.F09 (at the end of the output file), you will find below a partial
printout that lists more data about the fault current distribution.

Page 5-24
 Chapter 5. Ground Current Distribution Analysis

<----- BUS -----> <-------- NET CURRENT AT SUBSTATION BUS ---------> <------ SHUNT POTENTIAL AT CENTRAL STATION ------>
No. Type Active (A) Reactive (A) Magnitude (A) Angle(deg) Active (V) Reactive (V) Magnitude (V) Angle(deg)
==== ============ ============ ============ ============= ========== ============ ============ ============= ==========
1 PHSA 4965.3 -27790. 28230. -79.870 4239.6 -6532.3 7787.5 -57.015
2 GRDW -2511.8 4258.4 4944.0 120.534 4239.6 -6532.3 7787.5 -57.015
============ ============ ============= ========== ============ ============ ============= ==========
TOTAL CURRENT DISCHARGED 2453.5 -23531. 23659. -84.048
BY CENTRAL STATION GROUND

GRID IMPEDANCE TOTAL FAULT CURRENT TOTAL NEUTRAL CURRENT TOTAL EARTH CURRENT GROUND POTENTIAL RISE
--------------------- ----------------------- ----------------------- ----------------------- -----------------------
R (ohms) +jX ACTIVE (A) REACTIVE (A) ACTIVE (A) REACTIVE (A) ACTIVE (A) REACTIVE (A) ACTIVE (V) REACTIVE (V) *
MAGN. (A) ANGLE (deg.) MAGN. (A) ANGLE (deg.) MAGN. (A) ANGLE (deg.) MAGN. (V) ANGLE (deg.) #
<--------> <--------> <--------> <--------> <--------> <--------> <--------> <--------> <--------> <-------->
0.2932 0.150 2453.49 -23531.27 0.00 0.00 2453.49 -23531.27 4239.64 -6532.33 *
23658.83 -84.048 0.00 -87.614 23658.83 -84.048 7787.54 -57.015 #

These results are summarized below:

115 kV Fault

Total Phase-to-Ground Current at Fault Location: 34,999.1 A -80.95

Net Fault Current from Remote Sources: 28,230 A-79.87
Fault Current Discharged in Soil by Grounding Grid: 23,659 A -84.05
(83.8 % of net fault current)
Fault Current Returning Via Overhead Ground Wires: 4944.0 A 120.53
(17.5 % of net fault current)
Ground Potential Rise (GPR) of Lakeshore Substation, at Fault: 7787.5 V -57.01

Note that the difference between the “total phase-to-ground current at fault” and the “net fault
current into substation” consists primarily of current flowing between the fault and the 230 kV
transformer ground connections (circulating current).

As mentioned earlier, the ground impedances of the substation terminals were assumed to be 0.01 
which is a conservative assumption. In fact, when 0.000001  is used instead of 0.01 , the current
flowing into the Lakeshore substation grounding grid remains almost unchanged.

The fault current components flowing in the skywires of the transmission lines connecting
Lakeshore Substation to Willow, Alexander and Appleby Substations can be examined in the output
file SP_CULAK.F09. In particular, the currents in Section 1 (nearest to the Lakeshore Substation) of
the overhead ground conductors represent the currents that are not discharged by Lakeshore
grounding system during the fault. These currents, which will be used in the next chapter to compute
the ground potential rise during the fault, are listed in the table below.

Terminal Real Part Imaginary Part Magnitude (A) Phase

(A) (A) (Degree)
Willow -1453.0 2197.1 2634.1 123.48
Appleby -484.1 1004.0 1114.7 115.74
Alexander -574.7 1057.2 1203.3 118.53
For example, the current for Terminal Willow can be found in the output file as follows:

Page 5-25
 Chapter 5. Ground Current Distribution Analysis

TERMINAL NO. 1, WILLOW

------------------------------

Sect. <----- BUS -----> <------------ SECTION CURRENT ( Amps ) ----------> Tower <-------- TOWER <SHUNT> POTENTIAL ( V ) --------->
No. No. TYPE ACTIVE REACTIVE MAGNITUDE ANGLE(deg.) No. ACTIVE REACTIVE MAGNITUDE ANGLE(deg.)
==== === ============ ============ ============ ============ =========== ===== ============ ============ ============ ===========
1 1 PHSA 1030.2 -5729.1 5821.0 -79.806 0 4239.6 -6532.3 7787.5 -57.015
1 2 GRDW -1453.0 2197.1 2634.1 123.478 0 4239.6 -6532.3 7787.5 -57.015
2 1 PHSA 1030.2 -5729.1 5821.0 -79.806 1 4776.8 -6606.6 8152.6 -54.132
2 2 GRDW -1395.9 2106.6 2527.2 123.530 1 3881.9 -6153.6 7275.8 -57.755

The currents in the skywires can also be plotted. Select the Series Current tab and under Plots,
select the displayed terminal. The graph will automatically be plotted.

Figure 5.5 Current Flowing in Willow Transmission Line Conductors Versus Number of
Spans from Lakeshore Substation.
The plot above shows that a greater percentage of the fault current splits off to the overhead ground
wires during fault conditions than during the field tests (see Section 2.1), primarily due to the effect
of magnetic induction from the fault currents flowing in the transmission line phases, an effect not
present when the grid energization takes place from an independent source.

The fault current flowing in the overhead ground wires of the transmission lines connecting
Lakeshore Substation to Alexander and Appleby Substations can be plotted similarly. In displayed
terminal, select the Appleby or the Alexander Terminal. The results are shown below.

Page 5-26
 Chapter 5. Ground Current Distribution Analysis

Figure 5.6 Current Flowing in Appleby Transmission Line Conductors Versus Number of
Spans from Lakeshore Substation.

Figure 5.7 Current Flowing in Alexander Transmission Line Conductors Versus Number of
Spans from Lakeshore Substation.

Page 5-27
 Chapter 5. Ground Current Distribution Analysis

We will now plot the currents discharged into the earth by the tower grounds of these transmission
lines. Select Shunt Currents tab and select the displayed terminal The results are displayed below:

Figure 5.8 Current Flowing in Tower Grounds of Willow Transmission Line (Towers or
“Sections” Numbered Starting at Lakeshore).

Figure 5.9 Current Flowing in Tower Grounds of Appleby Transmission Line (Towers
or “Sections” Numbered Starting at Lakeshore).

Page 5-28
 Chapter 5. Ground Current Distribution Analysis

Figure 5.10 Current Flowing in Tower Grounds of Alexander Transmission Line (Towers or
“Sections” Numbered Starting at Lakeshore).

Page 5-29
This page is intentionally left blank
 Chapter 6. Performance Evaluation of Lakeshore Substation

CHAPTER 6
PERFORMANCE EVALUATION OF
LAKESHORE SUBSTATION
Now that we have determined the soil structure, grounding system performance and fault current
magnitude and distribution, we are ready to evaluate if our proposed design is safe and adequate.
This chapter describes the detailed steps that were taken to compute touch voltages, grounding grid
potentials, and longitudinal currents throughout Lakeshore Substation, in order to determine at what
locations, if any, mitigative measures are required.

6.1 SAFETY CRITERIA

Before describing the computer modeling, let us first identify the safety objectives.

6.1.1 Touch Voltages

The first safety criterion used for the evaluation of the grounding system performance is the touch
voltage limit. The touch voltage is usually defined as the difference in potential between a point on
the earth’s surface, where a person is standing, and an exposed conductive surface within reach of
that person.

ANSI/IEEE Standard 80-20132 provides a methodology for determining maximum acceptable touch
voltages, based on the minimum current required to induce ventricular fibrillation in a human
subject. The touch voltage limit is a function of shock duration (i.e., fault clearing time), system
characteristics (for short fault clearing times), body weight, and foot contact resistance (which
depends on the electrical resistivity of the material, such as crushed rock or soil, on which the person
is standing). The table below shows how touch voltage varies as a function of earth surface covering
material, for a 0.5 s fault clearing time, a system X/R ratio3 of 20, and a 50 kg body weight.

Surface Layer Touch Voltage Limit (V)

Type Resistivity (-m)
Native Soil 107 191
3” Crushed Rock 2000 381
The crushed rock surface layer is assumed to be 3” thick and overlying a soil with a resistivity of
106.8 -m. The crushed rock resistivity provided in the table is a typical value agreed upon by SES

2
In this project, the IEEE Standard #80 (2013 version) criteria are used to assess the safety status of the system.

3
This corresponds to the 230 kV system which results in the worst case faults, as discussed later in this chapter.

Page 6-1
 Chapter 6. Performance Evaluation of Lakeshore Substation

following discussion on the nature of the rock used and corresponds to crushed rock when wetted.
Resistivity varies as a function of the type of rock, the size of the stones, the moisture content and
the degree of contamination (e.g., filling of the voids between stones by finer lower resistivity
material).

6.1.2 Step Voltages

A similar table can be compiled for step voltages, defined as the difference in potential between two
earth surface points spaced 1 m (3.28 ft) apart.

Surface Layer Step Voltage Limit (V)

Type Resistivity ( -m)
Native Soil 107 274
3” Crushed Rock 2000 1033

Within a substation and within 1 m (3.28 ft) outside the perimeter fence, step voltages are lower than
touch voltages; furthermore, the maximum acceptable values are higher than for touch voltages.
Consequently, satisfying the touch voltage safety criteria in this area automatically ensured
satisfaction of the step voltage safety criteria. Indeed, it was found that step voltages in the
substation and in an area extending 30 feet outside the substation were safe throughout. Outside the
substation, no computations were performed. However, it is unlikely for hazardous step voltages to
exist at such remote locations when they are safe closer to the substation.

6.1.3 GPR Differentials

Significant potential differences between distant parts of the grounding system can give rise to local
touch voltages or equipment stress voltages when low voltage insulated conductors connect
equipment at two such locations. Appropriate protection must be in place at such locations, rated for
the GPR differentials that can arise. This study provides the necessary data to identify such
locations, if applicable.

6.1.4 Determining Safe Touch and Step Voltages Criteria Using

CDEGS
The safe touch and step voltages can be estimated easily using the CDEGS Output Processor. The
only requirement is that you must have a finished MALZ (or MALT) run so that CDEGS Output
Processor can be invoked. In this case, we choose one of the MALZ runs (MZ_FGD2B.F05) in the
Fall-of-Potential analysis.

Page 6-2
 Chapter 6. Performance Evaluation of Lakeshore Substation

6.1.4.1 Start Up Procedures

In the SES Software group folder, double-click the CDEGS icon to start the CDEGS program
interface (if not already started). You will be prompted for a Working Directory and a Current Job
ID. Enter the complete path of your working directory in the Working Directory box; enter FGD2B
as the Current Job ID.

Select Examine in the Session Mode list, and

click the MALZ button located in the toolbar.
The MALZ SESResultsViewer screen will
appear and you are now ready to make a safety
analysis.

Select the Specify in Threshold Module input

mode option and click on the button located next
to the Input Mode for the Define Safety
Threshold. This will bring the SESThreshold
module to calculate the safety limits.

The gravel installed on the surface of the

Lakeshore substation is assumed to be 3 inch
thick and overlying a soil with a resistivity of
107 -m. The crushed rock has an estimated
resistivity (when wet) of 2000 ohm-m. The
maximum clearing time of the backup relays is
0.5 s. To reproduce the results of the IEEE Std.80-2013, the IEEE Std.80-2013 method should be
selected for the Foot Resistance Calculation Method. Also, the User-Defined option should be
selected for the Decrement Factor, and 1 should be entered in the Decr. 1 box. This is because that
version of the Standard recommends using 1 for the decrement factor for values of the fault clearing
time greater than or equal to 0.5 seconds, as is the case here. (In the new version of the standard, it is
recommended to use the computed value of the decrement factor for all values of the fault clearing
time).

Page 6-3
 Chapter 6. Performance Evaluation of Lakeshore Substation

The information entered in the Network and Zone specification followed the above screenshot. If
this information is entered in the Specifications screen as shown above, you can then click on
Compute Only and Show Report. The following report appears on your screen.

Page 6-4
 Chapter 6. Performance Evaluation of Lakeshore Substation

The table above indicates that touch voltages of 489 Volts less and step voltages of 1466 Volts or
less are safe if a 3 inch crushed rock of 2000 -m is overlying a native soil with a resistivity of 107
-m.

To find out the corresponding limits when no crushed rock covering is installed, select the option
Account for Resistance of Material Underfoot, and click Compute Only. The touch and step
voltages of 164 Volts or less are safe if no surface crushed rock is present at Lakeshore Substation.

6.2 COMPUTER MODEL

6.2.1 Modeling of the Lakeshore Substation Grounding System
Lakeshore Substation is located near Broad River, which crosses the city from south to north. The
substation is interconnected via 115 kV transmission lines, and via 23 kV and 33 kV distribution
lines to other substations. A metallic fence that can be contacted by the public surrounds the
substation. Two gas substations flank Lakeshore Substation on the north and south sides. Several gas
pipelines are present around the substation, which interconnect the two gas substations. The
substation dimensions are about 1000 ft x 700 ft.

Because nearby water pipes are bonded to the grounding system indirectly via neutral wires of the
distribution feeders of the city, the overall ground conductor network should include these
conductors in order to obtain accurate results. The transmission line overhead ground wires also
constitute part of the substation’s extensive grounding system. Attempts to model in detail every
major component of this ground network quickly lead to computer time and memory limitations.
Fortunately, however, it is conservative and reasonably accurate to model only a skeleton of this
network, consisting of the substation grounding network and water pipes of the residential area
around the substation.

The grounding network consists of the following major components:

 The grounding system of the substation.
 The buried portion of the substation metallic fence and ground loops.
 The grounding systems of the gas substations.
 The transmission line towers and distribution poles near the substation and associated
overhead ground wires and neutral wires connected to the substation.
 The water pipes in the residential area near the substation.

Page 6-5
 Chapter 6. Performance Evaluation of Lakeshore Substation

Figure 6.1 Grounding System at the Lakeshore Substation.

Figure 6.1 shows the grounding system that was used together with the water pipes to build an initial
MALZ input file. The number of conductors modeled in the electric substation is probably lower
than the number that actually exists. The fences for Lakeshore Substation and the gas substations on
both sides of Lakeshore Substation are removed to form a reduced grounding system that is used in
the computations. For touch voltages, the reduced grounding system gives higher values than the
detailed grounding system and thus makes the study more conservative. The reduced grounding
system will have a slightly higher ground impedance than that of the detailed grounding system. The
difference will be small because the ground impedance is dependent mainly on the area covered by
the grounding grid and is relatively insensitive to the conductor density of the grid.

6.2.2 MALZ Input Files

The MALZ module of the CDEGS software package was used for the detailed modeling of the
grounding system. Figure 6.1 shows the conductors modeled.

The grounding system of Lakeshore Substation and the associated gas substations is buried at a
depth of 1.5. The conductors of the grounding system are modeled as bare 4/0 copper conductors.
As shown in Figure 6.1, there are many vertical ground rods in Lakeshore Substation: they are
driven to various depths, ranging from 10 to 50. The diameter of each ground rod is 5/8 inch. Four
gas lines have been modeled. The gas pipes are made of steel with a resistivity equal to 12 times that
of copper and a permeability of 250 times that of air. Two 4 gas pipes (4.5 OD and 0.25
thickness) are located along the river side of the substation. A 10 pipe (10.75 OD and 0.25

Page 6-6
 Chapter 6. Performance Evaluation of Lakeshore Substation

thickness) and a 12 pipe (12.75 OD and 0.188 thickness) are located along Esplanade Road. The
gas lines are buried at a depth of 3.0. All gas pipes are insulated and connected to the main
grounding grid with bare conductors in the model.

Figure 6.2 shows the complete grounding system which includes portions of the skywires of the
transmission lines and the water pipes near the substation. A similar grounding system was used in
the analysis of the Fall-of-Potential measurements discussed in Chapter 3 (see Figure 5.3). Skywires
of the transmission lines are galvanized high strength steel conductors. The neutral wires of the
distribution lines are assumed to be 4/0 copper conductors. The diameter of each 115 kV
transmission line skywire is 0.36”. The total lengths of transmission lines and distribution lines
included in the modeling are indicated in Figure 6.2.

Figure 6.2 Complete Conductor Network.

The water pipe is made of steel with a resistivity equal to 17 times that of copper and a permeability
of 300 times that of air. It is assumed that no coating is present for the water pipes. The water pipes
are assumed to be 3 pipes (1/8 inch wall thickness) and buried at a depth of 3.0. The area of water
pipes being modeled is indicated in Figure 6.2. The first part of the water pipe network is modeled as
a rectangular grid (Residential Area 1). Only a single loop is used to model the area further away
from the substation (Residential Area 2).

6.2.3 Computation of Touch and Step Voltages at Lakeshore

Substation
Recall that the computed GPR of the substation during a 115 kV fault is 7788 V. A maximum touch
voltage of less than 4.8% of the GPR of the substation (i.e., 374 Volts) would keep the whole
substation below the safe touch voltage limit (i.e., 381 Volts). Similarly, a maximum step voltage of

Page 6-7
 Chapter 6. Performance Evaluation of Lakeshore Substation

less than 13% of the GPR of the substation (i.e., 1013 Volts) would keep the whole substation below
the safe step voltage limit (i.e., 1033 Volts) where crushed rock is present; elsewhere, a maximum
step voltage of 3.5 % would be required. Our objective then was to upgrade the grounding system
such that (a) the maximum touch voltage anywhere in the substation (including the area along the
perimeter fence on the outside) does not exceed 4.8% of the GPR of the grounding system, (b) the
maximum step voltage in the vicinity of the substation (up to 30 ft outside the substation, in this
study) does not exceed 3.5% of the GPR of the grounding system.

A reduced grounding system, which excludes the water pipes and overhead ground wires, was used
to compute the touch voltages at the Lakeshore substation. This is mainly because inclusion of these
conductors, while necessary for the computation of the grid impedance and GPR, has a relatively
small effect on touch and step voltages as a percentage of the grid GPR. Their omission constitutes a
conservative approximation, which allows more detailed modeling of the substation area.

Figure 6.3 shows the existing grounding system of the Lakeshore Substation.

(580,407)

(3,3) (481,3)

Figure 6.3 Existing Conductor Network of Lakeshore Substation.

A single-phase-to-ground fault was simulated at one of the 115 kV busses of the substation. The
fault location is labeled F in Figure 6.3. A nominal value of 1000 A was injected into the grid, since
we are primarily interested in the touch voltage as a percentage of the GPR of the grid. The scalar
potential and GPR of the grid conductors can be estimated by a scaling factor, , equal to the ratio of
the fault current injection point GPR computed for the detailed grid model to the corresponding GPR
computed with the smaller grid model used for the touch voltage calculations.

As shown in Figure 6.4, the scalar potentials are computed at a number of observation points which
are defined by 163 parallel profiles at the earth surface, from Y =-204 to Y= 444, in 4 steps. Each
profile consists of 321 observation points starting at X = -220 and spaced at 4 increments. This
array of observation points extends about 30 outside the fence perimeter.

Page 6-8
 Chapter 6. Performance Evaluation of Lakeshore Substation

Figure 6.4 163 Observation Point Profiles.

The two-layer horizontal soil model corresponding to Traverse 2, representing the soil resistivities
measured closest to the substation, was used to determine touch and step voltages associated with the
grounding system of Lakeshore Substation. Note that touch and step voltages are quantities that are
most sensitive to the local soil structure. Traverse 3 was also used initially, but Traverse 2 proved to
be more conservative and so only Traverse 2 was retained for the final design phase.

6.2.4 Grounding System Upgrade

The design of the grounding system upgrade was based on reduction of the touch voltage to less than
4.8% of the GPR of the grounding system using a grounding system model in which the net fault
current is injected into the grid at a single location (this is the standard approach to grounding system
design). With respect to substation grounding, the touch voltage is usually defined as the difference
in potential between the grounding grid and a point on the earth’s surface. For a grounding grid as
extensive as that of Lakeshore Substation, however, the potential of the grounding grid varies from
one location to another, so more than one definition is possible. For this study, a reach-touch voltage
with a search radius of 100 was used in the computation: i.e., touch voltages have been determined
based on the GPR of the grounding grid conductor which results in the greatest touch voltage and
which is partially or wholly within 100 of the earth surface point at which each touch voltage is to
be evaluated. This 100 feet radius was selected to account for the possibility of personal working
with mobile electrical tools or equipment powered via grounded electric wires of up to 100 feet.

Figure 6.5 to Figure 6.6 show the two preliminary designs of the grounding system. Appendix F
shows the final design of the grounding system obtained from the design procedure described above.
A number of 10 ground rods were added to Figure 6.6 to reach this final design. Subsequent
modeling, however, as described in Section 6.3.2 showed that consideration of circulating currents
flowing to the 230 kV/115 kV transformer and connection points of overhead ground wires, neutral
conductors and water pipes can result in considerable GPR differentials from one part of the grid to

Page 6-9
 Chapter 6. Performance Evaluation of Lakeshore Substation

another and therefore excessive touch voltages within a radius on the order of 100 from the fault,
when there are no buried conductors nearby. The grounding system upgrade recommended by SES
therefore also includes a minimum of 1 new bare buried 4/0 copper connection between each piece
of equipment and structure and the grounding grid, within the existing part of the electric substation.

Figure 6.5 First Preliminary Design of Grounding System of Lakeshore Substation.

Figure 6.6 Second Preliminary Design of Grounding System of Lakeshore Substation.

Page 6-10
 Chapter 6. Performance Evaluation of Lakeshore Substation

6.2.5 Preparation of MALZ Input Files

Corresponding to the grounding system upgrade described in the preceding section, a total of seven
MALZ input files have been prepared. The following table identifies the grounding system used in
each of the input file.

MALZ File Grounding System

MZ_SAFEX.F05 Existing Grounding System (Figure 6.3)
MZ_SAF01.F05 First Preliminary Design of Grounding System (Figure 6.5)
MZ_SAF02.F05 Second Preliminary Design of Grounding System (Figure 6.6)
MZ_SAF03.F05 Final Design of Grounding System (Appendix F)
MZ_TRGPR.F05 First Preliminary Design of Grounding System (Figure 6.5) plus Water Pipes
MZ_NGROD.F05 Final Design of Grounding System (Appendix F) Without Ground Rods at
Existing Substation (two-layer soil model from Traverse 2)
MZ_SAF2C.F05 Final Design of Grounding System (Appendix F) Without Ground Rods at
Existing Substation (four-layer soil model from Traverse 2)

The first four input files were used to examine the reduction of the touch and step voltages by
upgrading the grounding system of the Lakeshore substation. The fifth input file was used to
compute the ground potential rise of the Lakeshore substation.

As mentioned in Chapter 2, several different soil structures could have been used in this study,
including a four-layer soil from Traverse 2 (see Table 2.1), which include layers with highly
contrasting resistivities and thickness of 1-2. It is unlikely, however, that such soil structure occurs
in this way throughout the substation site, particularly after disturbing of the soil and addition of any
backfill by construction. The last two input files were therefore purposely constructed to study the
influence of different soil models on the touch and step voltages. Note that all of the ground rods at
the existing electrical Lakeshore Substation were ignored in order to run the four-layer soil model.
The number of conductor segments in this case would have exceeded the maximum number of
conductor segments allowed in MALZ if these ground rods were included.

Since detailed instructions about how to setup the MALZ input file have been given in Chapter 3, we
will only describe the modifications required to create these input files based on the input file
MZ_FAL2B.F05 used in the Fall-of-Potential analysis. One of the modifications is to replace 10
observations points by a number of observation points which are defined by 163 parallel profiles as
shown in Figure 6.4. These profiles are defined in Edit | Create Object | Detailed Grid screen.

Page 6-11
 Chapter 6. Performance Evaluation of Lakeshore Substation

Modification of the grounding system is rather simple since it only involves adding/removing
conductors. Some detailed description of the input file MZ_TRGPR.F05 will be given in the next
section since it simulates a realistic fault.

6.2.6 Submission of MALZ Runs

Use the procedure outlined in Section 3.4.2 to submit the input files to the MALZ computation
program.

6.3 COMPUTATION RESULTS

The following values were computed in each design stage:

 Touch voltages throughout the substation.

 Step voltages outside the substation fence. The observation points were designed to cover an area
extending 30 ft outside the substation fence.

 Ground potential rise (with respect to remote earth) of each conductor segment in order to study
potential differences between different parts of the grid.

6.3.1 Extracting Touch and Step Voltages Using the CDEGS Output
Processor
The touch and step voltages can be examined easily using CDEGS Output Processor. In this section,
we will describe how to use CDEGS Output Processor to produce spot-2D plots for touch and step
voltages for the final design of the ground system. The touch and step voltages for other intermediate
grounding system upgrade will be summarized in the next section.

6.3.1.1 Start Up Procedures

In the SES Software group folder, double-click the CDEGS icon to start the CDEGS program
interface (if not already started). You will be prompted for a Current Job ID; enter SAF03 Enter
the complete path of your working directory in the Working Directory box.

Page 6-12
 Chapter 6. Performance Evaluation of Lakeshore Substation

Click the MALZ button in the toolbar and then select Examine in the Session Mode list: the MALZ
SESResultViewer will appear.

Click the Computations

option button. To plot the
reach-touch voltage with a
search radius of 100’, select
Scalar Potentials in the
category list and Reach Touch
Voltages in the Result
Selection list. Then, select
Worst Spherical from the
Reference GPR list. Click on
the More button in the
Computations section and
enter 100’ in the Search
Radius of Reference GPR
box and select the Percentage
of the reference GPR and
enter 4.8 %. In the main
window, select the Spot 2D
option button in Plot View.

Enter 4.8 in the Touch Voltage next to Threshold

Value. This instructs the program to display all reach-
touch voltage values exceeding 4.8 % of the Reference
GPR with color gradation (transparent for values less
than 4.8 %, yellow to red for values from 4.8% up to
the maximum value of 44.5%). Now click the Plot
button. The following plot is produced. Please note that
we have requested a large number of observation points
(over 50,000) in the MALZ computations.

Page 6-13
 Chapter 6. Performance Evaluation of Lakeshore Substation

We now illustrate another useful feature that allows you

to find out the highest and lowest touch voltages in a
region. Click the Observation Points and Profiles
Filters button, check the Use Search Area box and fill
in the various fields as shown hereafter. Specify as
many points as required (one point per data line) to
define a polygonal shape delimiting the area you wish
to scan for computation results. The shape of the
polygon can be irregular, with a large number of
vertices or "corners".

This step specifies a Zoom Area limited by the existing

grounding system outer loop in Figure 6.3. Please note
that it is important that the points defining the zoom
polygon be specified in a specific order. The points
should follow the perimeter of the polygon in a
clockwise or counterclockwise manner: every successive point should define a line segment drawn
between that point and the preceding one. All vertices must lie in the same plane in order for
observation points to be found in the search zone: often, this plane is at the earth's surface (z=0).

Page 6-14
 Chapter 6. Performance Evaluation of Lakeshore Substation

Click OK and click on the

Export button. Type the
number 10 in the appropriate
field as shown in order to
display and save the ten
highest and touch voltages
found within the zoom area.
Click Proceed. This generates
a csv file. The pertinent
portions of the Report file are
shown hereafter. A similar
report can be done for the ten
lowest values.

The values of the step voltages everywhere within the substation and 30 outside the substation can
be displayed using similar plot views as for the touch voltages. If you select the Step Voltages
(Spherical) item from the Determine list, ask for a color spot 2D view and enter 3.5 in the Step
Voltage(in %) box under Plotting Threshold (which instructs the program to display all step
voltage values exceeding 3.5% of Reference GPR with color gradation), you will obtain a plot
indicating that the step voltages everywhere except near the corners of the grounding system do not
exceed 3.5% of the GPR of the grounding system, the maximum safe step voltage as mentioned
before.

6.3.2 Touch and Step Voltages

The touch voltages are shown in Figure 6.7 to Figure 6.10, which present, for each grounding
system, plan view plots of the grounding grid, with color indicating areas where touch voltages are
excessive (i.e., over 4.8% of the GPR of the grounding system).

As shown, only small areas achieve satisfactory touch voltages for the existing grounding system of
Lakeshore Substation. Note that much of the area where the future 230 kV/115 kV transformer is to
be located has been left uncolored because there are no modeled conductors within 100 feet which
can be touched. The areas with excessive touch voltages have been reduced significantly with the
first design of the grounding system, in which some ground conductors (at a depth of 1.5) have been
added to the existing grounding system. As Figure 6.8 shows, only a few areas near the fence
perimeter exhibit touch voltages above 4.8%.

Page 6-15
 Chapter 6. Performance Evaluation of Lakeshore Substation

SCALAR POTENTIALS/REACH TOUCH VOLTAGES/WORST SPHERICAL [ID:SAFETY_EXISTGRID @ f=60.0000 Hz ]

LEGEND
1200 Maximum Value : 56.789
Minimum Threshold : 4.800

56.79

51.59

700 46.39

41.19
Y AXIS (FEET)

35.99

30.79
200 25.60

20.40

15.20

10.00
-300
-300 200 700 1200
X AXIS (FEET)
R-Touch Voltage (% Ref. GPR) [Wors]

Figure 6.7 Reach-Touch Voltages for Existing Grounding System, with Respect to Worst
Case Grid Conductor within 100 Radius.

Figure 6.8 Reach-Touch Voltages for First Design of Grounding System, with Respect to
Worst Case Grid Conductor within 100 Radius.

Page 6-16
 Chapter 6. Performance Evaluation of Lakeshore Substation

Subsequently, the areas with excessive touch voltages were almost removed by adding/moving
conductors along the perimeter of the grounding system; however, careful examination revealed that
some spots in the gas substations still exhibited touch voltages as high as 5.33% of the GPR of the
grounding system. To eliminate these excessive touch voltages throughout the entire substation, a
number of 10 ground rods were added along the fence perimeter, as shown in Appendix F. The
highest reach-touch voltage corresponding to this grid design is 4.56%. Figure 6.10 shows the
corresponding plot.

Figure 6.9 Reach-Touch Voltages for Second Design of Grounding System, with Respect to
Worst Case Grid Conductor within 100 Radius.

Page 6-17
 Chapter 6. Performance Evaluation of Lakeshore Substation

Figure 6.10 Reach-Touch Voltages for Final Design of Grounding System, with Respect to
Worst Case Grid Conductor within 100 Radius.

Step voltages have also been computed throughout the entire substation area (including a 30 wide
strip surrounding its perimeter). The results are shown in Figure 6.11. The step voltages immediately
outside the corners of the grounding system (and at a few other locations outside the grid perimeter
where conductors are interconnected), within a maximum distance of about 7 ft from the grid
perimeter, where surface gravel may not be present, slightly exceed the safety limit suggested by
ANSI/IEEE Standard 80. The ANSI/IEEE Standard 80 step voltage limit is 274 V for a surface soil
with a resistivity of 107 -m; where crushed rock is present, the limit is 1033 V. The maximum step
voltage outside the crushed rock region modeled in our study ranges from 450 to 650 V, depending
on the density of the observation points used. Note, however, that the standard refers to test results
indicating that 25 times as much current is required in the foot-to-foot circuit than in the hand-to-foot
circuit to produce the same current in the heart region, suggesting that step voltages must be several
times higher than the ANSI/IEEE Standard 80 limit in order to produce ventricular fibrillation,
which is the criterion used to determine the touch and step voltage limits. In fact, the standard states:
“Based on these conclusions, resistance values greater than 1000  could possibly be allowed,
where a path from one foot to the other foot is concerned.”

Page 6-18
 Chapter 6. Performance Evaluation of Lakeshore Substation

Figure 6.11 Step Voltages for Final Design of Grounding System.

On the other hand, the standard warns that a large step voltage may cause a person to fall and receive
a shock in a prone position between different body parts (e.g., from a reclosure); or the victim may
be working or resting in a prone position to begin with when the fault occurs. However, the standard
does not provide voltage limits for these types of postures, possibly because they are not often
encountered. Furthermore, the maximum step voltage is reached when a person’s foot is above the
outer ground conductor loop. At this location, the foot may very well be in contact with the surface
crushed rock and the maximum allowable step voltage will be higher than the limit for native soil
(i.e., it will become about 600 V instead of 274 V).

If it is desired to strictly comply with the ANSI/IEEE Standard 80 limit, then surface crushed rock
should be extended to partially cover the shaded areas shown in Figure 6.11, up to a distance of 1m
(3.28 feet) from the outer edge of each shaded area (note that the width of the shaded areas reaches a
maximum of about 7 feet). Specified in more simple terms, this would be achieved by extending the
crushed rock layer an additional 1.2 m from the perimeter fence, for a total width of 2.2 m from the
perimeter fence. Alternative solutions are more intrusive and difficult to achieve: for example,
gradient control wires covering the seven-foot area could be buried at progressively increasing
depths (to be determined); inclined ground rods could also be driven to accomplish the same result.

The presently proposed grounding system design is based on a maximum reach distance of 1 m (3.28
feet) from the fence line, in order to minimize the extent to which additional grid conductors must be
installed far outside the fence. At some locations, this will avoid placing grid conductors over gas
pipes. To maintain compatibility with this grounding design, it is important therefore that all gates
open inward, rather than outward, except in areas where touch voltages are satisfactory throughout
the swing region of a gate opening outward. If it is not possible to ensure inward opening gates

Page 6-19
 Chapter 6. Performance Evaluation of Lakeshore Substation

everywhere, then the grounding system and crushed rock layer must be extended outward at these
locations.

6.3.3 Ground Potential Rise

In order to determine the effect of currents circulating within the grounding system, but not injected
into the earth by it, the grounding grid was modeled with multiple fault current injection points. In
order to accommodate the water pipes, which constitute an important part of the grounding system
from the GPR differential point of view, the first design of the grounding grid was used in this
modeling, as shown in Figure 6.12. Figure 6.12 also shows the current injection points, including the
115 kV/230 kV transformer and the Willow, Appleby and Alexander 115 kV transmission lines,
which constitute the primary sources of circulating current.

Figure 6.12 A Realistic 115 kV Fault at Lakeshore Substation. Water Pipes and Circulating
Currents at 230 kV/115 kV Transformer Have Been Modeled.

An input file MZ_TRGPR.F05 has been prepared for this computation. The grounding system
consists of the first preliminary design of the grounding system of Lakeshore Substation (see Figure
6.5) and the water pipes. All of the overhead ground wires connected to the Lakeshore substation
(see Figure 6.1) have been removed. The influence due to the overhead ground wires to Willow,
Appleby and Alexander Substation are taken into account properly by assigning the appropriate
currents to these lines. The currents flowing in these overhead ground wires are listed in Section
5.3.3 and are indicated in Figure 6.12.
The energization currents are defined as follows:

Page 6-20
 Chapter 6. Performance Evaluation of Lakeshore Substation

They can be entered in the way described in Section 3.4.1.2. These currents were also applied to the
grounding system in the Main-Ground Conductors block of the MALZ (System) screen. The
characteristics of conductors and their energizations are assigned by selecting the appropriate code
(pointer) number in the data entry field under Main-Ground Conductors.

Figure E.1, Figure E.2 and Figure E.3 in Appendix E show the computation results. Figure E.1 and
Figure E.2 show the ground potential rise and longitudinal currents throughout the grid, respectively.
Figure E.3 shows the worst 100 reach touch voltage.

From Figure E.1, it can be seen that there are significant differences in the potential from one part of
the grid to another, the maximum being on the order of 1.0 kV, between the fault site and the south-
east corner of the substation. This 115 kV fault scenario shows that potential differences on the order
of 1 kV can occur between remote parts of the grounding grid as a result of circulating currents in
the substation’s grounding system. Changing the location of the fault may result in even higher GPR
differences from one part of the grid to another. Equipment connected to low voltage conductors that
are connected to remote parts of the substation may be subjected to considerable stress voltages as a
result and may cause excessive touch voltages as well for people contacting this equipment.

From Figure E.3, it can be seen that touch voltages with a radius of approximately 100 feet from the
fault are excessive when referred to a conductor as much as 100 feet away. On the other hand, close
to the fault, there is a non-colored region, indicating that when one is standing in the vicinity of a
buried ground conductor, touch voltages become acceptable. The conclusion here is that there must
be a buried ground conductor in the vicinity of all metallic structures which can be touched,
particularly if these structures are located in an area where a 115 kV ground fault could occur.

6.3.4 Touch Voltages Using a Four-Layer Soil Model

Figure 6.13 shows the touch voltages obtained using a four-layer soil model from Traverse 2 (see
Table 2.1). The final design of the grounding system without the ground rods at the existing
electrical substation was used for the computation. For comparison purpose, the touch voltages were
also computed using the two-layer soil model from Traverse 2 and the same grounding system as
that used in Figure 6.13. Figure 6.14 shows the results. As Figure 6.13 shows, only a small area near
the fault location achieves satisfactory touch voltages for the four-layer soil model, while Figure
6.14 shows that the touch voltages are below the safe touch voltage limit throughout the entire

Page 6-21
 Chapter 6. Performance Evaluation of Lakeshore Substation

substation if the two-layer soil model is used. It is therefore very important to decide appropriate soil
models when designing a substation ground system. We could have over-designed the grounding
system if the four-layer soil model were used.

Figure 6.13 Reach-Touch Voltages for Final Design of Grounding System without Ground
Rods at Existing Substation, with Respect to Worst Case Grid Conductor within
100 Radius. A Four-Layer Soil Model from Traverse 2 is used.

Figure 6.14 Reach-Touch Voltages for Final Design of Grounding System without Ground
Rods at Existing Substation, with Respect to Worst Case Grid Conductor within
100 Radius. A Two-Layer Soil Model from Traverse 2 is used.

Page 6-22
 Chapter 7. Conclusions and Recommendations

CHAPTER 7
CONCLUSIONS AND RECOMMENDATIONS
7.1 CONCLUSIONS
The adequacy of the Lakeshore Substation grounding system during fault conditions has been
studied from an electrical safety point of view, in terms of touch voltages, step voltages and GPR
(ground potential rise) differentials between different parts of the grounding system; an upgrade to
the existing grounding system has been designed to accommodate the presently anticipated fault
current levels and new equipment. This study revealed (and subsequent SES measurements
confirmed) that the electric substation is electrically continuous with the adjacent gas substations and
with the nearby water mains (e.g., via the distribution system neutral). The influences of these
structures have been accounted for in the detailed computer modeling of the grounding system and
associated 115 kV transmission lines performed with the CDEGS software package. Comprehensive
field measurements were made to supply data upon which the computer models are based and to
verify key results.

Soil Resistivity Measurements

Soil resistivity measurements have been made at 3 locations in and around the substation, using
special procedures and equipment to eliminate power system noise and interlead inductive coupling.
Measurements have been made up to 2000 ft spacing between current injection probes, in order to
determine the resistivities of the deeper soil layers that can have a significant influence on the
ground impedance of a grounding system as large as that of Lakeshore Substation. It was found that
on a large scale, a vertically layered soil, with a resistivity of 753 ohm-m to the southeast of the
substation and 200 ohm-m in the vicinity of the substation resulted in an excellent match with
measured apparent ground impedances. On a smaller scale, which is most important for the
computation of touch and step voltages near the substation, measurements suggested horizontally
layered soils, with low resistivities near the surface (on the order of 107 to 209 ohm-m) and higher
resistivities at greater depths (on the order of 317 to 753 ohm-m).

Grounding System Impedance Measurements

The low frequency grounding system impedance of the substation (including all other associated
grounding structures such as transmission line towers, gas substations, water pipes), was determined
to be 0.181, by measurements made according to the Fall-of-Potential method and subsequent
processing with the CDEGS software; the software indicates the location at which the measurements
best reflect the true ground impedance, based on the soil structure, grounding grid configuration,
positions of surrounding poles and towers, residential water pipes, and position of the test current
return electrode. The 60 Hz grounding system impedance is 0.315  according to the computer
model. Agreement between measured and computed impedances is excellent: the computed low
frequency ground impedance is within 7% of the measured value. This computer modeling shows
that the low measured value must result from interconnections with other structures which were
initially believed to be isolated from the substation (such as the adjacent gas substations) or simply

Page 7-1
 Chapter 7. Conclusions and Recommendations

not accounted for (such as the nearby water pipes). Prompting by SES resulted in further
measurements that confirmed the existence of such interconnections.

Touch and Step Voltage Measurements

Touch and step voltages were measured at 10 locations within and around the perimeter fence of the
existing part of the electric substation. After extrapolation to worst-case fault conditions, the
maximum step voltage during fault conditions was estimated to be 215 V; maximum touch voltages
exceeding 500 V were estimated, particularly near the perimeter fence. Similar values were obtained
from the detailed computer model. While the step voltage is not excessive, the touch voltage exceeds
the safety limit of 381 V by a significant margin with the existing grid design.

Detailed Computer Modeling

The main analysis consisted of computer simulations of a single phase-to-ground fault at one of the
115 kV busses of the substation. The computer models accounted for currents flowing out of the grid
into the static wires of each transmission line and into the nearby water pipes and gas substations,
voltage drops in the grid due to circulating currents, and the effects of soil layering. The static wire
currents were computed from detailed circuit models of the transmission lines, accounting for
inductive coupling between phase conductors and static wires. The grid performance was studied
based on the more conservative soil model derived from the measurements made inside the
substation. Touch voltages, step voltages, longitudinal currents flowing in conductors and ground
potential rise differentials were computed throughout the substation.

Results are presented in graphical form. In particular, touch voltages are represented as shaded areas
of varying intensity on plan view plots of the grounding system.

Overview of Computer Simulation Results

Principal results from the main study are as follows:

 Existing grounding mat impedance, without static wires and water pipes connected (60 Hz):
0.613.8
 New grounding mat impedance, without static wires and water pipes connected (60 Hz):
0.511.9
 Maximum ground potential rise (for worst-case fault scenario): 7.8 kV
 Maximum net fault current injected into earth by grid: 23.7 kA
 Maximum net fault current flowing into substation: 35.0 kA
 Fault current split (static and neutral wires/grid): 17%/84%
 Maximum potential difference between remote parts of new grid: on the order of 1 kV or higher
 Maximum ANSI/IEEE Std. 80-1986 tolerable touch and step voltages are as follows for the
parameters used in this study (i.e., 0.5-second fault clearing time, 50 kg body weight, X/R ratio
of 20, 3” crushed rock thickness, 107 -m native earth resistivity):
 Maximum safe touch voltage: 191 V (native soil only), 381 V (2,000 -m crushed rock
layer).
 Maximum safe step voltages: 274 V (native soil only), 1033 V (2,000 -m crushed rock
layer).

Page 7-2
 Chapter 7. Conclusions and Recommendations

 Highest local touch voltage (i.e., with respect to any grid conductor within 100 radius) computed
anywhere within or immediately outside (within 3.3 feet of the fence) the substation: less than
374 V (for the final grounding system design).
 The maximum computed step voltage is approximately 156 V, less than the 274 V limit for a 107
-m native earth surface.

Grounding System Design Upgrade

The grounding system in the existing electric substation area has been reinforced and expanded into
the new 230 kV/115 kV transformer area as part of the grounding system design upgrade.
Furthermore, additional conductors have been included in the two gas substations and in the new
unloading zone.

Computer modeling of fault conditions has shown that touch and step voltages throughout the
Lakeshore Substation site, including the two neighboring gas substations and unloading zone,
comply with the applicable ANSI/IEEE Standard 80-1986 limits with this new design, which is
described in Chapter 6 of this report (see Figure 6.7). The design includes a 3” (minimum) thick
layer of crushed rock, with a minimum wet resistivity of 2,000 ohm-m, which must be present
throughout the site, up to a distance of 3.3 ft beyond the perimeter fence.

7.2 RECOMMENDATIONS
SES recommends the following:
1. Grounding System Upgrade. It is recommended that the new grounding system design
described in Chapter 6 of this report be implemented. This design includes not only the new
grounding grid conductors and vertical rods shown in Appendix F, but also at least 1 new bare
buried 4/0 copper connection from each piece of equipment and structure to the grounding grid,
within the existing part of the electric substation. The design also includes a 3” thick (minimum)
layer of crushed rock, with a wet resistivity of 2,000 ohm-m (minimum), throughout the site; the
site comprises the electric substation, the two adjacent gas substations on the north and south
sides, and the gas unloading zone on the east side. The crushed rock must extend up to 1 m (i.e.,
3.3 feet) beyond the perimeter fence bounding this site such that a person touching any metallic
structure associated with any of the gas or electric facilities must necessarily be standing on
crushed rock.
This crushed rock layer must be maintained over time. The thinning of the layer and
contamination with sand, earth, grass and other such matter which fills the voids between the
stones with low resistivity material result in a significant lowering of the level of protection
provided by the crushed rock.
2. Perimeter Fence Gates. The presently proposed grounding system design is based on a
maximum reach distance of 1 m (3.28 feet) from the fence line, in order to minimize the extent to
which additional grid conductors must be installed far outside the fence. At some locations, this
will avoid placing grid conductors over gas pipes. To maintain compatibility with this grounding
design, it is important therefore that all gates open inward, rather than outward, except in areas
identifiable in Figure 6.10 where touch voltages are satisfactory throughout the swing region of a

Page 7-3
 Chapter 7. Conclusions and Recommendations

gate opening outward. If it is not possible to ensure inward opening gates everywhere, then the
grounding system and crushed rock layer must be extended outward at these locations.

3. Gas Pipelines Since the various gas station and gas pipeline grounds are solidly connected to the
substation ground, it is recommended that several (at least two) 4/0 insulated copper bonds be
added between the gas station and electric substation grounds to avoid the dependence on the
existing inadvertent bonds. No potential problems for the cathodic protection systems are
perceived since the existing interconnections between the ground eliminate dangerous potential
differences in this way and no detrimental effects have been reported to SES.
4. Protection of Equipment and Low Voltage Conductors. Based on one 115 kV fault scenario,
it has been determined that potential differences on the order of 1 kV or higher can occur
between remote parts of the grounding grid as a result of circulating currents in the substation’s
grounding system. Equipment connected to insulated (or isolated) low voltage conductors that
are connected to remote parts of the substation may be subjected to high stress voltages as a
result and may cause excessive potential differences if not grounded locally. Additional fault
simulations at representative locations throughout the substation area should be performed in
order to determine the extent of this GPR differential problem so that appropriate protection
levels can be defined for the low voltage equipment and appropriate mitigation designed for
stress voltages as well.
5. Protection of Communications Equipment Connected to Lines Leaving Substation. The
maximum ground potential rise of the substation is estimated to be 7.8 kV. Protection systems
for any communications equipment connected to lines leaving the substation should be rated
above this voltage level. Note that in calculating the required minimum protection level, induced
voltages from power lines running parallel or nearly parallel to communications lines must also
be considered. However, this maximum ground potential rise is only possible if the far end of the
connected equipment is at remote distance. In general however, the communications centre is
relatively close to the substation (a mile of two) and only a fraction of the full 7.8 kV GPR is
applicable.
6. Step Voltages Outside the Substation. Step voltages immediately outside the corners of the
grounding system (within a maximum distance of about 7 ft from the grid perimeter, where
surface crushed rock may not be present) slightly exceed the safety limit suggested by
ANSI/IEEE Standard 80. Note, however, that the standard refers to test results indicating that 25
times as much current is required in the foot-to-foot circuit than in the hand-to-foot circuit to
produce the same current in the heart region, suggesting that step voltages must be several times
higher than the ANSI/IEEE Standard 80 limit in order to produce ventricular fibrillation.
If strict compliance to the ANSI/IEEE Standard 80 limit is required, then surface crushed rock
should be extended to partially cover the applicable areas up to a distance of 1m (3.3 feet) from
the outer edge of each area. Specified in more simple terms, this would be achieved by extending
the crushed rock layer an additional 1.2 m from the perimeter fence, for a total width of 2.2 m
from the perimeter fence. Alternative solutions are more intrusive and difficult to achieve: for
example, gradient control wires covering the seven-foot area could be buried at progressively
increasing depths (to be determined); inclined ground rods could also be driven to accomplish
the same thing.
7. Transfer Potentials Outside the Substation. The substation grounding system appears to be
electrically interconnected to gas pipelines and to water pipes that serve the local area. These

Page 7-4
 Chapter 7. Conclusions and Recommendations

should be examined to determine the level of transfer voltages to nearby users of these utilities
and to evaluate the need for mitigative measures if any. Such a task requires knowledge of the
structures and conductors buried in the local area.

Page 7-5
This page is intentionally left blank
 Appendix A. Soil Resistivity Measurements: Tabulated Data

APPENDIX A
SOIL RESISTIVITY MEASUREMENTS:
TABULATED DATA
Table A.1 Soil Resistivity Data: Traverse 1.
Site Location: Cemetery South-East of Substation

Pin Source C Pin P Pin Apparent

Iinject Vsignal SP Q
Spacing Voltage Depth Depth Resistivity
(mA) (mV) (mV) (%)
(ft) (V) (in) (in) (-m)

1.0 100 4 2 41.00 4867 -52 0 227.3

1.5 100 4 2 41.18 3540 -537 0 246.9
2.5 100 4 2 43.95 2628 -68 0 286.3
5.0 200 4 2 89.05 3624 -143 0 389.7
7.5 200 12+ 6 128.18 4627 -22 0 518.5
10.0 400 12+ 6 120.47 4086.69 0 0 649.7
15.0 200 12+ 6 136.59 4145.4 -10 0 871.9
20.0 200 12+ 6 145.31 3964 -46 0 1045.0
30.0 400 12+ 6 164.78 14.790 0 0 5.2
50.0 400 12+ 6 194.62 2488 -165 0 1224.0
75.0 400 12+ 6 167.41 975.407 -67 0 836.9
100 400 12+ 6 209.60 383.76 -52 0 350.6
150 400 12+ 6 172.10 350.8 -22 0 585.5
250 400 12+ 6 245.3 331.2 -6 0 646.5
500 400 12+ 6 164.91 160.57 -51 0 932.3
660 400 12+ 6 197.62 56.681 39 0 362.5

Page A-1
 Appendix A. Soil Resistivity Measurements: Tabulated Data

Table A.2 Soil Resistivity Data: Traverse 2.

Site Location: Future 230 kV/115 kV transformer area

Pin Source C Pin P Pin Apparent

Iinject Vsignal SP Q
Spacing Voltage Depth Depth Resistivity
(mA) (mV) (mV) (%)
(ft) (V) (in) (in) (-m)

1.0 100 4 2 56.02 2564.6 39 0 87.7

1.5 200 4 2 94.14 3359 -24 0 102.5
2.5 200 4 2 123.3 3122 23 0 121.2
5.0 400 4 2 179.9 2609 -20 0 138.8
7.5 400 12+ 6 170.95 1549 -46 0 130.2
10.0 400 12+ 6 150.68 763.57 -72 0 97.1
15.0 400 12+ 6 146.90 442.8 45 0 86.6
25.0 400 12+ 6 127.04 360.54 10 0 127.2
50.0 400 12+ 6 169.15 383.56 -15 0 217.1
75.0 400 12+ 6 213.08 270.2 -63 0 182.1
100 400 12+ 6 124.83 195.9 -346 0 300.5
135 400 12+ 6 177.1 154.63 -96 0 220.6

Page A-2
 Appendix A. Soil Resistivity Measurements: Tabulated Data

Table A.3 Soil Resistivity Data: Traverse 3.

Site Location: West side of the substation along railway track

Pin Source C Pin P Pin Apparent

Iinject Vsignal SP Q
Spacing Voltage Depth Depth Resistivity
(mA) (mV) (mV) (%)
(ft) (V) (in) (in) (-m)

1.0 50 4 2 45.75 4023.3 -73 0 168.42

1.5 50 4 2 5.86 341.128 -287 0 166.79
2.5 200 4 2 140.43 4550.0 -176 0 155.13
5.0 400 4 2 237.52 3879.0 -75 0 156.38
7.5 400 12+ 6 211.48 2211.6 -225 0 150.21
10.0 400 12+ 6 232.74 1664.323 -500 0 136.95
15.0 400 12+ 6 235.07 1552.494 -110 0 189.72
25.0 400 12+ 6 290.7 1864.1 -67 0 307.01
50.0 400 12+ 6 288.21 1320.2 28 0 438.58
75.0 400 12+ 6 272.2 893.457 -425 0 471.47
100.0 400 12+ 6 273.85 695.991 -793 0 486.73
150.0 400 12+ 6 230.84 382.737 562 0 476.29
225.0 400 12+ 6 257.64 235.157 -133 0 393.30

Page A-3
This page is intentionally left blank
 Appendix B. Fall-of-Potential Impedance Measurements: Tabulated Data

APPENDIX B
FALL-OF-POTENTIAL IMPEDANCE
MEASUREMENTS: TABULATED DATA
Table B.1 Fall-of-Potential Impedance Data.
Site Data:

Current Return Electrode: 3350 ft south-east of substation fence (See Figure 3.3)
Fall-of-Potential Traverse: See Figure 3.3

Measured Voltages @ 0.25 Hz (mV)

Potential Apparent
Probe Multiplier Resistance
Distance VAC VBC VAB
from  VAC 
Grid   1.01
 VAB 
(ft) ()

390.244 1.0 12.275 276.889 262.533 0.047

764.335 1.0 14.318 279.726 265.410 0.054
1045.35 1.0 16.433 282.983 266.643 0.062
1329.24 1.0 27.377 293.147 265.187 0.104
1628.09 1.0 40.995 297.057 263.472 0.157
1845.44 11.13 4.00 23.101 19.129 0.211
2169.36 11.13 5.970 25.009 18.965 0.318
2503.35 11.13 9.381 28.742 19.275 0.492
2843.86 11.13 16.019 35.760 19.822 0.816
3188.8 11.13 20.595 40.167 19.773 1.052

Page B-1
This page is intentionally left blank
 Appendix C. Touch, Step and Long Reach Voltage Measurements: Tabulated Data

APPENDIX C
TOUCH, STEP AND LONG REACH VOLTAGE
MEASUREMENTS: TABULATED DATA
Table C.1 Touch, Step and Long Reach Voltage Measurements.

Site Description Touch Voltage @80 Hz Step Voltage @80 Hz Long Reach Voltage @80 Hz
LongReach HP: HP: HP:
Site No. Distance4 Injection Touch Injection Step Voltage Injection Long Reach
(ft) Current (mA) Voltage (mV) Current (mA) (mV) Current (mA) Voltage (mV)
1 51.8 478.9 20.316 477.2 2.936 470.4 41.585
2 51.8 485.4 3.102 486.3 0.94089 483.7 16.040
3 51.8 494.3 7.361 494.7 1.389 493.7 17.970
4 51.8 498.0 0.26075 499.0 0.015256 498.6 0.25166
5 33.5 475.8 7.721 477.1 1.706 473.6 12.819
6 9.4 484.8 0.8365 486.4 0.44561 486.0 1.716
7 16.6 494.3 3.668 495.7 1.262 495.0 5.696
8 6 500.5 2.313 501.6 0.95368 501.2 3.288
9 6 505.9 0.43696 506.6 0.025166 505.3 0.45879
10 24 510.7 0.106597 511.9 0.229391 511.4 1.133

4
Distance from structure to potential probe.

Page C-1
This page is intentionally left blank
 Appendix D. Fault Current Contributions for 115 Kv Bus Fault (Single Phase to Ground)

APPENDIX D
FAULT CURRENT CONTRIBUTIONS FOR 115
KV BUS FAULT (SINGLE PHASE TO
GROUND)
SEQUENCE THEVENIN IMPEDANCES AT FAULTED BUSES(in P.U. on 100 MVA base):

BUS NAME BSKV ZERO POSITIVE NEGATIVE

570 LAKESHORE 115 .00411 .02081 .00133 .01084 .00133 .01084

LINE TO GROUND FAULT AT BUS 570 [LAKESHORE 115]:

SEQUENCE /V0/ AN(V0) /V+/ AN(V+) /V-/ AN(V-) /3V0/ AN(3V0)

PHASE /VA/ AN(VA) /VB/ AN(VB) /VC/ AN(VC)

570 (KV L-G) 32.735 177.88 49.558 -.70 16.852 -177.94 98.204 177.88
LAKESHORE 115 .000 .00 74.218 -131.39 76.982 129.60

SEQUENCE /I0/ AN(I0) /I+/ AN(I+) /I-/ AN(I-) /3I0/ AN(3I0)

PHASE /IA/ AN(IA) /IB/ AN(IB) /IC/ AN(IC)

FROM 507 1 3076.5 -86.83 1850.1 -84.78 1850.1 -84.78 9229.6 -86.83
LAKESHORE230 6775.7 -85.71 1229.4 -89.93 1229.4 -89.93

FROM 560 1 1312.1 -79.51 2000.1 -82.80 2000.1 -82.80 3936.3 -79.51
STONE TE 115 5310.7 -81.99 694.2 90.96 694.2 90.96

FROM 560 2 1628.3 -77.46 1985.1 -82.51 1985.1 -82.51 4885.0 -77.46
STONE TE 115 5594.0 -81.04 390.3 75.96 390.3 75.95

FROM 567 1 .0 .00 .0 .00 .0 .00 .0 .00

R. M. HO 115 .0 .00 .0 .00 .1 22.90

FROM 571 1 .0 .00 .0 .00 .0 .00 .0 .00

BEACH 115 .0 .00 .0 .00 .0 .00

FROM 575 1 2047.4 -78.89 1891.0 -80.30 1891.0 -80.30 6142.1 -78.89
WILLOW 115 5828.9 -79.81 163.8 -62.28 163.8 -62.29

FROM 579 1 593.7 -79.95 707.7 -73.74 707.7 -73.74 1781.2 -79.95
DRAKE 115 2006.6 -75.57 133.8 134.93 133.8 134.93

FROM 590 1 593.7 -79.95 707.7 -73.74 707.7 -73.74 1781.2 -79.95
MCPHERSON115 2006.6 -75.57 133.8 134.93 133.8 134.94

FROM 594 1 683.2 -71.89 724.3 -77.23 724.3 -77.23 2049.5 -71.89
HARDWOOD 115 2129.8 -75.52 77.4 47.56 77.3 47.56

FROM 598 1 698.4 -78.24 485.1 -81.46 485.1 -81.46 2095.3 -78.24
OAKWOOD 115 1667.9 -80.11 215.9 -70.97 215.9 -70.97

FROM 712 1 .0 .00 .0 .00 .0 .00 .0 .00

LAKESHORE 33.0 .0 .00 .0 .00 .0 .00

FROM 906 1 359.1 -80.62 485.4 -77.89 485.4 -77.89 1077.2 -80.62
DOVE.1 115 1329.6 -78.63 127.9 109.79 127.9 109.79

FROM 907 1 706.3 -85.24 849.8 -82.58 849.8 -82.58 2119.0 -85.24
ALEXANDER.1 115 2405.4 -83.36 147.8 110.19 147.8 110.19

FAULT CURRENT AT BUS 570 [LAKESHORE 115]:

Page D-1
 Appendix D. Fault Current Contributions for 115 Kv Bus Fault (Single Phase to Ground)

570 11666.4 -80.95 11666.4 -80.95 11666.4 -80.95 34999.1 -80.95

LAKESHORE 115 34999.1 -80.95 .0 .00 .0 .00
AT BUS 570 [LAKESHORE 115] AREA 1 (KV L-G) V+: / .000/ .00

THEV. R, X, X/R: POSITIVE .00133 .01084 8.150

T H R E E P H A S E F A U L T
------- FROM -------AREA CKT I/Z /I+/ AN(I+) /Z+/ AN(Z+) APP X/R
507 [LAKESHORE 230] 1 1 AMP/OHM 7289.1 -86.84 11.96 88.23 32.286
560 [STONE TE 115] 1 1 AMP/OHM 7880.0 -84.86 .99 82.85 7.974
560 [STONE TE 115] 1 2 AMP/OHM 7821.0 -84.57 .99 82.56 7.658
567 [R. M. HO 115] 1 1 AMP/OHM .1 97.05 1.35 73.26 3.325
571 [BEACH 115] 1 1 AMP/OHM .0 .00 .00 .00 .000
575 [WILLOW 115] 1 1 AMP/OHM 7450.2 -82.36 1.53 78.98 5.137
579 [DRAKE 115] 1 1 AMP/OHM 2788.1 -75.80 1.57 71.05 2.912
590 [MCPHERSON 115] 1 1 AMP/OHM 2788.1 -75.80 8.01 71.03 2.909
594 [HARDWOOD 115] 1 1 AMP/OHM 2853.8 -79.29 4.23 77.08 4.358
598 [OAKWOOD 115] 1 1 AMP/OHM 1911.1 -83.52 1.85 82.62 7.722
712 [LAKESHORE 33.0] 1 1 AMP/OHM .0 .00 .00 .00 .000
906 [DOVE.1 115] 2 1 AMP/OHM 1912.4 -79.95 21.82 73.88 3.461
907 [ALEXANDER.1 115] 2 1 AMP/OHM 3348.0 -84.64 6.78 74.15 3.521

TOTAL FAULT CURRENT (AMPS) 45963.4 -83.00

SEQUENCE THEVENIN IMPEDANCES AT FAULTED BUSES(in P.U. on 100 MVA base):

BUS NAME BSKV ZERO POSITIVE NEGATIVE

507 LAKESHORE 230 .00390 .02015 .00118 .01082 .00118 .01082

LINE TO GROUND FAULT AT BUS 507 [LAKESHORE 230]:

SEQUENCE /V0/ AN(V0) /V+/ AN(V+) /V-/ AN(V-) /3V0/ AN(3V0)

PHASE /VA/ AN(VA) /VB/ AN(VB) /VC/ AN(VC)

507 (KV L-G) 64.485 177.57 98.618 -.80 34.209 -177.71 193.456 177.57
LAKESHORE 230 .000 .00 147.094 -131.07 153.382 129.06

SEQUENCE /I0/ AN(I0) /I+/ AN(I+) /I-/ AN(I-) /3I0/ AN(3I0)

PHASE /IA/ AN(IA) /IB/ AN(IB) /IC/ AN(IC)
FROM 505 1 1583.7 -78.47 1982.4 -81.08 1982.4 -81.08 4751.2 -78.47
STONEWOOD 230 5547.3 -80.34 406.7 88.71 406.7 88.71

FROM 506 1 2412.8 -78.41 3022.3 -81.29 3022.3 -81.29 7238.3 -78.41
STONE TE 230 8455.2 -80.47 624.6 87.49 624.6 87.49

FROM 570 1 1959.5 -87.71 934.4 -82.94 934.4 -82.94 5878.5 -87.71
LAKESHORE 115 3825.1 -85.38 1031.2 -92.03 1031.2 -92.03

FAULT CURRENT AT BUS 507 [LAKESHORE 230]:

507 5938.8 -81.48 5938.8 -81.48 5938.8 -81.48 17816.3 -81.48

LAKESHORE 230 17816.3 -81.48 .0 .00 .0 .00
AT BUS 507 [LAKESHORE 230] AREA 1 (KV L-G) V+: / .000/ .00

THEV. R, X, X/R: POSITIVE .00118 .01082 9.169

T H R E E P H A S E F A U L T
------- FROM -------AREA CKT I/Z /I+/ AN(I+) /Z+/ AN(Z+) APP X/R
505 [STONEWOOD 230] 1 1 AMP/OHM 7695.0 -83.38 5.34 83.34 8.566
506 [STONE TE 230] 1 1 AMP/OHM 11731.9 -83.59 1.60 83.34 8.566
570 [LAKESHORE 115] 1 1 AMP/OHM 3627.2 -85.24 2.99 88.23 32.286

TOTAL FAULT CURRENT (AMPS) 23052.7 -83.78

Page D-2
Appendix E. Ground Potential Rise, Longitudinal Currents And Touch Voltages Throughout
Lakeshore Substation Grounding System During 115 kV Fault With Circulating Currents
Modeled

APPENDIX E
GROUND POTENTIAL RISE, LONGITUDINAL
CURRENTS AND TOUCH VOLTAGES
THROUGHOUT LAKESHORE SUBSTATION
GROUNDING SYSTEM DURING 115 KV FAULT
WITH CIRCULATING CURRENTS MODELED

Page E-1
 Appendix E. Ground Potential Rise, Longitudinal Currents And Touch Voltages Throughout Lakeshore Substation
Grounding System During 115 kV Fault With Circulating Currents Modeled

Figure E.1
Figure E.2

Page E-2
Appendix E. Ground Potential Rise, Longitudinal Currents And Touch Voltages Throughout Lakeshore Substation
Grounding System During 115 kV Fault With Circulating Currents Modeled

Page E-3
 Appendix E. Ground Potential Rise, Longitudinal Currents And Touch Voltages Throughout
Lakeshore Substation Grounding System During 115 kV Fault With Circulating Currents
Modeled

Figure E.3 Reach-Touch Voltages for First Design of Grounding System, with Respect to
Worst Case Grid Conductor within 100 ft Radius: Fault with Circulating
Currents Modeled

Page E-4
 Appendix F. Final Upgraded Grounding Design

APPENDIX F
FINAL UPGRADED GROUNDING DESIGN

Page F-1
 1219'
6' 3' 6'
6' 3' 8'
3' 5' 3' 4“ PIPES

21.4'

13'
64'
25'
40' 15'

20' 20'
3'
3'

40'
63'
40'

120'
85'
3'

40'
40'

32 ' 50 ' 23'

6 0' 60 ' 60' 60' 30 ' 32 ' 2 3'

40'
40'

78 .5 ' 13' 3' 331'

75'
1 9'

40'
40'

120'

40'
125'
40'

ATIO N

587'
75'

40'
222'
29'
20' 20'

GAS ST
45'
60'

8 0' 80' 80 ' 8 0'

40'
3' 6'

97'
45'

40'
68'
16' 30'

3'

24'
9'

40'
18 ' 25 ' 3' 6'
NEW PIPES

31'
3'
50'

86.5' 81.5'
7 0'

42'
6' 3' UNLOADING
ZONE

50'
98.5'
3' 5 8' 24'
3'
3' 6'
12 PIPE

10 PIPE
251' 245' 146'
27' 110' 32'

All Grid Conductors Metallic Chain-Link Fence E xisting Grid Conductors

60’ Existing Fence Ground Conductor (below/near fence) New 4/0 AWG Stranded 10’ Copper-Clad Steel
and Ground Rods Ground Rods (5/8“ diameter) Existing Ground Rods
Sca le LEGEND Buried at 1.5’ New Fence Ground Conductor (below/near fenc e) Hard-Drawn Copper Conductors Gas Pipes

New Grounding System of Lakeshore Substation

 Appendix G. Command Input Mode

APPENDIX G
COMMAND INPUT MODE
Any of the interfaces listed below or a text editor can be used to prepare the input data. The
Windows Toolbox input modes convert the results of an input session to a Command Mode
compatible ASCII input file that can be edited at any time. This document describes the Windows
Toolbox mode in detail.

 The Windows Toolbox mode.

 The Command Mode.
 Plain text editor mode.

Printout G.1 is the resulting RESAP Command-Mode compatible input file which analyzes the
soil structure using the soil resistivity measurements from Traverse 1. The data for Traverse 1 can
be found in Table A.1 of Appendix A. This RESAP file can be edited directly by an experienced
user or is automatically produced when using one of the above-listed input interface modules. The
dialogue, character-based menu and Windows Toolbox input modes convert the results of an input
session to a Command mode compatible ASCII input file which can be edited at any time. Similar
files can be prepared quite easily by following the information contained in the template shown in
Figure G.1.

RESAP

TEXT,MODULE,SOIL RESISTIVITY MEASUREMENT AT LAKESHORE SUBSTATION

TEXT,MODULE,TRAVERSE 1 (CEMETERY SOUTH-EAST OF SUBSTATION).
TEXT,MODULE,TRIAL RUN.
OPTIONS
UNITS,BRITISH
RUN-IDENTIFICATION,LAK1T
PRINTOUT,DETAILED
MEASUREMENTS,RESISTIVITY
METHOD,WENNER
RESULTS,1.0,227.3,.333,.167
RESULTS,1.5,246.9,.333,.167
RESULTS,2.5,286.3,.333,.167
RESULTS,5.0,389.7,.333,.167
RESULTS,7.5,518.5,1.0,0.5
RESULTS,10.0,649.7,1.0,0.5
RESULTS,15.0,871.9,1.0,0.5
RESULTS,20.0,1045.0,1.0,0.5
RESULTS,30.0,5.2,1.0,0.5
RESULTS,50.0,1224.0,1.0,0.5
RESULTS,75.0,836.9,1.0,0.5
RESULTS,100.0,350.6,1.0,0.5
RESULTS,150.0,585.5,1.0,0.5
RESULTS,250.0,646.5,1.0,0.5
RESULTS,500.0,932.3,1.0,0.5
RESULTS,660.0,362.5,1.0,0.5
SOIL-TYPE,MULTILAYER

Page G-1
 Appendix G. Command Input Mode

HORIZONTAL
LAYER,TOP,0.,0.
LAYER,BOTTOM,0.
OPTIMIZATION
ACCURACY,0.025
ITERATIONS,500
METHODOLOGY
MARQUARDT
STEPSIZE,0.0001

ENDPROGRAM

Printout G.1 RESAP Input File RS_LAK1T.F05

Page G-2
 Appendix G. Command Input Mode

Figure G.1 RESAP Command-Mode Compatible Input File Template

Page G-3
 Appendix G. Command Input Mode

Printout G.2 to Printout G.5 are the resulting RESAP Command-Mode compatible input files which
analyze the soil structure using the soil resistivity measurements from Traverse 1 for different cases.
These input files can be easily created using your favorite text editor.

RESAP

TEXT,MODULE,SOIL RESISTIVITY MEASUREMENT AT LAKESHORE SUBSTATION

TEXT,MODULE,TRAVERSE 1 (CEMETERY SOUTH-EAST OF SUBSTATION).
TEXT,MODULE,FIRST RUN.
OPTIONS
UNITS,BRITISH
RUN-IDENTIFICATION,LAK1A
PRINTOUT,DETAILED
MEASUREMENTS,RESISTIVITY
METHOD,WENNER
RESULTS,1.0,227.3,.333,.167
RESULTS,1.5,246.9,.333,.167
RESULTS,2.5,286.3,.333,.167
RESULTS,5.0,389.7,.333,.167
RESULTS,7.5,518.5,1.0,0.5
RESULTS,10.0,649.7,1.0,0.5
RESULTS,15.0,871.9,1.0,0.5
RESULTS,20.0,1045.0,1.0,0.5
RESULTS,50.0,1224.0,1.0,0.5
RESULTS,75.0,836.9,1.0,0.5
RESULTS,150.0,585.5,1.0,0.5
RESULTS,250.0,646.5,1.0,0.5
RESULTS,500.0,932.3,1.0,0.5
SOIL-TYPE,MULTILAYER
HORIZONTAL
LAYER,TOP,0.,0.
LAYER,CENTRAL,0.,0.
LAYER,CENTRAL,0.,0.
LAYER,CENTRAL,0.,0.
LAYER,BOTTOM,0.
OPTIMIZATION
ACCURACY,0.025
ITERATIONS,500
METHODOLOGY
MARQUARDT
STEPSIZE,0.0001

ENDPROGRAM

Printout G.2 RESAP Input File RS_LAK1A.F05

RESAP

TEXT,MODULE,SOIL RESISTIVITY MEASUREMENT AT LAKESHORE SUBSTATION

TEXT,MODULE,TRAVERSE 1 (CEMETERY SOUTH-EAST OF SUBSTATION).
TEXT,MODULE,SECOND RUN.
OPTIONS
UNITS,BRITISH
RUN-IDENTIFICATION,LAK1B
PRINTOUT,DETAILED

Page G-4
 Appendix G. Command Input Mode

MEASUREMENTS,RESISTIVITY
METHOD,WENNER
RESULTS,1.0,227.3,.333,.167
RESULTS,1.5,246.9,.333,.167
RESULTS,2.5,286.3,.333,.167
RESULTS,5.0,389.7,.333,.167
RESULTS,7.5,518.5,1.0,0.5
RESULTS,10.0,649.7,1.0,0.5
RESULTS,15.0,871.9,1.0,0.5
RESULTS,20.0,1045.0,1.0,0.5
RESULTS,50.0,1224.0,1.0,0.5
RESULTS,75.0,836.9,1.0,0.5
RESULTS,150.0,585.5,1.0,0.5
RESULTS,250.0,646.5,1.0,0.5
RESULTS,500.0,932.3,1.0,0.5
SOIL-TYPE,MULTILAYER
HORIZONTAL
LAYER,TOP,0.,0.
LAYER,BOTTOM,0.
OPTIMIZATION
ACCURACY,0.025
ITERATIONS,500
METHODOLOGY
MARQUARDT
STEPSIZE,0.0001

ENDPROGRAM

Printout G.3 RESAP Input File RS_LAK1B.F05

RESAP

TEXT,MODULE,SOIL RESISTIVITY MEASUREMENT AT LAKESHORE SUBSTATION

TEXT,MODULE,TRAVERSE 1 (CEMETERY SOUTH-EAST OF SUBSTATION).
TEXT,MODULE,THIRD RUN.
OPTIONS
UNITS,BRITISH
RUN-IDENTIFICATION,LAK1C
PRINTOUT,DETAILED
MEASUREMENTS,RESISTIVITY
METHOD,WENNER
RESULTS,1.0,227.3,.333,.167
RESULTS,1.5,246.9,.333,.167
RESULTS,2.5,286.3,.333,.167
RESULTS,5.0,389.7,.333,.167
RESULTS,7.5,518.5,1.0,0.5
RESULTS,10.0,649.7,1.0,0.5
RESULTS,15.0,871.9,1.0,0.5
RESULTS,20.0,1045.0,1.0,0.5
RESULTS,50.0,1224.0,1.0,0.5
RESULTS,75.0,836.9,1.0,0.5
RESULTS,150.0,585.5,1.0,0.5
RESULTS,250.0,646.5,1.0,0.5
RESULTS,500.0,932.3,1.0,0.5
SOIL-TYPE,MULTILAYER

Page G-5
 Appendix G. Command Input Mode

HORIZONTAL
LAYER,TOP,236.0,4.0
LAYER,CENTRAL,3800.0,16.0
LAYER,CENTRAL,106.0,32.0
LAYER,BOTTOM,1432.0
COMPUTATIONS
LOCK,ALL
OPTIMIZATION
ACCURACY,0.025
ITERATIONS,500
METHODOLOGY
MARQUARDT
STEPSIZE,0.0001

ENDPROGRAM

Printout G.4 RESAP Input File RS_LAK1C.F05

RESAP

TEXT,MODULE,SOIL RESISTIVITY MEASUREMENT AT LAKESHORE SUBSTATION

TEXT,MODULE,TRAVERSE 1 (CEMETERY SOUTH-EAST OF SUBSTATION).
TEXT,MODULE,FOURTH RUN.
OPTIONS
UNITS,BRITISH
RUN-IDENTIFICATION,LAK1D
PRINTOUT,DETAILED
MEASUREMENTS,RESISTIVITY
METHOD,WENNER
RESULTS,1.0,227.3,.333,.167
RESULTS,1.5,246.9,.333,.167
RESULTS,2.5,286.3,.333,.167
RESULTS,5.0,389.7,.333,.167
RESULTS,7.5,518.5,1.0,0.5
RESULTS,10.0,649.7,1.0,0.5
RESULTS,15.0,871.9,1.0,0.5
RESULTS,20.0,1045.0,1.0,0.5
RESULTS,50.0,1224.0,1.0,0.5
RESULTS,75.0,836.9,1.0,0.5
RESULTS,150.0,585.5,1.0,0.5
RESULTS,250.0,646.5,1.0,0.5
RESULTS,500.0,932.3,1.0,0.5
SOIL-TYPE,MULTILAYER
HORIZONTAL
LAYER,TOP,208.5,1.82
LAYER,BOTTOM,753.0
COMPUTATIONS
LOCK,ALL
OPTIMIZATION
ACCURACY,0.025
ITERATIONS,500
METHODOLOGY
MARQUARDT
STEPSIZE,0.0001

Page G-6
 Appendix G. Command Input Mode

ENDPROGRAM

Printout G.5 RESAP Input File RS_LAK1D.F05

Printout G.6 shows the required MALZ input file MZ_FGD1D.F05 corresponding to the initial
grounding system of Lakeshore substation. The two-layer soil model from Traverse 1 is used. The
following provide step-by-step instructions about how to create this input file, how to submit the
MALZ run and how to obtain the computed Fall-of-Potential curve. Printout G.6 can be edited
directly by an experienced user or is automatically produced when using one of the above-listed
input interface modules.

Similar files can be prepared quite easily by following the information contained in the template
shown in Figure G.2.
MALZ

TEXT,MODULE,SIMULATION OF FALL-OF-POTENTIAL MEASUREMENT AT

TEXT,MODULE,LAKESHORE SUBSTATION.
TEXT,MODULE,TWO-LAYER SOIL MODEL FROM TRAVERSE 1.
TEXT,MODULE,CONDUCTOR NETWORK INCLUDES THE GROUNDING GRIDS
TEXT,MODULE,OF LAKESHORE SUBSTATION AND GAS SUBSTATION.
OPTIONS
UNITS,BRITISH
RUN-IDENTIFICATION,FOP_LAK1D_GRID_ALONE

SOIL-TYPE,MULTILAYER
HORIZONTAL
LAYER,TOP,208.5,1.82,,
LAYER,BOTTOM,753.0,,,
COMPUTATIONS
DETERMINE,POTENTIAL
OBSERVATION-POINTS
POINTS,1,-356.,560.,0.0
POINTS,1,-705.,695.,0.0
POINTS,1,-1020.,622.,0.0
POINTS,1,-1326.,432.,0.0
POINTS,1,-1615.,226.,0.0
POINTS,1,-1772.,-98.,0.0
POINTS,1,-2030.,-350.,0.0
POINTS,1,-2288.,-602.,0.0
POINTS,1,-2546.,-854.,0.0
POINTS,1,-2804.,-1106.,0.0
FREQUENCY,0.25,
SYSTEM
TOLERANCE,0.001,1.0,0.,0.,0.5
ENERGIZATION,Current,-1000.,0.,,,,,,Source-SES 1
ENERGIZATION,Current,1000.,0.,,,,,,Source-SES 2
SYSTEM
CHARACTERIST
CONDUCTOR-TY,Computed,12.,250.,0.,,,Steel
CONDUCTOR-TY,Computed,12.,250.,.1667,,,4" Gas Pipe
CONDUCTOR-TY,Computed,12.,250.,.5156,,,12" Gas Pipe
CONDUCTOR-TY,Computed,12.,250.,.4271,,,10" Gas Pipe
CONDUCTOR-TY,Computed,17.,300.,.1146,,,3" Water Pipe

SUBDIVISION,YES,
INDUCTION,NO
NETWORK

Page G-7
 Appendix G. Command Input Mode

MAIN-GROUND
CONDUCTOR,-1,0,0,0,3.,3.,1.5,481.,3.,1.5,.02,1,,,0.,0.
CONDUCTOR,-1,0,0,0,3.,3.,1.5,3.,407.,1.5,.02,1,,,0.,0.
CONDUCTOR,0,0,0,2,3.,407.,1.5,580.,407.,1.5,.02,1,,,0.,0.
CONDUCTOR,-1,0,0,0,28.,3.,.03,28.,3.,30.,.026,1,,,0.,0.
CONDUCTOR,-1,0,0,0,78.,3.,.03,78.,3.,20.,.026,1,,,0.,0.




CONDUCTOR,-1,0,0,0,348.6,390.,.03,348.6,390.,6.,.0417,1,,,0.,0.
CONDUCTOR,-1,0,0,0,354.,404.,.03,354.,404.,6.,.0417,1,,,0.,0.
CONDUCTOR,-1,0,0,0,362.6,385.6,.03,362.6,385.6,6.,.0417,1,,,0.,0.
CONDUCTOR,-1,0,0,0,368.,399.6,.03,368.,399.6,6.,.0417,1,,,0.,0.
CONDUCTOR,0,0,0,1,-3061.,-1357.,.04,-3061.,-1357.,2.04,.03,2,,,0.,0.

ENDPROGRAM

Printout G.6 MALZ Input File MZ_FGD1D.F05

Page G-8
 Appendix G. Command Input Mode

Figure G.2 MALZ Command Mode Compatible Input File Template

Page G-9
 Appendix G. Command Input Mode

Printout G.7 is the resulting TRALIN Command-Mode compatible input file. This file can be edited
directly by an experienced user or is automatically produced when using one of the above-listed
input interface modules.

Similar files can be prepared quite easily by following the information contained in the template
shown in Figure G.3.
TRALIN

TEXT,MODULE,Cross section of the transmission line from Lakeshore to Willow street.

TEXT,MODULE,Phase conductor: 477 MCM, Hawk 26/7. Average height: 60 feet.
TEXT,MODULE,Two overhead ground wires: 3/8 steel. Average height: 70 feet.
OPTIONS
UNITS,BRITISH
RUN-IDENTIFICATION,WILLOW
!KEEP_CIRCUIT_MODE
PARAMETERS
BASE-VALUES
FREQUENCY,60.
SOIL-TYPE
HORIZONTAL
LAYER,AIR,1E+18,,1.0,1.0
LAYER,TOP,151.0,11.5,1.0,1.0
LAYER,BOTTOM,487.0,,1.0,1.0
SYSTEM
SINGLE,1,1,0.42915,14.0,60.
SINGLE,1,2,0.18,7.,70.
SINGLE,1,2,0.18,-7.,70.

! Strands Info: CN=Hawk; NCS=7; CSR=0.05265; Perm=.838412; X1ft=.429899; Res=2.28986;

Rac=.197401
STRANDS,1,1,26,.029,.1969,.0677,.158,2,2
CLASS_INFO,ACSR,60,0
CONDUCTOR_INfo,Hawk

! Strands Info: CN=3/8 HS-AG; NCS=1; CSR=0.06; Perm=54.0755; GMR=-1; Res=13.6956; Rac=7.71
STRANDS,2,2,6,2.15,6.51001,.06,.06,3,2
CLASS_INFO,STEEL,60,0
CONDUCTOR_INfo,3/8 HS-AG

! Strands Info: CN=3/8 HS-AG; NCS=1; CSR=0.06; Perm=54.0755; GMR=-1; Res=13.6956; Rac=7.71
STRANDS,3,3,6,2.15,6.51001,.06,.06,3,2
CLASS_INFO,STEEL,60,0
CONDUCTOR_INfo,3/8 HS-AG

ENDPROGRAM

Printout G.7 Structured TRALIN Input File TR_WILLO.F05

Page G-10
 Appendix G. Command Input Mode

Figure G.3 TRALIN Command Mode Compatible Input File Template

Printout G.8 is the resulting SPLITS Command-Mode compatible input file that describes
completely the problem being modeled in the simplified current distribution analysis module. This

Page G-11
 Appendix G. Command Input Mode

file can be edited directly by an experienced user or is automatically produced when using one of the
above-listed input interface modules.

Similar files can be prepared quite easily by following the information contained in the template
shown Figure G.4.

SPLITS

TEXT,MODULE,Determine current distribution for a 115 kV fault at Lakeshore sub.

TEXT,MODULE,Four terminals: Willow, Appleby, Alexander and Others
TEXT,MODULE,Terminal Others represent all the other sources feeding Lakeshore
TEXT,MODULE,with the transmission lines having no ground wires.
OPTIONS
UNITS,BRITISH
RUN-IDENTIFICATION,CURR_LAKESHORE
PRINTOUT,DETAILED
OUTPUT,BOTH
SKIP,ECHO
NEUTRAL,YES
INTERCONNECT,YES
WARNINGS,NO
CONNECTION,YES
VARY,NO
SPAN-SCALING,1.0
MUTUAL-INTER,YES
REACTIVE-SH,SPAN-ONLY
RESISTIVE-SH,NO
SERIES-MUTUAL,SPAN-ONLY
TERMINAL,NO
SYSTEM
ZERO
GRID,LAKESHORE,0.2932,0.1496,0.0
! Open Connection Option - Specify
BUSS,PHSA,1,0.,0.,,,
! Open Connection Option - Specify
BUSS,GRDW,2,0.00001,0.0,,,
TERMINAL,WILLOW
EARTH,0.01,0,0
LINES
VOLTAGE,Polar,1,1,999.4249,-2.9235,5828.9,-79.8
VOLTAGE,Polar,2,2,0.000001,0.0,0.0,0.0
SECTIONS,1,26,0.07576
SELF,1,1,0.29194,1.4842,0.0000,-0.33950E+06,0.0,
SELF,2,2,3.3888,1.8232,68.,0.,0.0,
MUTUAL,Infinite,1,1,0.93883E-01,0.71768,2,2,0.0000,-0.60837E+06
TERMINAL,APPLEBY
EARTH,0.01,0,0
LINES
VOLTAGE,Polar,1,1,986.5969,-68.3024,1329.6,-78.6
VOLTAGE,Polar,2,2,0.000001,0.0,0.0,0.0
SECTIONS,1,486,0.094697
SELF,1,1,0.29182,1.4841,0.0000,-0.28262E+06,0.0,
SELF,2,2,6.6838,2.9057,76.,0.,0.0,
MUTUAL,Infinite,1,1,0.94014E-01,0.70314,2,2,0.0000,-0.11048E+07
TERMINAL,ALEXANDER
EARTH,0.01,0,0

Page G-12
 Appendix G. Command Input Mode

LINES
VOLTAGE,Polar,1,1,997.5405,-12.508,2405.4,-83.4
VOLTAGE,Polar,2,2,0.000001,0.0,0.0,0.0
SECTIONS,1,89,0.094697
SELF,1,1,0.29182,1.4841,0.0000,-0.28262E+06,0.0,
SELF,2,2,6.6838,2.9057,76.,0.,0.0,
MUTUAL,Infinite,1,1,0.94014E-01,0.70314,2,2,0.0000,-0.11048E+07
TERMINAL,OTHERS
EARTH,0.01,0,0
LINES
VOLTAGE,Polar,1,1,999.4169,-2.9686,18694.7,-79.5
VOLTAGE,Dummy,2,2
SECTIONS,1,2,1.0
SELF,1,1,0.29156,1.4843,0.0000,-0.24053E+06,0.0,

ENDPROGRAM

Printout G.8 Structured SPLITS Input File SP_CULAK.F05

Page G-13
 Appendix G. Command Input Mode

Figure G.4 SPLITS Command Mode Compatible Input File Template

Page G-14
 Notes

NOTES
Notes