DEDICATION

This Thesis is Gratefully Dedicated To

My Parents

iii

ACKNOWLEDGMENT

In the name of God, the Compassionate, the Merciful

All praise is for Allah, Lord of the Worlds, Master of the Day of Judgment whom we do
worship, and whose pleasure and aid we seek. Blessings and peace of Allah be upon his
last Prophet and Messenger Mohammed and upon his Family and Companions.

The contents of this thesis have been developed and improved by the contributions of
numerous people.

I would like to express my sincere gratitude to my thesis advisor, Professor Mohammed

Al-Shwehdi, for his steadfast encouragement, useful discussions, invaluable assistance,
advice, and comments. Without his tireless and insightful supervision, the completion of
this thesis would not have been possible. He has taught me as an undergraduate student on
how to do research and given me plenty of opportunities to present my work in front of
experts in the field at local and international conferences. He has also taught me many
important lessons in life which will always guide me throughout my career. The many
skills I have 1earnt from him will constantly remind me of how great a teacher he is.

Many thanks and appreciations are due to the members of my thesis committee: Dr. Jamil
M. Bakhashwain, Professor Essam Hassan, Dr. Zakariya Al-Hamouz, and Dr. Ibrahim
iv

Habiballah. Their encouragement, advice, patience and critical editing and correction have
enhanced this manuscript.

I would like also to express my special thanks to Mr. Mubarak Al-Mulhim, Transmission
Planning & Development Vice-President in the Saudi Electricity Company, for his kind
support in providing the necessary software to conduct this study.

I am forever profoundly indebted to my parents, to whom this work is dedicated, for their
unparalleled love, support and encouragement throughout my entire life.

I would like to express my profound gratitude to my little boy, Abdullateef, to whom I

owe my life, for missing me so much throughout my study.

But most of all my sincere love and deepest appreciation goes to my wife, UmAbdullateef, for her constant support, understanding and patience during my study.

Last but not least, I want to express my heartfelt gratitude to my brothers and sisters, Dr.
Saeed, Dr. Hussain, Maryam, Aisha, Khalid, Fawzia, Abdullah, Khalil and Mohammed,
for their emotional support and time spent to guide and advise me during my whole
education.

I have thanked just a few of the people who have been instrumental in shaping my career
so far, and I ask forgiveness from those who have been omitted unintentionally.

TABLE OF CONTENTS

LIST OF TABLES .........viii

LIST OF FIGURES ix
ABSTRACT (ENGLISH)...xi
ABSTRACT (ARABIC).xii
CHAPTER 1. INTRODUCTION ..1
1.1

RESEARCH OBJECTIVE 1

1.2

RESEARCH METHODOLOGY ..2

1.3

RESEARCH CONTRIBUTION ...3

1.4

THESIS ORGANIZATION ..4

1.5

GENERAL BACKGROUND ...5

1.6

MECHANISM OF EMI 6

1.7

EFFECTS OF EMI 13

CHAPTER 2. LITERATURE REVIEW ..16

2.1

GENERAL REVIEW ...16

2.2

EMI INTERFERENCE .17

2.3

SAFETY STANDARDS........21

2.3

MITIGATION OF EMI EFFECTS ...23

2.4

REVIEW AVAILABLE SOFTWARE FOR EMI STUDY .....26

vi

CHAPTER 3. EMI THEORETICAL ESSENTIALS AND CALCULATIONS.. 31

3.1 INDUCTIVE INTERFERENCE ..31
3.2

CONDUCTIVE INTERFERENCE ......41

3.4

CALCULATION OF THE INDUCED VOLTAGES ON

COMMUNICATION CABLES47

CHAPTER 4. EMI ANALYSIS FOR 2007 INVESTIGATION AREA .....49

4.1

INTRODUCTION ....49

4.2

TERMINOLOGY .........53

4.3

CONDUCTORS COORDINATES ......57

4.4

CONDUCTORS GROUNDING ......76

CHAPTER 5. CASE STUDY SIMULATION & RESULTS .......78

5.1

INTRODUCTION ........78

5.2

VALIDATION OF SOFTWARE RESULTS .......78

5.3

STEADY-STATE CONDITION ......82

5.4

TRANSIENT CONDITION .........94

CHAPTER 6. MITIGATION OF EMI INTERFERENCE .........100

CHAPTER 7. CONCLUSION ........106
NOMENCLATURE ........109
REFERENCES ........111
VITA ............116

vii

LIST OF TABLES

Table

Page

2.1

Standards of maximum allowable touch voltage level..................22

4.1

Line-Path Coordinates Measured in Faras-Qurayyah Right-of-Way....59

4.2

Physical characteristics of transmission line phase conductors .......64

4.3

Physical characteristics of transmission line ground wire conductors .....65

4.4

UA-1 Pipeline Characteristics ..66

4.5

QUU-1 Pipeline Characteristics ...67

4.6

UBTG-1 Pipeline Characteristics .................68

4.7

UJNGL-1 Pipeline Characteristics .......69

4.8

SHNGL-1 Pipeline Characteristics ..70

4.9

UA-4 Pipeline Characteristics ..71

4.10

UA-6 Pipeline Characteristics ..72

4.11

SEC Oil Pipeline Characteristics ..73

4.12

60 Water Pipeline Characteristics ...74

4.13

Communication Cable Characteristics ..75

4.14

Soil Resistivities ................77

5.1

Pipeline potential along the QUU-1 Pipeline ................81

5.2

Fault Currents Level for Faras-Qurayyah 380KV Transmission Line...97

viii

LIST OF FIGURES

Figure

Page

1.1

Inductive Coupling...8

1.2

Conductive Coupling ......12

3.1

Example of E.M.F. Induced in Normal Situation ...........36

4.1

380 KV Network with Pipelines & Cables to be Modeled .52

4.2

Partial Coordinates Map Generated by DGN Program ...58

4.3

Cross section of 380 KV Faras-Qurayyah Transmission Line ....62

4.4

Cross section of 380 KV Shedgum-Qurayyah Transmission Line ..............63

5.1

Pipeline Potential along The Axial Length of The QUU-1 Pipeline ...80

5.2

Current Level on 380KV Faras-Qurayyah Transmission Lines ..85

5.3

Current Level on 380KV Shedgum-Qurayyah Transmission Lines ...................86

5.4

Pipeline Potential on the UA-1 Pipeline during steady state condition ..87

5.5

Pipeline Potential on the SEC Oil Pipeline during steady state condition...88

5.6

Pipeline Potential on the Gas Pipeline during steady state condition .....89

5.7

Pipeline Potential on the QUU-1 Pipeline during steady state condition90

5.8

Pipeline Potential on the UA-4 Oil Pipeline during steady state condition.91

5.9

Pipeline Potential on the QUU-1 Pipeline during steady state condition92

5.10

Induced voltage on the Communication Cable during steady state condition.93

ix

5.11

Touch Voltage along The Axial Length of The UA-1 Pipeline .....98

5.12

Touch Voltage along The Axial Length of The SEC Oil Pipeline .....99

6.1

Typical Gradient Control Wire Installation ...101

6.2

Touch Voltage along The UA-1 Pipeline After Mitigation .......104

6.3

Touch Voltage along The SEC Oil Pipeline After Mitigation ...............105

THESIS ABSTRACT
NAME:

BANDER JUBRAN AL-GAHTANI

TITLE:

ELECTROMAGNETIC INTERFERENCE CAUSED BY A

HIGH VOLTAGE TRANSMISSION NETWORK ON BURIED
PIPELINES & COMMUNICATION CABLES

DEPARTMENT: ELECTRICAL ENGINEERING

DATE:

JANUARY, 2009

Electromagnetic fields, produced by the transmission lines on nearby oil and gas buried
pipelines and underground communication cables, generate uncontrolled voltages which
can be a safety problem and distort communications. This research evaluates and analyzes
the electromagnetic interference effects on oil and gas buried pipelines and underground
communication cables created by the nearby high voltage transmission lines in the Eastern
Province of Saudi Arabia. The study revealed that the maximum induced voltage on all
buried pipelines and communication cables during the steady state condition is within the
standard limit. However, the results during the short circuit condition exceed the safety
limits on some buried pipelines. A mitigation system using gradient control wires has
been simulated to reduce the pipeline potential to the safety limit.

MASTER OF SCIENCE DEGREE

KING FAHD UNIVERSITY OF PETROLEUM & MINERALS
DHAHRAN, SAUDI ARABIA

xi

: 2009

) (
.

.
.

.

31261

xii

CHAPTER I

INTRODUCTION

1.1 RESEARCH OBJECTIVES

The intention of this research is to conduct a comprehensive study on the

electromagnetic interference effects on oil and gas buried pipelines and underground
communication cables. This research also updates the previous studies, done years ago, to
analyze the inductive interference in a wide area of Saudi Electric transmission lines and
nearby oil and gas buried pipelines. The present area has been changed drastically since
new transmission lines were erected and some pipelines were removed. The objectives of
this research are to determine what are the induced voltages at all locations along buried
pipelines and communication cables, which remain within the vicinity of transmission
lines for significant distances, and to check whether these induced voltages are within
standards safe limit. The research will include the present steady-state conditions as well
as the transient-state conditions. Moreover, the present study will cover the effect of the
tower grounding resistance, soil resistivity, and distance between the transmission lines
and buried pipelines and communication cables on the reduction of EMI effects on these
pipelines and cables.
1

1.2 RESEARCH METHODOLOGY

The research started by collecting the required updated data from Saudi Electricity
Company (SEC) and Saudi Aramco (such as transmission line conductors, tower
configuration coordinates and characteristics, transmission lines loading, soil resistivity,
leakage, ground footing resistances, pipelines and communication cables layout drawings,
diameter, material, etc.). Due to the complexity of the case-study, which includes more
than one transmission lines and many oil and gas buried pipelines and underground
communication cables, it was difficult to calculate the induced voltages by hand
calculation. Thus, the case-study has been carried out through the following major steps
using the modeling and simulation of Current Distribution, Electromagnetics, Grounding,
and Soil Structure Analysis (CDEGS) software developed by the Safe Engineering
Services & Technologies (SES):

1. Determine the self and mutual impedances of all conductors under study.
2. Using the circuit model established with the impedance obtained in step 1,
determine the induced voltage in the buried pipelines and communication cables.
3.

Determine the stress voltages across the insulation or coating of the buried
pipelines and communication cables.

4. Analyze the effects of various mitigation measures.

1.3 RESEARCH CONTRIBUTIONS

This research will present a rigorous background to help engineers understand the
importance of the EMI problem, through the collection of data on the standards available,
and the modeling and simulation of practical cases.

The major benefits envisaged from this research are as follows:

1. Identify the technical merits of applying, planning and analyzing the interference
mechanism.
2. Encourage safe and reliable solutions to interference problems.
3. Calculate the induced voltage on the buried pipelines and communication cables
and compare them with standards.
4. In the case of excess over standards, conduct and implement a mitigation analysis.
5. Provide utility planners with new alternatives for installation of new transmission
lines and pipelines.
6. Allow safe and secure distances to a buried pipeline from a given transmission
line.
7. Provide a basis for continually updated studies and contracts/agreements; whereby
both the utility and end-users can benefit from electromagnetic investigations.

1.4 THESIS ORGANIZATION

Chapter 1 addresses the objective and methodology of this research, and it provides
general background about the EMI mechanisms and effects.

Chapter 2 gives a brief history of electromagnetic interference studies, including inductive

and conductive couplings between pipelines and power lines. Also, special consideration
is given to the available software used to conduct the electromagnetic interference studies.

Chapter 3 briefly discusses some theoretical essentials and calculations for inductive and
conductive interferences. It also considers the position of the pipelines or communication
cables which might comprise a succession of parallelisms, oblique approaches and
crossings with reference to the power lines.

The EMI Analysis for the investigation area is introduced in Chapter 4, and it covers the
geographical area of the 380 KV transmission lines between Faras and Qurayyah power
plants that are used to feed the power to several oil and gas facilities owned by Saudi
Aramco.

Chapter 5 presents the simulation results of the EMI analysis for the Faras-Qurayyah
case-study, and then Chapter 6 proposes a mitigation technique to limit the EMI
interference to the acceptable safe levels that meet the local and international standards.

Chapter 7 contains the conclusion and the summary of the research analysis, and it
highlights the future work.

1.5 GENERAL BACKGROUND

Metal pipelines are largely used to convey fluids and especially liquid or gaseous
hydrocarbons (i.e. oil or natural gas). Their length can reach several hundreds and even
thousands of kilometers. The pipelines are generally buried at shallow depths but they can
also be aerial. In order to prevent electrochemical corrosion of the metal, the underground
pipelines are provided with an outside insulating coating and connected to a cathodic
protection installation. For the sake of the cathodic protection, insulating flanges can
interrupt the electrical conduction of the pipeline at different places.

Because of the continuous growth of energy consumption, and of the tendency to site
power lines and pipelines along the same routes, high voltage structures are more and
more frequently located in the vicinity of metallic pipelines. Moreover, short-circuit
current becomes higher as electric networks increase in size and power. Therefore, there
has been and still is a growing concern about the following possible hazards resulting
from the influence of H.V. systems on metal pipelines [7, 38]:

safety of people entering in contact with the pipeline

6
-

risks of damage of the pipeline

risks of destruction of equipment connected with pipeline.

Metal pipelines and communication cables form conductors insulated from the earth,
and they may be on a part of their length exposed to influences of nearby high voltage
lines. Influences of H.V. lines can result from three types of couplings: capacitive,
inductive and conductive. Under fault conditions, the voltages on influenced pipelines can
reach a magnitude between several hundred volts and a few kilovolts. In normal
operation, influences are normally much lower, but nevertheless they can make problems.
Since the capacitive effect is negligible for the buried pipelines and communication
cables, only the inductive and conductive couplings are considered in this research. [9, 26]

1.6 MECHANISMS OF ELECTROMAGNETIC INTERFERENCE (EMI)

1.6.1 INDUCTIVE COUPLING MECHANISM

Buried pipelines or communication cables that run parallel to or in close proximity to

transmission lines are subjected to induced voltages caused by the time-varying
magnetic fields produced by the transmission line currents (Figure 1.1). The induced
e.m.f.s cause currents to flow in the buried pipeline and communication cable and also
voltages between them and the surrounding earth. [4]

7
The inductive influence of a H.V. line on a nearby pipeline depends basically on three
parameters:

Power transmission line currents and operating conditions. Under short circuit
conditions, induced e.m.fs depend on the fault current. The induced voltages can
be much higher than in normal situations but their duration is very short. [4]

Distance between electrical line and pipeline. The separation between the
transmission line and the pipeline is an important factor influencing the induced
voltage level, which is reduced with increasing separation. [37]

Exposure length. The length of exposure is the length of the zone where the
influence is significant. The influence is considered significant when the induced
e.m.f. due to a fault current with earth-return is higher than 10 V/km x kA, or in
other words when a 1 kA current with earth return produces an electromotive force
higher than 10 V per kilometer. Such values correspond approximately to
distances (in m) between the electrical line and the pipeline less than 200
(with soil receptivity in m ). [16]

Figure 1.1 Inductive Coupling. [3]

Although the total e.m.f increases with the exposure length, induced voltages increase
with the exposure lengths only where these are short (from 1 up to a few kilometers
depending on the pipeline coating). For long exposure lengths, there is a limitation of
the induced voltages due to the leakage impedance of the coating. [16]

For the communication cables, the inductive coupling occurs via the mutual
inductance between the power lines and the communication cables. The magnetic
flux, produced by the transmission line current, may induce noise voltage into an
adjacent communication cable, generating a loop current in the disturbed circuit. The
geometry of the conductors, as well as the geometric range between the power lines
and communication cables, determines the value of the mutual impedance and,
consequently, the intensity of the inductive coupling. [53]

1.6.2

CONDUCTIVE COUPLING MECHANISM

When a ground fault occurs at a power line tower (or in a power substation), there is
conductive coupling between the line tower (or a power substation) and a nearby
pipeline if the pipeline is directly connected to the ground electrode of the H.V.
system (i.e. inside a power station) or if the pipeline enters the zone influence of the
tower (or power substation), i.e. a noticeable ground potential rise (GPR) appears at
the pipeline location because of the fault current flowing into the soil. In practice,

10
conductive coupling most often results from the second case (ground potential rise at
pipeline location). [4]

In so far as a pipeline is not influenced by capacitive or inductive coupling, its

potential can be assumed to remain very close to the reference potential of remote
earth. Therefore, any GPR (ground potential rise) at the pipeline location is directly
applied to the pipeline insulating coating. Problems may appear when the GPR
exceeds the coating dielectric strength: in such a case, permanent, but usually very
limited, puncturing of the pipeline coating can be observed. Melting of the pipeline
steel may even occur, but only when the pipeline is very close to a tower grounding
electrode. [31]

When the coating material is not perfectly insulating (i.e. bitumen), or if the
pipeline is intentionally grounded inside the zone of influence of the faulted tower (or
substation), leakage currents flow from the soil into the pipeline. Thus a fraction of the
GPR is transferred to the metallic pipeline. This transferred potential can be
transmitted by the pipeline to a remote point such as an insulating flange, a pipeline
access point, or a cathodic protection system. Depending upon its amplitude, this
transferred potential may generate a dielectric stress upon the insulating flange or
upon the cathodic protection system, or it may create touch and step voltages which
may be applied to workers touching the pipeline at access points or staying nearby. A
similar situation appears when a pipeline section is directly bonded to the earth
electrode of a power station. [3]

11
Thus, touch voltages (between the pipeline and the earth) appear within and
outside the station. If safety precautions are not taken, such voltages might represent a
risk to workers (in the station) and to the public (outside the station). In addition, the
ground potential rise of the station is transmitted along the pipeline and, before
decreasing to a safe value, it can be applied to an insulating flange. [3, 4]

In the case of communication cable, the conductive coupling occurs when

transmission lines and communication cable have a common branch. The conductive
coupling is fairly common when the bonding and grounding systems used for the
power and telecommunications are not sufficiently isolated. [53]

12

Figure 1.2 Conductive coupling during line-to-ground fault condition. [4]

13

1.7 EFFECTS OF EMI

1.7.1 EFFECTS OF INDUCTIVE COUPLING

Induced voltages can be responsible for safety problems for people in contact with
an aerial or underground pipeline situated in the vicinity of H.V. lines. Most
national regulations insist that safety measures have to be taken when the voltages
on the pipeline exceed 50 or 65V under steady-state conditions. During H.V. faults
to the earth, much higher voltages are admissible, as the fault produces a short
duration stress and the admissible voltage depends on the stress duration. Risks due
to faults are limited, because of the limited rate of faults and the low probability that
somebody is in contact with the pipeline at the very moment when the danger level
is exceeded. Also, during H.V. earth faults, voltages on the pipeline can exceed the
withstand voltage level of the insulating flanges. The same danger exists for
equipment connected to the pipeline, especially for cathodic protection apparatus.
[26]

The electromagnetic interference may cause electrical and electronic malfunctions

and can prevent the proper use of the radio frequency spectrum. In data
communication, excessive electromagnetic interference hinders the ability of remote

14
receivers to successfully detect data packets. The end result is increased errors,
network traffic due to packet retransmissions, and network congestion. [53]

1.7.2 EFFECTS OF CONDUCTIVE COUPLING

When the transferred potential develops along a pipeline, workers touching the
pipeline (or staying close to it) may be subjected to electrical shock, which can
eventually result in ventricular fibrillation. The risk depends upon many factors:
duration of the fault, voltage amplitude, combined probability for people to be in an
exposed position during a phase-to-earth fault, voltage distribution around the access
point, quality of gloves and shoes that workers wear, etc. [9]

Any voltage difference between the metallic pipeline and the surrounding soil is
applied to the insulating coating. Investigations have shown that relatively low
voltage values (1000 to 2000 V) result in glow and arc discharges on the whole area
of bitumen coatings. During such phenomena, the pipelines transverse admittance
to the earth is increased (i.e. the coating becomes more conductive). If the coating
degradation is irreversible, it will further result in an increased current consumption
by the cathodic protection systems, and also in a smaller pipeline a voltage increase
in the case of inductive coupling with a H.V. line. Damage to polyethylene coating
will be usually more localized. [4]

15
High-intensity current passing through a small-size coating puncture would heat up
the pipeline steel and, in theory, could make it melt. Experiments and calculations
have shown that such a puncturing process cannot result from the sole transferred
potential mechanism: it can happen only if the pipeline is so close to the H.V.
tower footing (or the substation grounding grid) that an electric arc appears in the
soil and, by establishing a zero-resistance path between the electrode and the
pipeline, makes it possible for a large current to flow directly into the pipeline. [16]

Voltage transferred into a pipeline section can result in a dielectric stress across an
insulating flange. If the flange dielectric strength is exceeded, flashover will occur,
with the destruction of the insulating flange as a possible result. However, such an
accident is rather unlikely to occur, since voltages transferred by resistive coupling
are most often much lower than voltages resulting from inductive coupling against
which insulating flanges are dimensioned. [16]

Active cathodic protection system, including semi-conductor rectifiers (SCRs) can

be damaged by high voltage resulting from transferred potential if no protective
measures are taken. [4]

CHAPTER II

LITERATURE REVIEW

2.1

GENERAL REVIEW

Electromagnetic interference caused by electric transmission and distribution lines

on neighboring metallic utilities such as gas and oil pipelines became a major concern in
the early 60s due to the significant increase in the load and short-circuit current levels
needed to satisfy the energy required by the phenomenal industrial growth of Western
nations. Another reason for increased interference levels originates from the more recent
environmental concerns which obligate various utilities to share common corridors in an
effort to minimize the impact on wildlife and other related threats to nature. [11]

Electromagnetic interference problems were analyzed in the early days of

telegraph and telephone mainly as an inductive coupling problem between
telecommunications

circuits

(crosstalk)

and

between

electric

lines

and

telecommunications lines (electric noise). However, it is only in the mid 60s that the first
detailed investigations of a realistic interference analysis, including power lines and
pipelines, were published by Favez et al. [15]
16

17

2.2

EMI INTERFERENCE

The interference of power lines to closely located metallic structures, buried pipelines and
telecommunication cables has been a topic of interest over the past 25 years. The
inductive and conductive interferences were examined by researchers who produced
various reports, papers, and standards [1-56]. The widely known Carsons relations were
the basis for the initial attempts to study these interferences [12]. A technical
recommendation was developed in Germany based on these studies, which was revised
later, by utilizing more advanced and sophisticated analytical models in a computer
program [15].

During the late 1970s and early 1980s, two research projects of the Electrical Power
Research Institute (EPRI) and the American Gas Association (AGA) introduced practical
analytical expressions that could be computerized or programmed on handheld calculators
[18]. In the following years, EPRI and AGA jointly developed a computer program that
utilizes equivalent circuits with concentrated or distributed elements with the self and
mutual inductances being calculated using classic formulas from Carson et al [27].
Furthermore, CIGREs Study Committee 36 produced a report detailing the different
regulations existing in several countries and, some years later, published a general guide
on the subject, with a summary of its most important parts [16]. Moreover, a universal
algorithm was proposed that may be used to simulate uniformly both the inductive and

18
conductive interferences, whereas a more general method may be applied to pipeline
networks with complex geometries [6].

More recently, a finite-element method (FEM) was adopted to calculate the induced
voltages on pipelines. This method removes certain approximations that previous
approaches used. However, due to the large solution area of the problem, only twodimensional (2-D) FEM calculations were performed. This made the method applicable
only to symmetrical cases (e.g., parallel routings) and to cases where the pipeline has a
perfect coating, which is a situation rarely encountered in reality. Defects on pipeline
coatings are a common fact, especially in old pipelines, and they can range from a few
millimeters to several decimeters. In order to overcome the above limitations, an
improved hybrid method was introduced later, utilizing both FEM calculations and circuit
theory, that is capable of calculating unknown parameters of the problem, such as the
induced currents or voltages, and it was validated by comparing it with other published
results. [17,19]

During 1990-2001, the electromagnetic field method (EFM) and the conventional circuit
method (CCM) were proposed by the Safe Engineering Services & Technologies (SES)
Group to analyze electromagnetic interference between transmission lines, railways,
pipelines, communication lines or other metallic structures parallel to the transmission
lines. In the EFM case, the total interference level is obtained in one step without the need
to compute separately each individual component such as inductive and conductive
components. The main limitation of EFM is that it is difficult to handle very long right-ofways with many circuits. In the CCM case, interference levels due to induction and

19
conduction are computed separately. The total interference level is then obtained by
combining the inductive and conductive components, which is always a time-consuming
process. When the victim circuit is connected to the electrical substation grounding grid,
which is usually connected to the overhead ground wires, the total interference level can
no longer be computed accurately by CCM. Recently, the SES Group has adopted the
CCM approach where the total interference level can be computed efficiently and
accurately even where pipelines are connected to electric substation grounding systems.
[2, 14]

In 1994, Charge Simulation Method (CSM) was developed for calculating the induced
voltages on fence wires/pipelines underneath AC power transmission lines. The calculated
induced voltages compare favorably with those measured experimentally. [40]

In 2003, a local case study was conducted to analyze and evaluate the inductive effects on
some old parts of Saudi Aramco pipelines created by the operation of SEC 380KV power
lines in the some parts of the Eastern province of Saudi Arabia. A mathematical model is
given for the computation of the electrostatic effect of the power line on the pipelines. [3]

Nodal network analysis was used in 2004 to analyze the induced voltage on the buried gas
pipelines. The induced voltage on the 71.3 km long gas pipeline running parallel to the
22.9 kV power line is analyzed, and the maximum induced voltage is 4.78 V at the
starting point of the longest parallel segment. [54]

20
In 2005, a new technique was presented on the basis of the development of an artificial
neural network (ANN) model for predicting the electromagnetic interference effects on
gas pipelines shared right-of-way (ROW) with high voltage transmission lines. It was
demonstrated that the ANN-based model developed can predict the induced voltage with
high accuracy. The accuracy of the predicted induced voltage is very important for
designing mitigation systems that will increase overall pipeline integrity and make the
pipeline and equipments connected to pipeline safe for operating personnel. [55]

The influence of strong electromagnetic fields of power lines on telecommunication lines

was studied in two characteristic cases: when the power line is used only for power
transportation, and when the power line is used for transporting data. [53]

Study of the influence of the electrostatic and magnetostatic fields from a power
transmission line over a gas pipeline distribution system, for a non-parallel configuration
was published in 2008. That study was based on the nodal model analysis for power line,
quantifying the capacitive and self and mutual impedance effects, due to the geometrical
configuration of both systems, as they depend on the power line voltage and on the
current in conductors, respectively. [5]

Longitudinal induction voltage measurement on communication cables running parallel to

overhead lines was presented in April 2008. It aimed to briefly highlight the effect of
induced voltage in the telecommunication cables, and to explain methods by which the
longitudinal induced voltage can be measured, and to introduce a new method for this
measurement. [1]

21

The most recent study was conducted in November 2008, and it focused on the
possibilities of studying the electromagnetic interferences in common corridors shared by
electric transmission lines and other utilities, such as pipelines, by using professional
analysis and modeling software. The study confirmed the possibility of obtaining an
accurate modeling of extremely long common corridors, along which various parameters
may change, such as soil resistivity, power line current magnitude, fault location, and
victim line characteristics. [2]

2.3

SAFETY STANDARDS

Several international standards provide a methodology for determining the maximum

acceptable touch and step voltages, and they are all based on the minimum current
required to induce ventricular fibrillation. In addition, many national standards are set by
many countries to provide their own safety limits. In general, there is no worldwide
consensus on a maximum safe touch voltage level. Table 2.1 lists different countries and
standards for the maximum allowable touch voltage level. [41-44]

Unfortunately, Saudi Arabia has no national code standard to determine the maximum
safe limits for touch and step voltages. Instead, the Saudi Electricity Company (SEC) and
Saudi Aramco Company refer to the IEEE 80 standard for the maximum touch voltage
limit.

22

TABLE 2.1 Standards of Maximum Allowable Touch Voltage Level

Standards/Countries

IEEE 80-2000

Steady State
Max. Voltage (V)

15

IEC-479
NACE RP0177-2000

Fault State
Max. Time

Max. Voltage (V)

0.5

287

0.45

220

15

Saudi Arabia

No guidance
According to IEEE 80-2000

United States

25

According to IEEE 80-2000

Germany

65

0.5

1000

Sweden

15

0.5

600

Switzerland

50

0.3

300

South Africa

50

> 0.35

430

International
Telecommunication
Unions guidelines

60

0.5

430

23

2.4

MITIGATION OF EMI EFFECTS

A mitigation system designed to protect the buried pipeline and communication cable
subject to EMI interference must achieve several objectives. Under worst case power-line
load conditions, the buried pipeline or communication cable potentials with respect to
local earth must be reduced to acceptable levels for the safety of operating personnel and
the public. The mitigation system must ensure

the safety of the public and operating

personnel at exposed sites during fault conditions in the power line.

The mitigation system must also ensure that pipeline coating stress voltages remain within
acceptable limits to prevent damage to the coating or even to the pipeline steel. Following
are the most common mitigation techniques that can control induced voltage on an
influenced buried pipeline and communication cable.

2.4.1

LUMPED GROUNDING

The simplest method to lower EMI interference levels in the buried pipeline or
communication cable is to connect it to an earth electrode at certain locations. This
method is known as lumped grounding or a brute force method.

24

The soil resistivity in the area can affect the size of the required electrode significantly.
For example, 50 m vertical rod in 100 m soil achieves 3 . But 0.3 can be achieved
by six 100 m long vertical rods spaced 100 m apart and connected with a horizontal
conductor. If soil resistivity increases to 1000 m, these dimensions increase tenfold.
While it can still work well for mitigation systems with low impedance requirements and
in a very low soil resistivity, in many practical cases this method is impractical and very
expensive. [10]

2.4.2

CANCELLATION WIRE

Cancellation wire as a method was developed in the late 1980s. It consists of a long
buried wire parallel to the transmission line, often on the side of the transmission line
opposite to the buried pipeline or the communication cable, so that the transmission line is
located between the buried pipeline and the cancellation wire. With proper positioning,
the voltages induced in the wire are out-of-phase with voltages induced into the pipeline.
As one end of the cancellation wire is connected to the pipeline, these voltages cancel
each other when the other end of the wire is left free.

The problems with this method are that it cancels only the inductive component of the
fault currents, and it may transfer excessive voltages to its unconnected end. The method
requires the purchase of additional land for the placement of the wire. [31]

25
2.4.3

INSULATING JOINTS

Insulating joints divide the pipeline into several electrically isolated parts so that induced
voltage cannot reach high levels. Local ground is then connected to the pipeline at each
side of the insulating joint. Each earthing electrode is connected to the pipeline through a
surge diverter, which operates only when the voltage on the pipeline is higher than its
breakdown level. With this method, the pipeline is protected from stray currents that can
cause corrosion, and cathodic protection currents are prevented from leaking out. The
combination of insulating joints and permanent earths can be quite an effective way of
mitigating the induced voltages on the pipeline. But insulating joints are more
complicated in relation to maintenance. They can be shorted during operation (this case
has already been reported in the field). Insulating joints are tested only in the laboratory,
and thus their performance in the field during faults or lightning cannot be predicted.
Sealing and installation of the joints maybe difficult, and may lead to future leaks. Use of
insulating joints appears to be an old technique for mitigation of induced voltages in
pipelines. [31]

2.4.4

GRADIENT CONTROL WIRE

The latest method for mitigating induced voltages on the buried pipelines and
communication cables is the use of gradient control wire. It consists of one or two zinc
wires buried in parallel with the buried pipeline or communication cable, with regular

26
electrical connections to the pipeline or the communication cable. The connections should
be made through surge diverters, as in the case of insulating joints. Two insulating joints
are also present at the start and at the end of the protected structure.

Gradient control wires provide grounding to the protected structure in relation to inductive
interference. They also raise the potential of the local earth, reducing the touch and
coating stress voltages. Similarly, in relation to conductive interference, these wires
reduce the potential difference between the buried pipeline or communication cable and
the local earth by allowing the current to flow between them. [10, 35]

2.5

REVIEW OF AVAILABLE SOFTWARE FOR EMI STUDY

Solving problems that involve power system electromagnetic fields (EMF),

electromagnetic interference (EMI), and grounding tends to be complex, and many
interrelations exist among these three areas. Almost any attempt to simulate problems
involving current circulating outside phase conductors (i.e., in earth, neutral ground wires,
metal pipes, etc.) should take into account many aspects of EMF, EMI, and grounding
simultaneously.

The early analysis tools were limited in several ways, which have been overcome
by more recent research. While earlier software was based on the assumption of
essentially parallel facilities, cases arise in practice in which both the electric power lines
and the pipelines follow curved paths which intersect one another, diverge, re-converge,

27
etc., making them difficult to model accurately. Recently, field-theory based software
does away with the parallel assumption, and it accounts simultaneously for the inductive
and conductive couplings between the electric power lines and the pipelines. [21]

During a research project sponsored jointly by the Electric Power Research

Institute (EPRI) and the Pipeline Research Committee (PRC) of the American Gas
Association (A.G.A.) in 1989-1990, the ECCAPP software package was developed to
analyze the electromagnetic and conductive coupling effects between transmission lines
and nearby pipelines. ECCAPP enables users to predict electrical effects on gas pipelines
produced by normal-load and ground-fault currents from electrical transmission lines, and
also to design mitigation systems whenever these effects exceed tolerable levels.
ECCAPP has been utilized in some projects and studies, such as the capacitive coupling
between 750-KV single circuit and nearby pipelines. Also, it has been used to study the
effect of the earth layer and resistivity on the performance of the EMI mitigation system.
[27]
In 1991, the DECOP software package was developed using the Decoupled
method. DECOP decouples and reduces the equivalent ladder circuit by using circuit
techniques introduced in the Decoupled method. [13]

Over the past twenty years, Safe Engineering Services & Technologies (SES) has
been developing the Current Distribution, Electromagnetics, Grounding, and Soil
Structure Analysis (CDEGS) software package. CDEGS includes six specific engineering
applications modules that can analyze soil resistivity, design of grounding, and EMF &
EMI. References show different projects, studies and researches conducted with the

28
CDEGS software. A few years ago, SES developed an integrated software package, as
part of CDEGS, called Right-Of-Way. It consists of several engineering application
packages which analyze EMI interference and mitigation analyses, and a variety of other
engineering studies involving electrical power systems. [21]

The available software packages for EMI studies have been evaluated to select the most
appropriate one for our study. It was found that the Right-Of-Way package is the best
for the EMI interference and mitigation analysis. This selection is based on many facts.
Right-Of-Way has been proved by many studies and projects to be ideal for accurately
computing voltages and currents transferred from electric power lines and cables (by
inductive, capacitive and conductive coupling) to pipelines, railways, communication
lines and other such utilities, whether buried or above ground. It is especially designed to
simplify and to automate the modeling of complex right-of-way configurations. It can
automatically create phase-to-ground faults along any transmission line at regular
intervals throughout the right-of-way corridor, as specified by the user.

The Right-Of-Way software is used by more than 200 large well-known

companies such as Pacific Gas and Electric Company (California), Lower Colorado River
Authority (Texas), Houston Power and Light (Texas), Florida Power and Light, South
Carolina Electric and Gas, Rochester Gas and Electric (New York), Ontario Hydro,
Manitoba Hydro, TransAlta Utilities (Alberta), ARAMCO (Texas and Saudi Arabia),
SNC Group, Consulting Engineers (Quebec). [22]

29
Three modules in Right-Of-Way software are used to perform EMI analysis [22]:

1.

The TRALIN module calculates the self and mutual impedances of buried and
above-ground conductors such as transmission line phase wires, shield wires,
pipelines, and communication cables.

2.

The SPLITS module determines the current distribution in the transmission line
conductors, and the induced voltages on nearby buried pipelines and cables, by
performing circuit reduction using the double-sided elimination technique which
remains accurate for large numbers of transmission line sections and for large
numbers of conductors.

3.

The MALZ module performs the EMI analysis during the transient condition.

In more detail, an inductive and conductive interference analysis using the TRALIN
module along with the SPLITS and MALZ modules consists of the following steps:

1. Produce a single map showing in detail the transmission lines and all buried
pipelines and communication cables of interest in the study.
2. Measure the relative coordinates of the endpoints of all nonparallel transmission line
and buried pipeline or communication cable segments. Measure the spacing between
parallel transmission line conductors and buried pipelines or communication cables.
3. Determine the equivalent pipeline shunt or coating leakage resistances to ground.
4. Run the TRALIN module to get self and mutual impedances of phase bundles.

30
5. Run the SPLITS module to obtain the induced voltages in all buried pipeline and
communication cables.
6. Run the MALZ program to determine the EMI effect on buried pipelines and
communication cables during the transient condition.
7. Analyze the effects of the mitigation system.

CHAPTER III

EMI THEORETICAL ESSENTIALS & CALCULATIONS

3.1 INDUCTIVE INTERFERENCE

Calculation of the voltages appearing on the pipelines is normally worked out in two
steps:

Determination of the electromotive forces (e.m.f.) induced along the pipeline.

Calculation of voltages to earth in response to the induced e.m.f.s and calculation of

the circulating currents

A clear distinction has to be made between e.m.fs and voltages appearing on the pipeline.
E.m.fs are virtual electric generators inside the pipeline resulting from the influence of the
inductive coupling. These e.m.fs produced voltages on the pipeline, and only these
voltages represent the actual stresses on the pipeline and its equipment.

The zone of influence generally comprises a succession of parallelisms, approaches and

crossings. Expressions giving electromotive forces are given for parallelisms between
31

32
pipelines and disturbing circuits. For the calculation of induced voltages, approaches and
crossings may be assimilated to parallelisms, provided they are subdivided into short
lengths. All equations and calculations listed in the following sections are extracted from
the Power System Analysis [23] and the handbook of Cathodic Corrosion Protection [24].

3.1.1. DETERMINATION OF THE ELECTROMOTIVE FORCES

Two different situations of the power network have to be considered:

Fault conditions giving rise to the highest e.m.fs but only during rare and short periods
of time.

Normal operation producing smaller but permanent e.m.fs.

3.1.1.1. Fault Conditions. Among the different kinds of faults, short circuits between
one phase and the earth produce the most severe influences. Calculation is then applied to
the evaluation of the coupling between two circuits having the earth as return conductor.

In the simplest configuration, where the electrical line is not provided with earth wire(s),
and in the absence of other metallic conductors in the vicinity, the electromotive force E
affecting the circuit pipeline/earth per unit length is related to the fault current I
circulating in the phase conductor by the following expression [24]:

33
E = - Zm I

(3.1)

where Z m represents the mutual impedance per unit length of the circuits phase
conductor/earth and pipeline/earth ( / m ) and it can be calculated by using the Carso-

Clem expression [24]:

Z m (/m) =

o
2
1
+ j o f ln
+
8
gd 2

(3.2)

where o= 410-7 H/m

f = frequency (Hz)
g = 1.7811- Eulers constant

= soil resistivity ( m )

d = geometrical distance between conductors (m)

The validity of the calculations depends, among other things, on the knowledge of the
inducing currents. With modern meshed electrical networks, calculations of fault currents
are relatively complicated, and they require special computer programs. Electricity
utilities are familiar with such calculations, and values of currents to be used are available
from these companies.

34
Metallic conductors in the vicinity of the HV line or of the pipeline can reduce
disturbances. The current induced in such conductors by the HV line produces on the
pipeline an e.m.f. which partially cancels the e.m.f. due to the fault current. The screening
factor represents the ratio between the e.m.f. induced in presence of the conductor and the
e.m.f. induced in absence of the conductor. The main reduction effect is generally
produced by the earth wire(s) which equip the line. It is generally around 0.7 0.75 for
one earth wire and 0.5 0.55 for two earth wires. Wires placed along the pipeline
(especially bare wires) can also be efficient.

3.1.1.2.

Normal Operation. Different situations are to be considered. The simplest case

concerns a line without earth wires, when the currents are balanced.

A balanced system means the same amplitude with phase differences equal to 120 and
240 [23],

I1 = I ,

I2 =

I
1 j 3 ,
2

I3 =

I
1+ j 3
2

The residual e.m.f. comes from the difference in the distances between the pipeline and
each of the phase conductors. Formulas for calculations are given in [16].

35
Curve A of figure 3.1 shows the evolution with the distance of the 50 Hz e.m.f. produced
in a steady-state operation by a 400 kV line with vertical configuration of the conductors.
The emf decreases fast with the distance.

If the line is provided with earth wire(s), the current forced in the earth wire(s) can reach
10% of the phase current in each earth wire in the case of vertical configuration. It thus
creates a second e.m.f., which can increase stresses on the pipeline. Curve B of figure 3.1
shows the effect of the earth wires on a 400 kV line with vertical configuration of the
conductors.

Generally the currents are unbalanced, because of the different capacitances between the
phase conductor and the earth, and because of unbalanced loads. Supplementary e.m.f.s
can then be produced, which are a function of the unbalanced current. For unbalanced
systems, calculation will be preferably carried out by using the decomposition of the
currents in symmetrical components: positive, negative and zero-sequence components.

For close proximities between the line and the pipeline, the e.m.f. depends mainly on the
different distances between the pipeline and each phase conductor, while for greater
distances it results from the unbalanced current. Curve C of Figure 3.1 shows the
influence of a 400 kV line, with vertical configuration crossed by a current presenting a
positive sequence current equal to 1 kA and a zero-sequence current equal to 0.1 kA.

36

80
70
60

V/km

50

40
A
30
20
10
0
0

10

20

30

40

50

60

70

80

90

100

110

Distance (m)

Figure 3.1 Example of e.m.f. induced in normal situation. [16]

Curve A line without earth wire balanced currents (1000 A)

Curve B line with earth wire balanced currents (1000 A)
Curve C line with earth wire unbalanced currents (positive seq. current= 1000A &
zero seq. current = 100 A)

37

3.1.2. CALCULATION OF THE VOLTAGES ON THE PIPELINE

The following concerns the calculation of the response of the pipeline-earth electrical
circuit to the e.m.f.s. The voltage calculation method will be first demonstrated for the
simple theoretical case of a perfect parallelism. The principles for the general case will
be given in 3.1.2.2.

3.1.2.1. Perfect Parallelism Between The Electrical Line and Pipeline. The calculation
presented here is based on the following assumptions:

The pipeline is parallel to the disturbing line.

The leakage admittance of the pipeline is constant, i.e. for underground pipelines, the
coating resistance per unit length of the pipeline is uniform and independent of the
applied voltage.

The soil resistivity along the parallel routing is constant.

On the basis of the above assumptions, the equations of the circuit pipeline-earth are [16]:

dV(x)
+ z I(x) E(x) = 0
dx

(3.3)

38

dI(x)
+ y V(x)
dx

=0

(3.4)

where
z

= impedance per unit length of the circuit pipeline-earth

= admittance per unit length of the circuit pipeline-earth

E(x) = e.m.f. induced on the pipeline per unit length

This equation is the so-called transmission line equation, whose solution can be found
in the text books. It is only briefly recalled here for three particular cases which are worth
examining. [16]

Case I: The pipeline extends for a few kilometers beyond the parallel routing without
earthing:

V(x) =

E - (L - x )
e
- e x
2

I(x) =

E
2 - e - (L - x ) - e x
2Z

with =

(3.5)

(3.6)

zy propagation coefficient of the circuit pipeline earth.

The maximum pipeline potential occurs at the ends of the parallel routing at x = L
and x = 0

39

VO = VL = VR max =

E
1 - e L
2

(3.7)

Outside the exposure, the pipeline potential declines according to the exponential
function:

VR = VR max e x

(3.8)

with x= co-ordination outside the subdivided suction

Case II: the pipeline extends beyond the parallel routing at one extremity (A) and stops at
the other extremity (B) without earthing:

[ (

V(x) =

E x
e 2e- L - e 2 L e x
2

Vmax =

E
1 - e- L

V(o) =

-E
1 + e- 2 L + 2 e L
2

(3.9)

(3.10)

V (L) = Vmax =

E
1 - e- L

(3.11)

(3.12)

40

Case III: The pipeline is perfectly earthed at one extremity of the parallelism (A) while it
extends to the other extremity (B):

V (x) =

Vmax =

E x - x - L
e -e
e
2

E
1 - e- 2 L
2

(3.13)

V (o) = 0; V (L) = Vmax =

(3.14)

E
1 - e- 2 L
2

(3.15)

3.1.2.2. Non-Parallelisms Between The Electrical Line and Pipeline. The zone of
influence generally comprises a succession of parallelisms, oblique approaches and
crossings. Determination of e.m.f.s along the zone of influence requires a subdivision of
the pipeline into sections which will be assimilated to parallelisms.

The simplest evaluation consists in assimilating the complete zone of influence to a

parallelism, with a constant equivalent emf per unit length. This equivalent emf is given
by the expression [16]:

41

E=

1
L

i =1

(3.16)

Ei Li

where Ei = e.m.f. per unit length in section i

Li = length of section i
n = number of sections
L = total length of the zone of influence L =

1
L

i =1

Li

The maximum induced voltages are then given by applying expressions 3.7, 3.12 or 3.15
according to the cases: extension of the pipeline outside the zone of influence, earthing at
one extremity. Such a rough estimate is generally insufficient, but it helps to determine
whether admissible limits are likely to be exceeded, and thus whether a more precise
evaluation of the stresses is necessary. As this estimate is conservative, no more
calculations are needed if limits are not exceeded.

3.2 CONDUCTIVE INTERFERENCE

Electric stresses resulting from conductive coupling can be calculated in order to

predict the effects of conductive coupling to a buried pipeline. For this purpose, one has to
determine various electrical quantities: GPR at pipeline location, voltage applied to the
pipeline coating, voltage transferred to the metallic pipeline, voltage applied to insulating

42
flanges and to cathodic protection systems. The following paragraphs will provide
simplified methods for an approximate determination of these quantities. More accurate,
but more complex, methods are available in various software packages.

3.2.1 VOLTAGE TRANSFERRED TO A PIPELINE CLOSE TO A TOWER OR A

SUBSTATION

Because in practice coatings are not perfectly insulating, some voltage is transferred to a
metallic pipeline if a ground fault occurs on a nearby transmission line tower. The
magnitude of this transferred voltage obviously depends on the GPR at the pipeline
location and on the pipeline coating admittance. The variations of transferred potential
along the pipeline can be derived [16]:

For x > 0: V(x) = Vo e x

(3.17)

For x < 0: V(x) = Vo e x

(3.18)

where Vo = Ve (x ) dx
0

with:

: abscissa along the pipeline route (the origin is taken at the closest point to the
tower)

43
V(x)

: GPR along the pipeline at the abscissa x

V(x)

: pipeline voltage at abscissa x (with reference to remote earth)

: propagation constant of the buried insulated pipeline ( = [zy]1/2)

These simple analytical expressions still require the numerical integration of GPR V(x)
along the pipeline route. They show in a qualitative manner the influence of the pipeline
coating admittance y on the variations of transferred voltages Vo and V(x). The higher is y
(the poorer the coating insulation), the higher will be the maximum transferred voltage Vo
and the faster will be the transferred voltage V(x) decrease apart from abscissa x = 0.

3.2.2

VOLTAGE ACROSS THE PIPELINE INSULATING COATING

Since, in a resistive coupling, the voltage transferred to the pipeline is always low (as
compared to GPR), one can make the simplifying assumption that the voltage across the
coating equals the GPR at the pipeline location.

3.2.3

VOLTAGE TRANSFERRED TO A PIPELINE BONDED TO A GROUND

ELECTRODE INSIDE A STATION OR A SUBSTATION

Case I: the pipeline is electrically connected to the station ground mat, and it extends
outside the station area. If there is no interruption of the electric continuity of the

44
pipeline, the pipeline voltage can be assumed to decrease exponentially, and it is
therefore given by the following equation [16]:

V(x) = VS e - x

(3.19)

where:

: abscissa along the pipeline route outside the perimeter of the station (the origin
is taken at the outer limit of the station ground electrode, and the abscissa is
positive outwards from the station limit)

V(x) : pipeline voltage at abscissa x

VS

: potential rise of the station earth electrode

The equation 3.19 is valid as long as no insulating flange has been installed on the
pipeline close to the station (close meaning closer than 3 to 4 times the
characteristic length = 1/ of the insulated pipeline).

If there is an insulating flange at a distance xf close to the station, an additional term

must be added to equation 3.19 to take into account the reflection at xf :

V(x) = VS

e- x + e- (x - 2 x f ) - x
e
1 + e2 x f

(3.20)

The voltage applied to the insulating flange is given by the value of the difference
between V(xf) and the pipeline voltage on the other side of the flange. In most

45
practical cases, this difference equals V(xf) since the pipeline extends far beyond the
insulating flange and its voltage is negligible on this part (assuming no other coupling
mechanism is involved).

Case II: The pipeline is electrically interrupted by an insulating flange at the station
outer limit. The situation is then similar to the case of transferred potential analyzed in
section 3.2.1, and the equations 3.17 and 3.18 may be used.

3.2.4

VOLTAGE ACROSS AN INSULATING FLANGE

Voltage appears across an insulating flange (separating two sections of a pipeline) when
one of those sections is being submitted to transferred potential resulting from either a
GPR along the pipeline route or a direct bonding of the pipeline to a ground mesh (i.e.
inside a power station). In the first case, voltage across the flange can be estimated from
equations 3.17, 3.18, 3.19. In the second case, the mesh ground potential rise can be
computed by using methods presented in reference [16].

3.2.5

CURRENT FLOWING INTO THE PIPELINE THROUGH COATING

DEFECTS

As an example, consider a situation where a pipeline is buried near a H.V. tower, and let
us assume that the pipeline coating has a single defect: a hole with a cross-section. At the

46
defect point, the pipeline has a resistance to earth whose approximate value is
(considering the hole as an earth electrode having the form of a disk) [24]:

r=

(3.21)

If the GPR value is Ve at the pipeline location, the current flowing through the coating
defect is [24]:

I=

Ve
r

(3.22)

Thus the current density I d through the coating defect is [24]:

Id =

I
s

(3.23)

Taking typical values (=100 m, s=1 mm2, Ve= 5000 V), it can easily be shown that d
has such a low value that the metal pipeline temperature is not significantly increased
during a phase-to-ground fault on a H.V. system.

However, this conclusion is no longer true if soil ionization allows a high intensity arc
current to flow directly from the power system earth electrode into the pipeline. Because
of the high value of the disruptive electric field in the soil, such a discharge cannot occur

47
when the distance between the earth electrode and the pipeline exceeds approximately 0.5
meters, unless it is initiated by a high amplitude impulse current resulting from a stroke of
lightning to a H.V. tower.

3.3 CALCULATION OF THE INDUCED VOLTAGES ON

COMMUNICATION CABLES

When designing the power system, engineers take into account the currents, which may
flow into conductors due to normal operating conditions and more importantly due to
fault conditions. Faults may include earth, which cause the earth currents to rise rapidly.

Earth faults will cause current flow in earth-wires, and these currents generate induce
voltages on other conductors. The current in the shield is calculated as the shield produces
an induced voltage which opposes the voltage created by the phase wire. The shield
current, however, can decrease farther from the fault if the cable has ground contact along
its length. The resultant induced voltage is the difference between the voltage induced by
the faulted phase conductor and the shield. The value of induced voltage is calculated by
using the following formula [1]:

V = C.L.I.K

where:

(3.29)

48
V: induced longitudinal voltage [V]
C: mutual impedance per unit length [ohm/km]
L: length of exposure (between power and communication cable) [km]
I: fault current [A]
K: shielding factor {K=1 for no shielding}

The mutual impedance, C, of two parallel circuits having earth returns is given by

6 x 10 5
x 10 4 [ohm/km]
C = 2 f log e 1 +
2
d
f

(3.30)

where:
d: geometric separation between earth return circuits in meters
: earth resistivity in ohm-meter
f: system frequency in Hz

If the shield is not grounded on both ends, the shield current is zero and the shielding
factor K is 1.

CHAPTER IV

EMI ANALYSIS FOR 2007 INVESTIGATION AREA

4.1 Introduction

As mentioned earlier, the main objective of this research is to study and analyze the
electromagnetic interference effects on Saudi Aramco buried pipelines and underground
communication cables created by the operation of SEC 380 KV power lines in the
Kingdoms eastern province.

The area of investigation is about 130 x 55 km, and it covers the geographical area of
the 380 KV transmission lines between Faras and Qurayyah power plants that feed the
power to several oil and gas facilities owned by Saudi Aramco. This study is an update for
a similar study conducted twenty years ago by the Safe Engineering Services (SES)
Company. The old study did not consider the 380 KV Shedgum-Qurayyah transmission
lines which run parallel with the Faras-Qurayyah transmission lines for about 45 km.
Also, over the last twenty years, several buried pipelines and underground communication
cables have been removed or relocated.

49

50
One very important and time-consuming task, which must be performed in
electromagnetic interference analysis, is the collection and classification of large amounts
of data. As illustrated in the following section, various data/materials for the EMI study
have been collected. Briefly they can be classified as follows:

1.

2.

Conductor coordinates:

Height or burial depth of all conductors

Horizontal separation distances between all parallel conductors

Entire geographical area of interest, showing all conductors under study.

Conductor characteristics:

Physical dimensions of all conductors: overall radius, core radius, number and
radius of strands (if any), wall thickness, inner and outer radii of all coaxial
conductors (as in a cable), thickness of insulating coating (if any).

Resistivity and permeability of all conductors.

Conductivity and permittivity of insulating material (if any) making up each

conductor.

3.

Soil resistivity and leakage resistance:

Soil resistivity values or estimates for the entire geographical region of

interest.

Ground resistance values or estimates for all transmission line towers.

51

Impedance values of all regularly occurring grounds along non-energized

conductors.

4.

Termination impedances:

Ground impedances of all installations which provide grounding for nonenergized conductors in the study.

How each non-energized conductor in the study is terminated. If the conductor

terminates outside the geographical area of interest, equivalent shunt
impedance will be calculated.

5.

Which conductors are bonded together.

Boundary conditions:

Voltage magnitude and angle at phase buses of all transmission substations

involved in the study.

Magnitude and angle of current or power in each phase of the transmission

line.

Ground impedance of all substations involved in the study.

Figure 4.1 indicates the buried pipelines of interest in this study. These nine pipelines
were chosen because of their long lengths of exposure to the Faras-Qurayyah transmission
line and their proximity to the interference source. In addition to these buried pipelines, an
underground communication cable has also been modeled. It was chosen for the same
reason as those related to the pipelines.

52

Shedgum
Sub.

60 water line
9.6

15.65

UA-1

5.3

0.5

0.3

3.5

85

3.2

15.

7.4

2
16.
5.45

1.2

UBTG-1
UJNGL-1
SHNGL-1

11.65

55 KM

UA-4
UA-6
QUU-1

0.4

0.05

36

7.0

1.25
Communication
Cable

1.1

0.75

Oil To SEC

Faras
Sub.

Transmission Lines
Pipelines
Communication Cable

Qurayy.
Sub.

110 KM

Figure 4.1 380 KV network with buried pipelines & cables to be modeled. (All numbers
are in km)

53

4.2 TERMINOLOGY

The following terms will frequently appear in the discussion which follows. It is best,
therefore, that they be clearly defined immediately.

Conductor:

A conductor can be any of the following: a transmission line phase

conductor, a transmission line neutral conductor or shield wire, a pipeline,
a copper strand in a communication cable, the aluminum shield of a
communication cable, the steel armour of a communication cable, a
transmission line counterpoise, etc.

Line Path:

A line path is a group of conductors that are associated together for the
purpose of the easier management of right-of-way conductors. At any
given point along the transmission right-of-way, a line-path is composed of
one or several parallel conductors (or none) in which one of them is
expected to be the principal conductor while all other conductors are
defined as satellite conductors. For example, a single circuit transmission
line contains three phases: A, B, and C. If Phase A is the principal
conductor, then the other two phases are satellites of Phase A. A line-path
is not necessarily continuous: one group of conductors representing the
line-path may terminate at some point, while another group of conductors
representing the line-path may begin at a later point.

54

Principal :

There may be several principal conductors in a right-of-way. One

Conductor

principal conductor is chosen from each line path bundle of conductors (a

bundle is a group of parallel conductors). The relative coordinates of a
principal conductor are specified; the positions of other conductors in the
same bundle are specified as relative spacing from the principal
conductor, i.e. they become satellites of the principal conductor.

Satellite :
Conductor

A satellite conductor is any conductor that is parallel to the main

conductor or to a principal conductor and whose position is specified as
relative spacing from one of these. For instance, line-path 11 consists of
pipelines UBTG-1, UJNGL-1 and SHNGL-1. During the measurement of
the coordinates, UBTG-1 was used for the measurement and therefore
becomes a principal conductor; UJNGL-1 and SHNGL-1 then become
satellites. Only the coordinates of principal conductors are entered in
TRALIN software; whereas the satellites are specified in terms of their
spacing from their associated principal conductors.

Phase (bus): All conductors having the same potentials are assigned a phase number.

Each phase bundle is ultimately replaced by a single equivalent conductor

for the circuit analysis to be performed by the circuit modeling (SPLITS)
module.

55
Region:

A region is a portion of the transmission line right-of-way where the main

path (usually the transmission line) is straight, and where no significant
change occurs in the characteristics of any of the line-paths under study
except that a line-path need not exist throughout the region. The
characteristics of the path include the number of conductors, conductor
diameters, coating resistances, soil resistivity, etc.

Attribute Set: An attribute set defines the characteristics of all conductors in a line path

and the relative position of satellite conductors within a path. Several

regions can be associated to a given attribute set, even if the positions of
the line paths relative to each other are different from one region to the
other. It is practical to divide the transmission line right-of-way into
attribute sets that are referenced by the regions. An attribute set consists of
an integral number of transmission line sections.

Section:

The Right-of-Way program subdivides the transmission line regions into

sections, based on a nominal section (span) length specified by the user. A
section usually corresponds to an actual transmission line span.

Based on these definitions, the phases and line paths of the Faras-Qurayyah right-of-way
along with nearby buried pipelines and underground communications cables can be
defined as follows:
Phase 1: 380 KV Transmission Line Phase A Conductors
Phase 2: 380 KV Transmission Line Phase B Conductors

56
Phase 3: 380 KV Transmission Line Phase C Conductors
Phase 4: 380 KV Transmission Line Sky wires
Phase 5: Pipeline UA-1
Phase 6: Pipelines UA-4/UA-6
Phase 7: Pipeline 60 WATER
Phase 8: Pipeline QUU-1
Phase 9: Communication Cable Cores
Phase 10: Communication Cable Shields/Armours
Phase 11: Pipelines UBTG/UJNGL/SHJNGL
Phase 12: Pipeline SEC OIL
Phase 13: 380 KV Shedgum-Qurayyah Transmission Line Phase A Conductors
Phase 14: 380 KV Shedgum-Qurayyah Transmission Line Phase B Conductors
Phase 15: 380 KV Shedgum-Qurayyah Transmission Line Phase C Conductors
Phase 16: 380 KV Shedgum-Qurayyah Transmission Line Sky wires

Also, based on the above definitions, the transmission line right-of-way has been divided
into 340 sections, 30 regions and 10 attribute sets.

57

4.3 CONDUCTOR COORDINATES

The coordinates of the line paths under study in the Faras-Qurayyah right of way have
been measured by a special program (part of the generated map is shown in figure 4.2).

The coordinates of the transmission lines were measured first, after dividing the
transmission line into a series of straight-line segments or regions such that the
transmission line changes in one axis direction (e.g. x-axis). Then, the principal
conductors of each line path that contains buried pipeline or underground communication
cable were measured with respect to the transmission line coordinates.

Based on the above mentioned definition of the region and the software methodology, the
Faras Qurayyah right of way has been divided to 30 regions as shown in the table 4.1.

Table 4.1 lists the coordinates of the transmission lines with a multiplicative factor of 0.5
which converts grid unit to km. For example, in region 26 as shown in table 4.1, the SEC
Oil pipeline is running parallel with power transmission lines for about 22.75 km (45.5
grid units) and it is separated by 400 m (0.8 grid units).

58

Figure 4.2 Partial map generated by special program to measure the coordinates

59

TABLE 4.1 Line-Path coordinates measured in Faras-Qurayyah Right-of-Way

Region#
R1
R2
R3
R4
R5
R6
R7
R8
R9
R10
R11

Transmission
Line coordinates
Phase 1-4
(Grid units)
(0.0, 0.0)
(1.5, 0.0)
(0.0, 0.0)
(7.0, 0.0)
(0.0, 0.0)
(7.0, 0.0)
(0.0, 0.0)
(13.0, 0.0)
(0.0, 0.0)
(10.3, 0.0)
(0.0, 0.0)
(7.0, 0.0)
(0.0, 0.0)
(8.2, 0.0)
(0.0, 0.0)
(6.7, 0.0)
(0.0, 0.0)
(14.8, 0.0)
(0.0, 0.0)
(4.4, 0.0)
(0.0, 0.0)
(5.2, 0.0)

R12

(0.0, 0.0)
(11.0, 0.0)

R13

(0.0, 0.0)
(8.7, 0.0)

R14

(0.0, 0.0)
(7.5, 0.0)

Relative Line-Path Coordinates

(Grid units)
Phase 5

Phase 6

Phase 7

Phase 8

(1.1, -4.5)
(4.5, -1.5)
(6.3, 1.8)

(-0.5, -2.8)
(7.5, -2.8)
(0.7, -2.6)
(4.7, 0.0)
(6.0, 2.3)

(-3.0, -14.5)
(3.5, -11.5)
(2.8, -12.1)
(7.6, -3.0)
(7.9, -0.7)

(0.0, -2.0)
(1.4, -2.2)
(0.6, -2.3)
(7.1, -0.2)
(-0.1, 0.3)
(4.0, -0.2)
(6.8, -0.6)
(0.1, -0.5)
(12.7, 2.9)
(0.0, 3.0)
(10.5, 2.2)
(-0.3, 2.2)
(6.7, 3.3)
(0.4, 3.4)
(1.5, 3.2)
(8.2, 4.1)
(0.0, 4.1)
(7.3, 4.8)
(-0.6, 4.8)
(14.6, 10.0)
(-4.8, 8.9)
(-0.5, 13.5)
(-12.4, 7.5)
(-10.0, 11.5)

Phase 11

Phase 12

60
Region#

Phase 1-4
(Grid units)

R15

Phase 6

Phase 7

(0.0, 0.0)
(10.7, 0.0)

(1.2, 1.8)
(11.2, 1.3)

(1.5, 2.4)
(12.7, 4.5)

R16

(0.0, 0.0)
(10.9, 0.0)

(-0.4, 1.3)
(7.9, 6.4)

(-1.0, 5.0)
(1.8, 7.8)
(5.6, 11.2)

R17

(0.0, 0.0)
(3.0, 0.0)

R18

(0.0, 0.0)
(3.4, 0.0)

R19
R20
R21
R22
R23
R24
R25
R26
R27
R28
R29
R30

(0.0, 0.0)
(11.0, 0.0)
(0.0, 0.0)
(3.0, 0.0)
(0.0, 0.0)
(17.7, 0.0)
(0.0, 0.0)
(5.6, 0.0)
(0.0, 0.0)
(18.6, 0.0)
(0.0, 0.0)
(7.1, 0.0)
(0.0, 0.0)
(10.0, 0.0)
(0.0, 0.0)
(45.5, 0.0)
(0.0, 0.0)
(5.0, 0.0)
(0.0, 0.0)
(5.7, 0.0)
(0.0, 0.0)
(4.0, 0.0)
(0.0, 0.0)
(2.0, 0.0)

Phase 5

Phase 8

Phase 11

Phase 12

(0.5, -0.7)
(3.5, 0.5)
(10.1, 0.3)
(0.1, 0.3)
(4.5, 2.5)
(10.5, 0.8)
(0.1, 0.8)
(2.3, -1.5)
(0.4, -1.4)
(2.5, -1.5)
(3.9, -1.2)
(-0.5, -1.2)
(8.2, -9.5)
(2.1, 3.4)
(17.4, -2.4)
(0.5, -2.4)
(5.3, -2.5)
(0.2, -2.5)
(15.2, 1.1)
(18.6, 5.5)
(3.2, 9.5)
(7.1, -0.73)
(0.0, -0.8)
(10.0, -0.8)
(0.0, -0.8)
(45.5, -0.8)
(0.0, -0.6)
(5.0, -5.3)

61
4.3.1 TRANSMISSION LINE CONDUCTOR

The Faras-Qurayyah transmission line is a single circuit, with 4-bundle conductors

per phase, mounted in horizontal configuration on a lattice steel structure as
illustrated by figure 4.3. On the other hand, the Shedgum-Qurayyah Transmission
line is a double circuit, with 4-bundle conductors per phase, mounted in vertical
configuration on a lattice steel structure as shown in figure 4.4.

Tables 4.2 and 4.3 list, respectively, the physical characteristics of the
transmission line phase conductors as well as ground wire conductors such as
sectional area, overall diameter, strands number and GMR. The conductors of both
transmission lines have the same characteristics. The coordinates of the
transmission lines are specified to the TRALIN package in terms of their average
absolute heights and their X coordinates relative to the reference conductor.

4.3.2 BURIED PIPELINES & COMMUNICATION CABLES

All pipelines under study are buried so that their centers are 1.5 m below the
earths surface, while all communication cables are buried 0.6 m below the earths
surface Tables 4.4 to 4.12 list the characteristics for all buried pipelines such as
radius, wall thickness, length, coating thickness and the carrying liquid or gas
type. Table 4.13 lists the characteristics of the underground communication cable.

62

Figure 4.3 Cross section of 380 KV Faras-Qurayyah Transmission Lines

63

Figure 4.4 Cross section of 380 KV Shedgum-Qurayyah Transmission Lines

64

TABLE 4.2 Physical Characteristics of Transmission Line Phase Conductors

Parameter

Data

Type

ACAR

Sectional area

547.4

Overall diameter

30.4 mm

Overall radius

15.2 mm

Conductor weight

1.506 kg/m

Ultimate tensile strength

12338 kg

Maximum sag

15 m

Number of outer strands

18

Number of inner strands

19

Outer strands radius

2.17 mm

AC resistance (@25C)

0.0582 -km

GMR

0.0117 m

Core radius

0.01085 m

65

TABLE 4.3 Physical Characteristics of Transmission Line Ground Wire Conductors

Parameter

Data

Type

7/5 AWG AS

Sectional area

170.18

Overall diameter

13.9 mm

Overall radius

6.95 mm

Conductor weight

0.8006 kg/m

Ultimate tensile strength

13256 kg

Maximum sag

9.5 m

Number of strands

Outer strands radius

2.31 mm

AC resistance (@25C)

1.037 -km

GMR

9.02 x 10-4 m

Core radius

2.31 m

66

TABLE 4.4 UA-1 Pipeline Characteristics

Parameter

Data

Service

Arab Light Crude

Radius

0.381 m

Wall thickness

0.00635 m

Material GR. Of pipe

X52

Length

46400 m

Flange rating

300#

Max. operating pressure

600 PSIG

Design temperature

171 F

Coating resistance

6503 -m2

Coating thickness

0.01 m

rwhole

0.391 m

router

0.381 m

rinner

0.37465 m

conductor

17.0 cu

conductor

250.0 0

coating

658797 -m

coating

Ycoating

3.68 x 10-4 siemens/m

67

TABLE 4.5 QUU-1 Pipeline Characteristics

Parameter

Data

Service

Seawater

Radius

0.762 m

Wall thickness

0.0127

Material GR. Of pipe

X60

Length

50570 m

Flange rating

300#

Max. operating pressure

720 PSIG

Design temperature

170 F

Coating thickness

0.01 m

Coating resistance

6503 -m2

Coating thickness

0.01 m

rwhole

0.772 m

router

0.762 m

rinner

0.7507 m

conductor

17.0 cu

conductor

250.0 0

coating

654558 -m

coating

Ycoating

7.36 x 10-4 siemens/m

68

TABLE 4.6 UBTG-1 Pipeline Characteristics

Parameter

Data

Service

Sweet Gas

Radius

0.533 m

Wall thickness

0.0159 m

Material GR. Of pipe

X60

Length

16240 m

Flange rating

400#

Max. operating pressure

960 PSIG

Design temperature

120 F

Coating resistance

7432 -m2

Coating thickness

0.01 m

rwhole

0.543 m

router

0.533 m

rinner

0.5171 m

conductor

17.0 cu

conductor

250.0 0

coating

750170 -m

coating

Ycoating

4.51 x 10-4 siemens/m

69

TABLE 4.7 UJNGL-1 Pipeline Characteristics

Parameter

Data

Service

NGL C2+ Gas

Radius

0.381 m

Wall thickness

0.013 m

Material GR. Of pipe

X60

Length

133930 m

Flange rating

600#

Max. operating pressure

900 PSIG

Design temperature

120 F

Coating resistance

7432.2 -m2

Coating thickness

0.01 m

rwhole

0.391 m

router

0.381 m

rinner

0.368 m

conductor

17.0 cu

conductor

250.0 0

coating

752931 -m

coating

Ycoating

3.22 x 10-4 siemens/m

70

Table 4.8 SHNGL-1 Pipeline Characteristics

Parameter

Data

Service

NGL C2+ Gas

Radius

0.381 m

Wall thickness

0.0111 m

Material GR. Of pipe

X60

Length

130012 m

Flange rating

600#

Max. operating pressure

1225 PSIG

Design temperature

200 F

Coating resistance

11148 -m2

Coating thickness

0.01 m

rwhole

0.391 m

router

0.381 m

rinner

0.369 m

conductor

17.0 cu

conductor

250.0 0

coating

1129367 -m

coating

Ycoating

2.15 x 10-4 siemens/m

71

TABLE 4.9 UA-4 Pipeline Characteristics

Parameter

Data

Service

Arab Light Crude

Radius

0.533 m

Wall thickness

0.0159 m

Material GR. Of pipe

X60

Length

52496 m

Flange rating

300#

Max. operating pressure

649 PSIG

Design temperature

150 F

Coating resistance

7432 -m2

Coating thickness

0.01 m

rwhole

0.543 m

router

0.533 m

rinner

0.5171 m

conductor

17.0 cu

conductor

250.0 0

coating

750170 -m

coating

Ycoating

4.51 x 10-4 siemens/m

72

TABLE 4.10 UA-6 Pipeline Characteristics

Parameter

Data

Service

Arab Light Crude

Radius

0.5842 m

Wall thickness

0.0159 m

Material GR. Of pipe

X60

Length

17090 m

Flange rating

300#

Max. operating pressure

585 PSIG

Design temperature

170 F

Coating resistance

7432 -m2

Coating thickness

0.01 m

rwhole

0.5942 m

router

0.5842 m

rinner

0.5683 m

conductor

17.0 cu

conductor

250.0 0

coating

749563 -m

coating

Ycoating

4.94 x 10-4 siemens/m

73

TABLE 4.11 SEC Oil Pipeline Characteristics

Parameter

Data

Service

Oil

Radius

0.3048 m

Wall thickness

0.0061 m

Material GR. Of pipe

X52

Length

52400 m

Flange rating

300#

Max. operating pressure

600 PSIG

Design temperature

170 F

Coating resistance

13935 -m2

Coating thickness

0.01 m

rwhole

0.3148 m

router

0.3048 m

rinner

0.29845 m

conductor

17.0 cu

conductor

250.0 0

coating

1416236 -m

coating

Ycoating

1.37 x 10-4 siemens/m

74

TABLE 4.12 60 Water Pipeline Characteristics

Parameter

Data

Service

Water

Radius

1.52 m

Wall thickness

0.015

Material GR. Of pipe

X60

Length

12350 m

Flange rating

300#

Max. operating pressure

900 PSIG

Design temperature

130 F

Coating thickness

0.01 m

Coating resistance

6503 -m2

Coating thickness

0.01 m

rwhole

1.53 m

router

1.52 m

rinner

1.505 m

conductor

17.0 cu

conductor

250.0 0

coating

654558 -m

coating

Ycoating

7.36 x 10-4 siemens/m

75

Table 4.13 Communication Cable characteristics

Cable Radius

0.019 m

Core Inner Radius

0.0 m

Core Outer Radius

0.000455 m (19 AWG)

r Core
r Core

1.0 (relative resistivity with

respect to annealed copper)
1.0 (relative permeability)

r Core Insulation

0.0 (conductivity)

r Core Insulation

1.0 (relative permittivity)

Sheath Inner Radius

0.013 m

Sheath Outer Radius

0.0132 m

r Sheath

1.5625 (aluminum)

r Sheath

1.0

r Sheath Insulation

0.0

r Sheath Insulation

1.0

Armour Inner Radius

0.016 m

Armour Outer Radius

0.01615 m

r Armour

17.0 (Steel)

r Armour

250.0

r Armour Insulation

0.0

r Armour Insulation

1.0

76

4.4 CONDUCTORS GROUNDING

The CDEGS program requires the soil resistivity in each region set of the right-of-way, in
order to determine accurately the self impedances of all line-paths. Table 4.14 lists the soil
resistivity value applicable for each region set.

Also, the CDEGS program requires the values of any diffuse or regularly occurring
impedances between the line-paths and the earth. These take the form of transmission
phase wire capacitances, pipeline coating resistances or ground resistances of splice points
on communication cables. Since great care is taken to isolate transmission line phase
wires from earth, only capacitive impedance exists. The value of this impedance can be
obtained by running the TRALIN program for the ACAR phase wire bundles. The
capacitive impedance of all transmission line phases is approximately -j 26664000.0 -m.

For irregularly occurring grounds on buried pipelines, following are the large grounding
installations for pipelines:

1. QUU-1 pipeline is bonded to the pump house ground (0.06 ) at Jadidah Booster
Station
2. SEC Oil pipeline is bonded to seawater treatment plant ground (0.05 ).

77

TABLE 4.14 Soil Resistivities

Region Set

Soil Resistivity
(-m)

Region

Starting Section

Ending Section

11

12

19

21

35

36

48

49

57

58

67

68

75

76

93

10

94

98

11

99

104

12

105

118

13

119

129

14

130

138

15

139

151

16

152

164

17

165

168

18

169

172

19

173

186

20

187

190

21

191

212

22

213

219

23

220

242

13

24

243

251

13

25

252

263

26

264

319

27

320

325

28

326

332

29

333

337

30

338

340

10

21

27

22

90

27

51

13

16

CHAPTER V

CASE STUDY SIMULATION & RESULTS

5.1 INTRODUCTION

The case study explained in the previous chapter has been modeled and simulated by
using CDEGS software to calculate the induced voltages along the concerned pipelines
due to inductive and conductive interferences during both steady-state and transient
conditions. The following sections will analyze the simulation results of the induced
voltages on all buried pipelines and underground communication cables.

5.2 VALIDATION OF SOFTWARE RESULTS

The simulation results obtained by CDEGS software have been verified by comparing the
induced voltages calculated by CDEGS with the field-measured ones performed by the
pipeline department in Saudi Aramco on QUU-1 pipeline (11 Km long). Figure 5.1 and

78

79
table 5.1 show the results of the comparison. Fortunately, the measurement was done
during the peak load on the 380 KV Faras-Qurayyah transmission lines where the current
reached 900 A per phase. The comparison revealed acceptable convergence between the
measured induced voltages and the simulated ones under the same condition.

Moreover, extensive scientific validations of the CDEGS software, by using field tests
and comparisons with analytical or published research results, have been conducted by
Safe Engineering Services & Technologies Ltd. (SES) as well as other independent
researchers, and they have shown excellent agreement between the simulation results and
the reference ones. These validation tests have been documented in tens of technical
papers and scientific researches published in prestigious international journals. [27-33]

80

4500
4000
3500
3000
2500
2000
1500
1000
500
0

Measurement
CDEGS Results

0
40
0
44
0
55
0
90
10 0
0
20 0
0
30 0
0
36 0
0
36 0
0
36 1
0
37 2
5
40 0
0
50 0
0
60 0
0
70 0
0
80 0
0
90 0
0
10 0
0
11 00
00
0

Potential (m V)

QUU-1 Pipeline Potential

Distance (m)

Figure 5.1 Pipeline potential along the axial length of the QUU-1 Pipeline

81

TABLE 5.1 Pipeline Potential along the QUU-1 Pipeline

Location
(Meter)

Measured value
(mV)

Computed value
(mV)

Error %

245

300

18.3

400

310

400

22.5

440

340

400

15.0

550

450

400

12.5

900

885

1000

11.5

1000

870

1000

13.0

2000

3650

3900

6.4

3000

1050

1100

4.5

3600

1035

1100

5.9

3750

1040

1100

5.5

4000

1055

1100

4.1

5000

1060

1100

3.6

6000

1130

1190

5.0

7000

1640

2000

18.0

8000

1090

1200

9.2

9000

330

400

17.5

10000

410

500

18.0

11000

590

700

15.7

82

5.3 STEADY-STATE CONDITION

The rights-of-way of 380KV Faras-Qurayyah and Shedgum-Qurayyah were modeled

under worst-case steady-state conditions, with a maximum current of 900 A and 1200 A
per phase, respectively, as shown in figures 5.2 & 5.3. These values were obtained from
the SEC Dispatcher during different loading cycles.

The induced voltages along the buried pipelines under study have been calculated by the
software. The touch voltage is the difference between the pipeline potential and earth
surface potential. Because the earth surface potential is very small (close to 0 V), the
touch voltage is actually very close to the pipeline potential.

The resulting induced voltage along the crude oil buried pipeline UA-1 is shown in figure
5.4. The zone of influence comprises parallelisms, approaches and crossings between the
power transmission lines and the buried pipeline which greatly affects the induced voltage
level on the pipeline. The induced voltage began to increase from 2 V at 5 km from the
Faras Substation, where the pipeline is 400 m away from the right-of-way (ROW), to 15
V at 7.6 km where the separation between the buried pipeline and the transmission lines is
50 m. Then, it decreased to below 2 V where the pipeline crosses and runs away from the
ROW.

83

The UA-1 Pipeline recorded the highest induced voltage among all buried pipelines under
study, and it reached the maximum allowable touch voltage 15 of volts. This relative high
induced voltage was expected, due to the vicinity and the extensive parallel exposure of
the UA-1 pipeline to the power transmission lines.

Figure 5.5 shows the calculated induced voltage along the SEC Oil buried pipeline.
Although it runs parallel with power transmission lines for about 30 km, the induced
voltage was in the order of 6 volts. However, this relatively low induced voltage was
expected, because the buried pipeline is mostly located 400-500 m away from the power
transmission lines and it is also bonded to the Seawater Treatment Plant ground. The
maximum induced voltage occurs at the bending points of the pipeline. This is because
the strong discontinuity of the EMF at these points forces a large leakage current from the
pipeline, resulting in higher pipeline potentials at these points.

The computed induced voltages along the other buried pipelines (crude pipeline UA-4,
water pipeline QUU-1, 60 water pipeline, and gas pipeline) were in the order of 2-6
volts. These results are realistic since these pipelines are run far away from the power
transmission lines and do not have perfect parallelism along the right of way. Also, the
underground communication cables that mostly located 500 meters away from the power
lines have a maximum induced voltage of 6 volts.

84

Figure 5.6 shows the induced voltage along the gas pipeline that smoothly approaches and
crosses the Faras-Qurayyah transmission lines. The maximum induced voltage occurred
in the crossing area, and it reached 13 volts.

Figures 5.7, 5.8 & 5.9 show the induced voltages along the QUU-1 and UA-4 pipelines.
Both pipelines behave quite similarly in terms of approaching and crossing the ROW.
However, compared with the gas pipeline in figure 5.6, the induced voltages were much
lower because these pipelines cross the ROW sharply. As expected, the maximum
induced voltage occurred in the crossing area, and it reached 3.5 and 1.8 volts on the
QUU-1 and UA-4 pipelines, respectively.

Figure 5.10 shows the induced voltage along the underground communication cable that
is located mostly more than 500 meters away from the ROW, but it approaches the
transmission lines once where the horizontal separation is about 200 meters. The
maximum induced voltage reached 5.5 volts at the closest point between the
communication cable and the transmission lines.

Based on the simulation results, the maximum touch voltages along all buried pipelines
and underground communication cables do not exceed 15 volts, and therefore no
mitigation is required according to the Saudi Electricity Company, IEEE and IEC
standards.

85

Figure 5.2 Current level on 380KV Faras-Qurayyah Transmission Lines

86

Figure 5.3 The current level on 380KV Shedgum-Qurayyah Transmission Lines

87

1600

16
Transmission lines

Induced voltage

1200

Separation (m)

14

UA-1 Pipeline

12

1000

10

800

600

400

200

0
15.5

12

10.8

7.6

5 km

-200

-2

-400

-4

Figure 5.4 Pipeline potential along the axial length of the UA-1 Pipeline

Induced voltage (V)

1400

88

3000

SEC Oil Pipeline

Induced voltage

2500

S ep ara tio n (m )

Transmission lines

2000

1500

1000

500

0
90

94

98

102

106

110

-500

114

118

122

126

130

-1
km

-1000

-2

-1500

-3

Figure 5.5 Pipeline potential along the axial length of the SEC Oil Pipeline

In d u c ed vo ltag e (V )

3500

89

3000

13

2500

11

Separation (m)

1500

5
1000
3
500
1
0
0.1

3.75

4.2

4.6

-1500

7.6

9.3

km

-500
-1000

5.7

Transmission lines
Gas Pipeline
Induced voltage

Figure 5.6 Pipeline potential along the axial length of the Gas Pipeline

-1
-3
-5
-7

Induced voltage (V)

2000

90

1500
9

Separation (m)

5
500

3
1

0
0.35

0.9

1.05

1.45

1.65

4.65

Induced voltage (V)

1000

-1

km
-3

-500
Transmission lines

-1000

QUU-1 Pipeline

-5
-7

Induced voltage

Figure 5.7 Pipeline potential along the axial length of the QUU-1 Pipeline (Case-1)

1500

1000

500

0
0

4.75

5.35

5.8

6.25

7.1

km
-500

-1

-1000

-2

-1500

-3
Transmission lines

-2000

UA-4 Oil Pipeline

-4

Induced voltage

Figure 5.8 Pipeline potential along the axial length of the UA-4 Oil Pipeline

Induced voltage (V)

Separation (m)

91

1600

1400

1200

1000

800

600

400

200

0
3.6

-200
-400

Induced voltage (V)

Separation (m)

92

4.4

5.6

km
Transmission lines
QUU-1

5.7

-1
-2

Induced voltage

Figure 5.9 Pipeline potential along the axial length of the QUU-1 Pipeline (Case-2)

93

1200

Separation (m)

800

600

400

200

0
0.1

0.5

1.75

3.55

4.4

6.3

6.85

6.9

km
Transmission lines
Communication cable
Induced voltage

Figure 5.10 Induced voltage along the communication cable

7.6

Induced voltage (V)

1000

94

5.4 Transient Condition

Single line-to-ground fault has been simulated at 10% intervals throughout the FarasQurayyah transmission lines. The fault current level computed by the CDEGS software
matches the actual levels provided by SEC as shown in the table 5.2.

The following sections show the touch voltages along all buried pipelines and
underground communication cables during single line-to-ground fault at 10% intervals
throughout the Faras-Qurayyah transmission line starting with a fault at Faras substation.

The maximum safe touch voltage limit can be calculated according to the following
ANSI/IEEE 80 equation as well as the IEC-479 standard:

Vtouch =

116 + (0.17 )
t

where:
= Surface soil resistivity in ohms-meters
t = Fault duration in seconds.
Therefore, for 500 ohm-meter top soil resistivity and 0.5 second fault clearing time, the
safe touch voltage limit is 287 volts for a person whose weight is 50 kg.

95
The simulation results, as predicted, have shown that the touch voltage levels are directly
proportional to the soil resistivity, while they are inversely proportional to the separation
distance. Following is the summarized results analysis of the touch voltage along all the
pipelines during the proposed fault locations:

1) The touch voltages along all buried pipelines and communication cables except the
UA-1 and SEC oil pipelines were below the safety touch voltage limit 287 volts. This
result was expected, because these buried pipelines are mostly located more than 500
m away from the ROW, and they are far away from the power substations. Moreover,
the soil resistivities at the locations of these pipeline are relatively low (20-50 m).

2) The touch voltage reaches 870 V on the nearby UA-1 pipeline during the fault at 10%
from the Faras Substation, as shown in figure 5.7. Also, it exceeds the safety limit
during the simulated faults at 20-50% from the Faras Substation. This high touch
voltage resulted from the pipeline being close to the faulted transmission line towers
(70 m away) as well as the Faras Substation (8 km away).

3) The touch voltage reaches 650 V on the nearby SEC-Oil pipeline during the fault at
90% from the Faras Substation, as shown in figure 5.8. Also, it exceeds the safety
limit during the simulated faults at 60-90% from the Faras Substation. The pipeline is
mostly 400-500 m away from the transmission lines, but one of its ends crosses the
ROW near the transmission line tower, which highly affects the touch voltage levels.

96

The coating stress voltage is expected to be in the order of touch voltage, since most of
the potential drop between the earth surface and the pipeline steel occurs across the
pipeline coating. There is no problem regarding the pipeline coating stress voltage,
because these pipelines have a coating of fusion bonded epoxy which can withstand
voltage up to 3000 V.

97

TABLE 5.2 Fault Currents Level for Faras-Qurayyah 380KV Transmission Line

Fault Location
Terminal

Section
% From Faras

SEC

CDEGS

Current (A)

Current (A)

Number
Faras

Qurayyah

25

85

7644

7550

50

170

4490

4440

75

255

2987

2965

25

85

3241

3225

50

170

4859

4870

75

255

8576

8310

98

1600

900

1400

800

600

Separation (m)

1000

500

800

400
600
300
400

200

200

100

0
15.5

12

10.8

7.6

5 km

-200

-100

-400

-200
Transmission lines

Fault Location

UA-1 Pipeline
Induced voltage

Figure 5.11 Touch voltage along the axial length of the UA-1 Pipeline

Induced voltage (V)

700

1200

3500

700

3000

600

2500

500

2000

400

1500

300

1000

200

500

100

90

94

98

102

106

110

114

118

122

-500

126

130

0
-100

km
-1000
-1500

-200
Transmission lines

SEC Oil Pipeline

Fault Location

Induced voltage

-300

Figure 5.12 Touch voltage along the axial length of the SEC Oil Pipeline

Induced voltage (V)

Separation (m)

99

CHAPTER VI

MITIGATION OF EMI INTERFERENCE

The simulation results of the system show that a high level of touch voltages has existed
in some pipelines, which need to be reduced to the touch voltage limit as per the IEEE and
ICE standards (the other standards refer to IEEE for this limit).

Various techniques have been developed to mitigate AC voltages on buried pipelines,

such as lumped grounding, cancellation of wires, bonding across isolation flanges and
ground mats. However, the most popular and cost effective mitigation technique is the
application of gradient control wire. The gradient control wires are generally made of bare
zinc extruded over a thin gauge steel wire. The mitigation typically consists of one or two
bare wires / ribbons, buried parallel to the pipeline to be protected, and connected to the
pipeline at regular intervals. Figure 6.1 shows a schematic arrangement of pipeline
connected to the zinc ribbon for mitigation of EMI interference. The mitigation wire
reduces the effects of inductive and conductive interference. The gradient control wires
provide grounding for the pipe, decreasing the induced pipe potential rise at the same time
as the potential of the local earth is raised due to the gradient control wires, thus reducing
the potential difference between the earth and the pipe. [34, 35]

100

101

Figure 6.1 Typical gradient control wire installation. [35]

102

The simulation results have been analyzed to find out the best cost-effective locations to
install the gradient control wire for the pipelines that need mitigation. Following is a
summary of the maximum touch voltages on these pipelines that exceed the touch voltage
limit:

4) The touch voltage reaches 870 V on the UA-1 pipeline during the fault at 10% from
the Faras Substation.
5) The touch voltage reaches 650 V on the SEC-Oil pipeline during the fault at 90%
from the Faras Substation.

So, by using CDEGS software, the following proposed installations of gradient control
wires have been simulated to check their mitigation performance:

1050 m gradient control wire installed on UA-1 pipeline between tower # 7 to

tower #10 from Faras Substation.

1050 m gradient control wire installed on UA-1 pipeline between tower # 17 to

tower #20 from Faras Substation.

1050 m gradient control wire installed on UA-1 pipeline from tower # 30 to tower
#33 with reference to Faras Substation.

350 m gradient control wire installed on SEC Oil pipeline between tower # 252 to
tower #253 from Faras Substation.

700 m gradient control wire installed on SEC Oil pipeline between tower # 271 to
tower #273 from Faras Substation.

103
6

700 m gradient control wire installed on SEC Oil pipeline between tower # 304 to
tower #306 from Faras Substation.

1050 m gradient control wire installed on SEC Oil pipeline between tower # 317
to tower #320 from Faras Substation.

Figures 6.2 and 6.3 show the simulation results for the above mentioned pipelines after
installing the proposed gradient control wires.

The touch voltages on the UA-1 and SEC Oil pipelines have been reduced to 180V and
144V respectively, which are far below the safe touch voltage limit (287 V).

The rough cost estimate of installing gradient control wires is about $ 25,000 per
kilometer including the materials and the installation cost [31]. So, the proposed
mitigation system for the UA-A and SEC Oil Pipelines costs around $ 125,000.

1600

900

1400

800

1200

700
600

Separation (m)

1000

500

800

400
600
300
400

200

200

100

0
15.5

12

10.8

7.6

km

-200

-100

-400

-200
Transmission lines

Fault Location

SEC Oil Pipeline

Induced voltage
Induced voltage (after mitigation)

Figure 6.2 Touch voltage along the UA-1 Pipeline after mitigation

Induced voltage (V)

104

3500

700

3000

600

2500

500

2000

400

1500

300

1000

200

500

100

90

94

98

102

106

110

114

118

122

126

130

-500

0
-100

km
-1000

-200
SEC Oil Pipeline

-1500

Transmission lines

Fault Location

Induced voltage
Induced voltage (after mitigation)

Figure 6.3 Touch voltage along the SEC Oil Pipeline after mitigation

-300

Induced voltage (V)

Separation (m)

105

CHAPTER VII

CONCLUSION

Electromagnetic fields, produced by the transmission lines on nearby pipelines and

communication cables, generate uncontrolled voltages which can be a safety problem and
distort communications. Therefore, there has been and still is growing concern about
possible hazards resulting from the influence of High Voltage systems on metal pipelines.

This research covered the basis of electromagnetic field interference (EMI) theory, and it
illustrated an actual comprehensive local case-study by using well known software which
was acquired to assist in the simulation and evaluation of such EMI problems. It
calculated, evaluated and analyzed interference effects on buried pipelines and
underground communication cables, due to the nearby high voltage transmission lines.

The local case-study focused on the electromagnetic interference effects on Saudi Aramco
buried pipelines and underground communication cables created by the nearby two 380
KV transmission lines operated by SEC in the Eastern Province of Saudi Arabia. Due to
the complexity of the case-study, which includes more than one transmission lines and
many buried pipelines, it was difficult to calculate the induced voltage by hand

106

107
calculation. Thus, it was carried out using a well-known software program. The program
was subjected to a validation test where the program simulation result was compared with
the field measurements result. The test has shown good agreement between the simulated
and measured values.

The local case-study of a 380KV transmission network with the nearby buried pipelines
and underground communication cables was modeled, simulated, evaluated, and analyzed
to ensure that the calculated induced voltages on these pipelines and communication
cables are within international standards such as IEEE 80-2000 and IEC-479 and/or
whether they need some mitigation measures.

The study revealed that the maximum induced voltage on all buried pipelines and
underground communication cables during the steady state condition is within the
standard limit and ranging between 0.06 and 15 volts. Most of these pipelines and
communication cables are located more than 400 m away from the ROW, except one
pipeline that runs close to the ROW for about 3.5 km and recorded a maximum of 15
volts.

However, the resulting touch voltages during the short circuit condition exceed the safety
limits on two pipelines, and they reached 650-870 volts. These pipelines cross the ROW
near the transmission line towers, and they run parallel with the transmission lines for a
significant distance. The other buried pipelines and communication cables recorded low
touch voltages, because they are mostly located more than 500 m away from the ROW,

108
and they are far away from the power substations. Moreover, the soil resistivities at the
locations of these pipelines are relatively low (20-50 m).

A mitigation system using gradient control wires has been simulated to reduce the
pipeline potential to the safety limit. The proposed mitigation system significantly
reduced the touch voltages on the two concerned pipelines during the short circuit
condition. The mitigated touch voltages were much below the standards safe limits.

While there has been a significant level of research on the performance of the mitigation
systems for the EMI effects on the buried pipelines during the steady-state and fault
conditions, little is known about their performance during lightning strikes. The EMI
analysis and the mitigation system performance during the lightning condition is a
direction for future research.

NOMENCLATURE

ACAR:

Aluminum Conductor Alloy Reinforced

AWG:

American Wire Gauge

C:

Capacitance per unit length (F/m)

d:

Geometrical distance between conductors (m)

E:

Electromotive force induced per unit length (V/m)

EF :

Electrical field (V/m)

f:

Frequency (Hz)

g:

Eulers constant g = 1.7811

GMR:

Geometric mean radius

h:

Height of the pipeline

I:

Current intensity (A)

IF :

Fault current (A)

Id :

Current density (A/m2)

j:

L:

Length (of a circuit, of the zone of influence) (m)

R:

Resistance ()

rwhole:

Radius of the pipeline including the coating layer

router:

Outer radius of the pipeline

rinner:

Inner radius of the pipeline

s:

Area of coating defect

V:

Voltage induced on a conductor

y:

Admittance of a circuit per unit length (/m)-1

Z:

Impedance ()

Zm :

Mutual impedance of two circuits per unit length (/m)

z:

Impedance of a circuit per unit length (/m)

zy = propagation coefficient of a circuit (m)-1

Electrical permeability of the air

o = 8.85 x 10-12 F/m

o:

Magnetic permeability of the air

o = 4 10-7 H/m

Soil resistivity (m)

2f (rad/s)

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VITA
Name:

BANDER JUBRAN AL-GAHTANI

Education:

Master of Science (M.S.) degree in Electrical Engineering

King Fahd University of Petroleum & Minerals

Bachelor of Engineering (B.E.) degree in Electrical Engineering

King Fahd University of Petroleum & Minerals

Date of Birth:

12th June 1979

Contact:

qahtanb@yahoo.com