CIGRE SC B4 TUTORIAL ON

HVDC AND POWER ELECTRONICS

TUTORIAL SESSION III AGRA 2015

HVDC Ground Electrode Design

WG B4.61
Joanne Hu
RBJ Engineering Corp
Winnipeg Canada
 1

HVDC GROUND ELECTRODES

 Introduction
 Basic DC System Configurations
 Types of Electrodes
 Electrode Site Selection
 Electrode Design and Interference Issues
 Minimizing Electrode Impact
 Environmental Considerations

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INTRODUCTION
 3

PURPOSE OF HVDC ELECTRODES

 Provide ground reference for DC Circuit

 Provides a path for dc unbalance current in bipolar operation
 Provide a current path in case of pole trip while in bipolar
operation
 The ground is a very low resistance (low loss) conductor when
operating in monopolar mode

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BASIC HVDC SYSTEM CONFIGURATIONS
 5

BASIC HVDC SYSTEM CONFIGURATIONS

 Monopolar
 Ground Return
 Dedicated Neutral Conductor

 Bipolar
 Ground Return
 Dedicated Neutral Conductor

 Metallic Return Using Other Pole Conductor

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 6

Ground current
equal to pole current

MONOPOLAR CONFIGURATION WITH ELECTRODES

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 7

Monopolar Mode
Dedicated Neutral
Neutral conductor Current = Pole Current

No DC Ground current

Current Flow

MONOPOLAR CONFIGURATION WITH DMR

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 8

Small ground current

Either direction
<1-2% of nominal

BIPOLAR CONFIGURATION WITH ELECTRODES

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 9

Current Flow

Bipolar Mode
Dedicated Neutral

Small Neutral Conductor Current

- either direction <1% of nominal
No DC Ground Current

Current Flow

BIPOLAR CONFIGURATION WITH DMR

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 11

BIPOLAR CONFIGURATION WITH ELECTRODES – OPERATED

IN MONOPOLAR MODE USING GROUND RETURN
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 12
Monopolar Mode
Dedicated Neutral
Neutral conductor Current = Pole Current

No DC Ground current

Current Flow
Current Flow

Monopolar Mode
Dedicated Neutral

Neutral conductor Current = Pole Current

No DC Ground current

BIPOLAR CONFIGURATION WITH ELECTRODES – OPERATED

IN MONOPOLAR MODE USING DMR Agra
 16

HOW FREQUENTLY IS ELECTRODE USED

 Very low current ~1% of rated – continuously
 Pole forced outages
 5 per pole per year with typical duration of 2 hours
 total 20 hours/year - about 2 days/yr
 Pole scheduled outages
 about 5 days/pole /year – 10 days/yr total
 Thus total duration high current operation
 ~ 12 days per year.

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TYPES OF HVDC ELECTRODES
 18

TYPES OF HVDC ELECTRODES

 Land Electrodes
 Shallow buried rings
 Vertical well electrodes
 Deep electrodes (usually impractical)
 Shore Electrodes (Beach & Pond)
 Suspended type in lagoon
 Shallow well and manhole
 Sea Electrodes
 Enclosed box
 Electrode sleds

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 19
TYPES OF HVDC ELECTRODES
Type Active part Advantage Disadvantage Example/Figure
placed in
Land soil close to converter temperature rise, high Nelson River BP1
Radisson (Shallow ring electrode)
site minimum 20km, potentials, electro-
low electrode line osmosis, only part of
power losses time in operation

Sea sea low resistance to Must maintain low Kontek, Bjäverskov

remote earth, no current density to avoid

temperature rise, no chlorine
risk for electro-
osmosis
Shore soil saturated low resistance to Needs to cope with Skagerrak,
Lövens Breddning
with water remote earth tidal water depth
(Beach)
variation

Shore sea water easy to exchange high current density, Gotland, massangä

active part high potentials

(Pond)
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 ELECTRODE SHAPES & CONFIGURATION-
20
LAND ELECTRODE
Line electrode Distribution cable Jumpers

(subject to end fringing

effects, which is enhanced
during outages) Electrode body Sectionalizing switches Electrode line(s)

Ring electrode

(Symmetry avoids
S1
S2
Electrode (Element/Coke)
0
S1
Feeder Cable
Distribution Cable

fringing effects except

S9

S3
Jumper Cable

during outages of some

S1
Electrode Section (1-10)

S8

S4
Cable Joints: Distribution
cable and Jumper Cable

sub-electrodes)
S5
S7
S6 Cable Joints: Feeder cable
and Distribution Cable

Vertical electrode
(placed in a line or ring Distribution cable

Depth of burial
formation, ring is
Jumper
cable

preferred to equalize

Length
current distribution
between elements) Vertical electrode
elements
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ELECTRODE SHAPES & CONFIGURATION 21
SEA AND BEACH
Sea electrode with
titanium net
( Titanium only suitable for
one polarity of operation, i.e.
anode)

Beach electrode

(Shallow wells on beach,

subject to tidal water
variation, design needs to
allow for unequal current
distribution.)

Pond electrode

(Shallow wells on beach,

subject to tidal water
variation, design needs to
allow for unequal current Agra
distribution.)
 22
SELECTION OF ELECTRODE TYPE
The selection of the electrode type should consider the following
factors:
 The distance between the converter station and the sea
 The predominant soil resistivity in the vicinity of the converter
station
 Permitted duration and duties of electrode operation
 Operation and maintenance philosophy
 Cost
 Land use
 Safety at the electrode site
 Total number of possibly affected infrastructure units Agra
Electrode Site Selection
 24

ELECTRODE SITE SELECTION

 General aspects of site selection

 Technical, economic and time aspects
 Geophysical, geological and hydrological aspects
 Process of geophysical and geological investigations

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 25

Electrode Duty Available

Social/Land Use Geological Initial Field
Infrastructure Data Geophysical and Investigations
Environmental Data Hydrological Data

Desktop
Site Exclusion Identify/Select
Start Geoscientific Obtain Site Access
Study Candidate Area
Study

Change
Parameters No Can a good site be Yes
or found? Detailed Field
Add More Areas Investigations

No
Permitting
Land Acquisition
Line Easements Preliminary
Confirm Site Acceptable Site
Design and
Selection Conditions?
Yes Modelling

Proceed to
Detailed Design

FLOW CHART FOR SITE SELECTION PROCESS

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 26

Site exclusion
Human settlement Overlay criteria Identification of
Process excluded sites
Satellite building
count

Roads
Divide
Water body Layers into
(Wetlands, Rivers,
etc.) SPATIAL Usable
LAYERS and
Environmentally unusable
protected areas

Agricultural
capability

SITE EXCLUSION PROCESS IN A GEOGRAPHIC INFORMATION SYSTEM

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 27
TECHNICAL, ECONOMIC AND TIME
ASPECTS OF SITE SELECTION

 OPERATION IN MONOPOLAR MODE

 RATED AND OVERLOAD CURRENT
 CONVERTER STATION LOCATION
 LINE SERVITUDES OR RIGHT-OF-WAYS AND LAND ACQUISITION
 ENVIRONMENTAL AND OTHER PERMITS
 POSSIBLE IMPACT ON INFRASTRUCTURE
 CONSTRUCTABILITY AND ACCESSIBILITY
 ALLOWED POTENTIALS AND POTENTIAL GRADIENTS

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GEOPHYSICAL, GEOLOGICAL AND 28

HYDROLOGICAL ASPECTS OF SITE

SELECTION
 Land Electrodes
 Influence on the magnitude of the electric field by geophysical
factors
 Influence on the electrode performance by geophysical factors

 Sea and Shore Electrodes

 Magnitude of electrode field

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 29
PROCESS OF GEOPHYSICAL AND
GEOLOGICAL INVESTIGATIONS

 Geoscientificdesktop study and definition of

candidate areas
 Preliminary design using simple resistivity model
 Initial field investigations
 Site selection
 Following detailed field investigations
 Detailed resistivity model
 Preliminary design and electrode modelling
 Borehole investigations
 Test electrode
 Permitting, land acquisition, line servitudes Agra
 30

MODEL BASED ON MAGNETOTELLURIC SURVEY [1] MAP BASED ON AIRBORNE ELECTROMAGNETIC MEASUREMENTS IN
FINLAND THAT HIGHLIGHTS LOW-RESISTIVITY GRAPHITE BEARING
STRUCTURES (RED-PURPLE) IN THE GROUND [2]

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Impact of Electrode
 32
TYPES OF IMPACTS
 Corrosion -may cause corrosion in metallic structures. Specifically, in large metallic and
unprotected pipes or in large buried metallic structures (e.g.: transmission lines with
shield wires, others).
 Transformer Saturation - DC current may interfere with transmission and distribution
lines and transformers through the grounding system.
 Transfer Potentials - Current may cause potential rises in large metallic structures due
to transferred potentials. For example long metallic fences and radial irrigation systems
may be .
 Telephone interference - The extended operation may cause signal interferences in
communication systems due to the constant ripple cause by the converter stations.
 Emissions - DC current may cause chemical reactions in contact with the conductive
media (sea water or moist soil), which may produce gases while corrosion of the
elements may release metallic ions.
 Soil Heating - DC current for long periods of time may cause soil overheating close to
the active parts of the electrode, which may alter the conductive media properties and the
physical properties of the soil itself.
 Groundwater heating - DC current for long periods of time may cause water heating,
even up to the boiling point, close to the active parts of the electrode, which may alter the
surrounding environment.
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 33

IMPACT ON INFRASTRUCTURE

 Buried Metallic Objects

 Non-insulated objects, i.e. the metal is directly and continuously in contact with
the surrounding soil.
 Objects coated with insulating material such as polyethylene and normally
cathodic protected.
 The earthing grids of substations which are interconnected by the power lines.

 Non-insulated Buried Metallic Objects

 Insulated Metallic Objects
 AC Grid

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IMPACT ON ENVIRONMENT

 Compass deviations
 Chemical emissions
 Effects on fauna
 Effects on flora

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ELECTRODE INTERFERENCE ISSUES

 Can be classified as near and far effects

 Near effects primarily deal with safety
 step voltages
 transferred potentials

 electric field in water

 these have been discussed above

 Far effects generally deal with interference with other facilities

 Corrosion of buried structures (cables, pipe systems, bridges, etc)
 Currents in transformer neutrals (saturation)

 Compass deviation due to electrode cables in sea

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 37

CORROSION RATES OF METALS

Material Atomic Valence Density Total Loss of

(metal) weight (V) (g/cm3) loss of thickness
(ma) weight (mm/mA/m2/yr)
(kg/A*yr)

Aluminum 26.98 3 2.65 2.94 0.0011

Copper 63.54 2 8.95 10.38 0.0012
Iron 55.85 2 7.85 9.13 0.0012
Lead 207.21 2 11.35 33.86 0.0030
Magnesium 24.32 2 1.70 3.97 0.0023
Zinc 65.38 2 7.10 10.68 0.0015

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 38
EFFECT OF ELECTRODE GPR ON
PIPELINES
Pipeline
V1 Ip V2

Cathodic Anodic
Idc

Idc (anodic)
Ground Potential Rise (V)

V1

V2

Distance (km)
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 39

MITIGATING GPR ON PIPELINES

 Add or improve cathodic protection

 Replace sacrificial anodes with rectifier systems
 Possibly increase rectifier ratings

 Add additional insulating flanges to mitigate high pipe-to-soil

voltages

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EFFECT ON TRANSMISSION LINES

-Sectionalization of shield wires

reduces impact

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SACRIFICIAL ANODES

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EFFECT ON TRANSFORMERS
Transmission Line
V1 V2

 Increased
 Exciting current
Transformer Transformer
It/3  Audible noise

 Losses

 Leakage flux
It
It
 Temperature rise
Idc
Idc (anodic)
 Allowable direct current
Ground Potential Rise (V)

V1
is small
V2

Distance (km)

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MITIGATING GPR ON TRANSFORMERS

 Find a more favorable electrode site - lower GPR

 Move the electrode farther away if possible
 Use resistors in ground connection – possibly bypass during faults
 Use series capacitors in lines to block dc currents
 Use ungrounded transformer winding arrangements
 Separate primary and secondary neutral connections

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 44
MITIGATION OF EXCESSIVE NEUTRAL
CURRENT
Transmission Line
V1 V2

Transformer Transformer
It/3

Series Capacitors

Neutral Grounding Resistors It

It

Idc
Idc (anodic)
Ground Potential Rise (V)

V1

V2

Distance (km)
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 45

EFFECT ON SUBMARINE CABLES

Land Sea
Cathodic

Ic

Anodic

Solution is to locate
the HVDC sea
HVDC Cathode electrode further
away from the cable

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 46
COMPASS DEFLECTION
667 A
5
4.37 1

4

 35 m depth
Compass Deflection (Degrees)

i
 5 degrees from
north south
2

0.03 3
0 20 0 40 0 60 0 80 0
0 i 80 0

Dista nce (m )

5 10
5
5
510

4 10
5
Magnetic Field (Tesla)

3 10
5
Bi

BE
2 10
5

1 10
5

8
2.88 510
0 20 0 40 0 60 0 80 0
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0 i 80 0

Dista nce (m )
Electrode Design Aspects
 48
GENERAL DESIGN CONSIDERATIONS
 Design Criteria
 Safety requirements for Humans and animals
 Current Density
 Interference
 Operating duties
 Electrode life cycle
 Reliability
 Temperature rise
 Chemical emissions

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 49
GENERAL ELECTRODE DESIGN PROCESS
Define Current Ratings and Check Temperature Rise
Start
Operational Requirements and Thermal Rating

Define/Select Check
Safety Criteria Meets Thermal Yes
Environmental
Requirements
Influences

Soil No
Perform Trial Design to
Resistivity
Meet Safety Criteria
and Site Meets
including Specified Outages No
Size Data Adjust Design Environmental
Requirements

Design Meets No Yes

Safety Criteria Yes Economically
Feasible Identify Zone of
Yes Influence and Facilities
that may be affected
Check Physical Constraints No
Site size
Current Density Burial Depth
No Facilities affected
below threshold

Meets Physical Yes

Yes
Constraints
Identify and Design
Suitable Mitigation for
Affected Facilities
Adjust Design

No Practical and
Yes Design Is Economical
Constructable
Yes
No
Finalize Design

Review Site Agra

Selection Complete
 50

SAFETY CRITERIA – OVERALL CONCEPT

 Operation of the electrodes shall not result in unsafe conditions

for people or animals either in publically accessible areas or
within controlled areas accessible only to authorized
maintenance workers
 Operational conditions fall into two categories:
 conditions which can persist for 10 seconds or longer which, for
safety purposes, are considered to be continuous, and
 transient conditions which would persist for 10 seconds or less

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 51

STEP VOLTAGES/TOUCH VOLTAGE

 Limited to values that will not exceed the following criteria:

 The step/touch voltage in publically accessible areas under
continuous operating conditions should not exceed a value that
would result in continuous body currents (IBC) above the threshold of
perception. (IBC<5 mA)
 The step/touch voltage during short time and transient operating
conditions and transient faults shall not exceed a value that would
result in body currents exceeding the lowest threshold of let-go-
current. (IBt < 30 mA)

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 5mA) 0mA)
re L imit ( re Limit (3
xp o su p o su
Co n tin u ous E ansient Ex
Tr 52

30

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Safety Criteria based on Limits Published in IEC 60479-1

 53
SAFETY CRITERIA – VOLTAGE &
GRADIENT

 Within Electrode Site

 Step voltage
 Touch voltage
 Metal-to-metal touch voltage

 Extend for significant distances into publicly accessible areas:

 Transferred potential, and
 Voltage gradient in water (if applicable)

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 54
IB=Et / RB

RB
IB=Et / (RB +Rf/2)
IB=Es / (RB +2Rf)
RB
RB

Rf Rf
1m Rf Rf

1.25m
2m
Surface Potential Rise (V)

Surface Potential Rise (V)

Surface Potential Rise (V)

Et
Es

Et
Distance (m) Distance (m) Distance (m)

(A) (B) (C)

STEP VOLTAGE TOUCH POTENTIAL METAL TO METAL TOUCH VOLTAGE

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 Grounded point Wooden (insulating) fence posts
IB=Et / (RB +Rf/2)
55
RB

Rf Rf
Surface Potential Rise (V)

Unspecified distance
Et

Distance (m)

Conceptual Illustration of Transferred Potential

IB=Ew / RB
𝐼𝐵𝑐∗𝑅𝐵
𝐸𝑤𝑐 < , 𝐸𝑤𝑐 < 2.5𝑉
2
𝐼𝐵𝑡∗𝑅𝐵
𝐸𝑤𝑡 < 2
, 𝐸𝑤𝑡 < 15𝑉
2m
Ew

Conceptual Illustration for Safety with Electrical Gradient in Water

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 56
PHYSICAL DESIGN CONSTRAINS AND
CRITERIA
 Operating Duties and Project Life Cycle
 Current Density
A current density of less than 0.5 A/m2 to 1 A/m2 is recommended for
land electrodes [1] and 6 A/m2 to 10 A/m2 for sea electrodes.
 Thermal Stability
 Polarity – Anodic and/or Cathodic
 Material

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 57

DATA REQUIRED FOR DESIGN

 Current Rating
 Continuous, short time and transient
 Soil Physical and Chemical Prosperities
 Resistivity
 Thermal capacity
 Thermal conductivity
 Highest natural ambient soil temperature
 Depth to water table.
 Type of soil or rock material
 Moisture content
 Susceptibility to electro osmosis
 Chemical properties

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 58

DESIGN LIMITS AND CONSIDERATIONS

 Electrode dc resistance
 Thermal stability at specified current ratings
 Design life based on corrosion of electrode elements
 Current density
 Current sharing between sub-electrodes
 Potential interference with other nearby facilities

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 59

CALCULATION METHODS

 Mathematical Calculation (Analytical equations)

 Only applicable to simple soil structures such as uniform, 2 or 3
layers soil resistivity distribution

 Simulations using numerical methods

 FEM
 Can Handle Complicated soil resistivity distribution
 More accurate current density and GPR and Gradient calculation
near electrode
 Should perform sufficient studies to cover the range of expected
variation in soil resistivity and extent including seasonal changes

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 60

SIMULATION
 Soil resistivity measurement
 deep – down to Moho (crust/mantle interface) – by means of MT
measurements (very low frequency);
 near-surface – hundreds of meters – by means of electromagnetic (TDEM)
soundings;(intermediate frequency)
 shallow – tens of meters – by means of vertical electrical (Schlumberger or
Wenner) or electromagnetic (nanoTEM) soundings (higher frequency)
 Resistivity Structure
 Detailed and near-surface model – close to the electrode (up to two times
its diameter) – using the data form the shallow and near-surface surveys;
Shallow soil resistivity values as determined from the shallow site
measurements ca be used for the model of radius up to a few
hundred metres and depth to 50-100 m.
 Wide area model – covering all the interference area, by means of a 3D
model – using the data from the deep survey to depth and distance of up to
100 km.
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 70

Ground Potential Rise - (Volts)

70
65

61
50
65
45
60 60
40 55 55
35
30
50 50
25 45 45
Resistivity - (Ohm-m) 20
40 40
15
10 35 35
5
70 0
60
50 200
40
30
20
10
0
100
400

-y)
60

(m
-x
0
200

km
50

-
200

tre
-(
45

re

Cen
0

nt
100

Ce
-100

m
Dist

fro
ance 0
-20

fro
0 400
from

ce
200

ce
Cen 0

tan
an
tre - -100 -200 -40
0 -200

st
(

Dis
km- -400

Di
y) Centre - (m-x)
-200 Distance from

EXAMPLE OF A TOP LAYER RESISTIVITY AS MODELED EXAMPLE OF A LOCAL CALCULATED GROUND

IN AREA WITHIN 250KM OF THE ELECTRODE POTENTIAL RISE A SHALLOW DOUBLE RING
ELECTRODE WITH ONE PART OF THE ELECTRODE OUT
OF SERVICE

200

Potential Gradient - (Volts/m)

150
100
50
0
-50 300
-100

)
200

m-y
-150

e-(
-200 100

entr
0

mC
e fro
-100

anc
-200
-300 -200

Dist
-100 0 100 200 -300
300
Distance from Centre - (m-x)

EXAMPLE OF A LOCAL CALCULATED POTENTIAL EXAMPLE OF CALCULATED POTENTIAL GRADIENT OF A

GRADIENT OF A SHALLOW DOUBLE RING ELECTRODE DEEP WELL ELECTRODE

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 62
VERIFICATION OF DESIGN BY
MEASUREMENTS

 Electrode resistance
 Step and touch voltages
 Ground potential rise
 Current distribution in sub-electrodes

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Different Types of Electrode Design
 64
LAND ELECTRODES
 Nelson River BP1/BP2
 4000 A rating
 Concentric rings
 244/305m diameter
 50 Ohm m soil
 Not fenced
 Designed for step voltage
safety
 Thermal time constant 32
days

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 65

SHALLOW BURIED RING ELECTRODE

0.5
Conductor 1.0

Drip Irrigation Piping and nozzles

2.6

High Silicon Chromium Electrode Elements

0.75 Coke

0.75

0.50
1.00 Conductor buried at 0.5m depth directly over the center of the coke bed

2.40 Drip Irrigation Piping and nozzles buried at 1 m depth

2.13

0.75
1.87
11.0

22.1

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 66

SAFETY NEAR LAND ELECTRODES

 Step potentials
 must be limited to < 5 +.03ρs V/m
 Will be safe for people and animals

 Transferred touch potentials

 must avoid placing metallic structures near the electrodes
 Provide isolation for cables entering the electrode site

 Thermal stability considerations

 Analytical calculations are very conservative
 Generally results in an over dimensioned electrode

 In practical designs, thermal stability would likely be achieved when step

voltage criterion is satisfied - but it needs to be checked

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 67

SURFACE POTENTIALS

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 68

EXISTING LAND ELECTRODES

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 69

EXISTING ELECTRODES -LAND

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 70

SHORE ELECTRODE ON BEACH

𝜌
𝑅1 = 𝐿𝑛4𝐿 − 1
2𝜋𝐿
1 𝜌 4𝐿 2𝐿 1.781
𝑅𝑛 = 𝐿𝑛 − 1 + + 𝐿𝑛
𝑛 2𝜋𝐿 𝑎 𝑠 𝑒

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 71

RESISTANCE OF SHORE ELECTRODES

For
α= 0.2 Radian (10 °)
ρ1= 0.2 Ohm m
ρ2= 100 Ohm m
Less than 1/3rd of the current
flows back into the earth
The voltage rise is typically 20
times less than for a land
electrode
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 72

SHORE ELECTRODE IN LAGOON

Perimeter Fence

Many European and

one Korean electrode
Enclosed Lagoon
are similar
Timber Bridge Structure

Suspended Electrodes
Average spacing 3 m
Switch
House

Rock Fill Breakwater

50 m Minimum

LAGOON

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 73
SHORE ELECTRODE SUSPENDED IN
WATER

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 74

SICILY – PUNTA TRAMONTANA - 2500A

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 75

SHORE ELECTRODE ON BREAKWATER

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 76

EXISTING ELECTRODES

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 77

SEA ELECTRODE OPEN DESIGN

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 78

SEA ELECTRODE ENCLOSED DESIGN

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 79

EXISTING SEA ELECTRODES

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 80

EXISTING SEA ELECTRODES

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 81
CONSIDERATIONS FOR SHORE / SEA
ELECTRODES
 Electric field of 2.5V/m
 Uncomfortable to people/divers
 Can stun fish

 Design for a limit of about 1V/m

 No thermal considerations since water will remove the heat by
convection
 Sea electrodes will require a connecting cable which can
cause compass deflections if running north-south. East west
cables do not affect compass direction.
 Shore/pond electrodes have negligible impact on compass
direction
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 82

SEPARATION DISTANCES ELECTRODES

Facility Distance
(km)
Substations (grounded transformers) 10

Oil or gas pipelines 8

Submarine cables 5
Urban areas gas and sewer lines 5
Railways 2
Rural Power Distribution 2
Wharfs 1
Bridges 1
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 83
SEPARATION DISTANCES SEA/SHORE
ELECTRODES
 Generally smaller than comparable distances from land
electrodes because of lower voltage rise
 Major facilities need to be checked during site investigations

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 84
STEPS IN SELECTING AN ELECTRODE
SITE
 Preselect area based on separation distances from major
facilities
 Land -Determine if local conditions are favorable
 Low shallow resistivity
 Determine deep earth resistivity (Magneto-telluric measurements)

 Shore – Identify location

 Sheltered with rapid increase in water depth
 Ability to fence the site

 Area where large freshwater runoff is unlikely

 Sea
 Away from ship lanes and fishing zones
 Relatively deep water not subject to silting
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Other Aspects
 86

OTHER ASPECTS

 Connection between the converter station and the electrode

station
 Auxiliary systems for electrode stations monitoring of electrode
station may require station service supply.
 Testing and commissioning associated with electrodes.
 Operation and maintenance of electrodes stations.

Agra
Summary of Electrode Design
 88

SUMMARY
 Potential environmental impacts from electrodes can be reduced to
tolerable levels or eliminated either by
 Suitable selection of the electrode site for impacts remote from the
electrode and
 Good design techniques if the impacts are near the electrode or on the
electrode site
 Advances in tools for Site selection and Design
 Magnetotelluric (MT), audio magnetotelluric (AMT) and airborne
geophysical measurements (AGM) electrical resistivity tomography (ERT)
soil resistivity survey and interpretation techniques.
 Improved access to land use and facilities databases
 Greatly improved modelling techniques using finite element software
capable of very fine resolution in the area of the electrode while providing
adequate resolution of very deep soil structure and structure of soil in three
dimensions surrounding the electrode. This allows consideration of
reasonable ranges of sensitivity in soil resistivity.
Agra
Questions?