IEC TS 62344:2013

IEC/TS 62344 ®
Edition 1.0 2013-01
TECHNICAL
SPECIFICATION
colour
inside
Design of earth electrode stations for high-voltage direct current (HVDC) links –
General guidelines
IEC/TS 62344:2013(E)
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IEC/TS 62344 ®
Edition 1.0 2013-01
TECHNICAL
SPECIFICATION
colour
inside
Design of earth electrode stations for high-voltage direct current (HVDC) links –

General guidelines
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XC
ICS 29.240.99 ISBN 978-2-83220-575-4

– 2 – TS 62344 © IEC:2013(E)
CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 10
2 Normative references . 10
3 Terms and definitions . 10
3.22 current-releasing density . 13
4 System conditions . 14
4.1 General principles . 14
4.2 System parameters related to earth electrode design . 14
4.2.1 Amplitude and duration of the current . 14
4.2.2 Polarity . 14
4.2.3 Designed lifespan . 15
4.2.4 Common earth electrodes . 15
5 Design of land electrode stations . 15
5.1 Main technical parameters . 15
5.1.1 General principles . 15
5.1.2 Temperature rise . 16
5.1.3 Earthing resistance . 16
5.1.4 Step voltage . 17
5.1.5 Touch voltage . 17
5.1.6 Current density . 17
5.1.7 Field intensity in fish ponds . 18
5.2 Electrode site selection and parameter measurement . 18
5.2.1 General principles . 18
5.2.2 Data collection survey . 18
5.2.3 Distance from converter station (substation) . 18
5.2.4 Environment conditions . 19
5.2.5 Terrain and landform . 19
5.2.6 Measurement of soil parameters . 19
5.2.7 Geological exploration . 19
5.2.8 Topographical map . 19
5.2.9 Values selected during design . 19
5.3 Earth electrode and associated components . 20
5.3.1 General principles for material selection . 20
5.3.2 Selection of feeding rods and characteristics . 20
5.3.3 Chemical and physical properties of petroleum coke . 21
5.3.4 Current-guiding system . 21
5.3.5 Bus . 22
5.3.6 Electrode line monitoring device . 22
5.4 Electrode arrangement . 22
5.4.1 General principles . 22
5.4.2 Filling coke . 22
5.4.3 Selection of earth electrode shape. 22
5.4.4 Earth electrode corridor (right of way) . 23
5.4.5 Distance between sub-electrodes in the arrangement . 23
5.4.6 Burial depth of the earth electrodes . 23

TS 62344 © IEC:2013(E) – 3 –
5.4.7 Segmentation of earth electrodes . 24
5.5 Minimum size of earth electrode . 24
5.5.1 General principles . 24
5.5.2 Total earth electrode length . 24
5.5.3 Side length of coke section . 24
5.5.4 Diameter of feeding rods . 25
5.6 Current guiding system . 26
5.6.1 General principles . 26
5.6.2 Placement of the current-guiding wire . 26
5.6.3 Connection of current-guiding wire . 26
5.6.4 Selection of current-guiding wire cross-section . 27
5.6.5 Insulation of the current-guiding wire . 27
5.6.6 Disconnecting switch . 27
5.6.7 Connection of the feeding cable. 27
5.6.8 Connection of jumper cables . 28
5.6.9 Selection of cable structure . 28
5.6.10 Selection of cable cross-section . 28
5.6.11 Selection of cable insulation . 28
5.6.12 Cable welding position . 29
5.6.13 Welding . 29
5.6.14 Mechanical protection for cable . 29
5.7 Auxiliary facilities . 29
5.7.1 Online monitoring . 29
5.7.2 Soil treatment . 29
5.7.3 Exhaust equipment . 30
5.7.4 Fence . 30
5.7.5 Marker . 30
6 Design of sea electrode station and shore electrode station . 30
6.1 Main technical parameters . 30
6.1.1 Temperature rise . 30
6.1.2 Earthing resistance . 30
6.1.3 Step voltage . 31
6.1.4 Touch voltage . 32
6.1.5 Voltage gradient in water . 32
6.1.6 Current density . 32
6.2 Electrode site selection and parameter measurement . 32
6.2.1 General principles . 32
6.2.2 Data collection survey . 32
6.2.3 Distance from converter station (substation) . 32
6.2.4 Environment conditions . 33
6.2.5 Measurement of soil parameters . 33
6.3 Earth electrode and associated components . 33
6.3.1 General principles for material selection . 33
6.3.2 Common feeding rods and characteristics . 33
6.3.3 Chemical properties of petroleum coke . 34
6.3.4 Current-guiding system . 34
6.3.5 Bus . 34
6.3.6 Electrode line monitoring device . 34
6.4 Electrode arrangement . 34

– 4 – TS 62344 © IEC:2013(E)
6.4.1 General principles . 34
6.4.2 Filling coke . 34
6.4.3 Selection of earth electrode shape. 34
6.4.4 Segmentation of earth electrodes . 35
6.5 Current-guiding system . 35
6.5.1 Placement of the current-guiding wire . 35
6.5.2 Connection of current-guiding system . 35
6.5.3 Selection of cable cross-section . 36
6.5.4 Insulation of the current-guiding system . 36
6.5.5 Selection of cable structure . 36
6.5.6 Mechanical protection for cable . 36
6.6 Auxiliary facilities . 36
7 Impact on surrounding facilities and mitigation measures . 37
7.1 Impact on insulated metallic structures and mitigation measures . 37
7.1.1 General principles . 37
7.1.2 Relevant limits . 37
7.1.3 Mitigation measures . 37
7.2 Impact on bare metallic structures . 37
7.2.1 General principles . 37
7.2.2 Relevant limits . 37
7.2.3 Mitigation measures . 37
7.3 Impact on the power system (power transformer, grounding network, and
surrounding towers) . 38
7.3.1 General principles . 38
7.3.2 Relevant limits . 38
7.3.3 Mitigation measures . 38
7.4 Impact on electrified railway . 38
7.5 Other facilities (such as greenhouses and water pipes) . 39
Annex A (informative) Basic concepts of earth electrodes . 40
Annex B (informative) Soil parameter measurement method . 52
Annex C (informative) Electrode line design . 60
Annex D (informative) Assessment of measurement method . 63
Annex E (informative) Earth electrode electrical parameter calculation method . 67
Annex F (informative) Thermal time constant . 78
Annex G (informative) Schematic diagram of online monitoring system . 80
Annex H (informative) Calculation method for corrosion of nearby metal structures
caused by earth electrodes . 81
Annex I (informative) Calculation method for d.c. current flowing through a.c.
transformer neutral near earth electrodes . 83
Annex J (informative) Chemical aspects . 86
Annex K (informative) Simple introduction of shore electrodes . 87
Bibliography . 89

Figure 1 – Electrode cross-section . 22
Figure 2 – Vertical arrangement . 23
Figure 3 – Placement of the current-guiding wire . 26
Figure 4 – Feeding cable . 28

TS 62344 © IEC:2013(E) – 5 –
Figure 5 – Resistivity layers with sea or shore electrodes . 31
Figure 6 – Sea electrode . 34
Figure 7 – Sea bottom electrode with titanium nets . 35
Figure 8 – Titanium net . 36
Figure 9 – Impact of earth electrodes on a.c. systems (transformer, grounding network,
tower) . 38
Figure A.1 – HVDC power transmission system structure . 40
Figure A.2 – Schematic diagram of the structure of a monopolar earth (sea water)
return system . 41
Figure A.3 – Schematic diagram of the structure of monopolar metallic return system . 41
Figure A.4 – Schematic diagram of the structure of bipolar neutral grounded at both
ends . 42
Figure A.5 – Schematic diagram of the structure of bipolar neutral grounded at one end . 42
Figure A.6 – Schematic diagram of the structure of bipolar neutral line . 43
Figure A.7 – Schematic diagram of touch voltage and step voltage . 44
Figure A.8 – Schematic diagram of single circular earth electrode . 45
Figure A.9 – Axial distribution of step voltage of single circular earth electrode . 45
Figure A.10 – 3-D distribution of step voltage of single circular earth electrode . 46
Figure A.11 – Schematic diagram of double circular earth electrode . 46
Figure A.12 – Axial distribution of step voltage of double circular earth electrode . 46
Figure A.13 – 3-D distribution of step voltage of double circular earth electrode . 47
Figure A.14 – Schematic diagram of triple circular earth electrode . 47
Figure A.15 – Axial distribution of step voltage of triple circular earth electrode . 47
Figure A.16 – 3-D distribution of step voltage of triple circular earth electrode . 48
Figure B.1 – Equivalent circuit of Wenner method . 54
Figure B.2 – Equivalent circuit of Schlumberger method . 54
Figure B.3 – Equivalent circuit of dipole-dipole method . 55
Figure E.1 – π shape equivalent circuit of an individual earth electrode unit . 67
Figure E.2 – Ohm’s Law applied to cylinder conductor . 68
Figure E.3 – Continuity of axial component of the electric field in the soil and in the
conductor . 68
Figure E.4 – Spatial division of the earth electrode . 68
Figure E.5 – Network for solving axis current . 69
Figure E.6 – Horizontally layered soil . 71
Figure E.7 – Geometrical structure of a tetrahedron unit . 72
Figure E.8 – Structure of a double-circle d.c. earth electrode . 76
Figure E.9 – Ground potential and step voltage distribution of a double-circle earth
electrode . 77
Figure F.1 – Earth electrode temperature rise characteristics. 78
Figure G.1 – Schematic diagram of earth electrode online monitoring system . 80
Figure H.1 – Calculation of current flowing through a metal pipe . 82
Figure I.1 – Schematic diagram of ground resistance network and underground
voltage source . 83
Figure I.2 – Circuit model for the analysis of d.c. distribution of a.c. systems . 85
Figure K.1 – Top view of shore electrode, beach type . 87

– 6 – TS 62344 © IEC:2013(E)
Figure K.2 – Shore electrode, pond type . 87

Table 1 – Composition of iron-silicon alloy electrode . 21
Table 2 – Chemical composition of the coke after calcination . 21
Table 3 – Physical properties of petroleum coke used for earth electrodes . 21
Table 4 – Electric corrosion characteristics of different materials . 26
Table B.1 – Soil (rock) resistivity . 52
Table B.2 – Soil thermal capacity . 53
Table B.3 – Soil thermal conductivity . 53
Table B.4 – Number of measurement points with different pole distances . 56
Table E.1 – Model of soil with two layers . 77

TS 62344 © IEC:2013(E) – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DESIGN OF EARTH ELECTRODE STATIONS
FOR HIGH-VOLTAGE DIRECT CURRENT (HVDC) LINKS –
GENERAL GUIDELINES
FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
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The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC 62344, which is a technical specification, has been prepared by IEC technical committee
115: High-voltage direct current (HVDC) transmission for d.c. voltages above 100 kV.
This technical specification cancels and replaces IEC/PAS 62344 published in 2007. This first
edition constitutes a technical revision.

– 8 – TS 62344 © IEC:2013(E)
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
115/53/DTS 115/64/RVC
Full information on the voting for the approval of this technical specification can be found in
the report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• transformed into an International Standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
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TS 62344 © IEC:2013(E) – 9 –
INTRODUCTION
The high-voltage d.c. earth electrode is an important part of the d.c. power transmission
system. It takes on the task of guiding the current into the earth under the monopolar metallic
return operation mode, and the unbalanced current under the bipolar operation mode. Further,
it secures and provides the reference potential of valve neutral point under the bipolar/
monopolar operation mode, to protect the safe operation of valves.
D.C. earth electrodes include land electrodes, sea electrodes, and shore electrodes. Today,
there are around tens of d.c. electrodes in the world. Their influence on the nearby and far
away environment is produced when there is d.c. current continuously leaking into the earth
through d.c. earth electrodes.
Their influence on the surrounding environment includes:
a) influence on humans, mainly due to step voltage, touch voltage and transferred voltage;
b) influence on the electrode itself, mainly reflected by earth temperature rise and corrosion
on the electrode;
c) influence on nearby ponds and organisms in the sea;
d) influence on the a.c. power system, mainly reflected by the d.c. voltage excursion of
transformer neutral point;
e) influence on buried metallic objects, mainly revealed by the corrosion on buried metallic
pipelines, a.c. grounding grids, tower foundations for power transmission lines and
armoured cables, etc.
For years, a great deal of experience has been accumulated in the research and design work
in many countries, and relevant native standards or enterprise standards have been
developed. The aim of this Technical Specification is to develop the design guide for d.c.
earth electrodes, on the site selection, material selection, shape, buried depth, adoption of
equipment and connection styles, etc. It could be referred to by the specialized employees in
different countries, to ensure the safe operation of earth electrode under different modes,
control the influence on the environment nearby and the environment far away to the
acceptable level, and to reasonably decrease engineering costs.
To ensure this Technical Specification is more scientific, precise and practical,
IEC/PAS 62344:2007 is referred to, and some research results obtained in recent years are
adopted.
– 10 – TS 62344 © IEC:2013(E)
DESIGN OF EARTH ELECTRODE STATIONS
FOR HIGH-VOLTAGE DIRECT CURRENT (HVDC) LINKS –
GENERAL GUIDELINES
1 Scope
This Technical Specification applies to the design of earth electrode stations for high-voltage
direct current (HVDC) links. It is intended to provide necessary guidelines, limits, and
precautions to be followed during the design of earth electrodes to ensure safety of personnel
and earth electrodes and prevent any significant impact they may exert on d.c. power
transmission systems and the surrounding environment.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC/TS 60479-1, Effects of current on human beings and livestock – Part 1: General aspects
IEC/TS 61201, Use of conventional touch voltage limits – Application guide
IEC 61936-1, Power installations exceeding 1 kV a.c. – Part 1: Common rules
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
earth electrode
ground electrode (US)
structure with a conductor or a group of conductors embedded in the soil or immersed in sea
water, directly or surrounded with a specific conductive medium
EXAMPLE  Coke, providing an electric connection to the earth, for transmission of d.c. current from a d.c. system.
[SOURCE: IEC 60050-195:1998, 195-02-01]
3.2
land electrode
earth electrode buried in the ground more than 1 km away from the coastline
3.3 shore electrode
3.3.1
beach electrode
electrode located on the beach inside the waterline (usually less than 1 km away from the
waterline), and the active part of the electrode makes contact with the soil or with
underground water, but not directly with seawater or pond electrodes

TS 62344 © IEC:2013(E) – 11 –
3.3.2
pond electrode
electrode usually placed outside but within 100 m of the waterline, having electrodes directly
in contact with sea water, within a small area which is usually protected against waves and
possible ice damage by a breakwater
3.4
sea electrode
electrode located away from the shoreline at a distance deeper than 100 m into the sea
3.5
electrode station
whole system which guides current from electrode line to the earth or sea water, usually
including, in addition to the electrode itself, the feeding cable, towers, switchgear and
necessary auxiliary equipment
3.6
common earth electrode
earth electrode system, which is composed of a single earth electrode or multiple earth
electrodes in parallel, shared by multiple converter stations
Note 1 to entry: It mainly consists of earth electrodes and intertie lines between sub- earth electrodes in different
electrode sites.
3.7
electrode site
site where the earth electrode is located
3.8
electrode line
overhead line or underground cable used to connect the neutral bus in a converter station to
the earth electrode station
3.9
feeding rod
earthing conductor buried underground or in the sea for guiding earthing current into the
surrounding medium (soil or sea water)
Note 1 to entry: They are the most important devices in an earth electrode station.
3.10
feeding cable
cable used to guide current from current-guiding wire to feeding rods
3.11
current-guiding wire
main branch used to conduct current from electrode line (or bus) to feeding cables
3.12
current guiding system
system used to guide the current from electrode line to feeding rods
Note 1 to entry: It consists of current-guiding wire(s), disconnecting switches, feeding cables and connections.
3.13
jumper cable
cable used to connect two feeding rods placed at some distance from each other
EXAMPLE  At two sides of a channel.

– 12 – TS 62344 © IEC:2013(E)
3.14
earth return operation mode
operation mode in the HVDC power transmission system, using d.c. lines and earth (or sea
water) as the current loop
3.15
earth return system
series of devices designed and built specifically for earth return operation mode
Note 1 to entry: It mainly consists of the electrode line, earth electrode, current guiding system, and other
auxiliary facilities.
3.16
rated current under monopolar mode
current of a converter station at rated power in monopolar (operation) mode
3.17
maximum overload current
maximum current for which the associated d.c. system(s) is designed for monopolar operation
for longer than several minutes
3.18
maximum transient overcurrent
average maximum current flowing through the earth electrode for a few seconds when a
system disturbance occurs
3.19
unbalanced current
difference of current between two poles during operation of a bipolar d.c. system
Note 1 to entry: For symmetrical bipolar operation mode, the unbalance current flowing can be controlled
automatically by the control system within about 1 % of the rated current.
Note 2 to entry: For asymmetrical bipolar operation mode, the current flowing through the earth electrode is the
difference in currents between the two poles.
3.20
cathode
electrode capable of emitting negative charge carriers to and/or receiving positive charge
carriers from the medium of lower conductivity
Note 1 to entry: The direction of electric current is from the medium of lower conductivity, through the cathode, to
the external circuit.
Note 2 to entry: In some cases (e.g. electrochemical cells), the term "cathode" is applied to one or another
electrode, depending on the electric operating condition of the device. In other cases (e.g. electronic tubes and
semiconductor devices), the term "cathode" is assigned to a specific electrode.
[SOURCE: IEC 60050-151:2001, 151-13-03]
3.21
anode
electrode capable of emitting positive charge carriers to and/or receiving negative charge
carriers from the medium of lower conductivity
Note 1 to entry: The direction of electric current is from the external circuit, through the anode, to the medium of
lower conductivity.
Note 2 to entry: In some cases (e.g. electrochemical cells), the term "anode" is applied to one or another
electrode, depending on the electric operating condition of the device. In other cases (e.g. electronic tubes and
semiconductor devices), the term "anode" is assigned to a specific electrode.
[SOURCE: IEC 60050-151:2001, 151-13-02]

TS 62344 © IEC:2013(E) – 13 –
3.22 current-releasing density
3.22.1
current-releasing density per unit length
current released to earth from a unit length of feeding rod (in A/m)
3.22.2
current-releasing density per unit area
current released to earth from a unit area of coke surface (in A/m )
3.23
designed lifespan
designed operational lifespan of the earth electrode, typically of the same order as the
operational lifespan of the converter station
3.24
corrosion lifespan
time integral of current when a earth electrode runs as an anode, such as monopolar
operation and bipolar operation with unbalanced current, during its designed lifespan, in the
unit of ampere hour (Ah)
3.25
thermal time constant
time required for the temperature of the soil to reach the steady state temperature at the initial
rate of rise of temperature
Note 1 to entry: In practice the soil temperature rises nonlinearly when earthing current is released into earth
through an electrode, see Annex F.
3.26
earthing resistance
resistance between an earth electrode and earth at an infinite distance
3.27
step voltage
voltage between two points on the Earth's surface that are 1 m distant from each other, which
is considered to be the stride length of a person
[SOURCE: IEC 60050-195:1998, 195-05-12]
3.28
touch voltage
potential difference between a grounded metallic structure and any point on the earth 1 m
from the structure
3.29
transferred voltage
potential difference applied to a person when this person stands on the ground near the earth
electrode and touches a conductor grounded at a remote site, or when this person stands on
the ground far away from the earth electrode and touches a conductor grounded near the
electrode site
3.30
insulated metallic structures
metallic structures buried in the ground near an earth electrode and coated with insulating
material
– 14 – TS 62344 © IEC:2013(E)
3.31
bare metallic structures
metallic structures buried in the ground near an earth electrode and not coated with insulating
material
3.32
coefficient of uneven current distribution
ratio of maximum current-releasing density at any specific point of an earth electrode, to the
average current-releasing density of that earth electrode
Note 1 to entry: This parameter reflects the uniformity of current released from the earth electrode to the
surrounding medium and is a dimensionless quantity.
3.33
equivalent earthing current
ratio of time integral of current of an earth electrode operated as a cathode or anode to its
designed lifespan
Note 1 to entry: It is used to analyze the corrosion impact on underground metallic objects in the vicinity of the
electrode.
4 System conditions
4.1 General principles
The system conditions to be considered during earth electrode design mainly include the
amplitude and duration of the current relating to the earth electrode, and designed lifespan
and polarity.
4.2 System parameters related to earth electrode design
4.2.1 Amplitude and duration of the current
The operation current and duration of d.c. earth return operation systems should normally be
specified in local regulations, bid documents, or specifications. In the absence of such
documents that can be used as a reliable source, the following values may be used as a
reference during design:
a) the amplitude of earth electrode rated current is equal to the system rated current (I ).
N
The maximum duration of this current corresponds to that of the monopolar earth return
operation mode of the earth electrode. For a bipolar system, the interval from the time
when the monopolar system is put into service to the time when the bipolar system is put
into service is typically used;
b) the amplitude of the maximum overload current is typically 1,1~1,3 I . The maximum
N
duration of this current is generally the time allowed for operation at maximum overload
current after the cooling equipment is put into service;
c) the amplitude of the maximum transient overcurrent is determined through system stability
calculation, typically in the range of 1,25~1,5 I . The maximum duration is generally a few
N
or less than 1 s;
d) the amplitude of unbalanced current is the difference of the operating currents of two
...