IEC TS 62344:2022

IEC TS 62344 ®
Edition 2.0 2022-05
TECHNICAL
SPECIFICATION
colour
inside
Design of earth electrode stations for high-voltage direct current (HVDC) links –
General guidelines
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IEC TS 62344 ®
Edition 2.0 2022-05
TECHNICAL
SPECIFICATION
colour
inside
Design of earth electrode stations for high-voltage direct current (HVDC) links –
General guidelines
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.240.99 ISBN 978-2-8322-1035-2
– 2 – IEC TS 62344:2022 © IEC 2022
CONTENTS
FOREWORD . 9
INTRODUCTION . 11
1 Scope . 12
2 Normative references . 12
3 Terms and definitions . 12
4 System conditions . 16
4.1 General principles . 16
4.2 System parameters related to earth electrode design . 16
4.2.1 Amplitude and duration of the current . 16
4.2.2 Polarity . 16
4.2.3 Designed lifespan . 16
4.2.4 Common earth electrodes . 17
5 Design of land electrode stations . 17
5.1 Main technical parameters . 17
5.1.1 General principles . 17
5.1.2 Temperature rise . 17
5.1.3 Earthing resistance . 17
5.1.4 Step voltage . 18
5.1.5 Touch voltage . 19
5.1.6 Current density . 19
5.1.7 Field intensity in fish ponds . 19
5.2 Electrode site selection and parameter measurement . 19
5.2.1 General principles . 19
5.2.2 Data collection survey . 20
5.2.3 Distance from converter station (substation) . 20
5.2.4 Environment conditions, terrain and landform . 20
5.2.5 Geophysical and geological surveys . 20
5.2.6 Topographical map . 20
5.2.7 Values selected during design . 20
5.3 Earth electrode and associated components . 21
5.3.1 General principles for material selection . 21
5.3.2 Selection of electrode elements and characteristics . 21
5.3.3 Chemical and physical properties of petroleum coke . 22
5.3.4 Current-guiding system . 22
5.3.5 Bus . 22
5.3.6 Electrode line and its monitoring device . 23
5.4 Electrode arrangement . 23
5.4.1 General principles . 23
5.4.2 Filling coke . 23
5.4.3 Selection of earth electrode shape . 23
5.4.4 Earth electrode corridor (right of way) . 24
5.4.5 Distance between sub-electrodes in the arrangement . 24
5.4.6 Burial depth of the earth electrodes . 24
5.4.7 Segmentation of earth electrodes . 25
5.5 Minimum size of earth electrode. 25
5.5.1 General principles . 25

5.5.2 Total earth electrode length . 25
5.5.3 Area of the surface of the coke-soil interface . 25
5.5.4 Diameter of electrode elements . 26
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 . 27
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 . 28
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 . 29
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 Moisture replenishment . 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 General . 30
6.1.2 Temperature rise . 30
6.1.3 Earthing resistance . 30
6.1.4 Step voltage . 30
6.1.5 Touch voltage . 30
6.1.6 Voltage gradient in water . 30
6.1.7 Current density . 31
6.2 Electrode site selection and parameter measurement . 31
6.2.1 General principles . 31
6.2.2 Data collection survey . 31
6.2.3 Distance from converter station (substation) . 31
6.2.4 Environment conditions . 31
6.2.5 Measurement of ground/water parameters . 32
6.3 Earth electrode and associated components . 32
6.3.1 General principles for material selection . 32
6.3.2 Common electrode elements and characteristics . 32
6.3.3 Chemical properties of petroleum coke . 33
6.3.4 Current-guiding system . 33
6.3.5 Bus . 33
6.3.6 Electrode line monitoring device . 33
6.4 Electrode arrangement . 33
6.4.1 General principles . 33
6.4.2 Filling coke . 33

– 4 – IEC TS 62344:2022 © IEC 2022
6.4.3 Selection of earth electrode shape . 33
6.4.4 Segmentation of earth electrodes . 34
6.5 Current-guiding system . 34
6.5.1 Placement of the current-guiding wire . 34
6.5.2 Connection of current-guiding system . 34
6.5.3 Selection of cable cross-section . 35
6.5.4 Insulation of the current-guiding system . 35
6.5.5 Selection of cable structure . 35
6.5.6 Mechanical protection for cable . 35
6.6 Auxiliary facilities . 35
7 Impact on surrounding facilities and mitigation measures . 35
7.1 Impact on insulated metallic structures and mitigation measures. 35
7.1.1 General principles . 35
7.1.2 Relevant limits . 36
7.1.3 Mitigation measures. 36
7.2 Impact on bare metallic structures . 36
7.2.1 General principles . 36
7.2.2 Relevant limits . 36
7.2.3 Mitigation measures. 36
7.3 Impact on the power system (power transformer, grounding network, and
surrounding towers) . 36
7.3.1 General principles . 36
7.3.2 Relevant limits . 37
7.3.3 Mitigation measures. 37
7.4 Impact on electrified railway . 37
7.5 Other facilities (such as greenhouses and water pipes) . 37
Annex A (informative) Basic concepts of earth electrodes . 38
A.1 Basic concepts . 38
A.2 Operation mode . 38
A.2.1 General . 38
A.2.2 Monopolar system . 38
A.2.3 Bipolar system . 39
A.2.4 Symmetric unbalanced system. 41
A.2.5 Back-to-back converter station . 41
A.3 Dangerous impact and accumulated impact . 41
A.3.1 General . 41
A.3.2 Safety risks of DC earth electrode . 41
A.3.3 Accumulated effect of DC earth electrodes . 46
A.4 Impact on an AC grid . 47
A.4.1 General . 47
A.4.2 DC current path to AC system . 48
A.4.3 DC magnetic bias of AC transformer . 48
Annex B (informative) Earth electrode design process . 50
B.1 Site selection process . 50
B.2 Earth electrode design process . 51
Annex C (informative) Test results of human body resistance . 53
C.1 Basic information of test subjects . 53
C.2 Test method . 54
C.3 Test results . 54

Annex D (informative) Soil parameter measurement method . 57
D.1 General requirements . 57
D.2 Measurement of resistivity of shallow ground . 58
D.2.1 Measurement method of resistivity . 58
D.2.2 Measurement requirements . 60
D.2.3 Measurement range . 61
D.2.4 Data accuracy . 61
D.2.5 Seasonal coefficient . 61
D.2.6 Processing of measurement data . 61
D.3 Measurement of resistivity of deep soil (MT method) . 61
D.4 Measurement of soil volume thermal capacity . 62
D.5 Measurement of soil thermal conductivity . 62
D.6 Measurement of maximum natural temperature of soil . 63
D.7 Measurement of soil moisture and groundwater table . 63
D.8 Measurement of soil chemical characteristics . 63
D.9 Geological exploration . 63
D.10 Topographical map . 63
Annex E (informative) Electrode line design . 64
E.1 Overview. 64
E.2 Main design principles . 64
E.3 Selection and layout of conductor and earth wire . 65
E.3.1 Selection of conductor . 65
E.3.2 Selection of earth wire . 65
E.3.3 Layout of conductor and earth wire . 65
E.4 Insulation coordination and earthing for lightning protection . 65
E.4.1 Type and number of insulators . 65
E.4.2 Arcing horn gap . 65
E.4.3 Earthing for lightning protection . 66
E.5 Other considerations . 66
Annex F (informative) Assessment of measurement method . 67
F.1 General guidance . 67
F.2 Experiment (testing) items . 67
F.2.1 Visual inspection of the earth electrode . 67
F.2.2 Current guiding system current distribution measurement . 67
F.2.3 Measurement of earthing resistance . 68
F.2.4 Measurement of step voltage on the ground and potential gradient in
water near the earth electrode . 68
F.2.5 Measurement of touch voltage . 69
F.2.6 Measurement of soil surface potential profile . 69
F.2.7 Measurement of earth electrode temperature rise . 70
Annex G (informative) Earth electrode electrical parameter calculation method. 71
G.1 General . 71
G.2 Network method calculation model for DC earth electrode . 71
G.3 Moment method calculation model for DC earth electrodes . 71
G.4 Finite element method calculation model for DC earth electrodes . 76
G.5 Calculation of earthing resistance, step voltage, touch voltage, electric field
intensity and current density . 78
G.5.1 General . 78
G.5.2 Calculation of earthing resistance . 78

– 6 – IEC TS 62344:2022 © IEC 2022
G.5.3 Calculation of step voltage . 78
G.5.4 Calculation of touch voltage . 78
G.5.5 Calculation of electric field intensity . 78
G.5.6 Calculation of current density . 79
G.6 Application description . 79
G.6.1 Original parameters . 79
G.6.2 Example using the moment method . 79
Annex H (informative) Thermal time constant . 82
Annex I (informative) Online monitoring system . 84
I.1 Schematic diagram of online monitoring system . 84
I.2 Composition of online monitoring system . 84
Annex J (informative) Calculation method for corrosion of nearby metal structures
caused by earth electrodes . 86
J.1 Consumption of metal structure due to corrosion . 86
J.2 Estimate of leakage current in metal pipes . 86
J.3 Calculation of the leakage current of the metal pipe . 87
Annex K (informative) Calculation method for DC current flowing through AC

transformer neutral near earth electrodes . 88
Annex L (informative) Chemical processes in sea electrodes . 91
Annex M (informative) Simple introduction of shore electrodes . 92
M.1 General . 92
M.2 Beach electrodes . 92
M.3 Pond electrodes . 92
Bibliography . 94

Figure 1 – Electrode cross-section . 23
Figure 2 – Vertical arrangement . 24
Figure 3 – Placement of the current-guiding wire . 27
Figure 4 – Feeding cable . 28
Figure 5 – Sea electrode . 33
Figure 6 – Sea bottom electrode with titanium nets . 34
Figure 7 – Titanium net . 35
Figure 8 – Impact of earth electrodes on AC systems (transformer, grounding network,
tower) . 37
Figure A.1 – HVDC power transmission system structure . 38
Figure A.2 – Schematic diagram of monopolar earth/sea water return system . 39
Figure A.3 – Schematic diagram of monopolar dedicated metallic return system . 39
Figure A.4 – Schematic diagram of bipolar earth/sea water system . 39
Figure A.5 – Schematic diagram of rigid bipolar system . 40
Figure A.6 – Schematic diagram of bipolar dedicated metallic return system . 41
Figure A.7 – Schematic diagram of touch voltage and step voltage . 42
Figure A.8 – Schematic diagram of single circular earth electrode . 43
Figure A.9 – Axial distribution of step voltage of single circular earth electrode . 43
Figure A.10 – 3-D distribution of step voltage of single circular earth electrode . 44
Figure A.11 – Schematic diagram of double circular earth electrode . 44
Figure A.12 – Axial distribution of step voltage of double circular earth electrode . 44

Figure A.13 – 3-D distribution of step voltage of double circular earth electrode . 45
Figure A.14 – Schematic diagram of triple circular earth electrode . 45
Figure A.15 – Axial distribution of step voltage of triple circular earth electrode . 46
Figure A.16 – 3-D distribution of step voltage of triple circular earth electrode . 46
Figure B.1 – Flow chart of earth electrode site selection process . 50
Figure B.2 – Flow chart of earth electrode process . 52
Figure C.1 – Age distribution of test samples . 53
Figure C.2 – Height distribution of test samples . 53
Figure C.3 – Weight distribution of test samples . 54
Figure C.4 – Schematic diagram of test circuit . 54
Figure C.5 – Histogram of foot-to-foot human body resistance distribution . 55
Figure C.6 – Cumulative probability distribution of foot-to-foot body resistance by
occupation . 56
Figure D.1 – Equivalent circuit of Wenner method . 59
Figure D.2 – Equivalent circuit of Schlumberger method . 59
Figure D.3 – Equivalent circuit of dipole-dipole method . 60
Figure G.1 – π shape equivalent circuit of an individual earth electrode unit. 71
Figure G.2 – Ohm’s Law applied to cylinder conductor . 72
Figure G.3 – Continuity of axial component of the electric field in the soil and in the
conductor . 72
Figure G.4 – Spatial division of the earth electrode . 72
Figure G.5 – Network for solving axis current . 73
Figure G.6 – Horizontally layered soil . 74
Figure G.7 – Geometrical structure of a tetrahedron unit . 76
Figure G.8 – Structure of a double-circle DC earth electrode . 80
Figure G.9 – Ground potential and step voltage distribution of a double-circle earth
electrode . 81
Figure H.1 – Earth electrode temperature rise characteristics . 82
Figure I.1 – Schematic diagram of earth electrode online monitoring system . 84
Figure J.1 – Calculation of current flowing through a metal pipe . 87
Figure K.1 – Schematic diagram of ground resistance network and underground
voltage source . 88
Figure K.2 – Circuit model for the analysis of DC distribution of AC systems. 90
Figure M.1 – Top view of shore electrode, beach type . 92
Figure M.2 – Shore electrode, pond type . 92

Table 1 – Composition of iron-silicon alloy electrode . 22
Table 2 – Chemical composition of the petroleum coke after calcination . 22
Table 3 – Physical properties of petroleum coke used for earth electrodes . 22
Table 4 – Electric corrosion characteristics of different materials . 26
Table C.1 – Statistical test results (foot-to-foot body resistance) . 55
Table C.2 – Cumulative probability distribution of foot-to-foot human body resistance . 56
Table D.1 – Soil (rock) / Water resistivity . 57
Table D.2 – Soil volume thermal capacity . 58

– 8 – IEC TS 62344:2022 © IEC 2022
Table D.3 – Soil thermal conductivity . 58
Table D.4 – Number of measurement points with different potential probes spacing. 61
Table G.1 – Model of soil with two layers . 80

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DESIGN OF EARTH ELECTRODE STATIONS
FOR HIGH-VOLTAGE DIRECT CURRENT (HVDC) LINKS –
GENERAL GUIDELINES
FOREWORD
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IEC TS 62344 has been prepared by IEC technical committee 115: High Voltage Direct Current
(HVDC) transmission for DC voltages above 100 kV. It is a Technical Specification.
This second edition cancels and replaces the first edition published in 2013. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
– Changed the requirement of earthing resistance limit for short-time unipolar earth system in
5.1.3.
– Corrected the coefficient before ρ from 0,015 9 to 0,008 in touch voltage limit calculation
s
formula (3) in 5.1.5.
– Deleted the analytical calculation formulas of earthing resistance for sea and shore
electrodes in 6.1.3.
2 2 2
– Changed the current density limit from 100 A/m to 40 A/m ~ 50 A/m for the sea electrodes
that are not accessible to human beings or to marine fauna in 6.1.7.

– 10 – IEC TS 62344:2022 © IEC 2022
– Extended some detailed technical requirements for the measurement of ground/water soil
parameters in 6.2.5.
– Reformulated the types and characteristics of electrode element material for sea and shore
electrodes in 6.3.2.
– Added an informative Annex B: Earth electrode design process.
– Added an informative Annex C: Test results of human body resistance.
– Deleted the formula for calculating the average soil resistivity using harmonic mean when
processing the measurement data in D.2.6 of Annex D.
– Extended some detailed technical requirements of electrode online monitoring system in
Annex H.
– CIGRE 675:2017 is added to the bibliography.
– Terminology and way of expressions are modified using more commonly used terms in the
HVDC electrode design industries and English speaking countries, so as to make the
readers understand the content more easily.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
115/276/DTS 115/293/RVDTS
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Specification is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
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• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates that it
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INTRODUCTION
The high-voltage DC earth electrode is an important part of the DC power transmission system.
It takes on the task of guiding the current into the earth under the monopolar earth return
operation mode, and the unbalanced current under the bipolar operation mode. Further, it
secures and provides the reference potential of converter neutral point under the bipolar/
monopolar operation mode, to protect the safe operation of the valves.
DC earth electrodes include land electrodes, sea electrodes, and shore electrodes. Today,
there are around tens of DC electrodes in the world. Their influence on the nearby and far away
environment is produced when there is DC current continuously leaking into the earth through
DC 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 ground temperature rise and corrosion
on the electrode;
c) influence on nearby ponds and organisms in the sea;
d) influence on the AC power system, mainly reflected by the DC voltage excursion of
transformer neutral point;
e) influence on buried metallic objects, mainly revealed by the corrosion of buried metallic
pipelines, AC grounding grids, tower foundations for power transmission lines and armoured
cables, etc.
A great deal of experience has been accumulated in the research and design work in many
countries, and relevant national standards or enterprise standards have been developed. The
aim of this document is to develop the design guide for DC earth electrodes, on the site selection,
material selection, shape, buried depth, adoption of equipment and connection styles, etc. It
can be referred to by the electrode design engineers in different countries, to ensure the safe
operation of earth electrode unde
...