oSIST prEN ISO 24695:2026

Oil and gas industries including lower carbon energy - The effects of High Voltage DC interference to buried pipelines - Measures to be implemented (ISO/DIS 24695:2026)

This document describes technical measures to be carried out at crossings and parallelisms of buried
metal pipelines influenced by HVDC systems.
It provides guidance on how the design, construction, operation, maintenance, and decommissioning
phases of HVDC systems affect buried metal pipelines.
Electrical interference conditions (AC and DC) to pipeline systems are described, and acceptable levels
of interference are discussed.
Minimum separation distances are recommended.
The following aspects are not covered in this document:
-Contractual responsibilities
-Personnel safety

Öl‑ und Gasindustrie einschließlich kohlenstoffarmer Energieträger - Auswirkungen von Hochspannungs‑Gleichstrom‑Interferenzen auf erdverlegte Rohrleitungen - Umzusetzende Maßnahmen (ISO/DIS 24695:2026)

Les effets de l'interférence de la Haute Tension CC sur les pipelines enterrés - Mesures à mettre en oeuvre (ISO/DIS 24695:2026)

Naftna in plinska industrija, vključno z nizkoogljično energijo - Vplivi visokonapetostnih motenj enosmernega toka (DC) na vkopane cevovode - Ukrepi za izvajanje (ISO/DIS 24695:2026)

Ta dokument opisuje tehnične ukrepe, ki jih je treba izvesti na križiščih in vzporednostih zakopanih kovinskih cevovodov, na katere vplivajo HVDC sistemi.
Ponuja smernice o tem, kako faze načrtovanja, gradnje, obratovanja, vzdrževanja in razgradnje HVDC sistemov vplivajo na zakopane kovinske cevovode.
Opisani so pogoji električnih motenj (AC in DC) na cevovodne sisteme, razpravljeni pa so tudi sprejemljivi nivoji motenj.
Priporočene so minimalne varnostne razdalje.
Naslednji vidiki niso zajeti v tem dokumentu:
- Pogodbene odgovornosti
- Varnost osebja

General Information

• Status: Not Published
• Public Enquiry End Date: 14-Jun-2026
• ICS: 29.240.99 - Other equipment related to power transmission and distribution networks
• ICS: 75.200 - Petroleum products and natural gas handling equipment
• Technical Committee: IPKZ - Protection of metals against corrosion
• Current Stage: 4020 - Public enquire (PE) (Adopted Project)
• Start Date: 09-Apr-2026
• Due Date: 27-Aug-2026
• Ref Project: prEN ISO 24695 - Oil and gas industries including lower carbon energy - The effects of High Voltage DC interference to buried pipelines - Measures to be implemented (ISO/DIS 24695:2026)

Overview

oSIST prEN ISO 24695:2026:2026 - "Oil and gas industries including lower carbon energy – The effects of High Voltage DC interference to buried pipelines – Measures to be implemented" - is a proposed European and ISO standard developed by CEN. This document provides comprehensive guidance for managing and mitigating the effects of high voltage direct current (HVDC) system interference on buried metal pipelines. It addresses technical measures across the full pipeline lifecycle: design, construction, operation, maintenance, and decommissioning.

The standard focuses on pipeline systems in the oil, gas, and emerging lower carbon energy sectors when affected by HVDC installations. With the increase in HVDC projects for bulk power transmission, underground and subsea cable systems are often installed in proximity to critical pipeline networks, raising concerns about DC and electromagnetic interference (EMI), corrosion risks, and operational integrity.

Key Topics

• HVDC System Interference:
  The document details how both DC and electromagnetic interference from HVDC power transmission systems can impact buried pipelines.

  • DC interference, particularly under earth return operation or fault conditions, can accelerate corrosion on pipeline exteriors.
  • Electromagnetic interference (EMI) can induce hazardous voltages and increased corrosion risk, especially in areas where HVDC lines run parallel or cross pipelines.

• Technical and Mitigative Measures:
  The standard outlines technical approaches for minimising interference risks, including:

  • Determining minimum safe separation distances between HVDC installations and pipeline routes.
  • Calculation and measurement methods to assess interference during all project phases.
  • Protective criteria for both DC and EMI conditions to ensure pipeline integrity.
  • Risk assessment based on HVDC operational modes (monopolar, bipolar, fault scenarios).

• Lifecycle Application:
  This standard applies throughout the pipeline lifecycle:

  • Design and planning: evaluating HVDC impacts before construction.
  • Installation: implementing precautionary crossing and separation measures.
  • Operation and maintenance: ongoing monitoring, measurement, and coordination between HVDC and pipeline operators.
  • Decommissioning: addressing legacy HVDC impacts on pipelines.

• Operational Coordination:
  Guidelines are included for information sharing and emergency planning between pipeline and HVDC system operators to ensure rapid response and risk mitigation.

Applications

This standard is practical for several key applications in the energy sector:

• Oil and Gas Pipelines: Ensuring the safe and reliable operation of buried metal pipelines in regions with new or existing HVDC transmission infrastructure.
• Lower Carbon Energy Projects: Applicable to hydrogen, biogas, and CO₂ pipelines, supporting the transition to low-carbon networks co-located with HVDC systems.
• HVDC Transmission Planning: Enabling power sector stakeholders to design transmission routes and converter stations with minimal impact on existing underground infrastructure.
• Engineering and Asset Integrity: Assisting engineers, asset managers, and corrosion specialists in assessing, modelling, and mitigating the impacts of DC and EMI on pipeline assets.

Related Standards

For complete compliance and best practice, oSIST prEN ISO 24695:2026 should be used together with the following standards:

• ISO 15589-1:2015: Petroleum, petrochemical and natural gas industries – Cathodic protection of pipeline systems – Part 1: On-land pipelines
• ISO 18086:2019: Corrosion of metals and alloys – Determination of AC corrosion – Protection criteria
• ISO 21857:2021: Prevention of corrosion on pipeline systems influenced by stray currents
• IEC 61936-2:2023: Power installations exceeding 1 kV AC and 1.5 kV DC – Part 2: DC
• EN 50443:2011: Effects of electromagnetic interference on pipelines caused by high voltage AC electric traction systems and power supply systems

Practical Value

By adopting oSIST prEN ISO 24695:2026:

• Pipeline and HVDC system operators reduce the risk of corrosion, equipment damage, and operational hazards due to DC and electromagnetic interference.
• Infrastructure planners can make informed decisions on transmission and pipeline corridor layouts.
• The standard provides a common technical reference to facilitate coordination and safe integration of power and pipeline infrastructure in evolving energy systems.
• Enhances asset protection and regulatory compliance in the context of expanding HVDC grids and sustainable pipeline networks.

Standards Content (Sample)

SLOVENSKI STANDARD
01-junij-2026
Naftna in plinska industrija, vključno z nizkoogljično energijo - Vplivi
visokonapetostnih motenj enosmernega toka (DC) na vkopane cevovode - Ukrepi
za izvajanje (ISO/DIS 24695:2026)
Oil and gas industries including lower carbon energy - The effects of High Voltage DC
interference to buried pipelines - Measures to be implemented (ISO/DIS 24695:2026)
Öl‑ und Gasindustrie einschließlich kohlenstoffarmer Energieträger - Auswirkungen von
Hochspannungs‑Gleichstrom‑Interferenzen auf erdverlegte Rohrleitungen -
Umzusetzende Maßnahmen (ISO/DIS 24695:2026)
Les effets de l'interférence de la Haute Tension CC sur les pipelines enterrés - Mesures
à mettre en oeuvre (ISO/DIS 24695:2026)
Ta slovenski standard je istoveten z: prEN ISO 24695
ICS:
29.240.99 Druga oprema v zvezi z Other equipment related to
omrežji za prenos in power transmission and
distribucijo električne energije distribution networks
75.200 Oprema za skladiščenje Petroleum products and
nafte, naftnih proizvodov in natural gas handling
zemeljskega plina equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 24695
ISO/TC 67/SC 2
Oil and gas industries including
Secretariat: UNI
lower carbon energy — The effects
Voting begins on:
of High Voltage DC interference to
2026-03-30
buried pipelines — Measures to be
Voting terminates on:
implemented
2026-06-22
ICS: 75.200; 29.240.99
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS.
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Reference number
ISO/DIS 24695:2026(en)
DRAFT
ISO/DIS 24695:2026(en)
International
Standard
ISO/DIS 24695
ISO/TC 67/SC 2
Oil and gas industries including
Secretariat: UNI
lower carbon energy — The effects
Voting begins on:
of High Voltage DC interference to
buried pipelines — Measures to be
Voting terminates on:
implemented
ICS: 75.200; 29.240.99
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2026
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
BE CONSIDERED IN THE LIGHT OF THEIR
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
or ISO’s member body in the country of the requester.
NATIONAL REGULATIONS.
ISO copyright office
RECIPIENTS OF THIS DRAFT ARE INVITED
CP 401 • Ch. de Blandonnet 8
TO SUBMIT, WITH THEIR COMMENTS,
CH-1214 Vernier, Geneva
NOTIFICATION OF ANY RELEVANT PATENT
Phone: [phone]
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 24695:2026(en)
ii
ISO/DIS 24695:2026(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviations and symbols . 5
5 Definition of an HVDC transmission system . 5
6 Sources of Interference . 7
6.1 General .7
6.2 DC Interference .7
6.3 Electromagnetic Interference (EMI) . .7
6.4 Converters .8
6.5 HVDC Overhead Power lines (normal and fault conditions) .8
6.5.1 Inductive Coupling .8
6.5.2 Conductive Coupling .8
6.5.3 Normal Operating Conditions .8
6.5.4 Maintenance Operation .8
6.5.5 Abnormal Conditions.8
6.5.6 Fault Conditions .9
6.6 HVDC buried power cables (normal and fault conditions) .9
6.6.1 General .9
6.6.2 Normal operating conditions .9
6.6.3 Fault conditions .9
6.6.4 Inductive coupling . .9
6.6.5 Conductive coupling .10
6.7 Earth Electrodes .10
6.8 Earth electrode line .10
6.9 Corona .10
7 Measurements and calculations of Interference to buried pipelines .11
7.1 General .11
7.2 Calculations during the planning and design phases . 12
7.2.1 DC interference . 12
7.2.2 EMI – Electromagnetic Interference . 12
7.3 Measurements during operation stage . 13
7.4 Zone of influence and separation distances (DC interference) .14
7.5 Zone of Influence and separation distances (EMI) .14
8 Effects of HVDC interference and Classification of Risk .15
9 Interference to buried pipelines by monopolar HVDC systems .15
9.1 DC Interference risk level – Monopolar systems . 15
9.2 EMI Risks –Monopolar systems .16
9.2.1 Normal operating conditions .16
9.2.2 DC Transient fault conditions . .16
10 Interference to pipelines by Bipolar HVDC systems . 17
10.1 DC Interference risk level – Bipolar systems (normal operation) .17
10.2 EMI Risks –Bipolar systems.18
10.2.1 Normal Operating conditions .18
10.2.2 DC Transient fault conditions . .19
11 Protection Criteria . 19
11.1 Protection criteria (DC Interference) .19
11.1.1 Anodic interference .19

iii
ISO/DIS 24695:2026(en)
11.1.2 Cathodic interference . 20
11.1.3 Protection Criteria (EMI) . 20
12 Thermal influence of the HVDC system.20
13 HVDC projects and existing adjacent infrastructure .21
14 Operational Information Exchange and Coordination for Pipeline and HVDC Systems .21
14.1 Operational information exchange .21
14.2 Normal operation . 22
14.2.1 Pipeline operator measures and possible impacts on HVDC systems . 22
14.2.2 HVDC operator’s measures with possible impact on other pipelines . 23
14.3 Emergency operation . . 23
14.3.1 Exceptional operation of pipeline systems . 23
14.3.2 HVDC systems . . . 23
14.4 Changes to crossings and proximity points .24
Annex A (informative) HVDC CONFIGURATIONS .25
Annex B (informative) CORONA .31
Annex C (informative) Competence requirements for modellers assessing HVDC interference
on pipeline systems .33
Annex D (informative) Earth Potential Rise .36
Annex E (informative) BARNES LAYER .39
Annex F (informative) Method to determine the soil potential to remote earth through voltage
gradient measurements . 41
Annex G (informative) Principles of the influence of direct currents from external sources on
buried metal pipelines .43
Annex H (informative) Technical measures for design phase of the HVDC system . 47
Annex I (informative) Separation distances under DC interference.49
Annex J (informative) Separation distance under DC side fault conditions (inductive coupling) .53
Bibliography .57

iv
ISO/DIS 24695:2026(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent
rights identified during the development of the document will be in the Introduction and/or on the ISO list of
patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,
as well as information about ISO's adherence to the World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee TC 67, Subcommittee SC 2.
A list of all parts in the ISO series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

v
ISO/DIS 24695:2026(en)
Introduction
The International Organization for Standardization (ISO) [and/or] International Electrotechnical
Commission (IEC) draw[s] attention to the fact that it is claimed that compliance with this document may
involve the use of a patent.
ISO [and/or] IEC take[s] no position concerning the evidence, validity and scope of this patent right.
The holder of this patent right has assured ISO [and/or] IEC that he/she is willing to negotiate licences under
reasonable and non-discriminatory terms and conditions with applicants throughout the world. In this
respect, the statement of the holder of this patent right is registered with ISO [and/or] IEC. Information may
be obtained from the patent database available at www.iso.org/patents.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights other than those in the patent database. ISO [and/or] IEC shall not be held responsible for identifying
any or all such patent rights.

vi
DRAFT International Standard ISO/DIS 24695:2026(en)
Oil and gas industries including lower carbon energy — The
effects of High Voltage DC interference to buried pipelines —
Measures to be implemented
1 Scope
This document describes technical measures to be carried out at crossings and parallelisms of buried metal
pipelines influenced by HVDC systems. It provides guidance on how the design, construction, operation,
maintenance, and decommissioning phases of HVDC systems affect buried metal pipelines. Electromagnetic,
DC interference and thermal influences on pipeline coatings are described.
Acceptable levels of interference are discussed.
Guidance is provided for calculation methods to establish an acceptable separation distance between the
pipeline and the source of interference.
The following aspects are not covered in this document:
— Interference from other AC sources
— Contractual responsibilities
— Personnel safety.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 15589-1:2015, Petroleum, petrochemical and natural gas industries — Cathodic protection of pipeline
systems — Part 1: On-land pipelines
ISO 18086:2019, Corrosion of metals and alloys — Determination of AC corrosion — Protection criteria
ISO 21857:2021, Petroleum, petrochemical and natural gas industries — Prevention of corrosion on pipeline
systems influenced by stray currents
IEC 60479-1:2018 ED1:2018, Effects of current on human beings and livestock - Part 1: General aspects
IEC 61936-2:2023 ED1:2023, Power installations exceeding 1 kV AC and 1,5 kV DC - Part 2: DC
EN 50443:2011, Effects of electromagnetic interference on pipelines caused by high voltage a.c. electric traction
systems and/or high voltage a.c. power supply systems
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp

ISO/DIS 24695:2026(en)
3.1
High-voltage direct-current system (HVDC system)
power transmission system that transfers energy using direct current at high voltage between two or
more grid connection points. The system consists of at least two converter substations with corresponding
earthing systems and direct current transmission lines (overhead lines or buried or immersed cables)
3.2
conductive coupling
transfer of energy occurring when a part of the current belonging to the interfering system returns to the
system earth via the interfered system
Note 1 to entry: Also, when the voltage to the reference earth of the ground in the vicinity of the influenced object
rises because of a default in the interfering system, and the results of which are conductive voltages and currents.
3.3
Electromagnetic Interference (EMI)
interference phenomenon resulting from conductive, capacitive and inductive coupling between systems
and which can cause disturbance, malfunction, damage and danger
[SOURCE: EN 50443:2011]
3.4
earth electrode
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
[1]
[SOURCE: IEC TS 62344:2022 ED2:2022 ]
3.5
pond electrode
electrode usually placed outside but within 100 m of the waterline, having electrodes directly in contact
with the seawater, within a small area which is usually protected against waves and possible ice damage by
a breakwater
[1]
[SOURCE: IEC TS 62344:2022 ED2:2022 ]
3.6
sea electrode
electrode located away from the shoreline at a distance deeper than 100 m into the sea
[1]
[SOURCE: IEC TS 62344:2022 ED2:2022 ]
3.7
electrode station
whole facility which transfers current to/from the electrode line (3.8) to/from the earth or sea water, usually
including the feeding cable, towers, switchgear, fencing an any necessary auxiliary equipment in addition to
the electrode itself
[1]
[SOURCE: IEC TS 62344:2022 ED2:2022 ]
3.8
electrode line
overhead line or underground cable used to connect the neutral bus in a converter station to the earth
electrode (3.4) station
[1]
[SOURCE: IEC TS 62344:2022 ED2:2022 ]

ISO/DIS 24695:2026(en)
3.9
earth return operation mode
operation mode in the HVDC power transmission system, using DC lines and earth (or seawater) as the
current loop
[1]
[SOURCE: IEC TS 62344:2022 ED2:2022 ]
3.10
earth return system
set of devices designed and built specifically for earth return operation mode (3.9)
Note 1 to entry: It mainly consists of the electrode line (3.8), earth electrode (3.4), current guiding system, and other
auxiliary facilities.
[1]
[SOURCE: IEC TS 62344:2022 ED2:2022 ]
3.11
unbalanced current
difference of current between two poles during operation of a bipolar DC system (3.16)
Note 1 to entry: For balanced bipolar operation mode, the unbalanced current flowing can be controlled automatically
by the control system with about 1% of the related current.
Note 2 to entry: For balanced bipolar operation mode, the current flowing through the earth electrode (3.4) is the
difference in currents between the two poles.
[1]
[SOURCE: IEC TS 62344:2022 ED2:2022 ]
3.12
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 conditions of the device. In other cases, (e.g. electronic tubes and semiconductor
devices). The term “cathode” is assigned to a specific electrode.
[2]
[SOURCE: IEC 60050-151:2001/AMD3:2019 ED2:2019 ]
3.13
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.
[2]
[SOURCE: IEC 60050-151:2001/AMD3:2019 ED2:2019 ]
3.14
DC neutral point
common point of two monopoles forming a bipole converter or the earthed point of a monopole converter
[SOURCE: IEC 61936-2:2023 ED1:2023]

ISO/DIS 24695:2026(en)
3.15
DC electrode line
electrical connection between a DC earth electrode (3.20) and the DC installation
[SOURCE: IEC 61936-2:2023 ED1:2023]
3.16
DC system
all interconnected parts of a power system installation that is installed between and including the DC side
windings of the interface/converter transformers at each terminal except for the valve hall or converter hall
Note 1 to entry: Components connected to the AC side windings of the converter/interface transformers including the
AC windings themselves are not considered to be part of the DC system as defined for this standard.
[SOURCE: IEC 61936-2:2023 ED1:2023]
3.17
high voltage
DC voltage exceeding 1500 V DC
[SOURCE: IEC 61936-2:2023 ED1:2023]
3.18
converter unit
indivisible operative unit comprising all equipment between the point of connection on the AC side (or DC
side for DC/DC converters) and the point of connection on the DC side, essentially one or more converters,
together with converter transformers, control equipment, essential protective and switching devices and
auxiliaries, if any, used for conversion
[SOURCE: IEC 61936-2:2023 ED1:2023]
3.19
converter station
part of a DC system (3.16) which consists of one or more converter units (3.18) including DC switchgear, DC
fault current controlling devices, if any, installed in a single location together with buildings, reactors, filters,
reactive power supply, control, monitoring, protective, measuring and auxiliary equipment
[SOURCE: IEC 61936-2:2023 ED1:2023]
3.20
DC earth electrode
array of conductive elements placed in the earth, or the sea, which provides a low resistance path between a
point in the DC system (3.16) and the earth and is capable of carrying continuous current for some extended
period
Note 1 to entry: An earth electrode (3.4) may be located at a point some distance from the HVDC substation.
Note 2 to entry: Where the electrode is placed in the sea, it may be termed as a sea electrode (3.6).
[SOURCE: IEC 61936-2:2023 ED1:2023]
3.21
Voltage source converter (VSC)
electronic device that converts DC voltage into AC voltage, or vice versa, by controlling the voltage and
frequency of the output AC waveform
Note 1 to entry: Usually using an Insulated Gate Bipolar Transistor (IGBT) and an AC filter.
3.22
thermal conductivity
measure of the ability of a material to conduct heat

ISO/DIS 24695:2026(en)
3.23
normal operation
operational state in which the system functions within its prescribed design parameters, without activation
of protective actions or alarms, while all subsystems operate as intended
3.24
maintenance operation
operational state in which the system functions within its prescribed design parameters for routine
maintenance
Note 1 to entry: This can include a bipolar system operating in monopolar configuration.
3.25
abnormal operation
operational state in which the system functions outside its prescribed specified design parameters
Note 1 to entry: This includes commissioning, and testing.
3.26
fault conditions
condition initiated by the detection of an electrical fault within an HVDC system, where automated
protection systems activate to isolate, clear, or mitigate the fault while preserving equipment integrity and
grid stability
4 Abbreviations and symbols
AGI Above Ground Installation
CP Cathodic Protection
CSC Current Source Converters
csv Comma Separated Value
EMI Electromagnetic interference
EPR Earth Potential Rise
NOTE Synonymous with ROEP (rise of earth potential) and GPR (ground potential rise).
FFT Fast Fourier Transform
HVAC High Voltage AC
HVDC High Voltage DC
IGBT Insulated Gate Bipolar Transistor
LCC Line Commutated Converter
RMS Root Mean Square
VSC Voltage Source Converter
5 Definition of an HVDC transmission system
A typical HVDC (High Voltage Direct Current) transmission system consists of two main terminals (Figure 1),
the sending terminal and the receiving terminal.

ISO/DIS 24695:2026(en)
At the sending terminal, there is a converter that functions as a rectifier, converting alternating current (AC)
power from the grid into direct current (DC).
Conversely, at the receiving terminal, there is another converter acting as an inverter, which converts the DC
power back into AC for distribution into a local grid.
The connection between the sending and receiving terminals can be established using overhead lines,
underground/submarine cables, or a combination of both, depending on factors such as distance,
environmental considerations, and project requirements.
Inside the converters, power electronic valves, which are essentially high-powered electronic switches,
facilitate the control of power flow. These valves enable precise regulation of the electricity being
transmitted, allowing for efficient and reliable operation.
Modern HVDC systems use two main converter technologies, conventional line-commutated current source
converters (CSCs) and self-commutated voltage source converters (VSCs), which can be part of different
systems like back-to-back, monopolar, bipolar, homopolar, and multi-terminal setups. Additional schematic
diagrams and explanatory notes can be found in Annex A.
Depending on the technology, HVDC systems can operate differently under normal, emergency, and fault
condition.
One key feature of HVDC systems is their ability to reverse the direction of power flow as needed. This
is achieved by configuring the converters at the terminals to operate as either rectifiers or inverters
interchangeably. As a result, power can be transmitted bi-directionally, providing flexibility and enhancing
the system's overall reliability. More details on HVDC configurations can be found in Annex A.
Key
1 converter transformer
2 converter (I)
3 converter (II)
4 converter station
5 DC Line
6 AC grid (I)
7 AC grid (II)
8 DC power transmission system
Figure 1 — HVDC Power Transmission Structure (Simplified Layout)

ISO/DIS 24695:2026(en)
6 Sources of Interference
6.1 General
The technology of HVDC systems entails topologies, components and operating characteristics that affect
the interference situations (DC interference and Electromagnetic Interference (EMI)) and impacts on
pipeline systems.
6.2 DC Interference
DC interference, caused by HVDC systems, is a disturbance that primarily affects metallic pipelines through
conduction via the earth or other electrolytes. For buried or submerged pipelines, this interference can
accelerate corrosion on their external surfaces. The corrosive effect is mainly due to the combination of the
[3]
earth/seawater return current's magnitude and the duration of exposure .
DC interference can arise from:
— The normal operation of unbalanced monopole configurations, using electrodes to facilitate current
return through the earth or sea.
— The normal operation of bipolar configurations, where electrodes are used to conduct any unbalanced
current that arises between the two poles of the system. This unbalanced current, typically limited to
0.5% to 1% of the rated current of each pole, results from minor differences between the converter units
at each station.
— Temporary operation (e.g. maintenance or emergencies) of bipolar configurations that are run as
monopolar systems, using electrodes to facilitate current return through the earth or sea.
6.3 Electromagnetic Interference (EMI)
— Close proximity of HVDC and pipeline systems can result in circumstances that give rise to increased
external corrosion risks to the pipeline, hazardous electrical conditions (e.g. touch voltages) on the
interfered pipelines and associated systems.
— Consideration should be given to:
— the impact of harmonic currents and voltages on the DC side, under the normal operating conditions
of the HVDC systems
— the impact of DC-side fault conditions of the HVDC systems
NOTE The DC-side fault conditions are described in §10.3.2 of IEC 61936-2:2023 ED1:2023
— monopolar operations.
DC side faults within the HVDC installation site shall be assessed to identify the worst-case scenario for
Electromagnetic Interference (EMI) affecting nearby pipeline systems. The types of faults that can be
relevant, include:
— Pole-to-earth fault
— Two-pole-to-earth fault
— Metallic-return-to-earth fault
— Electrode-line-to-earth fault.
The HVDC operator can provide the pipeline operator or owner with waveform data for short-circuit
currents for each type of DC fault type, including the fault time duration for each case.

ISO/DIS 24695:2026(en)
6.4 Converters
The normal operation of HVDC systems fundamentally entails a constant or static DC magnetic field emission.
However, consideration should be given to the effect of harmonic currents and harmonic voltages on the
HVDC system. The generation and propagation of harmonics is dependent on the type of DC converters of the
HVDC system. The harmonic profile of the DC converters is influenced by whether the converters are line-
commutated converters (LCC) or voltage-sourced converters (VSC) [§ 4.2.9 IEC 61936-2:2023 ED1:2023].
Harmonics can cause interference in nearby pipeline systems through inductive coupling. While most
inductive coupling calculations focus on the fundamental frequency (50/60 Hz), the presence of harmonics
introduces the risk of unacceptable levels of higher-frequency inductive coupling, on pipelines. Thus, the
effect of harmonics generated by the HVDC system on nearby pipelines and other infrastructure located
close to DC overhead lines or cables should be examined.
To avoid unacceptable risks to the integrity of the pipeline the operator will need to know the induced
voltages. The HVDC system operator and the pipeline operator shall collaborate to provide all the information
necessary for the induced voltage calculations.
6.5 HVDC Overhead Power lines (normal and fault conditions)
Interference situations on pipeline systems from HVDC overhead power lines can occur under normal,
maintenance, abnormal operation and fault conditions.
Where applicable, inductive and conductive effects shall be combined, to comprehensively address any
adverse effects on the pipelines.
6.5.1 Inductive Coupling
The inductive coupling is possible because DC faults, even of short duration, are generally fast transient
phenomena. Thus, the fault current comprises a wide frequency spectrum, ranging from relatively low
frequencies to several thousand hertz (kHz). Therefore, significant inductive interference can occur under
DC fault conditions, on nearby pipelines.
6.5.2 Conductive Coupling
When a DC ground fault occurs at an overhead line structure, a nearby pipeline can be also influenced
through conductive coupling. This can occur when a large fault current flowing into the earth from the
structure (e.g. lattice tower) increases the earth potential local to the pipeline. This causes the earth around
the pipeline to be at a relatively high potential with respect to the pipeline metal potential. This can result in
increased coating stress voltages on the pipeline.
6.5.3 Normal Operating Conditions
Some degree of inductive coupling with buried pipelines can be expected. Inductive coupling is typically
more of a concern with AC systems in the vicinity of pipeline systems. It can still occur under the normal
operation of the HVDC systems, particularly when the harmonics generated by the converters are
propagated in the DC overhead power lines. The presence of harmonics introduces the risk of unacceptable
levels of higher-frequency inductive coupling.
6.5.4 Maintenance Operation
A higher level of interference is to be expected since the operating parameters are different from normal
operation. Under monopolar operation some interference mechanisms will be exacerbated.
6.5.5 Abnormal Conditions
Abnormal conditions cover many scenarios. Control systems will quickly adjust the operating conditions
to safe limits, which can result in exacerbated interference. Under monopolar operation some interference
mechanisms will be exacerbated.

ISO/DIS 24695:2026(en)
6.5.6 Fault Conditions
During DC-side fault conditions on HVDC overhead power lines, buried pipelines can experience both
inductive and conductive coupling effects.
6.6 HVDC buried power cables (normal and fault conditions)
6.6.1 General
Interference situations on pipeline systems from HVDC buried cables can occur under both normal and fault
conditions. These interference situations originate from the rich frequency spectrum of the DC fault current
as well as from possible injections of the fault current into the earth in areas that are common to buried
pipeline routings.
For assessing EMI from HVDC cable networks, it is necessary to understand and account for the electrical-
circuit behaviour and topology/technology of the systems involved. To comprehend the behaviour of a HVDC
system under DC-side faults, it is essential to know:
— the functional and protective earthing configurations of the system,
— winding configurations of the interface/converter transformers,
— the type of cables and their bonding configuration,
— the converters’ operational configuration.
These elements will principally determine the stages of a DC-side fault response as well as its peak value.
[4]
Typically, the DC fault analysis of such systems can be confined into two stages :
1) the capacitive discharge stage
2) the AC grid side current feeding stage.
During Stage 1 the stored DC side capacitive energy of the system (including cables) will be discharged
through the ground fault. This will result in a transient current flowing for some milliseconds.
During Stage 2, it is possible to have AC grid current feeding the DC side fault (through the IGBT anti-parallel
diodes or protective thyristors), until the converter’s AC breaker is tripped. If the converter is of the fault-
blocking type, the contribution to the DC fault current is blocked or considerably reduced by the converter.
6.6.2 Normal operating conditions
Under normal operating conditions, some inductive coupling with buried pipelines can occur when
harmonics propagate through the HVDC cable. However, the cable's metallic sheath can act as a shield if it is
grounded at both ends. This limits the inductive coupling, thereby reducing the severity of the interference
situation.
6.6.3 Fault conditions
During DC-side fault conditions on HVDC DC power cables, buried pipelines can experience both inductive
and conductive coupling effects.
6.6.4 Inductive coupling
Inductive coupling is possible because DC faults, even of short duration, are
...