IEC 61936-2:2023

IEC 61936-2 ®
Edition 1.0 2023-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Power installations exceeding 1 kV AC and 1,5 kV DC –
Part 2: DC
Installations électriques de puissance de tension supérieure à 1 kV en courant
alternatif et 1,5 kV en courant continu –
Partie 2: Courant continu
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IEC 61936-2 ®
Edition 1.0 2023-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Power installations exceeding 1 kV AC and 1,5 kV DC –

Part 2: DC
Installations électriques de puissance de tension supérieure à 1 kV en courant

alternatif et 1,5 kV en courant continu –

Partie 2: Courant continu
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.020, 29.080.01 ISBN 978-2-8322-7541-2

– 2 – IEC 61936-2:2023 © IEC 2023
CONTENTS
FOREWORD . 6
INTRODUCTION . 9
1 Scope . 10
2 Normative references . 11
3 Terms, definitions, symbols and abbreviated terms . 12
3.1 Terms and definitions . 12
3.2 Symbols and abbreviated terms . 14
4 Fundamental requirements . 14
4.1 General . 14
4.1.1 General requirements . 14
4.1.2 Agreements between supplier and user . 16
4.2 Electrical requirements . 17
4.2.1 Methods of DC neutral point earthing . 17
4.2.2 Voltage classification . 19
4.2.3 Current in normal operation . 19
4.2.4 Short-circuit current . 19
4.2.5 Rated frequency . 19
4.2.6 Corona . 20
4.2.7 Electric and magnetic fields . 20
4.2.8 Overvoltages . 20
4.2.9 Harmonics . 20
4.2.10 Electromagnetic compatibility . 21
4.2.11 Radio interference . 21
4.3 Mechanical requirements . 22
4.4 Climatic and environmental conditions . 22
4.4.1 General . 22
4.4.2 Normal conditions . 23
4.4.3 Special conditions . 24
4.5 Particular requirements . 25
4.5.1 Effects of small animals and micro-organisms. 25
4.5.2 Noise level . 25
4.5.3 Transport . 26
5 Insulation . 26
5.1 General . 26
5.2 Selection of insulation level. 26
5.2.1 General . 26
5.2.2 Consideration of methods of neutral earthing . 26
5.2.3 Consideration of rated withstand voltages for AC and specified
withstand voltages for DC . 26
5.3 Verification of withstand values . 26
5.4 Minimum clearances of live parts . 27
5.5 Minimum clearances between parts under special conditions . 27
5.6 Tested connection zones . 27
6 Electrical Equipment . 28
6.1 General requirements . 28
6.2 Specific requirements . 28

6.2.1 Switching devices . 28
6.2.2 Power transformers and reactors . 28
6.2.3 Prefabricated type-tested switchgear . 28
6.2.4 Instrument transformers . 28
6.2.5 Surge arresters . 29
6.2.6 Capacitors . 29
6.2.7 Line traps . 29
6.2.8 Insulators . 29
6.2.9 Insulated cables . 29
6.2.10 Conductors and accessories . 29
6.2.11 Rotating electrical machines . 29
6.2.12 Generating units . 29
6.2.13 Generating unit main connections . 29
6.2.14 Static converters . 30
6.2.15 Fuses . 30
6.2.16 Electrical and mechanical interlocking . 30
6.2.17 Resistors . 30
6.2.18 Cooling system . 30
7 DC Installations . 30
7.1 General . 30
7.1.1 Common requirements . 30
7.1.2 Circuit arrangement . 31
7.1.3 Documentation . 31
7.1.4 Transport routes . 31
7.1.5 Aisles and access areas . 31
7.1.6 Lighting . 31
7.1.7 Operational safety . 31
7.1.8 Labelling . 31
7.2 Outdoor DC installations of open design . 31
7.2.1 General . 31
7.2.2 Protective barrier clearances . 32
7.2.3 Protective obstacle clearances . 32
7.2.4 Boundary clearances . 32
7.2.5 Minimum height over access area . 32
7.2.6 Clearances to buildings . 33
7.2.7 External fences or walls and access doors . 34
7.3 Indoor DC installations of open design . 34
7.4 Installation of prefabricated type-tested switchgear . 34
7.5 Requirements for buildings . 35
7.5.1 General . 35
7.5.2 Structural provisions . 35
7.5.3 Rooms for switchgear . 35
7.5.4 Maintenance and operating areas . 35
7.5.5 Doors . 36
7.5.6 Draining of insulating liquids . 36
7.5.7 Heating, ventilation and air conditioning (HVAC) . 36
7.5.8 Buildings which require special consideration . 36
7.6 High voltage/low voltage prefabricated substations . 36
7.7 Electrical installations on mast, pole and tower . 36

– 4 – IEC 61936-2:2023 © IEC 2023
8 Safety measures . 37
8.1 General . 37
8.2 Protection against direct contact . 37
8.2.1 General . 37
8.2.2 Measures for protection against direct contact . 37
8.2.3 Protection requirements . 37
8.3 Means to protect persons in case of indirect contact . 37
8.4 Means to protect persons working on or near electrical installations . 37
8.5 Protection from danger resulting from arc fault . 38
8.6 Protection against direct lightning strokes . 38
8.7 Protection against fire . 38
8.8 Protection against leakage of insulating liquid and SF . 38
8.9 Identification and marking . 38
9 Protection, automation and auxiliary systems . 38
9.1 Protection systems. 38
9.2 Automation systems . 38
9.3 Auxiliary systems . 38
9.4 Basic rules for electromagnetic compatibility of control systems . 38
10 Earthing systems . 39
10.1 General . 39
10.2 Fundamental requirements . 39
10.2.1 Safety criteria . 39
10.2.2 Functional requirements . 40
10.2.3 High and low voltage earthing systems . 40
10.3 Design of earthing systems . 41
10.3.1 General . 41
10.3.2 Power system faults. 41
10.3.3 Lightning and transient overvoltages. 41
10.4 Construction of earthing systems . 42
10.5 Measurements . 42
10.6 Maintainability . 42
10.6.1 Inspections . 42
10.6.2 Measurements . 42
11 Inspection and testing . 42
11.1 General . 42
11.2 Verification of specified performances . 42
11.3 Tests during installation and commissioning . 42
11.4 Trial running . 42
12 Operation and maintenance manual . 42
Annex A (informative) Example of typical DC voltages with possible insulation levels
and corresponding air clearances . 43
Annex B (normative) Method of calculating the voltage limit . 46
Bibliography . 47

Figure 1 – Simplified example of a VSC scheme layout showing demarcation of scope
of this document with IEC 61936-1 . 14
Figure 2 – Simplified example of a LCC bipole scheme layout showing demarcation of
scope of this document with IEC 61936-1 . 15

Figure 3 – DC neutral point earthing for various DC configurations . 18
Figure 4 – Approaches with buildings (within closed electrical operating areas) . 34
Figure 5 – Touch voltage limit DC . 40

Table 1 – References to subclauses where agreement between supplier and user is
required . 16
Table A.1 – Typical DC voltages and switching / lightning impulse withstand voltage . 44
Table A.2 – Correlation between presumed rated switching impulse Withstand voltages
and minimum phase-to-earth air clearances . 45
Table A.3 – Correlation between presumed rated lightning impulse withstand voltages
and minimum phase-to-earth clearances . 45

– 6 – IEC 61936-2:2023 © IEC 2023
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
POWER INSTALLATIONS EXCEEDING 1 kV AC AND 1,5 kV DC –

Part 2: DC
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
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the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 61936-2 has been prepared by IEC technical committee 99: Insulation co-ordination and
system engineering and erection of electrical power installations above 1 kV AC and 1,5 kV DC.
It is an International Standard.
This first edition cancels and replaces the IEC TS 61936-2 published in 2015. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) references to IEC 61936-1 updated to IEC 61936-1:2021;
b) alignment with IEC 61936-1:2021 where required;

c) the scope has been improved to clarify the application of this document, including an
improved definition of a DC installation;
d) missing and obsolete terms and definitions have been updated including improvement of
existing terms;
e) added new definitions of DC system and converter unit;
f) added symbols and abbreviated terms;
g) expansion and improvement of the general requirements, including addition of simplified
diagrams showing examples of VSC and LCC DC systems (Figure 1 and Figure 2);
h) addition of Table 1 which shows where agreements between supplier and user are needed;
i) clause on electrical requirements has been restructured and improved;
j) schematic diagrams for various DC system configurations and neutral point locations added
(Figure 3);
k) addition of new content for harmonics and new clauses for electromagnetic compatibility
and radio interference;
l) addition of content specific to DC installations for normal and special conditions;
m) clause on insulation (Clause 5) has been significantly restructured and rewritten with a
change in approach in the clauses on minimum clearances that references relevant parts of
IEC 60071;
n) clause on electrical equipment has been restructured and improved;
o) clause on DC installations has been restructured and improved;
p) clause on protection, control and auxiliary systems has been restructured and improved,
with content added to the clause on protection systems that is specific to DC installations;
q) clause on earthing has been restructured and improved;
r) clause on inspection and testing has been restructured and improved, including addition of
references specific to DC installations;
s) Annex A has been replaced with a new Annex A (informative), where the table of rated
insulation levels and minimum clearances in air have been replaced with a table of typical
DC voltages and presumed switching and lightning impulse withstand voltages;
t) tables added to Annex A showing the correlation between presumed switching and lightning
impulse withstand voltages and minimum phase-to-earth air clearances;
u) Annex B has been improved and references updated.
The text of this International Standard is based on the following documents:
Draft Report on voting
99/413/FDIS 99/436/RVD
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 International Standard 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
described in greater detail at www.iec.ch/publications.

– 8 – IEC 61936-2:2023 © IEC 2023
A list of all parts in the IEC 61936 series, published under the general title Power installations
exceeding 1 kV AC and 1,5 kV DC, can be found on the IEC website.
Notes concerning particular conditions in certain countries are provided in Annex G of
IEC 61936-1: 2021.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

INTRODUCTION
There are few national laws, standards and internal rules dealing with the matter coming within
the scope of this standard, and these practices have been taken as a basis for this work.
This part of IEC 61936 contains the minimum requirements and some additional information
which ensures an acceptable reliability of a DC installation with nominal voltages above 1,5 kV
DC and its safe operation.
The publication of this document is believed to be a decisive step towards the gradual alignment
all over the world of the practices concerning the design and erection of high voltage power
installations.
Particular requirements for transmission and distribution installations as well as particular
requirements for power generation and industrial installations are included in this document.
The relevant laws or regulations of an authority having jurisdiction take precedence.

– 10 – IEC 61936-2:2023 © IEC 2023
POWER INSTALLATIONS EXCEEDING 1 kV AC AND 1,5 kV DC –

Part 2: DC
1 Scope
This part of IEC 61936 provides, in a convenient form, requirements for the design and the
erection of DC installations in systems with nominal voltages above 1,5 kV DC, so as to provide
safety and proper functioning for the use intended.
For the purpose of interpreting this document, a DC installation is considered to be one of the
following:
a) A converter station or DC switching station;
b) one (or more) DC generating or storage unit(s), such as solar farms or battery storage units,
located on a single site, the DC installation includes DC equipment and cables with all
associated power electronics, controlgear, switchgear and all electrical auxiliary systems.
Connections between DC generating or storage units located on different sites are excluded;
c) DC installation erected on offshore facilities for the purpose of generation, transmission,
distribution and/or storage of electricity; or
d) DC transition station (between overhead lines and underground cable or between different
sections of underground cables).
This International Standard does not apply to the design and erection of any of the following:
– overhead and underground lines between separate installations;
– electric railways;
– mining equipment and installations;
– installations on ships according to IEC 60092 series and offshore units according to
IEC 61892 series, which are used in the offshore petroleum industry for drilling, processing
and storage purposes;
– electrostatic equipment (e.g. electrostatic precipitators, spray-painting units);
– test sites;
– medical equipment, e.g. medical X-ray equipment;
– valve hall or converter hall.
This document does not apply to the requirements for carrying out live working on electrical
installations.
This document does not apply to the design of factory-built, type-tested thyristor valves, VSC
valves and switchgear for which separate IEC standards exist.

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.
IEC 60060-1, High-voltage test techniques – Part 1: General definitions and test requirements
IEC 60071-1, Insulation co-ordination – Part 1: Definitions, principles and rules
IEC 60071-2:2023, Insulation co-ordination – Part 2: Application guidelines
IEC 60071-5 , Insulation co-ordination – Part 5: Procedures for high voltage direct current
(HVDC) converter stations
IEC 60071-11, Insulation co-ordination – Part 11：Definitions, principles and rules for HVDC
system
IEC 60079-10-1, Explosive atmospheres – Part 10-1: Classification of areas – Explosive gas
atmospheres
IEC 60079-10-2, Explosive atmospheres – Part 10-2: Classification of areas – Combustible dust
atmospheres
IEC 60479-1, Effects of current on human beings and livestock – Part 1: General aspects
IEC 60529, Degrees of protection provided by enclosures (IP Code)
IEC 60664-1, Insulation coordination for equipment within low-voltage supply systems – Part 1:
Principles, requirements and tests
IEC TS 60815-1, Selection and dimensioning of high-voltage insulators intended for use in
polluted conditions – Part 1: Definitions, information and general principles
IEC TS 60815-4, Selection and dimensioning of high-voltage insulators intended for use in
polluted conditions – Part 4: Insulators for d.c. systems
IEC 61000-6-5:2015, Electromagnetic compatibility (EMC) – Part 6-5: Generic standards –
Immunity for equipment used in power station and substation environment
IEC 61936-1:2021, Power installations exceeding 1 kV AC and 1,5 kV DC – Part 1: AC
IEC 61975, High-voltage direct current (HVDC) installations – System tests
IEC/IEEE 60076‑57‑129, Power transformers – Part 57-129: Transformers for HVDC
applications
___________
IEC 60071-5 has been replaced by IEC 60071-11 and IEC 60071-12.

– 12 – IEC 61936-2:2023 © IEC 2023
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61936-1 and the
following apply.
3.1.1
electronic valve device
indivisible electronic device for electronic power conversion or electronic power switching,
comprising a single non-controllable or bistably controlled unidirectionally conducting current
path
Note 1 to entry: Typical electronic valve devices are thyristors, power rectifier diodes, power switching bipolar and
field effect transistors and insulated-gate bipolar transistors (IGBT).
Note 2 to entry: Two or more electronic valve devices may be integrated on a common semiconductor chip
(examples: a thyristor and a rectifier diode in a reverse conducting thyristor, a power switching field effect transistor
with its inverse diode) or packaged in a common case (semiconductor power module). These combinations are to be
considered as separate electronic valve devices.
[SOURCE: IEC 60050-551:1998, 551-14-02]
3.1.2
nominal DC voltage
U
dn
suitable approximate value of DC voltage used to designate or identify a
system, expressed as the absolute value of the pole to earth voltage
3.1.3
highest DC voltage
U
dm
highest mean or average pole DC voltage to earth, excluding harmonics,
commutation and dynamic overshoots, but including expected measurement tolerance, for
which the installation is designed in respect of its insulation
3.1.4
DC neutral point
common point of two monopoles forming a bipole converter or the earthed point of a monopole
converter
3.1.5
DC electrode line
electrical connection between a DC earth electrode and the DC installation
3.1.6
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.
3.1.7
high voltage
DC voltage exceeding 1 500V DC

3.1.8
low voltage
DC voltage not exceeding 1 500V DC
3.1.9
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
3.1.10
converter station
part of a DC system which consists of one or more converter units 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
3.1.11
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 and the earth and is capable of carrying continuous
current for some extended period
Note 1 to entry: An earth electrode 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 sea electrode.
[SOURCE: IEC 60633:2019, 8.17, modified –The indication "DC" has been added to the term
and in the definition, the words “conducting elements” have been replaced by “conductive
elements” and “DC circuit” have been replaced by “DC system”.]
3.1.12
pole
part of a DC system consisting of all the equipment in the HVDC substations and interconnecting
transmission lines, if any, which during normal operation, exhibit a common direct voltage
polarity with respect to earth
[SOURCE: IEC 60633:2019, 8.5, modified – The term “HVDC system pole” has been replaced
by “pole” and in the definition, the words “HVDC system” have been replaced by “DC system”.]
3.1.13
withstand voltage
value of the test voltage to be applied under specified conditions in a withstand voltage
test, during which a specified number of disruptive discharges is tolerated
Note 1 to entry: The withstand voltage is designated as:
a) conventional assumed withstand voltage, when the number of disruptive discharges tolerated is zero. It is deemed
to correspond to a withstand probability P = 100 %;
w
b) statistical withstand voltage, when the number of disruptive discharges tolerated is related to a
specified withstand probability. In this document, the specified probability is P = 90 %.
w
Note 2 to entry: In this document, the conventional assumed withstand voltages are specified for non-self-restoring
insulation. The statistical withstand voltages are specified for self-restoring insulation.
[SOURCE: IEC 60071-1:2019, 3.24]

– 14 – IEC 61936-2:2023 © IEC 2023
3.2 Symbols and abbreviated terms
HVDC High voltage direct current
LCC line commutated converter
N minimum clearance of danger zone as defined in IEC 61936-1:2021
POI point of Interconnection
R DC resistance
dc
U highest DC voltage
dm
VSC voltage source converter
4 Fundamental requirements
4.1 General
4.1.1 General requirements
This document applies to the part of a DC installation on the DC side of the converter or
interface transformer, as taken from the center of the transformer as shown in Figure 1 for VSC
DC installations and in Figure 2 for LCC DC installations. For AC installations outside of this
area, IEC 61936-1 applies.
In these simplified representations, filters and reactors are shown for illustrative purposes only.
Such filters possibly are not required and if they are, can be located at other positions within
the DC installation.
Figure 1 – Simplified example of a VSC scheme layout showing
demarcation of scope of this document with IEC 61936-1

Figure 2 – Simplified example of a LCC bipole scheme layout showing
demarcation of scope of this document with IEC 61936-1
DC installations and equipment shall be capable of withstanding electrical, mechanical, climatic
and environmental influences anticipated on site.
Site selection should take into account matters including, but not limited to:
– access to allow for construction, maintenance and operations activities;
– community impact including proximity to sensitive sites, visual, noise, amenity and traffic;
– environmental impact including consideration of pollution, ventilation, fauna and flora;
– impact of topography, earthquake zones, fault lines, flood paths, swamps, avalanches or
landslides;
...