IEC 60071-12:2022

Insulation co-ordination - Part 12: Application guidelines for LCC HVDC converter stations

IEC 60071-12:2022 applies guidelines on the procedures for insulation co-ordination of line commutated converter (LCC) stations for high-voltage direct current (HVDC) project, whose aim is evaluating the overvoltage stresses on the converter station equipment subjected to combined DC, AC power frequency, harmonic and impulse voltages, and determining the specified withstand voltages for equipment.
This document deals only with metal-oxide surge arresters, without gaps, which are used in modern HVDC converter stations. The criteria for determining the protective levels of series and/or parallel combinations of surge arresters used to ensure optimal protection are also presented. Typical arrester protection schemes and stresses of arresters are presented.
Annex A contains examples of insulation co-ordination for LCC HVDC converters which support the concepts described in the main text, and the basic analytical techniques used.

Coordination de l’isolement - Partie 12: Lignes directrices en matière d’application pour stations de conversion à courant continu haute tension (CCHT) équipées de convertisseurs commutés par le réseau (LCC)

L'IEC 60071-12:2022 applique des lignes directrices concernant les procédures de coordination de l’isolement des stations de conversion équipées de convertisseurs commutés par le réseau (LCC) pour des installations à courant continu haute tension (CCHT), dont l’objectif est d’évaluer les contraintes de surtension exercées sur le matériel soumis à des tensions combinées de fréquence, d'harmoniques et d'impulsions de courant continu et alternatif et de déterminer les tensions de tenue spécifiées pour le matériel.
Le présent document traite seulement des parafoudres à oxyde métallique, sans éclateurs, qui sont utilisés dans les stations de conversion à CCHT modernes. Les critères de détermination des niveaux de protection des combinaisons de montages en série et/ou en parallèle des parafoudres utilisés pour assurer une protection optimale sont également présentés, de même que les schémas types de la protection par parafoudre et les contraintes des parafoudres.
L’Annexe A comporte des exemples de coordination de l’isolement pour les convertisseurs CCHT LCC qui prennent en charge les concepts décrits dans le corps du texte, ainsi que les techniques d’analyse de base employées.

General Information

• Status: Published
• Publication Date: 13-Oct-2022
• ICS: 29.080.30 - Insulation systems
• Technical Committee: TC 99 - Insulation co-ordination and system engineering of high voltage electrical power installations above 1,0 kV AC and 1,5 kV DC
• Drafting Committee: JWG 13 - TC 99/JWG 13
• Current Stage: PPUB - Publication issued
• Start Date: 11-Nov-2022
• Completion Date: 14-Oct-2022

Relations

• Replaces: IEC 60071-5:2014 - Insulation co-ordination - Part 5: Procedures for high-voltage direct current (HVDC) converter stations
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 60071-12
®

Edition 1.0 2022-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE


Insulation co-ordination –
Part 12: Application guidelines for LCC HVDC converter stations

Coordination de l’isolement –
Partie 12: Lignes directrices en matière d’application pour stations de
conversion à courant continu haute tension (CCHT) équipées de convertisseurs
commutés par le réseau (LCC)

IEC 60071-12:2022-10(en-fr)

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IEC 60071-12

®


Edition 1.0 2022-10




INTERNATIONAL



STANDARD




NORME


INTERNATIONALE











Insulation co-ordination –

Part 12: Application guidelines for LCC HVDC converter stations



Coordination de l’isolement –

Partie 12: Lignes directrices en matière d’application pour stations de

conversion à courant continu haute tension (CCHT) équipées de convertisseurs


commutés par le réseau (LCC)













INTERNATIONAL

ELECTROTECHNICAL

COMMISSION


COMMISSION

ELECTROTECHNIQUE


INTERNATIONALE




ICS 29.080.30 ISBN 978-2-8322-5845-3




Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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– 2 – IEC 60071-12:2022 © IEC 2022
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms, definitions, symbols and abbreviated terms . 7
3.1 Terms and definition . 7
3.2 Symbols and abbreviated terms . 8
3.2.1 General . 8
3.2.2 Subscripts . 8
3.2.3 Letter symbols . 8
3.2.4 Abbreviated terms . 9
4 Typical LCC HVDC converter station schemes . 9
5 Voltages and overvoltages in service . 12
5.1 Continuous operating voltages at various locations in the converter station . 12
5.2 Peak continuous operating voltage (PCOV) and crest continuous operating
voltage (CCOV) . 16
5.3 Sources and types of overvoItages . 18
5.4 Temporary overvoltage . 18
5.4.1 General . 18
5.4.2 Temporary overvoltage on the AC side . 18
5.4.3 Temporary overvoltages on the DC side . 19
5.5 Slow-front overvoltages . 19
5.5.1 General . 19
5.5.2 Slow-front overvoltages on the AC side . 19
5.5.3 Slow-front overvoltages on the DC side . 20
5.6 Fast-front, very-fast-front and steep-front overvoltages . 20
6 Arrester characteristics and stresses . 21
6.1 Arrester characteristics . 21
6.2 Arrester specification . 22
6.3 Arrester stresses. 23
6.3.1 General . 23
6.3.2 AC bus arrester (A) . 24
6.3.3 AC filter arrester (FA) . 24
6.3.4 Transformer valve winding arresters (T). 25
6.3.5 Valve arrester (V) . 25
6.3.6 Bridge arrester (B) . 28
6.3.7 Converter unit arrester (C) . 28
6.3.8 Mid-point DC bus arrester (M) . 29
6.3.9 Converter unit DC bus arrester (CB) . 29
6.3.10 DC bus and DC line/cable arrester (DB and DL/DC) . 30
6.3.11 Neutral bus arrester (E, EL, EM in Figure 3, EB, E1, EL, EM in Figure 1) . 30
6.3.12 DC reactor arrester (DR) . 31
6.3.13 DC filter arrester (FD) . 32
6.3.14 Earth electrode station arrester. 32
6.4 Protection strategy . 32
6.4.1 General . 32
6.4.2 Insulation directly protected by a single arrester . 32
6.4.3 Insulation protected by more than one arrester in series . 32

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IEC 60071-12:2022 © IEC 2022 – 3 –
6.4.4 Valve side neutral point of transformers . 33
6.4.5 Insulation between phase conductors of the converter transformer . 33
6.4.6 Summary of protection strategy . 33
6.5 Summary of events and stresses . 36
7 Design procedure of insulation co-ordination . 37
7.1 General . 37
7.2 Arrester requirements . 38
7.3 Representative overvoltages (U ) . 38
rp
7.4 Determination of the co-ordination withstand voltages (U ) . 40
cw
7.5 Determination of the required withstand voltages (U ) . 40
rw
7.6 Determination of the specified withstand voltage (U ) . 40
w
8 Study tools and system modelling . 40
8.1 General . 40
8.2 Study approach and tooIs . 40
8.3 System details . 41
8.3.1 Modelling and system representation . 41
8.3.2 AC network and AC side of the LCC HVDC converter station . 43
8.3.3 DC overhead line/cable and earth electrode line details . 44
8.3.4 DC side of an LCC HVDC converter station details . 44
Annex A (informative) Example of insulation co-ordination for LCC HVDC converter
stations . 45
A.1 General . 45
A.2 Example for LCC HVDC converter station in a pole with one 12-pulse

converter . 45
A.2.1 Arrester protective scheme . 45
A.2.2 Arrester stresses, protection and insulation levels . 45
A.2.3 Transformer valve side withstand voltages. 50
A.2.4 Air-insulated smoothing reactors withstand voltages . 50
A.2.5 Results . 52
A.3 Example for LCC HVDC converter station in a pole with two 12-pulse
converters in series . 54
A.3.1 Arrester protective scheme . 54
A.3.2 Arrester stresses, protection and insulation levels . 55
A.3.3 Transformer valve side withstand voltages. 59
A.3.4 Smoothing reactor withstand voltages . 61
A.3.5 Results . 62
Bibliography . 64

Figure 1 – Possible arrester locations in a pole with two 12-pulse converters in series . 11
Figure 2 – Possible arrester locations for a back-to-back converter station . 12
Figure 3 – LCC HVDC converter station in a pole with one 12-pulse converter . 13
Figure 4 – Continuous operating voltages at various locations (location identification
according to Figure 3) . 15
Figure 5 – Operating voltage of a valve arrester (V), rectifier operation and definition of
PCOV and CCOV . 17
Figure 6 – Operating voltage of a mid-point arrester (M), rectifier operation . 17
Figure 7 – Operating voltage of a converter bus arrester (CB), rectifier operation . 17
Figure 8 – One pole of an LCC HVDC converter station . 43

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– 4 – IEC 60071-12:2022 © IEC 2022
Figure A.1 – AC and DC arresters (LCC HVDC converter station in a pole with one 12-
pulse converter) . 52
Figure A.2 – Valve arrester stresses for slow-front overvoltages from AC side . 53
Figure A.3 – Arrester V2 stress for slow-front overvoltage from AC side . 53
Figure A.4 – Valve arrester stresses for earth fault between valve and upper bridge

transformer bushing . 54
Figure A.5 – Arrester V1 stress for earth fault between valve and upper bridge
transformer bushing . 54
Figure A.6 – AC and DC arresters (LCC HVDC converter station in a pole with two 12-
pulse converters in series) . 63

Table 1 – Symbol description . 12
Table 2 – Arrester protection on the DC side: one 12-pulse converter (Figure 3) . 34
Table 3 – Arrester protection on the DC side: two 12-pulse converters in series
(Figure 1) . 35
Table 4 – Events stressing arresters: one 12-pulse converter (Figure 3) . 36
Table 5 – Types of arrester stresses for different events: one 12-pulse converter
(Figure 3) . 37
Table 6 – Arrester requirements . 38
Table 7 – Representative overvoltages and required withstand voltages . 39
Table 8 – Origin of overvoltages and associated frequency ranges . 42

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IEC 60071-12:2022 © IEC 2022 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

INSULATION CO-ORDINATION –

Part 12: Application guidelines for LCC HVDC converter stations

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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IEC 60071-12 has been prepared by IEC technical committee 99: Insulation co-ordination and
system engineering of high voltage electrical power installations above 1,0 kV AC and 1,5 kV
DC. It is an International Standard.
On the basis of technical experience gained and the development of HVDC, sufficient
consensus has emerged to establish a series insulation co-ordination standard for HVDC
system. The standard series for HVDC system belongs to IEC 60071 standard series, and a list
of all parts in the IEC 60071 series, published under the general title Insulation co-ordination,
can be found on the IEC website.

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– 6 – IEC 60071-12:2022 © IEC 2022
1
This International Standard replaces, in conjunction with IEC 60071-11 , IEC 60071-5
published in 2014. IEC 60071-5 provides basic principles and guidance for insulation
coordination of high-voltage direct current (HVDC) converter stations. IEC 60071-11 specifies
the principles on the procedures for the determination of the specified withstand voltages,
creepage distance and air clearances for the equipment and the installations of these systems.
IEC 60071-12 provides guidelines on the procedures for insulation co-ordination of line
commutated converter (LCC) stations for high-voltage direct current (HVDC) project, whose aim
is to give guidance for the determination of the specified withstand voltages for equipment.
IEC 60071-12 retains the technical content of IEC 60071-5 of the guidelines on the procedures
for insulation coordination of LCC converter stations, and there are no essentially technical
amendments. An example for LCC HVDC converter station in a pole with two 12-pulse
converters in series is provided in annex. Examples of insulation co-ordination for controlled
series capacitor converter (CSCC) and capacitor commutated converters (CCC) in IEC 60071-
5 are no longer dealt with in this document.
The text of this International Standard is based on the following documents:
Draft Report on voting
99/368/FDIS 99/379/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/standardsdev/publications.
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,
• replaced by a revised edition, or
• amended.


___________
1
 Under preparation. Stage at the time of publication: IEC/CFDIS 60071-11:2022.

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IEC 60071-12:2022 © IEC 2022 – 7 –
INSULATION CO-ORDINATION –

Part 12: Application guidelines for LCC HVDC converter stations



1 Scope
This part of IEC 60071 applies guidelines on the procedures for insulation co-ordination of line
commutated converter (LCC) stations for high-voltage direct current (HVDC) project, whose aim
is evaluating the overvoltage stresses on the converter station equipment subjected to
combined DC, AC power frequency, harmonic and impulse voltages, and determining the
specified withstand voltages for equipment.
This document deals only with metal-oxide surge arresters, without gaps, which are used in
modern HVDC converter stations. The criteria for determining the protective levels of series
and/or parallel combinations of surge arresters used to ensure optimal protection are also
presented. Typical arrester protection schemes and stresses of arresters are presented.
Annex A contains examples of insulation co-ordination for LCC HVDC converters which support
the concepts described in the main text, and the basic analytical techniques used.
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.
2
IEC 60071-11 , Insulation co-ordination – Part 11：Definitions, principles and rules for HVDC
system
IEC 60099-4, Surge arresters – Part 4: Metal-oxide surge arresters without gaps for a.c.
systems
IEC 60633, High-voltage direct current (HVDC) transmission – Vocabulary
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definition
For the purposes of this document, the terms and definitions given in IEC 60071-11 and the
following 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
___________
2
 Under preparation. Stage at the time of publication: IEC/CFDIS 60071-11:2022.

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– 8 – IEC 60071-12:2022 © IEC 2022
3.1.1
crest value of continuous operating voltage
CCOV
highest continuously occurring crest value of the voltage at the equipment on the DC side of
the converter station excluding commutation overshoots
3.1.2
peak value of continuous operating voltage
PCOV
highest continuously occurring crest value of the voltage at the equipment on the DC side of
the converter station including commutation overshoots and commutation notches
3.1.3
valve protective firing
means of protecting the thyristors from excessive forward voltage, rate of change of voltage or
forward voltage applied during the reverse recovery time, by firing the thyristors into conduction
3.2 Symbols and abbreviated terms
3.2.1 General
The list covers only the most frequently used symbols and abbreviated terms, some of which
are illustrated graphically in the single-line diagram of Figure 1 and Figure 2. For a more
complete list of symbols which has been adopted for LCC HVDC converter stations, and also
for insulation co-ordination, refer to the standards listed in the normative references (Clause 2)
and to the Bibliography.
3.2.2 Subscripts
0(zero) at no load (IEC 60633)
d direct current or voltage (IEC 60633)
i ideal (IEC 60633)
max maximum (IEC 60633)
n pertaining to harmonic component of order n (IEC 60633)

3.2.3 Letter symbols
K altitude correction factor (IEC 60071-1)
a
K co-ordination factor (IEC 60071-1)
c
K safety factor (IEC 60071-1)
s
U continuous operating voltage of an arrester
c
U crest value of continuous operating voltage
ccov
U continuous operating voltage of an arrester including harmonics
ch
U ideal no-load direct voltage (IEC 60633)
di0
U maximum value of U ta
...