IEC 60071-2:2023

IEC 60071-2 ®
Edition 5.0 2023-05
REDLINE VERSION
INTERNATIONAL
STANDARD
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HORIZONTAL PUBLICATION
Insulation co-ordination –
Part 2: Application guidelines

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IEC 60071-2 ®
Edition 5.0 2023-05
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
HORIZONTAL PUBLICATION
Insulation co-ordination –
Part 2: Application guidelines
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.080.30 ISBN 978-2-8322-7074-5

– 2 – IEC 60071-2:2023 RLV © IEC 2023
CONTENTS
FOREWORD . 9
1 Scope . 11
2 Normative references . 11
3 Terms, definitions, abbreviated terms and symbols . 12
3.1 Terms and definitions . 12
3.2 Abbreviated terms . 12
3.3 Symbols . 12
4 Concepts governing the insulation co-ordination . 18
5 Representative voltage stresses in service . 19
5.1 Origin and classification of voltage stresses . 19
5.2 Characteristics of overvoltage protection devices . 20
5.2.1 General remarks . 20
5.2.2 Metal-oxide surge arresters without gaps (MOSA) . 20
5.2.3 Line surge arresters (LSA) for overhead transmission and distribution
lines . 22
5.3 General approach for the determination of representative voltages and
overvoltages . 23
5.3.1 Continuous (power-frequency) voltage . 23
5.3.2 Temporary overvoltages . 23
5.3.3 Slow-front overvoltages . 26
5.3.4 Fast-front overvoltages . 32
5.3.5 Very-fast-front overvoltages . 36
5.4 Determination of representative overvoltages by detailed simulations . 37
5.4.1 General overview . 37
5.4.2 Temporary overvoltages . 37
5.4.3 Slow-front overvoltages . 38
5.4.4 Fast-front overvoltages . 39
5.4.5 Very-fast-front overvoltages . 43
6 Co-ordination withstand voltage . 44
6.1 Insulation strength characteristics . 44
6.1.1 General . 44
6.1.2 Influence of polarity and overvoltage shapes . 46
6.1.3 Phase-to-phase and longitudinal insulation . 47
6.1.4 Influence of weather conditions on external insulation . 47
6.1.5 Probability of disruptive discharge of insulation . 47
6.2 Performance criterion . 49
6.3 Insulation co-ordination procedures . 49
6.3.1 General . 49
6.3.2 Insulation co-ordination procedures for continuous (power-frequency)
voltage and temporary overvoltage . 50
6.3.3 Insulation co-ordination procedures for slow-front overvoltages . 51
6.3.4 Insulation co-ordination procedures for fast-front overvoltages . 56
6.3.5 Insulation co-ordination procedures for very-fast-front overvoltages . 57
7 Required withstand voltage . 57
7.1 General remarks . 57
7.2 Atmospheric correction . 57
7.2.1 General remarks . 57

7.2.2 Altitude correction . 58
7.3 Safety factors. 59
7.3.1 General . 59
7.3.2 Ageing . 60
7.3.3 Production and assembly dispersion . 60
7.3.4 Inaccuracy of the withstand voltage . 60
7.3.5 Recommended safety factors (K ) . 60
s
8 Standard withstand voltage and testing procedures . 61
8.1 General remarks . 61
8.1.1 Overview . 61
8.1.2 Standard switching impulse withstand voltage . 61
8.1.3 Standard lightning impulse withstand voltage . 61
8.2 Test conversion factors . 62
8.2.1 Range I. 62
8.2.2 Range II . 62
8.3 Determination of insulation withstand by type tests . 63
8.3.1 Test procedure dependency upon insulation type . 63
8.3.2 Non-self-restoring insulation . 63
8.3.3 Self-restoring insulation . 63
8.3.4 Mixed insulation . 64
8.3.5 Limitations of the test procedures . 65
8.3.6 Selection of the type test procedures . 65
8.3.7 Selection of the type test voltages . 65
9 Special considerations for overhead lines apparatus and transmission line . 66
9.1 Overhead line . 66
9.1.1 General remarks . 66
9.1.2 Insulation co-ordination for operating voltages and temporary
overvoltages . 67
9.1.3 Insulation co-ordination for slow-front overvoltages . 67
9.1.4 Insulation co-ordination for lightning fast-front overvoltages . 68
9.2 Cable line . 69
9.2.1 General . 69
9.2.2 Insulation co-ordination for operating voltages and temporary
overvoltages . 69
9.2.3 Insulation co-ordination for slow-front overvoltages . 69
9.2.4 Insulation co-ordination for fast-front overvoltages . 70
9.2.5 Overvoltage protection of cable lines . 70
9.3 GIL (gas insulated transmission line) / GIB (Gas-insulated busduct) . 71
9.3.1 General . 71
9.3.2 Insulation co-ordination for operating voltages and temporary
overvoltages . 71
9.3.3 Insulation co-ordination for slow-front overvoltages . 71
9.3.4 Insulation co-ordination for fast-front overvoltages . 72
9.3.5 Overvoltage protection of GIL/GIB lines . 72
9.4 Special considerations for substations Substation . 68
9.4.1 General remarks . 72
9.4.2 Insulation co-ordination for overvoltages. 73
Annex A (informative) Determination of temporary overvoltages due to earth faults . 76
Annex B (informative) Weibull probability distributions . 80

– 4 – IEC 60071-2:2023 RLV © IEC 2023
B.1 General remarks . 80
B.2 Disruptive discharge probability of external insulation . 81
B.3 Cumulative frequency distribution of overvoltages . 84
Annex C (informative) Determination of the representative slow-front overvoltage due
to line energization and re-energization . 86
C.1 General remarks . 86
C.2 Probability distribution of the representative amplitude of the prospective
overvoltage phase-to-earth . 86
C.3 Probability distribution of the representative amplitude of the prospective

overvoltage phase-to-phase . 89
C.4 Insulation characteristic . 91
C.5 Numerical example . 93
Annex D (informative) Transferred overvoltages in transformers . 100
D.1 General remarks . 100
D.2 Transferred temporary overvoltages . 101
D.3 Capacitively transferred surges . 101
D.4 Inductively transferred surges . 103
Annex E (informative) Determination of lightning overvoltages by simplified method . 107
E.1 General remarks . 107
E.2 Determination of the limit distance (X ) . 107
p
E.2.1 Protection with arresters in the substation . 107
E.2.2 Self-protection of substation . 108
E.3 Estimation of the representative lightning overvoltage amplitude. 109
E.3.1 General . 109
E.3.2 Shielding penetration . 109
E.3.3 Back flashovers . 110
E.4 Simplified method approach . 112
E.5 Assumed maximum value of the representative lightning overvoltage . 114
Annex F (informative) Calculation of air gap breakdown strength from experimental

data . 116
F.1 General . 116
F.2 Insulation response to power-frequency voltages . 116
F.3 Insulation response to slow-front overvoltages . 117
F.4 Insulation response to fast-front overvoltages . 118
Annex G (informative) Examples of insulation co-ordination procedure . 122
G.1 Overview. 122
G.2 Numerical example for a system in range I (with nominal voltage of 230 kV) . 122
G.2.1 General . 122
G.2.2 Part 1: no special operating conditions . 123
G.2.3 Part 2: influence of capacitor switching at station 2 . 130
G.2.4 Part 3: flow charts related to the example of Clause G.2 . 132
G.3 Numerical example for a system in range II (with nominal voltage of 735 kV) . 137
G.3.1 General . 137
G.3.2 Step 1: determination of the representative overvoltages –
values of U . 137
rp
G.3.3 Step 2: determination of the co-ordination withstand voltages –
values of U . 138
cw
G.3.4 Step 3: determination of the required withstand voltages – values of
U . 139
rw
G.3.5 Step 4: conversion to switching impulse withstand voltages (SIWV) . 140
G.3.6 Step 5: selection of standard insulation levels . 141
G.3.7 Considerations relative to phase-to-phase insulation co-ordination . 141
G.3.8 Phase-to-earth clearances . 142
G.3.9 Phase-to-phase clearances . 143
G.4 Numerical example for substations in distribution systems with U up to
m
36 kV in range I . 143
G.4.1 General . 143
G.4.2 Step 1: determination of the representative overvoltages –
values of U . 144
rp
G.4.3 Step 2: determination of the co-ordination withstand voltages –

values of U . 144
cw
G.4.4 Step 3: determination of required withstand voltages – values of U . 145
rw
G.4.5 Step 4: conversion to standard short-duration power-frequency and
lightning impulse withstand voltages . 146
G.4.6 Step 5: selection of standard withstand voltages . 147
G.4.7 Summary of insulation co-ordination procedure for the example of

Clause G.4 . 147
Annex H (informative) Atmospheric correction – Altitude correction application
example . 149
H.1 General principles . 149
H.1.1 Atmospheric correction in standard tests . 149
H.1.2 Task of atmospheric correction in insulation co-ordination . 150
H.2 Atmospheric correction in insulation co-ordination . 152
H.2.1 Factors for atmospheric correction . 152
H.2.2 General characteristics for moderate climates . 152
H.2.3 Special atmospheric conditions . 153
H.2.4 Altitude dependency of air pressure . 154
H.3 Altitude correction . 155
H.3.1 Definition of the altitude correction factor . 155
H.3.2 Principle of altitude correction . 156
H.3.3 Altitude correction for standard equipment operating at altitudes up to
1 000 m . 157
H.3.4 Altitude correction for standard equipment operating at altitudes above
1 000 m . 157
H.4 Selection of the exponent m . 158
H.4.1 General . 158
H.4.2 Derivation of exponent m for switching impulse voltage . 158
H.4.3 Derivation of exponent m for critical switching impulse voltage . 161
Annex I (informative) Evaluation method of non-standard lightning overvoltage shape
for representative voltages and overvoltages . 164
I.1 General remarks . 164
I.2 Lightning overvoltage shape . 164
I.3 Evaluation method for GIS . 164
I.3.1 Experiments . 164
I.3.2 Evaluation of overvoltage shape . 165
I.4 Evaluation method for transformer . 165
I.4.1 Experiments . 165
I.4.2 Evaluation of overvoltage shape . 166

– 6 – IEC 60071-2:2023 RLV © IEC 2023
Annex J (informative) Insulation co-ordination for very-fast-front overvoltages in UHV
substations . 171
J.1 General . 171
J.2 Influence of disconnector design . 171
J.3 Insulation co-ordination for VFFO . 172
Annex K (informative) Application of shunt reactors to limit TOV and SFO of high
voltage overhead transmission line . 174
K.1 General remarks . 174
K.2 Limitation of TOV and SFO . 174
K.3 Application of the neutral grounding reactor to limit resonance overvoltage
and secondary arc current . 174
K.4 SFO and Beat frequency overvoltage limited by neutral arrester . 175
K.5 SFO and FFO due to SR de-energization . 176
K.6 Limitation of TOV by Controllable SR . 176
K.7 Insulation coordination of the SR and neutral grounding reactor . 176
K.8 Self-excitation TOV of synchronous generator . 176
Annex L (informative) Calculation of lightning stroke rate and lightning outage rate . 177
L.1 General . 177
L.2 Description in CIGRE [37] . 177
L.3 Flash program in IEEE [49] . 178
L.4 [Case Study] Calculation of Lightning Stroke Rate and Lightning Outage
Rate (Appendix D in CIGRE TB 839 [37]) . 178
L.4.1 Basic flow of calculation method . 178
L.4.2 Comparison of Calculation Results with Observations . 181
Bibliography . 183

Figure 1 – Range of 2 % slow-front overvoltages at the receiving end due to line
energization and re-energization [27] . 28
Figure 2 – Ratio between the 2 % values of slow-front overvoltages phase-to-phase

and phase-to-earth [28], [29] . 29
Figure 3 – Diagram for surge arrester connection to the protected object . 36
Figure 4 – Modelling of transmission lines and substations/power stations . 42
Figure 5 – Distributive discharge probability of self-restoring insulation described on a
linear scale . 52
Figure 6 – Disruptive discharge probability of self-restoring insulation described on a
Gaussian scale . 52
Figure 7 – Evaluation of deterministic co-ordination factor K . 53
cd
Figure 8 – Evaluation of the risk of failure . 54
Figure 9 – Risk of failure of external insulation for slow-front overvoltages as a function

of the statistical co-ordination factor K . 56
cs
Figure 10 – Dependence of exponent m on the co-ordination switching impulse
withstand voltage . 59
Figure 11 – Probability P of an equipment to pass the test dependent on the difference
K between the actual and the rated impulse withstand voltage . 65
Figure 12 – Example of a schematic substation layout used for the overvoltage stress
location . 72
Figure A.1 – Earth fault factor k on a base of X /X for R /X = R = 0 . 77
0 1 1 1 f
Figure A.2 – Relationship between R /X and X /X for constant values of earth fault
0 1 0 1
factor k where R = 0 . 78
Figure A.3 – Relationship between R /X and X /X for constant values of earth fault
0 1 0 1
factor k where R = 0,5 X . 78
1 1
Figure A.4 – Relationship between R /X and X /X for constant values of earth fault
0 1 0 1
factor k where R = X . 79
1 1
Figure A.5 – Relationship between R /X and X /X for constant values of earth fault
0 1 0 1
factor k where R = 2X . 79
1 1
Figure B.1 – Conversion chart for the reduction of the withstand voltage due to placing

insulation configurations in parallel . 85
Figure C.1 – Probability density and cumulative distribution for derivation of the
representative overvoltage phase-to-earth . 87
Figure C.2 – Example for bivariate phase-to-phase overvoltage curves with constant
probability density and tangents giving the relevant 2 % values . 95
Figure C.3 – Principle of the determination of the representative phase-to-phase

overvoltage U . 97
pre
Figure C.4 – Schematic phase-phase-earth insulation configuration . 98
Figure C.5 – Description of the 50 % switching impulse flashover voltage of a phase-
phase-earth insulation . 98
Figure C.6 – Inclination angle of the phase-to-phase insulation characteristic in range
"b" dependent on the ratio of the phase-phase clearance D to the height H above
t
earth . 99
Figure D.1 – Distributed capacitances of the windings of a transformer and the
equivalent circuit describing the windings . 105
Figure D.2 – Values of factor J describing the effect of the winding connections on the
inductive surge transference . 106
Figure H.1 – Principle of the atmospheric correction during test of a specified

insulation level according to the procedure of IEC 60060-1 . 150
Figure H.2 – Principal task of the atmospheric correction in insulation co-ordination
according to IEC 60071-1 . 151
Figure H.3 – Comparison of atmospheric correction δ × k with relative air pressure
h
p/p for various weather stations around the world . 154
Figure H.4 – Deviation of simplified pressure calculation by exponential function in this

document from the temperature dependent pressure calculation of ISO 2533 . 155
Figure H.5 – Principle of altitude correction: decreasing withstand voltage U of
equipment with increasing altitude . 156
Figure H.6 – Sets of m-curves for standard switching impulse voltage including the
variations in altitude for each gap factor . 161
Figure H.7 – Exponent m for standard switching impulse voltage for selected gap
factors covering altitudes up to 4 000 m . 161
Figure H.8 – Sets of m-curves for critical switching impulse voltage including the
variations in altitude for each gap factor . 162
Figure H.9 – Exponent m for critical switching impulse voltage for selected gap factors
covering altitudes up to 4 000 m . 162
Figure H.10 – Accordance of m-curves from Figure 10 with determination of exponent
m by means of critical switching impulse voltage for selected gap factors and altitudes. 163
Figure I.1 – Examples of lightning overvoltage shapes . 166

– 8 – IEC 60071-2:2023 RLV © IEC 2023
Figure I.2 – Example of insulation characteristics with respect to lightning overvoltages
of the SF gas gap (Shape E) . 167
Figure I.3 – Calculation of duration time T . 167
d
Figure I.4 – Shape evaluation flow for GIS and transformer . 168
Figure I.5 – Application to GIS lightning overvoltage . 169
Figure I.6 – Example of insulation characteristics with respect to lightning overvoltage
of the turn-to-turn insulation (Shape C) . 169
Figure I.7 – Application to transformer lightning overvoltage . 170
Figure J.1 – Insulation co-ordination for very-fast-front overvoltages. 173
Figure L.1 – Outline of the CIGRE method for lightning performance of an overhead
line . 178
Figure L.2 – Flowchart to calculate lightning outage rate of transmission lines . 180
Figure L.3 – Typical conductor arrangements of large-scale transmission lines . 181
Figure L.4 – Lightning stroke rate to power lines -calculations and observations- . 181
Figure L.5 – Lightning outage rate -calculations and observations- . 182

Table 1 – Test conversion factors for range I, to convert required SIWV to SDWV and
LIWV . 62
Table 2 – Test conversion factors for range II to convert required SDWV to SIWV . 63
Table 3 – Selectivity of test procedures B and C of IEC 60060-1 . 64
Table B.1 – Breakdown voltage versus cumulative flashover probability – Single

insulation and 100 parallel insulations . 83
Table E.1 – Corona damping constant K . 108
co
Table E.2 – Factor A for various overhead lines . 114
Table F.1 – Typical gap factors K for switching impulse breakdown phase-to-earth
(according to [1] and [4]) . 120
Table F.2 – Gap factors for typical phase-to-phase geometries . 121
Table G.1 – Summary of minimum required withstand voltages obtained for the
example shown in G.2.2 . 129
Table G.2 – Summary of required withstand voltages obtained for the example shown
in G.2.3 . 131
Table G.3 – Values related to the insulation co-ordination procedure for the example
in G.4. 148
Table H.1 – Comparison of functional expressions of Figure 10 with the selected
parameters from the derivation of m-curves with critical switching impulse . 163
Table I.1 – Evaluation of the lightning overvoltage in the GIS of UHV system . 167
Table I.2 – Evaluation of lightning overvoltage in the transformer of 500 kV system . 170

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSULATION CO-ORDINATION –
Part 2: Application guidelines

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
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This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition IEC 60071-2:2018. A vertical bar appears in the margin
wherever a change has been made. Additions are in green text, deletions are in
strikethrough red text.
– 10 – IEC 60071-2:2023 RLV © IEC 2023
IEC 60071-2 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.
This fifth edition cancels and replaces the fourth edition published in 2018. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Clause 4 Concepts governing the insulation co-ordination has been added.
b) Subclause 5.3 has been revised, and Subclause 5.4 Detailed simulation has been added
because it is widely applied in the recent practices of insulation coordination.
c) Special considerations for cable line and GIL/GIB have been added in Clause 9.
d) Annex K (informative) Application of line shunt reactor to limitation of TOV and SFO in high
voltage overhead transmission lines has been added.
e) Annex L (informative) Calculation of lightning stroke rate and lightning outage rate has been
added.
The text of this International Standard is based on the following documents:
Draft Report on voting
99/356/CDV 99/392/RVC
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.
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.
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,
•
...