IEC 60071-2:2018
(Main)Insulation co-ordination - Part 2: Application guidelines
Insulation co-ordination - Part 2: Application guidelines
IEC 60071-2:2018 constitutes application guidelines and deals with the selection of insulation levels of equipment or installations for three-phase electrical systems. It gives guidance for the determination of the rated withstand voltages for ranges I and II of IEC 60071-1 and to justify the association of these rated values with the standardized highest voltages for equipment. It covers three-phase systems with nominal voltages above 1 kV. This edition includes the following significant technical changes with respect to the previous edition:
a) the annex on clearance in air to assure a specified impulse withstand voltage installation is deleted because the annex in IEC 60071-1 is overlapped;
b) 4.2 and 4.3 on surge arresters are updated;
c) 4.3.5 on very-fast-front overvoltages is revised. Annex J on insulation co-ordination for very-fast-front overvoltages in UHV substations is added;
d) Annex H on atmospheric correction – altitude correction is added.
e) Annex I on evaluation method of non-standard lightning overvoltage shape is added.
It has the status of a horizontal standard in accordance with IEC Guide 108.
Coordination de l'isolement - Partie 2: Lignes directrices en matière d'application
L'IEC 60071-2:2018 constitue des lignes directrices en matière d'application et concerne le choix des niveaux d'isolement des matériels ou des installations pour les réseaux triphasés. Elle a pour objet de donner des recommandations pour la détermination des tensions de tenue assignées pour les plages I et II de l'IEC 60071-1 et de justifier l'association de ces valeurs assignées avec les valeurs normalisées des tensions les plus élevées pour le matériel. Il traite des réseaux triphasés de tension nominale supérieure à 1 kV. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) l'annexe relative à la distance d'isolement dans l'air pour installation garantissant une tension de tenue aux chocs spécifiée est supprimée car cette annexe est déjà présente dans l'IEC 60071-1;
b) 4.2et 4.3relatifs aux parafoudres ont été mis à jour;
c) 4.3.5relatif aux surtensions à front très rapide a été révisé. L'Annexe J relative à la coordination de l'isolement pour les surtensions à front très rapide dans les postes UHT a été ajoutée;
d) l'Annexe H relative à la correction atmosphérique – correction de l'altitude a été ajoutée;
e) l'Annexe I relative à la méthode d'évaluation de la forme de la surtension de foudre non normalisée a été ajoutée.
Elle a le statut de norme horizontale conformément au Guide IEC 108.
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IEC 60071-2 ®
Edition 4.0 2018-03
REDLINE VERSION
INTERNATIONAL
STANDARD
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HORIZONTAL STANDARD
Insulation co-ordination –
Part 2: Application guidelines
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IEC 60071-2 ®
Edition 4.0 2018-03
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
HORIZONTAL STANDARD
Insulation co-ordination –
Part 2: Application guidelines
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.080.30 ISBN 978-2-8322-5498-1
– 2 – IEC 60071-2:2018 RLV IEC 2018
CONTENTS
FOREWORD . 9
General .
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 . 13
4 Representative voltage stresses in service . 18
4.1 Origin and classification of voltage stresses . 18
4.2 Characteristics of overvoltage protective protection devices. 18
4.2.1 General remarks . 20
4.2.2 Metal-oxide surge arresters without gaps (MOSA) . 21
Spark gaps .
4.2.3 Line surge arresters (LSA) for overhead transmission and distribution
lines . 22
4.3 Representative voltages and overvoltages . 23
4.3.1 Continuous (power-frequency) voltage . 23
4.3.2 Temporary overvoltages . 23
4.3.3 Slow-front overvoltages . 27
4.3.4 Fast-front overvoltages . 33
4.3.5 Very-fast-front overvoltages [13] . 37
5 Co-ordination withstand voltage . 38
5.1 Insulation strength characteristics . 38
5.1.1 General . 38
5.1.2 Influence of polarity and overvoltage shapes . 40
5.1.3 Phase-to-phase and longitudinal insulation . 40
5.1.4 Influence of weather conditions on external insulation . 41
5.1.5 Probability of disruptive discharge of insulation . 41
5.2 Performance criterion . 43
5.3 Insulation co-ordination procedures . 43
5.3.1 General . 43
5.3.2 Insulation co-ordination procedures for continuous (power-frequency)
voltage and temporary overvoltage . 44
5.3.3 Insulation co-ordination procedures for slow-front overvoltages . 46
5.3.4 Insulation co-ordination procedures for fast-front overvoltages . 51
6 Required withstand voltage . 52
6.1 General remarks . 52
6.2 Atmospheric correction . 52
6.2.1 General remarks . 52
6.2.2 Altitude correction . 52
6.3 Safety factors. 54
6.3.1 General . 54
6.3.2 Ageing . 54
6.3.3 Production and assembly dispersion . 54
6.3.4 Inaccuracy of the withstand voltage . 54
6.3.5 Recommended safety factors (K ) . 55
s
7 Standard withstand voltage and testing procedures . 55
7.1 General remarks . 55
7.1.1 Overview . 55
7.1.2 Standard switching impulse withstand voltage . 55
7.1.3 Standard lightning impulse withstand voltage . 56
7.2 Test conversion factors . 56
7.2.1 Range I. 56
7.2.2 Range II . 57
7.3 Determination of insulation withstand by type tests . 57
7.3.1 Test procedure dependency upon insulation type . 57
7.3.2 Non-self-restoring insulation . 58
7.3.3 Self-restoring insulation . 58
7.3.4 Mixed insulation . 58
7.3.5 Limitations of the test procedures . 59
7.3.6 Selection of the type test procedures . 60
7.3.7 Selection of the type test voltages . 60
8 Special considerations for overhead lines . 61
8.1 General remarks . 61
8.2 Insulation co-ordination for operating voltages and temporary overvoltages . 61
8.3 Insulation co-ordination for slow-front overvoltages . 61
8.3.1 General . 61
8.3.2 Earth-fault overvoltages . 62
8.3.3 Energization and re-energization overvoltages . 62
8.4 Insulation co-ordination for lightning overvoltages . 62
8.4.1 General . 62
8.4.2 Distribution lines . 62
8.4.3 Transmission lines . 63
9 Special considerations for substations . 63
9.1 General remarks . 63
9.1.1 Overview . 63
9.1.2 Operating voltage . 63
9.1.3 Temporary overvoltage . 63
9.1.4 Slow-front overvoltages . 64
9.1.5 Fast-front overvoltages . 64
9.2 Insulation co-ordination for overvoltages . 64
9.2.1 Substations in distribution systems with U up to 36 kV in range I . 64
m
9.2.2 Substations in transmission systems with U between 52,5 kV and
m
245 kV in range I . 65
9.2.3 Substations in transmission systems in range II . 66
Annex (normative) Clearances in air to assure a specified impulse withstand voltage
installation .
Annex A (informative) Determination of temporary overvoltages due to earth faults . 71
Annex B (informative) Weibull probability distributions . 75
B.1 General remarks . 75
B.2 Disruptive discharge probability of external insulation . 76
B.3 Cumulative frequency distribution of overvoltages . 78
Annex C (informative) Determination of the representative slow-front overvoltage due
to line energization and re-energization . 81
– 4 – IEC 60071-2:2018 RLV IEC 2018
C.1 General remarks . 81
C.2 Probability distribution of the representative amplitude of the prospective
overvoltage phase-to-earth . 81
C.3 Probability distribution of the representative amplitude of the prospective
overvoltage phase-to-phase . 81
C.4 Insulation characteristic . 83
C.5 Numerical example . 85
Annex D (informative) Transferred overvoltages in transformers . 91
D.1 General remarks . 91
D.2 Transferred temporary overvoltages . 92
D.3 Capacitively transferred surges . 92
D.4 Inductively transferred surges . 94
Annex E (informative) Lightning overvoltages . 98
E.1 General remarks . 98
E.2 Determination of the limit distance (X ) . 98
p
E.2.1 Protection with arresters in the substation . 98
E.2.2 Self-protection of substation . 99
E.3 Estimation of the representative lightning overvoltage amplitude. 100
E.3.1 General . 100
E.3.2 Shielding penetration . 100
E.3.3 Back flashovers . 101
E.4 Simplified method . 103
E.5 Assumed maximum value of the representative lightning overvoltage . 104
Annex F (informative) Calculation of air gap breakdown strength from experimental
data . 106
F.1 General . 106
F.2 Insulation response to power-frequency voltages . 106
F.3 Insulation response to slow-front overvoltages . 107
F.4 Insulation response to fast-front overvoltages . 108
Annex G (informative) Examples of insulation co-ordination procedure . 112
G.1 Overview. 112
G.2 Numerical example for a system in range I (with nominal voltage of 230 kV) . 112
G.2.1 General . 112
G.2.2 Part 1: no special operating conditions . 113
G.2.3 Part 2: influence of capacitor switching at station 2 . 120
G.2.4 Part 3: flow charts related to the example of Clause G.2 . 122
G.3 Numerical example for a system in range II (with nominal voltage of 735 kV) . 127
G.3.1 General . 127
G.3.2 Step 1: determination of the representative overvoltages –
values of U . 127
rp
G.3.3 Step 2: determination of the co-ordination withstand voltages –
values of U . 128
cw
G.3.4 Step 3: determination of the required withstand voltages – values of
U . 129
rw
G.3.5 Step 4: conversion to switching impulse withstand voltages (SIWV) . 130
G.3.6 Step 5: selection of standard insulation levels . 130
G.3.7 Considerations relative to phase-to-phase insulation co-ordination . 131
G.3.8 Phase-to-earth clearances . 132
G.3.9 Phase-to-phase clearances . 133
G.4 Numerical example for substations in distribution systems with U up to
m
36 kV in range I . 133
G.4.1 General . 133
G.4.2 Step 1: determination of the representative overvoltages –
values of U . 133
rp
G.4.3 Step 2: determination of the co-ordination withstand voltages –
values of U . 134
cw
G.4.4 Step 3: determination of required withstand voltages – values of U . 135
rw
G.4.5 Step 4: conversion to standard short-duration power-frequency and
lightning impulse withstand voltages . 136
G.4.6 Step 5: selection of standard withstand voltages . 137
G.4.7 Summary of insulation co-ordination procedure for the example of
Clause G.4 . 137
Annex H (informative) Atmospheric correction – Altitude correction . 139
H.1 General principles . 139
H.1.1 Atmospheric correction in standard tests . 139
H.1.2 Task of atmospheric correction in insulation co-ordination . 140
H.2 Atmospheric correction in insulation co-ordination . 142
H.2.1 Factors for atmospheric correction . 142
H.2.2 General characteristics for moderate climates . 142
H.2.3 Special atmospheric conditions . 143
H.2.4 Altitude dependency of air pressure . 144
H.3 Altitude correction . 145
H.3.1 Definition of the altitude correction factor . 145
H.3.2 Principle of altitude correction . 146
H.3.3 Standard equipment operating at altitudes up to 1 000 m . 147
H.3.4 Equipment operating at altitudes above 1 000 m . 147
H.4 Selection of the exponent m . 148
H.4.1 General . 148
H.4.2 Derivation of exponent m for switching impulse voltage . 148
H.4.3 Derivation of exponent m for critical switching impulse voltage . 151
Annex I (informative) Evaluation method of non-standard lightning overvoltage shape
for representative voltages and overvoltages . 154
I.1 General remarks . 154
I.2 Lightning overvoltage shape . 154
I.3 Evaluation method for GIS . 154
I.3.1 Experiments . 154
I.3.2 Evaluation of overvoltage shape . 155
I.4 Evaluation method for transformer . 155
I.4.1 Experiments . 155
I.4.2 Evaluation of overvoltage shape . 155
Annex J (informative) Insulation co-ordination for very-fast-front overvoltages in UHV
substations . 162
J.1 General . 162
J.2 Influence of disconnector design . 162
J.3 Insulation co-ordination for VFFO . 163
Bibliography . 165
Figure 1 – Range of 2 % slow-front overvoltages at the receiving end due to line
energization and re-energization . 26
– 6 – IEC 60071-2:2018 RLV IEC 2018
Figure 2 – Ratio between the 2 % values of slow-front overvoltages phase-to-phase
and phase-to-earth . 27
Figure 3 – Diagram for surge arrester connection to the protected object . 34
Figure 4 – Distributive discharge probability of self-restoring insulation described on a
linear scale . 42
Figure 5 – Disruptive discharge probability of self-restoring insulation described on a
Gaussian scale . 43
Figure 6 – Evaluation of deterministic co-ordination factor K . 43
cd
Figure 7 – Evaluation of the risk of failure . 44
Figure 8 – Risk of failure of external insulation for slow-front overvoltages as a function
of the statistical co-ordination factor K . 46
cs
Figure 9 – Dependence of exponent m on the co-ordination switching impulse
withstand voltage . 48
Figure 10 – Probability P of an equipment to pass the test dependent on the difference
K between the actual and the rated impulse withstand voltage . 54
Figure 11 – Example of a schematic substation layout used for the overvoltage stress
location (see 7.1) . 58
Figure A.1 – Earth fault factor k on a base of X /X for R /X = R = 0. 64
0 1 1 1
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 . 64
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 . 65
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 . 65
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 . 66
1 1
Figure B.1 – Conversion chart for the reduction of the withstand voltage due to placing
insulation configurations in parallel . 72
Figure C.1 – Example for bivariate phase-to-phase overvoltage curves with constant
probability density and tangents giving the relevant 2 % values . 79
Figure C.2 – Principle of the determination of the representative phase-to-phase
overvoltage U . 80
pre
Figure C.3 – Schematic phase-phase-earth insulation configuration . 81
Figure C.4 – Description of the 50 % switching impulse flashover voltage of a phase-
phase-earth insulation . 81
Figure C.5 – 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 . 82
Figure D.1 – Distributed capacitances of the windings of a transformer and the
equivalent circuit describing the windings . 88
Figure D.2 – Values of factor J describing the effect of the winding connections on the
inductive surge transference . 89
Figure H.1 – Principle of the atmospheric correction during test of a specified
insulation level according to the procedure of IEC 60060-1 . 132
Figure H.2 – Principal task of the atmospheric correction in insulation co-ordination
according to IEC 60071-1 . 133
Figure H.3 – Comparison of atmospheric correction δ × k with relative air pressure
h
p/p for various weather stations around the world . 135
Figure H.4 – Deviation of simplified pressure calculation by exponential function in this
document from the temperature dependent pressure calculation of ISO 2533 . 137
Figure H.5 – Principle of altitude correction: decreasing withstand voltage U of
equipment with increasing altitude . 138
Figure H.6 – Sets of m-curves for standard switching impulse voltage including the
variations in altitude for each gap factor . 142
Figure H.7 – Exponent m for standard switching impulse voltage for selected gap
factors covering altitudes up to 4 000 m . 143
Figure H.8 – Sets of m-curves for critical switching impulse voltage including the
variations in altitude for each gap factor . 144
Figure H.9 – Exponent m for critical switching impulse voltage for selected gap factors
covering altitudes up to 4 000 m . 144
Figure H.10 – Accordance of m-curves from Figure 9 with determination of exponent m
by means of critical switching impulse voltage for selected gap factors and altitudes . 145
Figure I.1 – Examples of lightning overvoltage shapes . 149
Figure I.2 – Example of insulation characteristics with respect to lightning overvoltages
of the SF gas gap (Shape E) . 150
Figure I.3 – Calculation of duration time T . 150
d
Figure I.4 – Shape evaluation flow for GIS and transformer . 151
Figure I.5 – Application to GIS lightning overvoltage . 152
Figure I.6 – Example of insulation characteristics with respect to lightning overvoltage
of the turn-to-turn insulation (Shape C) . 152
Figure I.7 – Application to transformer lightning overvoltage . 153
Figure J.1 – Insulation co-ordination for very-fast-front overvoltages. 156
Table – Recommended creepage distances .
Table – Correlation between standard lightning impulse withstand voltages and
minimum air clearances .
Table – Correlation between standard switching impulse withstand voltages and
minimum phase-to-earth air clearances.
Table – Correlation between standard switching impulse withstand voltages and
minimum phase-to-phase air clearances .
Table 1 – Test conversion factors for range I, to convert required SIWV to SDWV and
LIWV . 52
Table 2 – Test conversion factors for range II to convert required SDWV to SIWV . 52
Table 3 – Selectivity of test procedures B and C of IEC 60060-1 . 54
Table B.1 – Breakdown voltage versus cumulative flashover probability – Single
insulation and 100 parallel insulations . 70
Table E.1 – Corona damping constant K . 91
co
Table E.2 – Factor A for various overhead lines . 96
Table F.1 – Typical gap factors K for switching impulse breakdown phase-to-earth
(according to [1] and [4]) . 102
Table F.2 – Gap factors for typical phase-to-phase geometries . 103
Table G.1 – Summary of minimum required withstand voltages obtained for the
example shown in G.2.2 . 111
Table G.2 – Summary of required withstand voltages obtained for the example shown
in G.2.3 . 113
Table G.3 – Values related to the insulation co-ordination procedure for the example
in G.4. 130
Table H.1 – Comparison of functional expressions of Figure 9 with the selected
parameters from the derivation of m-curves with critical switching impulse. 145
– 8 – IEC 60071-2:2018 RLV IEC 2018
Table I.1 – Evaluation of the lightning overvoltage in the GIS of UHV system . 150
Table I.2 – Evaluation of lightning overvoltage in the transformer of 500 kV system . 153
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSULATION CO-ORDINATION –
Part 2: Application guidelines
FOREWORD
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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
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This redline version of the official IEC Standard allows the user to identify the changes
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– 10 – IEC 60071-2:2018 RLV IEC 2018
International Standard IEC 60071-2 has been prepared by IEC technical committee 28:
Insulation co-ordination.
This fourth edition cancels and replaces the third edition published in 1996. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) the annex on clearance in air to assure a specified impulse withstand voltage installation
is deleted because the annex in IEC 60071-1 is overlapped;
b) 4.2 and 4.3 on surge arresters are updated;
c) 4.3.5 on very-fast-front overvoltages is revised. Annex J on insulation co-ordination for
very-fast-front overvoltages in UHV substations is added;
d) Annex H on atmospheric correction – altitude correction is added.
e) Annex I on evaluation method of non-standard lightning overvoltage shape is added.
The text of this International Standard is based on the following documents:
FDIS Report on voting
28/255/FDIS 28/256/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
It has the status of a horizontal standard in accordance with IEC Guide 108.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://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.
IMPORTANT – The 'colour inside' logo on the cover page of this publication 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.
INSULATION CO-ORDINATION –
Part 2: Application guidelines
1 General
1 Scope
This part of IEC 60071 constitutes an application guidelines and deals with the selection of
insulation levels of equipment or installations for three-phase electrical systems. Its aim is to
give guidance for the determination of the rated withstand voltages for ranges I and II of
IEC 60071-1 and to justify the association of these rated values with the standardized highest
voltages for equipment.
This association is for insulation co-ordination purposes only. The requirements for human
safety are not covered by this document.
This document covers three-phase systems with nominal voltages above 1 kV. The values
derived or proposed herein are generally applicable only to such systems. However, the
concepts presented are also valid for two-phase or single-phase systems.
This document covers phase-to-earth, phase-to-phase and longitudinal insulation.
This document is not intended to deal with routine tests. These are to be specified by the
relevant product committees.
The content of this document strictly follows the flow chart of the insulation co-ordination
process presented in Figure 1 of IEC 60071-1:2006. Clauses 4 to 7 correspond to the squares
in this flow chart and give detailed information on the concepts governing the insulation co-
ordination process which leads to the establishment of the required withstand levels.
This document emphasizes the necessity of considering, at the very beginning, all origins, all
classes and all types of voltage stresses in service irrespective of the range of highest voltage
for equipment. Only at the end of the process, when the selection of the standard withstand
voltages takes place, does the principle of covering a particular service voltage stress by a
standard withstand voltage apply. Also, at this final step, this document refers to the
correlation made in IEC 60071-1 between the standard insulation levels and the highest
voltage for equipment.
The annexes contain examples and detailed information which explain or 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 c
...
IEC 60071-2 ®
Edition 4.0 2018-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
HORIZONTAL STANDARD
NORME HORIZONTALE
Insulation co-ordination –
Part 2: Application guidelines
Coordination de l'isolement –
Partie 2: Lignes directrices en matière d'application
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IEC 60071-2 ®
Edition 4.0 2018-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
HORIZONTAL STANDARD
NORME HORIZONTALE
Insulation co-ordination –
Part 2: Application guidelines
Coordination de l'isolement –
Partie 2: Lignes directrices en matière d'application
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.080.30 ISBN 978-2-8322-5405-9
– 2 – IEC 60071-2:2018 IEC 2018
CONTENTS
FOREWORD . 8
1 Scope . 10
2 Normative references . 10
3 Terms, definitions, abbreviated terms and symbols . 11
3.1 Terms and definitions . 11
3.2 Abbreviated terms . 11
3.3 Symbols . 11
4 Representative voltage stresses in service . 16
4.1 Origin and classification of voltage stresses . 16
4.2 Characteristics of overvoltage protection devices . 17
4.2.1 General remarks . 17
4.2.2 Metal-oxide surge arresters without gaps (MOSA) . 17
4.2.3 Line surge arresters (LSA) for overhead transmission and distribution
lines . 19
4.3 Representative voltages and overvoltages . 19
4.3.1 Continuous (power-frequency) voltage . 19
4.3.2 Temporary overvoltages . 20
4.3.3 Slow-front overvoltages . 23
4.3.4 Fast-front overvoltages . 29
4.3.5 Very-fast-front overvoltages [13] . 33
5 Co-ordination withstand voltage . 34
5.1 Insulation strength characteristics . 34
5.1.1 General . 34
5.1.2 Influence of polarity and overvoltage shapes . 35
5.1.3 Phase-to-phase and longitudinal insulation . 36
5.1.4 Influence of weather conditions on external insulation . 36
5.1.5 Probability of disruptive discharge of insulation . 37
5.2 Performance criterion . 38
5.3 Insulation co-ordination procedures . 39
5.3.1 General . 39
5.3.2 Insulation co-ordination procedures for continuous (power-frequency)
voltage and temporary overvoltage . 40
5.3.3 Insulation co-ordination procedures for slow-front overvoltages . 40
5.3.4 Insulation co-ordination procedures for fast-front overvoltages . 45
6 Required withstand voltage . 46
6.1 General remarks . 46
6.2 Atmospheric correction . 46
6.2.1 General remarks . 46
6.2.2 Altitude correction . 46
6.3 Safety factors. 48
6.3.1 General . 48
6.3.2 Ageing . 48
6.3.3 Production and assembly dispersion . 48
6.3.4 Inaccuracy of the withstand voltage . 48
6.3.5 Recommended safety factors (K ) . 49
s
7 Standard withstand voltage and testing procedures . 49
7.1 General remarks . 49
7.1.1 Overview . 49
7.1.2 Standard switching impulse withstand voltage . 49
7.1.3 Standard lightning impulse withstand voltage . 50
7.2 Test conversion factors . 50
7.2.1 Range I. 50
7.2.2 Range II . 51
7.3 Determination of insulation withstand by type tests . 51
7.3.1 Test procedure dependency upon insulation type . 51
7.3.2 Non-self-restoring insulation . 52
7.3.3 Self-restoring insulation . 52
7.3.4 Mixed insulation . 52
7.3.5 Limitations of the test procedures . 53
7.3.6 Selection of the type test procedures . 54
7.3.7 Selection of the type test voltages . 54
8 Special considerations for overhead lines . 55
8.1 General remarks . 55
8.2 Insulation co-ordination for operating voltages and temporary overvoltages . 55
8.3 Insulation co-ordination for slow-front overvoltages . 55
8.3.1 General . 55
8.3.2 Earth-fault overvoltages . 56
8.3.3 Energization and re-energization overvoltages . 56
8.4 Insulation co-ordination for lightning overvoltages . 56
8.4.1 General . 56
8.4.2 Distribution lines . 56
8.4.3 Transmission lines . 57
9 Special considerations for substations . 57
9.1 General remarks . 57
9.1.1 Overview . 57
9.1.2 Operating voltage . 57
9.1.3 Temporary overvoltage . 57
9.1.4 Slow-front overvoltages . 58
9.1.5 Fast-front overvoltages . 58
9.2 Insulation co-ordination for overvoltages . 58
9.2.1 Substations in distribution systems with U up to 36 kV in range I . 58
m
9.2.2 Substations in transmission systems with U between 52,5 kV and
m
245 kV in range I . 59
9.2.3 Substations in transmission systems in range II . 60
Annex A (informative) Determination of temporary overvoltages due to earth faults . 61
Annex B (informative) Weibull probability distributions . 65
B.1 General remarks . 65
B.2 Disruptive discharge probability of external insulation . 66
B.3 Cumulative frequency distribution of overvoltages . 68
Annex C (informative) Determination of the representative slow-front overvoltage due
to line energization and re-energization . 71
C.1 General remarks . 71
C.2 Probability distribution of the representative amplitude of the prospective
overvoltage phase-to-earth . 71
– 4 – IEC 60071-2:2018 IEC 2018
C.3 Probability distribution of the representative amplitude of the prospective
overvoltage phase-to-phase . 71
C.4 Insulation characteristic . 73
C.5 Numerical example . 75
Annex D (informative) Transferred overvoltages in transformers . 81
D.1 General remarks . 81
D.2 Transferred temporary overvoltages . 82
D.3 Capacitively transferred surges . 82
D.4 Inductively transferred surges . 84
Annex E (informative) Lightning overvoltages . 88
E.1 General remarks . 88
E.2 Determination of the limit distance (X ) . 88
p
E.2.1 Protection with arresters in the substation . 88
E.2.2 Self-protection of substation . 89
E.3 Estimation of the representative lightning overvoltage amplitude. 90
E.3.1 General . 90
E.3.2 Shielding penetration . 90
E.3.3 Back flashovers . 91
E.4 Simplified method . 93
E.5 Assumed maximum value of the representative lightning overvoltage . 95
Annex F (informative) Calculation of air gap breakdown strength from experimental
data . 96
F.1 General . 96
F.2 Insulation response to power-frequency voltages . 96
F.3 Insulation response to slow-front overvoltages . 97
F.4 Insulation response to fast-front overvoltages . 98
Annex G (informative) Examples of insulation co-ordination procedure . 102
G.1 Overview. 102
G.2 Numerical example for a system in range I (with nominal voltage of 230 kV) . 102
G.2.1 General . 102
G.2.2 Part 1: no special operating conditions . 103
G.2.3 Part 2: influence of capacitor switching at station 2 . 110
G.2.4 Part 3: flow charts related to the example of Clause G.2 . 112
G.3 Numerical example for a system in range II (with nominal voltage of 735 kV) . 117
G.3.1 General . 117
G.3.2 Step 1: determination of the representative overvoltages –
values of U . 117
rp
G.3.3 Step 2: determination of the co-ordination withstand voltages –
values of U . 118
cw
G.3.4 Step 3: determination of the required withstand voltages – values of
U . 119
rw
G.3.5 Step 4: conversion to switching impulse withstand voltages (SIWV) . 120
G.3.6 Step 5: selection of standard insulation levels . 120
G.3.7 Considerations relative to phase-to-phase insulation co-ordination . 121
G.3.8 Phase-to-earth clearances . 122
G.3.9 Phase-to-phase clearances . 122
G.4 Numerical example for substations in distribution systems with U up to
m
36 kV in range I . 123
G.4.1 General . 123
G.4.2 Step 1: determination of the representative overvoltages –
values of U . 123
rp
G.4.3 Step 2: determination of the co-ordination withstand voltages –
values of U . 124
cw
G.4.4 Step 3: determination of required withstand voltages – values of U . 125
rw
G.4.5 Step 4: conversion to standard short-duration power-frequency and
lightning impulse withstand voltages . 126
G.4.6 Step 5: selection of standard withstand voltages . 126
G.4.7 Summary of insulation co-ordination procedure for the example of
Clause G.4 . 127
Annex H (informative) Atmospheric correction – Altitude correction . 129
H.1 General principles . 129
H.1.1 Atmospheric correction in standard tests . 129
H.1.2 Task of atmospheric correction in insulation co-ordination . 130
H.2 Atmospheric correction in insulation co-ordination . 132
H.2.1 Factors for atmospheric correction . 132
H.2.2 General characteristics for moderate climates . 132
H.2.3 Special atmospheric conditions . 133
H.2.4 Altitude dependency of air pressure . 134
H.3 Altitude correction . 135
H.3.1 Definition of the altitude correction factor . 135
H.3.2 Principle of altitude correction . 136
H.3.3 Standard equipment operating at altitudes up to 1 000 m . 137
H.3.4 Equipment operating at altitudes above 1 000 m . 137
H.4 Selection of the exponent m . 138
H.4.1 General . 138
H.4.2 Derivation of exponent m for switching impulse voltage . 138
H.4.3 Derivation of exponent m for critical switching impulse voltage . 141
Annex I (informative) Evaluation method of non-standard lightning overvoltage shape
for representative voltages and overvoltages . 144
I.1 General remarks . 144
I.2 Lightning overvoltage shape . 144
I.3 Evaluation method for GIS . 144
I.3.1 Experiments . 144
I.3.2 Evaluation of overvoltage shape . 145
I.4 Evaluation method for transformer . 145
I.4.1 Experiments . 145
I.4.2 Evaluation of overvoltage shape . 145
Annex J (informative) Insulation co-ordination for very-fast-front overvoltages in UHV
substations . 152
J.1 General . 152
J.2 Influence of disconnector design . 152
J.3 Insulation co-ordination for VFFO . 153
Bibliography . 155
Figure 1 – Range of 2 % slow-front overvoltages at the receiving end due to line
energization and re-energization . 25
Figure 2 – Ratio between the 2 % values of slow-front overvoltages phase-to-phase
and phase-to-earth . 26
Figure 3 – Diagram for surge arrester connection to the protected object . 33
– 6 – IEC 60071-2:2018 IEC 2018
Figure 4 – Distributive discharge probability of self-restoring insulation described on a
linear scale . 41
Figure 5 – Disruptive discharge probability of self-restoring insulation described on a
Gaussian scale . 41
Figure 6 – Evaluation of deterministic co-ordination factor K . 42
cd
Figure 7 – Evaluation of the risk of failure . 43
Figure 8 – Risk of failure of external insulation for slow-front overvoltages as a function
of the statistical co-ordination factor K . 45
cs
Figure 9 – Dependence of exponent m on the co-ordination switching impulse
withstand voltage . 47
Figure 10 – Probability P of an equipment to pass the test dependent on the difference
K between the actual and the rated impulse withstand voltage . 53
Figure 11 – Example of a schematic substation layout used for the overvoltage stress
location . 57
Figure A.1 – Earth fault factor k on a base of X /X for R /X = R = 0. 62
0 1 1 1
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 . 62
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 . 63
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 . 63
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 . 64
1 1
Figure B.1 – Conversion chart for the reduction of the withstand voltage due to placing
insulation configurations in parallel . 70
Figure C.1 – Example for bivariate phase-to-phase overvoltage curves with constant
probability density and tangents giving the relevant 2 % values . 77
Figure C.2 – Principle of the determination of the representative phase-to-phase
overvoltage U . 78
pre
Figure C.3 – Schematic phase-phase-earth insulation configuration . 79
Figure C.4 – Description of the 50 % switching impulse flashover voltage of a phase-
phase-earth insulation . 79
Figure C.5 – 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 . 80
Figure D.1 – Distributed capacitances of the windings of a transformer and the
equivalent circuit describing the windings . 86
Figure D.2 – Values of factor J describing the effect of the winding connections on the
inductive surge transference . 87
Figure H.1 – Principle of the atmospheric correction during test of a specified
insulation level according to the procedure of IEC 60060-1 . 130
Figure H.2 – Principal task of the atmospheric correction in insulation co-ordination
according to IEC 60071-1 . 131
Figure H.3 – Comparison of atmospheric correction δ × k with relative air pressure
h
p/p for various weather stations around the world . 133
Figure H.4 – Deviation of simplified pressure calculation by exponential function in this
document from the temperature dependent pressure calculation of ISO 2533 . 135
Figure H.5 – Principle of altitude correction: decreasing withstand voltage U of
equipment with increasing altitude . 136
Figure H.6 – Sets of m-curves for standard switching impulse voltage including the
variations in altitude for each gap factor . 140
Figure H.7 – Exponent m for standard switching impulse voltage for selected gap
factors covering altitudes up to 4 000 m . 141
Figure H.8 – Sets of m-curves for critical switching impulse voltage including the
variations in altitude for each gap factor . 142
Figure H.9 – Exponent m for critical switching impulse voltage for selected gap factors
covering altitudes up to 4 000 m . 142
Figure H.10 – Accordance of m-curves from Figure 9 with determination of exponent m
by means of critical switching impulse voltage for selected gap factors and altitudes . 143
Figure I.1 – Examples of lightning overvoltage shapes . 147
Figure I.2 – Example of insulation characteristics with respect to lightning overvoltages
of the SF gas gap (Shape E) . 148
Figure I.3 – Calculation of duration time T . 148
d
Figure I.4 – Shape evaluation flow for GIS and transformer . 149
Figure I.5 – Application to GIS lightning overvoltage . 150
Figure I.6 – Example of insulation characteristics with respect to lightning overvoltage
of the turn-to-turn insulation (Shape C) . 150
Figure I.7 – Application to transformer lightning overvoltage . 151
Figure J.1 – Insulation co-ordination for very-fast-front overvoltages. 154
Table 1 – Test conversion factors for range I, to convert required SIWV to SDWV and
LIWV . 51
Table 2 – Test conversion factors for range II to convert required SDWV to SIWV . 51
Table 3 – Selectivity of test procedures B and C of IEC 60060-1 . 53
Table B.1 – Breakdown voltage versus cumulative flashover probability – Single
insulation and 100 parallel insulations . 67
Table E.1 – Corona damping constant K . 89
co
Table E.2 – Factor A for various overhead lines . 94
Table F.1 – Typical gap factors K for switching impulse breakdown phase-to-earth
(according to [1] and [4]) . 100
Table F.2 – Gap factors for typical phase-to-phase geometries . 101
Table G.1 – Summary of minimum required withstand voltages obtained for the
example shown in G.2.2 . 109
Table G.2 – Summary of required withstand voltages obtained for the example shown
in G.2.3 . 111
Table G.3 – Values related to the insulation co-ordination procedure for the example
in G.4. 128
Table H.1 – Comparison of functional expressions of Figure 9 with the selected
parameters from the derivation of m-curves with critical switching impulse. 143
Table I.1 – Evaluation of the lightning overvoltage in the GIS of UHV system . 148
Table I.2 – Evaluation of lightning overvoltage in the transformer of 500 kV system . 151
– 8 – IEC 60071-2:2018 IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSULATION CO-ORDINATION –
Part 2: Application guidelines
FOREWORD
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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 rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60071-2 has been prepared by IEC technical committee 28:
Insulation co-ordination.
This fourth edition cancels and replaces the third edition published in 1996. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) the annex on clearance in air to assure a specified impulse withstand voltage installation
is deleted because the annex in IEC 60071-1 is overlapped;
b) 4.2 and 4.3 on surge arresters are updated;
c) 4.3.5 on very-fast-front overvoltages is revised. Annex J on insulation co-ordination for
very-fast-front overvoltages in UHV substations is added;
d) Annex H on atmospheric correction – altitude correction is added.
e) Annex I on evaluation method of non-standard lightning overvoltage shape is added.
The text of this International Standard is based on the following documents:
FDIS Report on voting
28/255/FDIS 28/256/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
It has the status of a horizontal standard in accordance with IEC Guide 108.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://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.
IMPORTANT – The 'colour inside' logo on the cover page of this publication 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.
– 10 – IEC 60071-2:2018 IEC 2018
INSULATION CO-ORDINATION –
Part 2: Application guidelines
1 Scope
This part of IEC 60071 constitutes application guidelines and deals with the selection of
insulation levels of equipment or installations for three-phase electrical systems. Its aim is to
give guidance for the determination of the rated withstand voltages for ranges I and II of
IEC 60071-1 and to justify the association of these rated values with the standardized highest
voltages for equipment.
This association is for insulation co-ordination purposes only. The requirements for human
safety are not covered by this document.
This document covers three-phase systems with nominal voltages above 1 kV. The values
derived or proposed herein are generally applicable only to such systems. However, the
concepts presented are also valid for two-phase or single-phase systems.
This document covers phase-to-earth, phase-to-phase and longitudinal insulation.
This document is not intended to deal with routine tests. These are to be specified by the
relevant product committees.
The content of this document strictly follows the flow chart of the insulation co-ordination
process
...
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