Insulation co-ordination - Part 1: Definitions, principles and rules

This part of IEC 60071 applies to three-phase AC systems having a highest voltage for
equipment above 1 kV. It specifies the procedure for the selection of the rated withstand
voltages for the phase-to-earth, phase-to-phase and longitudinal insulation of the equipment
and the installations of these systems. It also gives the lists of the standard withstand
voltages from which the rated withstand voltages are selected.
This document describes that the selected withstand voltages are associated with the highest
voltage for equipment. This association is for insulation co-ordination purposes only. The
requirements for human safety are not covered by this document.
Although the principles of this document also apply to transmission line insulation, the values
of their withstand voltages can be different from the standard rated withstand voltages.
The apparatus committees are responsible for specifying the rated withstand voltages and the
test procedures suitable for the relevant equipment taking into consideration the
recommendations of this document.
NOTE In IEC 60071-2, all rules for insulation co-ordination given in this document are justified in detail, in
particular the association of the standard rated withstand voltages with the highest voltage for equipment. When
more than one set of standard rated withstand voltages is associated with the same highest voltage for equipment,
guidance is provided for the selection of the most suitable set.
This horizontal standard is primarily intended for use by technical committees in the
preparation of standards in accordance with the principles laid down in IEC Guide 108.
One of the responsibilities of a technical committee is, wherever applicable, to make use of
horizontal standards in the preparation of its publications. The contents of this horizontal
standard will not apply unless specifically referred to or included in the relevant publications.

Isolationskoordination - Teil 1: Begriffe, Grundsätze und Anforderungen

Coordination de l'isolement Partie 1: Définitions, principes et règles

IEC 60071-1:2019 est disponible sous forme de IEC 60071-1:2019 RLV qui contient la Norme internationale et sa version Redline, illustrant les modifications du contenu technique depuis l'édition précédente.L'IEC 60071-1:2019 s'applique aux réseaux à tension alternative triphasée dont la tension la plus élevée pour le matériel est supérieure à 1 kV. Elle spécifie la procédure à suivre pour le choix des tensions de tenue assignées normalisées pour l'isolation phase-terre, l'isolation entre phases et l'isolation longitudinale du matériel et des installations de ces réseaux. Elle donne également les listes des valeurs normalisées parmi lesquelles les tensions de tenue assignées normalisées sont choisies. Le présent document décrit que les tensions de tenue choisies sont associées aux tensions les plus élevées pour le matériel. Cette association est destinée aux seules fins de la coordination de l'isolement. Les exigences concernant la sécurité des personnes ne sont pas couvertes par le présent document. Bien que les principes du présent document s'appliquent également à l'isolation des lignes de transport d'énergie, les valeurs des tensions de tenue peuvent être différentes des tensions de tenue assignées normalisées. Il appartient aux comités de produits de spécifier les tensions de tenue et les procédures d'essai appropriées aux matériels correspondants, en prenant les recommandations du présent document en considération. NOTE Toutes les règles relatives à la coordination de l'isolement données dans le présent document sont justifiées en détail dans l'IEC 60071-2, en particulier en ce qui concerne l'association des tensions de tenue assignées normalisées avec les tensions les plus élevées pour le matériel. Lorsque plusieurs séries de tensions de tenue assignées normalisées sont associées à la même valeur de la tension la plus élevée pour le matériel, une ligne directrice est donnée pour le choix de la série la plus appropriée. Les principales modifications par rapport à l'édition précédente sont les suivantes: a) toutes les références ont été mises à jour en faveur des normes IEC actuelles et la bibliographie est supprimée; b) certaines définitions ont été modifiées afin d'éviter les chevauchements et de favoriser une bonne compréhension; c) les symboles littéraux ont été modifiés et corrigés afin de garantir la cohérence avec les normes IEC concernées; d) plusieurs titres ont été modifiés en vue d'une meilleure compréhension (voir les Articles A.2 et A.3, ainsi que l'Annexe B).

Koordinacija izolacije - 1. del: Definicije, načela in pravila

General Information

Status
Published
Publication Date
03-May-2021
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
15-Apr-2021
Due Date
20-Jun-2021
Completion Date
04-May-2021

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SLOVENSKI STANDARD
SIST EN IEC 60071-1:2021
01-junij-2021
Nadomešča:
SIST EN 60071-1:2006
SIST EN 60071-1:2006/A1:2010
Koordinacija izolacije - 1. del: Definicije, načela in pravila
Insulation co-ordination - Part 1: Definitions, principles and rules
Ta slovenski standard je istoveten z: EN IEC 60071-1:2019
ICS:
01.040.29 Elektrotehnika (Slovarji) Electrical engineering
(Vocabularies)
29.080.01 Električna izolacija na Electrical insulation in
splošno general
SIST EN IEC 60071-1:2021 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN IEC 60071-1:2021
---------------------- Page: 2 ----------------------
SIST EN IEC 60071-1:2021
EUROPEAN STANDARD EN IEC 60071-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2019
ICS 29.080.30 Supersedes EN 60071-1:2006 and all of its amendments
and corrigenda (if any)
English Version
Insulation co-ordination - Part 1: Definitions, principles and rules
(IEC 60071-1:2019)

Coordination de l'isolement Partie 1: Définitions, principes Isolationskoordination - Teil 1: Begriffe, Grundsätze und

et règles Anforderungen
(IEC 60071-1:2019) (IEC 60071-1:2019)

This European Standard was approved by CENELEC on 2019-09-12. CENELEC members are bound to comply with the CEN/CENELEC

Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC

Management Centre or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation

under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the

same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,

Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the

Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2019 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Ref. No. EN IEC 60071-1:2019 E
---------------------- Page: 3 ----------------------
SIST EN IEC 60071-1:2021
EN IEC 60071-1:2019 (E)
European foreword

The text of document 99/199/CDV, future edition 9 of IEC 60071-1, prepared by IEC/TC 99 "Insulation

co-ordination and system engineering of high voltage electrical power installations above 1,0 kV AC

and 1,5 kV DC" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as

EN IEC 60071-1:2019.
The following dates are fixed:

• latest date by which the document has to be implemented at national (dop) 2020-06-12

level by publication of an identical national standard or by endorsement

• latest date by which the national standards conflicting with the (dow) 2022-09-12

document have to be withdrawn

This document supersedes EN 60071-1:2006 and all of its amendments and corrigenda (if any).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.

Endorsement notice

The text of the International Standard IEC 60071-1:2019 was approved by CENELEC as a European

Standard without any modification.

In the official version, for Bibliography, the following notes have to be added for the standards

indicated:
IEC 60507 NOTE Harmonized as EN 60507
IEC 60633 NOTE Harmonized as EN IEC 60633
---------------------- Page: 4 ----------------------
SIST EN IEC 60071-1:2021
EN IEC 60071-1:2019 (E)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

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.

NOTE 1 Where an International Publication has been modified by common modifications, indicated by (mod), the relevant

EN/HD applies.

NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available here:

www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60038 - IEC standard voltages EN 60038 -
IEC 60060-1 - High-voltage test techniques - Part 1: General EN 60060-1 -
definitions and test requirements
IEC 60071-2 - Insulation co-ordination - Part 2: Application EN IEC 60071-2 -
guidelines
IEC 60099-4 - Surge arresters - Part 4: Metal-oxide surge EN 60099-4 -
arresters without gaps for a.c. systems
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SIST EN IEC 60071-1:2021
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SIST EN IEC 60071-1:2021
IEC 60071-1
Edition 9.0 2019-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
HORIZONTAL STANDARD
NORME HORIZONTALE
Insulation co-ordination –
Part 1: Definitions, principles and rules
Coordination de l'isolement –
Partie 1: Définitions, principes et règles
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.080.30 ISBN 978-2-8322-7171-1

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
---------------------- Page: 7 ----------------------
SIST EN IEC 60071-1:2021
– 2 – IEC 60071-1:2019  IEC 2019
CONTENTS

FOREWORD ........................................................................................................................... 4

1 Scope .............................................................................................................................. 6

2 Normative references ...................................................................................................... 6

3 Terms and definitions ...................................................................................................... 7

4 Abbreviated terms and symbols ..................................................................................... 14

4.1 General ................................................................................................................. 14

4.2 Subscripts ............................................................................................................. 14

4.3 Letter symbols ...................................................................................................... 14

4.4 Abbreviations ........................................................................................................ 15

5 Procedure for insulation co-ordination ........................................................................... 15

5.1 General outline of the procedure ........................................................................... 15

5.2 Determination of the representative voltages and overvoltages (U ) .................... 16

5.3 Determination of the co-ordination withstand voltages (U ) ................................. 18

5.4 Determination of the required withstand voltage (U ) .......................................... 18

5.5 Selection of the rated insulation level .................................................................... 19

5.6 List of standard rated short-duration power frequency withstand voltages ............. 20

5.7 List of standard rated impulse withstand voltages ................................................. 20

5.8 Ranges for highest voltage for equipment ............................................................. 20

5.9 Environmental conditions ...................................................................................... 20

5.9.1 Normal environmental conditions ................................................................... 20

5.9.2 Standard reference atmospheric conditions ................................................... 20

5.10 Selection of the standard insulation level .............................................................. 20

5.11 Background of the standard insulation level .......................................................... 24

5.11.1 General ......................................................................................................... 24

5.11.2 Standard rated switching impulse withstand voltage ...................................... 25

5.11.3 Standard rated lightning impulse withstand voltage ........................................ 25

6 Requirements for standard withstand voltage tests ........................................................ 25

6.1 General requirements ........................................................................................... 25

6.2 Standard short-duration power-frequency withstand voltage tests ......................... 26

6.3 Standard impulse withstand voltage tests.............................................................. 26

6.4 Alternative test situation ........................................................................................ 27

6.5 Phase-to-phase and longitudinal insulation standard withstand voltage tests

for equipment in range I ........................................................................................ 27

6.5.1 Power-frequency tests ................................................................................... 27

6.5.2 Phase-to-phase (or longitudinal) insulation lightning impulse tests ................. 28

6.6 Phase-to-phase and longitudinal insulation standard withstand voltage tests

for equipment in range II ....................................................................................... 28

Annex A (normative) Clearances in air to assure a specified impulse withstand voltage

installation ............................................................................................................................ 29

A.1 General ................................................................................................................. 29

A.2 Lightning impulse .................................................................................................. 30

A.3 Switching impulse ................................................................................................. 31

Annex B (informative) Rated insulation levels for highest voltages of equipment U

not standardized by IEC ........................................................................................................ 33

Bibliography .......................................................................................................................... 34

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SIST EN IEC 60071-1:2021
IEC 60071-1:2019  IEC 2019 – 3 –

Figure 1 – Flow chart for the determination of rated or standard insulation level ................... 16

Table 1 – Classes and shapes of overvoltages, Standard voltage shapes and Standard

withstand voltage tests ......................................................................................................... 17

Table 2 – Standard insulation levels for range I (1 kV < U ≤ 245 kV) .................................. 22

Table 3 – Standard insulation levels for range II (U > 245 kV) ............................................ 23

Table A.1 – Correlation between standard rated lightning impulse withstand voltages

and minimum air clearances ................................................................................................. 30

Table A.2 – Correlation between standard rated switching impulse withstand voltages

and minimum phase-to-earth air clearances .......................................................................... 31

Table A.3 – Correlation between standard rated switching impulse withstand voltages

and minimum phase-to-phase air clearances ........................................................................ 32

Table B.1 – Rated insulation levels for highest voltages of equipment U not

standardized by IEC.............................................................................................................. 33

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SIST EN IEC 60071-1:2021
– 4 – IEC 60071-1:2019  IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
INSULATION CO-ORDINATION –
Part 1: Definitions, principles and rules
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 in addition to other activities, IEC publishes International Standards, Technical Specifications,

Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC

Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested

in the subject dealt with may participate in this preparatory work. International, governmental and non-

governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely

with the International Organization for Standardization (ISO) in accordance with conditions determined by

agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence

between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

the latter.

5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

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) 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 60071-1 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.
This ninth edition cancels and replaces the eighth edition published in 2006 and
Amendment 1:2010. This edition constitutes a technical revision.
It has the status of a horizontal standard in accordance with IEC Guide 108.
The main changes from the previous edition are as follows:

a) all references are updated to current IEC standards, and the bibliography is deleted;

b) some definitions are clarified in order to avoid overlapping and ensure clear understanding;

c) letter symbols are changed and corrected in order to keep the consistency with relevant

IEC standards;

d) some titles are changed to clarify understanding (see Clauses A.2, A.3 and Annex B).

---------------------- Page: 10 ----------------------
SIST EN IEC 60071-1:2021
IEC 60071-1:2019  IEC 2019 – 5 –
The text of this International Standard is based on the following documents:
CDV Report on voting
99/199/CDV 99/227/RVC

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 publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

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 the base publication and its amendments will

remain unchanged until the stability date indicated on the IEC web site under

"http://webstore.iec.ch" in the data related to the specific publication. At this date, the

publication 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 publication using a colour printer.

---------------------- Page: 11 ----------------------
SIST EN IEC 60071-1:2021
– 6 – IEC 60071-1:2019  IEC 2019
INSULATION CO-ORDINATION –
Part 1: Definitions, principles and rules
1 Scope

This part of IEC 60071 applies to three-phase AC systems having a highest voltage for

equipment above 1 kV. It specifies the procedure for the selection of the rated withstand

voltages for the phase-to-earth, phase-to-phase and longitudinal insulation of the equipment

and the installations of these systems. It also gives the lists of the standard withstand

voltages from which the rated withstand voltages are selected.

This document describes that the selected withstand voltages are associated with the highest

voltage for equipment. This association is for insulation co-ordination purposes only. The

requirements for human safety are not covered by this document.

Although the principles of this document also apply to transmission line insulation, the values

of their withstand voltages can be different from the standard rated withstand voltages.

The apparatus committees are responsible for specifying the rated withstand voltages and the

test procedures suitable for the relevant equipment taking into consideration the

recommendations of this document.

NOTE In IEC 60071-2, all rules for insulation co-ordination given in this document are justified in detail, in

particular the association of the standard rated withstand voltages with the highest voltage for equipment. When

more than one set of standard rated withstand voltages is associated with the same highest voltage for equipment,

guidance is provided for the selection of the most suitable set.

This horizontal standard is primarily intended for use by technical committees in the

preparation of standards in accordance with the principles laid down in IEC Guide 108.

One of the responsibilities of a technical committee is, wherever applicable, to make use of

horizontal standards in the preparation of its publications. The contents of this horizontal

standard will not apply unless specifically referred to or included in the relevant publications.

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 60038, IEC standard voltages

IEC 60060-1, High-voltage test techniques – Part 1: General definitions and test requirements

IEC 60071-2, Insulation co-ordination – Part 2: Application guidelines

IEC 60099-4, Surge arresters – Part 4: Metal-oxide surge arresters without gaps for a.c.

systems
---------------------- Page: 12 ----------------------
SIST EN IEC 60071-1:2021
IEC 60071-1:2019  IEC 2019 – 7 –
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
insulation co-ordination

selection of the dielectric strength of equipment in relation to the operating voltages and

overvoltages which can appear on the system for which the equipment is intended, and taking

into account the service environment and the characteristics of the available preventing and

protective devices

Note 1 to entry: By "dielectric strength" of the equipment, is meant here its rated insulation level (3.36) or its

standard insulation level (3.37).

[SOURCE: IEC 60050-614:2016, 614-03-08, modified – Note 1 to entry has been added]

3.2
external insulation

distances in atmospheric air, and the surfaces in contact with atmospheric air of solid

insulation of the equipment which are subject to dielectric stresses and to the effects of

atmospheric and other environmental conditions from the site, such as pollution, humidity,

vermin, etc.

Note 1 to entry: External insulation is either weather protected or non-weather protected, designed to operate

outside or inside closed shelters, respectively.

[SOURCE: IEC 60050-614:2016, 614-03-02, modified – Note 1 to entry has been added]

3.3
internal insulation

internal distances of the solid, liquid, or gaseous insulation of equipment which are protected

from the effects of atmospheric and other external conditions
[SOURCE: IEC 60050-614:2016, 614-03-03]
3.4
self-restoring insulation

insulation which completely recovers its insulating properties within a short time interval after

a disruptive discharge

Note 1 to entry: Insulation of this kind is generally, but not necessarily, external insulation.

Note 2 to entry: This definition applies only when the discharge is caused by the application of a test voltage

during a dielectric test. However, discharges occurring in service may cause a self-restoring insulation to lose

partially or completely its original insulating properties.
[SOURCE: IEC 60050-614:2016, 614-03-04]
3.5
non-self-restoring insulation

insulation which loses its insulating properties, or does not recover them completely, after a

disruptive discharge
---------------------- Page: 13 ----------------------
SIST EN IEC 60071-1:2021
– 8 – IEC 60071-1:2019  IEC 2019

Note 1 to entry: This definition applies only when the discharge is caused by the application of a test voltage

during a dielectric test. However, discharges occurring in service may cause a self-restoring insulation to lose

partially or completely its original insulating properties.
[SOURCE: IEC 60050-614:2016, 614-03-05]
3.6
insulation configuration terminal

any of the terminals between any two of which a voltage that stresses the insulation can be

applied
Note 1 to entry: The types of terminal are:

a) phase terminal, between which and the neutral is applied in service the phase-to-neutral voltage of the system;

b) neutral terminal, representing, or connected to, the neutral point of the system (neutral terminal of

transformers, etc.);

c) earth terminal, always solidly connected to earth in service (tank of transformers, base of disconnectors,

structures of towers, ground plane, etc.).
3.7
insulation configuration

complete geometric configuration of the insulation in service, consisting of the insulation and

of all terminals and including all elements (insulating and conducting) which influence its

dielectric behaviour

Note 1 to entry: The insulation configurations defined in 3.7.1 to 3.7.4 are identified.

3.7.1
three-phase insulation configuration

insulation configuration having three phase terminals, one neutral terminal and one earth

terminal
3.7.2
phase-to-earth insulation configuration

three-phase insulation configuration where two phase terminals are disregarded and, except

in particular cases, the neutral terminal is earthed
3.7.3
phase-to-phase insulation configuration

three-phase insulation configuration where one phase terminal is disregarded. In particular

cases, the neutral and the earth terminals are also disregarded
3.7.4
longitudinal insulation configuration

insulation configuration having two phase terminals and one earth terminal, the phase

terminals belonging to the same phase of a three-phase system temporarily separated into

two independently energized parts (e.g. open switching devices)

Note 1 to entry: The four terminals belonging to the other two phases are disregarded or earthed. In particular

cases one of the two phase terminals considered is earthed.
3.8
nominal voltage of a system
suitable approximate value of voltage used to designate or identify a system
[SOURCE: IEC 60050-601:1985, 601-01-21, modified – A symbol has been added.]
---------------------- Page: 14 ----------------------
SIST EN IEC 60071-1:2021
IEC 60071-1:2019  IEC 2019 – 9 –
3.9
highest voltage of a system

highest value of the phase-to-phase operating voltage (RMS value) which occurs under

normal operating conditions at any time and at any point in the system

[SOURCE: IEC 60050-601:1985, 601-01-23, modified – Clear meaning on the voltage has

been added.]
3.10
highest voltage for equipment

highest value of phase-to-phase voltage (RMS value) for which the equipment is designed in

respect of its insulation as well as other characteristics which relate to this voltage in the

relevant equipment standards

Note 1 to entry: Under normal service conditions specified by the relevant apparatus committee, this voltage can

be applied continuously to the equipment.
[SOURCE: IEC 60050-614:2016, 614-03-01]
3.11
isolated neutral system

system where the neutral point is not intentionally connected to earth, except for high

impedance connections for protection or measurement purposes
[SOURCE: IEC 60050-601:1985, 601-02-24]
3.12
solidly earthed neutral system
system whose neutral point(s) is(are) earthed directly
[SOURCE: IEC 60050-601:1985, 601-02-25]
3.13
impedance earthed (neutral) system

system whose neutral point(s) is(are) earthed through impedances to limit earth fault currents

[SOURCE: IEC 60050-601:1985, 601-02-26]
3.14
resonant earthed (neutral) system

system in which one or more neutral points are connected to earth through reactances which

approximately compensate the capacitive component of a single-phase-to-earth fault current

Note 1 to entry: With resonant earthing of a system, the residual current in the fault is limited to such an extent

that an arcing fault in air is usually self-extinguishing.
[SOURCE: IEC 60050-601:1985, 601-02-27]
3.15
earth fault factor

at a given location of a three-phase system, and for a given system configuration, the ratio of

the highest RMS phase-to-earth power-frequency voltage on a healthy phase during a fault to

earth affecting one or more phases at any point on the system to the RMS phase-to-earth

power-frequency voltage which would be obtained at the given location in the absence of any

such fault
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SIST EN IEC 60071-1:2021
– 10 – IEC 60071-1:2019  IEC 2019
[SOURCE: IEC 60050-614:2016, 614-03-06, modified – A symbol has been added and
description on voltage has been modified.
3.16
continuous voltage

power-frequency voltage, considered having constant RMS value, continuously applied to any

pair of terminals of an insulation configuration
3.17
overvoltage
voltage:

– between one phase conductor and earth or across a longitudinal insulation having a peak

value exceeding the peak of the highest voltage of the system divided by 3 ;

– between phase conductors having a peak value exceeding the amplitude of the highest

voltage of the system

Note 1 to entry: Unless otherwise clearly indicated, such as for surge arresters, overvoltage values expressed in

p.u. refer to U × 2 3
[SOURCE: IEC 60050-61
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Questions, Comments and Discussion

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