SIST EN 60076-3:2002
(Main)Power transformers -- Part 3: Insulation levels, dielectric tests and external clearances in air
Power transformers -- Part 3: Insulation levels, dielectric tests and external clearances in air
EN following parallel vote * Supersedes HD 398.3 S1:1986
Leistungstransformatoren -- Teil 3: Isolationspegel, Spannungsprüfungen und äußere Abstände in Luft
Transformateurs de puissance -- Partie 3: Niveaux d'isolement, essais diélectriques et distances d'isolement dans l'air
Power transformers - Part 3: Insulation levels, dielectric tests and external clearances in air (IEC 60076-3:2000 + Corrigendum 2000)
General Information
Relations
Standards Content (Sample)
SLOVENSKI SIST EN 60076-3:2002
prva izdaja
STANDARD
oktober 2002
Power transformers - Part 3: Insulation levels, dielectric tests and external
clearances in air (IEC 60076-3:2000 + Corrigendum 2000)
ICS 29.180 Referenčna številka
SIST EN 60076-3:2002(en)
© Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno
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EUROPEAN STANDARD EN 60076-3
NORME EUROPÉENNE
EUROPÄISCHE NORM May 2001
ICS 29.180 Supersedes HD 398.3 S1:1986 + A1:1995
English version
Power transformers
Part 3: Insulation levels, dielectric tests and external clearances in air
(IEC 60076-3:2000 + corrigendum 2000)
Transformateurs de puissance Leistungstransformatoren
Partie 3: Niveaux d'isolement, essais Teil 3: Isolationspegel, Spannungs-
diélectriques et distances d'isolement prüfungen und äußere Abstände in Luft
dans l'air (IEC 60076-3:2000 + corrigendum 2000)
(CEI 60076-3:2000 + corrigendum 2000)
This European Standard was approved by CENELEC on 2001-01-01. 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 Central Secretariat 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 Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic,
Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway,
Portugal, Spain, Sweden, Switzerland and United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2001 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60076-3:2001 E
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EN 60076-3:2001 - 2 -
Foreword
The text of document 14/347/FDIS, future edition 2 of IEC 60076-3, prepared by IEC TC 14, Power
transformers, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 60076-3 on 2001-01-01.
This European Standard supersedes HD 398.3 S1:1986 + A1:1995.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2001-10-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2004-01-01
Annexes designated "normative" are part of the body of the standard. Annexes designated
"informative" are given for information only. In this standard, annexes D, ZA and ZB are normative and
annexes A, B and C are informative.
Annexes ZA and ZB have been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 60076-3:2000 + corrigendum December 2000 was approved
by CENELEC as a European Standard with the following editorial modification.
In subclause 12.3, delete note 3.
__________
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- 3 - EN 60076-3:2001
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions of any
of these publications apply to this European Standard only when incorporated in it by amendment or
revision. For undated references the latest edition of the publication referred to applies (including
amendments).
NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
Publication Year Title EN/HD Year
)
1
IEC 60050-421 International electrotechnical vocabulary--
(IEV)
Chapter 421: Power transformers and
reactors
)
1)
2
IEC 60060-1 High-voltage test techniques HD 588.1 S1 1991
Part 1: General definitions and test
requirements
2)
1)
IEC 60060-2 Part 2: Measuring systems EN 60060-2 1994
+ A11 1998
IEC 60071-1 1993 Insulation co-ordination EN 60071-1 1995
Part 1: Definitions, principles and rules
)
3
IEC 60071-2 1976 Part 2: Application guide HD 540.2 S1 1991
2)
1)
IEC 60076-1 Power transformers EN 60076-1 1997
(mod) Part 1: General
IEC 60137 1995 Insulated bushings for alternating EN 60137 1996
voltages above 1 kV
2)
1)
IEC 60270 High-voltage test techniques - Partial EN 60270 2001
discharge measurements
1)
IEC 60722 Guide to the lightning impulse and--
switching impulse testing of power
transformers and reactors
1) 2)
IEC 60790 Oscilloscopes and peak voltmeters for HD 479 S1 1986
impulse tests
)
1
Undated reference
)
2
Valid edition at date of issue
)
3
HD 540.2 S1 is superseded by EN 60071-2:1997, which is based on IEC 60071-2:1996.
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EN 60076-3:2001 - 4 -
Publication Year Title EN/HD Year
2)
1)
IEC 61083-1 Digital recorders for measurements in EN 61083-1 1993
(mod) high-voltage impulse tests
Part 1: Requirements for digital
recorders
2)
1)
IEC 61083-2 Part 2: Evaluation of software used for EN 61083-2 1997
the determination of the parameters of
impulse waveforms
CISPR 16-1 1993 Specification for radio disturbance and--
immunity measuring apparatus and
methods
Part 1: Radio disturbance and immunity
measuring apparatus
____________
Annex ZB
(normative)
Special national conditions
Special national condition: National characteristic or practice that cannot be changed even over a long
period, e.g. climatic conditions, electrical earthing conditions. If it affects harmonization, it forms part of
the European Standard or Harmonization Document.
For the countries in which the relevant special national apply these provisions are normative, for other
countries they are informative.
Clause Special national condition
12.3 France
Partial discharge measurements during short-duration a.c. test on non-uniform insulated
high-voltage windings are not acceptable.
____________
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INTERNATIONAL IEC
STANDARD 60076-3
Second edition
2000-03
Power transformers –
Part 3:
Insulation levels, dielectric tests and
external clearances in air
© IEC 2000 Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical,
including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
PRICE CODE
XA
Commission Electrotechnique Internationale
International Electrotechnical Commission
ɆɟɠɞɭɧɚɪɨɞɧɚɹɗɥɟɤɬɪɨɬɟɯɧɢɱɟɫɤɚɹɄɨɦɢɫɫɢɹ
For price, see current catalogue
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60076-3 © IEC:2000 – 3 –
CONTENTS
Page
FOREWORD . 7
INTRODUCTION . 11
Clause
1 Scope . 13
2 Normative references . 13
3 Definitions. 15
4 General. 15
5 Highest voltage for equipment and insulation level. 17
6 Rules for some particular transformers . 21
7 Insulation requirements and dielectric tests – Basic rules. 23
7.1 General. 23
7.2 Insulation requirements . 25
7.3 Dielectric tests . 29
7.4 Insulation requirements and tests for the neutral terminal of a winding. 33
8 Tests on a transformer having a tapped winding . 35
9 Repeated dielectric tests . 37
10 Insulation of auxiliary wiring. 37
11 Separate source AC withstand voltage test . 37
12 Induced AC voltage tests (ACSD, ACLD) . 39
12.1 General. 39
12.2 Short-duration induced AC withstand voltage test (ACSD) for transformers
with uniformly insulated high-voltage windings . 39
12.3 Short-duration AC withstand voltage test (ACSD) for transformers with
non-uniformly insulated high-voltage windings . 45
12.4 Long-duration induced AC voltage test (ACLD) with non-uniformly and/or
uniformly insulated high-voltage windings, according to table 1 . 49
13 Lightning impulse (LI) test . 55
13.1 General. 55
13.2 Test sequence . 57
13.3 Test connections. 57
13.4 Records of test. 61
13.5 Test criteria. 61
14 Test with lightning impulse chopped on the tail (LIC). 61
14.1 General. 61
14.2 Chopping gap and characteristics of the chopping . 63
14.3 Test sequence and test criteria. 63
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60076-3 © IEC:2000 – 5 –
Clause Page
15 Switching impulse test (SI) . 63
15.1 General. 63
15.2 Test sequence and records . 65
15.3 Test connections. 65
15.4 Test criteria. 67
16 External clearances in air . 67
16.1 General. 67
16.2 Bushing clearance requirements as determined by transformer insulation
withstand voltages. 69
Annex A (Informative) Application guide for partial discharge measurements during
induced a.c. withstand voltage test on transformers according to 12.2, 12.3 and 12.4 . 85
Annex B (informative) Overvoltage transferred from the high-voltage winding to
a low-voltage winding. . 99
Annex C (informative) Information on transformer insulation and dielectric tests
to be supplied with an enquiry and with an order . 103
Annex D (normative) ACSD . 105
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60076-3 © IEC:2000 – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
POWER TRANSFORMERS –
Part 3: Insulation levels, dielectric tests and
external clearances in air
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the 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, the IEC publishes International Standards. 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. The 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 the 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 National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60076-3 has been prepared by IEC technical committee 14: Power
transformers.
This second edition cancels and replaces the first edition published in 1980, amendment 1
(1981) and IEC 60076-3-1 (1987).
The text of this standard is based on the following documents:
FDIS Report on voting
14/347/FDIS 14/355/RVD
Full information on the voting for the approval of this 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 3.
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60076-3 © IEC:2000 – 9 –
Annexes A, B and C are for information only.
Annex D forms an integral part of this standard.
The committee has decided that the contents of this publication will remain unchanged
until 2008. At this date, the publication will be
reconfirmed;
withdrawn;
replaced by a revised edition, or
amended.
The contents of the corrigendum of December 2000 have been included in this copy.
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60076-3 © IEC:2000 – 11 –
INTRODUCTION
This part of IEC 60076 specifies the insulation requirements and the corresponding insulation
tests with reference to specific windings and their terminals. It also recommends clearances in
air between live parts of bushings on oil-immersed power transformers and to objects at earth
potential (clause 16). Guidance can be obtained from IEC 60071.
The insulation levels and dielectric tests which are specified in clauses 4, 5, 6 and 7 in this
standard apply to the internal insulation only. Whilst it is reasonable that the rated withstand
voltage values which are specified for the internal insulation of the transformer should also be
taken as a reference for its external insulation, this may not be true in all cases. A failure of the
non-self-restoring internal insulation is catastrophic and normally leads to the transformer
being out of service for a long period, while an external flashover may involve only a short
interruption of service without causing lasting damage. Therefore, it may be that, for increased
safety, higher test voltages are specified by the purchaser for the internal insulation of the
transformer than for the external insulation of other components in the system. When such a
distinction is made, the external clearances must be adjusted to fully cover the internal
insulation test requirements.
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60076-3 © IEC:2000 – 13 –
POWER TRANSFORMERS –
Part 3: Insulation levels, dielectric tests and
external clearances in air
1 Scope
This International Standard applies to single-phase and three-phase oil-immersed power
transformers (including auto-transformers), with the exception of certain small and special
transformers, as defined in the scope of IEC 60076-1. It identifies transformer windings to their
highest voltage for equipment U associated with their corresponding rated insulation levels
m
and details the relevant applicable dielectric tests and minimum external clearances in air
between live parts of bushings and to objects at earth potential.
For categories of power transformers and reactors which have their own IEC standards, this
standard is applicable only to the extent in which it is specifically called up by cross reference
in the other standards.
2 Normative references
The following normative documents contain provisions which, through reference in this text,
constitute provisions of this part of IEC 60076. For dated references, subsequent amendments
to, or revisions of, any of these publications do not apply. However, parties to agreements
based on this part of IEC 60076 are encouraged to investigate the possibility of applying the
most recent editions of the normative documents indicated below. For undated references, the
latest edition of the normative document referred to applies. Members of IEC and ISO maintain
registers of currently valid International Standards.
IEC 60050(421), International Electrotechnical Vocabulary (IEV) – Chapter 421: Power
transformers and reactors
IEC 60060-1, High-voltage test techniques – Part 1: General definitions and test requirements
IEC 60060-2, High-voltage test techniques – Part 2: Measuring systems
IEC 60071-1:1993, Insulation coordination – Part 1: Definitions, principles and rules
IEC 60071-2:1976, Insulation coordination – Part 2: Application guide
IEC 60076-1, Power transformers – Part 1: General
IEC 60137:1995, Bushings for alternating voltages above 1 000 V
IEC 60270, Partial discharge measurements
IEC 60722, Guide to the lightning impulse and switching impulse testing of power transformers
and reactors
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60076-3 © IEC:2000 – 15 –
IEC 60790, Oscilloscopes and peak voltmeters for impulse tests
IEC 61083-1, Digital recorders for measurements in high-voltage impulse tests – Part 1:
Requirements for digital recorders
IEC 61083-2, Digital recorders for measurements in high-voltage impulse tests – Part 2:
Evaluation of software used for the determination of the parameters of impulse waveforms
CISPR 16-1:1993, Specification for radio disturbance and immunity measuring apparatus and
methods – Part 1: Radio disturbance and immunity measuring apparatus
3 Definitions
For the purpose of this part of IEC 60076, the following definitions apply. Other terms used
have the meanings ascribed to them in IEC 60076-1 or in IEC 60050(421).
3.1
highest voltage for equipment U applicable to a transformer winding
m
the highest r.m.s. phase-to-phase voltage in a three-phase system for which a transformer
winding is designed in respect of its insulation
3.2
rated insulation level
a set of standard withstand voltages which characterize the dielectric strength of the insulation
3.3
standard insulation level
a rated insulation level, the standard withstand voltages of which are associated to U as
m
recommended in tables 2 and 3 of IEC 60071-1
3.4
uniform insulation of a transformer winding
the insulation of a transformer winding when all its ends connected to terminals have the same
rated insulation level
3.5
non-uniform insulation of a transformer winding
the insulation of a transformer winding when it has a neutral terminal end for direct or indirect
connection to earth, and is designed with a lower insulation level than assigned for the line
terminal
4 General
The insulation requirements for power transformers and the corresponding insulation tests are
given with reference to specific windings and their terminals.
For oil-immersed transformers, the requirements apply to the internal insulation only. Any
additional requirements or tests regarding external insulation which are deemed necessary
shall be subject to agreement between supplier and purchaser, including type tests on a
suitable model of the configuration.
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60076-3 © IEC:2000 – 17 –
If the purchaser intends to make the connections to the transformer in a way which may reduce
the clearances provided by the transformer alone, this should be indicated in the enquiry.
When an oil-immersed transformer is specified for operation at an altitude higher than 1 000 m,
clearances shall be designed accordingly. It may then be necessary to select bushings
designed for higher insulation levels than those specified for the internal insulation of the
transformer windings, see clause 16 of this standard and 4.2 of IEC 60137.
Bushings are subject to separate type and routine tests according to IEC 60137, which verify
their phase-to-earth insulation, external as well as internal.
It is presupposed that bushings and tap-changers are specified, designed and tested in
accordance with relevant IEC standards. The insulation tests on the complete transformer,
however, constitute a check on the correct application and installation of these components.
The insulation test shall generally be made at the supplier's works with the transformer
approximately at ambient temperature, but at least at 10 °C.
The transformer shall be completely assembled as in service including supervisory equipment.
It is not necessary, however, to fit elements which do not influence the dielectric strength of the
internal insulation, for example, the external cooling equipment.
If a transformer fails to meet its test requirements and the fault is in a bushing, it is permissible
to replace this bushing temporarily with another bushing and continue the test on the
transformer to completion without delay. A particular case arises for tests with partial discharge
measurements, where certain types of commonly used high-voltage bushings create difficulties
because of their relatively high level of partial discharge in the dielectric. When such bushings
are specified by the purchaser, it is permitted to exchange them for bushings of a partial
discharge free type during the testing of the transformer, see annex A.
Transformers for cable box connection or direct connection to metal-enclosed SF installations
6
should be designed so that temporary connections can be made for insulation tests, using
temporary bushings, if necessary. By agreement, oil/SF bushings may for that reason be
6
replaced by appropriate oil/air bushings.
When the supplier intends to use non-linear elements or surge arresters, built into the
transformer or externally fitted, for the limitation of transferred overvoltage transients, this shall
be brought to the purchaser's attention at the tender and order stage and it is recommended
that it be indicated on the transformer rating plate circuit diagram.
5 Highest voltage for equipment and insulation level
To each winding of a transformer, both for the line and neutral side, is assigned a value of
highest voltage for equipment U , see 3.1.
m
The rules for coordination of transformer insulation with respect to transient overvoltages are
formulated differently depending on the value of U .
m
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60076-3 © IEC:2000 – 19 –
When rules about related tests for different windings in a transformer are in conflict, the rule for
the winding with the highest U value shall apply for the whole transformer.
m
Rules for a number of special classes of transformers are given in clause 6.
Standardized values of U are listed in tables 2 to 4. The value to be used for a transformer
m
winding is the one equal to, or nearest above, the rated value of the winding.
NOTE 1 Single-phase transformers intended for connection in star to form a three-phase bank are designated by
phase-to-earth rated voltage, for example 400/ 3 kV. The phase-to-phase value determines the choice of U in this
m
case, consequently, U = 420 kV.
m
NOTE 2 It may happen that certain tapping voltages are chosen slightly higher than a standardized value of U ,
m
but that the system to which the winding will be connected has a system highest voltage which stays within the
standard value. The insulation requirements are to be coordinated with actual conditions, and therefore this
standard value should be accepted as U for the transformer, and not the nearest higher value.
m
NOTE 3 In certain applications with very special conditions the specification of other combinations of withstand
voltages may be justified. In such cases, general guidance should be obtained from IEC 60071-1.
NOTE 4 In certain applications, delta-connected windings are earthed through one of the external terminals. In
those applications, a higher withstand voltage with respect to the highest voltage for equipment U may be required
m
for this winding and should be agreed between supplier and purchaser.
The highest voltage for equipment U and its assigned withstand voltages, that is, their
m
insulation level, determine the dielectric characteristics of a transformer. They are verified by a
set of dielectric tests depending on U , see clause 7.
m
The value of U and the insulation level which are assigned to each winding of a transformer
m
are part of the information to be supplied with an enquiry and with an order. If there is a
winding with non-uniform insulation, the assigned U and the insulation level of the neutral
m
terminal shall also be specified by the purchaser, see 7.4.3.
The rated withstand voltages for all windings shall appear on the rating plate. The principles of
the standard abbreviated notation are shown in some examples below.
The classifications on the insulation design shall independently of the test procedure be
derived from the values in table 2, 3 and 4 or from IEC 60071-1. Since in most cases the long-
duration induced AC tests are quality control tests in respect to service conditions and not
design proving tests, the insulation level shall be characterized as follows:
U is the highest voltage for equipment
m
SI/LI/AC,
where applicable –/LI/AC.
The abbreviations here and in the examples below have the following meaning:
SI is the switching impulse withstand voltage for the line terminals of the winding with the
highest U ;
m
LI is the lightning impulse withstand voltage for the line and neutral terminals of each
individual winding;
AC is the short duration induced and separate source AC withstand voltage for the line and
neutral terminals of each individual winding;
h.v. high voltage;
l.v. low voltage;
m.v. medium voltage.
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60076-3 © IEC:2000 – 21 –
Example 1:
U (h.v.) = 72,5 kV and U (l.v.) = 12 kV, both uniformly insulated, Y connected
m m
Insulation levels: h.v. line terminal and neutral LI/AC 325/140 kV
l.v. line terminal and neutral LI/AC 60/28 kV
Example 2:
U (h.v.) line = 245 kV, Y connected;
m
U (h.v.) neutral = 52 kV;
m
U (m.v.) line = 72,5 kV, uniform insulation, Y connected;
m
U (l.v.) line = 24 kV, D connected.
m
Insulation levels: h.v. line terminal SI/LI 650/850
...
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