SIST EN IEC 60034-15:2025

SLOVENSKI STANDARD
01-november-2025
Električni rotacijski stroji - 15. del: Nivo vzdržljivostii na impulzno napetost
oblikovno navitih statorskih tuljav pri rotacijskih izmeničnih strojih (IEC 60034-
15:2025)
Rotating electrical machines - Part 15: Impulse voltage withstand levels of form-wound
stator coils for rotating a.c. machines (IEC 60034-15:2025)
Drehende elektrische Maschinen - Teil 15: Steh-Stoßspannungspegel von Formspulen
im Ständer drehender Wechselstrommaschinen (IEC 60034-15:2025)
Machines électriques tournantes - Partie 15: Niveaux de tenue au choc électrique des
bobines de stator préformées des machines tournantes à courant alternatif (IEC 60034-
15:2025)
Ta slovenski standard je istoveten z: EN IEC 60034-15:2025
ICS:
29.160.01 Rotacijski stroji na splošno Rotating machinery in
general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 60034-15

NORME EUROPÉENNE
EUROPÄISCHE NORM August 2025
ICS 29.160.01 Supersedes EN 60034-15:2009
English Version
Rotating electrical machines - Part 15: Impulse voltage withstand
levels of form-wound stator coils for rotating a.c. machines
(IEC 60034-15:2025)
Machines électriques tournantes - Partie 15: Niveaux de Drehende elektrische Maschinen - Teil 15: Steh-
tenue au choc électrique des bobines de stator des Stoßspannungspegel von Formspulen für
machines à courant alternatif Ständerwicklungen drehender Wechselstrommaschinen
(IEC 60034-15:2025) (IEC 60034-15:2025)
This European Standard was approved by CENELEC on 2025-07-11. 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,
Türkiye 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
© 2025 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 60034-15:2025 E

European foreword
The text of document 2/2234/FDIS, future edition 4 of IEC 60034-15, prepared by TC 2 "Rotating
machinery" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2026-08-31
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2028-08-31
document have to be withdrawn
This document supersedes EN 60034-15:2009 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.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 60034-15:2025 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 standard indicated:
IEC 60071-1 NOTE Approved as EN IEC 60071-1
IEC 61083-2:2013 NOTE Approved as EN 61083-2:2013 (not modified)
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.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 60060-1 2010 High-voltage test techniques - Part 1: EN 60060-1 2010
General definitions and test requirements

IEC 60034-15 ®
Edition 4.0 2025-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Rotating electrical machines –
Part 15: Impulse voltage withstand levels of form-wound stator coils for rotating
a.c. machines
Machines électriques tournantes –
Partie 15: Niveaux de tenue au choc électrique des bobines de stator des
machines à courant alternatif
ICS 29.160.01  ISBN 978-2-8327-0452-3

IEC 60034-15:2025-06(en-fr)
– 2 – IEC 60034-15:2025 © IEC 2025
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references. 7
3 Terms and definitions . 7
4 Impulse voltage withstand levels . 12
4.1 General . 12
4.2 Impulse withstand levels . 12
4.3 Enhanced impulse withstand levels . 13
5 Sample tests . 14
5.1 General . 14
5.2 Standard lightning impulse voltage withstand test . 15
5.3 Steep-front impulse voltage withstand test . 15
5.4 Power-frequency voltage withstand test . 16
6 Routine tests . 16
7 Reporting . 17
Annex A (informative) Principles involved in the specification of impulse voltage
withstand levels and test procedures . 18
A.1 Impulse voltage stress of a machine winding. 18
A.2 Impulse voltage withstand level of a machine winding . 18
A.3 Indirect proof of impulse voltage withstand levels by sample tests on coils . 19
Annex B (informative) Testing details . 20
B.1 General . 20
B.2 Principal circuit diagrams . 20
B.2.1 General . 20
B.2.2 Circuit diagram SLI test . 20
B.2.3 Circuit diagram SFI test . 21
B.3 Voltage measurement . 22
B.4 Practical layout of the test set-up . 22
B.5 Oscillograms of tests on sample coils . 24
B.5.1 General . 24
B.5.2 Checking of input wave shape . 24
B.5.3 Standard lightning impulse . 24
B.5.4 Steep-front impulses . 26
Annex C (normative) Requirements on sample coils . 29
C.1 General . 29
C.2 Requirements for RR and SVPI sample coils . 29
C.3 Requirements for GVPI sample coils . 29
Annex D (normative) Routine steep-front impulse testing . 31
D.1 General . 31
D.2 Separate stator coils . 31
D.3 Complete stators . 32
D.4 Example of the test circuit for routine tests . 32
Annex E (normative) Procedure for calculation of parameters of lightning impulse
voltages with superimposed overshoot or oscillations . 34
E.1 General . 34

IEC 60034-15:2025 © IEC 2025 – 3 –
E.2 Basis of the procedure . 34
E.3 Procedure for evaluation of parameters of lightning impulses . 35
Annex F (informative) Procedure for manual calculation from graphical waveforms. 38
Annex G (informative) Background to the introduction of the test voltage factor for
evaluation of impulses with overshoot . 39
G.1 General . 39
G.2 Research and development to provide a solution . 40
Bibliography . 43

Figure 1 – Impulse voltage curve . 8
Figure 2 – Test voltage function . 10
Figure 3 – Full impulse voltage time parameters . 11
Figure B.1 – Standard lightning impulse circuit . 21
Figure B.2 – Steep-front impulse circuit . 22
Figure B.3 – Layout for standard lightning impulse tests. . 23
Figure B.4 – Layout for steep-front impulse tests. . 23
Figure B.5 – Example of test set-up for steep-front impulse test . 24
Figure B.6 – Example of standard lightning impulse waveform on an undamaged coil . 25
Figure B.7 – Magnified detail of standard lightning impulse waveform as shown in
Figure B.6 . 25
Figure B.8 – Example of steep-front impulse on an undamaged coil . 26
Figure B.9 – Example of collected steep-front impulses on undamaged coils (5
negative pulses) . 26
Figure B.10 – Example of recorded waveform of a failing coil . 27
Figure B.11 – Comparison of failing coil with undamaged coil . 28
Figure B.12 – Various breakdown graphs of five coils of same design . 28
Figure C.1 – Examples of GVPI slot simulations . 30
Figure D.1 – Example of the test circuit for routine tests . 33
Figure E.1 – Recorded and base curve showing overshoot and residual curve . 35
Figure E.2 – Test voltage curve (addition of base curve and filtered residual curve) . 36
Figure E.3 – Recorded and test voltage curves . 37
Figure G.1 – "Effective" test voltage function in IEC 60060-1:1989 . 39
Figure G.2 – Representative experimental points from European experiments and test

voltage function . 41

Table 1 – Standard impulse voltage withstand levels for sample coils used in AC
rotating machines . 13

– 4 – IEC 60034-15:2025 © IEC 2025
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ROTATING ELECTRICAL MACHINES –

Part 15: Impulse voltage withstand levels of stator coils
for rotating AC machines
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
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Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
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consensus of opinion on the relevant subjects since each technical committee has representation from all
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6) All users should ensure that they have the latest edition of this publication.
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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) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 60034-15 has been prepared by IEC technical committee 2: Rotating machinery. It is an
International Standard.
This fourth edition cancels and replaces the third edition published in 2009. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
TM
• harmonize the standard test levels with IEEE Std 522 [2];
• introduce an enhanced surge impulse voltage withstand level;
• introduce the option to test up to the point of electrical breakdown;
• improve the evaluation of the recorded impulses in case of oscillations and overshoot;

IEC 60034-15:2025 © IEC 2025 – 5 –
• indicate that converter fed machines are excluded from the scope;
• provide guidance on the execution of impulse tests.
The text of this International Standard is based on the following documents:
Draft Report on voting
2/2234/FDIS 2/2247/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
NOTE A table of cross-references of all IEC TC 2 publications can be found on the IEC TC 2 dashboard on the IEC
website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
– 6 – IEC 60034-15:2025 © IEC 2025
INTRODUCTION
IEC 60071-1 [1] specifies general requirements for the phase-to-earth insulation, phase-to-
phase and the longitudinal insulation of equipment in three phase AC systems and states that
each apparatus committee is responsible for specifying the insulation levels and test
procedures for its equipment, taking into consideration the recommendations of
IEC 60071-1 [1].
The object of this document is to specify these requirements for rotating electrical AC machines.
Experience has shown that the values given in this document meet the insulation requirements
for the essential stresses in service. An explanation of the principles adopted in preparing these
requirements is given in Annex A. This document is not intended for electronic converter-fed
machines.
___________
Numbers in square brackets refer to the Bibliography.

IEC 60034-15:2025 © IEC 2025 – 7 –
ROTATING ELECTRICAL MACHINES –

Part 15: Impulse voltage withstand levels of stator coils
for rotating AC machines
1 Scope
This part of IEC 60034 relates to AC machines incorporating form-wound stator coils that are
intended to be connected to a standard grid supply. It specifies the test procedures and voltages
to be applied to sample coils, as well as routine tests performed on coils mounted in the stator
core.
The purpose of this document is to show the ability of a stator winding to resist voltage
transients originating from the grid the machine is connected to. Annex A gives further
information.
The stator windings and coils for converter-fed machines are excluded from the scope of this
document.
This document is not intended for use on complete windings since it is difficult to determine
when the turn insulation has failed due to the test.
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 60060-1:2010, High-voltage test techniques – Part 1: General definitions and test
requirements
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
sample test
test carried out on (sample) coils in new condition which adequately represent the configuration
of the finished item to be used in the machine for the purpose of evaluating the manufacturing
procedures and processes incorporated in the insulation system
3.2
routine test
test carried out on coils during manufacture

– 8 – IEC 60034-15:2025 © IEC 2025
3.3
form-wound stator coil
coil that is preformed to shape, insulated, and substantially completed before insertion into the
stator
3.4
impulse voltage
intentionally applied aperiodic transient voltage, which usually rises rapidly to a peak value and
then falls more slowly to zero
SEE: Figure 1.
Figure 1 – Impulse voltage curve
3.5
lightning impulse voltage
impulse voltage with a front time T less than 20 µs
SEE: Figure 3.
3.6
full lightning impulse voltage
lightning impulse voltage, which is not interrupted by a disruptive discharge
3.7
overshoot
increase of amplitude of an impulse voltage due to a damped oscillation at the peak caused by
the circuit
Note 1 to entry: Such oscillations (frequency range usually 0,1 MHz to 2 MHz) are caused by circuit inductance and
sometimes cannot be avoided in large circuits or for inductive test objects. Methods for the evaluation of overshoot
are given in Annex E.
3.8
recorded curve
graphical or digital representation of the test data of an impulse voltage
3.9
base level
level of a record of an impulse measuring system when there is zero input to the recording
instrument
IEC 60034-15:2025 © IEC 2025 – 9 –
3.10
base curve
estimate of a full lightning impulse voltage without a superimposed (damped) oscillation
Note 1 to entry: See Annex E.
3.11
residual curve
R(t)
difference between the recorded curve and the base curve
Note 1 to entry: See Annex E.
3.12
extreme value
U
e
maximum value of the recorded curve measured from the base level in the same sense as the
applied impulse
3.13
base curve maximum
U
b
maximum value of the base curve
3.14
test voltage function
amplitude-frequency function which is defined to represent the response of insulation to
impulses with overshoot and which is given by:
k()f =
(1)
1+ 2,2 f
where f is the frequency in MHz
SEE: Figure 2.
– 10 – IEC 60034-15:2025 © IEC 2025

Figure 2 – Test voltage function
3.15
filtered residual curve
(t)
R
f
residual curve filtered by the test voltage function
3.16
test voltage curve
summation of the base curve and the filtered residual curve
Note 1 to entry: The test voltage curve is a mathematical representation of the filtering process and is not a physical
entity or an equivalent impulse.
SEE: Figure 2.
3.17
equivalent smooth impulse
estimated lightning impulse voltage without overshoot having a peak value equal to the
maximum value of the test voltage curve and the same front time and time to half value as the
related test voltage curve
Note 1 to entry: An equivalent smooth impulse has the same dielectric breakdown behaviour as the recorded curve.
3.18
value of the test voltage
U
t
maximum value of the test voltage curve measured from the base level in the same sense as
the applied impulse
3.19
overshoot magnitude
β
difference between the extreme value of the recorded curve U and the maximum value of the
e
base curve U
b
IEC 60034-15:2025 © IEC 2025 – 11 –
3.20
relative overshoot magnitude
β′
ratio of the overshoot magnitude to the extreme value, usually expressed as a percentage
3.21
front time
T
virtual parameter defined as 1/0,6 times the interval T between the instants when the impulse
AB
is 30 % and 90 % of the peak value of the voltage curve
Note 1 to entry: See Figure 3, points A and B.

Figure 3 – Full impulse voltage time parameters
Note 2 to entry: This front time definition is applicable to both the standard lightning impulse as well as to the steep-
front impulse as described in this document.
Note 3 to entry: In this document exclusively the term "front time" is used. This quantity should not be confused
with the term "rise time" that is used in other documents, but usually defined as being the time between the 10 %
and 90 % value of the pulse final magnitude.
3.22
time to half value
T
virtual parameter defined as the time interval between the instant preceding that corresponding
to point A of the voltage curve, by a time 0,3T , (O ), and the instant when the voltage curve
1 1
has decreased to half of the peak of the voltage curve
SEE: Figure 3.
3.23
standard lightning impulse
SLI
lightning impulse with a front time of 1,2 µs ± 0,36 µs and a time to half value T of 50 µs ±
10 µs
– 12 – IEC 60034-15:2025 © IEC 2025
3.24
SLI test voltage
U
P
value of the test voltage of a standard lightning impulse with a tolerance of -3 %
3.25
steep-front impulse
SFI
lightning impulse with a front time of 0,2 µs ± 0,1 µs
3.26
SFI test voltage
U’
P
value of the test voltage of a steep-front impulse with a tolerance of -3 %
3.27
slot simulation
slot model
rigid metal fixture to simulate the actual stator slot with at least the same length as the stator
core and the same width as the slots in the stator core
Note 1 to entry: The slot simulation is not necessarily built up from sheets of electrical core sheet material.
4 Impulse voltage withstand levels
4.1 General
Impulse voltage withstand levels are defined to test the insulation between the conductors and
the earthed outside surface of the coil as well as to test the insulation that is stressed when a
voltage is applied across both terminals of the coil. As the steep-front voltage of the pulses
proceeds through the coil windings, turn by turn they stress the interturn insulation between the
strands as well as the main wall insulation of the coil. Based on experience of laboratory tests,
it is assumed that when a steep-front voltage impulse across the terminals of a single coil is
applied with a voltage level that is around 70 % of the standard lightning withstand voltage for
the main wall insulation, the actual situation for the entry (first) coil of a complete stator winding
is approximated. Since there does not exist a simple general method to determine the actual
voltage stress in a winding of a certain design (see Annex A for further explanation), no distinct
test levels for the individual interturn insulation itself are given in this document.
While performing impulse tests, overshoot or oscillations, or both, can occur. See Annex E for
information on dealing with this situation.
4.2 Impulse withstand levels
The impulse withstand levels for a specific rated voltage U shall be calculated in accordance
N
with the following formulae.
For the standard lightning impulse (SLI) withstand level between the conductors and the earthed
outside surface of the main wall insulation:
with a minimum U of 8 kV
UU= 5 (2)
P
PN
IEC 60034-15:2025 © IEC 2025 – 13 –
For the steep-front impulse (SFI) withstand level across the terminals of the coil with one
terminal connected to the earth:
′ with a minimum U’ of 5,6 kV
UU= 3,5 (3)
PN P
With the SFI, the outside surface of the main wall insulation should preferably be directly
connected to earth. More details to be found in 5.3 and Annex B.
Table 1 gives the impulse voltage withstand levels for some common rated voltages rounded to
one decimal.
Without any particular indication a stator winding is considered to be able to withstand the levels
defined in this standard category. These levels are considered as those not being surpassed
by the voltage excursions occurring in a direct-on-line application of a stator winding on a
normal grid.
TM
NOTE This level is in line with the level as defined in IEEE Std 522 [2] .
Table 1 – Standard impulse voltage withstand levels for sample
coils used in AC rotating machines
Rated voltage Rated SLI voltage withstand level Rated SFI voltage withstand level
(RMS value) (see NOTE 1) (see NOTE 2)
U U U’
N P P
kV kV kV
2,3 9,4 6,6
3 12,2 8,6
9,4
3,3 13,5
4 16,3 11,4
6 24,5 17,1
6,6 26,9 18,9
10 40,8 28,6
11 44,9 31,4
13,2 53,9 37,7
13,8 56,3 39,4
15 61,2 42,9
18 73,5 51,4
22 89,8 62,9
NOTE 1 The levels in Column 2 are based on a standard lightning impulse (SLI) having a value of the impulse
voltage U with a tolerance of −3 %.
P
NOTE 2 The levels in Column 3 are based on a steep-front lightning impulse (SFI) having a front time of
with a tolerance of −3 %.
(0,2 ± 0,1) µs and a value of the impulse voltage U’
P
4.3 Enhanced impulse withstand levels
A user can request for an enhanced impulse withstand level, for instance, when special
operation conditions occur (such as very frequent switching or aborted starts), a specific grid
layout is present (for instance feeding by overhead lines) or other special circumstances are
present. This might lead to an enhanced winding insulation design to be implemented.

– 14 – IEC 60034-15:2025 © IEC 2025
In this case an enhanced impulse voltage withstand capability is specified where the standard
levels as found in the previous clause are increased by a default value of 15 kV (for the SLI)
and 11 kV (for the SFI). The resulting test voltage shall be limited to twice the standard voltage
values as defined in 4.2. Formulae (4) and (5) give the calculation of the levels to be applied.
Application of these test levels are subject on the explicit agreement between user and
manufacturer. Upon agreement a deviation from the default increase is allowed.
kV
U minimum UU+15;2
{ } (4)
P,enhanced P P
kV
U ′ minimum UU′′+11;2
{ } (5)
P, enhanced P P
NOTE With the default increases as stated, the SLI voltage values (Formula (4)) are within the middle of the LI
ranges as specified in IEC 60071-1 [1]. The SFI test level increase (Formula (5)) is again 70 % of the SLI level.
5 Sample tests
5.1 General
Sample tests are carried out as an indirect proof of compliance as explained in Clause A.3. The
test coils are selected from the entire set of coils produced for a certain stator winding. In case
of global impregnated systems, the selected (green) coils should preferably be embedded in
adequate slot simulations and subsequently processed (impregnated and cured), preferably
together with the stator concerned.
The test coils shall have completed their manufacturing process, including the application of
corona protection layer and stress grading, if applicable, and including all diagnostic tests and
measurements that are performed during normal coil production. Processed (impregnated and
cured) sample coils related to global impregnated systems should preferably be tested without
dismounting them from their slot simulations. Other sample coils, in the case of single coil
production, shall be either embedded in earthed slots or fitted with the slot portion wrapped in
earthed conducting tape or foil. Annex C gives further requirements for the sample coils.
In all cases special attention is required for the connection leads. The length of the leads shall
be sufficient to prevent flashover(s) during the impulse tests. This implies that in some cases
the coils to be tested have to be provided with connection leads with an increased length (for
instance in case of global impregnation sample coils). As an alternative the connection leads
could be extended which requires special care to thoroughly insulate the transition region (for
instance when the randomly chosen coils from a complete set of resin-rich coils have too short
leads).
The number of sample coils shall be at least two. Preferably, first the standard lightning impulse
test should be executed on each of the coils followed by the steep-front impulse test.
All sample coils shall withstand the electrical tests described below. In the case of a failure, the
manufacturer shall investigate the cause and report the findings. Failure in an impulse test can
be detected from the visualized shape of the signal, recorded by an appropriate measurement
system connected to the leads of the coil, or due to a visible defect of the coil insulation.
Examples of signals from undamaged and failed (broken down) coils are shown in B.5.4.
In case a coil fails during the tests, a further set of two coils may be tested (provided that these
are available) and, when the subsequent tests are successful, the entire set of stator coils or
the impregnated and cured stator winding can be accepted. In case two or more coils fail (either
being the first two or one of the first coils and one or more of the second set), the entire set of
stator coils or the processed stator winding shall be rejected (discarded).
=
=
IEC 60034-15:2025 © IEC 2025 – 15 –
Examples of test circuits for individual coils are given in Annex B. It should be noted that the
test circuit layout has a large influence on the impulse shape, particularly with the steep-front
impulse.
On the details of the tests, agreement should be reached between manufacturer and user.
NOTE Successfully carrying out sample tests does not automatically guarantee that the corresponding stator
winding will survive all transients in service.
5.2 Standard lightning impulse voltage withstand test
To test the main wall insulation of the coil a standard lightning impulse voltage shall be applied
between the interconnected terminals of the coil and earth.
The test voltage shall be generated by an impulse generator applying an impulse voltage with
a front time of 1,2 µs ± 0,36 µs and a time to half value of 50 µs ± 10 µs as specified in
IEC 60060-1. The number of impulses shall be at least five and of the same polarity.
The test shall commence by applying an impulse at a reduced voltage level (maximum 50 % of
the final test level) to check the front time and to have a reference impulse shape for comparison
to determine whether breakdown has occurred at the final test level.
The voltage value between the coil terminals and earth shall be according to the values
specified by 4.2, Table 1, Formula (2) or any deviating test level as agreed upon. The tolerance
on U is -3 %.
P
This test level can be regarded as the BIL (basic insulation level) of the main wall insulation of
the coil.
Care shall be taken to avoid oscillations, although with the standard lightning impulse testing
usually no substantial oscillation is present. However, in those cases where it happens the
evaluation procedure as described in Annex E shall be applied. A compact circuit, limiting stray
inductances, is recommended to minimize oscillations.
5.3 Steep-front impulse voltage withstand test
The steep-front impulse voltage test is carried out to test the ability of the coil insulation to
withstand a voltage across the terminals of the coil and will particularly stress the interturn
insulation but also the main wall insulation. The test is carried out by applying a steep-front
impulse voltage between the two terminals of the sample coil with one terminal earthed. The
outside surface of the coil shall either directly or indirectly be connected to earth as well. To
lower the front time, it can be helpful to insert a resistor in the connection to earth, however
leaving the outside surface of the coil electrically floating should be avoided since this
principally alters the voltage distribution in the coil.
The voltage impulses are usually generated by the (heavily damped oscillatory) discharge of a
capacitor.
Due to the physical properties of the impulse generators used and due to the properties of the
coils to be tested oscillations often occur on the steep-front impulses. Care should be taken to
minimize this phenomenon (more information in Annex B).
In case oscillation is present on the impulse that is recorded, and all possible measures, such
as limiting the stray inductance by using a compact circuit, as described in Annex B have been
taken to improve the impulse shape, refer to Annex E and Annex F on the evaluation methods
of the impulse in case of oscillations or overshoot, or both. Further background information on
the evaluation method is given in Annex G as well as in IEC 60060-1.

– 16 – IEC 60034-15:2025 © IEC 2025
The test shall commence by applying an impulse at a reduced voltage level (maximum 50 % of
the final test level) to check the front time and to have a reference impulse shape for comparison
to determine whether breakdown has occurred at the final test level.
The voltage value (maximum value of the voltage curve) between the terminals of the sample
coil shall have the values given by 4.2, Table 1, Formula (3) or any deviating level as agreed
is -3 %.
upon. The tolerance on U’
P
The number of impulses applied to the sample at the required test level shall be at least five of
the same polarity. The front time of the impulse at the terminals of the sample coil shall be
0,2 µs ± 0,1 µs. It is imperative to measure the voltage using a measurement device including
its voltage divider with sufficient bandwidth (typically at least up to 50 MHz) directly at the
terminals of the coil.
The front time of the last voltage impulse applied during a test should be checked for
compliance.
A significant deviation of the recorded waveshape compared to the reference waveshape is
considered a failure of the coil, even when no visual damage is present or when subsequent
testing delivers seemingly no deviations. An exception is when the deviation of the wave shape
is clearly caused by external circumstances such as a flashover or external disturbances.
As a complementary informative test and based on agreement between the manufacturer and
the customer it is suggested to increase gradually the voltage value U’ up to the value where
P
the insulation reaches breakdown. The highest voltage achieved before breakdown and the
voltage at the breakdown event shall be recorded in the test report. If breakdown occurs during
this test, the coil shall not be used in a machine.
The increment value shall be adapted to the testing equipment but will be 5 kV or less. High
value increments (for instance 10 kV) will lead to rapid break down and will conceal a more
accurate detection of the breakdown voltage. Once the breakdown point has been achieved a
second impulse of the same magnitude shall be applied to confirm the breakdown value. This
value should be stated as "informative only" in the test report. When the second impulse does
not confirm the breakdown, the voltage can be increased again until breakdown occurs.
5.4 Power-frequency voltage withstand test
A power-frequency voltage withstand test may be used instead of the standard lightning impulse
voltage withstand test described in 5.2. In this case, a voltage with an RMS value of
(2U + 1) kV shall be applied for 1 min between coil terminals and earth. The applied voltage
N
shall then be increased at the rate of 1 kV/s up to an RMS value of 2 × (2U + 1) kV, followed
N
by an immediate reduction at a rate of at least 1 kV/s to zero. There shall be no voltage
breakdown during the sequence. The corresponding impulse voltage withstands level of the
main wall insulation, and the overhang corona protection (end winding stress grading) are then
considered to fulfill at least the requirements of Table 1, column 2 "Lightning impulse".
In case of an enhanced impulse test level as specified according to 4.3, the alternative power-
frequency test is
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