IEC TS 60034-18-42:2008

IEC/TS 60034-18-42
Edition 1.0 2008-08
TECHNICAL
SPECIFICATION
SPÉCIFICATION
TECHNIQUE
Rotating electrical machines –
Part 18-42: Qualification and acceptance tests for partial discharge resistant
electrical insulation systems (Type II) used in rotating electrical machines fed
from voltage converters
Machines électriques tournantes –
Partie 18-42: Essais de qualification et d’acceptation des systèmes d’isolation
électrique résistants aux décharges partielles (Type II) utilisés dans des
machines électriques tournantes alimentées par convertisseurs de tension

IEC/TS 60034-18-42:2008
All rights reserved. Unless otherwise specified, 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 either IEC or
IEC's member National Committee in the country of the requester.
If you have any questions about IEC copyright or have an enquiry about obtaining additional rights to this publication,
please contact the address below or your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite
ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie
et les microfilms, sans l'accord écrit de la CEI ou du Comité national de la CEI du pays du demandeur.
Si vous avez des questions sur le copyright de la CEI ou si vous désirez obtenir des droits supplémentaires sur cette
publication, utilisez les coordonnées ci-après ou contactez le Comité national de la CEI de votre pays de résidence.

IEC Central Office
3, rue de Varembé
CH-1211 Geneva 20
Switzerland
Email: inmail@iec.ch
Web: www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.
ƒ Catalogue of IEC publications: www.iec.ch/searchpub
The IEC on-line Catalogue enables you to search by a variety of criteria (reference number, text, technical committee,…).
It also gives information on projects, withdrawn and replaced publications.
ƒ IEC Just Published: www.iec.ch/online_news/justpub
Stay up to date on all new IEC publications. Just Published details twice a month all new publications released. Available
on-line and also by email.
ƒ Electropedia: www.electropedia.org
The world's leading online dictionary of electronic and electrical terms containing more than 20 000 terms and definitions
in English and French, with equivalent terms in additional languages. Also known as the International Electrotechnical
Vocabulary online.
ƒ Customer Service Centre: www.iec.ch/webstore/custserv
If you wish to give us your feedback on this publication or need further assistance, please visit the Customer Service
Centre FAQ or contact us:
Email: csc@iec.ch
Tel.: +41 22 919 02 11
Fax: +41 22 919 03 00
A propos de la CEI
La Commission Electrotechnique Internationale (CEI) est la première organisation mondiale qui élabore et publie des
normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications CEI
Le contenu technique des publications de la CEI est constamment revu. Veuillez vous assurer que vous possédez
l’édition la plus récente, un corrigendum ou amendement peut avoir été publié.
ƒ Catalogue des publications de la CEI: www.iec.ch/searchpub/cur_fut-f.htm
Le Catalogue en-ligne de la CEI vous permet d’effectuer des recherches en utilisant différents critères (numéro de référence,
texte, comité d’études,…). Il donne aussi des informations sur les projets et les publications retirées ou remplacées.
ƒ Just Published CEI: www.iec.ch/online_news/justpub
Restez informé sur les nouvelles publications de la CEI. Just Published détaille deux fois par mois les nouvelles
publications parues. Disponible en-ligne et aussi par email.
ƒ Electropedia: www.electropedia.org
Le premier dictionnaire en ligne au monde de termes électroniques et électriques. Il contient plus de 20 000 termes et
définitions en anglais et en français, ainsi que les termes équivalents dans les langues additionnelles. Egalement appelé
Vocabulaire Electrotechnique International en ligne.
ƒ Service Clients: www.iec.ch/webstore/custserv/custserv_entry-f.htm
Si vous désirez nous donner des commentaires sur cette publication ou si vous avez des questions, visitez le FAQ du
Service clients ou contactez-nous:
Email: csc@iec.ch
Tél.: +41 22 919 02 11
Fax: +41 22 919 03 00
IEC/TS 60034-18-42
Edition 1.0 2008-08
TECHNICAL
SPECIFICATION
SPÉCIFICATION
TECHNIQUE
Rotating electrical machines –
Part 18-42: Qualification and acceptance tests for partial discharge resistant
electrical insulation systems (Type II) used in rotating electrical machines fed
from voltage converters
Machines électriques tournantes –
Partie 18-42: Essais de qualification et d’acceptation des systèmes d’isolation
électrique résistants aux décharges partielles (Type II) utilisés dans des
machines électriques tournantes alimentées par convertisseurs de tension

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
V
CODE PRIX
ICS 29.160 ISBN 2-8318-9966-4
– 2 – TS 60034-18-42 © IEC:2008
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.7
2 Normative references .7
3 Terms and definitions .8
4 Voltage effects from converter operation .10
4.1 Voltages at the terminals of the converter-fed machine .10
4.2 Electrical stresses in the insulation system of machine windings .13
4.2.1 General .13
4.2.2 Voltages stressing the phase/phase insulation.14
4.2.3 Voltages stressing the phase/ground insulation .14
4.2.4 Voltages stressing the turn insulation .14
5 Type II insulation systems .14
6 Stress factors for converter-fed Type II insulation systems .15
7 Qualification and acceptance tests .16
7.1 General .16
7.2 Qualification tests.16
7.3 Acceptance test.17
8 Qualification of turn insulation .17
8.1 General .17
8.2 Test methods .17
9 Qualification of ground wall insulation systems.19
9.1 General .19
9.2 Test methods .19
9.3 Use of 50 Hz or 60 Hz life data to predict the service life with a converter
drive.20
10 Qualification of the stress control and corona protection system.21
10.1 General .21
10.2 Test methods .22
11 Preparation of test objects.23
11.1 General .23
11.2 Turn/turn samples .23
11.3 Coils.24
12 Qualification test procedures .24
12.1 General .24
12.2 Turn/turn samples .24
12.3 Coils.24
12.4 Stress control samples .25
13 Qualification test pass criteria .25
13.1 Turn/turn samples .25
13.2 Coil samples .25
13.3 Stress control samples .26
14 Acceptance test for Type II insulation systems (Type test).26
14.1 General .26
14.2 Acceptance test methods .26

TS 60034-18-42 © IEC:2008 – 3 –
14.3 Acceptance test pass criteria.26
15 Analysis, reporting and classification .26
Annex A (informative) .27
Annex B (informative) .29
Annex C (informative) .31
Figure 1 – Voltage impulse waveshape parameters .10
Figure 2 – Phase/phase voltage at the terminals of a machine fed by a 3-level
converter .11
Figure 3 – Possible jump voltages (U ) at the machine terminals associated with a
j
converter drive.12
Figure 4 – Maximum voltage enhancement at the machine terminals as a function of
cable length for various impulse rise times for a 2-level converter.13
Figure 5 – Design examples.14
Figure 6 – Life lines of turn and mainwall insulation. .18
Figure 7 – Example of a life curve for a Type II mainwall insulation system.21
Figure 8 – Example of the construction of a turn/turn test sample for rectangular
conductors.23
Figure A.1 – Example of a simple converter voltage simulation circuit.27
Figure A.2 – Typical waveform generated from the spark gap oscillator .28
Figure B.1 – Representation of the phase to ground voltage at the terminals of a
machine fed from a 3-level converter .29
Table 1 – Influence of features of the converter drive voltage on acceleration of ageing
of components of Type II insulation systems.15
Table B.1 – Contribution to electrical ageing by 1 kHz impulses from a 3-level
converter as a percentage of the ageing from the 50 Hz fundamental voltage for
various values of voltage endurance coefficient (n).30

– 4 – TS 60034-18-42 © IEC:2008
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ROTATING ELECTRICAL MACHINES –
Part 18-42: Qualification and acceptance tests for partial
discharge resistant electrical insulation systems (Type II) used
in rotating electrical machines fed from voltage converters
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 provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
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.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC 60034-18-42, which is a Technical Specification, has been prepared by IEC technical
committee 2: Rotating machinery.

TS 60034-18-42 © IEC:2008 – 5 –
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
2/1482/DTS 2/1502/RVC
Full information on the voting for the approval of this technical specification 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 of IEC 60034 series, under the general title Rotating electrical machines, can
be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – TS 60034-18-42 © IEC:2008
INTRODUCTION
The approval of electrical insulation systems for use in rotating electrical machines driven
from voltage converters is set out in two Technical Specifications. They separate the systems
into those which are not expected to experience partial discharge activity within specified
conditions in their service lives (Type I) and those which are expected to withstand partial
discharge activity in any part of the insulation system throughout their service lives (Type II).
For both Type I and Type II insulation systems, the drive system integrator should inform the
machine manufacturer what voltage will appear at the machine terminals in service. The
machine manufacturer will then decide upon the severity of the tests appropriate for qualifying
the insulation system. The severity is based on the impulse rise time, the peak to peak
voltage and, in the case of Type II systems, the impulse repetition rate.
IEC/TS 60034-18-41
Type I insulation systems are dealt with in IEC/TS 60034-18-41. They are generally used in
rotating machines rated at less than 700 V r.m.s. and tend to have random wound stators. In
this Technical Specification, the necessary normative references and definitions are given
together with a review of the effects arising from converter operation. Having established the
technical foundation for the evaluation procedure, the conceptual approach is then described.
IEC/TS 60034-18-42
In this Technical Specification, the tests for qualification and acceptance of electrical
insulation systems chosen for Type II rotating electrical machines are described. These
insulation systems are generally used in rotating machines and tend to have form-wound
coils, mostly rated above 700 V r.m.s. The qualification procedure is completely different from
that used for Type I insulation systems and involves destructive ageing of insulated test
objects under accelerated conditions. The manufacturer requires a life curve for the insulation
system that can be interpreted to provide an estimate of life under the service conditions with
converter drive. Great importance is attached to the qualification of any stress grading system
that is used and testing here should be performed under repetitive impulse conditions. If the
insulation system can be shown to provide an acceptable life under the appropriate ageing
conditions, it is qualified for use. Acceptance testing is performed on coils made using this
insulation system when subjected to a voltage endurance test.
This Technical Specification should be read in conjunction with IEC/TS 60034-18-41, which
provides a background to the technology of converter drive/machine systems.
The winding insulation systems intended for converter-fed machines and converter
technologies are evolving rapidly. In addition, there is on-going research into the best ways to
test such insulation systems. It is expected therefore that there will be improvements in these
Technical Specifications over the next few years.

TS 60034-18-42 © IEC:2008 – 7 –
ROTATING ELECTRICAL MACHINES –
Part 18-42: Qualification and acceptance tests for partial
discharge resistant electrical insulation systems (Type II) used
in rotating electrical machines fed from voltage converters
1 Scope
This Technical Specification defines criteria for assessing the insulation system of stator/rotor
windings of single or polyphase AC machines which are subjected to repetitive impulse
voltages, such as pulse width modulation (PWM) converters, and expected to withstand
partial discharge activity during service. It specifies electrical qualification and acceptance
tests on representative samples which verify fitness for operation with voltage-source
converters.
This document does not apply to:
– Rotating machines which are fed by converters only for starting.
– Electrical equipment and systems for traction.
NOTE Although this Technical Specification deals with voltage-source converters, it is recognised that there are
other types of converters that can create repetitive impulse voltages. For these converters, a similar approach to
testing can be used if needed.
2 Normative references
The following referenced documents are indispensable for the application 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 60034-18-1, Rotating electrical machines – Functional evaluation of insulation systems –
Part 18-1: General guidelines
IEC 60034-18-32, Rotating electrical machines – Functional evaluation of insulation systems –
Part 18-32: Test Procedures for form-wound windings – Electrical evaluation of insulation
systems used in machines up to and including 50 MVA and 15 kV
IEC/TS 60034-18-41, Rotating electrical machines – Part 18-41: Qualification and type tests
for Type I electrical insulation systems used in rotating electrical machines when fed from
voltage converters
IEC 60216-3, Electrical insulating materials – Thermal endurance properties – Part 3:

Instructions for calculating thermal endurance characteristics
IEC/TS 61251, Electrical insulating materials – A.C. voltage endurance evaluation –
Introduction
IEC 61800-4, Adjustable speed electrical power drive systems – Part 4: General requirements
– Rating specifications for a.c. power drive systems above 1 000 V a.c. and not exceeding
35 kV
IEC 62068-1, Electrical insulating systems – Electrical stresses produced by repetitive
impulses – Part 1: General method of evaluation of electrical endurance

– 8 – TS 60034-18-42 © IEC:2008
IEC 62539, Guide for the statistical analysis of electrical insulation breakdown data
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
voltage endurance coefficient
symbol: n
exponent of the inverse power model or exponential model on which the relationship between
life and stressing voltage amplitude for a specific insulation system depends
3.2
life
time to failure
3.3
stress grading material
material generally having a non-linear resistivity characteristic, applied to the endwindings of
stators to reduce the maximum surface electrical stress
3.4
corona protection material
material which is used to coat a stator bar within the slot portion of the stator core to avoid
slot discharges
3.5
impulse rise time
symbol: t
r
time for the voltage impulse to go from 0 % to 100 % (See Figure 1)
NOTE Unless otherwise stated, it is estimated as 1,25 times the time for the voltage to rise from 10 % to 90 %.
3.6
electrical insulation system
insulating structure containing one or more electrical insulating materials together with
associated conducting parts employed in an electrotechnical device
[IEC 62068-1]
3.7
(electric) stress
electric field in V/mm
3.8
rated voltage
symbol: U
N
voltage assigned, generally by the manufacturer, for a specified operating condition of a
machine
3.9
fundamental frequency
first frequency, in the spectrum obtained from a Fourier transform of a periodic time function,
to which all the frequencies of the spectrum are referred
NOTE For the purposes of this Technical Specification, the fundamental frequency of the machine terminal
voltage is the one defining the speed of the converter-fed machine.

TS 60034-18-42 © IEC:2008 – 9 –
3.10
steady state voltage impulse magnitude
symbol: U
a
final magnitude of the voltage impulse (see Figure 1)
3.11
peak (impulse) voltage
symbol: U
p
maximum numerical value of voltage reached during a unipolar voltage impulse (e.g. U in
p
Figure 1)
NOTE 1 For bi-polar voltage impulses, it is half the peak to peak voltage (See Figure 2).
NOTE 2 The peak to peak voltage, Upk/pk is shown in Figure 2.
3.12
voltage overshoot
symbol: U
b
magnitude of the peak voltage in excess of the steady state impulse voltage (see Figure 1)
3.13
impulse repetition frequency
average number of voltage impulses per unit time generated by the converter (switching
frequency)
3.14
jump voltage
symbol : U
j
change in voltage at the terminals of the machine occurring at the start of each impulse when
fed from a converter (see Figure 3)
3.15
peak to peak impulse voltage
symbol : U’
pk/pk
peak to peak voltage at the impulse frequency (See Figure 2)
3.16
peak to peak voltage
symbol : U
pk/pk
peak to peak voltage at the fundamental frequency (See Figure 2)
3.17
partial discharge
electrical discharge that only partially bridges the insulation between conductors
NOTE It may occur inside the insulation or adjacent to a conductor.

– 10 – TS 60034-18-42 © IEC:2008
U
U
p
0,9U
p
U
b
U
a
0,1U
p
t
t t
10 90
IEC  1402/08
Key
U voltage t time
Figure 1 – Voltage impulse waveshape parameters
4 Voltage effects from converter operation
4.1 Voltages at the terminals of the converter-fed machine
Modern converter output voltage rise times may be in the 50 ns to 2 000 ns range due to
power semiconductor switching characteristics. The voltage appearing at the terminals of a
converter-driven machine depends upon several characteristics of the power drive system
(see IEC 61800-4), such as
• operating line voltage of the converter
• architecture and control regime of the converter
• filters between the converter and machine
• length and characteristics of the cable between them
• design of the machine winding
• grounding system
In order to apply this Technical Specification to the qualification and testing of the insulation
system of a winding, it is necessary to specify the required parameters of the voltage
appearing at the machine terminals (Clause 6). In the case of 2-level or other U converters,
depending on the rise time of the voltage impulse at the converter output and on the cable
length and machine impedance, the impulses generate voltage overshoots at the machine
terminals. This voltage overshoot is created by reflected waves at the interface between cable
and machine or converter terminals due to impedance mismatch. The voltage appearing at the
machine terminals when fed from a 3-level converter is shown in Figure 2. The figure shows
one cycle at the fundamental frequency.

TS 60034-18-42 © IEC:2008 – 11 –
U
U
pk/pk
t
U′
pk/pk
IEC  1403/08
Figure 2 – Phase/phase voltage at the terminals of a machine fed by a 3-level converter
Two examples of the maximum change in voltage at the impulse frequency, U , are shown in
j
Figure 3. This parameter is important in defining the voltage enhancement that can occur
across the first or last coil in the stator. Although the smaller U in Figure 3 is the most
j
common instantaneous voltage change occurring at the machine terminals, there is a
possibility that on rare occasions this jump in voltage may occur at the moment of switching
between stages, in which case the larger of the two voltages shown in Figure 3 can occur.
Examples of the enhancements that are produced for various rise times and cable lengths in
the case of a 2-level converter are given in Figure 4, where the worst case is shown, arising
from an infinite impedance load. In this case, the enhancement to the voltage for an impulse
rise time of 1 000 ns is insignificant below about 15 m and only exceeds a factor of 1,2 when
the cable length is greater than 50 m.

– 12 – TS 60034-18-42 © IEC:2008
U
t
U
j
U
j
IEC  1404/08
Figure 3 – Possible jump voltages (U ) at the machine
j
terminals associated with a converter drive

TS 60034-18-42 © IEC:2008 – 13 –
2,1
2,0
1,9
1,8
1,7
1,6
U /U
p a
1,5
1,4
1,3
1,2
1,1
1,0
1 10 100
l  (m)
IEC  1405/08
Key
Ɣ t = 50 ns
r
ż t = 100 ns
r
ź t = 200 ns
r
∇ t = 1 000 ns
r
l cable length
Figure 4 – Maximum voltage enhancement at the machine terminals as a function of
cable length for various impulse rise times for a 2-level converter
4.2 Electrical stresses in the insulation system of machine windings
4.2.1 General
If a winding experiences short rise time voltage impulses with significant magnitude, high
voltage stresses will be created in the following locations (Figures 5a and 5b):
– between conductors in different phases,
– between a conductor and ground,
– between adjacent turns, generally in the line-end coil.
Due to space and surface charge creation within the insulation components, the electric
stress is not only defined by the instantaneous voltage itself but also by the peak voltages
that have been stressing the insulation previously. Generally, it has been shown by
experience that, within certain limits valid for drive systems, the stressing parameter is the
peak/peak voltage. This is also the reason why a unipolar voltage produces the same stress
as a bi-polar voltage having a peak/peak voltage of the same value.

– 14 – TS 60034-18-42 © IEC:2008
a
b
3 1
d
a
b
e
c
c
IEC  1406/08
IEC  1407/0
Key
a phase insulation /endwinding insulation 1 phase to phase
b ground insulation 2 phase to ground
c turn insulation 3 turn to turn
d slot corona protection
e stress grading
Figure 5a – Example of a random wound design Figure 5b – Example of a form-wound design
Figure 5 – Design examples
4.2.2 Voltages stressing the phase/phase insulation
The maximum voltage stress on the phase/phase insulation is determined by the design of the
winding and by the characteristics of the phase/phase voltage.
4.2.3 Voltages stressing the phase/ground insulation
The maximum voltage stress on the phase to ground insulation is determined by the design of
the winding and by the characteristics of the phase to ground voltage.
4.2.4 Voltages stressing the turn insulation
The voltage stressing the turn insulation is determined by the jump values of the phase to
ground voltage (amplitude and rise time) and by the design of winding (number of coils,
number and length of the turns). If this voltage is not known, it may be estimated to be the
phase to ground jump voltage divided by the number of turns (for a normal coil) or layers of
the coil (for transverse coils). There is a further enhancement which occurs due to the
travelling wave along the conductor.
5 Type II insulation systems
If any part of an insulation system is likely to have to withstand PD during its life, it is defined
to be Type II and should therefore contain materials that resist PD. Typically, machines with a
rated voltage ≥ 700 V use Type II insulation systems. Manufacturers usually assign a rated
voltage to a machine based on power frequency. This assumes that voltage from the power
supply is 50 Hz or 60 Hz sinusoidal. In the case of machines driven from converters, the
conventional definition of voltage rating is no longer applicable, although the manufacturer
may still assign a rated voltage for 50 Hz or 60 Hz operation and put it on the rating plate on
the machine. The rating of the insulation system for converter operation should be defined

TS 60034-18-42 © IEC:2008 – 15 –
using the stress factors under which its qualification was achieved. The power frequency
rated voltage assigned by the manufacturer to the machine may not be appropriate to the
insulation system when powered from a converter.
6 Stress factors for converter-fed Type II insulation systems
The converter drive integrator should specify to the machine designer the voltage that will
appear at the machine terminals. This information should be included in the purchase
specification, in addition to the traditional parameters such as rated voltage, thermal class,
humidity, etc. Specifically, the limiting values are to be defined for the following parameters of
the voltage that appear at the machine terminals.
a) Fundamental and impulse voltage repetition frequencies at the machine terminals.
b) Peak to peak voltages of the fundamental and repetition frequencies as well as the jump
voltages that are expected to occur at the machine terminals.
c) The impulse rise time, t
r.
Table 1 gives an indication of the significance of the features of the machine terminal voltage
to the ageing of components of a Type II insulation system. In machines having Type II
insulation systems, the main wall, phase to phase and turn to turn insulation materials are
generally based on combinations of organic and inorganic materials. For stators operating
above 700 V, there may be slot corona protection present, which is designed to provide a
grounded screen to the insulated stator winding in contact with the slot wall. The surface of
the insulation on the conductor is subject to a stress concentration as it emerges from the slot
and, for higher voltage machines, it may be treated with stress grading material to avoid the
occurrence of surface arcing. These five components (turn to turn, mainwall, phase to phase,
slot corona and stress grading) constitute a typical Type II insulation system. Phase to phase
voltages are present where two coils are in contact in the same slot. However, in this case
there exist two layers of mainwall insulation, usually separated by an insulating spacer, and
so the voltage stress is not considered to be of significant magnitude to merit testing of phase
to phase insulation systems. No specific testing is therefore recommended for phase/phase
insulation. The insulation components assessed in qualification and acceptance tests are
shown in Table 1.
Table 1 – Influence of features of the converter drive voltage on acceleration
of ageing of components of Type II insulation systems
Insulation Fundamental Impulse Fundamental Jump Impulse repetition Impulse
component frequency repetition frequency voltage frequency pk/pk rise time
frequency pk/pk voltage voltage (U’ )
pk/pk
Turn to turn
żƔ ż Ɣ ż Ɣ
insulation
Main wall
Ɣż Ɣ ż ż ż
insulation
Corona
żƔ Ɣ Ɣ Ɣ Ɣ
protection layer
and stress
grading
NOTE ż Less significant Ɣ More significant
For insulation systems designed for use under power frequency supply, the long and short-
term effects of rated line-to-ground voltage across the mainwall insulation and along the
length of the stress grading are of principal concern. The turn insulation is generally specified
by the maximum short rise-time surge requirement of the design; such surge events are
generally of very short duration and are relatively infrequent compared with the impulse
repetition rate. For this reason, the acceptance requirements are generally satisfied by the
ability of the mainwall winding to withstand a power frequency withstand test and the turn

– 16 – TS 60034-18-42 © IEC:2008
insulation to withstand a surge test. The ability of the system to meet the design life
requirements is usually satisfied by longer-term voltage endurance testing at 50 Hz or 60 Hz.
This endurance test allows the designer to establish the long-term capability of the mainwall
insulation system.
In the case of converter-fed systems, the more complex voltage waveform produced by the
drive will provide a different stress distribution in the winding. The mainwall, stress grading
and corona protection systems are affected by the magnitude of the voltage overshoot, U ,
b
the rate of rise of voltage and the impulse voltage repetition rate. The last of these may
increase dielectric heating in the mainwall insulation, the corona protection layer and the
stress grading material. As the rise time of the impulses decreases, the voltage stress usually
increases on the insulation between adjacent turns on the line end coil of multi-turn coils. The
combination of these factors and their effect on the insulation system as a whole are
extremely difficult to quantify.
7 Qualification and acceptance tests
7.1 General
There are two stages to the testing of Type II electrical insulation systems for machines fed
from converter drives. The first stage is qualification of the mainwall insulation and turn
insulation systems. Each system will be defined by each manufacturer’s unique design rules
governing parameters, such as, insulation materials, acceptable stresses, stress control
materials and application techniques, processing routes and dimensional guides. It is these
design rules that are being qualified. For qualification of Type II mainwall insulation systems,
coils or bars are subjected to accelerated electrical ageing to determine an electrical life
curve. A method of calculating life for converter-fed systems using data from power frequency
voltage endurance tests is also possible in some cases. Separate testing is carried out for the
stress control system and the turn insulation. If it can be shown that the turn insulation or the
mainwall insulation is not expected to experience PD activity during service, the voltage
endurance testing of that part of the insulation system may be omitted.
The second stage is an acceptance test. In this test, complete coils made to production
standard are subjected to a 50 Hz or 60 Hz voltage endurance test. It is performed by
agreement between the purchaser and manufacturer.
7.2 Qualification tests
For the purposes of this Technical Specification, qualification testing is performed to qualify
the materials, design rules and processing of an insulation system to resist PD in a winding
under a given set of stresses. These tests are based on the general procedures for functional
evaluation of insulation systems described in IEC 60034-18-1, according to which the
insulation system intended to be used under converter conditions (candidate system) is
compared to an insulation system having service experience under line-fed conditions or in
converter operation (reference system).
For Type II insulation systems, the qualification of the mainwall and turn insulation systems is
through voltage endurance testing at room temperature or at elevated temperature (see for
example IEC 60034-18-32). By using different over-voltages or frequencies, a life curve may
be established (Clause 9). Note that interactive ageing mechanisms between turn and
mainwall insulation are ignored in this document. On the basis of the following assumptions,
the life of the insulation system under impulse conditions may be estimated from a life curve,
even though it has been derived from sinusoidal voltage testing.
a) The ageing rate due to impulse and power frequency voltages is the same, provided the
peak/peak values and the number of fundamental voltage cycles are the same.
b) The lifetime exponent, n, is not frequency dependent below 1 kHz.

TS 60034-18-42 © IEC:2008 – 17 –
Qualification of the stress grading and corona protection systems is undertaken through a
separate ageing test in which a representative sample of insulated winding in a simulated slot
is exposed to impulse voltage stresses similar to those expected in service for a period of
time to determine if any visible damage occurs, such as discolouration or burning.
The use of service experience as an alternative to qualification testing is subject to agreement
between purchaser and manufacturer.
7.3 Acceptance test
In the case of Type II insulation systems, production coils in simulated slots are subjected to a
50 Hz or 60 Hz sinewave voltage, applied across the mainwall insulation for 250 h with a
peak/peak value equal to the 4,3 times the maximum peak to peak voltage appearing across
the mainwall insulation under converter operation (Annex C). This is a quality test of the
mainwall insulation and a withstand does not imply an acceptable service life with a converter
drive. However, it is feasible to undertake it within the contract period and thereby establish
the absence of major flaws in the production system.
8 Qualification of turn insulation
8.1 General
The turn insulation in the coils of a machine winding operating from a sinusoidal power supply
is generally specified according to the requirement to withstand discrete voltages of high
magnitude and short duration. The concerns governing turn insulation design are distinct from
those for the main wall insulation. The materials, dimensions and processes used in the
construction of turn insulation may be different from those of the main wall.
Depending on the expected phase/ground voltage in the machine, qualification of the turn
insulation may be required. The principal features of this voltage in regard to ageing of the
insulat
...