IEC 60034-18-32:2022

Rotating electrical machines - Part 18-32: Functional evaluation of insulation systems (Type II) - Electrical endurance qualification procedures for form-wound windings

IEC 60034-18-32:2022 describes qualification procedures for the evaluation of electrical endurance of insulation systems for use in rotating electrical machines using form-wound windings energized with sinusoidal power frequency voltage. The test procedures for the main wall insulation are comparative in nature, such that the performance of a candidate insulation system is compared to that of a reference insulation system with proven service experience. If no reference system is available, the diagram in Annex A is available for use. The qualification procedures of inverter duty insulation system for form-wound windings can be found in IEC 60034-18-42 or IEC 60034-18-41. A new and informative test procedure for the stress control system is introduced and defined in Annex B.
This second edition cancels and replaces the first edition published in 2010. This edition includes the following significant technical changes with respect to the previous edition:
a. Title modified.
b. Simplification of clauses.
c. Reduction in the number of test procedures.
d. Inclusion of full bars and coils as test objects.
e. A new clause dealing with failures and failure criteria.

Machines électriques tournantes - Partie 18-32: Evaluation fonctionnelle des systèmes d'isolation (Type II) - Procédures de qualification de l'endurance électrique pour enroulements préformés

IEC 60034-18-32:2022 décrit les procédures de qualification pour l'évaluation de l'endurance électrique des systèmes d'isolation utilisés dans les machines électriques tournantes à enroulements préformés sous tension sinusoïdale à la fréquence d'alimentation. Les procédures d'essai pour l'isolation principale sont comparatives, puisque les performances d'un système d'isolation candidat sont comparées à celles d'un système d'isolation de référence dont l'expérience en service a été démontrée. Si aucun système de référence n'est disponible, l'Annexe A décrit un diagramme utilisable. Les procédures de qualification d'un système d'isolation d'onduleur pour enroulements préformés peuvent être consultées dans l'IEC 60034‑18-42 ou l'IEC 60034-18-41. Une nouvelle procédure d'essai informative pour systèmes de contrôle de contrainte est introduite et définie à l'Annexe B.
Cette deuxième édition annule et remplace la première édition parue en 2010. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a. modification du titre;
b. simplification des articles;
c. diminution du nombre de procédures d'essai;
d. inclusion de barres et bobines complètes comme éprouvettes;
e. ajout d'un article qui traite des défaillances et des critères de défaillance.

General Information

• Status: Published
• Publication Date: 24-Jan-2022
• ICS: 29.160.01 - Rotating machinery in general
• Technical Committee: TC 2 - Rotating machinery
• Drafting Committee: MT 10 - TC 2/MT 10
• Current Stage: PPUB - Publication issued
• Start Date: 25-Jan-2022
• Completion Date: 10-Dec-2021

Relations

• Revises: IEC 60034-18-32:2010 - Rotating electrical machines - Part 18-32: Functional evaluation of insulation systems - Test procedures for form-wound windings - Evaluation by electrical endurance
• Effective Date: 05-Sep-2023

Overview

IEC 60034-18-32:2022-part of the IEC 60034 series-defines electrical endurance qualification procedures for insulation systems used in rotating electrical machines with form-wound windings energized by sinusoidal power-frequency voltage. This second edition (2022) replaces the 2010 edition and updates test scope, simplifies procedures, and adds new guidance for stress control systems and failure criteria. The standard uses comparative test methods: a candidate insulation system is evaluated against a reference system with proven field experience (Annex A offers a reference lifeline if none exists).

Key topics and requirements

• Electrical ageing (endurance) tests for mainwall insulation, turn insulation and stress control systems (new informative procedure in Annex B).
• Comparative evaluation approach: performance of a candidate system is compared to a reference system to determine qualification.
• Test objects: includes full bars and coils as permissible test specimens (expanded in this edition).
• Diagnostic sub-cycle and initial quality control tests to detect degradation during ageing (impulse, power-frequency and other diagnostics).
• Test conditions: procedures cover ageing at room and elevated temperatures, and specify how to select voltage levels and intended test lives.
• Failure definition and criteria: new clause on failures, failure location verification and pass/fail criteria.
• Reduced and full evaluation routes: options for full evaluation or reduced testing depending on risk and available reference data.
• Stress control system evaluation: informative Annex B introduces procedures and pass criteria for conductive slot/stress control coatings.
• Test standards referenced: cross-references to IEC 60034-18-1 and test-method standards such as IEC 61251 where applicable.

Practical applications

• Qualifying a new insulation system or materials for use in power and industrial motors with form-wound windings.
• Providing type approval data for motor manufacturers (OEMs) and insulation suppliers.
• Supporting R&D and material selection by comparing candidate systems to established references.
• Establishing procurement and acceptance criteria for components used in rotating machinery.
• Guiding test laboratories on reproducible electrical endurance procedures and failure analysis.

Who uses this standard

• Motor designers and manufacturers (OEMs)
• Insulation material and system manufacturers
• Independent testing and certification laboratories
• Reliability, R&D and validation engineers
• Procurement and specification authors in industrial and power sectors

Related standards

• IEC 60034-18-1 (general insulation system classification and guidance)
• IEC 60034-18-41 / IEC 60034-18-42 (qualification procedures for inverter-duty insulation systems)
• IEC 61251 (test procedures referenced)

Keywords: IEC 60034-18-32:2022, rotating electrical machines, form-wound windings, insulation systems, electrical endurance, mainwall insulation, stress control system, qualification procedures.

Standards Content (Sample)

IEC 60034-18-32 ®
Edition 2.0 2022-01
COMMENTED VERSION
INTERNATIONAL
STANDARD
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Rotating electrical machines –
Part 18-32: Functional evaluation of insulation systems (Type II) –
Electrical endurance qualification procedures for form-wound windings
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IEC 60034-18-32 ®
Edition 2.0 2022-01
COMMENTED VERSION
INTERNATIONAL
STANDARD
colour
inside
Rotating electrical machines –

Part 18-32: Functional evaluation of insulation systems (Type II) –

Electrical endurance qualification procedures for form-wound windings

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.160.01 ISBN 978-2-8322-4022-9

– 2 – IEC 60034-18-32:2022 CMV © IEC 2022
CONTENTS
FOREWORD . 5
INTRODUCTION . 7

1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 General considerations . 10
4.1 Relationship to IEC 60034-18-1 . 10
4.2 Selection and designation of test procedures . 10
4.3 Reference insulation system . 11
4.4 Test procedures (IEC 61251) . 11
4.4.1 General . 11
4.4.2 Electrical ageing of the mainwall insulation . 11
4.4.3 Electrical ageing of the stress control system . 11
4.4.4 Electrical ageing of the turn insulation . 12
4.5 Extent of tests . 12
4.5.1 Full evaluation of the mainwall insulation . 12
4.5.2 Reduced evaluation of the mainwall insulation . 12
4.5.3 Evaluation of the stress control system . 12
5 Test objects . 13
5.1 Construction of test objects . 13
5.2 Number of turns .
5.2 Number of test specimens . 13
5.3 Initial quality control tests . 13
6 Electrical ageing . 14
6.1 General . 14
6.2 Voltage levels and intended test lives of the mainwall insulation . 14
6.3 Test temperatures during electrical endurance testing of the mainwall
insulation . 14
6.3.1 Electrical ageing at room temperature . 14
6.3.2 Electrical ageing at elevated temperature . 14
6.3.3 Ageing procedure for the mainwall insulation . 14
6.4 Ageing procedure for the turn insulation .
6.4 Maintenance of stress grading control coatings . 15
7 Diagnostic sub-cycle . 15
7.1 General . 15
7.2 Voltage tests of the mainwall insulation. 15
7.2.1 Mainwall insulation test .
7.2.2 Turn insulation impulse test .
7.2.3 Turn insulation power frequency test .
7.3 Other diagnostic tests . 16
8 Failures of the mainwall insulation . 16
8.1 Failure location and verification. 16
8.2 Failed specimen observations . 16
8.3 Dimensional measurements .

9 Functional evaluation of the mainwall data . 17
9.1 General . 17
9.2 Full evaluation (same voltage level and same expected service life) . 17
9.3 Reduced evaluation (same voltage level and same expected service life) . 21
9.4 Recommended data to be recorded . 23
9.5 Determining qualification for performances different to the reference system . 24
9.5.1 Overview . 24
9.5.2 Case B: Qualification for the same phase to phase voltage and a
different expected service life . 24
9.5.3 Case C: Qualification for different voltage level and same expected
service life . 25
9.5.4 Case D: Qualification for different voltage level and different expected
service life . 26
9.5.5 Non-linearity of regression lines. 27
Annex A (normative) Reference life line for mainwall insulation in the absence of a

manufacturer’s reference life line . 28
Annex B (informative) . 29
B.1 Electrical ageing of the conductive slot coating . 29
B.2 Electrical ageing of the stress control coating . 29
B.3 Test objects . 29
B.4 Evaluation of the stress control system . 29
B.5 Ageing procedure for the conductive slot and stress control coating. 30
B.5.1 General . 30
B.5.2 Arrangement of temperature control by heater plates . 30
B.5.3 Heating by means of an oven . 30
B.5.4 Test parameter . 30
B.6 Qualification of the stress control system . 31
B.6.1 General . 31
B.6.2 Test procedure . 31
B.6.3 Test pass criteria . 31
B.7 Examples of deterioration marks at the stress control system . 32
Bibliography .
List of comments . 34

Figure 1 – Comparison of ageing data from candidate (C) and reference (R) insulation

systems showing qualification . 19
Figure 2 – Comparison of ageing data from candidate and reference insulation systems
showing failure to qualify . 21
Figure 3 – Comparison of reduced evaluation test data from four separate candidate
systems with that from the reference system . 23
Figure 4 – Candidate system qualified for the same voltage level and different expected

service life . 25
Figure 5 – Candidate system qualified for a higher voltage level and the same expected
service life . 26
Figure 6 – Candidate system qualified for a different service life and different voltage
level from the reference . 27
Figure A.1 – Reference lifeline for mainwall insulation . 28
Figure B.1 – Application of heater elements to a stator bar . 30
Figure B.2 – Typical deterioration mark at the conductive slot coating . 32

– 4 – IEC 60034-18-32:2022 CMV © IEC 2022
Table 1 – Test procedure designations .
Table 1 – Conditions for qualification of candidate system . 24
Table B.1 – Phase to ground test voltages and test temperatures . 31

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ROTATING ELECTRICAL MACHINES –

Part 18-32: Functional evaluation of insulation systems (Type II) –
Test Electrical endurance qualification procedures for form-wound
windings – Evaluation by electrical endurance 1

FOREWORD
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This commented version (CMV) of the official standard IEC 60034-18-32:2022 edition 2.0
allows the user to identify the changes made to the previous IEC 60034-18-32:2010 edition
1.0. Futhermore, comments from IEC TC 2 experts are provided to explain the reasons of
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A vertical bar appears in the margin wherever a change has been made. Additions are in
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This publication contains the CMV and the official standard. The full list of comments is
available at the end of the CMV.

– 6 – IEC 60034-18-32:2022 CMV © IEC 2022
IEC 60034-18-32 has been prepared by IEC technical committee 2: Rotating machinery. It is an
International Standard.
This second edition cancels and replaces the first edition published in 2010. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Title modified.
b) Simplification of clauses.
c) Reduction in the number of test procedures.
d) Inclusion of full bars and coils as test objects.
e) A new clause dealing with failures and failure criteria.
The text of this International Standard is based on the following documents:
Draft Report on voting
2/2068/FDIS 2/2075/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.
A list of all parts in the IEC 60034 series, published under the general title Rotating electrical
machines, can be found on the IEC website.
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/standardsdev/publications.
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,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

INTRODUCTION
IEC 60034-18-1 presents general principles for the evaluation of insulation systems used in
rotating electrical machines.
This document deals exclusively with insulation systems for form-wound windings (Type II) and
concentrates on electrical functional evaluation.
In IEC 60034-18-42, tests are described for qualification of Type II insulation systems in
voltage-source converter operation. These insulation systems are generally used in rotating
machines which have form-wound windings, mostly rated above 700 V r.m.s. The two standards
IEC 60034-18-41 and IEC 60034-18-42 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 experience and withstand partial discharge activity in any
part of the insulation system throughout their service lives (Type II).

– 8 – IEC 60034-18-32:2022 CMV © IEC 2022
ROTATING ELECTRICAL MACHINES –

Part 18-32: Functional evaluation of insulation systems (Type II) –
Test Electrical endurance qualification procedures for form-wound
windings – Evaluation by electrical endurance

1 Scope
This part of IEC 60034-18 describes test qualification procedures for the evaluation of electrical
endurance of insulation systems for use in a.c. or d.c. rotating electrical machines using form-
wound windings energized with sinusoidal power frequency voltage. The test procedures for
the main wall insulation are comparative in nature, such that the performance of a candidate
insulation system is compared to that of a reference insulation system with proven service
experience. The test procedures are principally directed at the insulation systems in air-cooled
machines but may also be used for evaluating parts of the insulation systems in hydrogen
cooled machines. Note that the qualification procedures of inverter duty insulation systems for
form-wound windings can be found in IEC 60034-18-42. If no reference system is available, the
diagram in Annex A is available for use. The qualification procedures of inverter duty insulation
system for form-wound windings can be found in IEC 60034-18-42 or IEC 60034-18-41. A new
and informative test procedure for the stress control system is introduced and defined in
Annex B. 2
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 60034-1, Rotating electrical machines – Part 1: Rating and performance
IEC 60034-15:2009, Rotating electrical machines – Part 15: Impulse voltage withstand levels
of form-wound stator coils for rotating a.c. machines
IEC 60034-18-1:2010, Rotating electrical machines – Part 18-1: Functional evaluation of
insulation systems – General guidelines
IEC TS 60034-18-33:2010, Rotating electrical machines – Part 18-33: Functional evaluation of
insulation systems – Test procedures for form-wound windings – Multifactor evaluation by
endurance under simultaneous thermal and electrical stresses
IEC 60034-18-41, Rotating electrical machines – Part 18-41: Partial discharge free electrical
insulation systems (Type I) used in rotating electrical machines fed from voltage converters –
Qualification and quality control tests
IEC 60034-18-42:2017, Rotating electrical machines – Part 18-42: Partial discharge resistant
electrical insulation systems (Type II) used in rotating electrical machines fed from voltage
converters – Qualification tests
IEC 60034-18-42:2017/AMD1:2020
IEC 60034-27-1, Rotating electrical machines – Part 27-1: Off-line partial discharge
measurements on the winding insulation

IEC 60034-27-3, Rotating electrical machines – Part 27-3: Dielectric dissipation factor
measurement on stator winding insulation of rotating electrical machines
IEC 60216-4-1, Electrical insulating materials – Thermal endurance properties – Part 4-1:
Ageing ovens – Single-chamber ovens
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.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
mainwall insulation
main electrical insulation that separates the conductors from the earthed stator/rotor core in
motor and generator windings
3.2
turn strand insulation
electrical insulation that covers each conductor in coils/bars
3.3
interturn turn insulation
electrical insulation that separates the conductor turns from each other in coils/bars
3.4
corona protection material
material which is used to coat a stator coil/bar within the slot portion of the stator core to avoid
slot discharges
3.5
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
conductive slot coating
conductive paint or tape layer in intimate contact with the mainwall insulation in the slot portion
of the coil side, often called semi-conductive coating
Note 1 to entry: The purpose is to prevent partial discharge from occurring between the coil/bar and the stator core.
3.5
stress control coating
paint or tape on the surface of the mainwall insulation that extends beyond the conductive slot
coating in high-voltage stator bars and coils
Note 1 to entry: The purpose of the coating is to prevent surface discharges near the slot exit or in the end winding
area.
– 10 – IEC 60034-18-32:2022 CMV © IEC 2022
3.6
stress control system
generic name for the combination of the conductive slot coating and stress control coating in
high-voltage stator bars and coils 3
3.7
confidence interval
range of values so defined that there is a specified probability that the value of a parameter
(voltage, stress or time) lies within it
3.8
test temperature
temperature of the outer surface of the bar/coil at the straight part of the bar/coil measured with
an appropriate selected and placed sensor
4 General considerations
4.1 Relationship to IEC 60034-18-1
The principles of IEC 60034-18-1 should be followed, unless the recommendations of this
document indicate otherwise.
4.2 Selection and designation of test procedures
One or more of the procedures in this document should be suitable for the majority of
evaluations. Evaluation is usually performed by the manufacturer of the machine/coils or by a
third-party laboratory. It is the manufacturer’s responsibility to justify the most suitable
procedure in Table 1 on the basis of past experience and knowledge of the insulation systems
to be compared.
The test procedure should be selected from Table 1 and designated by IEC 60034-18-32
procedure N, where N is the designation given in the Table 1. Subclauses 4.3, 4.4 and 4.5 give
guidance on how to select the test procedure.
Table 1 – Test procedure designations
Designation Applied ageing voltage Diagnostic tests
of test
Mainwall Interturn Mainwall Interturn Stress grading
procedure
insulation insulation insulation insulation (7.3)
N (6.3) (6.4) (7.2.1) (7.2.2 or 7.2.3)
AA Constant None Not required (A) No test (A) Optional (D)
CA Constant None Other test (C) No test (A) Optional (D)
AB Constant Yes Not required (A) Impulse test (B) Optional (D)
NOTE 1 The meaning of the letters of the diagnostic test are as follows: A – No test; B – Impulse test; C –
Other test (such as dissipation factor and partial discharge tests); D – Visual observation.
NOTE 2 Where a diagnostic test is not required on the mainwall insulation, the ageing voltage acts
simultaneously as the diagnostic factor.

All the above tests are carried out at room temperature. However, if they are to be performed
at any other temperature (see 6.2.2), the designation of the test procedure shall include the
Celsius temperature in brackets, e.g. AA(190). Each of the procedures may be used for the full
evaluation according to 4.5.1 or for the reduced evaluation according to 4.5.2.
Procedure AA is the preferred choice if the manufacturer has no past experience or knowledge
of the candidate system and the behaviour of the mainwall insulation is defined. 4

Following test procedures are described:
• Mainwall insulation
• Turn insulation only with the main insulation test
• Conductive slot coating (Annex B)
• Stress control coating (Annex B)
• Mainwall insulation, where voltage level and/or life time differs from the reference system
4.3 Reference insulation system
A reference insulation system should be tested using a test procedure equivalent to that used
for the candidate system (see IEC 60034-18-1). The reference insulation system should have
service experience at not less than 75 % of the intended maximum rated voltage of the
candidate system. When extrapolation of the insulation thickness is used, information such as
“different insulation thickness at same electrical field stress levels by obtaining equal or similar
breakdown time” should be provided showing the correlation between electrical lifetime and
electrical stress for the different insulation thicknesses. If no reference insulation system is
available the diagram in Annex A shall be used as criterion.
4.4 Test procedures (IEC 61251)
4.4.1 General
Electrical ageing tests are usually performed at fixed voltage levels until failure (mainwall
insulation) or in combination with elevated temperature until signs of deterioration occur
(conductive slot coating system). Statistical evaluation of the results of testing should be
performed according to IEC 62539.
4.4.2 Electrical ageing of the mainwall insulation
From such tests, characteristic times to failure at each voltage level are obtained. The results
for both the candidate system and the reference system should be reported on a graph, as
shown by the example in Figure 1, and compared. There is no proven physical basis for
⁄
extrapolation of this characteristic to the service voltage level 𝑈𝑈 √3, where UN is the r.m.s.
N
rated phase to phase voltage. Statistical evaluation of the results of testing should be performed
according to IEC 62539.
In service, electrical ageing of the mainwall insulation is primarily caused by continuous elec-
trical stress at power frequency. In addition, the insulation is required to withstand transient
overvoltage arising from switching surges or inverter supply. The ability of the mainwall
insulation to withstand transient overvoltage from converter supplies may be demonstrated by
the system’s performance using IEC 60034-18-42.
This document describes voltage electrical ageing of the mainwall insulation, carried out at
power frequency or at a frequency up to 10 times greater higher. In order to keep acceleration
of ageing in a linear progression, a maximum of 10 times of the power frequencies is
appropriate. Latest experiences with the application of IEC 60034-18-42 show that a frequency
of up to 1 000 Hz can be used as well. Care shall be taken that the dielectric losses do not
increase the temperature of the insulation beyond the service temperature to avoid additional
thermal ageing effects. (IEC TS 60034-18-33:2010, Table 1).
4.4.3 Electrical ageing of the stress control system
In order to allow a full qualification of the entire insulation system Annex B describes methods
to qualify the conductive slot coating and stress control coating. 5

– 12 – IEC 60034-18-32:2022 CMV © IEC 2022
4.4.4 Electrical ageing of the turn insulation
Electrical ageing of the turn insulation can arise due to the steady-state stress applied across
the mainwall insulation. This could be particularly significant at the edges of the conductors
where the electrical stress reaches a maximum.
Where multiturn coils or bars are used, the power frequency voltage between turns is sufficiently
low that ageing due to this electric stress is not of major significance. However, steep-fronted
surges on the winding caused by switching and other disturbances can generate sufficient
stress between turns for ageing to take place. Since the waveforms and frequency of occurrence
are variable and dependent upon circuit parameters, this International Standard recommends
that, for comparison purposes, electrical ageing of the turn insulation be performed using
IEC 60034-18-42.
In normal direct-on-line operation of rotating machines the turn insulation is subjected to a
stress significantly below the partial discharge inception voltage. Continuous electrical ageing
is then not taking place and turn insulation qualification is therefore excluded from this
document. Withstand against transient overvoltage should be tested according to
IEC 60034-15.
In converter fed or other types of special operation the turn insulation may continuously be
subjected to a stress above the partial discharge inception voltage. Electrical ageing should
then be performed according to IEC 60034-18-42. 6
4.5 Extent of tests
4.5.1 Full evaluation of the mainwall insulation
The extent of the electrical functional tests will depend upon the purpose of the evaluation. A
full evaluation will be needed where there are substantial differences in the compositions of
from the reference and candidate systems system according to IEC 60034-18-1.
4.5.2 Reduced evaluation of the mainwall insulation
There are situations when it will be sufficient to carry out reduced evaluation using the minimum
number of test specimens and the middle voltage level from used in the range of reference
tests.
Comparison of a candidate insulation system to a reference system, where there are no
intended or only minor differences in composition or manufacturing procedures (so-called minor
changes, see IEC 60034-18-1), may be carried out using only one voltage level but with the
recommended minimum number of test specimens (see 5.2). Reduced evaluation is allowed
only if the rated voltages are the same for both systems.
An example of a minor change might be the sourcing of the same material from a different
supplier or a change of pulping process. An example of a minor processing change might be
the installation of a new controller or new pipework in a vacuum pressure impregnation (VPI)
process. It should be emphasized that a minor change is one which is not expected to have a
significant effect on the insulation system. It is the responsibility of the manufacturer to justify
the use of the reduced qualification procedure
4.5.3 Evaluation of the stress control system
Annex B defines tests and criteria to evaluate conductive slot coating and stress control coating.

5 Test objects
5.1 Construction of test objects
Test objects should preferably be complete bars or coils made to normal design, material and
manufacturing standards procedures. Alternatively, they may be constructed to represent the
configuration of the finished winding component to be evaluated and be subjected to the full
normal or intended manufacturing processes. When using separate coils or bars as models,
creepage distances and any necessary voltage grading are to be appropriate to the stresses
applied during testing. A ground electrode should extend the full slot length of the model and
encircle cover at least the entire circumference two wide sides of the coil cross-section.
The sample preparation and test procedures described in IEC 60034-18-42 may be used for
qualifying stress grading systems applied to endwinding insulation.
Slot models for GVPI systems shall be made from rigid steel plates, not having any other
component inserted than in the actual system present and having a length equal to that of the
longest actual stator.
Test bars should be designed not to generate flashover between the end of stress control
coating and the end of the conductor of the test bar. For reducing excessive electrical stress
on the surface of test bars/coils by applying high voltage and/or high frequency, special
treatment, for example extending stress control coating length, can be applied for evaluating
the mainwall insulation. See also B.5. 7
5.2 Number of turns
For the turn insulation, it is generally necessary to use complete coils in order to include the
effects of shaping and conductor reinforcement. The number of turns and the thickness of the
turn insulation should be such that when the test voltage chosen in accordance with 6.1 is
applied, the turn dielectric stress is not less than the highest that would be imposed by applying
the appropriate test voltage to any design of coil for which the insulation system can be used.
Where a power frequency voltage is to be applied between the turns, the coil should be wound
with two parallel conductors, each insulated with turn insulation, or the coil has to be cut in the
end windings. When using VPI coils, the cut-through and separation of the conductors in this
area have to be done before impregnation. If the test procedure chosen (see 4.2) does not
apply a power frequency voltage between the turns, the test object can be a multiturn coil wound
in the normal manner with a single (or stranded) conductor. 8
5.2 Number of test specimens
An adequate number of test specimens shall be aged at each test voltage level in order to
obtain statistical confidence. This number should not be less than five six bars or three coils for
the qualification of the mainwall insulation per each test voltage level. 9
5.3 Initial quality control tests
Before starting the first ageing sub-cycle, The following quality control tests shall be performed:
– visual inspection of the test specimens;
– high-voltage tests voltage withstand test according to IEC 60034-1;
– dissipation factor test or/and partial discharge test according to IEC 60034-27-3 and
IEC 60034-27-1 respectively.
– 14 – IEC 60034-18-32:2022 CMV © IEC 2022
6 Electrical ageing
6.1 General
It is not practicable to design a single test method that simulates all the interactions between
the various insulation components. For example, to obtain a life curve for the mainwall insulation
system by applying overvoltage would subject the conductive slot coating to excessive stress.
Qualification has therefore been divided into separate test procedures. The primary aim is to
establish the lifetime curve of the mainwall insulation from which the expected lives may be
estimated. The second aim is to establish that the conductive slot coating and the stress control
coating is suitable for service. 10
6.2 Voltage levels and intended test lives of the mainwall insulation
For full evaluation as described in 4.5.1, at least three power frequency voltages should be
selected so that the intended mean time to failure at the highest voltage is about 100 h, and at
the lowest voltage above around 5 000 h. For reduced evaluation, where only one voltage level
is required (see 4.5.2), the voltage level should be chosen so that the intended mean time to
failure is about 1 000 h. The alternating voltage applied to the test objects should be maintained
within ± 3 %.
6.3 Test temperatures during electrical endurance testing of the mainwall insulation
6.3.1 Electrical ageing at room temperature
Electrical ageing is preferably carried out in air at room temperature at voltages and/or
frequencies higher than those in the steady-state operating conditions, in order to accelerate
the effects of electrical stress.
6.3.2 Electrical ageing at elevated temperature
Any appropriate means of heating may be used when the electrical ageing tests are performed
at elevated temperatures. If the endurance testing is to be performed at elevated temperatures,
then either external heating plates or oven heating are permitted (see also Clause B.5). Note
that these two methods may not produce the same results. The temperature rise due to the
applied electrical stress can affect the results, especially when using increased frequency, and
shall be recorded. If thermal ageing does occur, the testing should follow the procedures in
IEC 60034-18-33 for multifactor testing.
NOTE Electrical ageing of the mainwall insulation under power frequency and elevated temperature up to service
temperature may lead generally to longer time to failure values compared to tests at room temperature at same
electrical stress levels.
6.3.3 Ageing procedure for the mainwall insulation
The electrical stress is applied between the stator core or the outer conductive layer mock up /
slot electrode on the surface of the test specimen and the conductors. If the test object is a
multiturn coil, both the mainwall insulation and partly the turn insulation are aged by the
electrical stress during this period. However this procedure does not qualify the turn- to turn
insulation. For test procedures with sub-cycles (Clause 7), the duration of these sub-cycles
should be such that approximately ten sub-cycles are performed on a test specimen having a
median life. Higher than power frequency is allowed to shorten the test times but experience
has shown that the maximum acceptable acceleration factor is 10 times the power frequency.
Latest experiences with the application of IEC 60034-18-42 show that a frequency of up to 1
000 Hz can be used as shown in 4.4.2. Care should be taken that the dielectric losses do not
increase the temperature of the insulation so much that the results are affected beyond the
service temperature to avoid additional thermal ageing effects. (IEC TS 60034-18-33:2010,
Table 1). This is especially important at elevated temperatures. The same frequency should be
used for the candidate and reference insulation system. Increased frequency test results may
only be used for direct comparison if the lives of the systems are affected similarly by the
increase of frequency.
6.4 Ageing procedure for the turn insulation
Ageing of the turn insulation due to repetitive transient over-voltages is evaluated according to
procedure AB in Table 1. The mainwall insulation ageing sub-cycle is followed by a turn
insulation ageing sub-cycle consisting of the application of a power frequency voltage between
turns for 10 min. This voltage shall be
1,5 × U
N
n
where where U is the rated voltage of the insulation in kV and n is the number of turns, but not less
N
than 0,3 × U .
N
The temperature rise due to the applied electrical stress can affect the results, especially when
using increased frequency and should be recorded. Increased frequency test results may only
be used for direct comparison if the lives of the systems are affected similarly by the increase
in frequency. 11
6.4 Maintenance of stress grading control coatings
A stress grading control
...

IEC 60034-18-32 ®
Edition 2.0 2022-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Rotating electrical machines –
Part 18-32: Functional evaluation of insulation systems (Type II) –
Electrical endurance qualification procedures for form-wound windings

Machines électriques tournantes –
Partie 18-32: Evaluation fonctionnelle des systèmes d'isolation (Type II) –
Procédures de qualification de l'endurance électrique pour enroulements
préformés
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IEC 60034-18-32 ®
Edition 2.0 2022-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Rotating electrical machines –

Part 18-32: Functional evaluation of insulation systems (Type II) –

Electrical endurance qualification procedures for form-wound windings

Machines électriques tournantes –

Partie 18-32: Evaluation fonctionnelle des systèmes d'isolation (Type II) –

Procédures de qualification de l'endurance électrique pour enroulements

préformés
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.160.01 ISBN 978-2-8322-1047-8

– 2 – IEC 60034-18-32:2022 © IEC 2022
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 8
4 General considerations . 9
4.1 Relationship to IEC 60034-18-1 . 9
4.2 Selection and designation of test procedures . 9
4.3 Reference insulation system . 9
4.4 Test procedures . 9
4.4.1 General . 9
4.4.2 Electrical ageing of the mainwall insulation . 9
4.4.3 Electrical ageing of the stress control system . 10
4.4.4 Electrical ageing of the turn insulation . 10
4.5 Extent of tests . 10
4.5.1 Full evaluation of the mainwall insulation . 10
4.5.2 Reduced evaluation of the mainwall insulation . 10
4.5.3 Evaluation of the stress control system . 10
5 Test objects . 10
5.1 Construction of test objects . 10
5.2 Number of test specimens . 11
5.3 Initial quality control tests . 11
6 Electrical ageing . 11
6.1 General . 11
6.2 Voltage levels and intended test lives of the mainwall insulation . 11
6.3 Test temperatures during electrical endurance testing of the mainwall
insulation . 11
6.3.1 Electrical ageing at room temperature . 11
6.3.2 Electrical ageing at elevated temperature . 12
6.3.3 Ageing procedure for the mainwall insulation . 12
6.4 Maintenance of stress control coatings . 12
7 Diagnostic sub-cycle . 12
7.1 General . 12
7.2 Voltage test of the mainwall insulation . 12
7.3 Other diagnostic tests . 13
8 Failures of the mainwall insulation . 13
8.1 Failure location and verification. 13
8.2 Failed specimen observations . 13
9 Functional evaluation of the mainwall data . 13
9.1 General . 13
9.2 Full evaluation (same voltage level and same expected service life) . 13
9.3 Reduced evaluation (same voltage level and same expected service life) . 15
9.4 Recommended data to be recorded . 16
9.5 Determining qualification for performances different to the reference system . 17
9.5.1 Overview . 17

9.5.2 Case B: Qualification for the same phase to phase voltage and a
different expected service life . 17
9.5.3 Case C: Qualification for different voltage level and same expected
service life . 18
9.5.4 Case D: Qualification for different voltage level and different expected

service life . 19
9.5.5 Non-linearity of regression lines. 20
Annex A (normative) Reference life line for mainwall insulation in the absence of a
manufacturer’s reference life line . 21
Annex B (informative) . 22
B.1 Electrical ageing of the conductive slot coating . 22
B.2 Electrical ageing of the stress control coating . 22
B.3 Test objects . 22
B.4 Evaluation of the stress control system . 22
B.5 Ageing procedure for the conductive slot and stress control coating. 23
B.5.1 General . 23
B.5.2 Arrangement of temperature control by heater plates . 23
B.5.3 Heating by means of an oven . 23
B.5.4 Test parameter . 23
B.6 Qualification of the stress control system . 24
B.6.1 General . 24
B.6.2 Test procedure . 24
B.6.3 Test pass criteria . 24
B.7 Examples of deterioration marks at the stress control system . 25

Figure 1 – Comparison of ageing data from candidate (C) and reference (R) insulation
systems showing qualification . 14
Figure 2 – Comparison of ageing data from candidate and reference insulation systems
showing failure to qualify . 15
Figure 3 – Comparison of reduced evaluation test data from four separate candidate
systems with that from the reference system . 16
Figure 4 – Candidate system qualified for the same voltage level and different
expected service life . 18
Figure 5 – Candidate system qualified for a higher voltage level and the same
expected service life . 19
Figure 6 – Candidate system qualified for a different service life and different voltage
level from the reference . 20
Figure A.1 – Reference lifeline for mainwall insulation . 21
Figure B.1 – Application of heater elements to a stator bar . 23
Figure B.2 – Typical deterioration mark at the conductive slot coating . 25

Table 1 – Conditions for qualification of candidate system . 17
Table B.1 – Phase to ground test voltages and test temperatures . 24

– 4 – IEC 60034-18-32:2022 © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ROTATING ELECTRICAL MACHINES –

Part 18-32: Functional evaluation of insulation systems (Type II) –
Electrical endurance qualification procedures for form-wound windings

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
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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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
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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.
IEC 60034-18-32 has been prepared by IEC technical committee 2: Rotating machinery. It is an
International Standard.
This second edition cancels and replaces the first edition published in 2010. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) Title modified.
b) Simplification of clauses.
c) Reduction in the number of test procedures.
d) Inclusion of full bars and coils as test objects.
e) A new clause dealing with failures and failure criteria.

The text of this International Standard is based on the following documents:
Draft Report on voting
2/2068/FDIS 2/2075/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.
A list of all parts in the IEC 60034 series, published under the general title Rotating electrical
machines, can be found on the IEC website.
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/standardsdev/publications.
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,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

– 6 – IEC 60034-18-32:2022 © IEC 2022
INTRODUCTION
IEC 60034-18-1 presents general principles for the evaluation of insulation systems used in
rotating electrical machines.
This document deals exclusively with insulation systems for form-wound windings (Type II) and
concentrates on electrical functional evaluation.
In IEC 60034-18-42, tests are described for qualification of Type II insulation systems in
voltage-source converter operation. These insulation systems are generally used in rotating
machines which have form-wound windings, mostly rated above 700 V r.m.s. The two standards
IEC 60034-18-41 and IEC 60034-18-42 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 experience and withstand partial discharge activity in any
part of the insulation system throughout their service lives (Type II).

ROTATING ELECTRICAL MACHINES –

Part 18-32: Functional evaluation of insulation systems (Type II) –
Electrical endurance qualification procedures for form-wound windings

1 Scope
This part of IEC 60034-18 describes qualification procedures for the evaluation of electrical
endurance of insulation systems for use in rotating electrical machines using form-wound
windings energized with sinusoidal power frequency voltage. The test procedures for the main
wall insulation are comparative in nature, such that the performance of a candidate insulation
system is compared to that of a reference insulation system with proven service experience. If
no reference system is available, the diagram in Annex A is available for use. The qualification
procedures of inverter duty insulation system for form-wound windings can be found in
IEC 60034-18-42 or IEC 60034-18-41. A new and informative test procedure for the stress
control system is introduced and defined in Annex B.
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 60034-1, Rotating electrical machines – Part 1: Rating and performance
IEC 60034-15:2009, Rotating electrical machines – Part 15: Impulse voltage withstand levels
of form-wound stator coils for rotating a.c. machines
IEC 60034-18-1:2010, Rotating electrical machines – Part 18-1: Functional evaluation of
insulation systems – General guidelines
IEC TS 60034-18-33:2010, Rotating electrical machines – Part 18-33: Functional evaluation of
insulation systems – Test procedures for form-wound windings – Multifactor evaluation by
endurance under simultaneous thermal and electrical stresses
IEC 60034-18-41, Rotating electrical machines – Part 18-41: Partial discharge free electrical
insulation systems (Type I) used in rotating electrical machines fed from voltage converters –
Qualification and quality control tests
IEC 60034-18-42:2017, Rotating electrical machines – Part 18-42: Partial discharge resistant
electrical insulation systems (Type II) used in rotating electrical machines fed from voltage
converters – Qualification tests
IEC 60034-18-42:2017/AMD1:2020
IEC 60034-27-1, Rotating electrical machines – Part 27-1: Off-line partial discharge
measurements on the winding insulation
IEC 60034-27-3, Rotating electrical machines – Part 27-3: Dielectric dissipation factor
measurement on stator winding insulation of rotating electrical machines
IEC 60216-4-1, Electrical insulating materials – Thermal endurance properties – Part 4-1:
Ageing ovens – Single-chamber ovens

– 8 – IEC 60034-18-32:2022 © IEC 2022
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.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
mainwall insulation
main electrical insulation that separates the conductors from the earthed stator/rotor core in
motor and generator windings
3.2
strand insulation
electrical insulation that covers each conductor in coils/bars
3.3
turn insulation
electrical insulation that separates the conductor turns from each other in coils/bars
3.4
conductive slot coating
conductive paint or tape layer in intimate contact with the mainwall insulation in the slot portion
of the coil side, often called semi-conductive coating
Note 1 to entry: The purpose is to prevent partial discharge from occurring between the coil/bar and the stator core.
3.5
stress control coating
paint or tape on the surface of the mainwall insulation that extends beyond the conductive slot
coating in high-voltage stator bars and coils
Note 1 to entry: The purpose of the coating is to prevent surface discharges near the slot exit or in the end winding
area.
3.6
stress control system
generic name for the combination of the conductive slot coating and stress control coating in
high-voltage stator bars and coils
3.7
confidence interval
range of values so defined that there is a specified probability that the value of a parameter
(voltage, stress or time) lies within it
3.8
test temperature
temperature of the outer surface of the bar/coil at the straight part of the bar/coil measured with
an appropriate selected and placed sensor

4 General considerations
4.1 Relationship to IEC 60034-18-1
The principles of IEC 60034-18-1 should be followed, unless the recommendations of this
document indicate otherwise.
4.2 Selection and designation of test procedures
One or more of the procedures in this document should be suitable for the majority of
evaluations. Evaluation is usually performed by the manufacturer of the machine/coils or by a
third-party laboratory. It is the manufacturer’s responsibility to justify the most suitable
procedure on the basis of past experience and knowledge of the insulation systems to be
compared.
Following test procedures are described:
• Mainwall insulation
• Turn insulation only with the main insulation test
• Conductive slot coating (Annex B)
• Stress control coating (Annex B)
• Mainwall insulation, where voltage level and/or life time differs from the reference system
4.3 Reference insulation system
A reference insulation system should be tested using a test procedure equivalent to that used
for the candidate system (see IEC 60034-18-1). The reference insulation system should have
service experience at not less than 75 % of the intended maximum rated voltage of the
candidate system. When extrapolation of the insulation thickness is used, information such as
“different insulation thickness at same electrical field stress levels by obtaining equal or similar
breakdown time” should be provided showing the correlation between electrical lifetime and
electrical stress for the different insulation thicknesses. If no reference insulation system is
available the diagram in Annex A shall be used as criterion.
4.4 Test procedures
4.4.1 General
Electrical ageing tests are usually performed at fixed voltage levels until failure (mainwall
insulation) or in combination with elevated temperature until signs of deterioration occur
(conductive slot coating system). Statistical evaluation of the results of testing should be
performed according to IEC 62539.
4.4.2 Electrical ageing of the mainwall insulation
From such tests, characteristic times to failure at each voltage level are obtained. The results
for both the candidate system and the reference system should be reported on a graph, as
shown by the example in Figure 1, and compared. There is no proven physical basis for
⁄
extrapolation of this characteristic to the service voltage level 𝑈𝑈 √3, where UN is the r.m.s.
N
rated phase to phase voltage.
In service, electrical ageing of the mainwall insulation is primarily caused by continuous elec-
trical stress at power frequency. In addition, the insulation is required to withstand transient
overvoltage arising from switching surges or inverter supply. The ability of the mainwall
insulation to withstand transient overvoltage from converter supplies may be demonstrated by
the system’s performance using IEC 60034-18-42.

– 10 – IEC 60034-18-32:2022 © IEC 2022
This document describes electrical ageing of the mainwall insulation, carried out at power
frequency or higher. In order to keep acceleration of ageing in a linear progression, a maximum
of 10 times of the power frequencies is appropriate. Latest experiences with the application of
IEC 60034-18-42 show that a frequency of up to 1 000 Hz can be used as well. Care shall be
taken that the dielectric losses do not increase the temperature of the insulation beyond the
service temperature to avoid additional thermal ageing effects. (IEC TS 60034-18-33:2010,
Table 1)
4.4.3 Electrical ageing of the stress control system
In order to allow a full qualification of the entire insulation system Annex B describes methods
to qualify the conductive slot coating and stress control coating.
4.4.4 Electrical ageing of the turn insulation
In normal direct-on-line operation of rotating machines the turn insulation is subjected to a
stress significantly below the partial discharge inception voltage. Continuous electrical ageing
is then not taking place and turn insulation qualification is therefore excluded from this
document. Withstand against transient overvoltage should be tested according to
IEC 60034-15.
In converter fed or other types of special operation the turn insulation may continuously be
subjected to a stress above the partial discharge inception voltage. Electrical ageing should
then be performed according to IEC 60034-18-42.
4.5 Extent of tests
4.5.1 Full evaluation of the mainwall insulation
The extent of the electrical functional tests will depend upon the purpose of the evaluation. A
full evaluation will be needed where there are substantial differences from the reference system
according to IEC 60034-18-1.
4.5.2 Reduced evaluation of the mainwall insulation
There are situations when it will be sufficient to carry out reduced evaluation using the minimum
number of test specimens and the middle voltage level used in the reference tests.
Comparison of a candidate insulation system to a reference system, where there are no
intended or only minor differences in composition or manufacturing procedures (so-called minor
changes, see IEC 60034-18-1), may be carried out using only one voltage level but with the
recommended minimum number of test specimens (see 5.2). Reduced evaluation is allowed
only if the rated voltages are the same for both systems.
4.5.3 Evaluation of the stress control system
Annex B defines tests and criteria to evaluate conductive slot coating and stress control coating.
5 Test objects
5.1 Construction of test objects
Test objects should preferably be complete bars or coils made to normal design, material and
manufacturing procedures. Alternatively, they may be constructed to represent the
configuration of the finished winding component to be evaluated and be subjected to the full
normal or intended manufacturing processes. When using separate coils or bars as models,
creepage distances and any necessary voltage grading are to be appropriate to the stresses
applied during testing. A ground electrode should extend the full slot length of the model and
cover at least the two wide sides of the coil cross-section.

Slot models for GVPI systems shall be made from rigid steel plates, not having any other
component inserted than in the actual system present and having a length equal to that of the
longest actual stator.
Test bars should be designed not to generate flashover between the end of stress control
coating and the end of the conductor of the test bar. For reducing excessive electrical stress
on the surface of test bars/coils by applying high voltage and/or high frequency, special
treatment, for example extending stress control coating length, can be applied for evaluating
the mainwall insulation. See also B.5.
5.2 Number of test specimens
An adequate number of test specimens shall be aged at each test voltage level in order to
obtain statistical confidence. This number should not be less than six bars or three coils for the
qualification of the mainwall insulation per each test voltage level.
5.3 Initial quality control tests
The following quality control tests shall be performed:
– visual inspection of the test specimens;
– voltage withstand test according to IEC 60034-1;
– dissipation factor and partial discharge test according to IEC 60034-27-3 and
IEC 60034-27-1 respectively.
6 Electrical ageing
6.1 General
It is not practicable to design a single test method that simulates all the interactions between
the various insulation components. For example, to obtain a life curve for the mainwall insulation
system by applying overvoltage would subject the conductive slot coating to excessive stress.
Qualification has therefore been divided into separate test procedures. The primary aim is to
establish the lifetime curve of the mainwall insulation from which the expected lives may be
estimated. The second aim is to establish that the conductive slot coating and the stress control
coating is suitable for service.
6.2 Voltage levels and intended test lives of the mainwall insulation
For full evaluation as described in 4.5.1, at least three power frequency voltages should be
selected so that the intended mean time to failure at the highest voltage is about 100 h, and at
the lowest voltage around 5 000 h. For reduced evaluation, where only one voltage level is
required (see 4.5.2), the voltage level should be chosen so that the intended mean time to
failure is about 1 000 h. The alternating voltage applied to the test objects should be maintained
within ± 3 %.
6.3 Test temperatures during electrical endurance testing of the mainwall insulation
6.3.1 Electrical ageing at room temperature
Electrical ageing is preferably carried out in air at room temperature at voltages and/or
frequencies higher than those in the steady-state operating conditions, in order to accelerate
the effects of electrical stress.

– 12 – IEC 60034-18-32:2022 © IEC 2022
6.3.2 Electrical ageing at elevated temperature
If the endurance testing is to be performed at elevated temperatures, then either external
heating plates or oven heating are permitted (see also Clause B.5). Note that these two methods
may not produce the same results. The temperature rise due to the applied electrical stress can
affect the results, especially when using increased frequency, and shall be recorded. If thermal
ageing does occur, the testing should follow the procedures in IEC 60034-18-33 for multifactor
testing.
NOTE Electrical ageing of the mainwall insulation under power frequency and elevated temperature up to service
temperature may lead generally to longer time to failure values compared to tests at room temperature at same
electrical stress levels.
6.3.3 Ageing procedure for the mainwall insulation
The electrical stress is applied between the stator core or the mock up / slot electrode on the
surface of the test specimen and the conductors. If the test object is a multiturn coil, both the
mainwall insulation and partly the turn insulation are aged by the electrical stress during this
period. However this procedure does not qualify the turn- to turn insulation. For test procedures
with sub-cycles (Clause 7), the duration of these sub-cycles should be such that approximately
ten sub-cycles are performed on a test specimen having a median life. Higher than power
frequency is allowed to shorten the test times. Latest experiences with the application of
IEC 60034-18-42 show that a frequency of up to 1 000 Hz can be used as shown in 4.4.2. Care
should be taken that the dielectric losses do not increase the temperature of the insulation
beyond the service temperature to avoid additional thermal ageing effects.
(IEC TS 60034-18-33:2010, Table 1). This is especially important at elevated temperatures.
The same frequency should be used for the candidate and reference insulation system.
Increased frequency test results may only be used for direct comparison if the lives of the
systems are affected similarly by the increase of frequency.
6.4 Maintenance of stress control coatings
A stress control coating is usually applied to the outer surface of the coil or bar beyond the
earthed conductive slot coating. During the electrical endurance test of the main insulation,
deterioration may occur which does not result in insulation failure. Remedial action to the stress
grading material and forced air cooling are permitted during the progress of the voltage
endurance test on the basis that it is the mainwall insulation that is being tested rather than the
stress grading system.
7 Diagnostic sub-cycle
7.1 General
No diagnostic tests are required for the qualification of the mainwall insulation but may be
performed optionally.
Following each ageing sub-cycle, a diagnostic sub-cycle can be performed. Failure of any part
of the test specimen during a diagnostic test constitutes failure of the whole system and shall
be reported as such. The appropriate voltage tests are selected according to the chosen test
procedure as per 4.2.
7.2 Voltage test of the mainwall insulation
If a diagnostic test on the mainwall insulation is performed it shall be done with a power
frequency AC withstand test according to IEC 60034-15. Alternatively, a lighting impulse
voltage withstand test according to IEC 60034-15 may be used.

7.3 Other diagnostic tests
Optional diagnostic measurements may be performed for information or to determine end of
test life. These may replace the voltage tests. Factors such as insulation resistance, dielectric
dissipation factor, partial discharges and impulse test on the turn-to-turn insulation are
examples. An end-point criterion may be established for each diagnostic test, with suitable
justification reported.
8 Failures of the mainwall insulation
8.1 Failure location and verification
Failure of a specimen occurs when any electrical breakdown of the mainwall insulation occurs.
This will result in the over-current detection system interrupting current to the high voltage
transformer. Failure of the insulation should be verified by re-applying voltage gradually from
zero. A specimen insulation failure will prevent the reapplication of the full test voltage. Locating
the failure site is desirable and may be undertaken by seeing arcing or heating at the failure
site as the voltage is raised. Care shall be taken as locating the failure in applying voltage the
local failure area may be additionally damaged and the analysis of the breakdown channel might
be more difficult or even impossible. When specimen failure has been verified, the failed sample
should be isolated to allow testing to continue on the remaining samples.
Breakdown under stress control coating is acceptable, if only one breakdown of all tested
bars/coils at this location occurs. If there is more than one bar or coil affected with a breakdown
under the stress control coating, the number of bars or coils needs to be increased to get
statistically enough values for the lifetime of the mainwall insulation away from the stress control
coating. It is recommended in such a case to review design and manufacturing process for this
particular area.
8.2 Failed specimen observations
Each failed specimen should be examined to ensure that the failure is valid for statistical
interpretation. This may require some specimen dissection in the area around the insulation
puncture to identify the failure location and its probable cause.
9 Functional evaluation of the mainwall data
9.1 General
The evaluation of the test data should follow the guidelines set out below. Under the assumption
of a Weibull distribution, the appropriate statistical analysis should be applied to calculate the
significance of the candidate sample life with regard to that of the reference sample (see
IEC 62539). In order to avoid introducing new ageing phenomena the maximum test voltage
shall not exceed 4 times U .
N
The general rule is that the candidate insulation system is considered to be qualified if the 90 %
confidence interval of the used probability distribution of the breakdown time falls above or
within that obtained from the reference system (see IEC 60034-18-1).
If the reference line, given in Annex A, is used, an interpretation of results is mandatory. An
example of evalution and interpretation is given in IEC 60034-18-42.
9.2 Full evaluation (same voltage level and same expected service life)
Electrical endurance graphs of the candidate and the reference system are plotted as a log-log
representation of the time to failure (t), as a function of the ratio of test voltage (U ) and rated
t
voltage (U ), where U is the rated voltage of the reference system and the candidate system.
N N
The candidate system is qualified if:

– 14 – IEC 60034-18-32:2022 © IEC 2022
a) the upper 90 % confidence limit of the candidate system exceeds the upper 90 % confidence
limit of the reference system over the range of reference system test voltages, or
b) the lower 90 % confidence limit of the candidate system exceeds or is equal to the lower
90 % confidence limit of the reference system at the lowest test voltage and the regression
line of the mean values of the candidate system has a more gentle slope than that of the
reference system.
Ageing results for a candidate system which satisfies condition b) are shown in Figure 1. An
example of a candidate system which fails to qualify in respect of either condition a) or b) is
shown in Figure 2.
The slope of a modern insulation sys
...