EN 60034-18-21:1994

SLOVENSKI STANDARD
01-april-1999
Rotating electrical machines - Part 18: Functional evaluation of insulation systems
- Section 21: Test procedures for wire-wound windings - Thermal evaluation and
classification (IEC 60034-18-21:1992)
Rotating electrical machines -- Part 18: Functional evaluation of insulation systems --
Section 21: Test procedures for wire-wound windings - Thermal evaluation and
classification
Drehende elektrische Maschinen -- Teil 18: Funktionelle Bewertung von Isoliersystemen
-- Hauptabschnitt 21: Prüfverfahren für Runddraht-Wicklungen - Thermische Bewertung
und Klassifizierung
Machines électriques tournantes -- Partie 18: Evaluation fonctionnelle des systèmes
d'isolation -- Section 21: Procédures d'essai pour enroulements à fils - Evaluation
thermique et classification
Ta slovenski standard je istoveten z: EN 60034-18-21:1994
ICS:
29.080.30 Izolacijski sistemi Insulation systems
29.160.01 Rotacijski stroji na splošno Rotating machinery in
general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEI
NORME
I EC
INTERNATIONALE
34-18-21
INTERNATIONAL
Première
édition
STANDARD First edition
1992-07
Machines électriques tournantes
Dix-huitième partie:
systèmes d'isolation
Evaluation fonctionnelle des
enroulements
Section 21: Procédures d'essai pour
à fils – Evaluation thermique et classification
Rotating electrical machines
Part 18:
Functional evaluation of insulation systems
Section 21: Test procedures for wire-wound
windings – Thermal evaluation and classification
right — all rights reserved
© CEI 1992 Droits de reproduction réservés — Copy
No part of this publication may be reproduced or utilized in
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34-18-21 ©IEC —3—
CONTENTS
Page
FOREWORD 7
INTRODUCTION
Clause
1 Scope
2 Normative references
3 General considerations
11 3.1 Relationship to Section 1
3.2 Standard procedures 13
13 3.3 Reference insulation system
3.4 Test objects 13
3.5 Verification of diagnostic tests
3.6 Thermal ageing test procedure
3.7 Ageing temperatures and sub-cycle lengths
17 4 Procedure 1: Motorette test procedure
4.1 General
4.2 Test objects
4.3 Thermal ageing sub-cycle 19
4.4 Diagnostic sub-cycle
4.5 Analyzing, reporting and class ification
5 Procedure 2: Motor test procedure
5.1 General 23
5.2 Test objects
5.3 Thermal ageing sub-cycle
27 5.4 Diagnostic sub-cycle
29 5.5 Analyzing, reporting and classification
6 Procedure 3: Test procedure for stator windings in slots
6.1 General
6.2 Test objects 31
6.3 Thermal ageing sub-cycle
6.4 Diagnostic sub-cycle
6.5 Analyzing, reporting and classification

34-18-21 © IEC – 5 —
Clause Page
7 Procedure 4: Test procedure for pole windings
7.1 General
7.2 Test objects
7.3 Thermal ageing sub-cycle
7.4 Diagnostic sub-cycle
7.5 Analyzing, reporting and classification
8 Procedure 5: Test procedure for rotor windings in slots
8.1 General
8.2 Test objects
8.3 Thermal ageing sub-cycle
8.4 Diagnostic sub-cycle
8.5 Analyzing, reporting and classification
Annexes
A - Motorette construction (example)
B - Models for windings on poles (examples) 57
C - Equipment for moisture tests
Figures 65
34-18-21 ©IEC – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
ROTATING ELECTRICAL MACHINES
Part 18: Functional evaluation of insulation systems
Section 21: Test procedures for wire-wound windings –
Thermal evaluation and classification
FOREWORD
The formal decisions or agreements of the IEC on technical matters, prepared by Technical Committees on
1)
which all the National Committees having a special interest therein are represented, express, as nearly as
possible, an international consensus of opinion on the subjects dealt with.
They have the form of recommendations for international use and they are accepted by the National
2)
Committees in that sense.
In order to promote international unification, the IEC expresses the wish that all National Committees
3)
should adopt the text of the IEC recommendation for their national rules in so far as national conditions will
permit. Any divergence between the IEC recommendation and the corresponding national rules should, as
far as possible, be clearly indicated in the latter.
This section of International Standard IEC 34-18 has been prepared by Sub-Com-
mittee 2J: Classification of insulation systems for rotating machinery, of IEC Technical
Committee No. 2: Rotating machinery.
The text of this section is based on the following documents:
Six Months' Rule Report on Voting
2J(CO)9
2J(CO)5
Full information on the voting for the approval of this section can be found in the Voting
Report indicated in the above table.
Annexes A, B and C are for information only.

34-18-21 © IEC – 9 –
INTRODUCTION
Section 1 of IEC 34-18 presents general principles for the evaluation and classification of
insulation systems used in rotating electrical machines.
This section of IEC 34-18 deals with the thermal evaluation and classification of insulation
systems for wire-wound (usually random wound) windings.
Several standard test procedures are given for various types of wire-wound windings and
testing techniques.
18 of a series of publications dealing with the functional evalu-
This section belongs to Part
rts being:
ation of insulation systems for rotating electrical machines, the other pa
Section 1: General guidelines (IEC 34-18-1).
Section 31: Test procedures for form-wound windings (IEC 34-18-31).

34-18-21 © IEC -11 -
ROTATING ELECTRICAL MACHINES
Part 18: Functional evaluation of insulation systems
Section 21: Test procedures for wire-wound windings –
Thermal evaluation and classification
1 Scope
This section of IEC 34-18 gives test procedures for the thermal evaluation and classifi-
cation of insulation systems used or proposed for use in wire-wound alternating current
(a.c.) or direct current (d.c.) rotating electrical machines. The test procedures are compara-
tive in that the performance of a candidate insulation system is compared to that of a
reference insulation system with proven se rvice experience.
Section 21 shall be used in conjunction with Section 1.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute
provisions of this section of IEC 34-18. At the time of publication, the editions indicated
were valid. All standards are subject to revision, and pa rties to agreements based on this
section of IEC 34-18 are encouraged to investigate the possibility of applying the most
recent editions of the standards indicated below. Members of IEC and ISO maintain
registers of currently valid International Standards.
IEC 34-1: 1983, Rotating electrical machines - Part 1: Rating and performance.
IEC 455, Specification for solventless polymerisable resinous compounds used for
electrical insulation.
IEC 464, Specification for insulating varnishes containing solvent.
IEC 34-18-1: 1991, Rotating electrical machines - Pa rt 18: Functional evaluation of insula-
tion systems - Section 1: General guidelines.
3 General considerations
3.1 Relationship to Section 1
Section 1 describes general testing principles applicable to thermal endurance testing of
insulation systems in rotating machines. Unless the procedures of this pa rt indicate other-
wise, the principles of Section 1 shall be followed.

34-18-21 ©IEC –13 –
3.2 Standard procedures
4 through 8. The user of this standard
Five standard procedures are specified in clauses
shall select that test procedure which most closely corresponds to the type and size of the
windings to be tested and classified, also taking into account facilities and past
experience.
3.3 Reference insulation system
A reference insulation system shall be tested using the same test procedure as for the
candidate system. See 4.2 of Section 1.
The thermal class temperatures of the two systems shall not differ by more than 50 K.
3.4 Test objects
3.4.1 Construction of test objects
Tests for the selection of materials according to 5.2.1 of section 1 may be performed, as
appropriate.
Test objects may be actual machines, machine components or models. The components
and models should embody all the essential elements.
Insulation thickness, creepage distances and discharge protection where required shall be
appropriate for the intended maximum rated voltage and equipment standards or practice.
The systems compared shall have arrangements consistent with those to be used in
machines.
NOTE - It is recognized that markedly different values of test life may be obtained for the same insulating
materials, depending on insulation thicknesses and creepage distances.
s of a coil or winding may be used for evaluation, if
Test specimens simulating part
rts in se rvice can be reproduced reliably in the test.
stresses acting on these pa
Particular types of models have been used successfully in some countries and examples
of these are illustrated in annexes A and B.
rtain that the materials proposed for use in the new
The manufacturer should make ce
insulation system can be handled without deterioration of properties in the intended manu-
facturing processes.
3.4.2 Quality assurance tests
To eliminate defective test objects, they should be qualified first, as per 5.2.3 of Section 1,
by visual examination and then by over-voltage tests consistent with the machine or coil
tests in the manufacturing facility, or as described in the appropriate subclauses for
diagnostic tests, whichever voltage test is greater.

–15 –
34-18-21 © IEC
NOTE - When appropriate. additional screening (or qualifying) tests may be used, including the following:
insulation resistance measurement;
loss tangent and capacitance measurement;
partial discharge inception voltage measurement;
balance of phase currents while running;
repetitive surge;
leakage current;
high-voltage test.
Any widely deviating object should be discarded or inspected to determine the reason for
the deviation and appropriate allowances should be made for the deviations.
Verification of diagnostic tests
3.5
A preliminary ageing test according to 5.3.4 of Section 1, to check the feasibility of the
diagnostic sub-cycle, may be performed.
3.6 Thermal ageing test procedure
The test procedure consists of several ageing tests, performed at different ageing tempera-
tures. At each temperature, the test life of the insulation systems tested is determined.
Based on these test life values, the life at the class temperature is estimated relative to
that of the reference system at its class temperature.
Each ageing test is performed in cycles, each cycle consisting of a thermal ageing sub-
cycle and a diagnostic sub-cycle. The diagnostic sub-cycle may include a mechanical test,
a moisture test, a voltage test and other diagnostic tests.
Ageing temperatures and sub-cycle lengths
3.7
The considerations and procedures of 5.3.2 of Section 1 should be observed and followed.
For the normal procedure, the number of ageing temperatures shall be at least three.
Where the candidate insulation system represents a minor change from a classified
system, 5.3.2.2 of Section 1 may be followed.
Ageing temperatures and lengths of ageing sub-cycles may be selected from table 2 of
Section 1.
If the intended thermal class for the candidate insulation system differs from the known
class of the reference system, different ageing temperatures and sub-cycle lengths are to
be selected in an appropriate manner.
The lowest ageing temperature should be selected such as to produce the log mean test
life of about 5 000 h or more. This is generally accomplished by choosing the lowest
ageing temperature to correspond to an exposure period of 28 to 35 days or longer.

IEC - 17 -
34-18-21 ©
In addition, at least two higher ageing temperatures should be selected, separated by
intervals of 20 K or more. Intervals of 10 K may be suitable when tests are made at more
than three ageing temperatures.
To minimize the uncertainty introduced by extrapolation the lowest test temperature
should not exceed by more than 25 K the temperature to which the results will be extra-
polated.
4 Procedure 1: Motorette test procedure
4.1 General
4.1.1 Procedure 1
This procedure, using "motorette" type models as test objects, shall be referred to as
IEC 34-18-1, Procedure 1.
4.1.2 General features
This thermal endurance test procedure consists of several cycles. Each cycle consists of:
- a thermal ageing sub-cycle;
- a diagnostic sub-cycle which includes a mechanical test, a moisture test with test-
specimen cooling and a voltage test, performed in that order.
4.2 Test objects
4.2.1 Construction of test objects
The test object in this procedure, designated motorette, models the insulation system to
be tested.
The motorette shall be made to embody all of the essential elements and should be as
nearly as possible representative of a complete winding insulation system. The motorette
simulates a wire-wound winding of a slotted structure.
An example of a motorette used to test wire-wound winding insulation is described in
annex A.
4.2.2 Number of test objects
At least 10 motorettes should be tested at each ageing temperature, for each insulation
system.
4.2.3 Quality assurance tests
Before the first thermal ageing sub-cycle is started, the following quality assurance tests
shall be performed:
visual inspection of the test objects;
voltage tests according to IEC 34-1;

34-18-21 © IEC –19 –
- 400 V a.c. conductor-to-conductor test with 50 mA circuit breaker to detect failure.
4.2.4
Initial diagnostic tests
Each completed test object shall be subjected to the diagnostic tests of 4.4, before
starting the first thermal ageing sub-cycle.
4.3 Thermal ageing sub-cycle
4.3.1 Ageing temperatures and sub-cycle lengths
The procedures given in 3.7 shall be followed.
4.3.2 Means of heating
Ageing ovens according to 5.3.3 of Section 1 shall be used.
4.3.3 Ageing procedure
The motorettes shall be loaded directly into the hot ageing oven at the beginning of the
ageing sub-cycle, and removed from the oven directly to room temperature air at the end
of the sub-cycle.
In order to diminish the effects of differences in actual ageing temperatures between
individual motorettes, the locations of the motorettes in the ageing oven should be
randomized in successive heat ageing sub-cycles.
4.4 Diagnostic sub-cycle
4.4.1 Mechanical test
Following each sub-cycle of thermal ageing, after cooling to room temperature, each
motorette is subjected to mechanical stress on a shake table for a period of 1 h.
The motorettes are mounted so that the motion occurs at right angles to the plane of the
coils so that the coil ends are excited to vibrate as they would under radial end-winding
forces in an actual motor. This vibration test is made at room temperature and without any
applied voltage.
The preferred amplitude of the vibration corresponds to an acceleration of 1,5 g (0,2 mm
peak-to-peak amplitude at 60 Hz or 0,3 mm at 50 Hz). If the principle of service-related
stresses (see 5.5.1 of Section 1) leads to a larger vibration amplitude, it shall be used and
reported.
4.4.2
Moisture test
A moisture test of at least 48 h duration shall be performed, according to 5.5.2 of
Section 1. Visible moisture droplets, without puddles, shall be present on the windings
during the moisture test. The motorettes shall be at approximately room temperature, in
the 15 °C to 35 °C range. The actual motorette temperatures shall be reported. No voltage

34-18-21 ©IEC – 21 –
is applied to the test objects during this test. See annex C for examples of equipment for
such tests.
The principle of cooled test objects shall be used. See clause C.2 of annex C.
4.4.3 Voltage test
In order to check the condition of the test specimens and determine when the end of test
life has been reached, power-frequency voltage is applied after each successive exposure
to moisture, as follows:
Table 1 - Test voltages in procedure 1
Recommended power-frequency voltage for testing (Vr.m.s.)
Rated voltage
in service
Between conductors •
To frame Between coils
400 110 ± 10
110 - 400
110 ± 10
401 - 660 660
Under consideration
Under consideration Under consideration
661 -1 000
* Range of acceptable voltage; however, the value chosen should be used consistently.
The test voltage to be used to frame and between coils should correspond to the upper
limit of the voltage range for which that insulation system is intended. A voltage other than
660 V may be employed in order, for example, to permit the use of much test data taken at
600 V. Other test voltages may be used for end-point determination based on test experi-
ence as long as these voltages are maintained consistently for both the reference and the
candidate systems. Deviations from values given in table 1 shall be reported.
The voltages are applied for a period of 10 min while the test specimens are still in
the equipment for moisture test, wet with moisture. The applied voltage is held success-
ively, each time for 10 min using appropriate circuitry, first between the parallel wound
conductors, then from coil to coil, and finally from all coils to frame. It is suggested that
surge protectors be included in the test circuit to eliminate unintended high-voltage spikes.
Based on experience, one of the most significant factors in the testing of motorettes is the
characteristics of the circuit breakers used to detect failure. See clause A.3 of annex A.
4.4.4 Other diagnostic tests
Other diagnostic tests may be performed according to 5.5.4 of Section 1.

34-18-21 © IEC - 23 -
4.5 Analyzing, reporting and classification
The procedures given in 5.6 of Section 1 shall be followed. Additional items to be reported
are indicated in 4.4.1 and 4.4.3.
5 Procedure 2: Motor test procedure
5.1 General
5.1.1 Procedure 2
This procedure, using actual motors as test objects, shall be referred to as IEC 34-18-1,
Procedure 2.
5.1.2 General features
This thermal endurance test procedure consists of several cycles. Each cycle consists of:
- a thermal ageing sub-cycle;
a diagnostic test sub-cycle, which may include a moisture test. Voltage is applied
-
continuously during the running of the motor and is also a diagnostic factor.
Greater thermomechanical stress and higher concentration of the products of decompo-
sition occur during tests at higher than actual temperature. Also, it is recognized that
failures from abnormally high mechanical stress or voltages are generally of a different
rvice.
character from those failures which are produced in long se
Due to variations in control of key test parameters, manufacturing processes and methods
of testing motors, it is exceedingly difficult to compare motor tests of one facility to those
of another. It is the intent of this procedure to compare motor insulation systems within
one manufacturing and one testing facility.
Even though actual motors are tested, the results cannot be used to determine endurance
ice in an absolute sense. The tests can be used as a means of classifi-
time in actual se rv
cation only by comparing insulation systems.
5.2 Test objects
5.2.1 Construction of test objects
The test objects are complete motors. A motor may be modified for the test to increase its
mechanical life. To increase its temperature rise various techniques may be employed
provided no changes are made in the insulation system and its immediate environment.
In the tests on actual motors the dimensions of components and the manufacturing
processes of winding and shaping do affect the test results. Therefore, the manufacturing
processes should be those used or contemplated for use in normal production.

IEC 34-18-21 © –
25 –
5.2.2 Number of test objects
At least five motors should be tested at each ageing temperature for each insulation
system.
5.2.3 Quality assurance tests
Before the first thermal ageing sub-cycle is started, the following quality assurance tests
shall be performed:
- visual inspection before assembly of the motors;
- voltage tests according to IEC 34-1.
5.2.4 Initial diagnostic tests
Each completed test object shall be subjected to the diagnostic tests of 5.4, before start-
ing the first thermal ageing sub-cycle.
5.3 Thermal ageing sub-cycle
5.3.1 Ageing temperatures and sub-cycle lengths
The procedures given in 3.7 shall be followed.
Test temperatures shall be measured by the resistance method. Thermocouples may be
installed for purposes of control. The temperature should be controlled to the accuracy
prescribed in 5.3.3 of Section 1 after the thermal ageing temperature is reached. If the
temperature of any one motor deviates appreciably from the average for the group being
run at a common temperature it should be so reported and taken into account in the
analysis of the data.
5.3.2 Means of heating
The mode of heat generation is dictated by the type of motor being used in the test and
the laboratory equipment available. Higher than normal winding temperatures may be
obtained by increasing motor losses by such means as enlarging the air gap, starting and
reversing each motor, superimposition of direct current on the normal alternating current,
or by increasing the temperature of the air surrounding the motor. For temperature regu-
lation during the heat ageing po rtion of the cycle, the motors may be run at normal voltage
and frequency with an electrical control which automatically starts and stops or reverses
the direction of rotation of the motors at intervals. Other acceptable means of temperature
control include automatic voltage variation, adjustment of the surrounding air temperature,
or combinations thereof.
The means of heating shall be described in detail in the test report.
Single-phase motors shall have at least 250 sta rt-stop operations each day of the heat
ageing po
rtion of the cycle. The starting winding of a single-phase motor normally
operates at a much higher current density than the main winding during sta rting. During
each start it may reach a temperature of 10 K to 30 K higher than the main winding. In
order to ensure that the correct emphasis is placed on the main winding po rtion of the
insulation system, a reasonable number of starts should be employed.

34-18-21 © IEC – 27 –
Polyphase motors shall have at least 1 000 starts or reversals each day of the heat ageing
port
ion of the cycle. Often the electrical loss during reversal is used to maintain the
elevated temperatures, in which case the number of reversals may greatly exceed 1 000
per day. At the highest temperature test the total time of exposure is relatively short which
results in a relatively low number of reversals during the life of the test. At the lowest
temperature, the time of exposure may be 16 to 20 times as long as that of the highest
level. A wide variation in total number of starts would affect the slope of the time-
temperature curve within a cycle. Thus, it is recommended that the number of reversals at
the low temperature be no greater than twice those at the high temperature. Ideally an
equal number of reversals at each temperature should be sought.
5.3.3 Ageing procedure
Motors are run during the thermal ageing cycle as described in 5.3.2. The heating-up time
is to be considered as part of the thermal ageing period while the cooling-down time is not.
At the end of the ageing sub-cycle, motors are allowed to cool to room temperature before
starting the diagnostic sub-cycle. The cooling rate may be increased by running the
motors at no-load for a time, with unrestricted ventilation if the machines are open-
ventilated.
5.3.4 Mechanical stresses during the thermal ageing sub-cycle
Mechanical stress is obtained in tests on actual motors by the normal vibration of the
motor running and with starts or reversals, or both. There is mechanical shock from start-
ing or reversing. The vibration amplitude at twice the line frequency may be increased by
enlarging the air gap. Larger forces are present in the windings as a result of the high
currents during starting and reversing of the motors. In a test these mechanical forces
occur at elevated temperatures.
The test motors should either be solidly mounted or mounted on shock pads that will give
a uniform amount of shock to all motors. The mounting method shall be reported. The test
objects containing the candidate insulation system shall be mounted in the same way as
the test objects containing the reference system.
Diagnostic sub-cycle
5.4
5.4.1 Moisture test
A moisture test of at least 48 h shall be used, except that for totally enclosed machines
(degrees of protection IP44 or more) and for d.c. machines a moisture test is not manda-
tory because it may not be practicable. Moisture shall be visible on the windings as
droplets, without puddles, during the moisture test. To ensure visible condensation, the in-
sulation system should be at a lower temperature than the dew point of the surrounding
moisture-laden atmosphere at all times. The preferred method of meeting this requirement
is by the use of a condensation test chamber with cooled test objects described in
clause C.2 of annex C.
34-18-21 © IEC – 29 –
However, larger motors may be difficult to move and difficult to suppo rt in equipment for
moisture test, or such equipment may not be available. Other methods of applying
moisture include: placing an enclosing hood around the motor, or using a conventional
humidity cabinet or a fog chamber.
If totally enclosed machines are to be tested, end bells or the covers of terminal boxes
should be removed, or openings should be provided in the enclosures for the moisture
exposure.
No voltage is applied during the moisture exposure.
5.4.2 Voltage test
The diagnostic voltage test is carried out throughout the thermal ageing sub-cycle.
The motors should be started and run immediately after the moisture test while the wind-
ings are still wet. For machines that have to be reassembled prior to running, a power-
frequency high potential test should be applied at the highest rated voltage from windings
to frame for 10 min while wet before assembly. During at least part of the thermal ageing
sub-cycle the motors are to be run at their highest rated nameplate voltage. A power
source earthed through a current limiting impedance should be used and the motor frame
should be earthed so that voltage stresses are present during the entire thermal ageing
portion of the cycle. A detection circuit for current to frame should be used to detect when
insulation to the frame has failed. The end point of the motor life in these tests is fixed by
the electrical failure of its winding insulation, under a rated applied voltage. Indiscriminate
starting in either direction of rotation of a single-phase motor may indicate failure of the
starting winding.
It is suggested that surge protectors be included in the test circuit to eliminate unintended
high-voltage spikes.
5.4.3 Other diagnostic tests
The motors may be given a repeated surge comparison test applied to each winding or
phase of the motor in sequence. Since surge tests also stress frame insulation, no voltage
shall be used which is higher than the crest of the frame test voltage specified in IEC 34-1.
Other diagnostic tests may be performed according to 5.5.4 of Section 1.
Analyzing, reporting and classification
5.5
The procedures given in 5.6 of Section 1 shall be followed.
Additional items to be reported are indicated in 5.3.1 and 5.3.2.

34-18-21 © IEC – 31 –
6 Procedure 3: Test procedure for stator windings in slots
6.1 General
Procedure 3
6.1.1
This procedure, using windings assembled in the slots of a stator as test objects, shall be
referred to as IEC 34-18-21, Procedure 3.
6.1.2 General features
This thermal endurance test procedure consists of several cycles. Each cycle consists of:
a thermal ageing sub-cycle;
-
a diagnostic sub-cycle which includes a mechanical test, a moisture test and a volt-
-
age test, performed in that order.
6.2 Test objects
6.2.1 Construction of test objects
Test objects are actual windings or parts of actual windings in actual stators.
Each test object may contain several individual test specimens.
A test specimen shall contain features for testing turn insulation, coil-to-coil insulation and
coil-to-frame insulation.
The test objects shall be manufactured using the normal or intended manufacturing
process.
6.2.2 Number of test specimens
At each ageing temperature, at least ten specimens in a minimum of two test objects
should be tested at each ageing temperature for each insulation system.
6.2.3 Quality assurance tests
Before the first thermal ageing sub-cycle is started, the following quality assurance tests
shall be performed:
- visual inspection of the test objects;
- voltage tests according to IEC 34-1.
6.2.4 Initial diagnostic tests
Each completed test object shall be subjected to the diagnostic tests of 6.4, before start-
ing the first thermal ageing sub-cycle.

IEC –
34-18-21 © 33 –
6.3 Thermal ageing sub-cycle
Ageing temperatures and sub-cycle lengths
6.3.1
The procedures given in 3.7 shall be followed.
Means of heating
6.3.2
Ageing ovens according to 5.3.3 of Section 1, or internal resistance heating may be used
where applicable.
6.3.3 Ageing procedure
When ovens are used, the test objects shall be loaded directly into the hot ageing oven at
the beginning of the ageing sub-cycle, and removed from the oven directly to room
temperature air at the end of the sub-cycle, or cooled with equivalent effects.
The location of the test objects within the oven should be randomized, if feasible. See
4.3.3.
6.4 Diagnostic sub-cycle
6.4.1 Mechanical test
The test objects are cooled to approximately room temperature before testing.
rt. A
The method for producing mechanical stresses shall be described in the test repo
shake table may be used.
rvice stresses in
Mechanical stresses shall be at least as great as the highest transient se
magnitude, and of the same character.
Mechanical stresses shall be applied for at least 1 000 vibration cycles at transient stress
magnitude.
NOTE - An overcurrent test may be used to produce electrodynamic forces at least as great as the forces
arising when the motor rotation is reversed.
6.4.2 Moisture test
A moisture test of at least 48 h duration shall be performed according to 5.5.2 of
Section 1. Visible moisture droplets, without puddles, are to be present on the windings
during the moisture test. The test objects shall be at approximately room temperature, in
the 15 °C to 35 °C range. The actual test object temperature shall be reported. No voltage
is applied to the test specimens during this test. The preferred equipment for applying
moisture is described in clause C.1 of annex C.
6.4.3 Voltage test
In order to check the condition of the test specimens and determine when the end of test
life has been reached, voltage is applied after each successive exposure to moisture, as
follows.
34-18-21 © IEC – 35 –
Test voltages should be selected from table 1. Other test voltages may be used for end-
point determination based on test experience as long as these voltages are maintained
consistently for both the reference and candidate systems. Deviations from values given in
table 1 shall be reported.
A test voltage of 10 min duration is applied in sequence between turns, between coils, and
from all coils to frame. The voltage shall be applied while the specimens are still wet from
exposure, preferably while still in the humidity chamber, at approximately room tempera-
ture. It is suggested that surge protectors be included in the test circuit to eliminate
unintended high-voltage spikes.
6.4.4 Other diagnostic tests
Other diagnostic tests may be performed according to 5.5.4 of Section 1.
Analyzing, reporting and classification
6.5
The procedures given in 5.6 of Section 1 shall be followed.
Additional items to be reported are indicated in 6.4.1, 6.4.2 and 6.4.3.
7 Procedure 4: Test procedure for pole windings
7.1 General
7.1.1 Procedure 4
This procedure using pole windings as test objects, shall be referred to as IEC 34-18-21,
Procedure 4.
7.1.2
General features
This thermal endurance test procedure consists of several cycles. Each cycle consists of:
- a thermal ageing sub-cycle;
- a diagnostic sub-cycle, which includes a mechanical test, a moisture test and a
voltage test, performed in that order.
7.2 Test objects
7.2.1 Construction of test objects
The test object used in this procedure models the insulation system of field coils mounted
on a pole. It shall be made to embody all of the essential elements and should be as
nearly as possible representative of the complete winding insulation system.
a) Random wire-wound field coils
For random wire-wound field coils as used in small d.c. and synchronous machines,
appropriate and convenient models should be used as test objects.

34-18-21 © IEC – 37 –
An example of a model coil assembly for the purpose of testing random-wound stator
field coil insulation is described in annex B. Actual pole pieces taken from production
may be used if desired and may actually be necessary in some cases if the stresses
developed in the coil-pole assembly produce deflections of the formed-shell pole. Such
movement would introduce inappropriate variations from actual service conditions.
b) Precision wire-wound field coils
An example of a test object for layer-wound or precision-wound field coils as used for
example in larger d.c. machines is described in annex B. The test fixture is similar to
that for the random-wound coil but omits the curvature at the pole shoe.
7.2.2 Number of test objects
At least 10 test objects shall be tested at each ageing temperature for each insulation
system.
7.2.3 Quality assurance tests
Before the first thermal ageing sub-cycle is started, the following initial tests shall be
performed:
visual inspection of the test objects;
- voltage tests according to IEC 34-1.
7.2.4 Initial diagnostic tests
Each completed test object shall be subjected to the diagnostic tests of 7.4, before start-
ing the first thermal ageing sub-cycle.
Thermal ageing sub-cycle
7.3
7.3.1 Ageing temperatures and sub-cycle lengths
The procedures given in 3.7 shall be followed.
7.3.2 Means of heating
Ageing ovens according to 5.3.3 of Section 1 shall be used.
7.3.3 Ageing procedure
The test objects shall be loaded directly into the hot ageing oven at the beginning of the
ageing sub-cycle, and removed from the oven directly to room temperature air at the end
of the sub-cycle.
The location of the test objects within the oven should be randomized if feasible. See
4.3.3.
34-18-21 © IEC – 39 –
7.4 Diagnostic sub-cycle
7.4.1
Mechanical test
Following each sub-cycle of thermal ageing and after cooling to room temperature, each
test specimen shall be subjected to mechanical stress.
It is recommended that the mechanical stresses applied be of the same general nature as
would be experienced in service, and of a severity comparable with the highest stresses
expected in normal service.
The standard test for stator coils is the shake table test in accordance with 5.5.1 of
Section 1. The test objects should be so mounted that the motion occurs at right angles to
the plane of each of the conductor turns so that the coil ends are excited to vibrate as they
would under radial end-winding forces in an actual machine. This vibration test should be
made at room temperature and without applied voltage. The specimens shall be excited to
vibrate for a period of 1 h. The preferred amplitude of the vibration corresponds to an
acceleration of 1,5 g (15 m/s 2) corresponding to vibration peak-to-peak amplitude of
0,3 mm at 50 Hz or 0,2 mm at 60 Hz. If the general principle as given above requires a
larger amplitude, it shall be used and reported.
If some other method, following the general principle given above, is used, it shall be
reported in detail and justified. For example, salient-pole rotor coils might be rotated to
reproduce the centrifugal stresses encountered in service.
7.4.2
Moisture test
A moisture test of at least 48 h duration shall be performed. Visible moisture droplets, with-
out puddles, shall be present on the windings during the moisture test. The test objects
shall be at approximately room temperature, in the 15 °C to 35 °C range. The actual test
object temperature shall be reported. See annex C.
7.4.3
Voltage test
In order to check the condition of the test specimens and determine when the end of test
life has been reached, power-frequency voltage shall be applied after each exposure to
moisture.
Other test voltages may be used for end-point determination based on test experience as
long as the voltages are maintained consistently for both the reference and candidate
systems. Deviations from values given above shall be reported.
A test voltage of 10 min duration is applied in sequence between turns, between coils if
appropriate, and from all coils to frame. The voltage shall be applied while the specimens
are still wet from exposure, preferably while still in the humidity chamber at approximately
room temperature. It is suggested that surge protectors be included in the test circuit to
eliminate unintended high-voltage spikes.

IEC –41 –
34-18-21 ©
Table 2 - Test voltages in procedure 4
Recommended power-frequency voltage for testing (Vr m.
․)
Rated field winding
voltage
From coil to coil or
Between conductors *
(UN ) from coil to frame
110±10
35 or less
110 ± 10
36 - 250 500
110 ± 10
1 320
251 - 660
110±10
>66 2UN
Range of acceptable voltage; however, the value chosen should be used consistently.
*
7.4.4
Other diagnostic tests
Other diagnostic tests may be performed according to 5.5.4 of Section 1.
7.5 Analyzing, reporting and classification
The procedures given in 5.6 of Section 1 shall be followed. Additional items to be reported
are indicated in 7.3.1, 7.3.2 and 7.3.3.
8 Procedure 5: Test procedure for rotor windings in slots
8.1 General
8.1.1 Procedure 5
This procedure, using coils of windings assembled in the slots of a rotor as test objects,
shall be referred to as IEC 34-18-21, Procedure 5.
8.1.2 General features
This thermal endurance test procedure consists of several cycles. Each cycle consists of:
- a thermal ageing sub-cycle;
- a diagnostic sub-cycle, which includes a mechanical test, a moisture test and a
voltage test, performed in that order.
Test objects
8.2
8.2.1 Construction of test objects
For wire-wound armatures (rotors of d.c. machines), experience has shown that the test
object most suitably incorporating the desired characteristics of the wound rotor for the
evaluation of insulation systems is the rotor itself. Therefore, test objects are actual wind-
ings or parts of windings assembled in rotor slots.

lEC 34-18-21 © – 43 –
Normal armature manufacturing procedures should be followed for placement of insula-
tions, coil winding and resin or varnish treatment during construction of the test object.
Connections should be made to permit 1) turn to turn, 2) coil to coil and 3) coil to frame
dielectric proof tests or insulation condition measurements, generally in that sequence, so
as to maximize the data to be obtained. For this purpose the connection arrangement may
differ from normal practice. For commutator machines, one suggested connection
technique is to start and terminate each coil at the same commutator segment. This
produces a winding which is not operative as a machine but coils are isolated to permit
measurements. Other connection arrangements may be used to isolate turns or coils so as
to satisfy the test objectives. The test connection arrangements used shall be reported.
Commutator design and materials are important considerations for the test object. The
objective of the test may be the evaluation of the armature winding insulation only and
therefore it may be preferred to exclude the effects of the commutator. The rationale for
doing so may be differences in the cooling arrangements and therefore in the temperature
rises of the winding and of the commutator. The thermal capability of the materials
selected for the winding and commutator may therefore be different. For this situation, a
fixture may be used that replaces the commutator for the required coil terminations and
measurements.
Should the test objective be an evaluation of the winding and commutator as an assembly,
some modifications at the commutator will usually be required, particularly on small test
objects, to ensure valid measurements and useful data. Exposure of bare copper and the
sho distances between segments, and from segments to connections or to frame, which
rt
are inherent in the commutator design and function, may result in flashover or undue burn-
ing of insulations during overvoltage testing. To alleviate this condition, excess moisture
on the commutator from humidification may be removed by carefully directed forced air or
ace and bare
rf
wiping prior to application of voltage. Enclosure of the commutator su
connections may also be required.
8.2.2 Number of test specimens
At least 10 test specimens of each insulation system should be tested at each ageing
temperature. A rotor may be wound to incorporate more than one insulation system, each
adequately identified and isolated. Preferably, several rotors each containing a different
insulation system may be wound for test at each ageing temperature.
Quality assurance tests
8.2.3
Before the first thermal ageing sub-cycle is started, the following quality assurance tests
shall be performed:
visual inspection of the test objects;
voltage tests according to IEC 34-1.
Initial diagnostic tests
8.2.4
Each completed test object shall be subjected to the diagnostic tests of 8.4, before start-
ing the first thermal ageing sub-cycle.

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