SIST-TS CLC/TS 60034-18-33:2011
(Main)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/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/TS 60034-18-33:2010)
This part of IEC 60034-18 describes procedures for evaluation of insulation systems by endurance testing where thermal and electrical stresses are applied simultaneously. The procedures are intended for insulation systems used, or proposed to be used, in a.c. electrical machines using form-wound windings. The test procedures provide a comparison of performance between reference and candidate systems at combinations of voltage and temperature which have been used separately to assess quality in the past and which are chosen to produce failures within a suitable timescale and at stresses within practical limits. The outcome of the test on the candidate insulation system will indicate whether it is better or worse than the reference system with proven service experience but will not enable a lifetime in service to be calculated. The evaluation described in this technical specification does not include stress grading.
The test procedures in this technical specification are not intended to establish the interaction between thermal and electrical stress in the ageing process nor endurance lines. If additional information is required on this interaction or in order to achieve endurance lines, it is necessary to undertake further tests in which electrical ageing is carried out at constant temperature and different voltages (IEC 60034-18-32) and thermal ageing is performed at different temperatures and constant voltage.
Drehende elektrische Maschinen - Teil 18-33: Funktionale Bewertung von Isoliersystemen - Prüfverfahren für die multifunktionelle Bewertung von Wicklungen mit vorgeformten Elementen bei gleichzeitiger thermischer und elektrischer Beanspruchung der Isoliersysteme von drehenden Maschinen (IEC/TS 60034-18-33:2010)
Machines électriques tournantes - Partie 18-33: Évaluation fonctionnelle des systèmes d'isolation - Procédures d'essai pour enroulements préformés - Évaluation fonctionnelle à plusieurs facteurs par endurance sous contraintes thermiques et électriques simultanées des systèmes d'isolation utilisés dans les machines électriques tournantes (CEI/TS 60034-18-33:2010)
Električni rotacijski stroji - 18-33. del: Funkcionalna ocena izolacijskih sistemov - Postopki preskušanja formiranega navitja - Ocenjevanje po več faktorjih vzdržljivosti ob hkratnem toplotnem in električnem obremenjevanju (IEC/TS 60034-18-33:2010)
Ta del IEC 60034-18 opisuje postopke za oceno izolacijskih sistemov s preskusi vzdržljivosti, kjer so toplotne in električne obremenitve podane istočasno. Postopki so namenjeni za izolacijske sisteme, uporabljene ali predlagane za uporabo v električnih strojih izmeničnega toka, ki uporabljajo formirana navitja. Preskusni postopki zagotavljajo primerjavo delovanja med referenčnimi in mogočimi sistemi pri kombinaciji napetosti in temperatur, ki so bile v preteklosti uporabljene ločeno za ocenitev kakovosti in so izbrane za ustvarjanje napak v primernem časovnem merilu in pri obremenitvah v praktičnih mejah. Izid preskusa pri mogočem izolacijskem sistemu bo navajal, ali je boljši ali slabši kot referenčni sistem z dokazanimi uporabnimi izkušnjami, vendar ne bo omogočil izračuna življenjske dobe pri uporabi. Ocenjevanje, opisano v tej tehnični specifikaciji, ne vsebuje razvrščanja obremenitev.
Preskusni postopki v tej tehnični specifikaciji niso namenjeni vzpostavitvi interakcije med toplotnimi in električnimi obremenitvami niti v procesu staranja niti pri mejah vzdržljivosti. Če so potrebne dodatne informacije o tej interakciji ali da se dosežejo meje vzdržljivosti, je treba opraviti nadaljnje preskuse, v katerih je električno staranje izvedeno pri konstantni temperaturi in različnih napetostih (IEC 60034-18-32), toplotno staranje pa pri različnih temperaturah in konstantni napetosti.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST-TS CLC/TS 60034-18-33:2011
01-junij-2011
1DGRPHãþD
SIST-TP CLC/TR 60034-18-33:2005
(OHNWULþQLURWDFLMVNLVWURMLGHO )XQNFLRQDOQDRFHQDL]RODFLMVNLKVLVWHPRY
3RVWRSNLSUHVNXãDQMDIRUPLUDQHJDQDYLWMD2FHQMHYDQMHSRYHþIDNWRUMLK
Y]GUåOMLYRVWLREKNUDWQHPWRSORWQHPLQHOHNWULþQHPREUHPHQMHYDQMX ,(&76
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/TS 60034-18-33:2010)
Drehende elektrische Maschinen - Teil 18-33: Funktionale Bewertung von
Isoliersystemen - Prüfverfahren für die multifunktionelle Bewertung von Wicklungen mit
vorgeformten Elementen bei gleichzeitiger thermischer und elektrischer Beanspruchung
der Isoliersysteme von drehenden Maschinen (IEC/TS 60034-18-33:2010)
Machines électriques tournantes - Partie 18-33: Évaluation fonctionnelle des systèmes
d'isolation - Procédures d'essai pour enroulements préformés - Évaluation fonctionnelle
à plusieurs facteurs par endurance sous contraintes thermiques et électriques
simultanées des systèmes d'isolation utilisés dans les machines électriques tournantes
(CEI/TS 60034-18-33:2010)
Ta slovenski standard je istoveten z: CLC/TS 60034-18-33:2011
ICS:
29.080.30 Izolacijski sistemi Insulation systems
29.160.01 Rotacijski stroji na splošno Rotating machinery in
general
SIST-TS CLC/TS 60034-18-33:2011 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST-TS CLC/TS 60034-18-33:2011
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SIST-TS CLC/TS 60034-18-33:2011
TECHNICAL SPECIFICATION
CLC/TS 60034-18-33
SPÉCIFICATION TECHNIQUE
March 2011
TECHNISCHE SPEZIFIKATION
ICS 29.160 Supersedes CLC/TR 60034-18-33:2004
English version
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/TS 60034-18-33:2010)
Machines électriques tournantes - Drehende elektrische Maschinen -
Partie 18-33: Évaluation fonctionnelle des Teil 18-33: Funktionale Bewertung von
systèmes d'isolation - Isoliersystemen -
Procédures d'essai pour enroulements Prüfverfahren für die multifunktionelle
préformés - Bewertung von Wicklungen mit
Évaluation fonctionnelle à plusieurs vorgeformten Elementen bei gleichzeitiger
facteurs par endurance sous contraintes thermischer und elektrischer
thermiques et électriques simultanées des Beanspruchung der Isoliersysteme von
systèmes d'isolation utilisés dans les drehenden Maschinen
machines électriques tournantes (IEC/TS 60034-18-33:2010)
(CEI/TS 60034-18-33:2010)
This Technical Specification was approved by CENELEC on 2011-02-21.
CENELEC members are required to announce the existence of this TS in the same way as for an EN and to
make the TS available promptly at national level in an appropriate form. It is permissible to keep conflicting
national standards in force.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus,
the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,
Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia,
Spain, Sweden, Switzerland and the United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Management Centre: Avenue Marnix 17, B - 1000 Brussels
© 2011 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. CLC/TS 60034-18-33:2011 E
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SIST-TS CLC/TS 60034-18-33:2011
CLC/TS 60034-18-33:2011 - 2 -
Foreword
The text of the Technical Specification IEC/TS 60034-18-33:2010, prepared by IEC TC 2, Rotating
machinery, was submitted to the formal vote and was approved by CENELEC as CLC/TS 60034-18-33
on 2011-02-21.
This European Standard supersedes CLC/TR 60034-18-33:2004.
The main changes with respect to CLC/TR 60034-18-33:2004 are as follows:
a) the requirement to investigate the nature of interactions between thermal and electrical stresses has
been abandoned;
b) the use of single stress acceleration factors has been removed;
c) the selection of stress levels has been adjusted and the temperatures are now related to the thermal
class temperature of the insulation system;
d) the introduction of end-point criteria;
e) a simplified method to display results.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN and CENELEC shall not be held responsible for identifying any or all such patent
rights.
The following date was fixed:
– latest date by which the existence of the CLC/TS
has to be announced at national level (doa) 2011-08-21
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the Technical Specification IEC/TS 60034-18-33:2010 was approved by CENELEC as a
Technical Specification without any modification.
In the official version, for Bibliography, the following note has to be added for the standard indicated:
IEC 60034-18-32 NOTE Harmonized as EN 60034-18-33.
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SIST-TS CLC/TS 60034-18-33:2011
- 3 - CLC/TS 60034-18-33:2011
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year
IEC 60034-15 - Rotating electrical machines - EN 60034-15 -
Part 15: Impulse voltage withstand levels of
form-wound stator coils for rotating a.c.
machines
IEC 60034-18-1 2010 Rotating electrical machines - EN 60034-18-1 2010
Part 18-1: Functional evaluation of insulation
systems - General guidelines
IEC/TS 60034-18-42 - Rotating electrical machines - CLC/TS 60034-18-42 -
Part 18-42: Qualification and acceptance tests
for partial discharge resistant electrical
insulation systems (Type II) used in rotating
electrical machines fed from voltage
converters
IEC 60085 - Electrical insulation - Thermal evaluation EN 60085 -
and designation
IEC 60505 - Evaluation and qualification of electrical EN 60505 -
insulation systems
IEC 62539 - Guide for the statistical analysis of electrical - -
insulation breakdown data
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SIST-TS CLC/TS 60034-18-33:2011
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SIST-TS CLC/TS 60034-18-33:2011
IEC/TS 60034-18-33
®
Edition 2.0 2010-07
TECHNICAL
SPECIFICATION
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
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
P
ICS 29.160 ISBN 978-2-88912-066-6
® Registered trademark of the International Electrotechnical Commission
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SIST-TS CLC/TS 60034-18-33:2011
– 2 – TS 60034-18-33 © IEC:2010(E)
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.7
2 Normative references .7
3 General description of test procedures .8
3.1 Relationship to other standards .8
3.2 Test procedures .8
3.3 Reference insulation system.8
3.4 Characteristics of test procedures .8
3.4.1 General characteristics.8
3.4.2 Ageing sub-cycle .8
3.4.3 Conditioning and diagnostic sub-cycle .8
3.5 Means of heating and definition of thermal stress level.8
3.5.1 Methods of heating .8
3.5.2 Thermal stress level .9
3.5.3 Temperature measuring techniques.9
3.6 Means of electrical ageing.9
3.7 Definition of ageing sub-cycle duration .9
3.8 Reference operating conditions .10
3.8.1 General .10
3.8.2 Reference ageing factors.10
3.8.3 Reference conditioning factors .10
3.8.4 Reference diagnostic factors .10
4 Test objects.10
4.1 Construction of test objects .10
4.1.1 General aspects .10
4.1.2 Considerations on turns and strands in test objects .10
4.2 Number of test specimens .11
4.3 Initial quality control tests.11
4.4 Initial diagnostic tests.11
5 Ageing sub-cycle .11
5.1 Ageing stress levels .11
5.2 Acceleration factors.11
5.3 Duration and number of ageing sub-cycles .12
5.4 Full multifactor testing procedure .12
5.5 Single-point testing procedure .12
6 Conditioning and diagnostic sub-cycle.12
6.1 General .12
6.2 Mechanical tests .13
6.2.1 General mechanical test .13
6.2.2 Shake-table test .13
6.3 Moisture tests.13
6.3.1 General moisture test .13
6.3.2 Moisture test with water immersion.13
6.4 Voltage tests .13
6.5 Other diagnostic tests.14
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SIST-TS CLC/TS 60034-18-33:2011
TS 60034-18-33 © IEC:2010(E) – 3 –
7 End point criteria .14
8 Analyzing the data, reporting and evaluation .14
8.1 Analyzing the data.14
8.2 Reporting .14
8.3 Evaluation .14
Bibliography.15
Table 1 – Guidelines for the selection of stress levels.11
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SIST-TS CLC/TS 60034-18-33:2011
– 4 – TS 60034-18-33 © IEC:2010(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
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
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC/TS 60034-18-33, which is a technical specification, has been prepared by IEC technical
committee 2: Rotating machinery.
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SIST-TS CLC/TS 60034-18-33:2011
TS 60034-18-33 © IEC:2010(E) – 5 –
This new edition was originally issued as a technical report in 1995 but has been revised
extensively prior to re-issue as a technical specification. The main changes with respect to
the earlier version of this document are as follows.
a) the requirement to investigate the nature of interactions between thermal and electrical
stresses has been abandoned;
b) the use of single stress acceleration factors has been removed;
c) the selection of stress levels has been adjusted and the temperatures are now related to
the thermal class temperature of the insulation system;
d) the introduction of end-point criteria;
e) a simplified method to display results.
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
2/1581/DTS 2/1601/RVC
Full information on the voting for the approval of this technical specification can be found in
the report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 60034 series, published under the general title Rotating electrical
machines, can be found on the IEC website.
NOTE A table of cross-references of all IEC TC 2 publications can be found on the IEC TC 2 dashboard on the
IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be be
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.
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SIST-TS CLC/TS 60034-18-33:2011
– 6 – TS 60034-18-33 © IEC:2010(E)
INTRODUCTION
This document is being issued as a technical specification (according to the ISO/IEC
Directives, Part 1, 3.1.1.1) for provisional application in the field of insulation systems for
rotating electrical machines, because there is a need for guidance on how standards in this
field should be used to meet an identified need.
This document is not to be regarded as an International Standard. It is proposed for
provisional application so that information and experience of its use in practice may be
gathered. Comments on the content of this document should be sent to the IEC Central
Office.
Part 18-1 of IEC 60034 presents general guidelines for the evaluation and classification of
insulation systems used in rotating machines.
Part 18-33 deals exclusively with insulation systems for form-wound windings and
concentrates on multifactor functional evaluation under simultaneous thermal and electrical
ageing.
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SIST-TS CLC/TS 60034-18-33:2011
TS 60034-18-33 © IEC:2010(E) – 7 –
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
1 Scope
This part of IEC 60034-18 describes procedures for evaluation of insulation systems by
endurance testing where thermal and electrical stresses are applied simultaneously. The
procedures are intended for insulation systems used, or proposed to be used, in a.c. electrical
machines using form-wound windings. The test procedures provide a comparison of
performance between reference and candidate systems at combinations of voltage and
temperature which have been used separately to assess quality in the past and which are
chosen to produce failures within a suitable timescale and at stresses within practical limits.
The outcome of the test on the candidate insulation system will indicate whether it is better or
worse than the reference system with proven service experience but will not enable a lifetime
in service to be calculated. The evaluation described in this technical specification does not
include stress grading.
The test procedures in this technical specification are not intended to establish the interaction
between thermal and electrical stress in the ageing process nor endurance lines. If additional
information is required on this interaction or in order to achieve endurance lines, it is
necessary to undertake further tests in which electrical ageing is carried out at constant
temperature and different voltages (IEC 60034-18-32) and thermal ageing is performed at
different temperatures and constant voltage.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60034-15, 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 60034-18-42, Rotating electrical machines – Part 18-42: Qualification and acceptance
tests for partial discharge resistant electrical insulation systems (Type II) used in rotating
electrical machines fed from voltage converters
IEC 60085, Electrical insulation –Thermal evaluation and designation
IEC 60505, Evaluation and qualification of electrical insulation systems
IEC 62539, Guide for the statistical analysis of electrical insulation breakdown data
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SIST-TS CLC/TS 60034-18-33:2011
– 8 – TS 60034-18-33 © IEC:2010(E)
3 General description of test procedures
3.1 Relationship to other standards
The principles of IEC 60034-18-1 and IEC 60505 shall be followed, unless the
recommendations or proposals of this part indicate otherwise.
3.2 Test procedures
Testing may be performed either as a full multifactor or as a single point test procedure
involving the application of temperature and voltage simultaneously. The single point test
procedure provides a comparison at only one combination of thermal and electrical stress. It
results in less information on the performance of the candidate system, but this may be
sufficient in some cases, such as when there are minor changes in the insulation system (see
5.5). The procedure may also be used as a quality test of an existing or proven insulation
system.
3.3 Reference insulation system
A reference insulation system shall be tested using a test procedure equivalent to that used
for the candidate system in the same laboratory, using the same test equipment. The
performance of the reference insulation system shall be established by service experience
under normal operating conditions.
3.4 Characteristics of test procedures
3.4.1 General characteristics
In general, the tests are performed in cycles, each cycle consisting of ageing, conditioning
and diagnostic sub-cycles.
3.4.2 Ageing sub-cycle
The ageing sub-cycle includes the simultaneous application of thermal and electrical stresses.
3.4.3 Conditioning and diagnostic sub-cycle
The conditioning sub-cycle involves the application of mechanical stress and moisture. It is
followed by voltage tests and other diagnostic tests, as appropriate. When selecting the
values of parameters used in this sub-cycle, the set of reference operating conditions (see
3.8) shall be used as guidance. The operations in the sub-cycle are performed in the order
listed in Clause 6.
3.5 Means of heating and definition of thermal stress level
3.5.1 Methods of heating
The specimens shall be heated at a rate typical of normal service. Any appropriate means of
heating may be used, such as,
a) total enclosure in an oven;
b) heating of the conductors by a high current;
c) the application of heating plates to the mainwall insulation.
Approach (c) is preferred, as it permits better control of the sample temperature within the test
length and allows independent cooling of the stress grading region (see 3.6). It is likely that
removal of gases (NO and O ) will be required during high voltage ageing.
x 3
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SIST-TS CLC/TS 60034-18-33:2011
TS 60034-18-33 © IEC:2010(E) – 9 –
3.5.2 Thermal stress level
Where practicable, the thermal stress level is defined as the average conductor temperature
in the central part of the slot portion. Where it is considered impracticable to make an
accurate assessment of this temperature, the temperature of the outer surface of the main
insulation in the middle of the slot section may be used if the conductor is not the heat source.
The method used for the measurement of thermal stress level shall be the same for the
candidate and the reference systems. Where oven heating is applied, the oven temperature
may provide an acceptable value of thermal stress but only when it has been validated by
the procedure given in 3.5.3.
Where thermal stress is provided by current heating, the conductor temperature obtained
from resistance measurements is an acceptable value of thermal stress if precautions are
taken to maintain constant temperature with ± 5 K between specimens and within them.
3.5.3 Temperature measuring techniques
It is recommended that the temperature measurement be made at two stages
a) at equilibrium with only the thermal stress applied;
b) at equilibrium but after the additional application of the electrical stress.
Both temperatures are recorded for information, with the higher temperature defining the
thermal stress level.
Measurement of the temperature in the second stage is most safely carried out using the
extrapolated cooling curve technique, immediately after the removal of the electrical stress, or
by fibre-optic sensors
Higher local temperatures can occur (for example at the stress grading area). These
temperatures may be determined by using an IR detector. If failures occur systematically at
these points, the ageing stresses may be too high for the stress grading system that has been
used. This problem may be solved by an improvement to the stress grading system.
3.6 Means of electrical ageing
It is recommended that power frequency voltage be used to produce electrical ageing. The
a.c. ageing voltage is applied between the conductors and the stator core or the outer
conductive layer on the surface of the test specimen. The rms value of the test voltage shall
be as shown in Table 1. Conventional stress grading materials applied to the surface of the
test samples may not be able to provide satisfactory control of the electrical stress at the ends
of the test length when subjected to the high voltages and temperatures proposed in Table 1.
Overheating and sparking may occur. It may be necessary
...
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