IEC TS 61251:2008
(Main)Electrical insulating materials - A.C. voltage endurance evaluation - Introduction
Electrical insulating materials - A.C. voltage endurance evaluation - Introduction
IEC/TS 61251:2008(E) explains many of the factors involved in voltage endurance tests on electrical insulating materials and systems. It describes the voltage endurance graph, lists test methods illustrating their limitations and gives guidance for evaluating the a.c. voltage endurance of insulating materials and systems from the results of the tests. The terminology to be used in voltage endurance is defined and explained. It should be emphasized that where this technical specification is concerned with materials, the results may not be directly applicable to the performance of insulating systems. Voltage endurance tests are used to compare and evaluate insulating materials with regard to their various applications in electrical systems. Determining the ability of electrical insulating materials and systems to endure a.c. voltage stress is complex. The results of voltage endurance tests are influenced by many factors so this technical specification should only be considered as an attempt to present a unified view of voltage endurance for simplified planning and analysis. Some documents for the various practical cases exist and others are being developed. The main changes with respect to the previous edition are listed below:
- extension of the scope to cover electrical insulating material and insulation systems;
- removal of references to short time dielectric breakdown strength measurements as an indicator of voltage endurance.
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Standards Content (Sample)
IEC/TS 61251
Edition 2.0 2008-05
TECHNICAL
SPECIFICATION
Electrical insulating materials – A.C. voltage endurance evaluation –
Introduction
IEC/TS 61251:2008(E)
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IEC/TS 61251
Edition 2.0 2008-05
TECHNICAL
SPECIFICATION
Electrical insulating materials – A.C. voltage endurance evaluation –
Introduction
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
R
ICS 29.035.01; 17.220.99 ISBN 2-8318-9777-7
– 2 – TS 61251 © IEC:2008(E)
CONTENTS
FOREWORD.3
1 Scope and object.5
2 Normative references .5
3 Terms and definitions .5
4 Voltage endurance .7
4.1 Voltage endurance testing.7
4.2 Electrical stress.7
4.3 Voltage endurance (VE) graph .7
4.4 Short-time electric strength .8
4.5 Voltage endurance coefficient (VEC) – n .8
4.6 Differential VEC (n ) .8
d
4.7 Electrical threshold stress (E ).9
t
4.8 Voltage endurance relationship .9
5 Test methods .10
5.1 Introductory remark .10
5.2 Tests at constant stress .11
5.2.1 Conventional VE test .11
5.2.2 Diagnostic measurements.11
5.2.3 Detection of an electrical threshold.12
5.3 Tests at higher frequency .12
5.4 Progressive stress tests .13
5.5 Preliminary tests to determine the initial part of the VE line .14
5.6 Suggested test method.14
6 Evaluation of voltage endurance.15
6.1 Significance of the VEC.15
6.2 Significance of the electrical threshold stress .15
6.3 Dispersion of data and precision requirements .15
6.4 Presentation of the results.16
Annex A (informative) The Weibull distribution.17
Bibliography.19
Figure 1 – General voltage endurance line.8
Figure 2 – Determination of the differential VEC n at a generic point P of the VE line .9
d
Figure 3 – Plotting the VE line with progressive stress.13
TS 61251 © IEC:2008(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL INSULATING MATERIALS –
A.C. VOLTAGE ENDURANCE EVALUATION –
INTRODUCTION
FOREWORD
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The main task of IEC technical committees is to prepare International Standards. In
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• the required support cannot be obtained for the publication of an International Standard,
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• 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 61251, which is a technical specification, has been prepared by IEC technical
committee 112: Evaluation and qualification of electrical insulating materials and systems.
This second edition cancels and replaces the first edition which was issued in 1993. It
constitutes a technical revision.
– 4 – TS 61251 © IEC:2008(E)
The main changes with respect to the previous edition are listed below:
• extension of the scope to cover electrical insulating material and insulation systems;
• removal of references to short time dielectric breakdown strength measurements as an
indicator of voltage endurance;
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
112/88/DTS 112/95/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.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.
TS 61251 © IEC:2008(E) – 5 –
ELECTRICAL INSULATING MATERIALS –
A.C. VOLTAGE ENDURANCE EVALUATION –
INTRODUCTION
1 Scope
This technical specification explains many of the factors involved in voltage endurance tests
on electrical insulating materials and systems. It describes the voltage endurance graph, lists
test methods illustrating their limitations and gives guidance for evaluating the a.c. voltage
endurance of insulating materials and systems from the results of the tests.
The terminology to be used in voltage endurance is defined and explained. It should be
emphasized that where this technical specification is concerned with materials, the results
may not be directly applicable to the performance of insulating systems.
Voltage endurance tests are used to compare and evaluate insulating materials with regard to
their various applications in electrical systems. Determining the ability of electrical insulating
materials and systems to endure a.c. voltage stress is complex. The results of voltage
endurance tests are influenced by many factors so this technical specification should only be
considered as an attempt to present a unified view of voltage endurance for simplified
planning and analysis. Some documents for the various practical cases exist and others are
being developed.
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 60243 (all parts), Electric strength of insulating materials – Test methods
IEC 62539, Guide for the statistical analysis of electrical insulation dielectric breakdown data
(IEEE Standard 930:2004)
3 Terms, definitions and symbols
For the purposes of this document, the following terms, definitions and symbols apply.
3.1 Terms and definitions
3.1.1
voltage endurance
VE
measure of the ability of solid insulating materials to endure voltage
NOTE In this technical specification, only a.c. voltage is considered.
3.1.2
life
time of any technical system until its failure or loss of serviceability
– 6 – TS 61251 © IEC:2008(E)
3.1.3
voltage life
time for solid insulating materials to dielectric dielectric breakdown under constant voltage
stress
3.1.4
voltage endurance coefficient
VEC
numerical value of the reciprocal of the slope of a straight line log/log VE plot
3.1.5
specimen
representative test object for asses
...
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