EN 60216-6:2006

Electrical insulating materials - Thermal endurance properties - Part 6: Determination of thermal endurance indices (TI and RTE) of an insulating material using the fixed time frame method

Specifies the experimental and calculation procedures for deriving the thermal endurance characteristics, temperature index (TI) and relative thermal endurance index (RTE) of a material using the 'fixed time frame method (FTFM)'. In this protocol, the ageing takes place for a small number of fixed times, using the appropriate number of ageing temperatures throughout each time, the properties of the specimens being measured at the end of the relevant time interval. This differs from the procedure of IEC 60216-1, where ageing is conducted at a small number of fixed temperatures, property measurement taking place after ageing times dependent on the progress of ageing. The diagnostic tests employed in the fixed time frame method are restricted to destructive tests. The method has not as yet been applied to non-destructive or proof test procedures. Both the TI and the RTE determined according to the FTFM protocol are derived from experimental data obtained in accordance with the instructions of IEC 60216-1 and IEC 60216-2 as modified in this standard. The calculation procedures and statistical tests are modified from those of IEC 60216-3 and IEC 60216-5. The significant technical changes with respect to the previous edition are as follows. - This new edition has been supplemented by Annex G and the corresponding software.

Elektroisolierstoffe - Eigenschaften hinsichtlich des thermischen Langzeitverhaltens - Teil 6: Bestimmung der thermischen Langzeitkennwerte (TI und RTE) eines Isolierstoffes unter Anwendung des Festzeitrahmenverfahrens

Matériaux isolants électriques - Propriétés d'endurance thermique - Partie 6: Détermination des indices d'endurance thermique (TI et RTE) d'un matériau isolant en utilisant la méthode de "trame de durées fixes (fixed time frame)"

La présente partie de la CEI 60216 spécifie les méthodes expérimentales et de calcul à utiliser pour en extraire les caractéristiques d'endurance thermique, l'indice de température (TI) et l'indice d'endurance thermique relatif (RTE) d'un matériau en utilisant la méthode de 'trame de durées fixes (fixed time frame)'. Avec ce protocole, le vieillissement se produit après un petit nombre de durées déterminées, en utilisant le nombre approprié de températures de vieillissement tout au long de chaque durée pertinente, les propriétés des éprouvettes étant mesurées à la fin de chaque intervalle de temps. Cela diffère de la méthode de la CEI 60216-1, dans laquelle le vieillissement est effectué à un petit nombre de températures déterminées, la mesure des propriétés des éprouvettes se produisant après des durées de vieillissement variables en fonction de la progression du vieillissement. Les essais de diagnostic employés dans la méthode de trame de durées fixes sont limités aux essais destructifs. La méthode n'a pas encore été appliquée aux essais non destructifs ni aux procédures d'essais d'épreuves. Les deux indices d'endurance thermique TI et RTE déterminés selon le protocole FTFM (fixed time frame method), sont déduits des données expérimentales obtenues conformément aux instructions de la CEI 60216-1 et de la CEI 60216-2, et conformément aux modifications de la présente norme. Les méthodes de calcul et les essais statistiques sont différents de ceux de la CEI 60216-3 et de la CEI 60216-5. Par rapport à l'édition précédente, les modifications techniques majeures sont les suivantes. - Cette édition a été complétée par l'Annexe G et le logiciel correspondant.

Električno izolacijski materiali - Lastnosti v zvezi s toplotno vzdržljivostjo - 6. del: Ugotavljanje indeksov toplotne vzdržljivosti (TI - informacijska tehnologija in RTE - radijska in telekomunikacijska oprema) izolacijskega materiala z uporabo metode fiksnih časovnih okvirov (IEC 60216-6:2006)

Ta del IEC 60216 določa eksperimentalne in računske postopke za izpeljavo lastnosti toplotne vzdržljivosti, temperaturnih indeksov (TI) in relativnega indeksa toplotne vzdržljivosti (RTE) materiala z uporabo »metode fiksnih časovnih okvirov (FTFM)«. V tem protokolu staranje poteka pri majhnem številu fiksnih časov z uporabo ustreznega števila temperatur za staranje v vsakem času, lastnosti vzorcev pa se merijo na koncu ustreznega časovnega intervala. To se razlikuje od postopka v IEC 60216-1, kjer staranje poteka pri majhnem številu fiksnih temperatur, meritve lastnosti pa odvisno od napredovanja staranja potekajo po časih staranja.  Diagnostični preskusi, uporabljeni pri metodi s fiksnim časovnim okvirom, so omejeni na uničujoče preskuse. Metoda še ne velja za neuničujoče ali dokazne preskusne postopke. TI in RTE, ki se določita po protokolu FTFM, izhajata iz eksperimentalnih podatkov, pridobljenih v skladu z navodili IEC 60216-1 in IEC 60216-2, kot jih spreminja ta standard. Računski postopki in statistični preskusi so spremenjeni glede na tiste v IEC 60216-3 in IEC 60216-5.

General Information

• Status: Withdrawn
• Publication Date: 02-Nov-2006
• Withdrawal Date: 31-Aug-2009
• ICS: 17.220.99 - Other standards related to electricity and magnetism
• ICS: 29.035.01 - Insulating materials in general
• Technical Committee: CLC/SR 112 - Evaluation and qualification of electrical insulating materials and systems (to be defined)
• Drafting Committee: IEC/TC 112 - IEC_TC_112
• Parallel Committee: IEC/TC 112 - IEC_TC_112
• Current Stage: 9960 - Withdrawal effective - Withdrawal
• Start Date: 02-Jan-2026
• Completion Date: 02-Jan-2026
• Ref Project: SIST EN 60216-6:2010 - Electrical insulating materials - Thermal endurance properties - Part 6: Determination of thermal endurance indices (TI and RTE) of an insulating material using the fixed time frame method (IEC 60216-6:2006)

Relations

• Replaces: EN 60216-6:2004 - Electrical insulating materials - Thermal endurance properties - Part 6: Determination of thermal endurance indices (TI and RTE) of an insulating material using the fixed time frame method
• Effective Date: 28-Jan-2023
• Replaced By: EN IEC 60216-6:2023 - Electrical insulating materials - Thermal endurance properties - Part 6: Determination of thermal endurance indices (TI and RTI) of an insulating material using the fixed time frame method
• Effective Date: 22-Jan-2023

Overview

EN 60216-6:2006 (IEC 60216-6:2006) specifies experimental and calculation procedures for determining the thermal endurance characteristics of electrical insulating materials using the fixed time frame method (FTFM). The standard defines how to derive the temperature index (TI) and relative thermal endurance index (RTE) from destructive diagnostic tests after ageing specimens for a set of fixed times at multiple temperatures. It complements and modifies procedures in IEC 60216-1 and IEC 60216-2 and updates calculation/statistical methods from IEC 60216-3 and IEC 60216-5. Annex G and corresponding software were added in this edition.

Key topics and requirements

• Fixed Time Frame Method (FTFM): Ageing is performed for a small number of fixed times with appropriate ageing temperatures; properties are measured at the end of each time interval (contrast with fixed-temperature/flexible-time approach of IEC 60216-1).
• Thermal Endurance Indices: Procedures to calculate TI and RTE from experimental data, including regression analysis and statistical tests.
• Diagnostic tests: Restricted to destructive tests for property measurement; non-destructive or proof-test procedures are not covered.
• Ageing protocols: Guidance on selection of ageing times, temperatures and specimens; establishment of initial property values and end-points.
• Calculation & statistics: Modified calculation procedures and significance testing, precision considerations, derivation of temperature equivalents, and confidence limits.
• Reporting: Requirements for reporting results and the format of thermal endurance graphs.
• Tools: Annex G provides informative material and software to support calculations.

Practical applications

• Material qualification and lifetime prediction for electrical insulating materials used in motors, transformers, cables, capacitors and electrical equipment.
• Comparative assessment of materials using RTE for product selection and specification.
• Establishing service temperature guidelines using TI for design and safety analyses.
• Supporting compliance, reliability testing and product development in industries where thermal ageing influences insulation performance.

Who uses this standard

• Test laboratories and quality assurance teams performing thermal ageing and material characterization.
• Materials engineers and R&D teams developing insulating compounds.
• Manufacturers of electrical equipment seeking validated thermal endurance data.
• Certification bodies and standards organizations evaluating insulation lifetime claims.

Related standards

• IEC/EN 60216-1, -2, -3, -4 (oven specifications), -5 (RTE methods)
• IEC 60212 (standard pre-test conditions)
• IEC 60493-1 (statistical analysis of ageing data)

Keywords: EN 60216-6:2006, thermal endurance, fixed time frame method, TI, RTE, insulating materials, thermal ageing, destructive tests.

Standards Content (Sample)

SLOVENSKI STANDARD
01-februar-2010
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Electrical insulating materials - Thermal endurance properties - Part 6: Determination of
thermal endurance indices (TI and RTE) of an insulating material using the fixed time
frame method (IEC 60216-6:2006)
Elektroisolierstoffe - Eigenschaften hinsichtlich des thermischen Langzeitverhaltens - Teil
6: Bestimmung der thermischen Langzeitkennwerte (TI und RTE) eines Isolierstoffes
unter Anwendung des Festzeitrahmenverfahrens (IEC 60216-6:2006)
Matériaux isolants électriques - Propriétés d'endurance thermique - Partie 6:
Détermination des indices d'endurance thermique (TI et RTE) d'un matériau isolant en
utilisant la méthode de trame de durées fixes (fixed time frame) (IEC 60216-6:2006)
Ta slovenski standard je istoveten z: EN 60216-6:2006
ICS:
29.035.01 Izolacijski materiali na Insulating materials in
splošno general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 60216-6
NORME EUROPÉENNE
November 2006
EUROPÄISCHE NORM
ICS 17.220.99; 29.035.01 Supersedes EN 60216-6:2004

English version
Electrical insulating materials -
Thermal endurance properties
Part 6: Determination of thermal endurance indices (TI and RTE)
of an insulating material using the fixed time frame method
(IEC 60216-6:2006)
Matériaux isolants électriques -  Elektroisolierstoffe -
Propriétés d'endurance thermique Eigenschaften hinsichtlich des
Partie 6: Détermination des indices thermischen Langzeitverhaltens
d'endurance thermique (TI et RTE) Teil 6: Bestimmung der thermischen
d'un matériau isolant en utilisant
Langzeitkennwerte (TI und RTE)
la méthode de "trame de durées fixes eines Isolierstoffes unter Anwendung
(fixed time frame)" des Festzeitrahmenverfahrens
(CEI 60216-6:2006) (IEC 60216-6:2006)

This European Standard was approved by CENELEC on 2006-09-01. CENELEC members are bound to comply
with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and notified
to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, 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

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2006 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60216-6:2006 E
Foreword
The text of document 112/28/FDIS, future edition 2 of IEC 60216-6, prepared by IEC TC 112, Evaluation
and qualification of electrical insulating materials and systems, was submitted to the IEC-CENELEC
parallel vote and was approved by CENELEC as EN 60216-6 on 2006-09-01.
This European Standard supersedes EN 60216-6:2004.
The significant technical change with respect to EN 60216-6:2004 is as follows:
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
(dop) 2007-06-01
national standard or by endorsement
– latest date by which the national standards conflicting
(dow) 2009-09-01
with the EN have to be withdrawn
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 60216-6:2006 was approved by CENELEC as a European
Standard without any modification.
__________
- 3 - EN 60216-6:2006
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

1) 2)
IEC 60212 - Standard conditions for use prior to and HD 437 S1 1984
during the testing of solid electrical insulating
materials
IEC 60216-1 2001 Electrical insulating materials - Properties of EN 60216-1 2001
thermal endurance
Part 1: Ageing procedures and evaluation of
test results
1) 2)
IEC 60216-2 - Electrical insulating materials - Thermal EN 60216-2 2005
endurance properties
Part 2: Determination of thermal endurance
properties of electrical insulating materials -
Choice of test criteria
3)
IEC 60216-3 2002 Electrical insulating materials - Thermal EN 60216-3 2002
endurance properties
Part 3: Instructions for calculating thermal
endurance characteristics
1) 2)
IEC 60216-4-1 - Electrical insulating materials - Thermal EN 60216-4-1 2006
endurance properties
Part 4-1: Ageing ovens - Single-chamber
ovens
1) 2)
IEC 60216-4-2 - Electrical insulating materials - Thermal EN 60216-4-2 2000
endurance properties
Part 4-2: Ageing ovens - Precision ovens for
use up to 300 °C
1) 2)
IEC 60216-4-3 - Electrical insulating materials - Thermal EN 60216-4-3 2000
endurance properties
Part 4-3: Ageing ovens - Multi-chamber ovens

1) 2)
IEC 60216-5 - Electrical insulating materials - Thermal EN 60216-5 2003
endurance properties
Part 5: Determination of relative thermal
endurance index (RTE) of an insulating
material
1)
Undated reference.
2)
Valid edition at date of issue.
3)
EN 60216-3 is superseded by EN 60216-3:2006, which is based on IEC 60216-3:2006.

Publication Year Title EN/HD Year
IEC 60493-1 1974 Guide for the statistical analysis of ageing test - -
data
Part 1: Methods based on mean values of
normally distributed test results

NORME CEI
INTERNATIONALE
IEC
60216-6
INTERNATIONAL
Deuxième édition
STANDARD
Second edition
2006-05
Matériaux isolants électriques –
Propriétés d'endurance thermique –
Partie 6:
Détermination des indices d'endurance
thermique (TI et RTE) d'un matériau isolant
en utilisant la méthode de «trame de durées
fixes (fixed time frame)»
Electrical insulating materials –
Thermal endurance properties –
Part 6:
Determination of thermal endurance indices
(TI and RTE) of an insulating material using
the fixed time frame method
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Pour prix, voir catalogue en vigueur
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60216-6  IEC:2006 – 3 –
CONTENTS
FOREWORD.7

1 Scope.11
2 Normative references .11
3 Terms, definitions, symbols and abbreviated terms.13
3.1 Terms, abbreviations and definitions .13
3.2 Symbols and abbreviated terms.19
4 FTFM protocol .21
4.1 Principles and objectives.21
5 TI determination .23
5.1 Ageing procedures .23
5.2 Ageing times and temperatures .23
5.3 Test specimens .25
5.4 Diagnostic tests.27
5.5 Selection of end-points.27
5.6 Establishment of initial property value .29
5.7 Ageing conditions.29
5.8 Procedure for ageing.29
6 Calculation procedures.31
6.1 General principles .31
6.2 Precision of calculations.33
6.3 Derivation of temperatures equivalent to property values.33
6.4 Regression analysis (temperature on time).39
6.5 Statistical tests.43
6.6 Thermal endurance graph .47
7 Calculation and requirements for results.47
7.1 Calculation of thermal endurance characteristics.47
7.2 Reporting of results .49
8 Report .49
9 RTE determination.51
9.1 Objectives of RTE determination .51
10 Additional symbols .51
11 Experimental procedures .53
11.1 Selection of control material .53
11.2 Selection of diagnostic test for extent of ageing.53
11.3 Ageing procedures .53
12 Calculation procedures.53
12.1 General principles .53
12.2 Input data.55
12.3 RTE.55
12.4 Confidence limits.55
12.5 Extrapolation .59

60216-6  IEC:2006 – 5 –
13 Results and report .59
13.1 Results of statistical and numerical tests .59
13.2 Result .59
13.3 Report .61

Annex A (normative) Decision flow chart.63
Annex B (normative) Decision table .65
Annex C (informative) Statistical tables.67
Annex D (informative) Suggested ageing times and temperatures.73
Annex E (informative) Figures.77
Annex F (normative) Statistical significance of the difference between two regression
estimates .83
Annex G (informative) Computer programs for IEC 60216-6.85

Figure E.1 – Property-temperature graph with regression line.77
Figure E.2 – Thermal endurance graph .77
Figure E.3 – Ageing times and temperatures in relation to thermal endurance graph .79
Figure E.4 – Ageing times and temperatures in relation to thermal endurance graph .79
Figure E.5 – Ageing times and temperatures in relation to thermal endurance graph .81
Figure G.1 − Thermal endurance graph .95

Table B.1 − Decision table .65
Table C.1 – χ -Function.67
Table C.2– t–Function.67
Table C.3 – F-function, P = 0,05 .69
Table C.4 – F-function, P = 0,005 .71

60216-6  IEC:2006 – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL INSULATING MATERIALS –
THERMAL ENDURANCE PROPERTIES –

Part 6: Determination of thermal endurance indices (TI and RTE)
of an insulating material using the fixed time frame method

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
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with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60216-6 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, published in 2003. This edition
constitutes a technical revision.
The significant technical changes with respect to the previous edition are as follows.
− This new edition has been supplemented by Annex G and the corresponding software.

60216-6  IEC:2006 – 9 –
The text of this standard is based on the following documents:
FDIS Report on voting
112/28/FDIS 112/32/RVD
Full information on the voting for the approval of this standard 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.
IEC 60216, under the general title Electrical insulating materials – Thermal endurance
properties, consists of the following parts:
Part 1: Ageing procedures and evaluation of test results
Part 2: Determination of thermal endurance properties of electrical insulating materials –
Choice of test criteria
Part 3: Instructions for calculating thermal endurance characteristics
Part 4: Ageing ovens
Part 5: Determination of relative thermal endurance index (RTE) of an insulating material
Part 6: Determination of thermal endurance indices (TI and RTE) of an insulating material
using the fixed time frame protocol

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
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
60216-6  IEC:2006 – 11 –
ELECTRICAL INSULATING MATERIALS –
THERMAL ENDURANCE PROPERTIES –

Part 6: Determination of thermal endurance indices (TI and RTE)
of an insulating material using the fixed time frame method

1 Scope
This part of IEC 60216 specifies the experimental and calculation procedures for deriving the
thermal endurance characteristics, temperature index (TI) and relative thermal endurance
index (RTE) of a material using the “fixed time frame method (FTFM)”.
In this protocol, the ageing takes place for a small number of fixed times, using the appro-
priate number of ageing temperatures throughout each time, the properties of the specimens
being measured at the end of the relevant time interval. This differs from the procedure of
IEC 60216-1, where ageing is conducted at a small number of fixed temperatures, property
measurement taking place after ageing times dependent on the progress of ageing.
The diagnostic tests employed in the fixed time frame method are restricted to destructive
tests. The method has not as yet been applied to non-destructive or proof test procedures.
Both the TI and the RTE determined according to the FTFM protocol are derived from
experimental data obtained in accordance with the instructions of IEC 60216-1 and
IEC 60216-2 as modified in this standard. The calculation procedures and statistical tests are
modified from those of IEC 60216-3 and IEC 60216-5.
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 60212, Standard conditions for use prior to and during the testing of solid electrical
insulating materials
IEC 60216-1:2001, Electrical insulating materials – Properties of thermal endurance – Part 1:
Ageing procedures and evaluation of test results
IEC 60216-2, Electrical insulating materials – Thermal endurance properties – Part 2:
Determination of thermal endurance properties of electrical insulating materials – Choice of
test criteria
IEC 60216-3:2002, Electrical insulating materials – Thermal endurance properties – Part 3:
Instructions for calculating thermal endurance characteristics

60216-6  IEC:2006 – 13 –
IEC 60216-4-1, Electrical insulating materials – Thermal endurance properties – Part 4-1:
Ageing ovens – Single-chamber ovens
IEC 60216-4-2, Electrical insulating materials – Thermal endurance properties – Part 4-2:
Ageing ovens – Precision ovens for use up to 300 °C
IEC 60216-4-3, Electrical insulating materials – Thermal endurance properties – Part 4-3:
Ageing ovens – Multi-chamber ovens
IEC 60216-5, Electrical insulating materials − Thermal endurance properties – Part 5:
Determination of relative thermal endurance index (RTE) of an insulating material
IEC 60493-1:1974, Guide for the statistical analysis of ageing test data – Part 1: Methods
based on mean values of normally distributed test results
3 Terms, definitions, symbols and abbreviated terms
For the purposes of this document, the following terms, definitions, symbols and abbreviations
apply.
3.1 Terms, abbreviations and definitions
3.1.1
assessed thermal endurance index
ATE
numerical value of the temperature in degrees Celsius, up to which the control material
possesses known, satisfactory service performance in the specified application
NOTE 1 The ATE of a specific material may vary between different applications of the material.
NOTE 2 ATE is sometimes referred to as “absolute” thermal endurance index.
3.1.2
ageing temperature
temperature in degrees Celsius at which a group of specimens is thermally aged
3.1.3
end-point temperature
temperature in degrees Celsius at which a specimen is considered to have reached end-point
after ageing for a specified time
3.1.4
candidate material
material for which an estimate of the thermal endurance is required to be determined
NOTE The determination is made by simultaneous thermal ageing of the material and a control material.
3.1.5
central second moment of a data group
sum of the squares of the differences between the data values and the value of the group
mean divided by the number of data in the group

60216-6  IEC:2006 – 15 –
3.1.6
95 % confidence limit
statistical parameter, calculated from test data, which with 95 % confidence constitutes an
upper or lower limit for the true value of a quantity estimated by statistical analysis
NOTE 1 This implies that there is only 5 % probability that the true value of the quantity estimated is actually
larger (or smaller) than the upper (or lower) confidence limit.
NOTE 2 In other connections, confidence values other than 95 % may sometimes be used, e.g. in the linearity
test for destructive test data.
3.1.7
control material
material with known assessed thermal endurance index (ATE), preferably derived from
service experience, used as a reference for comparative tests with the candidate material
3.1.8
correlation coefficient
number expressing the completeness of the relation between members of two data sets, equal
to the covariance divided by the square root of the product of the variances of the sets
NOTE 1 The value of its square is between 0 (no correlation) and 1 (complete correlation).
NOTE 2 In this standard, the two data sets are the values of the independent variable and the means of the
corresponding dependent variable groups.
3.1.9
correlation time (RTE)
estimated time to end-point of the control material at a temperature equal to its ATE in
degrees Celsius
3.1.10
correlation time (TI)
hypothetical time to end-point used to calculate TI
NOTE Its usual value is 20 000 h.
3.1.11
covariance (of data sets)
for two sets of data with equal numbers of elements where each element in one set
corresponds to one in the other, sum of the products of the deviations of the corresponding
members from their set means, divided by the number of degrees of freedom
3.1.12
degrees of freedom
number of data values minus the number of parameter values
3.1.13
destructive test
diagnostic property test, where the test specimen is irreversibly changed by the property
measurement, in a way which precludes a repeated measurement on the same specimen
NOTE An example of a destructive test is measurement of electric strength. An example of a non-destructive test
is measurement of tg δ.
3.1.14
end-point line
line parallel to the temperature axis intercepting the property axis at the end-point value

60216-6  IEC:2006 – 17 –
3.1.15
halving interval
HIC
numerical value of the temperature interval in kelvins which expresses the halving of the time
to end-point taken at a time equal to TI
3.1.16
regression analysis
process of deducing the best fit line expressing the relation of corresponding members of two
data groups by minimizing the sum of squares of deviations of members of one of the groups
from the line
3.1.17
regression coefficients
coefficients of the equation of the best fit line derived by regression analysis
3.1.18
relative thermal endurance index
RTE
estimate of the thermal endurance of a candidate material, made by thermal ageing
simultaneously with the control material, as described in this standard
NOTE The value of RTE is the value of the temperature in degrees Celsius at which the estimated time to end-
point of the candidate material is the same as the estimated time to end-point of the control material at a
temperature equal to its ATE.
3.1.19
significance
probability of a value of a statistical function greater than a specified value
NOTE The value is equal to (1–p) where p is the cumulative distribution function value. Significance is
conventionally printed in upper case (P).
3.1.20
standard deviation
square root of the variance of a data group or sub-group
3.1.21
standard error of an estimate of the true value of a data group property
value of the standard deviation of the hypothetical sampling population of which the group
property may be considered to be a member
NOTE For an estimate of the group mean, the standard error is equal to the group standard deviation divided by
the square root of the number of data in the group, and indicates the uncertainty in the estimate of the true value of
the mean. This standard is concerned only with means and the difference between two means.
3.1.22
temperature index
TI
numerical value of the temperature in degrees Celsius derived from the thermal endurance
relationship at a time of 20 000 h (or other specified time)
3.1.23
temperature group (of specimens)
number of specimens being exposed together to thermal ageing at the same temperature in
the same oven
NOTE Where there is no risk of ambiguity, either temperature groups or test groups may be referred to simply as
“groups”.
60216-6  IEC:2006 – 19 –
3.1.24
test group (of specimens)
number of specimens removed together from a temperature group for destructive testing
NOTE Where there is no risk of ambiguity, either temperature groups or test groups may be referred to simply as
“groups”.
3.1.25
thermal endurance graph
graph in which the logarithm of the time to reach a specified end-point in a thermal endurance
test is plotted against the reciprocal thermodynamic (absolute) test temperature
3.1.26
thermal endurance graph paper
graph paper having a logarithmic time scale as the ordinate and values proportional to the
reciprocal of the thermodynamic (absolute) temperature as the abscissa
NOTE The ordinate is usually graduated in powers of ten (from 10 h to 100 000 h is often a convenient range).
The abscissa is usually graduated in a non-linear (Celsius) temperature scale oriented with temperature increasing
from left to right.
3.1.27
time group (of specimens)
all test groups removed for testing at the same time
3.1.28
variance of a data group
sum of the squares of the deviations of the data from a reference level defined by one or more
parameters divided by the number of degrees of freedom
NOTE The reference level may, for example be a mean value (1 parameter) or a line (2 parameters, here
intercept on the axis of the independent variable and slope).
3.2 Symbols and abbreviated terms
The following symbols are used in the calculations of Clauses 6, 7 and 12.
Symbol Description Clause
a
Regression coefficient: intercept of regression line with x-axis 6.4.3
b Regression coefficient: slope of regression line relative to y-axis 6.4.3
6.5.3
ˆ
b
Parameter derived from b for calculation of Y
r
c
b
6.3.4
p Regression coefficient for destructive test calculations
6.5.1
c Parameter in calculation of χ
F
F-distributed variance ratio for linearity test 6.3.3, 6.5.2
g, h, i, j Indexing parameters for regression calculations 6.3, 6.4
HIC Halving interval 7.1
k Number of ageing times 6.1.1
N Total number of x values 6.4.2
ij
n Number of x values in time group i 6.1.1
i ij
Annexes A,
P
Significance of the value of a statistical test function
B, and C
p End-point property value 6.3

e
60216-6  IEC:2006 – 21 –
p Property value h in temperature group g (time group i implied) 6.3

gh
Mean property value in temperature group g (time group i 6.3
p
g
implied)
q 6.5.1
Base of logarithms in calculation of χ
r Number of temperature groups selected in time group i 6.3.2
r
Square of correlation coefficient 6.4.3

s Total (non-regression) variance of x-values 6.5.2
2 Variance of property values in temperature group g (time group 6.3.2
s
1g
i implied)
2 6.5.2
s Value of s adjusted to allow for acceptable non-linearity
a
6.5.3
2 ˆ
s Parameter derived from s for calculation of Y
r
c
t Student's t-distributed stochastic variable 6.5.3
2 7.1
TC, TC Lower confidence limit of TI or TI (see s above)
a
a
a
t Value of t with probability p and N degrees of freedom 6.5.3
p,N
x Value of x, index number j , in time group i 6.3.4
ij
6.4.2
General mean of x-values
x
6.5.3
ˆ ˆ
Estimate of x, and its confidence limit
X , X
c
y Value of y for time group i 6.1.1
i
6.4.2
y General mean of y-values
6.5.3
ˆ ˆ
Estimate of y, and its confidence limit
Y , Y
c
6.1.1
Reciprocal kelvin temperature for ϑ
z
ij
ij
nd
6.4.2
µ ()y Central 2 moment of y values
6.3.2
ν
Total number of property values in time group (i implied)
2 2
6.5.1
χ χ distributed variable for variance equality (Bartlett's) test
ϑ 6.1.1
Ageing temperature for specimen group j in time group i
ij
Θ 6.1.1
273,15 K (corresponding to 0 °C)
τ 6.1.1
Ageing time for time group i
i
4 FTFM protocol
4.1 Principles and objectives
4.1.1 Principles of FTFM protocol
The FTFM (fixed time frame method) protocol is based upon the principle that thermal ageing
for determination of thermal endurance characteristics is carried out over a small number of
fixed times, with a sufficient range of ageing temperatures at each time to ensure that the
property values determined reach the end-point in a satisfactory manner.

60216-6  IEC:2006 – 23 –
In this it differs from the fixed temperature frame procedure of IEC 60216-1, where a small
number of ageing temperatures is employed, with ageing being carried out with testing at
intervals, until the end-point has been reached.
4.1.2 Objective of FTFM protocol
The objective of the protocol is to achieve the following advantages:
The determination of thermal endurance characteristics is completed in a fixed, pre-
determined time.
This enables much more efficient planning of the determination, and will often have
substantial commercial advantage. A simple TI determination will be completed in 5 kh,
whereas by the fixed temperature frame procedure, it may be necessary for ageing to be
considerably prolonged past this time to achieve the end-point at the lowest chosen ageing
temperature.
Each temperature to end-point (i.e. time-group mean) in the thermal endurance regression is
based on the temperatures selected in a time group. The number of temperatures selected
may be any number between three (3) and the number of temperature groups in a time group.
Since the largest source of systematic error in the fixed temperature frame procedure is
temperature error (actual indication error or temperature distribution error), systematic errors
can be considerably reduced. Errors from this source can lead to results which are either
inaccurate or invalid through incorrect assessment of linearity.
5 TI determination
5.1 Ageing procedures
Each test procedure shall specify the shape, dimensions and number of the test specimens,
the times of exposure, the property to which TI is related, the methods of its determination,
the end-point, and the derivation of the thermal endurance characteristics from the
experimental data.
The chosen property should, if possible, reflect in a significant fashion a function of the
material in practical use. A choice of properties is given in IEC 60216-2.
To provide uniform conditions, the conditioning of specimens after removal from the oven and
before measurement may need to be specified.
5.2 Ageing times and temperatures
In the majority of cases, the required thermal endurance characteristics are for a projected
duration of 20 000 h. However, there is often a need for such information related to other,
longer or shorter times. In cases of longer times, the times given as requirements or
recommendations in the text of this standard (e.g. 5 kh for the minimum value of the longest
ageing time) shall be increased in the ratio of the actual specification time to 20 kh.
In cases of shorter specification times, the related times may be decreased in the same ratio
if necessary.
60216-6  IEC:2006 – 25 –
Particular care will be needed for very short specification times, since the higher ageing
temperatures may lead into temperature regions which include transition points, e.g. glass
transition temperature or partial melting, with consequent non-linearity. Very long specification
times may also lead to non-linearity.
Recommendations for ageing times and temperatures are given in Annex D.
5.3 Test specimens
5.3.1 Preparation
The specimens used for the ageing test shall constitute a random sample from the population
investigated and shall be treated uniformly.
Since processing conditions may significantly affect the ageing characteristics of some
materials, it shall be ensured that, for example, sampling, cutting sheet from the supply roll,
cutting of anisotropic material in a given direction, moulding, curing, preconditioning, are
performed in the same manner for all specimens.
The material specifications or the standards for the diagnostic test methods will contain all
necessary instructions for the preparation of specimens.
The thickness of specimens is in some cases specified in the list of property measurements
for the determination of thermal endurance. See IEC 60216-2. If not, the thickness shall be
reported. Some physical properties are sensitive even to minor variations of specimen
thickness. In such cases the thickness after each ageing period may need to be determined
and reported if required in the relevant specification.
The thickness is also important because the rate of ageing may vary with thickness. Ageing
data of materials with different thicknesses are not always comparable. Consequently, a
material may be assigned more than one thermal endurance characteristic derived from the
measurement of properties at different thicknesses.
The tolerances of specimen dimensions shall be the same as those normally used for general
testing. Where specimen dimensions need smaller tolerances than those normally used, these
special tolerances shall be given.
Screening measurements ensure that specimens are of uniform quality and typical of the
material to be tested.
5.3.2 Number of specimens
The accuracy of endurance test results depends largely on the number of specimens aged at
each temperature.
The total number of specimens (N) is derived as follows:
N = a × b × c + d
60216-6  IEC:2006 – 27 –
where
a is the number of specimens in a test group undergoing identical treatment at one
temperature and discarded after determination of the property (usually five);
b is the number of treatments, i.e. total number of exposure temperatures, at one time;
c is the number of ageing time levels;
d is the number of specimens in the group used to establish the initial value of the
property. Normal practice is to select d = 2a when the diagnostic criterion is a
percentage change of the property from its initial level. When the criterion is an absolute
property level, d is usually given the value of zero, unless reporting of the initial value is
required.
It is good practice to prepare additional specimens, or at least to provide a reserve from the
original material batch from which such specimens may subsequently be prepared. In this way
any required ageing of additional specimens in case of unforeseen complications will
introduce a minimum risk of producing systematic differences between groups of specimens.
Such complications may arise, for example, if the thermal endurance relationship turns out to
be non-linear, or if specimens are lost due to thermal runaway of an oven.
5.4 Diagnostic tests
If IEC material specifications are available, property requirements in terms of acceptable
lower limits of TI values are usually given. If such material specifications are not available, a
selection of properties and methods for the evaluation of thermal endurance is given in
IEC 60216–2.
If such a method cannot be found, an international, national or institution standard or a
specially devised method should be used in that order of preference. In this case, the
diagnostic test shall be stated in the report, including the property, measurement procedure
and end-point.
5.5 Selection of end-points
The thermal endurance of materials may need to be characterized by different endurance data
(derived using different properties and/or end-points), in order to facilitate the adequate
selection of the material in respect of its particular application. See IEC 60216-2.
There are two alternative ways in which the end-point may be defined:
a) as a percentage increase or decrease in the measured value of the property from the
original level. This approach will provide comparisons among materials but bears a poorer
relationship than item b) to the property values required in normal service. For the
determination of the initial value, see 5.6;
b) as a fixed value of the property. This value might be selected with respect to usual service
requirements. End-points of proof tests are predominantly given in the form of fixed values
of the property.
The end-point should be selected to indicate a degree of deterioration of the insulating
material which has reduced its ability to withstand a stress encountered in actual service. The
degree of degradation indicated as the end-point of the test should be related to the allowable
safe value for the material property which is desired in practice.

60216-6  IEC:2006 – 29 –
5.6 Establishment of initial property value
Select the specimens for the determination of the initial value of the property to constitute a
random subset of those prepared for ageing. Before determining the property value these
specimens shall be conditioned by exposure to the lowest level of agei
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