IEC TS 60216-7-1:2015

Electrical insulation materials - Thermal endurance properties - Part 7-1: Accelerated determination of relative thermal endurance using analytical test methods (RTEA) - Instructions for calculations based on activation energy

IEC TS 60216-7-1:2015(E) describes the procedure for the evaluation of the thermal endurance of electrical insulating materials, based on thermal analysis methods for the evaluation of the activation energy of the thermal degradation reaction and a conventional life test providing a life point in the thermal endurance graph. The purpose of the test procedure is to estimate the relative temperature index (RTE).

General Information

• Status: Published
• Publication Date: 29-Mar-2015
• ICS: 19.020 - Test conditions and procedures in general
• ICS: 29.020 - Electrical engineering in general
• ICS: 29.035.01 - Insulating materials in general
• Technical Committee: TC 112 - Evaluation and qualification of electrical insulating materials and systems
• Drafting Committee: WG 1 - TC 112/WG 1
• Current Stage: PPUB - Publication issued
• Start Date: 30-Mar-2015
• Completion Date: 15-Jun-2015

Overview

IEC TS 60216-7-1:2015 is a Technical Specification from the IEC for assessing the thermal endurance of electrical insulation materials using accelerated analytical methods. It defines procedures to estimate the relative temperature endurance (RTE) by combining thermal analysis (to determine activation energy) with a conventional life test providing a single life point. The method is intended as a faster, screening-oriented approach to estimate relative temperature index (TI) and halving interval (HIC) for materials development and comparison.

Key topics and requirements

• Scope and purpose: Accelerated determination of RTE using analytical test methods (RTEA) based on measured activation energy of thermal degradation reactions.
• Analytical techniques: Use of thermal analysis methods such as differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) to obtain activation energy information. Both model-free and model-fitting approaches, and isothermal methods, are discussed.
• Calculation instructions: Step-by-step procedures for estimating kinetic parameters, calculating the analytical temperature endurance index (RTEA), and deriving RTE and HIC from activation energy and a conventional life-point measurement.
• Test-data requirements: A conventional life test at a selected high temperature (single-point) is required in addition to analytical data; calculations rely on a reference material with known TI/HIC for relative comparison.
• Limitations: Applicable only where a single predominant ageing reaction controls the end-point criteria. Because of inherent uncertainties in the analytical approach, the output is relative (RTE) rather than an absolute TI. The method is published as a Technical Specification pending wider validation (round-robin testing).
• Reporting: Requirements for the content of the test report are provided to ensure reproducibility and traceability.

Applications and practical value

• Rapid screening of new electrical insulation materials during R&D to prioritize candidates by thermal endurance.
• Comparative evaluation of materials when full long-term ageing tests are impractical or time-consuming.
• Supporting accelerated material qualification, selection, and formulation optimization in industries using insulating polymers, cables, components, and varnishes.
• Streamlining test schedules in product development to estimate relative lifetime at service temperatures.

Who should use this standard

• Materials scientists and polymer chemists performing thermal degradation studies.
• Test laboratories and quality-control teams conducting accelerated ageing evaluations.
• Design engineers and product developers needing quick comparative TI/RTE data.
• Certification bodies and technical committees evaluating accelerated test methods.

Related standards

• IEC 60216 series (Parts 1, 2, 5, 8) - thermal endurance procedures and RTE guidance
• IEC 60085 - Thermal evaluation and designation
• ISO 11357-6, ISO 11358-2/3 - DSC and TGA methods for oxidation induction time and activation energy

Keywords: IEC TS 60216-7-1:2015, electrical insulation materials, thermal endurance, RTE, activation energy, DSC, TGA, temperature index, TI, halving interval, accelerated testing.

Standards Content (Sample)

IEC TS 60216-7-1 ®
Edition 1.0 2015-03
TECHNICAL
SPECIFICATION
Electrical insulation materials – Thermal endurance properties –
Part 7-1: Accelerated determination of relative thermal endurance using
analytical test methods (RTE ) – Instructions for calculations based on
A
activation energy
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IEC TS 60216-7-1 ®
Edition 1.0 2015-03
TECHNICAL
SPECIFICATION
Electrical insulation materials – Thermal endurance properties –

Part 7-1: Accelerated determination of relative thermal endurance using

analytical test methods (RTE ) – Instructions for calculations based on

A
activation energy
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 19.020; 29.020; 29.035.01 ISBN 978-2-8322-2430-4

– 2 – IEC TS 60216-7-1:2015 © IEC 2015
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references. 6
3 Terms, definitions and abbreviations . 7
3.1 Terms and definitions . 7
3.2 Abbreviations . 9
4 General considerations . 9
4.1 Thermal degradation kinetics . 9
4.2 Thermal analysis . 10
4.3 Thermal endurance . 10
5 General basics . 11
5.1 Reaction rate, r . 11
5.2 Extent of reaction ξ . 12

5.3 Rate of conversion ξ . 12
5.4 Order of reaction, n . 12
5.5 Rate law . 13
6 Thermokinetic parameter estimation . 13
7 Analytical test methods . 16
7.1 General . 16
7.2 Isothermal methods . 16
7.3 Model-free methods . 16
7.4 Model-fitting methods . 17
7.5 Conventional reference point . 17
8 Calculation procedures . 17
8.1 Determination of the kinetic parameters . 17
8.2 Determination of analytical temperature endurance index, RTE , and halving
A
interval, HIC . 17
A
8.3 Determination of RTE . 17
A
8.3.1 General . 17
8.3.2 Calculation . 18
9 Test report. 19
Bibliography . 21

Figure 1 – Thermal endurance graph for the determination of the relative temperature
endurance (RTE) . 18

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL INSULATION MATERIALS –
THERMAL ENDURANCE PROPERTIES –

Part 7-1: Accelerated determination of relative thermal
endurance using analytical test methods (RTE ) –
A
Instructions for calculations based on activation energy

FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
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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,
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 60216-7-1, which is a technical specification, has been prepared by IEC technical
committee 112: Evaluation and qualification of electrical insulation materials and systems.

– 4 – IEC TS 60216-7-1:2015 © IEC 2015
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
112/298/DTS 112/314/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 in the IEC 60216 series, published under the general title Electrical insulating
materials – Thermal endurance properties, can be found 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
• 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.

INTRODUCTION
The existing procedures of the IEC 60216 series for the evaluation of thermal endurance of an
electrical insulation material can be time consuming. These methods are therefore of limited
use during development of new materials or screening of existing products for use as a
material in an electrical insulation. There is an important demand from industry for a rapid test
method of relative thermal endurance (RTE) / temperature index (TI) and halving interval
(HIC) to reduce project times and cost. A short-term test procedure for conventional thermal
endurance characterization is proposed in IEC 60216-5 and a simplified approach to data
processing is described in IEC 60216-8. Non-conventional methodology for thermal
endurance characterization which can reduce further test times is considered in this technical
specification.
The basic procedure is based on thermal analysis methods (DSC and TGA in particular, but
not restricted to them) to evaluate the activation energy of the thermal degradation of the
material. The activation energy is directly correlated with the HIC of the thermal endurance.
With this information, a single-point thermal endurance test, according to IEC 60216-1 and
IEC 60216-5, at the highest temperature of those selected for the conventional thermal ageing
procedure, is sufficient to calculate the temperature corresponding to a selected life, typically
20 000 h, i.e. an estimate of TI. However, due to the inherent uncertainty associated with this
analytical approach, only RTE can be provided for material characterization. This is obtained
performing the single-point thermal endurance test in the same conditions of temperature and
environment as a reference material of known thermal endurance characteristics, i.e. TI and
HIC.
The analytical test methods described in this technical specification may satisfy the demand
of shortening the insulating material characterization procedure, if used with care and
considering the restrictions these methods imply. At present, the universal applicability and
the accuracy of these methods is not validated, thus a round robin test is required to provide
an IEC standard based on these procedures. This part of IEC 60216 is therefore published as
a technical specification.
A general assessment process of the procedures will be developed in other sub-parts of
IEC 60216-7.
– 6 – IEC TS 60216-7-1:2015 © IEC 2015
ELECTRICAL INSULATION MATERIALS –
THERMAL ENDURANCE PROPERTIES –

Part 7-1: Accelerated determination of relative thermal
endurance using analytical test methods (RTE ) –
A
Instructions for calculations based on activation energy

1 Scope
This technical specification describes the procedure for the evaluation of the thermal
endurance of electrical insulating materials, based on thermal analysis methods for the
evaluation of the activation energy of the thermal degradation reaction and a conventional life
test providing a life point in the thermal endurance graph. The purpose of the test procedure
is to estimate the relative temperature index (RTE).
Predictions of thermal endurance based on this procedure are limited to ageing reactions
where one single reaction is predominant and directly correlated to the end-point criteria for a
specific application.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60085, Electrical insulation – Thermal evaluation and designation
IEC 60216-1, Electrical insulating materials – Thermal endurance properties – 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 60216-5, Electrical insulating materials – Thermal endurance properties – Part 5:
Determination of relative thermal endurance index (RTE) of an insulating material.
IEC 60216-8, Electrical insulating materials – Thermal endurance properties – Part 8:
Instructions for calculating thermal endurance characteristics using simplified procedures
ISO 11357-6, Plastics – Differential scanning calorimetry (DSC) – Part 6: Determination of
oxidation induction time (isothermal OIT) and oxidation induction temperature (dynamic OIT)
ISO 11358-2, Plastics – Thermogravimetry (TG) of polymers – Part 2: Determination of
activation energy
ISO 11358-3, Plastics – Thermogravimetry (TG) of polymers – Part 3: Determination of the
activation energy using the Ozawa-Friedman plot and analysis of the reaction kinetics

3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1
reaction rate
r
change of the concentration of a chemical entity as a function of time
[SOURCE: IUPAC “Goldbook”]
3.1.2
extent of reaction
ξ
progress of a chemical reaction equal to the number of chemical transformations
[SOURCE: IUPAC “Goldbook”]
3.1.3
rate of conversion

ξ
time derivative of the extent of reaction
[SOURCE: IUPAC “Goldbook”]
3.1.4
order of reaction
n
indication of the number of entities affecting the macroscopic rate of reaction
[SOURCE: IUPAC “Goldbook”]
3.1.5
diagnostic property
p
property to which TI is related
Note 1 to entry: See definition in IEC 60216-1.
3.1.6
rate law
empirical differential rate equation, an expression for the rate of a particular reaction in terms
of concentrations of chemical species
[SOURCE: IUPAC “Goldbook”]
3.1.7
reaction rate constant
k
proportionality factor k of a rate law
[SOURCE: IUPAC “Goldbook”]
– 8 – IEC TS 60216-7-1:2015 © IEC 2015
3.1.8
Arrhenius equation
empirical exponential law relating reaction rate constant to reciprocal of absolute temperature
[SOURCE: IUPAC “Goldbook”]
3.1.9
activation energy (Arrhenius activation energy)
E
a
empirical parameter characterizing the exponential temperature dependence of the reaction
rate constant
[SOURCE: IUPAC “Goldbook”]
3.1.10
pre-exponential factor
A
coefficient of the Arrhenius equation
[SOURCE: IUPAC “Goldbook”]
3.1.11
end-point
limit for a diagnostic property value based on which the thermal endurance is evaluated
3.1.12
time to end-point
failure time
time to reach the end-point or conventional failure
3.1.13
relative temperature endurance index
RTE
numerical 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 reference
material at a temperature equal to its assessed temperature index
Note 1 to entry: RTE is the relative temperature endurance index calculated through the analytical procedure.
A
3.1.14
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)
Note 1 to entry: TI is the temperature index calculated through the analytical procedure.
A
[SOURCE: IEC 60050-212:2010, 212-12-11, modified according to IEC 60216-1].
3.1.15
halving interval
HIC
numerical value of the temperature interval in kelvin which expresses the halving of the time
to end-point taken at the temperature equal to TI
Note 1 to entry: HIC is the halving interval calculated through the analytical procedure.
A
[SOURCE: IEC 60050-212:2010, 212-12-13, modified according to IEC 60216-1]

3.1.16
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 test temperature
[SOURCE: IEC 60050-212:2010, 212-12-10]
3.1.17
thermal endurance graph paper
graph paper having a logarithmic time scale as the ordinate, graduated in powers of ten (from
10 h to 100 000 h is often a convenient range) and values of the abscissa are proportional to
the reciprocal of the thermodynamic (absolute) temperature
Note 1 to entry: The abscissa is usually graduated in a non-linear (Celsius) temperature scale oriented with
temperature increasing from left to right.
3.2 Abbreviations
DSC scanning calorimetry
FTIR Fourier transform infrared
GC-MS gas chromatography–mass spectrometry
HIC halving interval
OIT oxygen induction time
RTE relative temperature endurance index
TGA thermogravimetric analysis
TI temperature index
4 General considerations
4.1 Thermal degradation kinetics
The general principles of IEC 60216 to determine the temperature index and halving interval
are based on the implicit assumption of a first-order kinetic of the thermal degradation
process of the insulation material. Only under these conditions the thermal endurance graph
is linear and halving interval is independent of the concentration of the reactants.
It is a plausible assumption that the condition of an insulating material at the time of reaching
the defined end-point criteria according to IEC 60216 is correlated to a certain conversion of
the thermal degradation process. Therefore, by knowing the reaction mechanism and kinetics
of the thermal degradation process of an insulation material, it should be possible to estimate
the thermal endurance of an insulating material.
The most important mechanisms for the degradation of insulating materials are thermal
oxidation, pyrolysis, and hydrolysis of the basic polymer. Unfortunately, from a theoretical
point of view, none of these reactions can be considered a priori as reactions with first-order
kinetics. Pyrolysis reactions follow in general zero-order kinetics, and oxidation and hydrolysis
reactions are reactions of higher order because concentration of oxygen, respectively water,
will determine the total reaction rate. The degradation reaction can be considered a
heterogeneous reaction having the insulating material as the solid phase and the
environmental atmosphere as the gas phase. Various processes will influence the total
reaction rate, such as adsorption of reactants (oxygen, water) and desorption (reaction
products), as well as diffusion of reactants and products in the solid and fluid phase. Only if
one of these reactions is predominant, can the overall observable reaction rate follow first-
order kinetics (“pseudo first-order”).
The most common method for the evaluation of the activation energy of a chemical reaction is
the determination of the concentration of reactants and/or products as a function of time and

– 10 – IEC TS 60216-7-1:2015 © IEC 2015
temperature. These experiments allow the identification of the order of the reaction and the
activation parameters according to the Arrhenius theory.
NOTE 1 These experiments will not necessarily give information about the reaction on a molecular level, because
the build-up of intermediate products with a short life time may not be observed if the reaction has not been
fractionated into a series of elementary reactions.
NOTE 2 The Eyring theory of the activated complex gives a fundamental understanding of elementary reactions
and the influence of the temperature and molecular statistics on the reaction rate. However, for first order reaction
the Arrhenius model can be considered with good accuracy.
For some insulating materials, like polyolefin-based plastics, the thermal endurance is
correlated to the concentration of stabilizers (anti-oxidant). The progressive consumption of
the stabilizer is a cause of enhanced oxidation rate. The reaction of the stabilizer follows a
first-order kinetics and is therefore an example where the use of the Arrhenius law for the
prediction of the thermal endurance of these materials can give good results.
Methods based on the obser
...