IEC TR 60216-7-2:2016

IEC TR 60216-7-2 ®
Edition 1.0 2016-08
TECHNICAL
REPORT
colour
inside
Electrical insulating materials – Thermal endurance properties –
Part 7-2: Results of the round robin tests to validate procedures of
IEC TS 60216-7-1 by non-isothermal kinetic analysis of thermogravimetric data

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IEC TR 60216-7-2 ®
Edition 1.0 2016-08
TECHNICAL
REPORT
colour
inside
Electrical insulating materials – Thermal endurance properties –

Part 7-2: Results of the round robin tests to validate procedures of

IEC TS 60216-7-1 by non-isothermal kinetic analysis of thermogravimetric data

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 19.020; 29.020; 29.035.01 ISBN 978-2-8322-3606-2

– 2 – IEC TR 60216-7-2:2016 © IEC 2016
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references. 7
3 Terms and definitions . 7
4 Test specimens . 8
5 Test apparatus . 9
5.1 Thermogravimetric analyser (TGA) . 9
5.2 Purge gas supplied into the TGA furnace . 9
6 Test procedures . 9
6.1 General . 9
6.2 Preconditioning of test samples . 10
6.3 TGA tests with multiple heating rates . 10
6.4 Calculation of the activation energy (E ) . 10
a
6.5 Determination of thermal endurance using TGA . 11
6.5.1 General . 11
6.5.2 Determination of RTE by given degree of conversion from reference
A
material (Method A) . 11
6.5.3 Determination of TI by fixed degree of conversion at 0,05 (Method B) . 12
A
7 Round robin test results . 12
7.1 TGA test results . 12
7.2 Degree of conversion correlated to the activation energy from conventional
heat ageing data . 12
7.3 HIC determined by Method A and Method B . 13
A
7.4 RTE determined by Method A and TI by Method B . 14
A A
7.5 Difference between RTE and TI determined by the conventional heat
A
ageing tests . 16
8 Observations from the round robin test results . 17
8.1 General . 17
8.2 Sample weight variation . 18
8.3 Humidity and hydrolysis of the sample . 19
8.4 Consideration on repeatability of TGA curves. 20
8.5 Baseline drift and responsiveness to heating rates of TGA . 21
9 Conclusion and recommendation . 24
Bibliography . 26

Figure 1 – Fitting curve of plots between degree of conversion and activation energy
determined by ISO 11358-2 (example) . 11
Figure 2 – Correlation between the initial sample mass of sample A and the difference
of RTE (TI ) from TI . 19
A A
Figure 3 – Correlation between the initial sample mass of sample B and the difference
of RTE (TI ) from TI . 19
A A
Figure 4 – Overlay charts of TGA curves in multiple heating rates in multiple
laboratories (enlarged) . 22
Figure 5 – Logarithm plots for activation energy calculation . 23
Figure 6 – Fitting curves of degree of conversion vs. activation energy by TGA . 24

Table 1 – Heat ageing properties of the test specimens by the conventional procedure
described in IEC 60216-5 . 9
Table 2 – Degree of conversion identical to the activation energy of the conventional
heat ageing . 13
Table 3 – HIC determined by Method A and Method B for dielectric strength . 13
A
Table 4 – HIC determined by Method A and Method B for tensile strength . 14
A
Table 5 – HIC determined by Method A and Method B for impact strength . 14
A
Table 6 – RTE determined by Method A and TI by Method B for dielectric strength . 15
A A
Table 7 – RTE determined by Method A and TI by Method B for tensile strength . 15
A A
Table 8 – RTE determined by Method A and TI by Method B for impact strength . 16
A A
Table 9 – Difference between RTE or TI , and TI for dielectric strength . 16
A A
Table 10 – Difference between RTE or TI , and TI for tensile strength . 17
A A
Table 11 – Difference between RTE or TI , and TI for impact strength . 17
A A
Table 12 – Comparison of degree of conversion with original or rerun data at 8 K/min . 21

– 4 – IEC TR 60216-7-2:2016 © IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL INSULATING MATERIALS –
THERMAL ENDURANCE PROPERTIES –

Part 7-2: Results of the round robin tests to validate procedures
of IEC TS 60216-7-1 by non-isothermal kinetic analysis
of thermogravimetric data
FOREWORD
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The main task of IEC technical committees is to prepare International Standards. However, a
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data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC TR 60216-2-7, which is a Technical Report, has been prepared by IEC technical
committee 112: Evaluation and qualification of electrical insulating materials and systems.

The text of this Technical Report is based on the following documents:
Enquiry draft Report on voting
112/354/DTR 112/370/RVC
Full information on the voting for the approval of this Technical Report 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 website 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.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – IEC TR 60216-7-2:2016 © IEC 2016
INTRODUCTION
IEC technical committee 112, (IEC/TC112) has been working on the development of
IEC TS 60216-7-1 that considers the use of activation energy determined through thermal
analytical tools plus abbreviated conventional heat ageing to determine a thermal index on a
polymeric compound. At the same time, the UL LTTA Forum has been discussing alternative
methods that could speed up the determination of a thermal index. Members of the
IEC/TC112 and of the UL LTTA Forum have joined efforts to determine whether the Technical
Specification developed by IEC/TC112 can be used to offer an alternative method of
evaluating polymeric compounds for a thermal index.
Members of IEC/TC112 and the UL LTTA Forum decided to conduct a round robin test (RRT)
using thermogravimetric analysis (TGA) according to ISO 11358-2 on a known compound,
with a known activation energy determined through conventional ageing with a view to
validate the acceptability of IEC TS 60216-7-1, and to determine whether a similar thermal
index could be calculated. The round robin testing was conducted with conventional TGA by
multiple heating rates. However, running isothermal tests can be a follow up of this RRT.

ELECTRICAL INSULATING MATERIALS –
THERMAL ENDURANCE PROPERTIES –

Part 7-2: Results of the round robin tests to validate procedures
of IEC TS 60216-7-1 by non-isothermal kinetic analysis
of thermogravimetric data
1 Scope
The purpose of this part of IEC 60216, which is a Technical Report, is to validate the
procedures of IEC TS 60216-7-1 in providing a similar temperature index to conventional
methods used in other parts of the IEC 60216 series.
These round robin test results do not provide statistical analysis for precisions. The round
robin test focuses on preliminary studies to understand the evaluation and calculation
procedures, influence on apparatus, and data variance among laboratories before
determination of precisions.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
activation energy
Arrhenius activation energy
E
a
empirical parameter characterizing the exponential temperature dependence of the reaction
rate constant
[SOURCE: IUPAC “Goldbook”]
3.2
end-point
limit for a diagnostic property value based on which the thermal endurance is evaluated
3.3
time to end-point
failure time
time to reach the end point or conventional failure
3.4
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
– 8 – IEC TR 60216-7-2:2016 © IEC 2016
3.5
temperature endurance 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 – the two notes have been deleted and
replaced by a new note.]
3.6
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
3.7
degree of conversion
α
quantity of products present at a particular time and temperature during a reaction compared
with the final quantity of the products
[SOURCE: ISO 11358-2:2014, 3.3, modified — the notes have been deleted]
4 Test specimens
For the round robin study, one generic type of polymer, liquid crystal polyester (LCP), was
pre-selected as the round robin study which assumes one single thermal degradation reaction
is predominant and directly correlated to the end-point of dielectric strength as a diagnostic
property.
LCP originally has very little entwining of molecules which exhibits crystalline properties as a
liquid and therefore, there is less thermal transformation between solid and liquid, or between
oven ageing conditions of conventional thermal endurance test and TGA conditions at higher
temperature range. In addition, LCP molecular chains align themselves when moulded, and
this generates a self-reinforcing effect, thereby resulting in high mechanical and electrical
stress resistance.
In this round robin, two LCP materials (LCP sample A, LCP sample B) were chosen for test
samples which already have the conventional heat oven ageing data of dielectric strength,
tensile strength, and impact strength to validate the acceptability of whether or not RTE can
A
be similar to RTE. Both sample A and sample B consist of 30 % glass fibres reinforced.
Configurations of monomers are only different between the samples which influence the
difference in thermal resistance, as shown in Table 1.
The samples were homogenized by freeze-pulverization from the test plaques respectively.
100 mg each of freeze-pulverized powders from the same batch were prepared and provided
to eleven testing laboratories for evaluation, after pre-drying at 140 °C for 4 h.

Table 1 – Heat ageing properties of the test specimens by
the conventional procedure described in IEC 60216-5
Time to end-point at Time to end-point at Time to end-point at
50 % retention of initial 50 % retention of initial 50 % retention of initial
Temperature
dielectric strength tensile strength impact strength
in ovens
h h h
LCP LCP LCP LCP LCP LCP
ºC
Sample A Sample B Sample A Sample B Sample A Sample B
290 1 141 1 215 1 860
285 2 896 1 789 2 870
280 1 917 3 229 2 655
275 5 591 3 083 4 164
270 4 300 4 597 3 920
265 8 255 6 706 8 412
260 5 848 7 625 6 640
250 9 600
Ea 130,6 142,3 165,2 145,9 134,5 102,9
TI 250,0 241,5 249,1 246,2 249,1 234,7

5 Test apparatus
5.1 Thermogravimetric analyser (TGA)
A thermogravimetric analyser (TGA) in accordance with ISO 11358-1 was used for
determination of RTE concerning the test samples. In fact, a number of commercial
A
instruments suitable for the document are available and various models of TGAs that the
laboratory participants have were used for evaluation of the test samples. Before the RRT,
weight and temperature calibrations were implemented based on ISO 11358-1 and TGA
apparatus manufacturer’s guidance.
5.2 Purge gas supplied into the TGA furnace
For purge gas into the TGA furnace, air was chosen to assume oxidative thermal degradation,
as well as degradation of electrical and mechanical strengths with test specimens in oven
ageing. Most of the laboratory participants selected dry air (water content less than 1 ppm ),
but air supplied from the facility (compressed air with or without air dryer) was used in a few
laboratories.
6 Test procedures
6.1 General
Thermal analysis with TGA of the test samples was evaluated with reference to ISO 11358-2
and IEC TS 60216-7-1 in principle. A few modifications of test conditions and more detailed
procedures were added as follows.
______________
ppm = part per million.
– 10 – IEC TR 60216-7-2:2016 © IEC 2016
6.2 Preconditioning of test samples
5 mg ± 0,5 mg of the test sample were initially measured in each laboratory and mounted on
the empty pan in the furnace opened. Then the furnace was closed and pre-conditioned in
equilibrium at 100 °C for 1 h before heating tests were started. The weight value just before
the heating test (time at 0 s in the heating run, or 60 min at the end of the equilibrium) was
used for calculation on the degree of conversion.
NOTE ISO 11358-2 requires using test samples of identical mass ±1 % of the initial weight in multiple heating
conditions which is much narrower than the above. Influence on the initial mass deviation is taken into
consideration in 7.2.
6.3 TGA tests with multiple heating rates
Multiple heating rates testing at 1 K/min, 2 K/min, 4 K/min, 6 K/min and 8 K/min were selected
for evaluation which gave the lowest and highest heating rates that differ by a factor of 8, in
accordance with ISO 11358-2. Evaluation temperature range was set between 100 °C and
700 °C. Each heating rate test was run one time each for sample A and sample B, but 8 K/min
was evaluated twice as an approximate check and to consider repeatability.
6.4 Calculation of the activation energy (E )
a
After TGA data with multiple heating rates were obtained, the activation energies were
calculated per certain given degrees of conversion in accordance with Equation (2) in
ISO 11358-2:2014. Then, both values of degree of conversion and the activation energies
were plotted between 1 % and 19 % with 2 % interval of degree of conversion to analyse the
cubic approximation for drawing the fitting curve of the plots as shown in Figure 1. Equation
(2) in ISO 11358-2:2014 was used for selection of appropriate activation energy and degree of
conversion to determine RTE .
A
For example, if the activation energy of a reference material was already determined as
150 kJ/mol by the conventional heat ageing (e.g. dielectric strength), the corresponding
degree of conversion of the reference material can be read and obtained with the equation of
the fitting curve graph (see Figure 1). Then the corresponding degree of conversion for this
reference material can be used for reading the activation energy of a candidate material from
another graph which was also evaluated with ISO 11358-2 and had another fitting curve of
activation energy and degree of conversion for the candidate material.
All TGA raw data were submitted by eleven laboratories participants and analysis with
ISO 11358-2 was carried out by one of the laboratories with their analytical tool, to avoid any
discrepancy among various software calculations.

0,20
3 2
y = 1,21E–07× – 5,36E–05× + 8,83E–03× – 4,90E–01
0,18
R = 9,94E–01
0,16
0,14
0,12
0,10
0,08
0,06
0,04
0,02
0 50 100 150 200 250
Activation energy (kJ/mol)
IEC
Figure 1 – Fitting curve of plots between degree of conversion and
activation energy determined by ISO 11358-2 (example)
6.5 Determination of thermal endurance using TGA
6.5.1 General
The activation energy given by the above procedure can be used for the determination of
RTE by calculating with time to end-point at the highest temperature which was determined
A
by the conventional heat ageing test under IEC 60216-5, and procedures in accordance with
IEC TS 60216-7-1.
In accordance with ISO 11358-2, various activation energies can be obtained per certain
degrees of conversion calculated with multiple heating rate data of TGA. Therefore, degrees
of conversion were chosen appropriately to be correlated to thermal degradation derived by
properties and the conventional heat ageing data which are described in 6.5.2 (Method A). On
the other hand, the fixed degree of conversion at 0,05 and the activation energy are
sometimes used experimentally for prediction of end-point of properties [1][2] , which is
described in 6.5.3 (Method B).
6.5.2 Determination of RTE by given degree of conversion from reference material
A
(Method A)
After the cubic approximation between the degree of conversion and the activation energy is
determined (see 6.4), the degree of conversion for the reference material is given from the
equation where the activation energy is the same as that from the Arrhenius equation of
conventional heat ageing data. The activation energy of the candidate material is then
determined from the cubic approximation of the candidate material where the degree of
conversion for the candidate material is assumed to be the same as the given degree of
conversion for the reference material. In Method A, RTE can be obtained.
A
______________
Numbers in square brackets refer to the Bibliography.
Degree of conversion
– 12 – IEC TR 60216-7-2:2016 © IEC 2016
6.5.3 Determination of TI by fixed degree of conversion at 0,05 (Method B)
A
In Method B, the fixed degree of conversion at 0,05 can be selected to calculate the activation
energy of the candidate material, with regard to practical experiences [2][3]. In Method B it is
unnecessary to use reference material data to determine the activation energy of the
candidate material in accordance with ISO 11358-2 and the thermal indices of materials can
be determined as TI by the activation energy when the degree of conversion is 0,05.
A
In this round robin test, TI and RTE at 20 000 h of LCP sample A and sample B were
A A
determined by u
...