IEC TS 62332-2:2014

IEC TS 62332-2 ®
Edition 1.0 2014-04
TECHNICAL
SPECIFICATION
SPECIFICATION
TECHNIQUE
colour
inside
Electrical insulation systems (EIS) –Thermal evaluation of combined liquid and
solid components –
Part 2: Simplified test
Systèmes d'isolation électrique (SIE) – Évaluation thermique de composants
liquides et solides combines –
Partie 2: Essai simplifié
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IEC TS 62332-2 ®
Edition 1.0 2014-04
TECHNICAL
SPECIFICATION
SPECIFICATION
TECHNIQUE
colour
inside
Electrical insulation systems (EIS) –Thermal evaluation of combined liquid and

solid components –
Part 2: Simplified test
Systèmes d'isolation électrique (SIE) – Évaluation thermique de composants

liquides et solides combines –

Partie 2: Essai simplifié
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX T
ICS 29.080.30 ISBN 978-2-8322-1514-2

– 2 – IEC TS 62332-2:2014 © IEC 2014
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 9
4 Thermal ageing test apparatus . 10
4.1 General description . 10
4.2 Sealed tubes . 10
4.3 Gas blanketing system . 11
4.4 Pressure relief system . 11
4.5 Ageing ovens . 11
5 Construction of the test object . 12
5.1 General . 12
5.2 Determination of component weights. 12
5.3 Test object . 12
5.3.1 Conductor insulation . 12
5.3.2 Other solid insulation components . 13
5.3.3 Liquid component . 13
5.3.4 Structural components . 13
5.3.5 Other components . 13
6 Test procedures . 14
6.1 General . 14
6.2 Preparation of the test objects . 14
6.2.1 General . 14
6.2.2 Reference test object . 14
6.2.3 Candidate test object . 15
6.3 Diagnostic tests . 16
6.3.1 General . 16
6.3.2 Solid insulation . 16
6.3.3 Liquid insulation . 16
6.4 End-point testing . 16
6.5 Simplified one-point test . 17
7 Analysis of data . 17
7.1 End-point criteria . 17
7.1.1 General . 17
7.1.2 End-of-life of the solid component. 17
7.1.3 Extrapolation of data . 17
7.2 Report. 17
Annex A (informative) Consideration of weight ratios . 19
A.1 Examples of transformers leading to actual weight ratios in Table A.1 . 19
A.2 Calculation of core steel surface ratios . 19
A.3 Calculation of copper components of test . 20
A.3.1 Wire enamel samples . 20
A.3.2 Bare copper samples . 20

Annex B (informative) Consideration of ageing time and temperature . 21
Annex C (informative) Aging example . 22
C.1 Reference system test . 22
C.2 Candidate system test . 22
Bibliography . 25

Figure 1 – Sealed tube example. 11
Figure B.1 – Reference EIS system . 21
Figure C.1 – Example of aging result at a temperature of 165 °C . 23
Figure C.2 – Aging life curve . 24

Table 1 – Reference component weight ratio calculations . 12
Table 2 – Reference EIS ageing conditions and candidate EIS ageing temperatures . 15
Table 3 – Recommended ageing temperatures and periods for expected thermal class . 15
Table A.1 – Examples obtained from industry sources . 19
Table A.2 – Examples of component volume ratio calculations . 19
Table C.1 – Calculation of end-of-life criteria for comparative evaluation . 22
Table C.2 – Example of aging experiment . 23

– 4 – IEC TS 62332-2:2014 © IEC 2014
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL INSULATION SYSTEMS (EIS) –
THERMAL EVALUATION OF COMBINED LIQUID
AND SOLID COMPONENTS –
Part 2: Simplified test
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
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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
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC TS 62332-2, which is a technical specification, has been prepared by IEC technical
committee 112: Evaluation and qualification of electrical insulating materials and systems.

The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
112/256/DTS 112/268/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 the parts in the IEC 62332 series, published under the general title Electrical
insulation systems (EIS) – Thermal evaluation of combined liquid and solid components, 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.
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 TS 62332-2:2014 © IEC 2014
INTRODUCTION
This technical specification describes a method for the thermal evaluation of electrical
insulation systems (EIS) for electrotechnical products with combined liquid and solid
components. More specifically, this part addresses liquid immersed power transformers.
Part 1 covers general test requirements. This Part 2 covers a simplified test method which
can be used as a screening test prior to conducting Part 1 testing or it can be used to
determine a thermal classification of an EIS. This method can also be used as a quality
control test to evaluate minor product changes.
This specification provides a standardized test method for sealed tube testing. The sealed
tube should contain all the primary EIS elements, and in relative component ratios which
compare with actual liquid immersed power transformers.
This technical specification has been prepared in conjunction with IEC TC 14, Power
transformers and IEC TC 10, Fluids for electrotechnical applications. Any comments or
suggestions from other technical committees to make this technical specification more general
are welcome.
ELECTRICAL INSULATION SYSTEMS (EIS) –
THERMAL EVALUATION OF COMBINED LIQUID
AND SOLID COMPONENTS –
Part 2: Simplified test
1 Scope
This part of IEC 62332, which is a technical specification, is applicable to EIS containing solid
and liquid components where the thermal stress is the dominant ageing factor, without
restriction to voltage class.
This part specifies a sealed tube test procedure for the thermal evaluation and qualification of
electrical insulation systems (EIS). One aspect of this procedure is to also provide a method
to assign thermal classifications to materials used in EIS where solid and liquid components
are both used. This procedure describes a comparative ageing method whereby a reference
system composed of kraft paper and mineral oil is compared to a candidate system of any
combination of solid and insulating liquid. The test procedures in this part are specifically
applicable to liquid immersed transformer insulation systems.
Similar procedures should also work for other electrotechnical devices with a combination of
liquid and solid components, such as bushings, cables or capacitors, but this will be added as
additional parts once experience is gained using this technical specification.
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 60156, Insulating liquids – Determination of the breakdown voltage at power frequency –
Test method
IEC 60216-2:2005, Electrical insulating materials – Thermal endurance properties – Part 2:
Determination of thermal endurance properties of electrical insulating materials – Choice of
test criteria
IEC 60216-3, Electrical insulating materials – Thermal endurance properties – Part 3:
Instructions for calculating thermal endurance characteristics
IEC 60216-4-1, Electrical insulating materials – Thermal endurance properties – Part 4-1:
Ageing ovens – Single-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 60243-1, Electrical strength of insulating materials – Test methods – Part 1: Tests at
power frequencies
– 8 – IEC TS 62332-2:2014 © IEC 2014
IEC 60247, Insulating liquids – Measurement of relative permittivity, dielectric dissipation
factor (tan δ) and d.c. resistivity
IEC 60296, Fluids for electrotechnical applications – Unused mineral insulating oils for
transformers and switchgear
IEC 60317 (all parts), Specifications for particular types of winding wires
IEC 60450, Measurement of the average viscometric degree of polymerization of new and
aged cellulosic electrically insulating materials
IEC 60505:2011, Evaluation and qualification of electrical insulation systems
IEC 60554-2, Cellulosic papers for electrical purposes – Part 2: Methods of test
IEC 60567, Oil-filled electrical equipment – Sampling of gases and of oil for analysis of free
and dissolved gases – Guidance
IEC 60599, Mineral oil-impregnated electrical equipment in service – Guide to the
interpretation of dissolved and free gases analysis
IEC 60763-2, Specification for laminated pressboard – Part 2: Methods of test
IEC 60814, Insulating liquids – Oil-impregnated paper and pressboard – Determination of
water by automatic coulometric Karl Fischer titration
IEC 60851-5, Winding wires – Test methods – Part 5: Electrical properties
IEC 61198, Mineral insulating oils– Methods for the determination of 2-furfural and related
compounds
IEC 61620, Insulating liquids – Determination of dielectric dissipation factor by measurement
of the conductance and capacitance – Test method
IEC 62021-1, Insulating liquids – Determination of acidity – Part 1: Automatic potentiometric
titration
IEC 62021-2, Insulating liquids – Determination of acidity – Part 2: Colourimetric titration
IEC 62021-3, Insulating liquids – Determination of acidity – Part 3: Test methods for non
mineral insulating oils
IEC TS 62332-1:2011, Electrical insulation systems (EIS) – Thermal evaluation of combined
liquid and solid components – Part 1: General requirements
ISO 2049, Petroleum products – Determination of colour (ASTM scale)
ISO 2211, Liquid chemical products – Measurement of colour in Hazen units (platinum-cobalt
scale)
ASTM D971, Standard Test Method for Interfacial Tension Of Oil Against Water By The Ring
Method
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply, some of which
are taken from IEC 60505.
3.1
electrical insulation system
EIS
insulating structure containing one or more electrical insulating materials (EIM) together with
associated conducting parts employed in an electrotechnical device
Note 1 to entry: EIMs with different temperature indices (ATE RTE according to IEC 60216-5) may be combined to
form an EIS, which has a thermal class that may be higher or lower than that of any of the individual components
according to IEC 60505.
[SOURCE: IEC 60505:2011, 3.1.1 – modified, the Note 1 to entry has been added]
3.2
candidate EIS
EIS under evaluation to determine its service capability (thermal)
3.3
reference EIS
evaluated and established EIS with either a known service experience record or a known
comparative functional evaluation as a basis
3.4
thermal class
designation of an EIS that is equal to the numerical value of the maximum temperature in
degrees Celsius for which the EIS is appropriate according to IEC 60085
Note 1 to entry: An EIS may be subjected to operating temperatures exceeding its thermal class, which can result
in shorter expected life.
3.5
EIS assessed thermal endurance index
EIS ATE
numerical value of the temperature in degrees Celsius for the reference EIS as derived from
known service experience or a known comparative functional evaluation
3.6
EIS relative thermal endurance index
EIS RTE
numerical value of the temperature in degrees Celsius for the candidate EIS which is relative
to the known EIS ATE of a reference EIS when both EIS are subjected to the same ageing
and diagnostic procedures in a comparative test
3.7
test object
piece of original equipment, a representation (model) of equipment, a component of or part of
equipment, including the EIS, intended for use in a functional test
3.8
thermal ageing factor
thermal stress that causes irreversible changes in the EIS

– 10 – IEC TS 62332-2:2014 © IEC 2014
3.9
diagnostic test
periodic application of a specified level of a diagnostic factor to a test object to determine
whether the end-point criterion has been reached
3.10
end-point criterion
selected value of either a property or a change of property that defines the end of a
component’s life
[SOURCE: IEC 61857-1:2008, 3.11, modified – "component's life" replaces "test object in a
functional test]
3.11
end-of-life
end of a test object’s life, as determined by any selected component meeting its end-point
criterion
3.12
sealed tube
sealed container partially filled with the liquid EIM and in which includes the solid EIM in
relative component ratios which compare with the actual electrotechnical device
3.13
halving value
HIC
numerical value of the temperature interval in Kelvins which expresses the halving of the time
to end-point taken at the temperature equal to TI
[SOURCE: IEC 60050-212:2010, 212-12-13, modified – "equal to TI" replaces the original
"corresponding to the temperature index or the relative temperature index"]
4 Thermal ageing test apparatus
4.1 General description
The thermal ageing test apparatus shall be designed to allow the ageing of solid and liquid
components. The reference and candidate EIS shall be exposed to test periods at selected
elevated temperatures. These test periods consist of a specific time exposure at the selected
temperature followed by diagnostic tests. The test system consists of the following elements:
• sealed tubes
• ageing ovens
• test objects.
4.2 Sealed tubes
Each sealed tube is a container constructed of stainless steel or other suitable materials such
as glass, the size to be determined by the size of the test objects. Additionally, the material
for the tube shall either not affect the ageing (such as glass or stainless steel) or identically
constructed tubes shall be used for all sets of experiments. The cell volume shall consider the
space required for thermal expansion of the liquid at ageing temperatures, as well as space
for the EIM to be evaluated. The EIM to be evaluated should be fully immersed in the liquid
during the entire test period. Either one or both ends of the cell shall be fitted with removable,
sealable bolt-on covers.
Ports shall be provided for
• sampling of the liquid,
• gas blanketing and associated pressure relief system.
For example, see Figure 1.
IEC  1019/14
Figure 1 – Sealed tube example
4.3 Gas blanketing system
A gas blanketing system shall be provided which simulates the insulation system used in the
transformer being evaluated. This can be a sealed gas system, which maintains a gas blanket
over the liquid in the cell for the purpose of reducing oxidation of the liquid. In each case, the
gas blanket in each cell shall be regulated to maintain a positive pressure as is described in
below in 4.4.
Free breathing liquid preservation systems are not included due to safety hazard of testing
liquids at temperatures above their flashpoints where additional oxygen is available. In the
case of a sealed test, the amount of available oxygen is limited.
NOTE Oxygen is known to increase ageing of insulation systems, so a test with air would be expected to be more
severe than one sealed with nitrogen.
4.4 Pressure relief system
A pressure relief valve shall be installed on each cell to prevent the internal cell pressure from
rising above the capability of the sealed tube. Additionally, the test should simulate the end
application which is under evaluation. As an example, for liquid-immersed transformer
applications, the transformer tanks are designed to operate at a pressure of up to 150 kPa.
The technical evaluation for this design should use a method (such as a pressure relief valve)
to control the pressure in the cells at a level consistent with the end use application being
evaluated. If not otherwise specified, choose a level of 150 kPa for this test pressure.
Pressure control has two functions. The first is for safety and the second is to control the
pressure at a low consistent level to better model the actual transformer application. This
pressure control can be accomplished by using a pressure relief value equal to that used on
the transformer for which the evaluation is being conducted, or by the means of an expanding
bellows which allows increasing gas space of the test cell without an increase of pressure.
4.5 Ageing ovens
The ageing ovens used shall meet the requirements of IEC 60216-4-1.

– 12 – IEC TS 62332-2:2014 © IEC 2014
5 Construction of the test object
5.1 General
The test object is designed to model the EIS portion of the transformer under evaluation and
usually consists of
• a conductor insulation,
• other solid insulation components,
• structural components,
• metallic materials (typically copper or aluminium and steel),
• an insulating liquid,
• other components in the candidate if they differ from the reference system and if they
reasonably affect the outcome of the test.
5.2 Determination of component weights
It is important that the ratios of weights of components used to construct the test object shall
be representative of the candidate transformer being modelled. Determine the percentage of
each individual component as a part of the total weight. The percentages shall be used to
determine the weight of those individual components to be used in the construction of the test
object. In a family of products with the same specific EIS, the ratio of weight of the individual
components to the total weight should be similar. Other components which affect aging based
on surface area are included on this basis.
Table 1 provides the weights and dimensions of the components to be used in the reference
test. This table is based on the ratio of materials assuming 100 g of solid for each type of EIS.
Each of the items in this table is described in more detail in the clauses following the table.
The reference should be selected that is most appropriate for the candidate under test.
Table 1 – Reference component weight ratio calculations
Transformer type
Test material descriptions Distribution Power – Core type Power – Shell type
Insulating liquid 1 330 g 760 g 330 g
Conductor insulation  10 g 10 g
Layer insulation 50 g
Low density pressboard 50 g 10 g 80 g
High density pressboard 80 g 10 g
Ratio – Liquid to solid 13,3 to 1 7,6 to 1 3,3 to 1
2 2 2
Surface area of core steel 9,6 cm 9,6 cm 9,6 cm
Enamel wire samples 5 samples 5 samples 5 samples
2 2 2
Surface area of copper 9,6 cm 9,6 cm 9,6 cm

In addition to the ratios of the solid and liquid insulation components shown in Table 1, other
materials as described in 5.3.4 and 5.3.5 should be included as well, but are not included
here for simplicity. Enamel wire samples are described in Annex A.
5.3 Test object
5.3.1 Conductor insulation
Depending on the type of transformer, the conductors can range from small round wires, to
larger rectangular wires or metal foils. The insulation for each of these may differ. The

insulation may be either enamel coating, conductors wrapped with thin insulating materials or,
in the case of the metal foils, thicker papers/films, sometimes with adhesive coatings.
The conductor insulation should be tested in a way that can allow estimation of the expected
thermal capability of the material when combined with a fluid. For thin wire wrap materials, the
test specimens can be pre-cut tensile strips. A minimum of 20 test specimens per ageing cell
should be included in each cell. For enamel coated round wires, twisted wire pairs of can be
aged, again with a minimum of 20 test specimens per ageing cell. For applications such as
distribution transformers, the thicker layer papers or films used with metal foils, can be
evaluated similar to the thin wire wrap materials.
For papers/films with adhesive coatings, a separate test to evaluate the technical
characteristic of the adhesive should be conducted. The failure mode for this test may be
bond strength retention of the adhesive rather than a tensile retention test of the base
paper/film insulation.
Include the same ratio of exposed surface area of the conductor metal (copper or aluminium)
as in the transformer being evaluated for paper/film wrapped conductors.
5.3.2 Other solid insulation components
Other solid materials are typically used in the transformers. These components include
pressboard products that are adjacent to the conductors (spacer materials), and as such
experience the same temperature extremes as the conductor insulation or other materials
which are used in the cooler part of the transformer (such as cylinders or oil-flow barriers). In
other type of designs, the insulated conductors may be separated by insulating papers which
again experience the same extreme temperatures as the conductor insulation. Each of these
materials should be included in the correct ratio as described in 5.2.
5.3.3 Liquid component
The cell shall be filled with the liquid component used in the transformer being evaluated. The
weight of the liquid shall be determined from requirements in 5.2 based on weight and
temperature calculations. Care shall be taken to allow space for expansion of the liquid in the
cell at elevated temperatures.
5.3.4 Structural components
Other materials are used in the transformer that are for “mechanical purposes” only, and have
no direct impact on electrical performance of the insulation system, but if they fail in the
application, could cause a degradation of the insulation system. Examples of such
components include, but are not limited to, tie cords, netting tapes, adhesive tapes, etc. Many
of these components are manufacturing aids, so a failure in operation is not a design problem,
as long as the components degrade in a way that does not affect the other materials
(chemical compatibility) or affect design parameters, e.g. block cooling.
These materials could be included in the test consistent with 5.2.
NOTE At present, no method has been developed as to how to evaluate the addition of these materials into the
test object. Once experience with this test specification has been obtained, a method to evaluate these materials
will be added.
5.3.5 Other components
For products being simulated, representative components that are not included in the EIS but
are expected to affect it, shall be included. Examples include pieces of core steel, material
supporting the leads, coatings, solder and enclosure materials. The relative weights of these
components should match those of the evaluated product, with the exception of magnetic core
steel and tank material. The relative quantity of magnetic core steel and tank shall be
determined, based on the surface area exposed to the liquid component. An example is given

– 14 – IEC TS 62332-2:2014 © IEC 2014
in Annex A. Core steel is considered a surface area rather than a weight ratio since only the
surface is available to affect the aging of the insulation system.
In addition to the core steel, these materials could be included in the test consistent with 5.2.
NOTE At present no method has been developed as to how to evaluate the addition of these materials into the
test object. Once experience with this test specification has been obtained, a method to evaluate these materials
will be added.
6 Test procedures
6.1 General
A three-temperature ageing test shall be completed to establish the thermal rating of the new
system. A reference EIS shall be used to validate the testing of the candidate EIS. Unless
otherwise stipulated by the equipment technical committee, the reference system shall be
cellulose solid insulation and mineral oil.
NOTE For transformers which include enamel coated wires, the enamel coated wires to be evaluated as part of
the reference EIS are specified in IEC 60317 – PVF (polyvinyl formal).
6.2 Preparation of the test objects
6.2.1 General
The quantity of samples of solid and liquid insulation should be sufficient to supply all
reference and candidate test objects and requirements for diagnostic testing.
All solid samples shall be pre-conditioned by drying. Lower temperature drying will take longer
than high temperatures, but will prevent damage of the insulation prior to the ageing
experiment. For optimum drying conditions, refer to the relevant material testing standards.
The moisture content of the solid insulation materials shall be between 0,25 % and 0,50 % at
the start of the ageing.
Immediately after drying, the conductor materials, other solid materials and all additional
materials shall be vacuum-impregnated with the liquid under evaluation. The impregnation
process is conducted for 6 h to 24 h, at 70 °C to 90 °C.
Prior to inserting the test objects into the ageing cell, remove the pre-conditioned solid and
liquid diagnostic test samples. Verify the initial moisture content after the impregnation
process to determine whether or not the materials are adequately dried prior to start-up.
A clean, dry ageing cell is then filled with the previously determined weight of liquid and the
impregnated solid components are inserted. The cell is quickly sealed then purged with dry
sealing gas.
Following its assembly, the ageing cell is placed into an ageing oven. The temperature of the
oven is then increased to the ageing temperature.
6.2.2 Reference test object
The reference EIS shall be composed of solid materials and liquid that have an established
performance in combination. At the time of issue of this technical specification, the only
established reference EIS is composed of cellulose solid materials and mineral oil. The EIS
ATE of this reference system is recognized to be 105 °C. However, if the equipment technical
committee has established another EIS with known performance, this may be used as the
reference EIS. The equipment technical committee should provide specific details:
• conductor with Kraft cellulose insulation (samples described in 5.3.1);

• non-inhibited mineral oil according to IEC 60296.
For verification of reference EIS ageing, a single set of three test objects composed of the
reference EIS shall be evaluated along with the candidate test objects. For the reference EIS
cellulose and mineral oil system, the ageing temperatures shall be as shown below.
Testing shall be carried out with three temperatures for the referenced EIS as shown in Table
2 below. Evaluate the per cent tensile strength of the three sets and average them for the
end of life criteria for the candidate system. Ageing times for the reference EIS is based on a
20,000 h life at the ATE (of 105 °C) with a HIC of 6 K.
Table 2 – Reference EIS ageing conditions and candidate EIS ageing temperatures
Insulation Expected increase Ageing time Ageing time Ageing time
system in thermal rating 3 536 h number 2: number 3:
625 h 110 h
°C °C °C °C
Reference EIS 130 145 160
Candidate EIS 10 140 155 170
20 150 165 180
30 160 175 190
40 170 185 200
50 180 195 210
60 190 205 220
The expected value for the reference EIS at the above times and temperatures is in the range
of 25 % tensile strength. For dielectric strength of enamel coated wire, the expected value is
in the range of 80 % retained dielectric strength. In either case, the property retention of the
reference EIS will determine the end of life criteria for the candidate EIS. Unless there is a
good reason for an alternative end of life test (other than tensile strength for solid insulation
and dielectric strength for enamel/wire coatings) these should be chosen.
6.2.3 Candidate test object
At least four ageing cells shall be used for the candidate system for each test temperature. At
least one cell shall have ageing results that extend past the end of life criteria determined
from the reference EIS testing for each test temperature.
Select the ageing temperatures for the candidate EIS, based on the expected thermal class
from IEC 60085, listed below in Table 3. The four ageing period durations are defined for
each ageing temperature.
Table 3 – Recommended agei
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