IEC 62631-3-4:2019

IEC 62631-3-4 ®
Edition 1.0 2019-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Dielectric and resistive properties of solid insulating materials –
Part 3-4: Determination of resistive properties (DC methods) – Volume
resistance and volume resistivity at elevated temperatures

Propriétés diélectriques et résistives des matériaux isolants solides –
Partie 3-4: Détermination des propriétés résistives (méthodes en courant
continu) – Résistance transversale et résistivité transversale aux températures
élevées
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IEC 62631-3-4 ®
Edition 1.0 2019-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Dielectric and resistive properties of solid insulating materials –

Part 3-4: Determination of resistive properties (DC methods) – Volume

resistance and volume resistivity at elevated temperatures

Propriétés diélectriques et résistives des matériaux isolants solides –

Partie 3-4: Détermination des propriétés résistives (méthodes en courant

continu) – Résistance transversale et résistivité transversale aux températures

élevées
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.220.99; 29.035.01 ISBN 978-2-8322-6688-5

– 2 – IEC 62631-3-4:2019 © IEC 2019
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Significance . 6
5 Method of test . 6
5.1 General . 6
5.2 Power supply and test voltages . 6
5.3 Equipment . 6
5.3.1 Specimens and electrodes . 6
5.3.2 Heating chamber . 7
5.3.3 Measuring leads . 7
5.3.4 Temperature control . 7
5.3.5 Special precautions during measurements . 8
5.4 Calibration . 8
6 Procedure . 8
6.1 Continuously increasing temperature (method A) . 8
6.2 Increasing the temperature by steps (method B) . 8
6.3 Precautions to be taken . 9
6.4 Calculation of volume resistivity . 9
7 Report . 9
Annex A (informative) Principle of test apparatus . 11
Bibliography . 14

Figure A.1 – Circuit diagram of test apparatus . 11
Figure A.2 – Structure diagram of test apparatus . 12
Figure A.3 – Pictures of test apparatus . 13

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DIELECTRIC AND RESISTIVE PROPERTIES OF SOLID
INSULATING MATERIALS –
Part 3-4: Determination of resistive properties (DC methods) –
Volume resistance and volume resistivity at elevated temperatures

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
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62631-3-4 has been prepared by IEC technical committee 112:
Evaluation and qualification of electrical insulating materials and systems.
This edition of IEC 62631-3-4 cancels and replaces IEC 60345 “Method of test for electrical
resistance and resistivity of insulating materials at elevated temperatures”, published in 1971.
This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to IEC 60345:
a) The revised standard becomes part of the series IEC 62631-3-x. Title of the standard is
changed and adapted to the series as Part 3-4.
b) Clauses 2 "Normative references", 3 "Terms and definitions", and 4 "Significance" are
added.
– 4 – IEC 62631-3-4:2019 © IEC 2019
c) Subclauses 5.2 "Power supply, Voltage", 5.3.1.2 "Number of test specimens" and 5.3.1.3
"Conditioning and pre-treatment of test specimens" are added.
d) In 5.3.5 "Special precautions during measurements", errors analysis in the measurement
of current are modified, and aligned with IEC 62631-3-1.
e) In 6.2 "Increasing the temperature by steps (method B)", the method for more than one
specimen is removed.
f) The standard atmospheric conditions for testing and conditioning, especially the
temperature, are replaced according to IEC 60212.
g) The circuit diagram of test apparatus is modified, and the structure diagram and pictures
of test apparatus are added in Annex A.
h) The orders of part clauses are adjusted.
The text of this International Standard is based on the following documents:
CDV Report on voting
112/406/CDV 112/445/RVC
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 62631 series, published under the general title Dielectric and
resistive properties of solid insulating materials, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• 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.
DIELECTRIC AND RESISTIVE PROPERTIES OF SOLID
INSULATING MATERIALS –
Part 3-4: Determination of resistive properties (DC methods) –
Volume resistance and volume resistivity at elevated temperatures

1 Scope
This part of IEC 62631 covers procedures for the determination of insulation resistance and
volume resistivity of insulating materials by applying DC-voltage and temperatures up to
800 °C. The typical application materials include high temperature mica plate and alumina
ceramics.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements 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 60212:2010, Standard conditions for use prior to and during the testing of solid electrical
insulating materials
IEC 62631-3-1，Dielectric and resistive properties of solid insulating materials – Part 3-1:
Determination of resistive properties (DC methods) – Volume resistance and volume
resistivity – General method
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
heating chamber
device which is used for supplying an elevated temperature to the specimen
3.2
volume resistance
part of the insulation resistance which is due to conduction through the volume
Note 1 to entry: Volume resistance is expressed in Ω.
3.3
volume resistivity
volume resistance of a material related to its volume
Note 1 to entry: Volume resistivity is expressed in Ωm.

– 6 – IEC 62631-3-4:2019 © IEC 2019
Note 2 to entry: For insulating materials, the volume resistivity is usually determined by means of measuring
electrodes arranged on a sheet of the material.
Note 3 to entry: According to IEC 60050-121: Electromagnetism, “conductivity” is defined as the “scalar or tensor
quantity, the product of which by the electric field strength in a medium is equal to the electric current density” and
“resistivity” as the "inverse of the conductivity when this inverse exists”. Measured in this way, the volume
resistivity is an average of the resistivity over possible heterogeneities in the volume incorporated in the
measurement; it includes the effect of possible polarization phenomena at the electrodes.
4 Significance
Some types of insulating materials are used under high temperatures up to 800 °C, such as
mica plate and alumina ceramics, when mica plate is used for supporting aluminum
electrolytic tank and alumina ceramics are used for high temperature crucibles or resistance
furnace tubes.
For these purposes, it is generally desirable to have the insulation resistance as high as
possible. Volume resistance and volume resistivity can be used as an aid in the choice of an
insulating material for a specific application. The change in resistivity with temperature may
be great and shall be known when designing for operation conditions.
5 Method of test
5.1 General
This method describes specific types of materials used at elevated temperatures; the typical
upper temperature limit is 800 °C. Different types of electrodes can be used, depending on
the specific measurement or product demands.
NOTE Thickness changes due to the high temperature can affect the measurement results.
5.2 Power supply and test voltages
A source of very steady DC voltage is required. This can be provided either by batteries or by
rectified and stabilized power supply. The degree of stability required is such that the change
in current due to any change in voltage is negligible compared with the current to be
measured. Commonly specified test voltages to be applied to the complete specimen are 10 V,
100 V, 500 V, 1 000 V. If not otherwise stipulated, a voltage of 500 V shall be used.
5.3 Equipment
5.3.1 Specimens and electrodes
5.3.1.1 Preparation of specimens and electrodes
For insulation resistance measurements, the specimens shall be of any suitable size and
shape and shall have electrodes already attached. When volume resistivity is measured,
guarded electrodes are suggested. The preferred dimensions of test specimens shall be those
given in the test procedures of IEC 62631-3-1. The specimen electrodes shall consist of fired-
on conducting paint or a conducting coating evaporated or sprayed onto the specimen
surfaces. Platinum is a suitable electrode material.
If other types of metal, such as silver or gold are used, make sure that they will not migrate
into the sample or oxidize at test temperature.
The specimens shall be mounted securely among electrode backing plates within the heating
chamber. These backing plates and their respective leads shall be made of a metal which is
mechanically stable and resistive to oxidation. High-heat-resistant alloys such as stainless
steel may also be utilized. The backing plates shall be of sufficient thickness to prevent
warping and to provide heat equalization between the specimens and the electrode backing
plates.
For mica plate and aluminium oxide specimen, a plate sample is recommended.
5.3.1.2 Number of test specimens
The number of specimens to be tested shall be determined by the relevant product standards.
If no such data is available, at least three specimens shall be tested.
5.3.1.3 Conditioning and pre-treatment of test specimen
Conditioning and any other pre-treatment of the test specimen shall be done according to the
relevant product standard. If no product standards exist, conditioning shall be done according
to IEC 60212 standard conditions for use prior to and during the testing of solid electrical
insulating materials.
5.3.2 Heating chamber
For heating the specimen, a suitable electric oven can normally be utilized up to 500 °C; a
resistance furnace shall be used if the testing temperature reaches 800 °C. The construction
shall be such that the specimen is subjected to a uniform temperature throughout its total
volume with temperature fluctuations as small as possible. The atmospheric conditions for
testing and conditioning shall be in accordance with IEC 60212. The samples shall be tested
during the heat preservation period.
An adequate muffle should be provided to shield the specimen from direct radiation by the
heating elements. This muffle may be made of a ceramic such as aluminum oxide or
equivalent. A grounded metallic shield of stainless steel or equivalent metal shall also be
provided within the oven. The shield shall act as a guard to prevent leakage currents between
the heating circuit and the measuring circuit.
In the case of very high resistance specimens, it may be necessary to disconnect the heating
element to prevent interference during the measurement.
A typical structure of heating chamber is shown in Annex A. Alternatively, the tests may be
performed in an inert atmosphere.
5.3.3 Measuring leads
Insulated measuring leads shall be brought into the furnace through high-resistance ceramic
insulators located in a cool zone and adequately guarded so as to prevent leakage current
from affecting the test results.
NOTE Alternatively, the leads can be passed through holes in the top or in the wall of the furnace which is
earthed. If stiff leads are used, they can be supported externally so as not to touch anything but their supports. The
supports will be relatively cool and thus can be made of any rigid insulating material.
5.3.4 Temperature control
The temperature control mode of the heating chamber shall be set by program. A means of
temperature control shall be provided which can maintain temperature tolerances according to
IEC 60212 standard conditions for use prior to and during the testing of solid electrical
insulating materials. The use of two thermocouples is recommended, one in the chamber for
control and a second for the direct measurement of the specimen temperature.
The temperature of the specimen shall be measured using a thermocouple mounted as close
as possible to the specimen without causing electrical interaction with the measurement of
resistance. For example, the thermocouple may be inserted directly into a hole extending
almost to the surface of the backing plate adjacent to the specimen. The hole can be drilled
from the opposite face of the plate perpendicular to the surface of the specimen or from the
side of the plate parallel to the specimen surface. If the thermocouple is mounted within the
electrode backing plate, the leads and the temperature-indicating instrument shall be

– 8 – IEC 62631-3-4:2019 © IEC 2019
adequately insulated or the thermocouple shall be disconnected or removed when
measurements are made.
5.3.5 Special precautions during measurements
Errors in the measurement of current may result from the fact that the current-measuring
device is shunted by the resistance between the guarded terminal and the guard system. To
ensure satisfactory operation of the equipment, a measurement should be made with the lead
from the voltage source to the specimen disconnected. Under this condition, the equipment
should indicate infinite resistance within its sensitivity. If suitable standards of known values
are available, they may be used to test the operation of the equipment.
If the material insulating the leads into the oven is subjected to heat, the insulation resistance
of the lead insulation may become low enough to affect the measurements. The leakage
resistance shall be determined by a separate measurement at each temperature.
Thermocouple potentials between dissimilar metals, when they are used in leads and
electrode holders, can cause measurement errors. A measurement of current, with the supply
voltage replaced by a short circuit, will indicate the magnitude of this thermocouple effect.
5.4 Calibration
The equipment shall be calibrated in the magnitude of the volume resistance measured at
room temperature.
NOTE Calibration resistors in the range up to 100 TΩ are commercially available.
6 Procedure
6.1 Continuously increasing temperature (method A)
This method is suitable for obtaining quickly an approximate relationship between resistance
and temperature of a single specimen over a wide temperature range. The method is suitable
only with materials for which the effects of dielectric absorption can be neglected, or for
obtaining comparative results for similar materials. The specimen shall be mounted tightly
between the electrode backing plates, but not so tightly that the specimen is distorted while
being heated. The specified voltage shall be applied to the test specimen and the temperature
shall be increased at a rate depending on the thickness of the material and not higher than
5 K/min. A sufficient number of resistance measurements shall be made, as the temperature
is increased, so as to define adequately the relationship between resistance and temperature.
6.2 Increasing the temperature by steps (method B)
This method is suitable for obtaining the relationship between resistance and temperature of a
single specimen more accurately than the one which is possible with continuously increasing
temperature. It is useful also with specimens for which dielectric absorption is a problem.
The test specimen shall be mounted tightly between the electrode backing plates but not so
tightly that the specimen is distorted while being heated. The temperature of the test
specimen shall be increased from room temperature to the desired test temperature and
subsequently from each test temperature step to the next.
NOTE 1 The test chamber is controlled in such a manner that the temperature of the electrode backing plate does
not exceed the desired test temperature. Usually the temperature step is kept long enough to ensure the sample
temperature meets the requirements in the high temperature range. If a temperature overshoot occurs, it will take
some time to wait for the sample end temperature to meet the final test temperature.
When the temperature of the electrode backing plate is within the desired test temperature
according to Table 2 of IEC 60212:2010, the voltage specified in the material specification
shall be applied to the specimen for 1 min (or for other times as specified) and the resistance
shall then be measured. When the measurement is completed, the voltage shall be removed

and the high voltage, measuring and guarded electrodes shall be connected to each other
(short-circuited).
A sufficient number of test temperatures, but no less than five, shall be selected to define
adequately the relationship between temperature and resistance over the desired range of
temperatures. At the lower temperatures, the temperature increments should be relatively
small, for example 10 K. As the test temperature is increased, the temperature increments
should also be increased.
NOTE 2 The logarithm of resistance (or resistivity) is often plotted as a function of the reciprocal absolute
temperature.
6.3 Precautions to be taken
When the current has not stabilized in the time specified for measurement, due to dielectric
relaxation, it may be necessary to determine the resistance as a function of time so that the
resistance value obtained at stabilization can be estimated.
When the resistance of the material being tested is relatively low, it may be necessary to
make the measurements at a reduced voltage to avoid the effects of specimen heating.
For those materials in which polarization effects play a part, with concentration of ions at one
or both electrodes, the results may be of doubtful value.
Unless the effect of thermal degradation is specially required, the specimen shall be kept at
the test temperature only long enough to attain thermal equilibrium. The maximum permissible
time of exposure to the test temperature should be determined by comparing values of
resistance (one minute of electrification) measured periodically over a time, which are
comparable to or longer than that expected in the tests (using an additional specimen).
After a series of tests at progressively higher temperatures, an additional measurement shall
be made at the starting temperature to determine whether the exposure to the elevated
temperatures has produced a permanent change in the specimens.
6.4 Calculation of volume resistivity
The volume resistivity shall be calculated from the following formula:
ρ = R × A / h
x
where
ρ is the volume resistivity in Ωm;
R is the volume resistance measured in Ω;
x
A is the effective area of the electrode in m ;
h is the thickness of the specimen in m.
7 Report
The report shall include the following:
• complete identification and description of the material tested, including source and
manufacturer’s code;
• shape and thickness of test specimens;
• type of electrodes and nature of the electrode backing plates;
• test voltage and time of electrification;

– 10 – IEC 62631-3-4:2019 © IEC 2019
• accuracy of the instrument and calibration method, depending on the measured values of
resistance, if necessary;
• curing conditions of the material and any pre-treatment;
• conditioning of samples and climatic conditions under test;
• description of test set-up and instrument used for the test;
• number of samples;
• each single value and the median of volume resistance and volume resistivity respectively
at each temperature;
• the method of increasing the temperature, i.e. method A or B;
• date of test;
• any other important observations if applicable.

Annex A
(informative)
Principle of test apparatus
An example of a circuit diagram is shown in Figure A.1 for measuring the insulation resistance
and volume resistivity of insulating materials at elevated temperatures.
Thermocouple
Top
of electrode
electrode
Thermocouple
of muffle
Test
specimen
Voltage
source
Ring
Guarded
electrode
electrode
A Picoammeter
Metallic shield
Oven wall
IEC
Figure A.1 – Circuit diagram of test apparatus
A typical structure diagram of test apparatus is shown in Figure A.2.
Pictures of test apparatus are given in Figure A.3, which include the appearance of the
...