IEC 62631-2-3:2024

Dielectric and resistive properties of solid insulating materials - Part 2-3: Relative permittivity and dissipation factor - Contact electrode method for insulating films - AC methods

IEC 62631-2-3:2024 specifies the measuring technology and the test method for the relative permittivity and dielectric dissipation factor of thin single layer insulating polymer film without any additional metallization on the sample surface. The adaptive thickness range is approximately 10 μm to 100 μm. The proposed frequency is the power frequency (50 Hz or 60 Hz), and it is also suitable in the technical frequency range from 1 Hz to 1 MHz.
The content of the corrigendum 1 (2025-04) has been included in this copy.

Propriétés diélectriques et résistives des matériaux isolants solides - Partie 2-3 : Permittivité relative et facteur de dissipation - Méthode d'électrode de contact pour films isolants - Méthodes en courant alternatif

L’IEC 62631-2-3:2024 spécifie la technologie de mesure et la méthode d’essai pour la permittivité relative et le facteur de dissipation diélectrique d’un film polymère isolant monocouche mince sans métallisation supplémentaire sur la surface de l’échantillon. La plage d’épaisseurs adaptatives est d’environ 10 μm à 100 μm. La fréquence proposée est la fréquence industrielle (50 Hz ou 60 Hz), et elle est également appropriée dans la plage de fréquences techniques comprises entre 1 Hz et 1 MHz.
Le contenu du corrigendum 1 (2025-04) a été pris en considération dans cet exemplaire.

General Information

• Status: Published
• Publication Date: 04-Apr-2024
• ICS: 17.220.99 - Other standards related to electricity and magnetism
• ICS: 29.035.01 - Insulating materials in general
• Technical Committee: TC 112 - Evaluation and qualification of electrical insulating materials and systems
• Drafting Committee: WG 4 - TC 112/WG 4
• Current Stage: PPUB - Publication issued
• Start Date: 05-Apr-2024
• Completion Date: 03-May-2024

Relations

• Corrected By: IEC 62631-2-3:2024/COR1:2025 - Corrigendum 1 - Dielectric and resistive properties of solid insulating materials - Part 2-3: Relative permittivity and dissipation factor - Contact electrode method for insulating films - AC methods
• Effective Date: 26-Oct-2025

Standards Content (Sample)

IEC 62631-2-3 ®
Edition 1.0 2024-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Dielectric and resistive properties of solid insulating materials –
Part 2-3: Relative permittivity and dissipation factor – Contact electrode method
for insulating films – AC methods

Propriétés diélectriques et résistives des matériaux isolants solides –
Partie 2-3 : Permittivité relative et facteur de dissipation – Méthode d'électrode
de contact pour films isolants – Méthodes en courant alternatif
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IEC 62631-2-3 ®
Edition 1.0 2024-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Dielectric and resistive properties of solid insulating materials –

Part 2-3: Relative permittivity and dissipation factor – Contact electrode method

for insulating films – AC methods

Propriétés diélectriques et résistives des matériaux isolants solides –

Partie 2-3 : Permittivité relative et facteur de dissipation – Méthode d'électrode

de contact pour films isolants – Méthodes en courant alternatif

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.220.99, 29.035.01 ISBN 978-2-8322-8684-5

– 2 – IEC 62631-2-3:2024 © IEC 2024
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions, abbreviated terms and symbols . 7
3.1 Terms and definitions . 7
3.2 Abbreviated terms and symbols . 9
4 Principle of method . 10
4.1 Principle of measurement. 10
4.2 Edge effect of electrodes . 11
5 Electrodes . 11
5.1 Design and manufacture of electrodes . 11
5.2 Edge effect of the measuring electrode . 13
6 Samples . 13
7 Measuring voltage . 13
8 Environmental conditions for measurements . 13
9 Measurement of thickness for films . 14
10 Measurement procedure . 14
11 Report . 14
12 Repeatability, reproducibility and replicability . 14
Annex A (normative) Correction method of measured permittivity and dielectric
dissipation factor for a sample with scabrous surfaces . 15
A.1 General . 15
A.2 Physical model . 15
A.3 Relationship between the measured permittivity and the real permittivity . 16
A.4 Relationship between the measured dielectric dissipation factor and the real
dielectric dissipation factor . 21
A.5 Method of correction for the sample with scabrous surfaces . 25
Annex B (informative) Suggestions for the manufacture of electrodes . 26
B.1 General . 26
B.2 Materials . 26
B.3 Manufacture of electrodes . 26
B.4 Evaluation methods of flatness and roughness. 26
B.5 Resistance of the measuring electrode system. 26
Bibliography . 27

Figure 1 – Diagram of the three-electrode system . 12
Figure A.1 – Schematic diagram of the profile including scabrous surfaces of sample
and polished flat electrodes, with the density thickness and apparent thickness
(mechanical thickness) . 15
Figure A.2 – Physical model of the scabrous surfaces of the sample and polished flat
electrodes . 15

Figure A.3 – Equivalent circuits with the sample, the gap and the electrodes . 16
Figure A.4 – Relationship between the measured permittivity, the real permittivity, the
void ratio and the contact ratio . 21
Figure A.5 – Relationship between the measured dielectric dissipation factor, the real
dielectric dissipation factor, the void ratio and the contact ratio . 25

Table 1 – Dimensional parameters of the three-electrode system and the relationship
between the measured ε for the thickness of sample and the measured capacitance . 12
x
– 4 – IEC 62631-2-3:2024 © IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DIELECTRIC AND RESISTIVE PROPERTIES OF
SOLID INSULATING MATERIALS –
Part 2-3: Relative permittivity and dissipation factor –
Contact electrode method for insulating films – AC methods

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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shall not be held responsible for identifying any or all such patent rights.
IEC 62631-2-3 has been prepared by IEC technical committee 112: Evaluation and qualification
of electrical insulating materials and systems. It is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
112/631/FDIS 112/641/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
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 webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
IMPORTANT – The "colour inside" logo on the cover page of this document 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 62631-2-3:2024 © IEC 2024
INTRODUCTION
Measuring the relative permittivity and the dielectric dissipation factor (tan δ) of thin insulating
polymer films with a thickness of approximately 10 μm to 100 μm without any additional layer
is important for insulation applications. There is currently a lack of suitable technology and
standard for the measurement of the relative permittivity and dielectric dissipation factor of very
thin single-layer polymer films. By using multilayer polymer films with 20 to 50 layers, it can be
feasible to get the average value of the relative permittivity and dielectric dissipation factor of
an insulating polymer film, but the effect of air gap inside should not be ignored. With metallized
electrodes on the surface of the polymer film, it is possible to get acceptable results of the
relative permittivity and dielectric dissipation factor of an insulating polymer film in research
laboratory. This document provides the measuring technology and the test method for the
relative permittivity and dielectric dissipation factor of thin insulating polymer films without any
additional layer or metallization on the sample, under technical frequency.

DIELECTRIC AND RESISTIVE PROPERTIES OF
SOLID INSULATING MATERIALS –
Part 2-3: Relative permittivity and dissipation factor –
Contact electrode method for insulating films – AC methods

1 Scope
This part of IEC 62631 specifies the measuring technology and the test method for the relative
permittivity and dielectric dissipation factor of thin single layer insulating polymer film without
any additional metallization on the sample surface. The adaptive thickness range is
approximately 10 μm to 100 μm. The proposed frequency is the power frequency (50 Hz or
60 Hz), and it is also suitable in the technical frequency range from 1 Hz to 1 MHz.
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 60674-2, Specification for plastic films for electrical purposes – Part 2: Methods of test
ISO 4593, Plastics – Film and sheeting – Determination of thickness by mechanical scanning
ISO 14644-1, Cleanrooms and associated controlled environments – Part 1: Classification of
air cleanliness by particle concentration
ISO 21920-2, Geometrical product specifications (GPS) – Surface texture: Profile – Part 2:
Terms, definitions and surface texture parameters
3 Terms, definitions, abbreviated terms and symbols
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1.1
thin insulating polymer film
insulating polymer film, planar, even and smooth, without any additional layer, with a 10 μm to
100 μm uniform thickness
– 8 – IEC 62631-2-3:2024 © IEC 2024
3.1.2
AC bridge
instrument that uses the balance method to measure the capacitance and loss of a capacitor
sample under AC voltage
EXAMPLE Capacitor bridge.
Note 1 to entry: The AC bridge usually works under power frequency with a very high accuracy and with a low
applied voltage.
Note 2 to entry: In some special cases, the AC bridge can also work under a technical frequency.
3.1.3
impedance material analyser
instrument that uses the AC current method to measure the capacitance and dielectric loss of
a capacitor
Note 1 to entry: The impedance material analyser works under a relatively low voltage and with a large band range,
but its accuracy is usually relatively low.
Note 2 to entry: The impedance material analyser uses five terminals to measure the device parameters and
therefore a suitable adaptor for the three-electrode sample is necessary.
3.1.4
power frequency
frequency used for the power system, which is usually of 50 Hz or 60 Hz
3.1.5
apparent thickness
mechanical thickness
thickness of a sample measured by a mechanical apparatus, which is equivalent to the "bulking
thickness" specified in IEC 60674-2
3.1.6
density thickness
thickness of a sample measured from the density of the sample, which is equivalent to the
"gravimetric thickness" specified in IEC 60674-2
3.1.7
void ratio
α
percentage increase between the apparent thickness and the density thickness, which is
dependent on the surface roughness
Note 1 to entry: For a sample with a scabrous surface, the apparent thickness and the density thickness are
different.
Note 2 to entry: The void ratio α is expressed in per cent (%) and is defined by Formula (1):
d − d
xd
α ⋅100(%)
(1)
d
x
where
d is the apparent thickness of the sample in μm;
x
d is the density thickness of the sample in μm.
d
Note 3 to entry: The apparent thickness and the density thickness should be measured by using the same sample
in accordance with ISO 4593.
=
3.1.8
contact ratio
η
percentage ratio of the contact area over the total area
Note 1 to entry: Samples with scabrous surfaces cannot have a perfect contact with the high flatness and low
roughness surface of the electrode. The contact area is the area between the dielectric material and the electrode
that remain in contact. The total area is the apparent area of the sample, usually equal to the area of the electrode.
Note 2 to entry: The contact ratio is dependent on the sample surface roughness and is defined by Formula (2):
S
contact
η ⋅100(%)
(2)
S
total
where
S is the contact area;
contact
S is the total area;
total
η is the contact ratio in %.
3.1.9
surface roughness of sample
R
a
arithmetic mean height in μm of the sample profile expressed by Formula (3) in accordance with
ISO 21920-2
l
e
R = zx dx (3)
( )
a
∫
l
e
where
l is the evaluation length of the sample profile;
e
z(x) is the function that describes the height of the assessed scale-limited profile.
3.2 Abbreviated terms and symbols
AC alternating current
HRC hardness Rockwell C scale
RH relative humidity
α void ratio
d apparent thickness of the sample in μm
x
d density thickness of the sample in μm
d
η contact ratio
R surface roughness of sample in μm
a
S area of the electrode
S contact area
contact
total area
S
total
l evaluation length of the sample profile
e
z(x) function that describes the height of the assessed scale-limited profile
=
– 10 – IEC 62631-2-3:2024 © IEC 2024

C complex capacitance
x
C real part of the complex capacitance
x
ε electric constant
ε complex permittivity
x
ε relative permittivity
x
ε′ real part of the complex permittivity
ε″ imaginary part of the complex permittivity
d thickness of the planar film sample
x
tan δ dielectric dissipation factor
k ratio between the measured dielectric dissipation factor and the real dielectric
dissipation factor
g gap between the guarded electrode and the measuring electrode
4 Principle of method
4.1 Principle of measurement

The complex capacitance C of the dielectric sample with the electrode can be obtained by
x
using an AC bridge or an impedance material analyser. For a planar, even and smooth film

sample, the relationship between the complex permittivity  and the complex capacitance C
ε
x x
is expressed by Equation (4).
εεS
0x

C =
(4)
x
d
x
where d is the thickness of the planar film sample, S is the area of the electrode and ε is the
x 0
electric constant (also called permittivity of vacuum). Therefore, the complex permittivity of the
dielectric materials can be derived as shown in Equation (5).
d
x

εC = .
(5)
xx
εS
The relationship of the complex permittivity  with the real part ε′, imaginary part ε″ and
ε
x
dielectric dissipation factor tan δ is expressed as shown in Equation (6).
′ ′′
ε ε+jε

x

′′
 ε
tanδ= ,
(6)

′
ε

′
εε=
x

=
where the real part ε′ is called relative permittivity ε , and the imaginary part ε″ is called dielectric
x
loss index. By using an AC bridge, the dielectric dissipation factor tan δ and the real part C of
x

the complex capacitance C can be measured directly. The relative permittivity ε of the
x x
dielectric material can be obtained by Equation (7).
d
x
εC=
(7)
xx
εS
4.2 Edge effect of electrodes
Owing to manufacturing limitations, the gap between the measuring electrode and the guard
ring will be more than 0,5 mm. Dielectric measurements are subject to the edge effect of
electrodes. In the case of samples having a thickness equal to or greater than 0,5 mm, the
guard ring electrode has been found effective to reduce the edge effect of electrodes. However,
for samples having a thickness less than 0,5 mm, the guard ring electrode does not significantly
reduce the edge effect since the gap between the measuring electrode and the guard ring is
much bigger than the thickness of the sample. In this case, owing to the limitation of mechanical
manufacture, the gap between the measuring electrode and the guard ring will be much bigger
than the thickness of the sample. See also 5.2.
5 Electrodes
5.1 Design and manufacture of electrodes
The design and manufacture of the measuring electrodes is the most critical parameter of this
test method. The measuring system is composed of three electrodes, a measuring electrode
(M), a guard electrode (G) and a high-voltage electrode (H). The allowed dimensions of the
electrodes are provided in Figure 1 and Table 1. The measuring electrode (M) and the high-
voltage electrode (H) shall have a surface roughness of less than 0,012 µm and a relative
flatness less than 0,5 µm. It shall be noted that the provided surface conditions are very
important to ensure adequate contact between the electrodes and the sample. Since the
thickness of the sample is relatively thin, the diameter of the measuring electrode should not
be too big to avoid a large, measured capacitance that would make the selection of the
measuring instrument difficult.

– 12 – IEC 62631-2-3:2024 © IEC 2024

Key
D diameter of the measuring electrode M
D inner diameter of the guarded electrode G
D outer diameter of the guarded electrode G
diameter of the high-voltage electrode H
D
Figure 1 – Diagram of the three-electrode system
In Figure 1, the gap between the guarded electrode and the measuring electrode, which can be
calculated by g = (D − D )/2, is kept to about 1 mm.
2 1
Table 1 – Dimensional parameters of the three-electrode system and the relationship
between the measured ε for the thickness of sample and the measured capacitance
x
D D D D H ε
1 2 3 4 1 x
mm mm mm mm mm
37,93 ± 0,05 39,93 ± 0,1 60 70 0,5 ± 0,02
CdpF ⋅ mm / 10 or
( ) ( )
x x
or 40,0 ± 0,1
CdnF ⋅ μm / 10
( ) ( )
x x
The material of electrode M and electrode H shall satisfy the following conditions: good
conductivity, non-ferromagnetic, anti-rust, and enough rigidity and hardness. More information
about the manufacture of electrodes can be found in Annex B.
The material of electrode G can be a metallic material with good conductivity, non-ferromagnetic,
anti-rust, like stainless steel or brass with surface plating protection, etc.

5.2 Edge effect of the measuring electrode
The sample thickness shall be between 10 µm and 100 µm, with the diameter D
(37,93 ± 0,05) mm of electrode M. Therefore, the ratio of the capacitance due to the edge effect
−3
of the measuring electrode to the measured capacitance of the sample is not more than 10 .
Since the measurement error caused by the edge effect is much smaller than the errors caused
by other factors, such as the measuring error of the thickness and the measurement error of
the electrode diameter, for the measurements described in this document, the edge effect error
can be neglected.
6 Samples
The sample is a polymer film without any additional layer and having a thickness between 10 µm
and 100 µm. The sample shall have a uniform thickness, a soft, planar, even and smooth
surface without an evaporated metallization electrode on it. The sample dimension shall be
2 2
larger than the diameter of the electrode H, approximately 80 mm × 80 mm . If the surface
roughness R of the sample is more than 0,05 µm or, if the void ratio of the sample is more than
a
1,0 %, except for porous or cellular materials, the measurement results shall be corrected by
the method described in Annex A.
The sample is placed between the measuring electrode M and the high-voltage electrode H.
The sample is not shown in Figure 1, because it is very thin compared to the sizes of the
electrodes.
7 Measuring voltage
The voltage applied on the sample shall ensure that the electric field between electrode H and
electrode M is below 10 kV/mm. To minimize the effect of non-linear phenomena, the applied
electric field should preferably be ≤ 3 kV/mm. If this is not possible, higher electric fields can
be used but it should be noted that non-linear phenomena may affect the measurements. If an
AC bridge is used, it is suggested that the voltage for the 20 μm sample be kept below 100 V.
When using an impedance material analyser, although the voltage applied on the sample is
relatively low, its sensitivity and accuracy are also relatively low, therefore the use of an AC
bridge is recommended for measurements.
8 Environmental conditions for measurements
To avoid any dust and any fine particles between the electrode and the sample, the
measurements shall be carried out in a clean chamber or in a clean room, in accordance with
ISO 14644-1.
To avoid any air gap or air bubble that may affect the contact condition between the electrode
and the sample, the measurements shall be performed in a vacuum condition. For the purpose
of this test, a vacuum condition with 1 Pa (0,007 5 Torr) has been found to be suitable.
NOTE Although no requirements are provided for the temperature conditions of the testing environment, if the
temperature is not a known factor potentially affecting the result of the sample under test, the test is initially performed
at ambient temperature.
The testing environment relative humidity shall be less than 50 %. Before the measurement,
the sample should be immersed in absolute ethanol for 2 s to 3 s then dried for use.
To ensure adequate contact conditions between the sample and the electrodes a pressure
between 20 kPa and 50 kPa shall be applied on the sample.

– 14 – IEC 62631-2-3:2024 © IEC 2024
9 Measurement of thickness for films
The thickness of the sample shall be measured in accordance with ISO 4593 and IEC 60674-2.
10 Measurement procedure
Five test specimens are prepared for the required treatments. Each specimen shall be cleaned
with absolute ethanol in a clean chamber to ensure that there are no visible particles on the
specimens. After further conditioning for 6 h under standard dry conditions (18 °C to 28 °C and
< 15 % RH), the surface of the specimens shall be checked again for the presence of particles.
Then relative permittivity and dielectric dissipation factor are acquired by the following steps:
1) Measure the thickness for each sample.
2) Measure the surface roughness of the samples if necessary.
3) Measure the apparent thickness and the density thickness of the samples.
4) Measure the capacitance and the dielectric dissipation factor for each sample.
5) Then permittivity and dielectric dissipation factor are acquired by Equation (5) and
Equation (6).
6) If the void ratio of the film sample α is more than 0,01, correct the measured results by using
the method in Annex A.
11 Report
The report shall include the following information:
– name, identification, materials specification, colour, source and manufacturer's code of the
specimen;
– temperature of the test specimen and relative humidity of the measuring environment;
– condition of the sample pre-treatment;
– vacuum for the measurement;
– measuring instrument identification and accuracy of test equipment;
– location and date of testing;
– test voltage and test frequency;
– mechanical pressure on the sample measuring electrode in Pascal;
– number of samples;
– numbers of tests, date and time of tests;
– each single value and the average of capacitance, permittivity and dielectric dissipation
factor respectively;
– any other important observations, if applicable.
12 Repeatability, reproducibility and replicability
The measurements of the relative permittivity and the dielectric dissipation factor are dependent
on numerous aspects.
Experiences have shown that measurements are valuable if the repeatability, the reproducibility
and the replicability for the relative permittivity are within 5 % and if the dielectric dissipation
factor is within 20 % of the measured value.

Annex A
(normative)
Correction method of measured permittivity and dielectric dissipation
factor for a sample with scabrous surfaces
A.1 General
For a sample with scabrous surfaces, in the case where the void ratio α is bigger than 0,01, it
is necessary to correct the measured results because the contact between the sample surface
and the electrodes is not so good.
A.2 Physical model
The contact condition between the scabrous surfaces of the sample and the polished flat
electrodes is shown in Figure A.1. The apparent thickness (mechanical thickness) is bigger than
the density thickness. The void ratio α is determined from the apparent thickness and the density
thickness.
Figure A.1 – Schematic diagram of the profile including scabrous surfaces of sample
and polished flat electrodes, with the density thickness and apparent thickness
(mechanical thickness)
The physical model for the scabrous surfaces of the sample and polished flat electrodes is
shown in Figure A.2. The air gap between the sample and the electrodes can be considered the
equivalent concentrated gap with the thickness d , and its surface area is determined by the
contact ratio η. The area of the equivalent concentrated gap is (1 − η)S, where S is the area of
the measuring electrode in Equation (4) and Equation (7).

Figure A.2 – Physical model of the scabrous surfaces
of the sample and polished flat electrodes

– 16 – IEC 62631-2-3:2024 © IEC 2024
Based on the physical model in Figure A.2, the diagrams of the equivalent circuit are shown in
Figure A.3.
Figure A.3 – Equivalent circuits with the sample, the gap and the electrodes
A.3 Relationship between the measured permittivity and the real permittivity
From the analysis of the equivalent circuit, the following relationship between the measured
permittivity ε and the real permittivity ε shown in Equation (A.1) can be derived. The
x r
relationship between the measured tan δ and the real tan δ is shown in Equation (A.2). In
x
Equation (A.1) and Equation (A.2), α is the void ratio of the film sample, η is the contact ratio,
with the limited condition: αη≤−1 .
22 2 2
 
α ηε +−αηε 2αηε +αε tan δ+
( r r rr)
 
εε= /
xr
  (A.1)
22 2 2 2 2 2
 
α ηε −2α ηε −αηε +α η+αη +αε +η −α−21η+
 r rr r 
22 2 22 2 2 2
α ε tan δ+α ε −2α ε −2αηε +α +2αη+2αε +η −2α−+21η
( r r rr r )
22 2 22 2 2 2 2 2

α ηε tan δδ+ (α ηε − 2α ηε − 2αη ε +α η+αη + 2αηε +η −−α 2η+ 1) tan
r r rr r
 (A.2)
tanδ =
x
22 2 2 22 2 2 2 2 2
α ηε +αη ε − 22αηε +αε tan δ+α ηε − α ηε −αη ε +α η+αη +αε +ηα−− 2η+ 1
( r r rr) r r r r
Equations (A.1) and (A.2) are very complex, but if the higher order term of tan δ is ignored, they
can be simplified to Equations (A.3) and (A.4) as follows:
1−η+αη(ε −1)
r (A.3)
εε=
xr
1−η+αε( −1)
r
(η++αη αε −1)± (η++αη αε −1) − 4αη(η+α−1)ε (A.4)
x x x
ε =
r
2αη
The result is the same as the result of the equivalent circuit without taking account of the
dielectric loss tan δ.
The simplified Equation (A.5) and Equation (A.6) for the relationship between the measured
tan δ and the real tan δ are as follows:
x
22 2 2 2 2 2
α ηε − 2α ηε − 2αη ε +α η+αη + 2αηε +η −α− 2η+1 tanδ
( )
r rr r
(A.5)
tanδ =
x
22 2 2 2 2 2
α ηε − 2α ηε −αη ε +α η+αη +αε +η −α− 21η+
r rr r

αε (1−η)

r (A.6)
tanδ 1+ tanδk= tanδ
 x x
αηα(ε −1) +η+ 22⋅ε − ηε +(1−ηα) −

rr r)
(

Equations (A.4) and (A.6) are still too complex to understand, so they are shown in figures.
The relationship between permittivity ε , and contact ratio η, is shown in Figure A.4.
r
=
– 18 – IEC 62631-2-3:2024 © IEC 2024

a) Relationship between permittivity ε and contact ratio η while ε = 1,6
r x
b) Relationship between permittivity ε and contact ratio η while ε = 1,8
r x
c) Relationship between permittivity ε and contact ratio η while ε = 2,0
r x
d) Relationship between permittivity ε and contact ratio η while ε = 2,2
r x
e) Relationship between permittivity ε and contact ratio η while ε = 2,4
r x
f) Relationship between permittivity ε and contact ratio η while ε = 2,6
r x
– 20 – IEC 62631-2-3:2024 © IEC 2024

g) Relationship between permittivity ε and contact ratio η while ε = 2,8
r x
h) Relationship between permittivity ε and contact ratio η while ε = 3,0
r x
i) Relationship between permittivity ε and contact ratio η while ε = 3,2
r x
j) Relationship between permittivity ε and contact ratio η while ε = 3,4
r x
Figure A.4 – Relationship between the measured permittivity,
the real permittivity, the void ratio and the contact ratio
A.4 Relationship between the measured dielectric dissipation factor and the
real dielectric dissipation factor
The dielectric loss tan δ, is given by:
 
α⋅ε ⋅−1 η
 ( ) 
r (A.7)
tanδ= 1+ ⋅⋅tanδk= tanδ
  xx
α⋅⋅η α⋅ ε −1 +η+22⋅ε − ⋅⋅ηε + 1−η −α
 ( ) ( ) 
( r rr)
 
There is only a small difference (1,02 ≤ k ≤ 1,32) between a measured tan δ and a real tan δ
x
in any case. They are shown in Figure A.5 as follows.

– 22 – IEC 62631-2-3:2024 © IEC 2024

a) Relationship between difference k and contact ratio η while ε = 1,6
r
b) Relationship between difference k and contact ratio η while ε = 1,8
r
c) Relationship between difference k and contact ratio η while ε = 2,0
r
d) Relationship between difference k and contact ratio η while ε = 2,2
r
e) Relationship between difference k and contact ratio η while ε = 2,4
r
f) Relationship between difference k and contact ratio η while ε = 2,6
r
– 24 – IEC 62631-2-3:2024 © IEC 2024

g) Relationship between difference k and contact ratio η while ε = 2,8
r
h) Relationship between difference k and contact ratio η while ε = 3,0
r
i) Relationship between difference k and contact ratio η while ε = 3,2
r
j) Relationship between difference k and contact ratio η while ε = 3,4
r
Figure A.5 – Relationship between the measured dielectric dissipation factor, the real
dielectric dissipation factor, the void ratio and the contact ratio
A.5 Method of correction for the sample with scabrous surfaces
When the surface roughness R of the sample is over 0,05 μm, or the void ratio of the sample
a
is bigger than 1,0 %, except in the case of porous or cellular materials, it is recommended to
correct the measured results.
The measured permittivity can be corrected by Equation (A.4), and the measured dielectric
dissipation factor can be corrected by Equation (A.6). They also can be corrected by using the
correcting curves in Figure A.4 and Figure A.5. For the correction factor α (void ratio), it can be
determined by the apparent thickness and density thickness in accordance with Equation (1).
For the correction factor η (contact ratio), it can be determined by the surface analysis and
Equation (2). The specific method can be found in ISO 25178-2. From Figure A.4 and
Figure A.5, it can be noted that the correcting permittivity (real permittivity) is not sensitive to
the contact ratio from 0,2 to 0,6. Therefore, for the sample with a single scabrous surface, it
can be 0,5. For the sample with a double scabrous surface, it can be 0,3. For the correcting
dielectric dissipation factor (real dielectric dissipation factor), there is only a small difference
(1,02 ≤ k ≤ 1,32) between a measured tan δ and a real tan δ in any case. Therefore, it can be
x
kept to k = 1,2 for the sample with a single scabrous surface, and to k = 1,25 for the sample
with a double scabrous surface.

– 26 – IEC 62631-2-3:2024 © IEC 2024
Annex B
(informative)
Suggestions for the manufacture of electrodes
B.1 General
The high flatness and the low roughness of the electrode’s measuring surface are key
requirements for measurement in this document. Therefore, the following recommendations are
provided.
B.2 Materials
The material for the measuring electrode M and the high-voltage electrode H shall have
adequate rigidity and hardness, not for the electrical measurement, but for the mechanical
manufacture, in order to obtain high flatness and low roughness as specified in 5.1. The
electrode manufacturer shall take into consideration both the material and the related heat
treatment process. The suggested hardness is within an HRC rating of 58 to 62. An example of
material is the alloy 7Mn15Cr2Al3V2WMo (C 0,65 to 0,75, Si ≤ 0,80, Mn 14,50 to 16,00,
...