IEC TS 62836:2020

IEC TS 62836 ®
Edition 1.0 2020-11
TECHNICAL
SPECIFICATION
colour
inside
Measurement of internal electric field in insulating materials – Pressure wave
propagation method
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IEC TS 62836 ®
Edition 1.0 2020-11
TECHNICAL
SPECIFICATION
colour
inside
Measurement of internal electric field in insulating materials – Pressure wave

propagation method
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.220.99; 29.035.01 ISBN 978-2-8322-8993-8

– 2 – IEC TS 62836:2020 © IEC 2020
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and abbreviated terms . 7
3.1 Terms and definitions . 7
3.2 Abbreviated terms . 7
4 Principle of the method . 8
5 Samples . 10
6 Electrode materials . 10
7 Pressure pulse wave generation . 10
8 Set-up of the measurement. 11
9 Calibrating the electric field . 12
10 Measurement procedure . 12
11 Data processing for the experimental measurement . 13
12 Measurement examples . 14
12.1 Samples. 14
12.2 Pressure pulse generation . 14
12.3 Calibration of sample and signal . 14
12.4 Testing sample and experimental results . 15
Annex A (informative) Preconditional method of the original signal for the PWP
method . 19
A.1 Simple integration limitation . 19
A.2 Analysis of the resiliency effect and correction procedure . 20
A.3 Example of the correction procedure on a PE sample . 21
A.4 Estimation of the correction coefficients . 22 ®
A.5 MATLAB code . 24
Annex B (informative) Linearity verification of the measuring system . 26
B.1 Linearity verification . 26
B.2 Sample conditions. 26
B.3 Linearity verification procedure . 26
B.4 Example of linearity verification. 26

Figure 1 – Principle of the PWP method . 9
Figure 2 – Measurement set-up for the PWP method . 11
Figure 3 – Sample of circuit to protect the amplifier from damage by a small discharge
on the sample . 11
Figure 4 – Measured current signal under –5,8 kV . 14
Figure 5 – First measured current signal (< 1 min) . 15
Figure 6 – Measured current signal under –46,4 kV, after 1,5 h under high voltage . 15
Figure 7 – Measured current signal without applied voltage, after 1,5 h under high
voltage . 16
Figure 8 – Internal electric field distribution under –5,8 kV . 16
Figure 9 – Internal electric field distribution under –46,4 kV, at the initial state . 17

Figure 10 – Internal electric field distribution under –46,4 kV, after 1,5 h under high
voltage . 17
Figure 11 – Internal electric field distribution without applied voltage after 1,5 h under

high voltage . 18
Figure A.1 – Comparison between practical and perfect pressure pulses . 19
Figure A.2 – Original signal of the sample free of charge under moderate voltage . 20
Figure A.3 – Comparison between original and corrected reference signals with a
sample free of charge under moderate voltage . 21
Figure A.4 – Electric field in a sample under voltage with space charge calculated
from original and corrected signals . 22
Figure A.5 – Geometrical characteristics of the reference signal for the correction

coefficient estimation . 23
Figure A.6 – Reference signal corrected with coefficients graphically obtained and
adjusted . 23
Figure A.7 – Electric field in a sample under voltage with space charge calculated with
graphically obtained coefficient and adjusted coefficient . 24
Figure B.1 – Voltage signals obtained from the oscilloscope by the amplifier with

different amplifications . 27
Figure B.2 – Current signals induced by the sample, considering the input impedance
and the amplification of the amplifier . 27
Figure B.3 – Relationship between the measured current peak of the first electrode
and applied voltage . 28

Table A.1 – Variants of symbols used in the text . 24

– 4 – IEC TS 62836:2020 © IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MEASUREMENT OF INTERNAL ELECTRIC FIELD IN INSULATING
MATERIALS – PRESSURE WAVE PROPAGATION METHOD

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 this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
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preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
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Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
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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.
IEC TS 62836 has been prepared by IEC technical committee 112: Evaluation and qualification
of electrical insulating materials and systems. It is a Technical Specification
The text of this Technical Specification is based on the following documents:
Draft Report on voting
112/472/DTS 112/499/RVDTS
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 Technical Specification 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/standardsdev/publications.

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.

– 6 – IEC TS 62836:2020 © IEC 2020
INTRODUCTION
High voltage insulating cables, especially high voltage DC cables, are subject to charge
accumulation and this may lead to electrical breakdown if the electric field produced by the
charges exceeds the electrical breakdown threshold. With the trend to multiply power plants,
especially green power plants such as wind or solar generators, more cables will be used for
connecting these power plants to the grid and share the electric energy between countries.
Therefore, the materials for the cables, and even the structure of these cables, when
considering electrodes or the junction between cables, need a standardized procedure for
testing how the internal electric field can be characterized. The measurement of the internal
electric field would give a tool for comparing materials and help to establish thresholds on the
internal electric field for high voltage applications in order to limit breakdown risks as much as
possible. The pressure wave propagation (PWP) method has been used by many researchers
to measure the space charge distribution and the internal electric field distribution in insulators.
However, since experimental equipment, with slight differences, is developed independently by
researchers throughout the world, it is difficult to compare the measurement results between
the different equipment.
The procedure outlined in this Technical Specification provides a reliable point of comparison
between different test results carried out by different laboratories in order to avoid interpretation
errors. The IEC has established a project team to develop a procedure for the measurement of
PWP.
MEASUREMENT OF INTERNAL ELECTRIC FIELD IN INSULATING
MATERIALS – PRESSURE WAVE PROPAGATION METHOD

1 Scope
This document provides an efficient and reliable procedure to test the internal electric field in
the insulating materials used for high-voltage applications, using the pressure wave propagation
(PWP) method. It is suitable for a sample with homogeneous insulating materials and an electric
field higher than 1 kV/mm, but it is also dependent on the thickness of the sample and the
pressure wave generator.
2 Normative references
There are no normative references in this document.
3 Terms, definitions and abbreviated terms
For the purposes of this document, the following terms, definitions and abbreviated terms 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 Terms and definitions
3.1.1
pressure wave propagation
PWP
pressure wave that is propagated in a material containing electric charges and measurement
of the induced electric signal from electrodes
3.2 Abbreviated terms
CB carbon black
EVA ethylene-vinyl acetate
LDPE low density polyethylene
LIPP laser induced pressure pulse
PE polyethylene
PIPP piezoelectric induced pressure pulse
PMMA poly (methyl methacrylate)
PWP pressure wave propagation
S/N signal to noise ratio
– 8 – IEC TS 62836:2020 © IEC 2020
4 Principle of the method
The principle of the PWP method is shown schematically in Figure 1.
The space charge in the dielectric and the interface charge are forced to move by the action of
a pressure wave. The charge displacement then induces an electrical signal in the circuit which
is an image of the charge distribution in short-circuit current measurement conditions. The
expression for the short-circuit current signal with time t is
d
∂p x, t
( )
, (1)
i t = C BE x dx
() ( )
∫
∂t
where
E(x) is the electric field distribution in the sample at position x;
d is the thickness of sample;
p(x, t) is the pressure wave in the sample, which depends on the electrode materials,
dielectric sample material, the condition of coupling on the interface, etc.;
is the sample capacitance without the action of a pressure wave.
C
C depends on the thickness of the sample, and its surface area which is equal to the area of
action of the pressure wave.
The constant B χ 1−a/ε only depends on the characteristics of the dielectric materials. In
( )
this formula, is the coefficient of compressibility of the material, ε is the permittivity of the
χ
material and a is the coefficient of electrostriction of the material. For heterogeneous dielectric
materials, B is a function of space. For homogeneous dielectric materials, B is not a function of
space and can be put outside of the integral. In this proposition, only homogeneous dielectric
materials are considered, so B is a constant.
In Equation (1), the electric field distribution can be obtained if it is deconvolved.
=
Key
x is the position of pulse front
f
d is the original thickness of sample
d ≈ d in the case of a narrow pulse
a) Applied pressure pulse and measured short-circuit current signal

b) Measuring schematics
Figure 1 – Principle of the PWP method
The applied pressure wave can be generated by different techniques, but the same kind of
analysis can be done for any of these techniques. The main practical PWP method can be
divided into two ways: a pressure pulse is induced by a powerful laser pulse, a technique called
LIPP method, and a pressure pulse generated by a piezoelectric device, a technique called
PIPP. The sensibility and resolution of the PWP method depends mainly on the amplitude and
width of the pressure pulse. The advantage of the LIPP method is to produce highly sensitive
measurements without contact. The advantage of the PIPP method is to obtain the
measurement with a high measuring rate and allow a cost measurement system.

– 10 – IEC TS 62836:2020 © IEC 2020
In the case of a narrow pulse, for example when the width of the pressure pulse is much smaller
than the thickness of the sample, τ is the pressure pulse duration with τ<<min d , d /v ,
( )
0sx

td

 ′′
i t dt = C BE x p x, t dx
( ) ( ) ( )

∫∫
, (2)


x=vt

 s
where
v is the sound speed in the sample;
s
E x,x=vt is the mean electric field during the pressure pulse width at the position x. For
( )
s
simplicity, it is shown as E(x=vt) in this document.
s
Because of sound loss and sound dispersion in polymer dielectrics, the amplitude of p( x,t) will
decrease, and the width of p x,t will increase during the propagation of a pressure pulse in
( )
p x,t
the sample. For polymer dielectrics, the sound dispersion is dominant, therefore, even if ( )
d
is not a constant in the dielectrics, its integral remains constant during its propagation
p( x,t)dx
∫
in the sample.
From the Equation (2) and from the signal obtained with a sample free of charges and submitted
d
to an intermediate voltage V , Bp x,t dx can be obtained since the electric field E x vt E
( ) ( )
0 s0
∫
is uniform in this case and the sample capacitance C is directly proportional to the thickness
of the sample. This can be used as a calibration base for the other measurements.
5 Samples
A dielectric insulating material is suggested, for example polyethylene, with a thickness of 1 mm
or 2 mm planar plaque sample with a diameter sufficiently large to avoid edge discharges,
typically larger than 20 cm with 5 cm centred electrodes for 60 kV.
6 Electrode materials
The selection of electrode materials depends on the method of the generation of the pressure
pulse wave. Usually, semi-conductive electrodes with ethylene-vinyl acetate (EVA) + carbon
black (CB) or polyethylene (PE) + carbon black (CB) are used. For laser PWP (also called LIPP),
the suitable thickness of the
...