SIST HD 429 S1:1998
(Main)Methods of test for volume resistivity and surface resistivity of solid electrical insulating materials
Methods of test for volume resistivity and surface resistivity of solid electrical insulating materials
Gives test procedures and calculations for the determination of volume and surface resistivity. Establishes recommendations for: values of voltage and time of application; nature and geometry of electrodes temperature and humidity of atmosphere and test specimens; conditioning of test specimens.
Prüfverfahren für den spezifischen Durchgangswiderstand und den spezifischen Oberflächenwiderstand von festen, elektrisch isolierenden Werkstoffen
Méthodes pour la mesure de la résistivité transversale et de la résistivité superficielle des matériaux isolants électriques solides
Définit les procédés de mesure ainsi que les calculs de résistivité transversale et résistivité superficielle. Etablit des recommandations pour les valeurs de tension et durée d'application - nature et géométrie des électrodes - température et humidité de l'atmosphère et des éprouvettes, conditionnement des éprouvettes.
Methods of test for volume resistivity and surface resistivity of solid electrical insulating materials (IEC 60093:1980)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST HD 429 S1:1998
01-oktober-1998
Methods of test for volume resistivity and surface resistivity of solid electrical
insulating materials (IEC 60093:1980)
Methods of test for volume resistivity and surface resistivity of solid electrical insulating
materials
Prüfverfahren für den spezifischen Durchgangswiderstand und den spezifischen
Oberflächenwiderstand von festen, elektrisch isolierenden Werkstoffen
Méthodes pour la mesure de la résistivité transversale et de la résistivité superficielle des
matériaux isolants électriques solides
Ta slovenski standard je istoveten z: HD 429 S1:1983
ICS:
29.035.01 Izolacijski materiali na Insulating materials in
splošno general
SIST HD 429 S1:1998 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST HD 429 S1:1998
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SIST HD 429 S1:1998
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SIST HD 429 S1:1998
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SIST HD 429 S1:1998
NORME
CEI
INTERNATIONALE IEC
93
INTERNATIONAL
Deuxième édition
STAN DARD
Second edition
1980
Méthodes pour la mesure de la résistivité
transversale et de la résistivité superficielle
des matériaux isolants électriques solides
Methods of test for volume resistivity
and surface resistivity of solid electrical
insulating materials
© CEI 1980 Droits de reproduction réservés — Copyright — all rights reserved
Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in
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les microfilms, sans l'accord écrit de l'éditeur. in writing from the publisher.
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SIST HD 429 S1:1998
CONTENTS
Page
FOREWORD 5
PREFACE 5
Clause
1. Scope 7
2. Definitions 7
Significance 9
3.
11
4. Power supply
11
5. Measuring methods and accuracy
15
6. Test specimens
17
7. Electrode material
8. Specimen handling and mounting 21
9. Conditioning 21
10. Test procedure 21
11. Calculation 23
12. Report 25
29
APPENDIX A — Examples of measuring methods and their accuracy
35
APPENDIX B — Formulae for calculating A and p
FIGURES 36
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SIST HD 429 S1:1998
INTERNATIONAL ELECTROTECHNICAL COMMISSION
METHODS OF TEST FOR VOLUME RESISTIVITY
AND SURFACE RESISTIVITY OF SOLID ELECTRICAL
INSULATING MATERIALS
FOREWORD
1)
The formal decisions or agreements of the IEC on technical matters, prepared by Technical Committees on which all the
National Committees having a special interest therein are represented, express, as nearly as possible, an international
consensus of opinion on the subjects dealt with.
2)
They have the form of recommendations for international use and they are accepted by the National Committees in that
sense.
3) In order to promote international unification, the IEC expresses the wish that all National Committees should adopt
the text of the IEC recommendation for their national rules in so far as national conditions will permit. Any divergence
between the IEC recommendation and the corresponding national rules should, as far as possible, be clearly indicated
in the latter.
PREFACE
This standard has been prepared by Sub-Committee 15A: Short-time Tests, of IEC Technical
Committee No. 15: Insulating Materials.
It forms the second edition of IEC Publication 93.
A first draft was discussed at the meeting held in Toronto in 1976. As a result of this meeting, a draft,
Document 15A(Central Office)35, was submitted to the National Committees for approval under the
Six Months' Rule in November 1977.
Amendments, Document 15A(Central Office)39, were submitted to the National Committees for
approval under the Two Months' Procedure in October 1979.
The National Committees of the following countries voted explicitly in favour of publication:
Austria Italy
Belgium Korea (Republic of)
Brazil - New Zealand
Bulgaria Norway
Canada Poland
Spain
China
Czechoslovakia Sweden
Denmark Switzerland
Egypt United Kingdom
France United States of America
Germany Yugoslavia
Ireland
Other IEC publications quoted in this standard:
Publications Nos. 167: Methods of Test for the Determination of the Insulation Resistance of Solid Insulating Materials.
212: Standard Conditions for Use Prior to and during the Testing of Solid Electrical Insulating
Materials.
260: Test Enclosures of Non-injection Type for Constant Relative Humidity.
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SIST HD 429 S1:1998
METHODS OF TEST FOR VOLUME RESISTIVITY
AND SURFACE RESISTIVITY OF SOLID ELECTRICAL
INSULATING MATERIALS
1. Scope
These methods of test cover procedures for the determination of volume and surface resistance
and calculations for the determination of volume and surface resistivity of solid electrical insulating
materials.
Both volume resistance and surface resistance tests are affected by the following factors: the
magnitude and time of voltage application,. the nature and geometry of the electrodes, and the
temperature and humidity of the ambient atmosphere and of the specimens during conditioning
and measurement. Recommendations are made for these factors.
2. Definitions
2.1 Volume resistance
The quotient of a direct voltage applied between two electrodes placed on two faces (opposite)
of a specimen, and the steady-state current between the electrodes, excluding current along the
surface, and neglecting possible polarization phenomena at the electrodes.
Note. — Unless otherwise specified, the volume resistance is determined after 1 min of electrification.
2.2 Volume resistivity
The quotient of a d.c. electric field strength and the steady-state current density within an
insulating material. In practice it is taken as the volume resistance reduced to a cubical unit
volume.
Note. — The SI unit of volume resistivity is the ohm metre. In practice the unit ohm centimetre is also used.
2.3 Surface resistance
The quotient of a direct voltage applied between two electrodes on a surface of a specimen,
and the current between the electrodes at a given time of electrification, neglecting possible
polarization phenomena at the electrodes.
Notes 1. — Unless otherwise specified, the surface resistance is determined after 1 min of electrification.
2. — The current generally passes mainly through a surface layer of the specimen and any associated moisture
and surface contaminant, but it also includes a component through the volume of the specimen.
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SIST HD 429 S1:1998
9
2.4 Surface resistivity
The quotient of a d.c. electric field strength, and the linear current density in a surface layer of an
insulating material. In practice it is taken as the surface resistance reduced to a square area.
The size of the square is immaterial.
Note. — The SI unit of surface resistivity is the ohm. In practice this is sometimes referred to as "ohms per square".
2.5 Electrodes
Measuring electrodes are conductors of defined shape, size and configuration in contact with
the specimen being measured.
General note. — Insulation resistance is the quotient of a direct voltage applied between two electrodes in contact with
a specimen and the total current between the electrodes. The insulation resistance depends on both
volume and surface resistivity of the specimen (see IEC Publication 167: Methods of Test for the
Determination of the Insulation Resistance of Solid Insulating Materials).
3. Significance
3.1 Insulating materials are used in general to isolate components of an electrical system from each
other and from earth; solid insulating materials may also provide mechanical support. For these
purposes it is generally desirable to have the insulation resistance as high as possible, consistent
with acceptable mechanical, chemical and heat-resisting properties. Surface resistance changes very
rapidly with humidity, while volume resistance changes only slowly, although the final change may
be greater.
3.2 Volume resistivity can be used as an aid in the choice of an insulating material for a specific
application. The change of resistivity with temperature and humidity may be great and must be
known when designing for operating conditions. Volume resistivity measurements are often used
in checking the uniformity of an insulating material, either with regard to processing or to
detect conductive impurities that affect the quality of the material and that may not be readily
detectable by other means.
3.3 When a direct voltage is applied between electrodes in contact with a specimen, the current
through it decreases asymptotically towards a steady-state value. The decrease of current with
time may be due to dielectric polarization and the sweep of mobile ions to the electrodes.
For materials having volume resistivities less than about 10 10 f2 m (10 12
S2 cm), the steady-
state is in general reached within 1 min, and the resistance is then determined after this time of
electrification. For materials of higher volume resistivity the current may continue to decrease
for several minutes, hours, days, or even weeks. For such materials, therefore, longer electrification
times are used, and, if relevant, the material is characterized by the time dependence of the volume
resistivity.
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SIST HD 429 S1:1998
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3.4 Surface resistance or surface conductance cannot be measured accurately, only approximated,
because more or less volume conductance is nearly always involved in the measurement.
The measured value is largely a property of the contamination of the surface of the specimen
at the time of measurement. However, the permittivity of the specimen influences the deposition
of contaminants, and their conductive capabilities are affected by the surface characteristics
of the specimen. Thus surface resistivity is not a material property in the usual sense, but can
be considered to be related to material properties when contamination is involved.
Some materials, such as laminates, may have quite different resistivities in a surface layer
and in the interior. It may therefore be of interest to measure the intrinsic property of a
clean surface. Cleaning procedures aimed at producing consistent results should be fully specified
bearing in mind the possible effect of solvents and other factors of the cleaning procedure on
the surface characteristics.
The surface resistance, especially when high, often changes in an erratic manner, and in general
depends strongly on the time of electrification; for measurements, 1 min of electrification is
usually specified.
4. Power supply
A source of very steady direct voltage is required. This may be provided either by batteries
or by a 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 100 V, 250 V,
500 V, 1000 V, 2500 V, 5000 V, 10000 V and 15000 V. Of these the most frequently used
are 100 V, 500 V and 1 000 V.
In some cases, the specimen resistance depends upon the polarity of the applied voltage.
If the resistance is polarity dependent, this should be indicated. The geometric (arithmetic mean
of the logarithmic exponents) mean of the two resistance values is taken as the result.
Since the specimen resistance may be voltage dependent, the test voltage should be stated.
5. Measuring methods and accuracy
5.1 Methods
The methods commonly in use for measuring high resistances are either direct methods or
comparison methods.
The direct methods depend upon simultaneous measurement of the direct voltage applied to the
unknown resistance and the current through it (voltmeter-ammeter method).
The comparison methods establish the ratio of the unknown resistance to the resistance of a
known resistor, either in a bridge circuit, or by comparison of currents through the resistances at
fixed voltage.
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Examples illustrating the principles are described in Appendix A.
The voltmeter-ammeter method requires a reasonably accurate voltmeter, but the sensitivity
and accuracy of the method depend mainly on the properties of the current measuring device, which
may be a galvanometer, an electronic amplifier instrument, or an electrometer.
The bridge method requires only a sensitive current detector as null indicator, and the accuracy
is mainly determined by the known bridge arm resistors, which are obtainable with high precision
and stability over a wide range of resistance values.
The accuracy of the current comparison method depends on the accuracy of the known resistor,
and on the stability and linearity of the current measuring device, including associated measuring
resistors, etc., whereas the exact values of current are insignificant, as long as the voltage is constant.
Determination of volume resistivity in accordance with Sub-clause 10.1 using a galvanometer
in the voltmeter-ammeter method is feasible for resistances up to about 10 11 Q. For higher values,
the use of a d.c. amplifier or electrometer is recommended.
In the bridge method, it is not possible to measure the current directly in the short-circuited
specimen (see Sub-clause 10.1).
The methods utilizing current measuring devices permit automatic recording of the current to
facilitate determination of the steady state (Sub-clause 10.1).
Special circuits and instruments for measuring high resistance are available. These may be used,
provided that they are sufficiently accurate and stable, and that, where needed, they enable the
specimen to be properly short-circuited, and the current measured before electrification.
5.2 Accuracy
The measuring device should be capable of determining the unknown resistance with an overall
accuracy of at least ± 10% for resistances below 10
1 ° Q, and ± 20% for higher values. See also
Appendix A.
5.3 Guarding
The insulation of the measuring circuit is composed of materials which, at best, have properties
comparable with those of the material under test. Errors in the measurement of the specimen may
arise from:
a)
stray current from spurious external voltages which are usually unknown in magnitude and
often sporadic in character;
b) undue shunting of the specimen resistance, reference resistors, or the current measuring device
by insulation, having resistance of unknown, and possibly variable magnitude.
An approximate correction of these difficulties may be obtained by making the insulation
resistance of all parts of the circuit as high as possible under the conditions of use. This may
lead to unwieldy apparatus which is still inadequate for measurement of insulation resistances
higher than a few hundred megohms. A more satisfactory correction is obtained by using the
technique of guarding.
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SIST HD 429 S1:1998
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Guarding depends on interposing, in all critical insulated parts, guard conductors which
intercept all stray currents that might otherwise cause errors. The guard conductors are connected
together, constituting the guard system and forming with the measuring terminals a three terminal
network. When suitable connections are made, stray currents from spurious external voltages are
shunted away from the measuring circuit by the guard system, the insulation resistance from
either measuring terminal to the guard system shunts a circuit element which should be of very
much lower resistance, and the specimen resistance constitutes the only direct path between
the measuring terminals. By this technique the probability of error is considerably reduced.
Figure 1, page 36, shows the basic connections for guarded electrodes used for volume resistance
and surface resistance measurements.
Proper use of the guard system for the method involving current measurement is illustrated
in Figures 5 and 7, pages 39 and 40, where the guard system is shown connected to the junction
of the voltage source and current-measuring device. In Figure 6, page 40, for the Wheatstone
bridge method, the guard system is shown connected to the junction of the two lower-valued
resistance arms. In all cases, to be effective, guarding shall be complete, and shall include any
control operated by the observer in making the measurement.
Electrolytic, contact, or thermal e.m.f.'s. existing between guard and guarded terminals can be
compensated if they are small. Care must be taken that such e.m.f.'s do not introduce
appreciable errors in the measurements.
Errors in current measurements may result from the fact that the current-measuring device
is shunted by the resistance between the guarded terminal and the guard system. This resistance
should be at least 10 and preferably 100 times that of the current-measuring device. In some
bridge techniques, the guard and measuring terminal are brought to nearly the same potential
but a standard resistor in the bridge is shunted by the resistance between the unguarded
terminal and the guard system. This resistance should be at least 10 and preferably 100 times
that of the reference resistor.
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.
6. Test specimens
6.1 Volume resistivity
For the determination of volume resistivity the test specimen may have any practicable form
that allows the use of a third electrode to guard against error from surface effect. For specimens
that have negligible surface leakage, the guard may be omitted when measuring volume
resistance, provided that it has been shown that its omission has negligible effect on the result.
The gap on the surface of the specimen between the guarded and guard electrodes should
be of uniform width and as narrow as possible provided that the surface leakage does not cause
error in the measurement. A gap of 1 mm is usually the smallest practicable.
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SIST HD 429 S1:1998
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Examples of electrode arrangements with three electrodes are shown in Figures 2 and 3,
pages 37 and 38. In the measurement of volume resistance, electrode No. 1 is the guarded
electrode, No. 2 is the guard electrode, and No. 3 is the unguarded electrode. The diameter
dl (Figure 2), or length 1 1 (Figure 3) of the guarded electrode should be at least ten times
the specimen thickness h and for practical reasons usually at least 25 mm. The diameter d4
(or length l4)
of the unguarded electrode, and the outer diameter d3 of the guard electrode
(or length l 3
between the outer edges of the guard electrodes) should be equal to the inner
diameter d2 of the guard electrode (or length 12 between the inner edges of the guard electrodes)
plus at least twice the specimen thickness.
6.2 Surface resistivity
For the determination of surface resistivity the test specimen may have any practicable form
that allows the use of a third electrode to guard against error from volume effects. The three
electrode arrangements of Figures 2 and 3 are recommended. The resistance of the surface gap
between electrodes Nos. 1 and 2 is measured directly by using electrode No. 1 as the guarded
electrode, electrode No. 3 as the guard electrode and electrode No. 2 as the unguarded electrode.
The resistance so measured includes the surface resistance between electrodes Nos. 1 and 2 and
the volume resistance between the same two electrodes. With suitable dimensioning of the
electrodes, however, the effect of the volume resistance can be made negligible for wide ranges
of ambient conditions and material properties. This condition may be achieved for the arrangement
of Figures 2 and 3 when the electrodes are dimensioned so that the surface gap width g is at
least twice the specimen thickness; 1 mm is normally the smallest practicable. The diameter
dl (or length 1 1) of the guarded electrode should be at least ten times the specimen thickness h,
and for practical reasons usually at least 25 mm.
Alternatively, straight electrodes or other arrangements with suitable dimensions may be used.
Note. — Due to the influence of current through the interior of the test specimen the calculated value of surface resistivity
may depend strongly on the specimen and electrode dimensions. For comparative determinations it is therefore
recommended to use specimens of identical form with the electrode arrangement of Figure 2 with 50 mm,
d =
1
d2 = 60 mm, and d 80 mm.
3 =
7.
Electrode material
7.1 General
The electrodes for insulating materials should be of a material that is readily applied, allows
intimate contact with the specimen surface and introduces no appreciable error because of electrode
resistance or contamination of the specimen. The electrode material should be corrosion resistant
under the conditions of the test. The following are typical electrode materials that may be used.
The electrodes shall be used with suitable backing plates of the given form and dimensions.
It may be advantageous to use two different electrode materials or two methods of application
to see if appreciable error is introduced.
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SIST HD 429 S1:1998
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7.2 Conductive silver paint
Certain types of commercially available, high-conductivity silver paints, either air-drying or
low-temperature-baking varieties ar
...
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