ASTM D3426-97(2004)
(Test Method)Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials Using Impulse Waves
Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials Using Impulse Waves
SIGNIFICANCE AND USE
Insulating materials used in high-voltage equipment may be subjected to transient voltage stresses, resulting from such causes as nearby lightning strokes. This is particularly true of apparatus such as transformers and switchgear used in electrical-power transmission and distribution systems. The ability of insulating materials to withstand these transient voltages is important in establishing the reliability of apparatus insulated with these materials.
Transient voltages caused by lightning may be of either positive or negative polarity. In a symmetrical field between identical electrodes, the polarity has no effect on the breakdown strength. However, with dissimilar electrodes there may be a pronounced polarity effect. It is common practice when using dissimilar electrodes, to make negative that electrode at which the higher gradient will appear. When asymmetrical electrodes are used for testing materials with which the tester has no previous experience or knowledge, it is recommended that he make comparative tests with positive polarity and negative polarity applied to the higher gradient, or smaller electrode, to determine which polarity produces the lower breakdown voltage.
The standard wave shape is a 1.2 by 50-μs wave, reaching peak voltage in approximately 1.2 μs and decaying to 50 % of peak voltage in approximately 50 μs after the beginning of the wave. This wave is intended to simulate a lightning stroke that may strike a system without causing failure on the system.
For most materials, the impulse dielectric strength will be higher than either its power frequency alternating voltage or its direct voltage dielectric strengths. Because of the short time involved, dielectric heating and other thermal effects are largely eliminated during impulse testing. Thus, the impulse test gives values closer to the intrinsic breakdown strength than do longer time tests. From comparisons of the impulse dielectric strength with the values obtained from longer time...
SCOPE
1.1 This test method covers the determination of dielectric strength of solid electrical insulating materials under simulated-lightning impulse conditions.
1.2 Procedures are given for tests using standard 1.2 by 50 s full-wave impulses.
1.3 This test method is intended for use in determining the impulse dielectric strength of insulating materials, either using simple electrodes or functional models. It is not intended for use in impulse testing of apparatus.
1.4 This test method is similar to IEC Publication 243-3. All procedures in this test method are included in IEC 243-3. Differences between this test method and IEC 243-3 are largely editorial.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific precaution statements are given in Section 9.
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Designation: D3426 − 97(Reapproved 2004) An American National Standard
Standard Test Method for
Dielectric Breakdown Voltage and Dielectric Strength of
Solid Electrical Insulating Materials Using Impulse Waves
This standard is issued under the fixed designation D3426; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2.2 American National Standard:
C 68.1 Techniques for Dielectric Tests (IEEE Standard No.
1.1 This test method covers the determination of dielectric
4)
strength of solid electrical insulating materials under
2.3 IEC Standard:
simulated-lightning impulse conditions.
Pub 243-3 Methods of Test for Electric Strength of Solid
1.2 Procedures are given for tests using standard 1.2 by 50
Insulating Materials—Part 3:Additional Requirements for
µs full-wave impulses. 3
Impulse Tests
1.3 This test method is intended for use in determining the
3. Terminology
impulse dielectric strength of insulating materials, either using
simple electrodes or functional models. It is not intended for
3.1 Definitions:
use in impulse testing of apparatus.
3.1.1 Reference should be made to Fig. 1 for the symbols
1.4 This test method is similar to IEC Publication 243-3.All mentioned.
3.1.2 full-impulse-voltage wave, n—an aperiodic transient
procedures in this test method are included in IEC 243-3.
DifferencesbetweenthistestmethodandIEC243-3arelargely voltage that rises rapidly to a maximum value, then falls less
rapidly to zero.
editorial.
3.1.3 peak value of an impulse voltage wave, n— the
1.5 This standard does not purport to address all of the
maximum value of voltage.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3.1.4 virtual-peak value of an impulse voltage wave, n—a
priate safety and health practices and determine the applica-
value derived from a recording of an impulse wave on which
bility of regulatory limitations prior to use. Specific precaution
high-frequency oscillations or overshoot of limited magnitude
statements are given in Section 9.
maybepresent.Iftheoscillationshaveamagnitudeofnomore
than5 %ofthepeakvalueandafrequencyofatleast0.5MHz,
2. Referenced Documents
a mean curve may be drawn, the maximum amplitude of which
is the virtual-peak value. If the oscillations are of greater
2.1 ASTM Standards:
magnitude, the voltage wave is not acceptable for standard
D149 Test Method for Dielectric Breakdown Voltage and
tests.
DielectricStrengthofSolidElectricalInsulatingMaterials
3.1.5 virtual-front time of an impulse voltage wave,
at Commercial Power Frequencies
n—equal to 1.67 times the interval t between the instants when
D374 Test Methods for Thickness of Solid Electrical Insu-
f
the voltage is 0.3 and 0.9 times the peak value (t , Fig. 1).
lation 1
D2413 Practice for Preparation of Insulating Paper and
3.1.6 virtual origin of an impulse voltage wave, n—thepoint
Board Impregnated with a Liquid Dielectric
of intersection O with the line of zero voltage of a line drawn
through the points of 0.3 and 0.9 times the peak voltage on the
front of an impulse voltage wave.
This test method is under the jurisdiction of ASTM Committee D09 on 3.1.7 virtual time to half-value of an impulse voltage wave,
Electrical and Electronic Insulating Materials and is the direct responsibility of
n—the time interval t between the virtual origin O and the
2 1
Subcommittee D09.12 on Electrical Tests.
instant on the tail when the voltage has decreased to half the
Current edition approved March 1, 2004. Published March 2004. Originally
peak value.
approved in 1975. Last previous edition approved in 1997 as D3426 – 97. DOI:
10.1520/D3426-97R04.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D3426 − 97 (2004)
FIG. 1 Full-Impulse Voltage Wave
4. Summary of Test Method down strength. However, with dissimilar electrodes there may
be a pronounced polarity effect. It is common practice when
4.1 A series of sets-of-three voltage waves of a specified
using dissimilar electrodes, to make negative that electrode at
shape (see 5.3) is applied to the test specimen. The voltage of
which the higher gradient will appear. When asymmetrical
successive sets is increased in magnitude until breakdown of
electrodes are used for testing materials with which the tester
the test specimen occurs.
has no previous experience or knowledge, it is recommended
4.2 The procedures for sampling and specimen preparation
that he make comparative tests with positive polarity and
are as specified in the material specification or other document
negative polarity applied to the higher gradient, or smaller
calling for the use of this test method. The surrounding
electrode, to determine which polarity produces the lower
medium (air or other gas, or oil or other liquid) is also as
breakdown voltage.
specified if it differs from the medium in which the specimens
5.3 The standard wave shape is a 1.2 by 50-µs wave,
are finally conditioned for test.
reaching peak voltage in approximately 1.2 µs and decaying to
5. Significance and Use
50 % of peak voltage in approximately 50 µs after the
beginning of the wave. This wave is intended to simulate a
5.1 Insulating materials used in high-voltage equipment
lightning stroke that may strike a system without causing
may be subjected to transient voltage stresses, resulting from
failure on the system.
such causes as nearby lightning strokes. This is particularly
true of apparatus such as transformers and switchgear used in
5.4 For most materials, the impulse dielectric strength will
electrical-power transmission and distribution systems. The
be higher than either its power frequency alternating voltage or
ability of insulating materials to withstand these transient
its direct voltage dielectric strengths. Because of the short time
voltages is important in establishing the reliability of apparatus
involved, dielectric heating and other thermal effects are
insulated with these materials.
largely eliminated during impulse testing. Thus, the impulse
5.2 Transient voltages caused by lightning may be of either testgivesvaluesclosertotheintrinsicbreakdownstrengththan
positive or negative polarity. In a symmetrical field between do longer time tests. From comparisons of the impulse dielec-
identical electrodes, the polarity has no effect on the break- tric strength with the values obtained from longer time tests,
D3426 − 97 (2004)
inferences may be drawn as to the modes of failures under the mens for testing in oil by vacuum-impregnation with oil do not
various tests for a given material.Appendix X1 ofTest Method remove the specimen from oil even momentarily prior to
D149 should be referred to for further information on this testing.
subject.
9. Procedure
6. Apparatus
9.1 Warning— Lethal voltages are a potential hazard dur-
6.1 Impulse Generator, capable of applying to the test
ing the performance of this test. It is essential that the test
specimen a standard 1.2 by 50-µs wave of either positive or
apparatus, and all associated equipment electrically connected
negative polarity.The virtual front time shall be 1.2 µs 6 30 %
to it, be properly designed and installed for safe operation.
and the virtual time to half value 50 µs 6 20 %.The maximum
Solidly ground all electrically conductive parts which it is
voltage and the energy-storage capability must be sufficient to
possible for a person to contact during the test. Provide means
...
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