ASTM D3756-97(2004)
(Test Method)Standard Test Method for Evaluation of Resistance to Electrical Breakdown by Treeing in Solid Dielectric Materials Using Diverging Fields
Standard Test Method for Evaluation of Resistance to Electrical Breakdown by Treeing in Solid Dielectric Materials Using Diverging Fields
SIGNIFICANCE AND USE
This is a laboratory test designed to simulate the effects of (1) the presence of rough interfaces between conductor or semiconductive screen and primary insulation in an insulation system, (2) the presence of foreign particles (contaminants) in an insulation system, and (3) the presence of small voids or cavities within the insulation.
This test method provides comparative data. The degree of correlation with actual performance in service has not been established.
SCOPE
1.1 This test method covers the evaluation and comparison of the resistance of solid organic dielectric materials to the initiation or growth, or both, of tubular tree-like channels resulting from partial discharge (corona) and molecular decomposition that occur in the region of very high, diverging electric fields.
1.2 This test method is primarily for use at a power frequency of 50 or 60 Hz.
1.3 The test may be carried out at room temperature or temperatures above or below room temperature. The temperature should not exceed the softening or melting point of the sample material.
1.4 This test method can be used for any solid material into which needles can be cast, molded, or inserted with heat after molding. The resistance to tree initiation is measured by the double-needle characteristic voltage, which is only applicable to non-opaque materials so that tree can be observed optically. The resistance to tree initiation and growth is reported by the double-needle voltage life, which is applicable to both opaque and non-opaque materials.
1.5 The values stated in SI units are to be regarded as the standard.
1.6 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.
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Standards Content (Sample)
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An American National Standard
Designation:D3756–97 (Reapproved 2004)
Standard Test Method for
Evaluation of Resistance to Electrical Breakdown by Treeing
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in Solid Dielectric Materials Using Diverging Fields
This standard is issued under the fixed designation D3756; 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.
INTRODUCTION
When failure occurs in solid organic dielectrics that are subjected to very high, continuous, and
nonuniform electrical gradients, it generally occurs by a mechanism called treeing. Materials of
different molecular structures have different degrees of resistance to failure by treeing, and this
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resistance can sometimes be increased by the addition of other materials in low concentration.
Treesthatgrowbyamoleculardegradationmechanismresultingfrompartialdischarge(corona)are
called electrical trees to distinguish them from water and electrochemical trees which are quite
different.
This test method makes use of two opposing thin cylindrical electrodes, one sharpened to a point,
the other with a hemispherical end. They are molded or inserted into blocks of the material to be
tested. Because of the shape of the electrodes this is often called a needle test. This test provides a
statistical estimate of electrical treeing initiation and propagation of solid dielectric materials in high,
diverging electrical fields.
1. Scope 1.4 This test method can be used for any solid material into
which needles can be cast, molded, or inserted with heat after
1.1 This test method covers the evaluation and comparison
molding. The resistance to tree initiation is measured by the
of the resistance of solid organic dielectric materials to the
double-needle characteristic voltage, which is only applicable
initiation or growth, or both, of tubular tree-like channels
to non-opaque materials so that tree can be observed optically.
resultingfrompartialdischarge(corona)andmoleculardecom-
The resistance to tree initiation and growth is reported by the
positionthatoccurintheregionofveryhigh,divergingelectric
3,4
double-needle voltage life, which is applicable to both opaque
fields.
and non-opaque materials.
1.2 This test method is primarily for use at a power
1.5 The values stated in SI units are to be regarded as the
frequency of 50 or 60 Hz.
standard.
1.3 The test may be carried out at room temperature or
1.6 This standard does not purport to address all of the
temperatures above or below room temperature. The tempera-
safety concerns, if any, associated with its use. It is the
ture should not exceed the softening or melting point of the
responsibility of the user of this standard to establish appro-
sample material.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
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This test method is under the jurisdiction of ASTM Committee D09 on
Electrical and Electronic Insulating Materials and is the direct responsibility of
2. Referenced Documents
Subcommittee D09.12 on Electrical Tests.
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2.1 ASTM Standards:
Current edition approved March 1, 2004. Published March 2004. Originally
approved in 1990. Last previous edition approved in 1997 as D3756 – 97. DOI: D149 Test Method for Dielectric Breakdown Voltage and
10.1520/D3756-97R04.
Dielectric Strength of Solid Electrical Insulating Materials
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Symposium on Engineering Dielectrics, ASTM STP 783 , ASTM, 1982, and
at Commercial Power Frequencies
Symposium on Engineering Dielectrics, ASTM STP 926, ASTM, 1986.
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D1711 Terminology Relating to Electrical Insulation
W. D. Wilkens, Chapter 7, “Statistical Methods for the Evaluation of Electrical
Insulating Systems,” Engineering Dielectrics, Vol IIB, Electrical Properties of Solid
Insulating Materials, Measurement Techniques, R. Bartnikas, Editor, ASTM STP
926 , ASTM, Philadelphia, 1987.
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R. M. Eichorn, Chapter 4, “Treeing in Solid Organic Dielectric Materials,” For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Engineering Dielectrics, Vol IIA, Electrical Properties of Solid Insulating Materi- contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
als: Molecular Structure and Electrical Behavior, R. Bartnikas and R. M. Eichorn, Standards volume information, refer to the standard’s Document Summary page on
Editors, ASTM STP 783, ASTM Philadelphia, 1983. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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D3756–97 (2004)
D1928 Practice for Preparation of Compression-Molded 6.2 Current—Se
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