ASTM D7894/D7894M-14

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Designation: D7894/D7894M − 14
Standard Test Method for
Thermal Endurance of Coating Powders Used for Integral
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Bus Bar Insulation Systems
This standard is issued under the fixed designation D7894/D7894M; 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.
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1. Scope 2.2 IEEE Document:
IEEE 101A Simplified Method for Calculation of the Re-
1.1 This test method provides a procedure for evaluating
gression Line
thermal endurance of coating powders by determining the
length of aging time at selected elevated temperatures required
3. Terminology
to achieve dielectric breakdown at room temperature at a
3.1 Definitions—For definitions of terms used in this test
pre-determined proof voltage. Thermal endurance is expressed
method refer to Terminology D1711.
in terms of a temperature index.
1.2 This test method is applicable to insulating powders 4. Summary of Test Method
used over a substrate material of copper or aluminum.
4.1 Specimens are aged in air at a minimum of three
temperatures above the expected use temperature of the mate-
1.3 Units—The values stated in either SI units or inch-
rial. Exposure to ambient stress conditions, followed by
pound units are to be regarded separately as standard. The
dielectric proof voltage tests in an electrically conductive
values stated in each system are not necessarily exact equiva-
solution, are periodically conducted to determine the time of
lents; therefore, each system shall be used independently of the
aging at each elevated temperature required to reduce the
other. Combining values from the two systems is likely to
breakdown voltage to a pre-selected percentage of the original
result in non-conformance with the standard.
breakdown value. These thermal life values are used to
1.4 This standard does not purport to address all of the
construct a thermal endurance graph by means of which it is
safety concerns, if any, associated with its use. It is the
possible to estimate a temperature index, corresponding to a
responsibility of the user of this standard to establish appro-
thermal life as specified in the material specification or as
priate safety and health practices and determine the applica-
agreed upon between the user and the supplier. It is possible
bility of regulatory limitations prior to use. Specific precau-
that a material will have multiple indices, each corresponding
tionary statements are given in Section 7.
to a different thermal life as required by a given application.
2. Referenced Documents
5. Significance and Use
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2.1 ASTM Standards:
5.1 Amajorfactoraffectingthelifeofinsulatingmaterialsis
D149 Test Method for Dielectric Breakdown Voltage and
thermal degradation. It is possible that other factors, such as
Dielectric Strength of Solid Electrical Insulating Materials
moisture and vibration, will cause failures after the material
at Commercial Power Frequencies
has been weakened by thermal degradation.
D1711 Terminology Relating to Electrical Insulation
5.2 Electrical insulation is effective in electrical equipment
D5423 Specification for Forced-Convection Laboratory Ov-
only as long as it retains its physical and electrical integrity.
ens for Evaluation of Electrical Insulation
The following are potential indicators of thermal degradation:
weight change, porosity, crazing, and generally a reduction in
flexibility. Thermal degradation is usually accompanied by an
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This test method is under the jurisdiction of ASTM Committee D09 on
ultimate reduction in dielectric breakdown.
Electrical and Electronic Insulating Materials and is the direct responsibility of
5.3 This test method is useful in determining the thermal
Subcommittee D09.01 on Electrical Insulating Varnishes, Powders and Encapsulat-
ing Compounds.
endurance of coating powders applied over a copper or
Current edition approved Nov. 1, 2014. Published November 2014. DOI:
aluminum substrate material.
10.1520/D7894_D7894M-14.
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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
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Standards volume information, refer to the standard’s Document Summary page on Available from Institute of Electrical and Electronics Engineers, Inc. (IEEE),
the ASTM website. 445 Hoes Ln., P.O. Box 1331, Piscataway, NJ 08854-1331, http://www.ieee.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D7894/D7894M − 14
6. Apparatus rupture of the test chamber. Design test equipment, test
chambers, and test sp
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