ASTM D1932-97
(Test Method)Standard Test Method for Thermal Endurance of Flexible Electrical Insulating Varnishes
Standard Test Method for Thermal Endurance of Flexible Electrical Insulating Varnishes
SCOPE
1.1 This test method covers the determination of the relative thermal endurance of flexible electrical insulating varnishes by determining the aging time necessary at elevated temperatures to decrease the dielectric breakdown of the varnish to an arbitrarily selected value when applied to a standard glass fiber fabric.
1.2 This test method does not apply to varnishes that lose a high percentage of their dielectric breakdown voltage when flexed before aging as prescribed in the screening test (Section 9). Examples of such varnishes are those used for high speed armatures and laminated structures. Also, this test method is not applicable to varnishes which distort sufficiently during thermal aging so that they cannot be tested using the curved electrode assembly.
1.3 Thermal endurance is expressed in terms of a temperature index.
1.4 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. For specific hazard statements, see Section 7.
1.5 The values stated in SI units are the standard.
Note 1--There is no equivalent IEC or ISO standard.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 1932 – 97 An American National Standard
Standard Test Method for
Thermal Endurance of Flexible Electrical Insulating
Varnishes
This standard is issued under the fixed designation D 1932; 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 (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope D 580 Specification for Greige Woven Glass Tapes and
Webbings
1.1 This test method covers the determination of the relative
D 618 Practice for Conditioning Plastics and Electrical
thermal endurance of flexible electrical insulating varnishes by
Insulating Materials for Testing
determining the aging time necessary at elevated temperatures
D 1346 Methods of Testing Electrical Insulating Varnishes
to decrease the dielectric breakdown of the varnish to an
for 180°C and Above
arbitrarily selected value when applied to a standard glass fiber
D 1711 Terminology Relating to Electrical Insulation
fabric.
D 2518 Specification for Woven Glass Fabrics for Electrical
1.2 This test method does not apply to varnishes that lose a
Insulation
high percentage of their dielectric breakdown voltage when
D 5423 Specification for Forced-Convection Laboratory
flexed before aging as prescribed in the screening test (Section
Ovens for Evaluation of Electrical Insulation
9). Examples of such varnishes are those used for high speed
2.2 IEEE Publications:
armatures and laminated structures. Also, this test method is
IEEE No. 101A Guide for the Statistical Analysis of Ther-
not applicable to varnishes which distort sufficiently during
mal Life Test Data (including Appendix A)
thermal aging so that they cannot be tested using the curved
2.3 IEC Publications:
electrode assembly.
IEC 216 Guide for the Determination of Thermal Endurance
1.3 Thermal endurance is expressed in terms of a tempera-
Properties of Electrical Insulating Materials (Parts 1 and
ture index.
2)
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3. Terminology
responsibility of the user of this standard to establish appro-
3.1 Definitions:
priate safety and health practices and determine the applica-
3.1.1 temperature index (TI), n—a number which permits
bility of regulatory limitations prior to use. For specific hazard
comparison of the temperature/time characteristics of an elec-
statements, see Section 7.
trical insulating material, or a simple combination of materials,
1.5 The values stated in acceptable metric units are to be
based on the temperature in degrees Celsius which is obtained
regarded as the standard.
by extrapolating the Arrhenius plot of life versus temperature
2. Referenced Documents to a specified time, usually 20 000 h.
3.1.2 thermal endurance graph, n—an Arrhenius plot.
2.1 ASTM Standards:
3.1.3 thermal life, n—the time necessary for a specific
D 149 Test Method for Dielectric Breakdown Voltage and
property of a material, or a simple combination of materials, to
Dielectric Strength of Solid Electrical Insulating Materials
degrade to a defined end point when aged at a specified
at Commercial Power Frequencies
temperature.
D 374 Test Methods for Thickness of Solid Electrical Insu-
3.1.4 thermal life curve, n—a graphical representation of
lation
thermal life at a specified aging temperature in which the value
1 3
This test method is under the jurisdiction of ASTM Committee D-9 on Annual Book of ASTM Standards, Vol 07.01.
Electrical and Electronic Insulating Materials and is the direct responsibility of Discontinued; see 1986 Annual Book of ASTM Standards, Vol 10.01.
Subcommittee D09.01 on Electrical Insulating Varnishes, Powders, and Encapsu- Annual Book of ASTM Standards, Vol 10.02.
lating Compounds. Available from the Institute of Electrical and Electronics Engineers, 345 E. 47th
Current edition approved Sept. 10, 1997. Published November 1997. Originally St., New York, NY 10017.
published as D 1932 – 67. Last previous edition D 1932 – 96. Available from American National Standards Institute, 11 West 42nd St., 13th
Annual Book of ASTM Standards, Vol 10.01. Floor, New York, NY 10036.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 1932
of a property of a material, or a simple combination of insulation. The electrodes used in this test method are designed
materials, is measured at room temperature and the values to elongate the outer surface of the specimen 2 % with respect
plotted as a function of time. to the neutral axis of the base fiber while being tested for
dielectric breakdown.
4. Summary of Test Method
6. Apparatus
4.1 Specimens are prepared using glass cloth coated with
the selected varnish to a specified build. 6.1 Electrode Test Fixture—The fixture shall be in accor-
4.2 Specimens are aged in air at a minimum of three dance with the dimensions shown in Fig. 1 and Fig. 2.
temperatures above the expected use temperature of the mate- Electrodes shall be of polished brass, with the upper electrode
rial. Dielectric breakdown voltage tests in air at room tempera- having a mass of 1.8 6 0.05 kg (4.0 6 0.1 lb).
ture are periodically made to determine the time of aging at 6.2 Dielectric Breakdown Test Set— The set shall meet the
each test temperature required to reduce the breakdown voltage requirements of Test Method D 149.
to a value of 12 kV/mm (300 V/mil) of original thickness. 6.3 Ovens—A forced draft constant-temperature oven con-
These values are used to construct a thermal endurance graph forming to Specification D 5423, Type II.
by which temperature indices may be estimated. 6.4 Micrometer—Dead-weight type specified in Test Meth-
4.3 This test method is not applicable to materials having an ods D 374, having a presser foot 6.356 0.03 mm (0.25 6 0.001
initial dielectric breakdown voltage of less than 12 kV/mm in.) in diameter and an anvil of at least 50 mm (2 in.) diameter
(300 V/mil) of original thickness unless lower endpoint values and shall exert a pressure of 0.17 6 0.01 MPa (25 6 2 psi) on
are agreed upon or indicated in the applicable material speci- the pressure foot.
fications. 6.5 Test Specimen Frame—A frame for each test specimen
made from a straight length (approximately 1 m (39 in.)) of
5. Significance and Use
round Nichrome AWG No. 14 wire. Bend the wire to form a
5.1 A major factor affecting the life of insulating materials is
rectangle having inside dimensions of 150 by 300 mm (6 by 12
thermal degradation. Other factors, such as moisture and in.). Overlap the ends of the wire approximately 50 mm (2 in.)
vibration, may cause failures after the material has been
at one corner. Attach the specimen to the frame.
weakened by thermal degradation. 6.6 Test Fixture for Aging Specimen— A suitable fixture for
5.2 An electrical insulating varnish is effective in protecting
mounting the specimen frames a minimum of 25 mm (1 in.)
electrical equipment only as long as it retains its physical and apart so that they are secured at top and bottom.
electrical integrity. 6.7 Dipping Apparatus—An apparatus capable of removing
5.3 The thermal degradation of the varnish results in weight the specimen from the varnish at the rate of 100 mm (4
loss, porosity, crazing, and generally a reduction in flexibility. in.)/min.
Degradation of the varnish can be detected by a decrease in
7. Hazards
dielectric strength, which is therefore used as the failure
criterion for this test method. 7.1 Precaution—Varnish must not be heated at tempera-
5.4 Electrical insulating varnishes undergo flexing in ser- tures above the flash point when inadequate ventilation and the
vice due to vibration and thermal expansion. For this reason, possibility of flames or sparks exist. Varnish should be stored
this functional test includes flexing and elongation of the in sealed containers. The precautions shall also apply to the
Insulation Thickness Dimension R Dimension H Dimension D
cm in. cm in. cm in. cm in.
0.018 0.007 0.455 0.179 0.815 0.321 0.871 0.344
Tolerance for R and D 5 0.003 cm (0.001 in.)
Tolerance for H 5 0.005 cm (0.002 in.)
FIG. 1 Single-Shot Curved Electrode Details
D 1932
(1 by 12 in.) test strips from the center of the specimen,
discarding the 12.5 by 300 mm ( ⁄2 by 12 in.) portion from each
side. Bend each of the five test strips once, 115 mm (4 ⁄2 in.)
from one end, 180° around a mandrel 3.175 mm (0.125 in.) in
diameter.
9.2 Measure the dielectric breakdown voltage on the bent
area of each five test strips. In like manner, make five
breakdown tests on the unbent area at a distance of 75 mm (3
in.) from the bend. Use the apparatus described in 6.2 in
accordance with the procedure described in 11.2, except use
6.4 mm ( ⁄4 in.) diameter electrodes as specified in Test Method
D 149.
9.3 Average the dielectric breakdown voltage for the five
bent and unbent areas respectively. The ratio of average
breakdown voltage of the bent area to the unbent area shall be
greater than 0.5 %, if this method is to be considered appli-
cable.
10. Selection of Test Temperatures
10.1 The material shall be exposed at not less than three
temperatures. Any temperature that gives a thermal life of less
than 100 h is considered too high to be used in this evaluation.
The lowest temperature chosen shall be such that (1) a thermal
life of at least 5000 h is obtained and (2) it not be more than
25°C higher than the estimated temperature index. Preferable
exposure temperatures shall differ by at least 20°C.
10.2 Exposure temperatures are to be selected in accordance
with those shown in Table 1 as indicated by the anticipated
FIG. 2 Curved Electrode and Holder
temperature index of the material under test. It is recommended
that exploratory tests be first made at the highest temperature to
handling of the called-for reagents and solvents.
obtain data establishing the validity of the 100 h minimum life
requirement (see 10.1), an
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