ASTM D1932-04(2009)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D1932 − 04(Reapproved 2009) An American National Standard
Standard Test Method for
Thermal Endurance of Flexible Electrical Insulating
Varnishes
This standard is issued under the fixed designation D1932; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 2. Referenced Documents
1.1 Thistestmethodcoversthedeterminationoftherelative 2.1 ASTM Standards:
thermal endurance of flexible electrical insulating varnishes by D149 Test Method for Dielectric Breakdown Voltage and
determining the time necessary at elevated temperatures to DielectricStrengthofSolidElectricalInsulatingMaterials
decrease the dielectric breakdown of the varnish to an arbi- at Commercial Power Frequencies
trarily selected value when applied to a standard glass fiber D374 Test Methods for Thickness of Solid Electrical Insu-
fabric. lation
D580 Specification for Greige Woven Glass Tapes and
1.2 This test method does not apply to varnishes that lose a
Webbings
high percentage of their dielectric breakdown voltage when
D1346 Test Method for Testing Electrical Insulating Var-
flexed before elevated temperature exposure as prescribed in
nishes for 180 C and Above (Withdrawn 1986)
the screening test (Section 9). Examples of such varnishes are
D1711 Terminology Relating to Electrical Insulation
those used for high speed armatures and laminated structures.
D2518 Specification for Woven Glass Fabrics for Electrical
Also, this test method is not applicable to varnishes which
Insulation
distort sufficiently during thermal elevated temperature expo-
D5423 Specification for Forced-Convection Laboratory Ov-
sure so that they cannot be tested using the curved electrode
ens for Evaluation of Electrical Insulation
assembly.
D6054 Practice for Conditioning Electrical Insulating Mate-
1.3 Thermal endurance is expressed in terms of a tempera-
rials for Testing
ture index.
2.2 IEEE Publications:
1.4 The values stated in SI units are to be regarded as IEEE No. 101A Guide for the Statistical Analysis of Ther-
standard. No other units of measurement are included in this mal Life Test Data (including Appendix A)
standard. 2.3 IEC Publications:
IEC 60216 Guide for the Determination of Thermal Endur-
NOTE 1—There is no equivalent IEC or ISO standard.
ance Properties of Electrical Insulating Materials (Part 1)
1.5 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-
bility of regulatory limitations prior to use. For specific hazard
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
statements, see Section 7.
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
This test method is under the jurisdiction of ASTM Committee D09 on the ASTM website.
Electrical and Electronic Insulating Materials and is the direct responsibility of The last approved version of this historical standard is referenced on
Subcommittee D09.01 on Electrical Insulating Varnishes, Powders and Encapsulat- www.astm.org.
ing Compounds. Available from the Institute of Electrical and Electronics Engineers, 1828 LSt.,
Current edition approved Oct. 1, 2009. Published February 2010. Originally NW, Suite 1202, Washington, DC 20036–5104.
approved in 1967. Last previous edition approved in 2004 as D1932 – 04. DOI: Available from American National Standards Institute, 25 West 43rd St., 4th
10.1520/D1932-04R09. Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D1932 − 04 (2009)
3.1.1 temperature index (TI), n—a number which permits (300 V/mil) of original thickness unless lower endpoint values
comparison of the temperature/time characteristics of an elec- are agreed upon or indicated in the applicable material speci-
trical insulating material, or a simple combination of materials, fications.
based on the temperature in degrees Celsius which is obtained
by extrapolating the Arrhenius plot of endpoint time versus
5. Significance and Use
temperature to a specified time, usually 20 000 h.
5.1 A major factor affecting the long term performance of
3.1.2 thermal endurance graph, n—an Arrhenius plot.
insulating materials is thermal degradation. Other factors, such
as moisture and vibration, may cause failures after the material
3.1.3 thermal endpoint time, n—the time necessary for a
has been weakened by thermal degradation.
specific property of a material, or a simple combination of
materials, to degrade to a defined end point when aged at a
5.2 An electrical insulating varnish is effective in protecting
specified temperature.
electrical equipment only as long as it retains its physical and
electrical integrity.
3.1.4 thermal life endpoint time, n—a graphical representa-
tion of thermal endpoint time at a specified exposure tempera-
5.3 The thermal degradation of the varnish results in weight
ture in which the value of a property of a material, or a simple
loss, porosity, crazing, and generally a reduction in flexibility.
combination of materials, is measured at room temperature and
Degradation of the varnish can be detected by a decrease in
the values plotted as a function of time.
dielectric strength, which is therefore used as the failure
criterion for this test method.
3.1.5 Refer to Terminology D1711 for definitions of other
terms.
5.4 Electrical insulating varnishes undergo flexing in ser-
vice due to vibration and thermal expansion. For this reason,
4. Summary of Test Method
this functional test includes flexing and elongation of the
insulation.The electrodes used in this test method are designed
4.1 Specimens are prepared using glass cloth coated with
the selected varnish to a specified build. to elongate the outer surface of the specimen 2 % with respect
to the neutral axis of the base fiber while being tested for
4.2 Specimens are exposed in air at a minimum of three
dielectric breakdown.
temperatures above the expected use temperature of the mate-
rial. Dielectric breakdown voltage tests in air at room tempera-
6. Apparatus
ture are periodically made to determine the exposure time at
eachtesttemperaturerequiredtoreducethebreakdownvoltage 6.1 Electrode Test Fixture—The fixture shall be in accor-
to a value of 12 kV/mm (300 V/mil) of original thickness. dance with the dimensions shown in Fig. 1 and Fig. 2.
These values are used to construct a thermal endurance graph Electrodes shall be of polished brass, with the upper electrode
by which temperature indices may be estimated. having a mass of 1.8 6 0.05 kg (4.0 6 0.1 lb).
4.3 This test method is not applicable to materials having an 6.2 Dielectric Breakdown Test Set—The set shall meet the
initial dielectric breakdown voltage of less than 12 kV/mm requirements of Test Method D149.
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 = 0.003 cm (0.001 in.)
Tolerance for H = 0.005 cm (0.002 in.)
FIG. 1 Single-Shot Curved Electrode Details
D1932 − 04 (2009)
8. Test Specimens
8.1 Prepare glass cloth panels 150 by 300 mm (6 by 12 in.)
with the 300 mm (12 in.) dimension parallel to the warp
threads. Use fabric style No. 116 in accordance with Specifi-
cation D2518. Heat clean the specimens as specified in
Methods D1346 to arrive at a volatile content not to exceed
0.1 % in accordance with Specification D580.
8.2 Prepare the test specimen by dipping a glass cloth panel
described in 8.1 in the varnish at the standard laboratory
atmosphere described in Practice D6054. Prior to dipping
panels, adjust the viscosity of the varnish to be tested by trial
so that two coats will give an over-all thickness of 0.178 6
0.0127 mm (0.007 6 0.0005 in.).
8.3 Immerse the panel in the varnish in the direction of the
300 mm (12 in.) length until bubbling stops, mechanically
withdraw at the rate of 90–110 mm (3.5–4.3 in.)/min, and then
allow to drain for ⁄2 h at the standard laboratory atmosphere.
8.4 Bake the specimen in the same vertical position as
dipped. Reverse the specimen, dip a second time, and drain as
above. Bake the specimen at such a temperature and for such
a time as specified by the varnish manufacturer.
8.5 Prepare a set of twelve or more specimens for each
exposure temperature.
9. Screening Test
FIG. 2 Curved Electrode and Holder
9.1 Prepare one test specimen. Condition the specimen 48 h
in the standard laboratory atmosphere. Cut five 25 by 300 mm
(1 by 12 in.) test strips from the center of the specimen,
discardingthe12.5by300mm( ⁄2by12in.)portionfromeach
6.3 Ovens—A forced draft constant-temperature oven con- 1
side. Bend each of the five test strips once, 115 mm (4 ⁄2 in.)
forming to Specification D5423, Type II.
from one end, 180° around a mandrel 3.175 mm (0.125 in.) in
diameter.
6.4 Micrometer—Dead-weight type specified in Test Meth-
odsD374,havingapresserfoot6.35 60.03mm(0.25 60.001
9.2 Measure the dielectric breakdown voltage on the bent
in.) in diameter and an anvil of at least 50 mm (2 in.) diameter
area of each five test strips. In like manner, make five
and shall exert a pressure of 0.17 6 0.01 MPa (25 6 2 psi) on
breakdown tests on the unbent area at a distance of 75 mm (3
the pressure foot.
in.) from the bend. Use the apparatus described in 6.2 in
accordance with the procedure described in 11.2, except use
6.5 Test Specimen Frame—A frame for each test specimen
6.4 mm ( ⁄4 in.) diameter electrodes as specified inTest Method
made from a straight length (approximately 1 m (39 in.)) of
D149.
round Nichrome AWG No. 14 wire. Bend the wire to form a
rectangle having inside dimensions of 150 by 300 mm (6 by 12
9.3 Average the dielectric breakdown voltage for the five
in.). Overlap the ends of the wire approximately 50 mm (2 i
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