ASTM D3145-97

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
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Designation: D 3145 – 97 An American National Standard
Standard Test Method for
Thermal Endurance of Electrical Insulating Varnishes by the
Helical Coil Method
This standard is issued under the fixed designation D 3145; 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 6054 Practice for Conditioning Electrical Insulating Ma-
terials for Testing
1.1 This test method covers the determination of the thermal
2.2 International Electrotechnical Commission Publica-
endurance of electrical insulating varnishes alone or in com-
tions:
binations with wire insulation. Changes in the helical coil bond
IEC 216 Guide for the Determination of Thermal Endurance
strength are used as the test criteria. The coils can be made
Properties of Electrical Insulation Materials (Parts 1 and
from bare aluminum or copper wire, or from film- or fiber-
2)
insulated magnet wire.
1.2 This standard does not purport to address all of the
3. Terminology
safety concerns, if any, associated with its use. It is the
3.1 Definitions of Terms Specific to This Standard:
responsibility of the user of this standard to establish appro-
3.1.1 bond strength, n—a measure of the force required to
priate safety and health practices and determine the applica-
separate surfaces which have been bonded together.
bility of regulatory limitations prior to use. For a specific
3.1.2 magnet wire, n—a metal electrical conductor, covered
precautionary statement, see Section 7.
with electrical insulation, for use in the assembly of electrical
1.3 The values stated in SI units are the standard. The values
inductive apparatus such as coils for motors, transformers,
given in parentheses are for information only.
generators, relays, magnets, etc.
NOTE 1—There is no similar or equivalent IEC standard.
3.1.2.1 Discussion—The electrical insulation is usually
composed of a film covering formed from a magnet wire
2. Referenced Documents
enamel applied over a bare conductor. In some specific
2.1 ASTM Standards:
applications, fibrous coverings, either taped or linear filament
D 1711 Terminology Relating to Electrical Insulation
served, are also used as electrical insulation.
D 1932 Test Method for Thermal Endurance of Flexible
3.1.3 varnish, electrical insulating, n— a liquid resin sys-
Electrical Insulating Varnishes
tem that is applied to and cured on electrical components
D 2307 Test Method for Relative Thermal Endurance of
providing electrical, mechanical and environmental protection.
Film-Insulated Round Magnet Wire
3.1.3.1 Discussion—There are two types of electrical insu-
D 2519 Test Method for Bond Strength of Electrical Insu-
lating varnishes—solvent-containing and solventless. Solvent-
lating Varnishes by the Helical Coil Test
containing types are solutions, dispersions or emulsions of a
D 3251 Test Method for Thermal-Aging Characteristics of
polymer or a mixture of polymers in a volatile, nonreactable
Electrical Insulating Varnishes Applied Over Film-
liquid. Solventless types are liquid resin systems free of
Insulated Magnet Wire
volatile, nonreactable solvents.
D 3850 Test Method for Rapid Thermal Degradation of
3.1.4 Refer to Terminology D 1711 for definitions of other
Solid Electrical Insulating Materials by Thermogravimet-
terms.
ric Method
D 5423 Specification for Forced Convection Laboratory
4. Summary of Test Method
Ovens for Evaluation of Electrical Insulation
4.1 Flexural strength of the helical coils is measured peri-
odically after exposure to several aging temperatures. The time
to reach an arbitrarily selected value of bond strength at each
This test method is under the jurisdiction of ASTM Committee D-9 on
aging temperature is determined. The logarithms of these times
Electrical and Electronic Insulating Materials and is the direct responsibility of
in hours are plotted as a function of the reciprocal temperature
Subcommittee D09.01 on Electrical Insulating Varnishes, Powders, and Encapsu-
(1/K) to give an Arrhenius plot.
lating Compounds.
Current edition approved Sept. 10, 1997. Published February 1998. Originally
published as D 3145 – 73. Last previous edition D 3145 – 93.
2 4
Annual Book of ASTM Standards, Vol 10.01. Available from American National Standards Institute, 11 West 42nd St., 13th
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D 3145
5. Significance and Use (see 9.1), and that this be used as a guide for the selection of
the lower test temperatures.
5.1 This test method is used to determine the effect of
9.3 Choose the exposure temperature so that any essentially
exposure to elevated temperatures on the bond strength of
linear portions of the Arrhenius plot (log of time to failure
combinations of magnet wire insulations and electrical insu-
versus the reciprocal of the absolute temperature) is well
lating varnishes. The results are used as a guide for the
established; that is, confirm the suspicion of significant non-
comparison and selection of varnishes and combinations of
linearity by test at one or more additional temperatures.
varnishes and wire insulation for specific applications. Test
Generally the additional temperatures are lower than the ones
Methods D 1932, D 3251, and D 3850 describe additional tests
previously tested.
for determining the thermal endurance of insulating varnishes.
A comprehensive evaluation of thermal aging should include a
10. Procedure
comparison of the thermal endurance determined in these
10.1 Suspend at least 20 sets of coils containing at least 3
different ways.
coils in each set vertically in each oven.
5.2 This test method is us
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