1、Designation: D1932 04 (Reapproved 2009)An American National StandardStandard Test Method forThermal Endurance of Flexible Electrical InsulatingVarnishes1This standard is issued under the fixed designation D1932; the number immediately following the designation indicates the year oforiginal adoption
2、or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript 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
3、1.1 This test method covers the determination of the relativethermal endurance of flexible electrical insulating varnishes bydetermining the time necessary at elevated temperatures todecrease the dielectric breakdown of the varnish to an arbi-trarily selected value when applied to a standard glass f
4、iberfabric.1.2 This test method does not apply to varnishes that lose ahigh percentage of their dielectric breakdown voltage whenflexed before elevated temperature exposure as prescribed inthe screening test (Section 9). Examples of such varnishes arethose used for high speed armatures and laminated
5、 structures.Also, this test method is not applicable to varnishes whichdistort sufficiently during thermal elevated temperature expo-sure so that they cannot be tested using the curved electrodeassembly.1.3 Thermal endurance is expressed in terms of a tempera-ture index.1.4 The values stated in SI u
6、nits are to be regarded asstandard. No other units of measurement are included in thisstandard.NOTE 1There is no equivalent IEC or ISO standard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standa
7、rd to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For specific hazardstatements, see Section 7.2. Referenced Documents2.1 ASTM Standards:2D149 Test Method for Dielectric Breakdown Voltage andDielectric Strength of Solid
8、Electrical Insulating Materialsat Commercial Power FrequenciesD374 Test Methods for Thickness of Solid Electrical Insu-lationD580 Specification for Greige Woven Glass Tapes andWebbingsD1346 Methods of Testing Electrical Insulating Varnishesfor 180C and Above3D1711 Terminology Relating to Electrical
9、InsulationD2518 Specification for Woven Glass Fabrics for ElectricalInsulationD5423 Specification for Forced-Convection LaboratoryOvens for Evaluation of Electrical InsulationD6054 Practice for Conditioning Electrical Insulating Ma-terials for Testing2.2 IEEE Publications:4IEEE No. 101A Guide for th
10、e Statistical Analysis of Ther-mal Life Test Data (including Appendix A)2.3 IEC Publications:IEC 60216 Guide for the Determination of Thermal Endur-ance Properties of Electrical Insulating Materials (Part 1)53. Terminology3.1 Definitions:3.1.1 temperature index (TI), na number which permitscompariso
11、n of the temperature/time characteristics of an elec-trical insulating material, or a simple combination of materials,based on the temperature in degrees Celsius which is obtainedby extrapolating the Arrhenius plot of endpoint time versustemperature to a specified time, usually 20 000 h.3.1.2 therma
12、l endurance graph, nan Arrhenius plot.3.1.3 thermal endpoint time, nthe time necessary for aspecific property of a material, or a simple combination ofmaterials, to degrade to a defined end point when aged at aspecified temperature.1This test method is under the jurisdiction of ASTM Committee D09 on
13、Electrical and Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.01 on Electrical Insulating Varnishes, Powders and Encapsulat-ing Compounds.Current edition approved Oct. 1, 2009. Published February 2010. Originallyapproved in 1967. Last previous edition approved in
14、 2004 as D1932 04. DOI:10.1520/D1932-04R09.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.4Availa
15、ble from the Institute of Electrical and Electronics Engineers, 1828 L St.,NW, Suite 1202, Washington, DC 200365104.5Available from American National Standards Institute, 25 West 43rd St., 4thFloor, New York, NY 10036.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohock
16、en, PA 19428-2959, United States.3.1.4 thermal life endpoint time, na graphical representa-tion of thermal endpoint time at a specified exposure tempera-ture in which the value of a property of a material, or a simplecombination of materials, is measured at room temperature andthe values plotted as
17、a function of time.3.1.5 Refer to Terminology D1711 for definitions of otherterms.4. Summary of Test Method4.1 Specimens are prepared using glass cloth coated withthe selected varnish to a specified build.4.2 Specimens are exposed in air at a minimum of threetemperatures above the expected use tempe
18、rature of the mate-rial. Dielectric breakdown voltage tests in air at room tempera-ture are periodically made to determine the exposure time ateach test temperature required to reduce the breakdown voltageto a value of 12 kV/mm (300 V/mil) of original thickness.These values are used to construct a t
19、hermal endurance graphby which temperature indices may be estimated.4.3 This test method is not applicable to materials having aninitial dielectric breakdown voltage of less than 12 kV/mm(300 V/mil) of original thickness unless lower endpoint valuesare agreed upon or indicated in the applicable mate
20、rial speci-fications.5. Significance and Use5.1 A major factor affecting the long term performance ofinsulating materials is thermal degradation. Other factors, suchas moisture and vibration, may cause failures after the materialhas been weakened by thermal degradation.5.2 An electrical insulating v
21、arnish is effective in protectingelectrical equipment only as long as it retains its physical andelectrical integrity.5.3 The thermal degradation of the varnish results in weightloss, porosity, crazing, and generally a reduction in flexibility.Degradation of the varnish can be detected by a decrease
22、 indielectric strength, which is therefore used as the failurecriterion for this test method.5.4 Electrical insulating varnishes undergo flexing in ser-vice due to vibration and thermal expansion. For this reason,this functional test includes flexing and elongation of theinsulation. The electrodes u
23、sed in this test method are designedto elongate the outer surface of the specimen 2 % with respectto the neutral axis of the base fiber while being tested fordielectric breakdown.6. Apparatus6.1 Electrode Test FixtureThe fixture shall be in accor-dance with the dimensions shown in Fig. 1 and Fig. 2.
24、Electrodes shall be of polished brass, with the upper electrodehaving a mass of 1.8 6 0.05 kg (4.0 6 0.1 lb).6.2 Dielectric Breakdown Test SetThe set shall meet therequirements of Test Method D149.6.3 OvensA forced draft constant-temperature oven con-forming to Specification D5423, Type II.6.4 Micro
25、meterDead-weight type specified in Test Meth-ods D374, having a presser foot 6.35 6 0.03 mm (0.25 6 0.001in.) in diameter and an anvil of at least 50 mm (2 in.) diameterand shall exert a pressure of 0.17 6 0.01 MPa (25 6 2 psi) onthe pressure foot.6.5 Test Specimen FrameA frame for each test specime
26、nmade from a straight length (approximately 1 m (39 in.) ofround Nichrome AWG No. 14 wire. Bend the wire to form arectangle having inside dimensions of 150 by 300 mm (6 by 12in.). Overlap the ends of the wire approximately 50 mm (2 in.)at one corner. Attach the specimen to the frame.6.6 Test Fixture
27、 for Exposing Specimen to ElevatedTemperatureA suitable fixture for mounting the specimenframes a minimum of 25 mm (1 in.) apart so that they aresecured at top and bottom.Insulation Thickness Dimension R Dimension H Dimension Dcm in. cm in. cm in. cm in.0.018 0.007 0.455 0.179 0.815 0.321 0.871 0.34
28、4Tolerance 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 DetailsD1932 04 (2009)26.7 Dipping ApparatusAn apparatus capable of removingthe specimen from the varnish at the rate of 90110 mm(3.54.3 in.)/min.7. Safety Precautions7.1 It is unsa
29、fe to use varnish at temperatures above theflash point without adequate ventilation, especially if thepossibility exists that flames or sparks are present. Storevarnish in sealed containers.8. Test Specimens8.1 Prepare glass cloth panels 150 by 300 mm (6 by 12 in.)with the 300 mm (12 in.) dimension
30、parallel to the warpthreads. Use fabric style No. 116 in accordance with Specifi-cation D2518. Heat clean the specimens as specified inMethods D1346 to arrive at a volatile content not to exceed0.1 % in accordance with Specification D580.8.2 Prepare the test specimen by dipping a glass cloth panelde
31、scribed in 8.1 in the varnish at the standard laboratoryatmosphere described in Practice D6054. Prior to dippingpanels, adjust the viscosity of the varnish to be tested by trialso that two coats will give an over-all thickness of 0.178 60.0127 mm (0.007 6 0.0005 in.).8.3 Immerse the panel in the var
32、nish in the direction of the300 mm (12 in.) length until bubbling stops, mechanicallywithdraw at the rate of 90110 mm (3.54.3 in.)/min, and thenallow to drain for12 h at the standard laboratory atmosphere.8.4 Bake the specimen in the same vertical position asdipped. Reverse the specimen, dip a secon
33、d time, and drain asabove. Bake the specimen at such a temperature and for sucha time as specified by the varnish manufacturer.8.5 Prepare a set of twelve or more specimens for eachexposure temperature.9. Screening Test9.1 Prepare one test specimen. Condition the specimen 48 hin the standard laborat
34、ory atmosphere. Cut five 25 by 300 mm(1 by 12 in.) test strips from the center of the specimen,discarding the 12.5 by 300 mm (12 by 12 in.) portion from eachside. Bend each of the five test strips once, 115 mm (412 in.)from one end, 180 around a mandrel 3.175 mm (0.125 in.) indiameter.9.2 Measure th
35、e dielectric breakdown voltage on the bentarea of each five test strips. In like manner, make fivebreakdown tests on the unbent area at a distance of 75 mm (3in.) from the bend. Use the apparatus described in 6.2 inaccordance with the procedure described in 11.2, except use6.4 mm (14 in.) diameter e
36、lectrodes as specified in Test MethodD149.9.3 Average the dielectric breakdown voltage for the fivebent and unbent areas respectively. The ratio of averagebreakdown voltage of the bent area to the unbent area shall begreater than 0.5, if this method is to be considered applicable.10. Selection of Te
37、st Temperatures10.1 Expose the material to at least three temperatures.Choose the lowest temperature such that it is not more than25C higher than the estimated temperature index. Exposuretemperatures should differ by at least 10C and preferably20C.10.2 Select exposure temperatures in accordance with
38、 thoseshown in Table 1 as indicated by the anticipated temperatureindex of the material under test. It is recommended thatexploratory tests be first made at the highest temperature toobtain data establishing the validity of the 100 h minimumendpoint time requirement and that this be used as a guide
39、forthe selection of the lower test temperatures.11. Procedure11.1 Thickness MeasurementMeasure the average thick-ness of one representative specimen from each set at five pointsalong its center before heat exposure. Determine the thicknessalong the center of the specimen parallel to its 300 mm (12 i
40、n.)length using the apparatus described in 6.4 and Test MethodsD374.Allow the presser foot to remain on the test specimen for2 s before taking a reading.11.2 Dielectric Breakdown Voltage (Initial)Condition onespecimen from each set of specimens for at least 48 h in thestandard laboratory atmosphere
41、for dielectric breakdown volt-age by the short-time method, using a rate of rise of 500 V/s.Make six dielectric breakdown measurements, 45 mm (134 in.)apart and starting 40 mm (112 in.) from one end of thespecimen. Insert the specimen in the curved electrode fixture(Fig. 2) so that the warp threads
42、are bent. Lower the electrodeslowly on the specimen.11.3 Exposure and Testing of the SpecimensTag fivespecimens with aluminum foil or otherwise permanently iden-tify them, and place in the test fixture described in 6.5. PlaceFIG. 2 Curved Electrode and HolderD1932 04 (2009)3the fixture containing th
43、e specimens in the oven which haspreviously been brought up to the highest selected temperatureand positioned so that it is at least 100 mm (4 in.) from thewalls at any point. Remove one specimen at each of three timeintervals equivalent approximately to 25, 50, and 100 % of theestimated insulation
44、endpoint time at the selected temperature.Immediately after removal, condition the specimen for4hinthe standard laboratory atmosphere and test for dielectricbreakdown voltage in the standard laboratory atmosphere asspecified in 11.2.11.3.1 At the time of 50 % of estimated endpoint time, tagfive addi
45、tional specimens and place them in the test fixture inthe oven. Similarly, at the time of 75 % of estimated endpointtime, place the remaining specimens in the oven.11.3.2 Plot the average dielectric breakdown voltage of eachspecimen as the ordinate corresponding to exposure time as theabscissa. If e
46、ndpoint time has been underestimated, removeone specimen of the first group remaining in the oven at 150 %of the estimated insulation endpoint time and test it aspreviously described.11.3.3 With information now available on the exposedspecimens, remove each of the remaining specimens at inter-vals s
47、o as to establish a curve of average dielectric breakdownvoltage versus exposure time. Fill in between available pointsor extend beyond if necessary. Continue the oven exposureuntil an average dielectric strength of 8 kV/mm (200 V/mil)(based on original average thickness) is reached or ovenexposure
48、has progressed to 10 000 h. Using this information,repeat the same procedure, using at least two other selectedexposure temperatures.12. Calculation12.1 Establish for each temperature the thermal endpointcurve best fitting the plot of average dielectric breakdownvoltage in kilovolts versus the expos
49、ure time in hours. Deter-mine from this curve the number of hours corresponding to anend point of 12 kV/mm (300 V/mil) of original thickness. Thisis the thermal endpoint time at that temperature. End pointsother than 12 kV/mm (300 V/mil) may be used as specified.12.2 Where the experimental points are scattered, makingaccurate fitting difficult, use the mathematical fitting method ofleast squares. Caution is suggested, however, since somematerials exhibit maxima in the breakdown voltage curve dueto further curing during heat exposure and erroneous re
