1、Designation: D 1932 04An American National StandardStandard Test Method forThermal Endurance of Flexible Electrical InsulatingVarnishes1This standard is issued under the fixed designation D 1932; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript 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. Scope1.1 This test m
3、ethod 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 fiberfabric.1.2
4、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 structures.Als
5、o, 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 This standard does not purport to addres
6、s all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For specific hazardstatements, see Section 7.1.5 The value
7、s stated in SI units are the standard.NOTE 1There is no equivalent IEC or ISO standard.2. Referenced Documents2.1 ASTM Standards:2D 149 Test Method for Dielectric Breakdown Voltage andDielectric Strength of Solid Electrical Insulating Materialsat Commercial Power FrequenciesD 374 Test Methods for Th
8、ickness of Solid Electrical Insu-lationD 580 Specification for Greige Woven Glass Tapes andWebbingsD 1346 Methods of Testing Electrical Insulating Varnishesfor 180C and Above3D 1711 Terminology Relating to Electrical InsulationD 2518 Specification for Woven Glass Fabrics for ElectricalInsulationD 54
9、23 Specification for Forced-Convection LaboratoryOvens for Evaluation of Electrical InsulationD 6054 Practice for Conditioning Electrical Insulating Ma-terials for Testing2.2 IEEE Publications:4IEEE No. 101A Guide for the Statistical Analysis of Ther-mal Life Test Data (including Appendix A)2.3 IEC
10、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 permitscomparison of the temperature/time characteristics of an elec-trical insulating material,
11、 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 thermal endurance graph, nan Arrhenius plot.3.1.3 thermal endpoint time, nthe time nec
12、essary 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 onElectrical and Electronic Insulating Materials and is the direct responsibility
13、ofSubcommittee D09.01 on Electrical Insulating Varnishes, Powders, and Encapsu-lating Compounds.Current edition approved March 1, 2004. Published March 2004. Originallyapproved in 1967. Last previous edition approved in 2003 as D 1932 03.2For referenced ASTM standards, visit the ASTM website, www.as
14、tm.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.4Available from the Institute of Electrical and Electronics Engineers, 1828 L St.,NW, Suite 1202, Washington, DC
15、 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 Conshohocken, PA 19428-2959, United States.3.1.4 thermal life endpoint time, na graphical representa-tion of therma
16、l 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 a function of time.3.1.5 Refer to Terminology D 1711 for definitions of otherterms.4. Summary of Test Met
17、hod4.1 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 temperature of the mate-rial. Dielectric breakdown voltage tests in air at room tempera-ture are periodically
18、 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 thermal endurance graphby which temperature indices may be estimated.4.3 This test method is not applicab
19、le 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 material speci-fications.5. Significance and Use5.1 A major factor affecting the long term performance ofins
20、ulating 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 varnish is effective in protectingelectrical equipment only as long as it retains its physical andelectri
21、cal 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 indielectric strength, which is therefore used as the failurecriterion for this test method.5.4 Electri
22、cal 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 used in this test method are designedto elongate the outer surface of the specimen 2 % with respectto the
23、 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.Electrodes shall be of polished brass, with the upper electrodehaving a mass of 1.8 6 0.05 kg (4.0 6 0.1
24、 lb).6.2 Dielectric Breakdown Test SetThe set shall meet therequirements of Test Method D 149.6.3 OvensA forced draft constant-temperature oven con-forming to Specification D 5423, Type II.6.4 MicrometerDead-weight type specified in Test Meth-ods D 374, having a presser foot 6.35 6 0.03 mm (0.25 60.
25、001 in.) in diameter and an anvil of at least 50 mm (2 in.)diameter and shall exert a pressure of 0.17 6 0.01 MPa (25 62 psi) on the pressure foot.6.5 Test Specimen FrameA frame for each test specimenmade from a straight length (approximately 1 m (39 in.) ofround Nichrome AWG No. 14 wire. Bend the w
26、ire 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 for Exposing Specimen to ElevatedTemperatureA suitable fixture for mounting the specimenframes a min
27、imum 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 0.344Tolerance for R and D = 0.003 cm (0.001 in.)Tolerance for H = 0.005 cm (0.002 in.)FIG. 1 Single-Shot
28、 Curved Electrode DetailsD19320426.7 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 unsafe to use varnish at temperatures above theflash point without adequate ventilation, especially if thepossibi
29、lity 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 parallel to the warpthreads. Use fabric style No. 116 in accordance with Specifi-cation D 2518. Heat clean th
30、e specimens as specified inMethods D 1346 to arrive at a volatile content not to exceed0.1 % in accordance with Specification D 580.8.2 Prepare the test specimen by dipping a glass cloth paneldescribed in 8.1 in the varnish at the standard laboratoryatmosphere described in Practice D 6054. Prior to
31、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 varnish in the direction of the300 mm (12 in.) length until bubbling stops, mechanicallywithdraw at the rate
32、 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 second time, and drain asabove. Bake the specimen at such a temperature and for sucha time as specified by the
33、 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 laboratory atmosphere. Cut five 25 by 300 mm(1 by 12 in.) test strips from the center of the specimen,discarding
34、 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 the dielectric breakdown voltage on the bentarea of each five test strips. In like manner, make fivebreakdo
35、wn 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 electrodes as specified in Test MethodD 149.9.3 Average the dielectric breakdown voltage for the fivebent
36、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 Test Temperatures10.1 Expose the material to at least three temperatures.Choose the lowest temperature suc
37、h 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 thoseshown in Table 1 as indicated by the anticipated temperatureindex of the material under test. It i
38、s 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 forthe selection of the lower test temperatures.11. Procedure11.1 Thickness MeasurementMeasure the avera
39、ge 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 in.)length using the apparatus described in 6.4 and Test MethodsD 374. Allow the presser foot to remain o
40、n the test specimenfor 2 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 for dielectric breakdown volt-age by the short-time method, using a rate of rise of 500 V/s.Make six d
41、ielectric 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 are bent. Lower the electrodeslowly on the specimen.11.3 Exposure and Testing of the SpecimensTag five
42、specimens with aluminum foil or otherwise permanently iden-tify them, and place in the test fixture described in 6.5. PlaceFIG. 2 Curved Electrode and HolderD1932043the fixture containing the specimens in the oven which haspreviously been brought up to the highest selected temperatureand positioned
43、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 endpoint time at the selected temperature.Immediately after removal, condition the specimen for4hinthe standar
44、d 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 additional specimens and place them in the test fixture inthe oven. Similarly, at the time of 75 % of estimated en
45、dpointtime, 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 endpoint time has been underestimated, removeone specimen of the first group remaining in the oven at 150 %of t
46、he 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 so as to establish a curve of average dielectric breakdownvoltage versus exposure time. Fill in between availab
47、le 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 has progressed to 10 000 h. Using this information,repeat the same procedure, using at least two other selecte
48、dexposure temperatures.12. Calculation12.1 Establish for each temperature the thermal endpointcurve best fitting the plot of average dielectric breakdownvoltage in kilovolts versus the exposure time in hours. Deter-mine from this curve the number of hours corresponding to anend point of 12 kV/mm (30
49、0 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 resultsmay be obtained using analytical methods unless there is aknowledgeable preselection of data points to be us
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