1、Designation: D1932 13Standard 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 or, in the case of revision, the year of last r
2、evision. 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 U.S. Department of Defense.1. Scope*1.1 This test method covers the determina
3、tion 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 This test method does not
4、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.Also, this test method is not
5、 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 units are to be regarded asstandard. No ot
6、her 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 standard to establish appro-priate safety and h
7、ealth 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 Electrical Insulating Materialsat Commerc
8、ial Power FrequenciesD374 Test Methods for Thickness of Solid Electrical Insu-lation (Withdrawn 2013)3D580 Specification for Greige Woven Glass Tapes andWebbingsD1346 Test Method for Testing Electrical Insulating Var-nishes for 180 C and Above (Withdrawn 1986)3D1711 Terminology Relating to Electrica
9、l InsulationD2518 Specification for Woven Glass Fabrics for ElectricalInsulation (Withdrawn 2013)3D5423 Specification for Forced-Convection Laboratory Ov-ens for Evaluation of Electrical InsulationD6054 Practice for Conditioning Electrical Insulating Mate-rials for Testing (Withdrawn 2012)32.2 IEEE
10、Publications:4IEEE No. 101A Guide for the 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:1This test method is u
11、nder the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.01 on Electrical Insulating Varnishes, Powders and Encapsulat-ing Compounds.Current edition approved April 1, 2013. Published April 2013. Originallyapprove
12、d in 1967. Last previous edition approved in 2009 as D1932 04 (2009).DOI: 10.1520/D1932-13.2For 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 Su
13、mmary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.4Available 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
14、43rd St., 4thFloor, New York, NY 10036.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.1 temperature index (TI), na number which permitscomparison of the temperature
15、/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 thermal endurance graph, n
16、an 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.3.1.4 thermal life endpoint time, na graphical representa-tion of thermal endpoint time
17、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 D1711 for definitions of otherterms.4. Summary of Test Method4.1 Specimens
18、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 made to determin
19、e 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 graphfor use to estimate temperature indices.4.3 This test method is not applicable to materials having
20、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 ofinsulating materials is th
21、ermal degradation. It is possible thatfactors, such as moisture and vibration, will cause failures afterthe material has been weakened by thermal degradation.5.2 An electrical insulating varnish is effective in protectingelectrical equipment only as long as it retains its physical andelectrical inte
22、grity.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 Electrical insu
23、lating 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 neutral
24、 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 lb).6.2
25、 Dielectric Breakdown Test SetThe set shall meet therequirements of Test Method D149.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
26、. 1 Single-Shot Curved Electrode DetailsD1932 1326.3 OvensA forced draft constant-temperature oven con-forming to Specification D5423, Type II.6.4 MicrometerDead-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 5
27、0 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 specimenmade from a straight length (approximately 1 m (39 in.) ofround Nichrome AWG No. 14 wire. Bend the wire to form arectangle having inside dimensions
28、 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 minimum of 25 mm (1 in.) apart so that they aresec
29、ured at top and bottom.6.7 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 thepossibility exist
30、s 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 D2518. Heat clean the specimens
31、 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 paneldescribed in 8.1 in the varnish at the standard laboratoryatmosphere described in Practice D6054. Prior to dippingpanels,
32、 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 of 90110 mm (
33、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 varnish manuf
34、acturer.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 the 12.5 by 3
35、00 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 fivebreakdown tests on th
36、e 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 MethodD149.9.3 Average the dielectric breakdown voltage for the fivebent and unbent area
37、s 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 such that it is no
38、t more than25C higher than the estimated temperature index. Exposuretemperatures shall differ by at least 10C and preferably 20C.10.2 Select exposure temperatures in accordance with thoseshown in Table 1 as indicated by the anticipated temperatureindex of the material under test. It is recommended t
39、hatexploratory 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.FIG. 2 Curved Electrode and HolderD1932 13311. Procedure11.1 Thickness
40、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 in.)length using the apparatus described in 6.4 and Test MethodsD374.Allow th
41、e 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 for dielectric breakdown volt-age by the short-time method, using a rate of
42、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 are bent. Lower the electrodeslowly on the specimen.11.3 Exposure and Testin
43、g of the SpecimensTag fivespecimens with aluminum foil or otherwise permanently iden-tify them, and place in the test fixture described in 6.5. Placethe fixture containing the specimens in the oven which haspreviously been brought up to the highest selected temperatureand positioned so that it is at
44、 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 standard laboratory atm
45、osphere 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 endpointtime, plac
46、e 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 the estimated ins
47、ulation 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 available pointsor exte
48、nd 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 selectedexposure temper
49、atures.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 (300 V/mil) of original thickness. Thisis the thermal endpoint time at that temperature. End pointsother than 12 kV/mm (300 V/mil) are also acceptable whenspecified.12.2 Where the experimental points are scattered, makingaccurate fitting difficult, use the mathematical fitti
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