1、Designation: D 257 07An American National StandardStandard Test Methods forDC Resistance or Conductance of Insulating Materials1This standard is issued under the fixed designation D 257; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisi
2、on, 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. Scope*1.1 These test methods
3、cover direct-current procedures forthe measurement of dc insulation resistance, volume resistance,and surface resistance. From such measurements and thegeometric dimensions of specimen and electrodes, both vol-ume and surface resistivity of electrical insulating materialscan be calculated, as well a
4、s the corresponding conductancesand conductivities.1.2 These test methods are not suitable for use in measuringthe electrical resistance/conductance of moderately conductivematerials. Use Test Method D 4496 to evaluate such materials.1.3 This standard describes several general alternativemethodologi
5、es for measuring resistance (or conductance).Specific materials can be tested most appropriately by usingstandardASTM test methods applicable to the specific materialthat define both voltage stress limits and finite electrificationtimes as well as specimen configuration and electrode geom-etry. Thes
6、e individual specific test methodologies would bebetter able to define the precision and bias for the determina-tion.1.4 The procedures appear in the following sections:Test Method or Procedure SectionCalculation 13Choice of Apparatus and Test Method 7Cleaning Solid Specimens 10.1Conditioning of Spe
7、cimens 11Effective Area of Guarded Electrode AppendixX2Electrode Systems 6Factors Affecting Insulation Resistance or ConductanceMeasurementsAppendixX1Humidity Control 11.2Liquid Specimens and Cells 9.4Precision and Bias 15Procedure for the Measurement of Resist-ance or Conductance12Referenced Docume
8、nts 2Report 14Sampling 8Significance and Use 5Specimen Mounting 10Summary of Test Methods 4Terminology 3Test Specimens for Insulation, Volume, and SurfaceResistance or Conductance Determination9Typical Measurement Methods AppendixX31.5 This standard does not purport to address all of thesafety conce
9、rns, 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.2. Referenced Documents2.1 ASTM Standards:2D 150 Test Methods for AC Loss Character
10、istics and Per-mittivity (Dielectric Constant) of Solid Electrical Insula-tionD 374 Test Methods for Thickness of Solid Electrical Insu-lationD 1169 Test Method for Specific Resistance (Resistivity) ofElectrical Insulating LiquidsD 1711 Terminology Relating to Electrical InsulationD 4496 Test Method
11、 for D-C Resistance or Conductance ofModerately Conductive MaterialsD 5032 Practice for Maintaining Constant Relative Humid-ity by Means of Aqueous Glycerin SolutionsD 6054 Practice for Conditioning Electrical Insulating Ma-terials for TestingE 104 Practice for Maintaining Constant Relative Humidity
12、by Means of Aqueous Solutions3. Terminology3.1 DefinitionsThe following definitions are taken fromTerminology D 1711 and apply to the terms used in the text ofthis standard.3.1.1 conductance, insulation, nthe ratio of the totalvolume and surface current between two electrodes (on or in aspecimen) to
13、 the dc voltage applied to the two electrodes.3.1.1.1 DiscussionInsulation conductance is the recipro-cal of insulation resistance.1These test methods are under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating Materials and are the direct responsibility ofSubcommittee D0
14、9.12 on Electrical Tests.Current edition approved May 15, 2007. Published June 2007. Originallyapproved in 1925. Last previous edition approved in 2005 as D 257 99(2005).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annu
15、al Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.2 cond
16、uctance, surface, nthe ratio of the currentbetween two electrodes (on the surface of a specimen) to the dcvoltage applied to the electrodes.3.1.2.1 Discussion(Some volume conductance is un-avoidably included in the actual measurement.) Surface con-ductance is the reciprocal of surface resistance.3.1
17、.3 conductance, volume, nthe ratio of the current in thevolume of a specimen between two electrodes (on or in thespecimen) to the dc voltage applied to the two electrodes.3.1.3.1 DiscussionVolume conductance is the reciprocalof volume resistance.3.1.4 conductivity, surface, nthe surface conductancem
18、ultiplied by that ratio of specimen surface dimensions (dis-tance between electrodes divided by the width of electrodesdefining the current path) which transforms the measuredconductance to that obtained if the electrodes had formed theopposite sides of a square.3.1.4.1 DiscussionSurface conductivit
19、y is expressed insiemens. It is popularly expressed as siemens/square (the sizeof the square is immaterial). Surface conductivity is thereciprocal of surface resistivity.3.1.5 conductivity, volume, nthe volume conductancemultiplied by that ratio of specimen volume dimensions(distance between electro
20、des divided by the cross-sectionalarea of the electrodes) which transforms the measured conduc-tance to that conductance obtained if the electrodes had formedthe opposite sides of a unit cube.3.1.5.1 DiscussionVolume conductivity is usually ex-pressed in siemens/centimetre or in siemens/metre and is
21、 thereciprocal of volume resistivity.3.1.6 moderately conductive, adjdescribes a solid mate-rial having a volume resistivity between 1 and 10 000 000V-cm.3.1.7 resistance, insulation, (Ri), nthe ratio of the dcvoltage applied to two electrodes (on or in a specimen) to thetotal volume and surface cur
22、rent between them.3.1.7.1 DiscussionInsulation resistance is the reciprocalof insulation conductance.3.1.8 resistance, surface, (Rs), nthe ratio of the dc voltageapplied to two electrodes (on the surface of a specimen) to thecurrent between them.3.1.8.1 Discussion(Some volume resistance is unavoid-a
23、bly included in the actual measurement.) Surface resistance isthe reciprocal of surface conductance.3.1.9 resistance, volume, (Rv), nthe ratio of the dc voltageapplied to two electrodes (on or in a specimen) to the currentin the volume of the specimen between the electrodes.3.1.9.1 DiscussionVolume
24、resistance is the reciprocal ofvolume conductance.3.1.10 resistivity, surface, (rs), nthe surface resistancemultiplied by that ratio of specimen surface dimensions (widthof electrodes defining the current path divided by the distancebetween electrodes) which transforms the measured resistanceto that
25、 obtained if the electrodes had formed the opposite sidesof a square.3.1.10.1 DiscussionSurface resistivity is expressed inohms. It is popularly expressed also as ohms/square (the size ofthe square is immaterial). Surface resistivity is the reciprocal ofsurface conductivity.3.1.11 resistivity, volum
26、e, (rv), nthe volume resistancemultiplied by that ratio of specimen volume dimensions(cross-sectional area of the specimen between the electrodesdivided by the distance between electrodes) which transformsthe measured resistance to that resistance obtained if theelectrodes had formed the opposite si
27、des of a unit cube.3.1.11.1 DiscussionVolume resistivity is usually ex-pressed in ohm-centimetres (preferred) or in ohm-metres.Volume resistivity is the reciprocal of volume conductivity.4. Summary of Test Methods4.1 The resistance or conductance of a material specimen orof a capacitor is determined
28、 from a measurement of current orof voltage drop under specified conditions. By using theappropriate electrode systems, surface and volume resistanceor conductance may be measured separately. The resistivity orconductivity can then be calculated when the required speci-men and electrode dimensions a
29、re known.5. Significance and Use5.1 Insulating materials are used to isolate components of anelectrical system from each other and from ground, as well asto provide mechanical support for the components. For thispurpose, it is generally desirable to have the insulation resis-tance as high as possibl
30、e, consistent with acceptable mechani-cal, chemical, and heat-resisting properties. Since insulationresistance or conductance combines both volume and surfaceresistance or conductance, its measured value is most usefulwhen the test specimen and electrodes have the same form asis required in actual u
31、se. Surface resistance or conductancechanges rapidly with humidity, while volume resistance orconductance changes slowly although the final change mayeventually be greater.5.2 Resistivity or conductivity may be used to predict,indirectly, the low-frequency dielectric breakdown and dissi-pation facto
32、r properties of some materials. Resistivity orconductivity is often used as an indirect measure of: moisturecontent, degree of cure, mechanical continuity, or deteriorationof various types. The usefulness of these indirect measure-ments is dependent on the degree of correlation established bysupport
33、ing theoretical or experimental investigations. A de-crease of surface resistance may result either in an increase ofthe dielectric breakdown voltage because the electric fieldintensity is reduced, or a decrease of the dielectric breakdownvoltage because the area under stress is increased.5.3 All th
34、e dielectric resistances or conductances depend onthe length of time of electrification and on the value of appliedvoltage (in addition to the usual environmental variables).These must be known and reported to make the measured valueof resistance or conductance meaningful. Within the electricalinsul
35、ation materials industry, the adjective “apparent” is gen-erally applied to resistivity values obtained under conditions ofarbitrarily selected electrification time. See X1.4.5.4 Volume resistivity or conductivity can be calculatedfrom resistance and dimensional data for use as an aid inD257072desig
36、ning an insulator for a specific application. The change ofresistivity or conductivity with temperature and humidity maybe great (1, 2, 3, 4),3and must be known when designing foroperating conditions. Volume resistivity or conductivity deter-minations are often used in checking the uniformity of ani
37、nsulating material, either with regard to processing or to detectconductive impurities that affect the quality of the material andthat may not be readily detectable by other methods.5.5 Volume resistivities above 1021Vcm (1019Vm), cal-culated from data obtained on specimens tested under usuallaborat
38、ory conditions, are of doubtful validity, considering thelimitations of commonly used measuring equipment.5.6 Surface resistance or conductance cannot be measuredaccurately, only approximated, because some degree of volumeresistance or conductance is always involved in the measure-ment. The measured
39、 value is also affected by the surfacecontamination. Surface contamination, and its rate of accumu-lation, is affected by many factors including electrostaticcharging and interfacial tension. These, in turn, may affect thesurface resistivity. Surface resistivity or conductivity can beconsidered to b
40、e related to material properties when contami-nation is involved but is not a material property of electricalinsulation material in the usual sense.6. Electrode Systems6.1 The electrodes for insulating materials should be of amaterial that is readily applied, allows intimate contact with thespecimen
41、 surface, and introduces no appreciable error becauseof electrode resistance or contamination of the specimen (5).The electrode material should be corrosion-resistant under theconditions of test. For tests of fabricated specimens such asfeed-through bushings, cables, etc., the electrodes employedare
42、 a part of the specimen or its mounting. Measurements ofinsulation resistance or conductance, then, include the contami-nating effects of electrode or mounting materials and aregenerally related to the performance of the specimen in actualuse.6.1.1 Binding-Post and Taper-Pin Electrodes, Fig. 1 andFi
43、g. 2, provide a means of applying voltage to rigid insulatingmaterials to permit an evaluation of their resistive or conduc-tive properties. These electrodes simulate to some degree theactual conditions of use, such as binding posts on instrumentpanels and terminal strips. In the case of laminated i
44、nsulatingmaterials having high-resin-content surfaces, somewhat lowerinsulation resistance values may be obtained with taper-pinthan with binding posts, due to more intimate contact with thebody of the insulating material. Resistance or conductancevalues obtained are highly influenced by the individ
45、ual contactbetween each pin and the dielectric material, the surfaceroughness of the pins, and the smoothness of the hole in thedielectric material. Reproducibility of results on differentspecimens is difficult to obtain.6.1.2 Metal Bars in the arrangement of Fig. 3 were prima-rily devised to evalua
46、te the insulation resistance or conduc-tance of flexible tapes and thin, solid specimens as a fairlysimple and convenient means of electrical quality control. Thisarrangement is somewhat more satisfactory for obtainingapproximate values of surface resistance or conductance whenthe width of the insul
47、ating material is much greater than itsthickness.3The boldface numbers in parentheses refer to the list of references appended tothese test methods.FIG. 1 Binding-Post Electrodes for Flat, Solid SpecimensFIG. 2 Taper-Pin ElectrodesD2570736.1.3 Silver Paint, Fig. 4, Fig. 5, and Fig. 6, is availableco
48、mmercially with a high conductivity, either air-drying orlow-temperature-baking varieties, which are sufficiently po-rous to permit diffusion of moisture through them and therebyallow the test specimen to be conditioned after the applicationof the electrodes. This is a particularly useful feature in
49、studying resistance-humidity effects, as well as change withtemperature. However, before conductive paint is used as anelectrode material, it should be established that the solvent inthe paint does not attack the material so as to change itselectrical properties. Reasonably smooth edges of guard elec-trodes may be obtained with a fine-bristle brush. However, forcircular electrodes, sharper edges can be obtained by the use ofa ruling compass and silver paint for drawing the outline circlesof the electrodes and filling in the enclosed areas by brush. Anarrow str
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