1、Designation: D257 07D257 14 An American National StandardStandard Test Methods forDC Resistance or Conductance of Insulating Materials1This standard is issued under the fixed designation D257; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、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 U.S. Department of Defense.1. Scope*1.1 These tes
3、t methods cover direct-current procedures for the measurement of dc insulation resistance, volume resistance, andsurface resistance. From such measurements and the geometric dimensions of specimen and electrodes, both volume and surfaceresistivity of electrical insulating materials can be calculated
4、, as well as the corresponding conductances and conductivities.1.2 These test methods are not suitable for use in measuring the electrical resistance/conductance of moderately conductivematerials. Use Test Method D4496 to evaluate such materials.1.3 This standard describes several general alternativ
5、e methodologies for measuring resistance (or conductance). Specificmaterials can be tested most appropriately by using standardASTM test methods applicable to the specific material that define bothvoltage stress limits and finite electrification times as well as specimen configuration and electrode
6、geometry. These individualspecific test methodologies would be better able to define the precision and bias for the determination.1.4 The procedures appear in the following sections:Test Method or Procedure SectionCalculation 13Choice of Apparatus and Test Method 7Cleaning Solid Specimens 10.1Condit
7、ioning of Specimens 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 Conductance12Refe
8、renced Documents 2Report 14Sampling 8Significance and Use 5Specimen Mounting 10Summary of Test Methods 4Terminology 3Test Specimens for Insulation, Volume, and SurfaceResistance or Conductance Determination9Typical Measurement Methods AppendixX31.4 This standard does not purport to address all of th
9、e safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.1 These test methods are under the jurisdiction ofASTM Committee D09 on
10、Electrical and Electronic Insulating Materials and are the direct responsibility of SubcommitteeD09.12 on Electrical Tests.Current edition approved May 15, 2007April 1, 2014. Published June 2007May 2014. Originally approved in 1925. Last previous edition approved in 20052007 asD257 99D257 07.(2005).
11、 DOI: 10.1520/D0257-07.10.1520/D0257-14.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM
12、 recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO B
13、ox C700, West Conshohocken, PA 19428-2959. United States12. Referenced Documents2.1 ASTM Standards:2D150 Test Methods for AC Loss Characteristics and Permittivity (Dielectric Constant) of Solid Electrical InsulationD374 Test Methods for Thickness of Solid Electrical Insulation (Withdrawn 2013)3D1169
14、 Test Method for Specific Resistance (Resistivity) of Electrical Insulating LiquidsD1711 Terminology Relating to Electrical InsulationD4496 Test Method for D-C Resistance or Conductance of Moderately Conductive MaterialsD5032 Practice for Maintaining Constant Relative Humidity by Means of Aqueous Gl
15、ycerin SolutionsD6054 Practice for Conditioning Electrical Insulating Materials for Testing (Withdrawn 2012)3E104 Practice for Maintaining Constant Relative Humidity by Means of Aqueous Solutions3. Terminology3.1 Definitions:3.1.1 The following definitions are taken from Terminology D1711 and apply
16、to the terms used in the text of this standard.3.1.2 conductance, insulation, nthe ratio of the total volume and surface current between two electrodes (on or in a specimen)to the dc voltage applied to the two electrodes.3.1.2.1 DiscussionInsulation conductance is the reciprocal of insulation resist
17、ance.3.1.3 conductance, surface, nthe ratio of the current between two electrodes (on the surface of a specimen) to the dc voltageapplied to the electrodes.3.1.3.1 Discussion(Some volume conductance is unavoidably included in the actual measurement.) Surface conductance is the reciprocal of surfacer
18、esistance.3.1.4 conductance, volume, nthe ratio of the current in the volume of a specimen between two electrodes (on or in thespecimen) to the dc voltage applied to the two electrodes.3.1.4.1 DiscussionVolume conductance is the reciprocal of volume resistance.3.1.5 conductivity, surface, nthe surfa
19、ce conductance multiplied by that ratio of specimen surface dimensions (distancebetween electrodes divided by the width of electrodes defining the current path) which transforms the measured conductance tothat obtained if the electrodes had formed the opposite sides of a square.3.1.5.1 DiscussionSur
20、face conductivity is expressed in siemens. It is popularly expressed as siemens/square (the size of the square is immaterial).Surface conductivity is the reciprocal of surface resistivity.3.1.6 conductivity, volume, nthe volume conductance multiplied by that ratio of specimen volume dimensions (dist
21、ancebetween electrodes divided by the cross-sectional area of the electrodes) which transforms the measured conductance to thatconductance obtained if the electrodes had formed the opposite sides of a unit cube.3.1.6.1 DiscussionVolume conductivity is usually expressed in siemens/centimetre or in si
22、emens/metre and is the reciprocal of volume resistivity.3.1.7 moderately conductive, adjdescribes a solid material having a volume resistivity between 1 and 10 000 000 -cm.3.1.8 resistance, insulation, (Ri), nthe ratio of the dc voltage applied to two electrodes (on or in a specimen) to the totalvol
23、ume and surface current between them.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 The last approved vers
24、ion of this historical standard is referenced on www.astm.org.D257 1423.1.8.1 DiscussionInsulation resistance is the reciprocal of insulation conductance.3.1.9 resistance, surface, (Rs), nthe ratio of the dc voltage applied to two electrodes (on the surface of a specimen) to thecurrent between them.
25、3.1.9.1 Discussion(Some volume resistance is unavoidably included in the actual measurement.) Surface resistance is the reciprocal of surfaceconductance.3.1.10 resistance, volume, (Rv), nthe ratio of the dc voltage applied to two electrodes (on or in a specimen) to the current inthe volume of the sp
26、ecimen between the electrodes.3.1.10.1 DiscussionVolume resistance is the reciprocal of volume conductance.3.1.11 resistivity, surface, (s), nthe surface resistance multiplied by that ratio of specimen surface dimensions (width ofelectrodes defining the current path divided by the distance between e
27、lectrodes) which transforms the measured resistance to thatobtained if the electrodes had formed the opposite sides of a square.3.1.11.1 DiscussionSurface resistivity is expressed in ohms. It is popularly expressed also as ohms/square (the size of the square is immaterial). Surfaceresistivity is the
28、 reciprocal of surface conductivity.3.1.12 resistivity, volume, (v), nthe volume resistance multiplied by that ratio of specimen volume dimensions (cross-sectional area of the specimen between the electrodes divided by the distance between electrodes) which transforms the measuredresistance to that
29、resistance obtained if the electrodes had formed the opposite sides of a unit cube.3.1.12.1 DiscussionVolume resistivity is usually expressed in ohm-centimetres (preferred) or in ohm-metres. Volume resistivity is the reciprocal ofvolume conductivity.4. Summary of Test Methods4.1 The resistance or co
30、nductance of a material specimen or of a capacitor is determined from a measurement of current or ofvoltage drop under specified conditions. By using the appropriate electrode systems, surface and volume resistance or conductancemay be are measured separately. The resistivity or conductivity can the
31、n be calculated when the requiredis calculated with theknown specimen and electrode dimensions are known.5. Significance and Use5.1 Insulating materials are used to isolate components of an electrical system from each other and from ground, as well as toprovide mechanical support for the components.
32、 For this purpose, it is generally desirable to have the insulation resistance as highas possible, consistent with acceptable mechanical, chemical, and heat-resisting properties. Since insulation resistance orconductance combines both volume and surface resistance or conductance, its measured value
33、is most useful when the testspecimen and electrodes have the same form as is required in actual use. Surface resistance or conductance changes rapidly withhumidity, while volume resistance or conductance changes slowly althoughwith the final change may eventually be greater.totalchange being greater
34、 in some cases.5.2 Resistivity or conductivity may be is used to predict, indirectly, the low-frequency dielectric breakdown and dissipationfactor properties of some materials. Resistivity or conductivity is often used as an indirect measure of: moisture content, degreeof cure, mechanical continuity
35、, or deterioration of various types. The usefulness of these indirect measurements is dependent onthe degree of correlation established by supporting theoretical or experimental investigations.Adecrease of surface resistance mayresult results either in an increase of the dielectric breakdown voltage
36、 because the electric field intensity is reduced, or a decreaseof the dielectric breakdown voltage because the area under stress is increased.5.3 All the dielectric resistances or conductances depend on the length of time of electrification and on the value of appliedvoltage (in addition to the usua
37、l environmental variables). These must be known and reported to make the measured value ofD257 143resistance or conductance meaningful. Within the electrical insulation materials industry, the adjective “apparent” is generallyapplied to resistivity values obtained under conditions of arbitrarily sel
38、ected electrification time. See X1.4.5.4 Volume resistivity or conductivity can be is calculated from resistance and dimensional data for use as an aid in designingan insulator for a specific application. The change Studies have shown changes of resistivity or conductivity with temperature andhumidi
39、ty may be great (1, 2, 3, 4),).4 and These changes must be known when designing for operating conditions. Volumeresistivity or conductivity determinations are often used in checking the uniformity of an insulating material, either with regardto processing or to detect conductive impurities that affe
40、ct the quality of the material and that mayare not be readily detectable byother methods.5.5 Volume resistivities above 1021 cm (1019 m), calculated from data obtained on specimens tested under usual laboratoryconditions, are of doubtful validity, considering the limitations of commonly used measuri
41、ng equipment.5.6 Surface resistance or conductance cannot be measured accurately, only approximated, because some degree of volumeresistance or conductance is always involved in the measurement. The measured value is also affected by the surfacecontamination. Surface contamination, and its rate of a
42、ccumulation, is affected by many factors including electrostatic chargingand interfacial tension. These, in turn, may affect the surface resistivity. Surface resistivity or conductivity can be is consideredto be related to material properties when contamination is involved but is not a material prop
43、erty of electrical insulation materialin the usual sense.6. Electrode Systems6.1 The electrodes for insulating materials should be of a material that is readily applied, allows are to allow intimate contactwith the specimen surface, and introduces no appreciable without introducing significant error
44、 because of electrode resistance orcontamination of the specimen (5). The electrode material should is to be corrosion-resistant under the conditions of the test. Fortests of fabricated specimens such as feed-through bushings, cables, etc., the electrodes employed are a part of the specimen orits mo
45、unting. Measurements In such cases, measurements of insulation resistance or conductance, then, conductance include thecontaminating effects of electrode or mounting materials and are generally related to the performance of the specimen in actualuse.6.1.1 Binding-Post and Taper-Pin Electrodes, Fig.
46、1 and Fig. 2, provide a means of applying voltage to rigid insulating materialsto permit an evaluation of their resistive or conductive properties. These electrodes simulateattempt to some degree simulate theactual conditions of use, such as binding posts on instrument panels and terminal strips. In
47、 the case of laminated insulatingmaterials having high-resin-content surfaces, somewhat lower insulation resistance values may be are obtained with taper-pin thanwith binding posts, due to more intimate contact with the body of the insulating material. Resistance or conductance valuesobtained are hi
48、ghly influenced by the individual contact between each pin and the dielectric material, the surface roughness of thepins, and the smoothness of the hole in the dielectric material. Reproducibility of results on different specimens is difficult toobtain.6.1.2 Metal Bars in the arrangement of Fig. 3 w
49、ere primarily devised to evaluate the insulation resistance or conductance offlexible tapes and thin, solid specimens as a fairly simple and convenient means of electrical quality control. This arrangement issomewhat more satisfactory for obtaining approximate values of surface resistance or conductance when the width of the insulatingmaterial is much greater than its thickness.4 The boldface numbers in parentheses refer to the list of references appended to these test methods.FIG. 1 Binding-Post Electrodes for Flat, Solid SpecimensD257 1446.1.3 S
