Example: tourism industry

Standard Test Methods for DC Resistance or Conductance of ...

Designation: D257 07An American National StandardStandard Test Methods forDC Resistance or Conductance of Insulating Materials1 This Standard is issued under the fixed designation D257; the number immediately following the designation indicates the year oforiginal adoption 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 Standard has been approved for use by agencies of the Department of Scope* These test Methods 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 as the corresponding conductancesand These test Methods are not suitable for use in measuringthe electrical Resistance / Conductance of moderately conductivematerials.

(cross-sectional area of the specimen between the electrodes divided by the distance between electrodes) which transforms the measured resistance to that resistance obtained if the electrodes had formed the opposite sides of a unit cube. 3.1.11.1 Discussion—Volume resistivity is usually ex-pressed in ohm-centimetres (preferred) or in ohm-metres.

Tags:

  Cross

Information

Domain:

Source:

Link to this page:

Please notify us if you found a problem with this document:

Other abuse

Transcription of Standard Test Methods for DC Resistance or Conductance of ...

1 Designation: D257 07An American National StandardStandard Test Methods forDC Resistance or Conductance of Insulating Materials1 This Standard is issued under the fixed designation D257; the number immediately following the designation indicates the year oforiginal adoption 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 Standard has been approved for use by agencies of the Department of Scope* These test Methods 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 as the corresponding conductancesand These test Methods are not suitable for use in measuringthe electrical Resistance / Conductance of moderately conductivematerials.

2 Use Test MethodD4496to evaluate such This Standard describes several general alternativemethodologies for measuring Resistance (or Conductance ).Specific materials can be tested most appropriately by usingstandard ASTM test Methods applicable to the specific materialthat define both voltage stress limits and finite electrificationtimes as well as specimen configuration and electrode geom-etry. These individual specific test methodologies would bebetter able to define the precision and bias for the The procedures appear in the following sections:Test Method or ProcedureSectionCalculation13 Choice of Apparatus and Test Method7 Cleaning Solid of Specimens11 Effective Area of Guarded ElectrodeAppendixX2 Electrode Systems6 Factors Affecting Insulation Resistance or ConductanceMeasurementsAppendixX1 Humidity Specimens and and Bias15 Procedure for the Measurement of Resist-ance or Conductance12 Referenced Documents2 Report14 Sampling8 Significance and Use5 Specimen Mounting10 Summary of Test Methods4 Terminology3 Test Specimens for Insulation, Volume, and SurfaceResistance or Conductance Determination9 Typical Measurement Standard does not purport to address all of thesafety concerns, if any, associated with its use.

3 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 Referenced Standards:2D150 Test Methods for AC Loss Characteristics and Per-mittivity (Dielectric Constant) of Solid Electrical Insula-tionD374 Test Methods for Thickness of Solid Electrical Insu-lationD1169 Test Method for Specific Resistance (Resistivity) ofElectrical Insulating LiquidsD1711 Terminology Relating to Electrical InsulationD4496 Test Method for D-C Resistance or Conductance ofModerately Conductive MaterialsD5032 Practice for Maintaining Constant Relative Humid-ity by Means of Aqueous Glycerin SolutionsD6054 Practice for Conditioning Electrical Insulating Ma-terials for TestingE104 Practice for Maintaining Constant Relative Humidityby Means of Aqueous Solutions3. The following definitions are taken fromTerminologyD1711and apply to the terms used in the text ofthis , insulation,n the ratio of the totalvolume and surface current between two electrodes (on or in aspecimen) to the dc voltage applied to the two Insulation Conductance is the recipro-cal of insulation test Methods are under the jurisdiction of ASTM CommitteeD09onElectrical and Electronic Insulating Materials and are the direct responsibility Electrical edition approved May 15, 2007.

4 Published June 2007. Originallyapproved in 1925. Last previous edition approved in 2005 as D257 99(2005).DOI: referenced ASTM standards, visit the ASTM website, , orcontact ASTM Customer Service at ForAnnual Book of ASTMS tandardsvolume information, refer to the Standard s Document Summary page onthe ASTM *A Summary of Changes section appears at the end of this (C) ASTM International. 100 Barr Harbour Drive, PO Box C700, West Conshohocken, Pennsylvania 19428-2959, United States Copyright by ASTM Int'l (all rights reserved); Wed Jul 11 19:48:55 EDT 2012 Downloaded/printed byUniversity of California Berkeley Library pursuant to License Agreement. No further reproductions , surface,n the ratio of the currentbetween two electrodes (on the surface of a specimen) to the dcvoltage applied to the (Some volume Conductance is un-avoidably included in the actual measurement.) Surface con-ductance is the reciprocal of surface , volume,n the ratio of the current in thevolume of a specimen between two electrodes (on or in thespecimen) to the dc voltage applied to the two Volume Conductance is the reciprocalof volume , surface,n the surface conductancemultiplied 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 Surface conductivity is expressed insiemens.

5 It is popularly expressed as siemens/square (the sizeof the square is immaterial). Surface conductivity is thereciprocal of surface , volume,n the volume conductancemultiplied by that ratio of specimen volume dimensions(distance between electrodes 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 Volume conductivity is usually ex-pressed in siemens/centimetre or in siemens/metre and is thereciprocal of volume conductive,adj describes a solid mate-rial having a volume resistivity between 1 and 10 000 , insulation, (Ri),n the ratio of the dcvoltage applied to two electrodes (on or in a specimen) to thetotal volume and surface current between Insulation Resistance is the reciprocalof insulation , surface, (Rs),n the ratio of the dc voltageapplied to two electrodes (on the surface of a specimen)

6 To thecurrent between (Some volume Resistance is unavoid-ably included in the actual measurement.) Surface Resistance isthe reciprocal of surface , volume, (Rv),n the ratio of the dc voltageapplied to two electrodes (on or in a specimen) to the currentin the volume of the specimen between the Volume Resistance is the reciprocal ofvolume , surface, (rs),n the 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 obtained if the electrodes had formed the opposite sidesof a Surface resistivity is expressed inohms. It is popularly expressed also as ohms/square (the size ofthe square is immaterial). Surface resistivity is the reciprocal ofsurface , volume, (rv),n the 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 sides of a unit Volume resistivity is usually ex-pressed in ohm-centimetres (preferred) or in resistivity is the reciprocal of volume Summary of Test The Resistance or Conductance of a material specimen orof a capacitor is determined from a measurement of current orof voltage drop under specified conditions.

7 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 are Significance and 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 possible, 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 use. Surface Resistance or conductancechanges rapidly with humidity, while volume Resistance orconductance changes slowly although the final change mayeventually be Resistivity or conductivity may be used to predict,indirectly, the low-frequency dielectric breakdown and dissi-pation factor properties of some materials.

8 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 bysupporting 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 All the 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 electricalinsulation materials industry, the adjective apparent is gen-erally applied to resistivity values obtained under conditions ofarbitrarily selected electrification time.

9 Volume resistivity or conductivity can be calculatedfrom Resistance and dimensional data for use as an aid inD257 072 Copyright by ASTM Int'l (all rights reserved); Wed Jul 11 19:48:55 EDT 2012 Downloaded/printed byUniversity of California Berkeley Library pursuant to License Agreement. No further reproductions 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 aninsulating 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 Volume resistivities above 1021V cm (1019V m), cal-culated from data obtained on specimens tested under usuallaboratory conditions, are of doubtful validity, considering thelimitations of commonly used measuring Surface Resistance or Conductance cannot be measuredaccurately, only approximated, because some degree of volumeresistance or Conductance is always involved in the measure-ment.

10 The measured 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 be related to material properties when contami-nation is involved but is not a material property of electricalinsulation material in the usual Electrode The electrodes for insulating materials should be of amaterial that is readily applied, allows intimate contact with thespecimen 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 a part of the specimen or its mounting.


Related search queries