ASTM_D_3756_-_97_2010.pdf

Designation:D375697(Reapproved 2010)Standard Test Method forEvaluation of Resistance to Electrical Breakdown by Treeingin Solid Dielectric Materials Using Diverging Fields1This standard is issued under the fixed designation D3756;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 reapproval.INTRODUCTIONWhen failure occurs in solid organic dielectrics that are subjected to very high,continuous,andnonuniform electrical gradients,it generally occurs by a mechanism called treeing.Materials ofdifferent molecular structures have different degrees of resistance to failure by treeing,and thisresistance can sometimes be increased by the addition of other materials in low concentration.2Trees that grow by a molecular degradation mechanism resulting from partial discharge(corona)arecalled electrical trees to distinguish them from water and electrochemical trees which are quitedifferent.This test method makes use of two opposing thin cylindrical electrodes,one sharpened to a point,the other with a hemispherical end.They are molded or inserted into blocks of the material to betested.Because of the shape of the electrodes this is often called a needle test.This test provides astatistical estimate of electrical treeing initiation and propagation of solid dielectric materials in high,diverging electrical fields.1.Scope1.1 This test method covers the evaluation and comparisonof the resistance of solid organic dielectric materials to theinitiation or growth,or both,of tubular tree-like channelsresulting from partial discharge(corona)and molecular decom-position that occur in the region of very high,diverging electricfields.3,41.2 This test method is primarily for use at a powerfrequency of 50 or 60 Hz.1.3 The test may be carried out at room temperature ortemperatures above or below room temperature.The tempera-ture should not exceed the softening or melting point of thesample material.1.4 This test method can be used for any solid material intowhich needles can be cast,molded,or inserted with heat aftermolding.The resistance to tree initiation is measured by thedouble-needle characteristic voltage,which is only applicableto non-opaque materials so that tree can be observed optically.The resistance to tree initiation and growth is reported by thedouble-needle voltage life,which is applicable to both opaqueand non-opaque materials.1.5 The values stated in SI units are to be regarded as thestandard.1.6 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 health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:5D149 Test Method for Dielectric Breakdown Voltage andDielectric Strength of Solid Electrical Insulating Materialsat Commercial Power FrequenciesD1711 Terminology Relating to Electrical Insulation1This test method is under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.12 on Electrical Tests.Current edition approved Oct.1,2010.Published October 2010.Originallyapproved in 1990.Last previous edition approved in 2004 as D3756 97(2004).DOI:10.1520/D3756-97R10.2Symposium on Engineering Dielectrics,ASTM STP 783,ASTM,1982,andSymposium on Engineering Dielectrics,ASTM STP 926,ASTM,1986.3W.D.Wilkens,Chapter 7,“Statistical Methods for the Evaluation of ElectricalInsulating Systems,”Engineering Dielectrics,Vol IIB,Electrical Properties of SolidInsulating Materials,Measurement Techniques,R.Bartnikas,Editor,ASTM STP926,ASTM,Philadelphia,1987.4R.M.Eichorn,Chapter 4,“Treeing in Solid Organic Dielectric Materials,”Engineering Dielectrics,Vol IIA,Electrical Properties of Solid Insulating Materi-als:Molecular Structure and Electrical Behavior,R.Bartnikas and R.M.Eichorn,Editors,ASTM STP 783,ASTM Philadelphia,1983.5For 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 Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 D1928 Practice for Preparation of Compression-MoldedPolyethylene Test Sheets and Test Specimens(Withdrawn2001)6D2275 Test Method for Voltage Endurance of Solid Electri-cal Insulating Materials Subjected to Partial Discharges(Corona)on the Surface2.2 Other Document:ANSI/IEEE 930-1987 IEEE Guide for the StatisticalAnaly-sis of Electrical Insulation Voltage Endurance Data73.Terminology3.1 Definitions:3.1.1 partial discharge,nrefer to D1711.3.2 Definitions of Terms Specific t