1、Designation: D495 14 An American National StandardStandard Test Method forHigh-Voltage, Low-Current, Dry Arc Resistance of SolidElectrical Insulation1This standard is issued under the fixed designation D495; the number immediately following the designation indicates the year oforiginal adoption or,
2、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.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scop
3、e1.1 This test method covers, in a preliminary fashion, thedifferentiation of similar materialsresistance to the action of ahigh-voltage, low-current arc close to the surface of insulation,when a conducting path is formed causing the material tobecome conducting due to the localized thermal and chem
4、icaldecomposition and erosion.1.2 The usefulness of this test method is very severelylimited by many restrictions and qualifications, some of whichare described in the following paragraphs and in Section 5.Generally, this test method shall not be used in materialspecifications. Whenever possible, al
5、ternative test methodsshall be used, and their development is encouraged.1.3 This test method will not, in general, permit conclusionsto be drawn concerning the relative arc resistance rankings ofmaterials that are potentially subjected to other types of arcs:for example, high voltage at high curren
6、ts, and low voltage atlow or high currents (promoted by surges or by conductingcontaminants).1.4 The test method is intended, because of its convenienceand the short time required for testing, for preliminary screen-ing of material, for detecting the effects of changes informulation, and for quality
7、 control testing after correlation hasbeen established with other types of simulated service arc testsand field experience. Because this test method is usuallyconducted under clean and dry laboratory conditions rarelyencountered in practice, it is possible that the prediction of amaterials relative
8、performance in typical applications and invarying “clean to dirty” environments will be substantiallyaltered (Note 1). Caution is urged against drawing strongconclusions without corroborating support of simulated servicetests and field testing. Rather, this test method is useful forpreliminary evalu
9、ation of changes in structure and compositionwithout the complicating influence of environmentalconditions, especially dirt and moisture.NOTE 1By changing some of the circuit conditions described hereinit has been found possible to rearrange markedly the order of arcresistance of a group of organic
10、insulating materials consisting ofvulcanized fiber and of molded phenolic and amino plastics, somecontaining organic, and some inorganic, filler.1.5 While this test method uses dry, uncontaminated speci-men surfaces, Test Method D2132, Test Methods D2303, andTest Method D3638 employ wet, contaminate
11、d specimensurfaces. Their use is recommended for engineering purposesand to assist in establishing some degree of significance to thistest method for quality control purposes.21.6 This test method is not applicable to materials that donot produce conductive paths under the action of an electricarc,
12、or that melt or form fluid residues that float conductiveresidues out of the active test area thereby preventing forma-tion of a conductive path.1.7 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are p
13、rovided for information onlyand are not considered standard.1.8 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-b
14、ility of regulatory limitations prior to use. For specificprecautionary statements, see 6.1.14, 6.1.19, Section 7, and10.1.1.2. Referenced Documents2.1 ASTM Standards:3D1711 Terminology Relating to Electrical Insulation1This test method is under the jurisdiction of ASTM Committee D09 onElectrical an
15、d Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.12 on Electrical Tests.Current edition approved April 1, 2014. Published May 2014. Originallyapproved in 1938. Last previous edition approved in 2004 as D495 94 (2004),which was withdrawn in January 2013 and reinst
16、ated in April 2014. DOI:10.1520/D0495-14.2Also helpful is Test Method D2302 for Wet Tracking Resistance of ElectricalInsulating Materials with Controlled Water-to-Metal Discharges. This test methodwas withdrawn and last appeared in the 1982 Annual Book of ASTM Standards, Part39.3For referenced ASTM
17、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 Conshohocke
18、n, PA 19428-2959. United States1D2132 Test Method for Dust-and-Fog Tracking and ErosionResistance of Electrical Insulating MaterialsD2303 Test Methods for Liquid-Contaminant, Inclined-Plane Tracking and Erosion of Insulating MaterialsD3638 Test Method for Comparative Tracking Index ofElectrical Insu
19、lating MaterialsD6054 Practice for Conditioning Electrical Insulating Mate-rials for Testing (Withdrawn 2012)42.2 IEC Standard:IEC 61621 Dry Solid Insulating MaterialsResistance TestTo High-Voltage, Low-Current Arc Discharges5NOTE 2IEC 61621 is technically equivalent to D495, and is directlybased up
20、on Test Method D495. IEC 61621 describes only the tungstenelectrodes, and does not include the stainless steel electrodes.3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this test method, referto Terminology D1711.3.2 Definitions of Terms Specific to This Standard:3.2.1 arc resi
21、stance, nthe total elapsed time in secondsfrom the start of this test procedure until failure occurs (seeSection 14).3.2.2 failure, nthe end-point of the test procedure em-ployed in this test method (see Section 14).3.2.3 normal orientation, na test condition in which theelectrodes are located on th
22、e upper surface of the specimen.3.2.4 inverted orientation, na test condition in which theelectrodes are located on the under surface of the specimen.3.2.4.1 DiscussionTests made with inverted orientationare more severe than tests made with normal orientation.Reduced data dispersion has been encount
23、ered when testingcertain materials using inverted orientation. With othermaterials, increased data dispersion may be encountered,especially with materials that evolve considerable gas duringtest.3.3 Abbreviations:3.3.1 The stainless steel strip electrodes are referred to ass.s.s. electrodes.4. Signi
24、ficance and Use4.1 The high-voltage, low-current type of arc resistance testis intended to simulate only approximately such service con-ditions as exist in alternating current circuits operating at highvoltage, but at currents limited to units and tens of milliam-peres.4.2 In order to distinguish mo
25、re easily among materials thathave low arc resistance, the early stages of this test method aremild, and the later stages are successively more severe. The arcoccurs intermittently between two electrodes resting on thesurface of the specimen, in normal or inverted orientation. Theseverity is increas
26、ed in the early stages by successivelydecreasing to zero the interval between flashes of uniformduration, and in later stages by increasing the current.4.3 Four general types of failure have been observed:4.3.1 Many inorganic dielectrics become incandescent,whereupon they are capable of conducting t
27、he current. Uponcooling, however, they return to their earlier insulating condi-tion.4.3.2 Some organic compounds burst into flame without theformation of a visible conducting path in the substance.4.3.3 Others are seen to fail by “tracking,” that is, a thinwiry line is formed between the electrodes
28、.4.3.4 The fourth type occurs by carbonization of the surfaceuntil sufficient carbon is present to carry the current.4.4 Materials often fail within the first few seconds after achange in the severity stage. When comparing the arc resis-tance of materials, much more weight shall be given to a fewsec
29、onds that overlap two stages than to the same elapsed timewithin a stage. Thus, there is a much greater difference in arcresistance between 178 and 182 s than between 174 and 178 s.NOTE 3Some investigators have reported attempts to characterize theremaining insulating value of the damaged area after
30、 failure by allowingthe specimen to cool to room temperature, without disturbance of theoriginal position of the electrodes, and then either (1) measuring theinsulation resistance between the electrodes or (2) determining thepercentage of breakdown voltage remaining relative to that obtained on anun
31、damaged area of the specimen.Arecommended circuit arrangement andtest procedure for carrying out the second of these two means ofcharacterizing the remaining insulating value of the damaged area isdescribed in Appendix X1. Still another, and obvious, method of reevalu-ating the damaged area after fa
32、ilure is to repeat the arc resistance test afterthe specimen has cooled, with the electrodes undisturbed from theiroriginal positions. However, keep in mind that none of these methods willbe universally applicable because of the severe physical damage to the testarea in many instances.5. Interferenc
33、es5.1 Changes in both the timing of the intermittent arc andthe current, as well as other changes affecting the nature of thedischarge, can affect the duration of a test of most specimenstaken from a group of dissimilar materials. Any of thesechanges can drastically alter a materials position in ord
34、er ofrank. Regardless of the conditions of anticipated use, do notuse data obtained by this test method to infer that the materialsexamined occupy an unchanging quality relationship to eachother.5.2 This test method describes two electrode systems: stain-less steel strip and tungsten rod. When testi
35、ng materials withpoor to moderate arc resistance (up to 180 s), use the stainlesssteel strip electrodes as the preferred technique. This techniquedecreases the variability often associated with the use of rodelectrodes on materials having poor or moderate arc resistance.All of the factors that affec
36、t the disparate behavior of rodelectrodes on such materials have not yet been fully reported.It is permissible to make additional tests with rod electrodes, soas to provide a basis for comparison with other data obtainedwith such electrodes. For values of arc resistance greater than180 s, the use of
37、 the tungsten rod electrodes is recommendedbecause the corners of the stainless steel strip electrodes erodeappreciably under such conditions. It is possible that resultsobtained with the use of the tungsten rod electrode system will4The last approved version of this historical standard is reference
38、d onwww.astm.org.5Available from American National Standards Institute, 11 W 42ndSt., NewYork, NY 10036.D495 142be different from those obtained with the use of the stainlesssteel strip electrode system.6. Apparatus6.1 The apparatus (see Fig. 1 for electrical circuit) isspecified to maximize data re
39、producibility among different testsets. The arc obtained will be relatively quiet, rather than thecrackly blue spark characteristic of a condenser discharge.Primary voltage control is made by a variable transformerrather than by a variable inductance because of its proveddeleterious effect on the pe
40、rformance of the arc.6.1.1 Transformer, TvA self-regulating transformer (non-power factor corrected) with a rated primary potential of 115 Vat 60 Hz ac, a rated secondary potential (on open circuit) of15 000 V, and a rated secondary current (on short circuit) of0.060 A.6.1.2 Variable Autotransformer
41、, Ta, An autotransformerrated at 7 A or more, and nominally adjustable up to 135 V.6.1.3 Voltmeter, V1An ac voltmeter, readable to 1 V in therange 90 to 130 V, is permanently connected across the outputof the autotransformer to indicate the voltage supplied to theprimary circuit.NOTE 4A constant pri
42、mary voltage supply is recommended. Com-mercially available line voltage stabilizers that do not distort the voltagewave form are suitable.6.1.4 Milliammeter, AAn ac milliammeter capable ofreading from 10 to 40 mA with an error of not over 65%.Before use, this meter shall be calibrated in a test cir
43、cuitcontaining no arc gap. Since this milliammeter is used onlywhen setting up or making changes in the circuit, it is to beshorted out by a by-pass switch when not in use.NOTE 5Although provision has been made for the suppression ofradio-frequency components of current in the arc, it will often be
44、desirableto check for their presence when the apparatus is first constructed. This isdone by use of a suitable thermocouple-type r-f milliammeter temporarilyinserted in series with the milliammeter.6.1.5 Current Control Resistors, R10,R20,R30,R40Fourresistors are required in series with the primary
45、of Tvbut inparallel with each other. These resistors must be adjustable topermit exact settings of the currents during calibration. R10isalways in the circuit to provide a 10 mA current. Its value isapproximately 60 , with a current rating of at least 114 A.Closing switch S20, to add R20in parallel
46、with R10, will providea 20 mA arc current. R20is about 50 with a current rating ofat least 134 A. Similarly, R30and R40have values of about 30 and 15 respectively, with associated current ratings of 2and 5 A. These resistors, when switched in, provide arccurrents of 30 mA and 40 mA respectively.6.1.
47、6 Suppressing Resistor, R3Rated at 15 000 and atleast 24 W. This resistor, along with the inductors in 6.1.7,isused to suppress parasitic high frequency in the arc circuit.6.1.7 Air Core InductorsInductance totaling from 1.2 to1.5 H is obtained from about 8 coils of No. 30 cotton- orenamel-covered w
48、ire. A single coil of this inductance must notbe used. Each coil consists of 3000 to 5000 turns of wirewound or insulating nonmetallic cores of about12 in. (12.7mm) diameter and58 in. (15.9) inside length.6.1.8 Interruptor, IThis motor-driven device is used togive the required cycles for the three l
49、ower steps of the test byopening and closing the primary circuit according to theschedule in Table 1, with an accuracy of 61120 s or better. Theinterruptor can be a synchronous motor driving three appro-priate sets of cams which actuate the contactor switches.6.1.9 Timer, TTA stop watch or electric interval timeroperating at 115 V ac, accurate to 1 s.6.1.10 Indicator Lamp, ILA6 W, 115 V lamp with a 2000 resistor, R1, in series. This lamp indicates the interruptingNOTE 1Switches SMto S40are aligned in the sequence of theirclosing, from bottom to t
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