1、Designation: D495 14Standard 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, in the case of revision, the y
2、ear 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. Scope1.1 This test method covers,
3、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 chemicaldecomposition and erosion.
4、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, alternative test methodsshall be
5、 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 currents, and low voltage atlow or h
6、igh 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 control testing after correla
7、tion 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 performance in typical applica
8、tions 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 evaluation of changes in structure
9、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 insulating materials consistin
10、g 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, contaminated specimensurfaces. Their use
11、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, or that melt or form fluid res
12、idues 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 provided for information onlyan
13、d 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-bility of regulatory limitation
14、s 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 and Electronic Insulating Materi
15、als 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 reinstated in April 2014. DOI:10.152
16、0/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 standards, visit the ASTM webs
17、ite, 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 State
18、s1D2132 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 Insulating MaterialsD6054 Practice
19、 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 upon Test Method D495. IEC 61621
20、 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 resistance, nthe total elapsed tim
21、e 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 the upper surface of the specime
22、n.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 encountered when testingcertain mater
23、ials 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. Significance and Use4.1 The high-vo
24、ltage, 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 more easily among materials that
25、have 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 increased in the early stages by succ
26、essivelydecreasing 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 the current. Uponcooling, howev
27、er, 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.4.3.4 The fourth type occurs
28、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 fewseconds that overlap two stages t
29、han 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 failure by allowingthe specim
30、en 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 anundamaged area of the specimen.A
31、recommended 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 failure is to repeat the arc res
32、istance 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. Interferences5.1 Changes in both the timi
33、ng 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 order ofrank. Regardless of the c
34、onditions 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 testing materials withpoor to moder
35、ate 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 affect the disparate behavior of ro
36、delectrodes 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 the tungsten rod electrodes i
37、s 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 referenced onwww.astm.org.5Available fr
38、om 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 reproducibility among different
39、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 performance of the arc.6.1.1 Tra
40、nsformer, 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, Ta, An autotransformerrated
41、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 primary voltage supply is recomme
42、nded. 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 circuitcontaining no arc gap. Sin
43、ce 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 desirableto check for their pr
44、esence 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 of Tvbut inparallel with each
45、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 with R10, will providea 20 mA
46、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.6.1.6 Suppressing Resistor, R3Rate
47、d 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 wire. A single coil of this ind
48、uctance 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 lower steps of the test byopeni
49、ng 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 top, during a test.FIG. 1 Arc-R
