1、Designation: D 2275 01(Reapproved 2008)e1An American National StandardStandard Test Method forVoltage Endurance of Solid Electrical Insulating MaterialsSubjected to Partial Discharges (Corona) on the Surface1This standard is issued under the fixed designation D 2275; the number immediately following
2、 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.e1NOTEThe units statement in subs
3、ection 1.2 was corrected and old footnote ten deleted to conform to ASTM guidelines onsole source editorially in July 2008.1. Scope1.1 This test method differentiates among solid electricalinsulating materials for use at commercial power frequencieswith respect to their voltage endurance under the a
4、ction ofcorona (see Note 1). In general, this test method is moremeaningful for rating materials with respect to their resistanceto prolonged a-c stress under corona conditions than is dielec-tric strength.NOTE 1The term “corona” is used almost exclusively in this testmethod instead of “partial disc
5、harge”, because it is a visible glow at theedge of the smaller electrode. This is a difference in location, not in kind.Partial discharges also occur at the edges of electrodes, and in generalcorona describes an electrical discharge irrespective of its location.1.2 The values stated in SI units are
6、to be regarded asstandard. The values given in parentheses are mathematicalconversions to inch-pound units that are provided for informa-tion only and are not considered standard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is therespon
7、sibility 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. For specific hazardstatements, see Section 7.2. Referenced Documents2.1 ASTM Standards:2D 149 Test Method for Dielectric Breakdown Volt
8、age andDielectric Strength of Solid Electrical Insulating Materialsat Commercial Power FrequenciesD 1711 Terminology Relating to Electrical InsulationD 1868 Test Method for Detection and Measurement ofPartial Discharge (Corona) Pulses in Evaluation of Insu-lation SystemsD 5032 Practice for Maintaini
9、ng Constant Relative Humid-ity by Means of Aqueous Glycerin SolutionsD 6054 Practice for Conditioning Electrical Insulating Ma-terials for TestingE41 Terminology Relating To ConditioningE 104 Practice for Maintaining Constant Relative Humidityby Means of Aqueous SolutionsE 171 Specification for Atmo
10、spheres for Conditioning andTesting Flexible Barrier Materials2.2 Special Technical Publications:Symposium on Corona, STP 198, ASTM, 1956.2Corona Measurement and Interpretation, Engineering Di-electrics, Vol 1, STP 669, ASTM, 1979.22.3 International Electrotechnical Commission (IEC)Documents:IEC Pub
11、lication 60343 Recommended test methods for de-termining the relative resistance of insulating materials tobreakdown by surface discharges32.4 Institute of Electrical and Electronic Engineers (IEEE)Document:IEEE SS 11205-TBR Guide for the Statistical Analysis ofElectrical Insulation Voltage Enduranc
12、e Data, 198743. Terminology3.1 For definitions of other terms used in this standard, referto Terminology D 1711 and Test Method D 1868.3.2 Definitions of Terms Specific to This Standard:3.2.1 threshold voltageThat voltage below which failurewill not occur under the test conditions irrespective of th
13、eduration of the test.3.2.1.1 DiscussionDemonstration of a threshold is diffi-cult when the slope of a volt-time curve is small, and failuretimes are long. High frequency tests are often an aid in1This test method is under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating
14、 Materials and is the direct responsibility ofSubcommittee D09.12 on Electrical Tests.Current edition approved May 1, 2008. Published July 2008. Originally approvedin 1964. Last previous edition approved in 2001 as D 2275 01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcon
15、tact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.4Availabl
16、e from Institute of Electrical and Electronics Engineers, Inc. (IEEE),445 Hoes Ln., P.O. Box 1331, Piscataway, NJ 08854-1331, http:/www.ieee.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.demonstration, by reducing the time requ
17、ired to reach anecessary number of voltage cycles.3.2.2 voltage endurance, nThe time that an insulatingmaterial can withstand a prolonged alternating voltage stressunder the action of surface corona.3.2.3 voltage stress-time curve, nA plot of the logarithmof the mean or median time to failure of a m
18、aterial againstvoltage stress (or the logarithm of voltage stress) for aparticular set of test conditions.3.2.3.1 DiscussionThe plot is the quantitative depiction ofthe voltage stress endurance over a range of voltage stress forthe conditions of test, and for the thickness tested. The curvesof a mat
19、erial obtained at two thicknesses are different.3.2.4 volt-time curve, nA plot of the logarithm of themean or median time to failure of a material against voltage (orthe logarithm of voltage) for a particular set of test conditions.3.2.4.1 DiscussionThe plot is the quantitative depiction ofthe volta
20、ge endurance over a range of voltage for the condi-tions of the test, which includes the particular thickness tested.4. Summary of Test Method4.1 In this test method, voltage sufficient to produce coronais applied to the specimen until failure occurs. Comparativevoltage endurance is the relative tim
21、e to failure of two differentmaterials of the same thickness when tested with similarelectrodes at the same voltage. Comparison is also possible interms of the magnitude of voltage stress (kV/mm or kV/in.)required to produce failure in a specified number of hours.4.2 Surface corona exists in the ele
22、ctrically stressed gaswhere electrodes are near insulation surfaces.4.3 As with most tests at constant stress, there may be alarge dispersion of times to failure for a given sample. Themedian time of nine specimens (time of fifth failure) may beused as the failure time for the sample. This removes t
23、henecessity of waiting for the last few to fail. The mean may alsobe determined statistically (see IEEE SS 11205-TBR for addi-tional information).4.4 Under the proper conditions, the test may be acceleratedby increasing the frequency of the applied voltage (seeAppendix X1).4.5 Standardized test cond
24、itions and conditioning prior totesting are important. In particular, tests with specified air flowat both low and moderate humidities may be informative. Inspecial cases, where a service condition is thought to alter thecorona endurance, this factor should be introduced as part ofthe test and repor
25、ted. Such conditions might include elonga-tion, elevated temperature, high humidity, other gases besidesair, pollution, etc.4.6 Additional information from the test may be obtained ifcorona-voltage levels and corona intensity are measured at thestart of the test and monitored at various stages of de
26、teriorationof the insulation. The voltage levels include corona-inceptionvoltage, corona-extinction voltage, and corona intensity usingTest Method D 1868. Also, comparative measurements ofcorona power or energy by bridge and oscilloscope techniquescan be informative (see ASTM STP 198 and STP 669).4.
27、7 If elevated frequencies are used to accelerate the test, itis recommended that the corona-discharge pulse heights andenergy per cycle at the test frequency be compared with thesevalues at rated power frequency. If the energy per cycle is thesame, it can be concluded that failure time is inverselyp
28、roportional to frequency.5. Significance and Use5.1 This test method is used to compare the endurance ofdifferent materials to the action of corona on the externalsurfaces. A poor result on this test does not indicate that thematerial is a poor selection for use at high voltage or at highvoltage str
29、ess in the absence of surface corona. Surface coronashould be distinguished from corona that occurs in internalcavities for which no standardized test has been developed.Evaluation of endurance by comparison of data on specimensof different thickness is not valid.5.2 The processing of the material m
30、ay affect the resultsobtained. For instance, residual strains produced by quenching,or high levels of crystallinity caused by slow cooling mayaffect the result.Also, the type of molding process, injection orcompression, may be important especially if the mixing offillers or the concentration and siz
31、es of gas-filled cavities arecontrolled in any degree by the process. Indeed, this testmethod may be used to examine the effects of processing.5.3 The data are generated in the form of a set of values oflifetimes at a voltage. The dispersion of failure times can beanalyzed using Weibull or extreme v
32、alue statistics to yield anestimate of the central value of the distribution and its standarddeviation. This is particularly recommended when the disper-sion of failure times is large, and a comparison of lifetimes oftwo materials must be made at a specified level of confidence.5.4 This test is ofte
33、n used to demonstrate the differencesbetween different classes of materials, and to illustrate theimportance of eliminating corona in any application of aparticular material. When the test is used for such purposes orother similar ones, the need for precision is reduced, andcertain time saving techn
34、iques, such as truncating a test at thetime of the fifth failure of a set of nine, and using that time asthe measure of the central tendency, are recommended. Twosuch techniques are described in 10.2. Both techniques removethe necessity of testing beyond median failure, and reduce therequired testin
35、g time to approximately half of that required toobtain failures on all specimens.5.5 Insulating materials operating in a gaseous medium aresubjected to corona attack at operating voltage on some typesof electrical apparatus in those regions where the voltagegradient in the gas exceeds the corona inc
36、eption level. On othertypes of equipment, where detectable corona is absent initially,it may appear later due to transient over-voltages or changes ininsulation properties attending aging. Certain inorganic mate-rials can tolerate corona for a long time. Many organicmaterials are damaged quickly by
37、corona, and for these,operation with no detectable corona is imperative. This testmethod intensifies some of the more commonly met conditionsof corona attack so that materials may be evaluated in a timethat is relatively short compared to the life of the equipment.As with most accelerated life tests
38、, caution is necessary inextrapolation from the indicated life to actual life under variousoperating conditions in the field.5.6 The failure produced by corona may be due to one ofseveral possible factors. The corona may erode the insulationD 2275 01 (2008)e12until the remaining insulation can no lo
39、nger withstand theapplied voltage.The corona may cause the insulation surface tobecome conducting. For instance, carbonization may occur, sothat failure occurs quickly. On the other hand, compounds suchas oxalic acid crystals may be formed, as with polyethylene, inwhich case the surface conductance
40、will vary with ambienthumidity, and at moderate humidities the conductance may beat the proper level to reduce the potential gradient at theelectrode edge, and thus cause either a reduction in the amountof corona, or its cessation, thus retarding failure. The coronamay cause a “treeing” within the i
41、nsulation, which mayprogress to failure. It may release gases within the insulationthat change its physical dimensions. It may change the physicalproperties of an insulating material; for instance, it may causethe material to embrittle or crack, and thus make it useless.5.7 Tests are often made in o
42、pen air, at 50 % relativehumidity. It may be important for some materials to make testsin circulating air at 20 % relative humidity or less (seeAppendix X1). If tests are made in an enclosure, the restrictionin the flow of air or other gas may influence the results (seeAppendix X2).5.8 The shape of
43、the (voltage stress)-(time-to-failure) curveis sometimes useful as an indicator of the useable electricstrength of a material in an application involving surfacecorona and its variation with time of application of voltage,though such comparisons are risky. (Specimen thickness,electrode system, the p
44、resence of more than one mechanism offailure, and the details of the ambient, including the nature ofthe surface corona, all have significant effects.) For instance,on log-log paper, the volt-time curve often obtained by theprocedures of this test for void-free materials such as polyeth-ylene sheet
45、generally has a continuous curvature that is slightlyconcave upward. The low voltage end of the curve tendstoward the horizontal and approaches a threshold voltagebelow which the curve does not go. A similar threshold wouldbe expected for many materials in an application involvingsurface corona. Mor
46、eover, if the material possesses a lowelectric strength (as measured by Test Method D 149), orespecially if in service there is another mechanism of failure inthe short time range of this test, the shape of the left hand endof the curve would be affected and would not reach the samehigh levels of st
47、ress as are exhibited by polyethylene either onthis test or in many service applications, including surfacecorona. In summary, voltage stress-time curves are useful toolsfor examining modes and mechanisms of failure, but must beused with care.5.9 For materials that possess a basic resistance to coro
48、na,such as mica, or, to a smaller degree, silicone rubber, the timerequired for the curve to reach the threshold produced bycorona may be greater by many orders of magnitude than thetime required for materials such as polyethylene, polyethyleneterephthalate, or polytetrafluoroethylene.5.10 The varia
49、bility of the time to failure is a function of theconstancy of the parameters of the test, such as the testvoltages, which should be monitored. It is also a significantmaterial property. The Weibull slope factor, b, is recommendedas a measure of variability. b is the slope obtained whenpercent failure is plotted against failure time on Weibullprobability paper. Such a plot is called a “Weibull probabilityplot” (see Fig. 1).5.11 The shape of the Weibull probability plot can provideadditional information. A non-straight-line plot may indicatemore than one mechanism of failu
