1、Designation: D3755 14 An American National StandardStandard Test Method forDielectric Breakdown Voltage and Dielectric Strength ofSolid Electrical Insulating Materials Under Direct-VoltageStress1This standard is issued under the fixed designation D3755; the number immediately following the designati
2、on 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.1. Scope1.1 This test method covers the determi
3、nation of dielectricbreakdown voltage and dielectric strength of solid electricalinsulating materials under direct-voltage stress.1.2 Since some materials require special treatment, refer-ence shall also be made to ASTM specifications or to the testmethod directly applicable to the material to be te
4、sted. See TestMethod D149 for the determination of dielectric strength ofelectrical insulating materials at commercial power frequen-cies.1.3 This test method is similar to IEC Publication 243-2.Allprocedures in this test method are included in IEC 243-2.Differences between this test method and IEC
5、243-2 are largelyeditorial.1.4 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 p
6、rior to use. Specific precautionstatements are given in Section 7.2. Referenced Documents2.1 ASTM Standards:2D149 Test Method for Dielectric Breakdown Voltage andDielectric Strength of Solid Electrical Insulating Materialsat Commercial Power FrequenciesD176 Test Methods for Solid Filling and Treatin
7、g Com-pounds Used for Electrical Insulation (Withdrawn 2013)3D877 Test Method for Dielectric Breakdown Voltage ofInsulating Liquids Using Disk ElectrodesD1711 Terminology Relating to Electrical InsulationD2436 Specification for Forced-Convection Laboratory Ov-ens for Electrical Insulation (Withdrawn
8、 1994)3D3487 Specification for Mineral Insulating Oil Used inElectrical Apparatus2.2 ANSI Standard:4ANSI C68.1 Techniques for Dielectric Tests, IEEE StandardNo. 4.2.3 IEC Standard:IEC 243-2 Methods of test for electric strength of solidinsulating materialsPart 2: Additional requirements fortests usi
9、ng direct voltage43. Terminology3.1 Definitions:3.1.1 creepage distance, nshortest distance between twoconductive parts (typically metal), measured along the surfaceof the dielectric insulator.3.1.2 dielectric breakdown voltage, nRefer to Terminol-ogy D1711.3.1.3 dielectric strength, nRefer to Termi
10、nology D1711.3.1.4 flashover, nRefer to Terminology D1711.4. Summary of Test Method4.1 The specimen, held in a properly designed electrodesystem, is electrically stressed by the application of an increas-ing direct voltage until internal breakdown occurs. The testvoltage is applied at a uniform rate
11、 of increase. The directvoltage is obtained from a high-voltage supply of adequatecurrent capacity and regulation, reasonably ripple-free, withfacilities for measuring and controlling the output voltage.5. Significance and Use5.1 This test method is intended for use as a control andacceptance test f
12、or direct-voltage applications. It can also be1This 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 May 15, 2014. Published June 2014. Orig
13、inallyapproved in 1979. Last previous edition approved in 2004 as D3755 97 (2004),which was withdrawn in January 2013 and reinstated in June 2014. DOI:10.1520/D3755-14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual
14、 Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.Co
15、pyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1used in the partial evaluation of material for specific end usesand as a means for detecting changes in material due to specificdeteriorating causes.5.2 Experience indicates that the break
16、down value obtainedwith direct voltage usually will be approximately 2 to 4 timesthe rms value of the 60-Hz alternating-voltage breakdown.5.3 For a nonhomogeneous test specimen, the distributionof voltage stress within the specimen is determined by imped-ance (largely capacitive) with alternating vo
17、ltage. With anincreasing direct voltage, the voltage distribution will still belargely capacitive, although this depends partly on the rate ofvoltage increase. After steady application of direct voltage thevoltage division across the test specimen is determined byresistance. The choice of direct or
18、alternating voltage dependsupon the purpose for which the breakdown test is to be used,and to some extent, on the intended application of the material.5.4 A more complete discussion of the significance ofdielectric breakdown tests is given in Appendix X1 of thismethod and in Appendix X1 of Test Meth
19、od D149. Thoseappendix sections of Test Method D149 that refer to alternatingvoltage are not applicable to the direct-voltage method.6. Apparatus6.1 Basic Direct-Voltage Power Supplies, or dielectric testsets of various voltage ratings, which can operate with one ofthe two output terminals grounded,
20、 are commonly availablecommercially. Such apparatus customarily includes the neces-sary voltage-control, voltage-measuring, and circuit-interrupting equipment. A provision for retaining the break-down voltage reading after breakdown is desirable.6.1.1 For a direct voltage derived from a rectified an
21、dfiltered power frequency source, ripple on the output voltageshall be less than 1 %. The criterion is met if the time constantof the circuit is at least 0.4 s. The time constant is product ofthe filter capacitance plus the specimen capacitance inmicrofarads, and the specimen insulation resistance (
22、in mega-ohms) corresponding to the parallel combination of the volt-meter circuit resistance and the specimen resistance.6.2 Voltage Control, that will enable the test voltage to beincreased at a linear rate. Preference shall be given to avariable-speed motor-driven voltage control over a manualcont
23、rol. The rate-of-rise of test voltage shall not vary more than620 % from the specified rate at any point.6.3 Voltmeter, to measure the voltage directly applied to theelectrode system. The response of the voltmeter shall be suchthat its time lag shall not introduce an error greater than 1 % offull sc
24、ale at any rate-of-rise used. The overall accuracy of thevoltmeter and the voltage-measuring device used shall be suchthat the measurement error will not exceed 62 % of full scaleand be in accordance with ANSI C68.1.6.4 Electrodes:6.4.1 For those cases when the insulating material is in theform of f
25、lat sheet or tape, or is of the nature of a semisolid (forexample, grease potting material, and so forth) the electrodesshall be selected from those listed in Table 1 of Test MethodD149. The electrode contact pressure shall be adequate toobtain good electrical contact.6.4.2 Where excellent electrode
26、 contact is consideredimportant, use paint or vaporized metal electrodes. Suchelectrodes shall also be used when specimen geometry preventsthe use of rigid, solid metal electodes. It is possible that theresults obtained with painted or sprayed electrodes will not becomparable with those obtained usi
27、ng other types of elec-trodes.6.5 Test ChamberFor tests under other than ambientconditions, the specimen must be placed in a suitable environ-mental chamber of adequate size. For tests at elevatedtemperatures, an oven that meets the requirements of Specifi-cation D2436 will be convenient. The test c
28、hamber must beequipped with safety devices (Section 7).6.6 Ground SwitchThe power supply shall be equippedwith a grounding switch that is gravity operated and designedto close in less than 0.5 s. The grounding switch shall connectthe high-voltage output terminal of the power supply andground termina
29、l through a low resistance when the inputsupply power is removed or the test chamber door is opened.7. Safety Precautions7.1 WarningLethal voltages are a potential hazard duringthe performance of this test. It is essential that the testapparatus, and all associated equipment electrically connectedto
30、 it, be properly designed and installed for safe operation.Solidly ground all electrically conductive parts that a personcan contact during the test. Provide means for use at thecompletion of any test to ground any parts that were at highvoltage during the test or have the potential for acquiring an
31、induced charge during the test or retaining a charge even afterdisconnecting the voltage source. Thoroughly instruct alloperators as to the correct procedures for performing testssafely. When making high-voltage tests, particularly in com-pressed gas or in oil, it is possible for the energy released
32、 atbreakdown to be sufficient to result in fire, explosion, orrupture of the test chamber. Design test equipment, testchambers, and test specimens so as to minimize the possibilityof such occurrences and to eliminate the possibility of personalinjury. If the potential for fire exists, have fire supp
33、ressionequipment available.7.2 When a direct-voltage test has been applied to the testspecimen, both the specimen and power supply can remaincharged after the test voltage source has been de-energized.This will present a hazard to test personnel. Direct-voltagetesting is more hazardous than testing
34、with alternating voltage,where the charge on the specimen is rapidly dissipated in thelow-impedance winding of the test transformer after the test isde-energized.7.3 The test specimen and high-voltage output of the powersupply must be enclosed in a grounded metallic screen. Accessto the test enclosu
35、re must be dependent upon prior groundingof the power supply and test specimen through a low resistanceas referred to in 6.6.7.4 A manual grounding stick must be used to completelydischarge the test specimen and power supply after the test andD3755 142prior to handling them. The grounding stick shal
36、l be left incontact with the test specimen and high-voltage transformerterminals for as long as feasible.7.5 WarningOzone is a physiologically hazardous gas atelevated concentrations. Levels of acceptable industrial expo-sure have been established by the American Conference ofGovernment and Industri
37、al Hygienists.5Ozone has a distinc-tive odor that is initially discernible at low concentrations, buttemporary loss of the sense of smell can occur. It is likely to bepresent wherever voltages exist that are sufficient to causepartial or complete discharges in air or other atmospherescontaining oxyg
38、en. When the odor of ozone is persistentlypresent or when ozone generating conditions continue, theconcentration of ozone in the atmosphere shall be measuredusing commercially available monitoring devices. Appropriatemeans, such as installation of exhaust vents, shall be taken tomaintain ozone conce
39、ntrations in working areas within accept-able levels.8. Criteria of Breakdown8.1 Dielectric breakdown is generally accompanied by anincrease in current in the test circuit that will activate a sensingelement such as a circuit breaker, a fuse, or current-sensingcircuit. If sensitivity of the element
40、is well coordinated with thecharacteristics of the test equipment and the material undertest, its operation will be a positive indication of breakdown.8.2 Failure of a circuit breaker to operate is not be a positivecriterion of the absence of breakdown.Abreaker can fail to tripbecause it is set for
41、too great a current or because ofmalfunction. On the other hand, if the tripping circuit is set fortoo low a current, currents due to leakage or partial discharge(corona) will cause it to trip before breakdown voltage isreached.8.3 Observe the specimen during the test to ascertain thattripping of th
42、e breaker or current-sensing circuit is not causedby flashover. When flashover is a problem, it will be necessaryto provide for more creepage distance around the electrodes, todecrease specimen thickness, or to immerse the specimen in aliquid dielectric (Section 13).8.4 Observation of actual rupture
43、 or decomposition is posi-tive evidence of specimen breakdown. In test position,however, these physical evidences of breakdown are notalways apparent. If breakdown is in question it is commonpractice to repeat the test on the same specimen. Breakdown isconfirmed when reapplication of test voltage re
44、sults in asubstantially lower breakdown voltage.9. Test Specimens9.1 For a description of test specimens of materials and theirpreparation, refer to the ASTM methods applicable to thematerials to be tested.9.2 Provide specimens that are representative of the materialto be tested. Prepare enough spec
45、imens to permit making fivetests. In the preparation of test specimens from solid materials,take care that the surfaces in contact with the electrodes areparallel and as plane and smooth as the material permits.9.3 Thin Solid Materials (Sheets and Plates Less than 3 mmThick)Prepare test specimens of
46、 sufficient area to preventflashover under the conditions of test.9.4 Thick Solid MaterialsThe breakdown of thick solidmaterials is generally so high that the specimen must beimmersed in insulating fluid to prevent flashover and tominimize partial discharge. See Section 13. Other techniquesthat can
47、be used to prevent flashover are:9.4.1 The machining of a recess in the test specimen for anelectrode.9.4.2 The use of shrouds on the test specimen.9.4.3 The application of a sealing apparatus under pressureto the upper and lower faces of the test specimen.10. Thickness10.1 The thickness used in com
48、puting the dielectric strengthshall be the average thickness of the specimen measured asspecified in the test method for the material involved. If notspecified, the thickness measurement shall be made at roomtemperature of 25 6 5C.10.2 If the material is laminar or known to vary in dielectricstrengt
49、h with orientation, such as caused by graininess, thespecimen shall be cut so that its thickness is in the direction ofthe electric field under use conditions.10.3 When thin materials, such as laminates, are to be testedin the direction of their width or length, special procedures willbe needed to avoid flashover, some of which are described in9.4.11. Number of Tests11.1 Unless otherwise specified, test five specimens.12. Conditioning12.1 The dielectric strength of most insulating materialsvaries with temperature and humidity. Condition such materi-als in a suitably cont
