1、Designation: D 2477 07Standard Test Method forDielectric Breakdown Voltage and Dielectric Strength ofInsulating Gases at Commercial Power Frequencies1This standard is issued under the fixed designation D 2477; 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the dielec-tric breakdown voltage
3、 and dielectric strength of insulatinggases used in transformers, circuit breakers, cables, and similarapparatus as an insulating medium. The test method is appli-cable only to gases with boiling points below room temperatureat atmospheric pressure.1.2 This standard may involve hazardous materials,
4、opera-tions, and equipment. This standard does not purport toaddress all of the safety concerns, if any, associated with itsuse. It is the responsibility of the user of this standard toestablish appropriate safety and health practices and deter-mine the applicability of regulatory limitations prior
5、to use.1.3 Mercury has been designated by EPA and many stateagencies as a hazardous material that can cause centralnervous system, kidney and liver damage. Mercury, or itsvapor, may be hazardous to health and corrosive to materials.Caution should be taken when handling mercury and mercurycontaining
6、products. See the applicable product MaterialSafety Data Sheet (MSDS) for details and EPAs website http:/www.epa.gov/mercury/faq.htm for additional informa-tion. Users should be aware that selling mercury and/ormercury containing products into your state may be prohibitedby state law.2. Referenced D
7、ocuments2.1 ASTM Standards:2D 2864 Terminology Relating to Electrical Insulating Liq-uids and Gases2.2 IEEE Standard:3No. 4 Standard Techniques for High Voltage Testing2.3 ASTM Adjuncts:Dielectric cell assembly and detail (2 drawings)43. Terminology3.1 Definitions: For definitions of terms used in t
8、his testmethod, refer to Terminology D 2864.4. Significance and Use4.1 The dielectric breakdown voltage and dielectric strengthof an insulating gas in a uniform field depends primarily on themolecular structure of the gas. As different gases are mixedeither by plan or by contamination, any change in
9、 dielectricbreakdown voltage and dielectric strength will depend on boththe nature and proportion of the individual gases. This testmethod uses plane and spherical electrodes which provide anearly uniform field (see Appendix) in the area of electricaldischarge. It is suitable for determining the die
10、lectric break-down voltage and dielectric strength of different gases andmixtures thereof for research and application evaluations andalso as a field test. A more complete discussion of thesignificance of the dielectric strength test is given in theAppendix.5. Apparatus5.1 Electrical Apparatus:5.1.1
11、 TransformerThe desired test voltage may be mostreadily obtained by a step-up transformer energized from avariable low-voltage commercial power frequency source. Thetransformer and controlling element shall be of such size anddesign that, with the test specimen in the circuit, the crest factor(ratio
12、 of maximum to mean effective) of the 60-Hz test voltagedoes not differ by more than 65 % from that of a sinusoidalwave over the upper half of the range of test voltage. The crestfactor may be checked by means of an oscilloscope, a spheregap, or a peak-reading voltmeter in conjunction with an rmsvol
13、tmeter. Where the waveform cannot be determined conve-niently, a transformer having a rating of not less than12 kVAat the usual breakdown voltage shall be used. Transformers oflarger kVA capacity may be used, but in no case should thepower frequency short circuit current in the specimen circuit beou
14、tside the range of 1 to 10 mA/kV of applied voltage. This1This test method is under the jurisdiction of ASTM Committee D27 onElectrical Insulating Liquids and Gases and is the direct responsibility of Subcom-mittee D27.05 on Electrical Test.Current edition approved Oct. 1, 2007. Published October 20
15、07. Originallyapproved in 1966. Last previous edition approved in 2002 as D 2477 02e1.2For 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
16、 page onthe ASTM website.3Available from The Institute of Electrical and Electronic Engineers, Inc.(IEEE), 445 Hoes Ln., P.O. Box 1331, Piscataway, NJ 08854-1331.4Detailed drawings of this apparatus are available at a nominal cost from:ASTMInternational Headquarters. Order Adjunct No. ADJD2477.1Copy
17、right ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.limitation of current may be accomplished by using a suitableexternal series resistor or by employing a transformer withsufficient inherent reactance.5.1.2 Circuit-Interrupting EquipmentThe
18、test transformerprimary circuit shall be protected by an automatic circuit-breaking device capable of opening (as nearly instantaneouslyas possible) on the current produced by the breakdown of thetest specimen; a circuit breaker that opens within 5 cycles maybe used if the short-circuit current as d
19、escribed in 5.1.1 doesnot exceed 200 mA. A prolonged flow of current at the time ofbreakdown causes contamination of the gases and damage ofthe electrodes, thereby affecting the subsequent test results, andincreasing the electrode and test cell maintenance and time oftesting.5.1.3 Voltage-Control Eq
20、uipmentThe rate of voltage riseshall be12 kV/s 6 20 %. Voltage control may be secured by amotor-driven variable-ratio-autotransformer. Preference isgiven to equipment having an approximately straight-linevoltage-time curve over the desired operating range. Motordrive is preferred to manual drive bec
21、ause of the ease ofmaintaining a reasonably uniform rate-of-voltage rise with thistest method. The rate-of-voltage rise may be calculated frommeasurements of the time required to raise the voltage betweentwo prescribed values. When motor-driven equipment is used,calibrate the speed control rheostat
22、in terms of rate-of-voltagerise for the test transformer used.5.1.4 VoltmeterMeasure the voltage by a method thatfulfills the requirements of IEEE Standard No. 4, giving crestand also (if available) rms values, preferably by means of:5.1.4.1 Avoltmeter connected to the secondary of a separatepotenti
23、al transformer, or5.1.4.2 A voltmeter connected to a well-designed tertiarycoil in the test transformer, or5.1.4.3 A voltmeter connected to the low-voltage side of thetest transformer.5.1.5 AccuracyThe combined accuracy of the voltmeterand voltage divider circuit is not to exceed 5 % at the rate ofv
24、oltage rise specified in 5.1.3.5.2 Evacuation and Filling Apparatus:5.2.1 Vacuum PumpThe vacuum pump shall have suffi-cient pumping capacity to be able to evacuate the test cell to apressure below 0.133 kPa (1 torr).5.2.2 Vacuum and Pressure GageEither a mercury ma-nometer, or one or more gages, cap
25、able of measuring pressuresbelow 0.133 kPa (1 torr) and also near atmospheric pressure.The manometer, or vacuum and pressure gages, shall becalibrated in kPa or millimetres of mercury (torr).5.2.3 ConnectionsVacuum-tight tubing and valves shallbe used while evacuating and purging the test cell and f
26、illing itwith the gas sample.5.3 Electrodes and Test Cell:4FIG. 1 Test CellD 2477 0725.3.1 The sphere and plane electrodes shall be mountedvertically as shown in Fig. 1. The sphere shall be a precisionsteel bearing ball 19.1 mm (0.75 in.) in diameter. The planeelectrode shall be of brass 38.1 mm (1.
27、50 in.) in diameter. Thegap setting shall be 2.54 6 0.025 mm (0.100 6 0.001 in.). Thetolerance of all dimensions is 62 %, unless otherwise stated.5.3.2 The cell shall consist of a borosilicate glass cylinderclamped by flanges to end plates which seal the cell andsupport the electrodes.5The lower pla
28、ne electrode shall befixed. The sphere electrode, held in place by a magnet, shall beadjustable by means of a micrometer screw suitably mountedthrough the top plate. The micrometer screw must be suitablefor setting the electrodes to within the specified tolerance. Thebottom plate shall have a valved
29、 port for evacuation andadmission of the sample. If considered more convenient, twoports, one in the top for evacuation and one in the bottom foradmission of the sample may be used. The dimensions areshown in Fig. 1.6. Sampling6.1 Obtain the gas sample from the gas cylinder or gas-filledequipment th
30、rough a pressure-reducing regulator valve so thatthe flow into the cell may be controlled. The sample and cellmust be at room temperature before the gas is admitted to thecell.7. Preparation of Cell7.1 Clean the cell except for the electrodes by washing withsoap or detergent, then rinse with distill
31、ed or demineralizedwater and oven-dry. Clean the cell whenever necessary toremove detectable decomposition products formed by thebreakdown arc, or when testing different gases.7.2 Clean the electrodes with crocus cloth and naphtha.When the sphere electrode becomes pitted, it may be turned toa new po
32、sition until it is necessary to replace it.7.3 Assemble the cell by positioning and tightening the twoend flanges and gaskets.7.4 Turn the micrometer screw until the sphere just touchesthe plane electrode. The point where contact is made is bestchecked by a continuity meter connected to the two elec
33、trodes.7.5 Note the reading on the micrometer, add 2.54 mm(0.100 in.), and adjust the micrometer to this new setting.8. Test Conditions8.1 The dielectric breakdown voltage of an insulating gasunder ambient conditions varies with temperature and pressure.The standard conditions for the test are 101 k
34、Pa (760 torr) and25C. If the ambient temperature deviates slightly from 25Cadjust the gas pressure for the test as follows:P 5 273 1 T! 3 101/298where:P = gas pressure for the test, kPa, andT = ambient temperature, C.8.2 As an alternative to the pressure adjustment in 8.1 thetest may be made at ambi
35、ent temperature and pressure and thedielectric breakdown result multiplied by an approximatefactor, F, calculated as follows:F 5 273 1 T!/2.95 Pwhere:T = ambient temperature, C, andP = ambient gas pressure, kPa.8.3 The breakdown voltage of an insulating gas may beaffected by irradiation of the gas i
36、n the electrode gap. Suchirradiation can occur from random sources such as sunlight,artificial lights of various types, and nearby radioactive mate-rials. It is recommended that the test cell be shielded from suchsources as much as possible during test runs. See X1.4 andX1.5 for further discussion.9
37、. Procedure9.1 Fill the cell as follows:9.1.1 Evacuate the cell to a pressure of less than 0.133 kPa(1 torr).9.1.2 Fill the cell with the gas to be tested to atmosphericpressure or slightly above.9.1.3 Again evacuate the cell to a pressure of less than 0.133kPa (1 torr).9.1.4 Fill the cell with the
38、gas to be tested to either thecalculated pressure as in 8.1 or to atmospheric pressure and usethe factor as calculated in 8.2.9.2 Apply the voltage by increasing from zero at the rate ofapproximately12 kV/s until breakdown occurs as indicated byoperation of the circuit-interrupting equipment. Record
39、 thebreakdown voltage.9.3 Make five breakdowns on the one filling of the cell.9.4 To test a second sample, repeat the purging and filling asdescribed in 9.1.1-9.1.4.10. Report10.1 Report the following information:10.1.1 Source of gas and its molecular identification,10.1.2 The five individual breakd
40、own values and theiraverage, all multiplied by the factor, F, when the procedure in8.2 is followed,10.1.3 Ambient temperature and the pressure of the gaswhen tested, and10.1.4 Frequency of the voltage source.11. Precision and Bias11.1 The repeatability to be expected within a laboratoryand the agree
41、ment that should be obtained between laboratoriesare tabulated in Table 1 as a guide. The tabulated values areobtained from a cooperative test program involving ten labo-ratories each testing seven gases in test cells of same design.12. Keywords12.1 breakdown voltage; dielectric strength; gases; ins
42、ulat-ing gases5Standard laboratory borosilicate glass pipe and connecting flanges may be used.D 2477 073APPENDIX(Nonmandatory Information)X1. SIGNIFICANCE OF THE DIELECTRIC STRENGTH TESTX1.1 Dielectric breakdown of an insulating gas occurswhen the gas is stressed in an electric field that exceeds th
43、edielectric strength of the gas. An electric field can be applied toa gas by means of submerging two metal electrodes of oppositepolarity into the gas. As the voltage across the electrodes israised to a critical value, a spark jumps between the electrodesmanifesting a dielectric breakdown of the gas
44、. The dielectricbreakdown voltage, however, depends on the electric fieldproduced by the electrodes and the spacing between them. Fora given spacing, the highest breakdown voltage can beachieved when the field is uniform between the electrodes,such as that produced by two parallel-plane electrodes o
45、finfinite size. The dielectric strength of a gas is then equal to thisvoltage at a unit spacing and is expressed as kilovolts percentimetre or per inch.X1.2 Since parallel-plane electrodes of infinite size areimpractical, parallel electrodes of finite dimension have beendesigned with special contour
46、s at the electrode edges so thatthe breakdown spark takes place in the parallel-plane region,although the field outside this region is nonuniform. Rogowskiand Rengier6,7have utilized exponential and sinusoidal con-tours, respectively, so that the electric stress is the highestbetween the planes. How
47、ever, these electrodes are difficult tomanufacture and relatively bulky as compared to the sphere-to-plane electrode configuration used in this test method.X1.3 Although the field produced by the sphere-planeelectrodes is largely nonuniform, yet in the limited region at theminimum spacing, where spa
48、rking is observed in the dielectricbreakdown tests of insulating gases, the field is practicallyuniform. The dielectric strength (in terms of average electricalfield) of air determined with this test method is 30 kV/cm,which is the same as determined with the parallel-planeelectrodes. Consequently,
49、this test method may be used fordetermining the dielectric strength as well as measuring thedielectric breakdown voltage of insulating gases.X1.4 The breakdown voltage of insulating gases may beaffected by irradiation of the gas in the electrode gap of the testcell. Random irradiation caused by sunlight, some artificiallight sources, and nearby radioactive materials, can causescatter in test results. It is recommended that reasonable care beused in shielding the test cell from such random sources.X1.5 The committee sponsoring this test method consid-ered modif
