ASTMD 149

Designation: D 149 – 97a (Reapproved 2004) An American National Standard Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commercial Power Frequencies1 This standard is issued under the fixed designation D 149; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval. This standard has been approved for use by agencies of the Department of Defense. 1. Scope 1.1 This test method covers procedures for the determina- tion of dielectric strength of solid insulating materials at commercial power frequencies, under specified conditions.2,3 1.2 Unless otherwise specified, the tests shall be made at 60 Hz. However, this test method may be used at any frequency from 25 to 800 Hz. At frequencies above 800 Hz, dielectric heating may be a problem. 1.3 This test method is intended to be used in conjunction with any ASTM standard or other document that refers to this test method. References to this document should specify the particular options to be used (see 5.5). 1.4 It may be used at various temperatures, and in any suitable gaseous or liquid surrounding medium. 1.5 This test method is not intended for measuring the dielectric strength of materials that are fluid under the condi- tions of test. 1.6 This test method is not intended for use in determining intrinsic dielectric strength, direct-voltage dielectric strength, or thermal failure under electrical stress (see Test Method D 3151). 1.7 This test method is most commonly used to determine the dielectric breakdown voltage through the thickness of a test specimen (puncture). It may also be used to determine dielec- tric breakdown voltage along the interface between a solid specimen and a gaseous or liquid surrounding medium (flash- over). With the addition of instructions modifying Section 12, this test method may be used for proof testing. 1.8 This test method is similar to IEC Publication 243-1. All procedures in this method are included in IEC 243-1. Differ- ences between this method and IEC 243-1 are largely editorial. 1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility 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. Specific hazard statements are given in Section 7. Also see 6.4.1. 2. Referenced Documents 2.1 ASTM Standards: 4 D 374 Test Methods for Thickness of Solid Electrical Insu- lation D 618 Practice for Conditioning Plastics for Testing D 877 Test Method for Dielectric Breakdown Voltage of Insulating Liquids Using Disk Electrodes D 1711 Terminology Relating to Electrical Insulation D 2413 Practice for Preparation of Insulating Paper and Board Impregnated with a Liquid Dielectric D 3151 Test Method for Thermal Failure of Solid Electrical Insulating Materials Under Electric Stress D 3487 Specification for Mineral Insulating Oil Used in Electrical Apparatus D 5423 Specification for Forced-Convection Laboratory Ovens for Electrical Insulation 2.2 IEC Standard: Pub. 243-1 Methods of Test for Electrical Strength of Solid Insulating Materials—Part 1: Tests at Power Frequencies5 1 This test method is under the jurisdiction of ASTM Committee D09 on Electrical and Electronic Insulating Materials and is the direct responsibility of Subcommittee D09.12 on Electrical Tests. Current edition approved March 1, 2004. Published March 2004. Originally approved in 1922. Last previous edition approved in 1997 as D 149 – 97a. 2 Bartnikas, R., Chapter 3, “High Voltage Measurements,” Electrical Properties of Solid Insulating Materials, Measurement Techniques, Vol. IIB, Engineering Dielectrics, R. Bartnikas, Editor, ASTM STP 926, ASTM, Philadelphia, 1987. 3 Nelson, J. K., Chapter 5, “Dielectric Breakdown of Solids,” Electrical Properties of Solid Insulating Materials: Molecular Structure and Electrical Behavior, Vol. IIA, Engineering Dielectrics, R. Bartnikas and R. M. Eichorn, Editors, ASTM STP 783, ASTM, Philadelphia, 1983. 4 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards volume information, refer to the standard’s Document Summary page on the ASTM website. 5 Available from the International Electrotechnical Commission, Geneva, Swit- zerland. 1 Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States. 免费网(www.freebz.net) 标准最全面 免费标准网(www.freebz.net) 无需注册 即可下载 2.3 ANSI Standard: C68.1 Techniques for Dielectric Tests, IEEE Standard No. 46 3. Terminology 3.1 Definitions: 3.1.1 dielectric breakdown voltage (electric breakdown voltage), n—the potential difference at which dielectric failure occurs under prescribed conditions in an electrical insulating material located between two electrodes. (See also Appendix X1.) 3.1.1.1 Discussion—The term dielectric breakdown voltage is sometimes shortened to “breakdown voltage.” 3.1.2 dielectric failure (under test), n—an event that is evidenced by an increase in conductance in the dielectric under test limiting the electric field that can be sustained. 3.1.3 dielectric strength, n—the voltage gradient at which dielectric failure of the insulating material occurs under spe- cific conditions of test. 3.1.4 electric strength, n—see dielectric strength. 3.1.4.1 Discussion—Internationally, “electric strength” is used almost universally. 3.1.5 flashover, n—a disruptive electrical discharge at the surface of electrical insulation or in the surrounding medium, which may or may not cause permanent damage to the insulation. 3.1.6 For definitions of other terms relating to solid insulat- ing materials, refer to Terminology D 1711. 4. Summary of Test Method 4.1 Alternating voltage at a commercial power frequency (60 Hz, unless otherwise specified) is applied to a test specimen. The voltage is increased from zero or from a level well below the breakdown voltage, in one of three prescribed methods of voltage application, until dielectric failure of the test specimen occurs. 4.2 Most commonly, the test voltage is applied using simple test electrodes on opposite faces of specimens. The specimens may be molded or cast, or cut from flat sheet or plate. Other electrode and specimen configurations may be used to accom- modate the geometry of the sample material, or to simulate a specific application for which the material is being evaluated. 5. Significance and Use 5.1 The dielectric strength of an electrical insulating mate- rial is a property of interest for any application where an electrical field will be present. In many cases the dielectric strength of a material will be the determining factor in the design of the apparatus in which it is to be used. 5.2 Tests made as specified herein may be used to provide part of the information needed for determining suitability of a material for a given application; and also, for detecting changes or deviations from normal characteristics resulting from pro- cessing variables, aging conditions, or other manufacturing or environmental situations. This test method is useful for process control, acceptance or research testing. 5.3 Results obtained by this test method can seldom be used directly to determine the dielectric behavior of a material in an actual application. In most cases it is necessary that these results be evaluated by comparison with results obtained from other functional tests or from tests on other materials, or both, in order to estimate their significance for a particular material. 5.4 Three methods for voltage application are specified in Section 12: Method A, Short-Time Test; Method B, Step-by- Step Test; and Method C, Slow Rate-of-Rise Test. Method A is the most commonly-used test for quality-control tests. How- ever, the longer-time tests, Methods B and C, which usually will give lower test results, may give more meaningful results when different materials are being compared with each other. If a test set with motor-driven voltage control is available, the slow rate-of-rise test is simpler and preferable to the step-by- step test. The results obtained from Methods B and C are comparable to each other. 5.5 Documents specifying the use of this test method shall also specify: 5.5.1 Method of voltage application, 5.5.2 Voltage rate-of-rise, if slow rate-of-rise method is specified, 5.5.3 Specimen selection, preparation, and conditioning, 5.5.4 Surrounding medium and temperature during test, 5.5.5 Electrodes, 5.5.6 Wherever possible, the failure criterion of the current- sensing element, and 5.5.7 Any desired deviations from the recommended proce- dures as given. 5.6 If any of the requirements listed in 5.5 are missing from the specifying document, then the recommendations for the several variables shall be followed. 5.7 Unless the items listed in 5.5 are specified, tests made with such inadequate reference to this test method are not in conformance with this test method. If the items listed in 5.5 are not closely controlled during the test, the precisions stated in 15.2 and 15.3 may not be realized. 5.8 Variations in the failure criteria (current setting and response time) of the current sensing element significantly affect the test results. 5.9 Appendix X1. contains a more complete discussion of the significance of dielectric strength tests. 6. Apparatus 6.1 Voltage Source—Obtain the test voltage from a step-up transformer supplied from a variable sinusoidal low-voltage source. The transformer, its voltage source, and the associated controls shall have the following capabilities: 6.1.1 The ratio of crest to root-mean-square (rms) test voltage shall be equal to =2 6 5 % (1.34 to 1.48), with the test specimen in the circuit, at all voltages greater than 50 % of the breakdown voltage. 6.1.2 The capacity of the source shall be sufficient to maintain the test voltage until dielectric breakdown occurs. For most materials, using electrodes similar to those shown in Table 1, an output current capacity of 40 mA is usually satisfactory. For more complex electrode structures, or for 6 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036. D 149 – 97a (2004) 2 免费标准网(www.freebz.net) 标准最全面 免费标准网(www.freebz.net) 无需注册 即可下载 testing high-loss materials, higher current capacity may be needed. The power rating for most tests will vary from 0.5 kVA for testing low-capacitance specimens at voltages up to 10 kV, to 5 kVA for voltages up to 100 kV. 6.1.3 The controls on the variable low-voltage source shall be capable of varying the supply voltage and the resultant test voltage smoothly, uniformly, and without overshoots or tran- sients, in accordance with 12.2. Do not allow the peak voltage to exceed 1.48 times the indicated rms test voltage under any circumstance. Motor-driven controls are preferable for making short-time (see 12.2.1) or slow-rate-of-rise (see 12.2.3) tests. 6.1.4 Equip the voltage source with a circuit-breaking device that will operate within three cycles. The device shall disconnect the voltage-source equipment from the power service and protect it from overload as a result of specimen breakdown causing an overload of the testing apparatus. If prolonged current follows breakdown it will result in unnec- essary burning of the test specimens, pitting of the electrodes, and contamination of any liquid surrounding medium. 6.1.5 The circuit-breaking device should have an adjustable current-sensing element in the step-up transformer secondary, to allow for adjustment consistent with the specimen charac- teristics and arranged to sense specimen current. Set the sensing element to respond to a current that is indicative of specimen breakdown as defined in 12.3. 6.1.6 The current setting can have a significant effect on the test results. Make the setting high enough that transients, such as partial discharges, will not trip the breaker but not so high that excessive burning of the specimen, with resultant electrode damage, will occur on breakdown. The optimum current setting is not the same for all specimens and depending upon the intended use of the material and the purpose of the test, it may be desirable to make tests on a given sample at more than one current setting. The electrode area may have a significant effect upon what the current setting should be. 6.1.7 The specimen current-sensing element may be in the primary of the step-up transformer. Calibrate the current- sensing dial in terms of specimen current. 6.1.8 Exercise care in setting the response of the current control. If the control is set too high, the circuit will not respond when breakdown occurs; if set too low, it may respond to leakage currents, capacitive currents, or partial discharge (corona) currents or, when the sensing element is located in the primary, to the step-up transformer magnetizing current. 6.2 Voltage Measurement—A voltmeter must be provided for measuring the rms test voltage. A peak-reading voltmeter may be used, in which case divide the reading by =2 to get rms values. The overall error of the voltage-measuring circuit shall not exceed 5 % of the measured value. In addition, the response time of the voltmeter shall be such that its time lag will not be greater than 1 % of full scale at any rate-of-rise used. 6.2.1 Measure the voltage using a voltmeter or potential transformer connected to the specimen electrodes, or to a separate voltmeter winding, on the test transformer, that is unaffected by the step-up transformer loading. 6.2.2 It is desirable for the reading of the maximum applied test voltage to be retained on the voltmeter after breakdown so that the breakdown voltage can be accurately read and re- corded. 6.3 Electrodes—For a given specimen configuration, the dielectric breakdown voltage may vary considerably, depend- ing upon the geometry and placement of the test electrodes. For this reason it is important that the electrodes to be used be described when specifying this test method, and that they be described in the report. TABLE 1 Typical Electrodes for Dielectric Strength Testing of Various Types of Insulating MaterialsA Electrode Type Description of Electrodes B,C Insulating Materials 1 Opposing cylinders 51 mm (2 in.) in diameter, 25 mm (1 in.) thick with edges rounded to 6.4 mm (0.25 in.) radius flat sheets of paper, films, fabrics, rubber, molded plastics, laminates, boards, glass, mica, and ceramic 2 Opposing cylinders 25 mm (1 in.) in diameter, 25 mm (1 in.) thick with edges rounded to 3.2 mm (0.125 in.) radius same as for Type 1, particularly for glass, mica, plastic, and ceramic 3 Opposing cylindrical rods 6.4 mm (0.25 in.) in diameter with edges rounded to 0.8 mm (0.0313 in.) radiusD same as for Type 1, particularly for varnish, plastic, and other thin film and tapes: where small specimens necessitate the use of smaller electrodes, or where testing of a small area is desired 4 Flat plates 6.4 mm (0.25 in.) wide and 108 mm (4.25 in.) long with edges square and ends rounded to 3.2 mm (0.125 in.) radius same as for Type 1, particularly for rubber tapes and other narrow widths of thin materials 5 Hemispherical electrodes 12.7 mm (0.5 in.) in diameterE filling and treating compounds, gels and semisolid compounds and greases, embedding, potting, and encapsulating materials 6 Opposing cylinders; the lower one 75 mm (3 in.) in diameter, 15 mm (0.60 in.) thick; the upper one 25 mm (1 in.) in diameter, 25 mm thick; with edges of both rounded to 3 mm (0.12 in.) radiusF same as for Types 1 and 2 7 Opposing circular flat plates, 150 mm diameterG, 10 mm thick with edges rounded to 3 to 5 mm radiusH flat sheet, plate, or board materials, for tests with the voltage gradient parallel to the surface A These electrodes are those most commonly specified or referenced in ASTM standards. With the exception of Type 5 electrodes, no attempt has been made to suggest electrode systems for other than flat surface material. Other electrodes may be used as specified in ASTM standards or as agreed upon between seller and purchaser where none of these electrodes in the table is suitable for proper evaluation of the material being tested. B Electrodes are normally made from either brass or stainless steel. Reference should be made to the standard governing the material to be tested to determine which, if either, material is preferable. C The electrodes surfaces should be polished and free from irregularities resulting from previous testing. D Refer to the appropriate standard for the load force applied by the upper electrode assembly. Unless otherwise specified the upper electrodes shall be 50 6 2 g. E Refer to the appropriate standard for the proper gap settings. F The Type 6 electrodes are those given in IEC Publication 243-1 for testing of flat sheet materials. They are less critical as to concentricity of the electrodes than are the Types 1 and 2 electrodes. G Other diameters may be used, provided that all parts of the test specimen are at least 15 mm inside the edges of the electrodes. H The Type 7 electrodes, as described in the table and in NoteG, are those given in IEC Publication 243-1 for making tests parallel to the surface. D 149 – 97a (2004) 3 免费标准网(www.freebz.net) 标准最全面 免费标准网(www.freebz.net) 无需注册 即可下载 6.3.1 One of the electrodes listed in Table 1 should be specified by the document referring to this test method. If no electrodes have been specified, select an applicable one from Table 1, or use other electrodes mutually acceptable to the parties concerned when the standard electrodes cannot be used due to the nature or configuration of the material being tested. See references in Appendix X2 for examples of some special electrodes. In any event the electrodes must be described in the report. 6.3.2 The electrodes of Types 1 through 4 and Type 6 of Table 1 should be in contact with the test specimen over the entire flat area of the electrodes. 6.3.3 The specimens tested using Type 7 electrodes should be of such size that all portions of the specimen will be within and no less than 15 mm from the edges of the electrodes during test. In most cases, tests using Type 7 electrodes are made with the plane of the electrode surfaces in a vertical position. Tests made with horizontal electrodes should not be directly com- pared with tests made with vertical electrodes, particularly when the tests are made in a liquid surrounding medium. 6.3.4 Keep the electrode surfaces clean and smooth, and free from projecting irregularities resulting from previous tests. If asperities have developed, they must be removed. 6.3.5 It is important that the original manufacture and subsequent resurfacing of electrodes be done in such a manner that the specified shape and finish of the electrodes and their edges are maintained. The flatness and surface finish of the electrode faces must be such that the faces are in close contact with the test specimen over the entire area of the electrodes. Surface finish is particularly important when testing very thin materials which are subject to physical damage from improp- erly finished electrodes. When resurfacing, do not change the transition between the electrode face and any specified edge radius. 6.3.6 Whenever the electrodes are dissimilar in size or shape, the one at which the lowest concentration of stress exists, usually the larger in size and with the largest radius, should be at ground potential. 6.3.7 In some special cases liquid metal electrodes, foil electrodes,