IEEE 99-1970 - IEEE Guide for Preparation of Test Procedures for the Thermal Evaluation of Insulation Systems for Electric Equipment.pdf

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1、No. 99 (Revision of AIEE No. IE, 1957) IEEE Guide for the Preparation of TEST PROCEDURES FOR THE THERMAL EVALUATION OF INSULATION SYSTEMS FOR ELECTRIC EQUIPMENT (In accordance with the principles outlined in IEEE Standards Publication No. 1) CONTENTS 99-1. Purpose 1 99-2. Scope99-3. ModelsConstructi

2、on and Number 1 99-4. Thermal Aging99-5. Humidification 2 99-6. Associated Materials99-7. Mechanical Stress99-8. Dielectric Stress99-9. Special Environments99-10. Method of Cooling99-11. Test Sequence 2 99-12. Length of Test Cycle99-13. Failure Criteria99-14. Mathematical Treatment of Thermal Aging

3、Data 3 99-15. Interpretation of Thermal Life Expectancy99-16. Specification of Minimum Life Expectancy and Variability 3 99-17. Form and Method for Reporting Results99-18. Identification of Insulation Systems 3 Appendix: Definition of Insulation SystemsACKNOWLEDGMENT The Institute wishes to acknowle

4、dge its indebtedness to those who have so freely given of their time and knowl edge and have conducted experimental work on which many of the IEEE publications are based. This publication was prepared by the IEEE Standards Coordinating Committee No. 4 whose membership was: G. L. Moses, Chairman, Wor

5、king Group H. P. Walker, Secretary P. E. Alexander P. L. Bellaschi J. L. Cantwell L. P. Mahon M. L. Manning K. N. Mathes H. E. Reymers M. L. Schmidt H. R. Sheppard C. L. Sidway NOTICE The IEEE will maintain this Guide current with the state of the technology. Comments on this Guide as well i suggest

6、ions for additional material that should be included are invited. These should be addressed to: Secretary IEEE Standards Committee The Institute of Electrical and Electronics Engineers, Inc. 345 East 47 Street New York, N. Y. 10017 Approved by the IEEE Standards Committee on April 22, 1970. Individu

7、al reprints of this Standard are available from the IEEE at $1.50 for members and $3.00 for nonmembers. IEEE Guide for the PREPARATION OF TEST PROCEDURES FOR THE THERMAL EVALUATION OF INSULATION SYSTEMS FOR ELECTRIC EQUIPMENT 99-1. PURPOSE It is the responsibility of IEEE Technical Committees to pre

8、pare functional Test Procedures for the thermal evaluation and classification of the insulation systems used in electric equipment. These Test Procedures involve accelerated thermal aging based on conditions of use and specify tests that the Committees deem pertinent. The objective of these Test Pro

9、cedures is to provide for the classification of insulation systems for electric equip ment in accordance with their temperature limits by test rather than by chemical composition of the component materials of the system. It is recognized that a given in sulation system may be used under different co

10、nditions of temperature, time, voltage, etc. Therefore, the evalu ation of an insulation system involves all of the various parameters of application and use of equipment but not the evaluation of separate component materials. The evaluation of insulating materials and simple combina tions thereof i

11、s provided for by separate material Test Procedures. It is the purpose of this Guide to provide a general form for the preparation of systems Test Procedures and to suggest the points to be considered by the Tech nical Committees in the preparation of specific instruc tions for the thermal evaluatio

12、n of insulation systems for equipment. For a detailed discussion of the principles on which this Guide is based, see IEEE Standards Publication No. 1. 99-2. SCOPE Test procedures for the thermal evaluation of insula tion systems for electric and electronic equipment should include introductory remar

13、ks necessary for a clear un derstanding of the objectives of the particular tests with respect to the industry served and of the special require ments that exist. If any different or new concepts of in sulation behavior, or use, are embodied in a Test Pro cedure, they should be clearly stated. Techn

14、ical Committees should attempt to assure that each Test Procedure: (a) gives statistically consistent results, (b) provides data free from bias of the tester, (c) includes, if models are used, results of these models representative of the equipment (the equipment it self may be evaluated where feasi

15、ble), (d) results in information that correlates with field ex perience in a satisfactory manner. 99-3. MODELSCONSTRUCTION AND NUMBER Wherever practicable, the equipment itself should be used for the thermal evaluation of insulation systems. However, when size and convenience require their use, insu

16、lation systems may be evaluated by models rather than by full-size equipment. Models should be made to embody the essential elements of the equipment they simulate. Design of experiment techniques should be em ployed in model construction and use. A model may contain more than one component part or

17、test unit. Test Procedures should specify the mini mum number of models and test units that are to be tested under each particular condition to obtain reason able statistical accuracy. The number of models required may be determined by an analysis of the results of pre liminary tests. Screening test

18、s should be included to assure uniform models typical of the systems being tested. 99-4. THERMAL AGING Evaluation tests involve thermal aging in combination with environmental exposure to other degrading and damaging conditions experienced by the equipment in its usual service. A primary objective o

19、f systems Test Procedures is the determination of changes in the essential characteristics of insulation systems under various degrees of thermal aging. Each test cycle shall include a temperature ex posure period. This portion of the test cycle is accom plished by periodic exposure of different mod

20、els or equip ment to controlled temperature conditions. The exposure temperatures, conditions, and the length of each cycle shall be specified. It is important to select aging tem peratures sufficiently high to give useful results in a reasonable time. However, the tests should not be so greatly acc

21、elerated that the data need be extrapolated so far on the temperature scale as to lead to an incon clusive evaluation of an insulation system. Therefore, it is suggested that any system being evaluated should have not less than three temperatures under study and that the lowest of these temperatures

22、 should be no greater than 25C above the expected limiting insulation temperature. The other higher temperatures should be separated by intervals of 20C or more (10C intervals may be suitable where more than three temperatures are studied). Equipment in service operates at various tempera tures from

23、 the inner hottest spot to the outer insulation surface and the insulation structural supports. The limit-1 ing test conditions depend on these various temperatures and the combinations of insulation used in the equip ment. Oven heating provides the most consistent control and recording of temperatu

24、re exposure but may not allow for the conditions described. Therefore, equipment that employs component materials of different temperature classes may require self-heating in spite of the problems associated with the generation of heat and with the de termination and control of temperatures. Accurac

25、y of temperature control and uniformity of temperature are extremely important and should be carefully checked whether ovens or self-generated heat is used. For uniformity it is suggested that the conditions be selected to produce the end of life for a normal system in approximately 10 cycles. Table

26、s 99-12a and 99-12b list procedures now in use as typical examples. 99-5. HUMIDIFICATION Humidification in varying degrees has been used to make dielectric tests more discerning of physical and thermal damage to electrical insulation systems. The presence of condensed moisture on windings permits ov

27、ervoltages to seek out and discern cracks and porosities in insulation whether such openings are the result of faulty construction, physical damage, or thermal aging. Humidity is recognized as a major cause of variation in the properties of electrical insulation, and it may cause several different t

28、ypes of insulation failure under electric stress. The absorption of moisture by solid insulation has a gradual effect of increasing dielectric loss and reducing insulation resistance, each of which contributes to a reduction in dielectric strength. Humidification on the surface of the insulation bri

29、ngs voltage to surfaces that otherwise would not be stressed when the insulation is subjected to electric stress. In some cases it is desirable to use atmospheric con ditions corresponding to 100 percent relative humidity for periodic moisture exposure. In other cases lesser de grees of humidificati

30、on may be employed successfully. 99-6. ASSOCIATED MATERIALS Test Procedures should take cognizance of the possible degrading effect of associated materials on insulation systems. Such materials may be part of the insulation system or adjacent parts in the physical support of the winding, in the equi

31、pment itself, or in the cooling media. The ventilation used during the aging of models should simulate service conditions. Consideration should be given to the escape or retention of decomposition products. 99-7. MECHANICAL STRESS For equipment usually subjected to vibration, physical shock, thermal

32、 cycling, or mechanical stress, the Test Procedure should include exposure to such conditions. These conditions should be similar in type to those encountered in service. To assure a reasonable factor of safety it is desirable that the mechanical stress should be greater in severity than normally en

33、countered in service. The most practical way of introducing me chanical stress is by means of vibration or shock, and in the case of transformer models, by short circuit. The type and severity of the forces should be specified. 99-8. DIELECTRIC STRESS Voltages higher than normal should be applied to

34、 all parts of the model or equipment under test. The test voltage should be sufficiently high so as to determine when any portion of the insulation system has de teriorated to a condition that is unreliable for continued service. 99-9. SPECIAL ENVIRONMENTS Where equipment operates under peculiar atm

35、ospheric conditions or is immersed in a liquid, the test conditions should be similar to the service conditions. 99-10. METHOD OF COOLING The Test Procedure should specify the model construc tion, the method of cooling during test, and the method of temperature determination to simulate service cond

36、i tions as far as practicable. 99-11. TEST SEQUENCE Each Test Procedure should specify the sequence of exposures and testing for the particular equipment. After the initial screening tests, the models or equipment should be subjected to a cycle that may include thermal aging, mechanical stress, humi

37、dification, and dielectric stress. This cycle is repeated until failure occurs. Special measurements or other exposures may be added to the foregoing sequence as deemed necessary or de sirable for a particular Test Procedure. 99-12. LENGTH OF TEST CYCLE Typical cycles for two types of equipment are

38、listed in Tables 99-12a and 99-12b. There should be a rational relation between length of cycle, exposure temperature, and expected operating temperature. It is recommended that the length of the aging cycle at each exposure tem perature be selected to approximate one-tenth of the useful life by thi

39、s test. Other values for thermal aging cycles may be established for specific equipment. The time or temperature may be adjusted to make the best use of test facilities. 99-13. FAILURE CRITERIA Each Test Procedure should be specific in describing the various criteria for the determination of failure

40、. The end point of life should reveal when the insulation sys tem is unfit for continued service. The life of an insula tion system at test temperature is defined as the num ber of full cycles withstood before failure plus one half-cycle, multiplied by the duration of the temperature exposure time i

41、n hours per cycle. 2 TABLE 99-12a TYPICAL TEMPERATURE AND EXPOSURE TIME IN DAYS PER CYCLE FOR MODELS OF MOTORS Estimated Limiting Insulation Temperature Range Exposure 1 2 3 4 5 Temperature 100-120 125-145 150-170 175-195 200-240 (degrees Celsius) Celsius Celsius Celsius Celsius Celsius 300 1 290 2

42、280 4 270 7 260 14 250 3 1 28 240 2 49 230 4 220 1 7 210 2 14 200 1 4 28 190. 2 7 49 180 1 4 14 170 2 7 28 160 4 14 49 150 2 7 28 140 14 49 130 28 120 J 49 99-14. MATHEMATICAL TREATMENT OF THERMAL AGING DATA The preferred method of treating and presenting data is described in IEEE Standards Publicat

43、ion No. 101, “Guide for the Statistical Analysis of Test Data.“ 99-15. INTERPRETATION OF THERMAL LIFE EXPECTANCY It is important for the uniformity of interpretation that the Test Procedure specify the following: (a) the permissible range of extrapolation, (b) limitations on the extrapolation of the

44、 lower con fidence limits and the average life expectancy. 99-16. SPECIFICATION OF MINIMUM LIFE EXPECTANCY AND VARIABILITY Minimum average test life (and lower confidence lim its) for acceptable insulation systems under the test con ditions may be specified by the responsible standardizing organizat

45、ion. 99-17. FORM AND METHOD FOR REPORTING RESULTS Each Test Procedure should specify the method and detail form for reporting test results. TABLE 99-12b TYPICAL TEMPERATURE AND EXPOSURE TIME IN DAYS PER CYCLE FOR MODELS OF VENTILATED DRY-TYPE TRANSFORMERS Duration of Temperature Exposure per Cycle (

46、days) Test Temperature Celsius (degrees), for Equipment with Limiting Insulation Temperatures of: 150 Celsius 220 Celsius 2 246 325 4 230 308 8 216 292 16 202 276 32 188 261 99-18. IDENTIFICATION OF INSULATION SYSTEMS Similar insulation systems may be used in different equipment and under varying ex

47、posure conditions. It is imperative for the sake of clarity that the test results be identified with the conditions of use and failure criteria as well as the temperature classification and de sired life expectancy. See the Appendix for a definition of insulation systems. APPENDIX: DEFINITION OF INS

48、ULATION SYSTEMS An insulation system is an assembly of insulating ma terials in a particular type, and sometimes size, of equipment. In general, a specific piece of equipment has one insulation system, but for some types of equip ment having two or more subassemblies, it may be de sirable to conside

49、r that there are a corresponding num ber of insulation systems. For classification purposes the insulation systems be ing considered for specific equipment procedures should be prepared using the following definition format for each class: “Class A Class insulation system is one that by experience or accepted test can be shown to have suitable thermal endurance when operating at the limiting Class temperature specified in the temperature rise standard for the equipment under consideration. Typical materials used in a Class system include , , with compatible bonding substances