1、BRITISH STANDARD BS7819:1995 IEC1026:1991 Guidelines for application of analytical test methods for thermal endurance testing of electrical insulating materialsBS7819:1995 This British Standard, having been prepared under the directionof the Electrotechnical Sector Board, was published underthe auth
2、ority of the Standards Board and comesintoeffect on 15August1995 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference GEL/15 Draft announced in BSI News April1995 ISBN 0 580 24431 8 Committees responsible for this British Standard The preparation of this
3、British Standard was entrusted by Technical Committee GEL/15, Insulating material, to Subcommittee GEL/15/2, Endurance Tests, upon which the following bodies were represented: AEA Technology Adhesive Tape Manufacturers Association Association of Manufacturers of Domestic Electrical Appliances Britis
4、h Cable Makers Confederation British Plastics Federation ERA Technology Ltd. University of Manchester Amendments issued since publication Amd. No. Date CommentsBS7819:1995 BSI 10-1999 i Contents Page Committees responsible Inside front cover National foreword ii Introduction 1 Section 1. General asp
5、ects 1 Scope and object 2 2 General principles 2 3 Analytical methods for reaction rate measurements 2 Section 2. Test procedure A, Single reaction case 4 Range of application for procedure A 4 5 Reaction rate measurements in procedure A 5 6 Conventional ageing tests in procedure A 5 7 Evaluation in
6、 procedure A 6 8 Reporting in procedure A 6 Section 3. Test procedure B, Multi-reaction case 9 Range of application for procedure B 7 10 Reaction rate measurements in procedure B 8 11 Calculations in procedure B 9 12 Conventional ageing tests in procedure B 11 13 Evaluation in procedure B 11 14 Repo
7、rting in procedure B 12 Section 4. Test procedure C, Multi-reaction with diffusion 15 Range of application for procedure C 13 16 Reaction rate measurements in procedure C 13 17 Calculations in procedure C 14 18 Conventional ageing tests in procedure C 15 19 Evaluation in procedure C 15 20 Reporting
8、in procedure C 15 Appendix A Presentation of the theoretical principles of test procedures B and C 17 Appendix B References 17 Figure 1 Example of an arrangement for reaction rate measurement in procedure A 18 Figure 2 Example of a test arrangement for reaction rate measurements for procedure A, B o
9、r C, using IDC 19 Figure 3 Evaluation of test results in procedure A 20 Figure 4 Procedure B or C: Evaluation of test results 21 List of references Inside back coverBS7819:1995 ii BSI 10-1999 National foreword This British Standard has been prepared by Technical Committee GEL/15. It is identical wit
10、h IEC1026:1991, Guidelines for application of analytical test methods for thermal endurance testing of electrical insulating materials, published by the International Electrotechnical Commission (IEC). A British Standard does not purport to include all the necessary provisions of a contract. Users o
11、f British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-references Publication referred to Corresponding British Standard IEC216 (series) BS5691 (series) Guide for the determination of ther
12、mal endurance properties of electrical insulating materials Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to22, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. T
13、his will be indicated in the amendment table on the inside front cover.BS7819:1995 BSI 10-1999 1 Introduction Analytical methods have been applied to investigations of ageing processes in electrical insulating materials and to the measurement of ageing reaction rates for more than25years. The refere
14、nce list attached to this report is limited to investigations where sensitive analytical methods have been applied for reaction rate measurements down to the application temperature range of materials. The first investigators 1,2 1)used gas chromatography or mass spectrometry as analytical methods i
15、n a way from which procedure A of this report could be developed, together with several later published results5,7,10,11. Later investigators used a new analytical instrument, the isothermal differential calorimeter 4, which, together with theoretical developments 9 and other publications 6,12,13,14
16、 is the basis of procedures B and C of this report. Other investigators have concentrated on the use of rapid analytical techniques (such as thermogravimetric analysis TGA and differential thermoanalysis DTA), and on the derivation of an estimate of thermal endurance solely on the basis of these mea
17、surements. While these methods may be valuable tools when developing new polymers or selecting materials for long-term thermal endurance testing, they do not belong to the scope of this report, since these methods lead to extrapolation of test results over a large temperature span, which may lead to
18、 erroneous conclusions. There is thus sufficient knowledge gathered in this field to prepare detailed procedures to be published as an IEC Report, in order to pave the way for the later standardization of the method. This report is also intended to stimulate further work on the application of analyt
19、ical methods for thermal endurance testing of insulating materials. This report is based on the following principles: 1) The analytical methods used must be sensitive enough to enable measurements of ageing reaction rates down to the application temperatures of the materials. 2) Several analytical m
20、ethods have been shown to be suitable for reaction rate measurements and to produce similar information about reaction rates. Therefore, the test procedures allow the use of several analytical methods. 3) Measurements of the ageing reaction rates serve the purpose of determining the rate of the agei
21、ng process (or of separate reactions), producing information e.g.about the slope of the thermal endurance graph. 4) Reaction rate values alone cannot be used to totally describe the thermal endurance of materials. They must be combined with ageing tests of the conventional type to produce actual the
22、rmal endurance values in the same form as IEC Publication216. 5) The goal of analytical reaction rate measurements is to ensure the same physicochemical ageing mechanism in the conventional ageing tests as at application temperatures, but at a much higher rate. 6) There are materials with ageing pro
23、cesses of different complexity. The test procedures should be either universal (applicable to any material) or also of different complexity. When test procedures which are described in this report are compared with the presently standardized conventional thermal endurance text methods specified in I
24、EC Publication216, the following differences may be revealed: test procedures in this report produce experimental data down to the application temperature range of materials, eliminating the need for extrapolation; the total testing time will be shorter since fewer conventional ageing tests with a s
25、horter duration are needed, and the analytical procedures themselves require little time; actual service conditions can be accurately simulated, especially regarding the ageing due to atmospheric humidity and oxidation. Following the principles1) to6) described above, three test procedures of increa
26、sing complexity are described in this report. These procedures may be found extremely useful in establishing some basic parameters of materials, additional to those obtained through using IEC Publication216. Throughout this report the terminology and concepts presented in IEC Publication216 are used
27、. 1) Numbers in square brackets refer to Appendix BReferences.BS7819:1995 2 BSI 10-1999 Section 1. General aspects 1 Scope and object This report describes test procedures for evaluation of the thermal endurance of electrical insulating materials, based on the combined use of sensitive analytical me
28、thods for the determination of test acceleration and of conventional ageing tests. It describes the conditions to be observed in the test procedures and shows how characteristics corresponding to temperature index (TI) and halving interval (HIC) of IEC Publication216 are derived from the test result
29、s. 2 General principles 2.1 Description of test procedures Thermal ageing of insulating materials is mainly composed of chemical reactions, which progressively cause changes in the physical properties of the material and in the end affect its functionality. The chemical composition (as a result of d
30、eterioration due to the thermal ageing reactions) and the value of any physical property of the material are therefore closely correlated. It is thus possible to provide means of estimating the long term performance of materials through suitable measurements of ageing reaction rates (which describe
31、the speed of degradation) combined with ageing tests of conventional type. Since the correlation given above may be of variable complexity, three test procedures (A, B and C) are presented in this guide, taking into account the increasing complexity of the ageing process. In procedure A, the thermal
32、 ageing process is treated as one reaction, assuming that one ageing reaction dominates the ageing process. In this case the time to end-point in a conventional ageing test is inversely proportional to the ageing reaction rate at the ageing temperature. The inverse values of reaction rates as functi
33、on of temperature can therefore be used to describe the thermal endurance graph, if the curve is fixed so that it contains a point determined from an actual conventional ageing test result. Based on this constructed thermal endurance graph, values of the thermal endurance characteristics correspondi
34、ng to temperature index TI and halving interval HIC (seeIEC Publication216) can be obtained. In procedures B and C, three ageing reactions are assumed to be important: thermal degradation proceeding in an inert atmosphere, oxidation and hydrolysis (or at least two of these reactions). It is assumed
35、that if there is more than one reaction of the same kind (e.g.several oxidative reactions), then one reaction dominates that reaction group (e.g.one oxidative reaction dominates the oxidative reactions). The main principle is to select the ageing conditions so as to accelerate all the three principa
36、l reactions by equal amounts, in order to simulate the real ageing process occurring at a lower temperature as closely as possible. This is accomplished in two steps. Firstly, through reaction rate measurements the acceleration of each of the three reactions is determined (at constant conditions). S
37、econdly, conventional ageing tests are performed using such concentrations of oxygen and water vapour that the equalizing of the process is achieved. This method of testing is also known as the EAP method (equalized ageing process). In procedure B, all the ageing reactions are assumed to be essentia
38、lly independent and homogeneous (i.e.to proceed identically everywhere in the test material). From the test results the thermal endurance characteristics as in procedure A can be calculated. If one of the ageing reactions is diffusion-controlled, it can no longer be treated as being independent of t
39、he dimensions of the material (mainly thickness). Procedure C gives instructions for handling such a case. 2.2 Selection of test procedures Depending on the degree of complexity of the material to be tested and the instrumentation at hand, an appropriate test procedure and analytical method should b
40、e selected. The basic assumptions presented for each procedure (Sub-clauses4.1, 9.1 and15.1) have to be fulfilled. 3 Analytical methods for reaction rate measurements 3.1 General requirements In this publication, only such features of analytical methods which are important for the reaction rate meas
41、urements are dealt with. The precise nature of the instrumentation that is required is dependent on the analytical methods that are chosen.BS7819:1995 BSI 10-1999 3 There are numerous methods suitable for measurements of ageing reaction rates of electrical insulating materials. Most important requir
42、ements for an analytical method are as follows: sensitivity of the method shall be high enough to enable reproducible measurements to be made at the application temperature range of the material or at the expected TI temperature. Different methods may be applied for different reactions, when appropr
43、iate; selectivity required of the method depends on the procedure used. In procedure A, either the “total” reaction rate or the rate of the strongest reaction is measured, so the selectivity is not very critical. In procedures B and C, a clear differentiation between the three principal reactions sh
44、all be made. With regard to the thermal degradation reaction, this separation may not be directly possible. In such case, a suitable differential technique can be applied (seee.g.Sub-clause3.5); duration of the measurements shall be short enough for the results to be obtained in a reasonable time. I
45、t is recognized that due to the high sensitivity required the time needed may be in the order of weeks, at the lowest temperature even up to1000h. It is essential that thermal ageing of the test material be as small as possible during the measurements. SeeSub-clause10.3; stabilized output. The measu
46、rement or sample collection time at each test temperature shall be long enough to allow the reaction rate being measured to stabilize. The stabilization time may depend on the thickness and material of the test specimens. 3.2 Gas chromatography and mass spectrometry The use of gas chromatography (GC
47、) or mass spectrometry (MS) is based on the fact that, as a consequence of thermal ageing reactions, gaseous reaction products are evolved. In numerous published investigations 10, etc. the term “Evolved Gas Analysis” (EGA) has been used in this connection. Through appropriate means the reaction pro
48、ducts are collected and quantitatively analysed. In both methods the reaction rate is measured as the rate of evolution of some gaseous reaction product (often CO and CO 2 ). Two different procedures are possible: periodical and continuous. Periodical procedure During a short heat exposure at the te
49、st temperature the test specimen is kept in a hermetically closed container. After this period a sample of the gas atmosphere from this container is analyzed, using GC or MS or a combination thereof. Continuous procedure During a short heat exposure a slow gas flow is fed through the specimen container. From time to time, samples collected at the outlet of the container are analyzed, using GC or MS or a combination thereof. For application of procedure B or C, the different reaction rates may be measured either simultaneously or separately. Simu
