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1、BRITISH STANDARD BS 7819:1995 IEC 1026:1991 Guidelines for application of analytical test methods for thermal endurance testing of electrical insulating materials Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 11:57:40 GMT+00:00 2006, Uncontrolled Copy, (c) BSI
2、 BS 7819:1995 This British Standard, having been prepared under the direction of the Electrotechnical Sector Board, was published under the authority of the Standards Board and comes into effect on 15 August 1995 BSI 10-1999 The following BSI references relate to the work on this standard: Committee
3、 reference GEL/15 Draft announced in BSI News April 1995 ISBN 0 580 24431 8 Committees responsible for this British Standard The preparation of this British Standard was entrusted by Technical Committee GEL/15, Insulating material, to Subcommittee GEL/15/2, Endurance Tests, upon which the following
4、bodies were represented: AEA Technology Adhesive Tape Manufacturers Association Association of Manufacturers of Domestic Electrical Appliances British Cable Makers Confederation British Plastics Federation ERA Technology Ltd. University of Manchester Amendments issued since publication Amd. No.DateC
5、omments Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 11:57:40 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7819:1995 BSI 10-1999i Contents Page Committees responsibleInside front cover National forewordii Introduction1 Section 1. General aspects 1Scope and o
6、bject2 2General principles2 3Analytical methods for reaction rate measurements2 Section 2. Test procedure A, Single reaction case 4Range of application for procedure A4 5Reaction rate measurements in procedure A5 6Conventional ageing tests in procedure A5 7Evaluation in procedure A6 8Reporting in pr
7、ocedure A6 Section 3. Test procedure B, Multi-reaction case 9Range of application for procedure B7 10Reaction rate measurements in procedure B8 11Calculations in procedure B9 12Conventional ageing tests in procedure B11 13Evaluation in procedure B11 14Reporting in procedure B12 Section 4. Test proce
8、dure C, Multi-reaction with diffusion 15Range of application for procedure C13 16Reaction rate measurements in procedure C13 17Calculations in procedure C14 18Conventional ageing tests in procedure C15 19Evaluation in procedure C15 20Reporting in procedure C15 Appendix A Presentation of the theoreti
9、cal principles of test procedures B and C17 Appendix B References17 Figure 1 Example of an arrangement for reaction rate measurement in procedure A18 Figure 2 Example of a test arrangement for reaction rate measurements for procedure A, B or C, using IDC19 Figure 3 Evaluation of test results in proc
10、edure A20 Figure 4 Procedure B or C: Evaluation of test results21 List of referencesInside back cover Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 11:57:40 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7819:1995 ii BSI 10-1999 National foreword This British S
11、tandard has been prepared by Technical Committee GEL/15. It is identical with IEC 1026:1991, 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 do
12、es not purport to include all the necessary provisions of a contract. Users of 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 toCorresponding British
13、Standard IEC 216 (series)BS 5691 (series) Guide for the determination of thermal endurance properties of electrical insulating materials Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 22, an inside back cover and a back cover. This standard
14、has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 11:57:40 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7819:1
15、995 BSI 10-19991 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 than 25 years. The reference list attached to this report is limited to investigations where sensitive
16、analytical methods have been applied for reaction rate measurements down to the application temperature range of materials. The first investigators 1,21) used gas chromatography or mass spectrometry as analytical methods in a way from which procedure A of this report could be developed, together wit
17、h several later published results 5, 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 is the basis of procedures B and C of this report. Other investigators
18、 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 measurements. While these methods may be valuable tools when developing ne
19、w 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 erroneous conclusions. There is thus sufficient knowledge gathered in
20、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 analytical methods for thermal endurance testing of insulating materials. Thi
21、s 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 methods have been shown to be suitable for reaction rate measurements an
22、d 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 ageing process (or of separate reactions), producing information e.g. about
23、 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 thermal endurance values in the same form as IEC Publication 216. 5) The
24、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 processes of different complexity. The test procedures should be either
25、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 IEC Publication 216, the following differences may be revealed: test p
26、rocedures 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 shorter duration are needed, and the analytical procedures themselves
27、 require little time; actual service conditions can be accurately simulated, especially regarding the ageing due to atmospheric humidity and oxidation. Following the principles 1) to 6) described above, three test procedures of increasing complexity are described in this report. These procedures may
28、 be found extremely useful in establishing some basic parameters of materials, additional to those obtained through using IEC Publication 216. Throughout this report the terminology and concepts presented in IEC Publication 216 are used. 1) Numbers in square brackets refer to Appendix B References.
29、Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 11:57:40 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7819:1995 2 BSI 10-1999 Section 1. General aspects 1 Scope and object This report describes test procedures for evaluation of the thermal endurance of electric
30、al insulating materials, based on the combined use of sensitive analytical methods 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
31、halving interval (HIC) of IEC Publication 216 are derived from the test results. 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 i
32、n the end affect its functionality. The chemical composition (as a result of deterioration 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 mat
33、erials through suitable measurements of ageing reaction rates (which describe 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 accoun
34、t the increasing complexity of the ageing process. In procedure A, the thermal 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
35、rate at the ageing temperature. The inverse values of reaction rates as function 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 therma
36、l endurance graph, values of the thermal endurance characteristics corresponding to temperature index TI and halving interval HIC (see IEC Publication 216) can be obtained. In procedures B and C, three ageing reactions are assumed to be important: thermal degradation proceeding in an inert atmospher
37、e, oxidation and hydrolysis (or at least two of these reactions). It is assumed 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 princ
38、iple is to select the ageing conditions so as to accelerate all the three principal 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 acc
39、eleration of each of the three reactions is determined (at constant conditions). Secondly, 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 ag
40、eing process). In procedure B, all the ageing reactions are assumed to be essentially 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 react
41、ions is diffusion-controlled, it can no longer be treated as being independent of the 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 in
42、strumentation at hand, an appropriate test procedure and analytical method should be selected. The basic assumptions presented for each procedure (Sub-clauses 4.1, 9.1 and 15.1) have to be fulfilled. 3 Analytical methods for reaction rate measurements 3.1 General requirements In this publication, on
43、ly such features of analytical methods which are important for the reaction rate measurements are dealt with. The precise nature of the instrumentation that is required is dependent on the analytical methods that are chosen. Licensed Copy: London South Bank University, London South Bank University,
44、Fri Dec 08 11:57:40 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7819:1995 BSI 10-19993 There are numerous methods suitable for measurements of ageing reaction rates of electrical insulating materials. Most important requirements for an analytical method are as follows: sensitivity of the method sh
45、all 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 appropriate; selectivity required of the method depends on the procedure used. In p
46、rocedure 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 shall be made. With regard to the thermal degradation reaction, this separatio
47、n may not be directly possible. In such case, a suitable differential technique can be applied (see e.g. Sub-clause 3.5); duration of the measurements shall be short enough for the results to be obtained in a reasonable time. It is recognized that due to the high sensitivity required the time needed
48、 may be in the order of weeks, at the lowest temperature even up to 1 000 h. It is essential that thermal ageing of the test material be as small as possible during the measurements. See Sub-clause 10.3; stabilized output. The measurement or sample collection time at each test temperature shall be l
49、ong 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) 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 products are collecte