1、BRITISH STANDARD BS 5823:1979 IEC 345:1971 Method of Test for electrical resistance and resistivity of insulating materials at elevated temperatures UDC 621.315.61.014.144:620.193.94BS5823:1979 This British Standard, having been prepared under the directionof the General Electrotechnical Engineering
2、 Standards Committee, was published under the authority ofthe Executive Board and comesinto effect on 31December1979 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference GEL/16 Draft for comment 79/21146 DC ISBN 0 580 11088 5 Cooperating organizations The
3、 General Electrotechnical Engineering Standards Committee, under whose direction this British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: Associated Offices Technical Committee British Approvals Service for
4、 Electric Cables Ltd British Electrical and Allied Manufacturers Association (BEAMA) British Radio Equipment Manufacturers Association British Steel Corporation Department of Energy (Electricity) Electric Cable Makers Confederation Electrical Contractors Association Electrical Contractors Associatio
5、n of Scotland Electrical Research Association* Electricity Supply Industry in England and Wales* Electronic Components Industry Federation* Engineering Equipment Users Association Health and Safety Executive Home Office Institution of Electrical Engineers Ministry of Defence* National Coal Board Oil
6、 Companies Materials Association Post Office* Telecommunication Engineering and Manufacturing Association (TEMA)* The organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this British Standa
7、rd: Adhesive Tape Manufacturers Association British Paper and Board Industry Federation (PIF) Department of Industry (British Calibration Service) Department of Industry (National Physical Laboratory) Electrical and Electronic and Insulation Association (BEAMA) Rotating Electrical Machines Associati
8、on (BEAMA) The Transmission and Distribution Association (BEAMA) Amendments issued since publication Amd. No. Date of issue CommentsBS5823:1979 BSI 12-1999 i Contents Page Cooperating organizations Inside front cover National foreword ii 1 Scope 1 2 Preparation of specimens and electrodes 1 3 Test e
9、quipment 1 4 Conditioning 2 5 Procedure 2 6 Expression of results 3 7 Test report 3 Figure 1 4 Publications referred to Inside back coverBS5823:1979 ii BSI 12-1999 National foreword This British Standard is identical with IEC Publication 345 “Method of test for electrical resistance and resistivity
10、of insulating materials at elevated temperatures” published in1971by the International Electrotechnical Commission (IEC). This British Standard is published under the direction of the General Electrotechnical Engineering Standards Committee. Terminology and conventions. The text of the International
11、 Standard has been approved as suitable for publication, without deviation, as a British Standard. Some terminology and certain conventions are not identical with those used in British Standards; attention is especially drawn to the following. In 5.1 and in 5.2 (twice) temperature intervals are stat
12、ed in “deg C”. In British Standards it is current practice to use “ C” to denote this interval. At present there is no corresponding British Standard for IECPublication93 which has been considered by the responsible technical committee and found to be acceptable for the purposes of this British Stan
13、dard. At present there is no corresponding British Standard for IECPublication167 but the reference constitutes informative matter only and, as no mandatory requirements are involved, the validity of this British Standard is not affected. Additional information. Figure 1 shows the thermocouple on th
14、e “live” side of the specimen. The accuracy of the results will not be adversely affected by mounting the thermocouple on the “earth” side of the specimen, provided that the requirements of3.6 are complied with. A British Standard does not purport to include all the necessary provisions of a contrac
15、t. 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 International Standard Corresponding British Standard IEC 212:1971 a BS 2844:1972 Memorandum on conditioning of
16、solid electrical insulating materials prior to and during testing (Technically equivalent) a Undated in the text. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 4, an inside back cover and a back cover. This standard has been updated (see cop
17、yright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS5823:1979 BSI 12-1999 1 1 Scope This test method covers procedures for the determination of insulation resistance and volume resistivity of insulating materials at tempera
18、tures up to at least800 C. The measurements shall be made in accordance with IEC Publication 93, Recommended Methods of Test for Volume and Surface Resistivities of Electrical Insulating Materials, and with IECPublication 167, Methods of Test for the Determination of the Insulation Resistance of Sol
19、id Insulating Materials, utilizing the following special procedures. 2 Preparation of specimens and electrodes For insulation resistance measurements, the specimens may be of any suitable size and shape and may have electrodes already attached (seeIECPublication 167). When volume resistivity is meas
20、ured, the specimens shall preferably be in the form of disks, a three electrode system shall be used, one of which is a guarded electrode. The thickness variation between any two places on the disk shall be no greater than 5% of the mean thickness. The specimen electrodes shall preferably be circula
21、r and consist of fired-on conducting paint or a conducting coating evaporated or sprayed onto the specimen faces. Gold or platinum are suitable electrode metals. Silver should not be used since it migrates at elevated temperatures. Thin layers of gold may lose their conductivity since the gold may a
22、gglomerate at the higher temperatures. It is difficult to apply evaporated or sprayed-on electrodes to porous test specimens and the results obtained with them are of doubtful value. To minimize surface effects at the edges of the specimen (due sometimes to handling in specimen preparation), it is r
23、ecommended that if no guarded electrode is used, the minimum distance from the electrodes to the specimen edge shall be0.5cm. 3 Test equipment 3.1 Resistance measurement (see Figure 1, page4) The resistance between electrodes shall be measured with a suitable device having therequired sensitivity an
24、d accuracy (seeIECPublication 93). 3.2 Heating chamber For heating the specimen, a suitable electric oven or furnace shall be used. The construction shall be such that the specimen is subjected to a uniform temperature throughout its total volume with temperature fluctuations as small as possible. A
25、n adequate muffle should be provided to shield the specimen from direct radiation by the heating elements. This muffle may be made of a ceramic such as aluminum oxide or equivalent. A grounded metallic shield of silver, stainless steel or equivalent metal shall also be provided within the oven. The
26、shield shall act as a guard to prevent leakage currents between the heating circuit and the measuring circuit. In the case of very high resistance specimens, it may be necessary to disconnect the heating element to prevent interference during the measurement. 3.3 Specimen holder The specimens shall
27、be mounted securely between two electrode backing plates within the heating chamber. These backing plates and their respective leads should be made of a metal which is mechanically stable and resistive to oxidation. High-heat-resistant alloys such as stainless steel may also be utilized. Alternative
28、ly, the tests may be performed in an inert atmosphere. The backing plates shall be of sufficient thickness to prevent warping and to provide heat equalization between the specimen and the electrode backing plates. The contact faces of the plates should be equal in size to the specimen electrodes, an
29、d one electrode backing plate should be movable so as to allow insertion and removal of the test specimen. 3.4 Measuring leads Insulated measuring leads should be brought into the furnace through high-resistance ceramic insulators located in a cool zone and adequately guarded so as to prevent leakag
30、e current from affecting the test results. NOTEAlternatively, the leads may be passed through holes in the top or in a wall of the furnace (which should be earthed). If stiff leads are used, they can be supported externally so as not to touch anything but their supports. The supports will be relativ
31、ely cool and thus can be made of any rigid insulating material. 3.5 Temperature control A means of temperature control shall be provided which can maintain temperature tolerances according to IEC Publication 212, Standard Conditions for Use prior to and during the Testing of Solid Electrical Insulat
32、ing Materials. The use of two thermocouples is recommended, one in the chamber for control and a second for the direct measurement of the specimen temperature.BS5823:1979 2 BSI 12-1999 The temperature of the specimen shall be measured using a thermocouple mounted as close as possible to the specimen
33、 without causing electrical interaction with the measurement of resistance. For example, the thermocouple may be inserted directly into a hole extending almost to the surface of thebacking plate adjacent to the specimen (seeFigure 1, page 4). The hole may be drilled from the opposite face of the pla
34、te perpendicular to the surface of the specimen or from the side of the plate parallel to the specimen surface. If the thermocouple is mounted within the electrode backing plate, the leads and the temperature-indicating instrument must be adequately insulated or the thermocouple must be disconnected
35、 or removed when measurements are made. 3.6 Special precautions during measurements If the material insulating the leads into the oven is subjected to heat, the insulation resistance of the lead insulation may become low enough to affect the measurements. Since the circuit is earthed between the cur
36、rent-measuring instrument and the voltage source (both sides of the specimen being insulated from earth), the conductance between the high potential lead and earth can be ignored if it does not constitute too large a current drain on the voltage source. A conductance between the low potential lead a
37、nd earth constitutes a shunt across the current-measuring instrument. The resistance toearth of the measuring electrode must be high(10to100 times) as compared to the input resistance of the current-measuring instrument (which may be as much as 10 117 for the most sensitive instruments). The leakage
38、 resistance must be determined by a separate measurement at each temperature. Thermocouple potentials between dissimilar metals, when they are used in leads and electrode holders, can cause measurement errors. A measurement of current, with the supply voltage replaced by a short circuit, will indica
39、te the magnitude of this thermocouple effect. 4 Conditioning The conditioning which a specimen should receive depends upon the material being tested; it should be specified in the material specification and should be selected from among those listed in Table I of IECPublication 212. 5 Procedure 5.1
40、Continuously increasing temperature (Method A) This method is suitable for obtaining quickly an approximate relationship between resistance and temperature of a single specimen over a wide temperature range. The method is suitable only with materials for which the effects of dielectric absorption 1)
41、can be neglected, or for obtaining comparative results for similar materials. The specimen shall be mounted tightly between the electrode backing plates, but not so tightly that the specimen is distorted while being heated. The specified voltage shall be applied to the test specimen and the temperat
42、ure shall be increased at a rate depending on the thickness of the material and not higher than 5deg C per minute. A sufficient number of resistance measurements shall be made, as the temperature is increased, so as to define adequately the relationship between resistance and temperature. 5.2 Increa
43、sing the temperature by steps (Method B) This method is suitable for obtaining the relationship between resistance and temperature of a single specimen more accurately than is possible with continuously increasing temperature. It is useful also with specimens for which dielectric absorption is a pro
44、blem. The method is also convenient when more than one specimen is to be tested. The need to wait for thermal equilibrium of each specimen, when several specimens are to be measured, is avoided if a specimen holder is provided for each specimen or if a means is provided for transferring the specimen
45、s from the heating chamber to the specimen holder without opening the chamber. The test specimen shall be mounted tightly between the electrode backing plates but not so tightly that the specimen is distorted while being heated. The temperature of the test specimen shall be increased as rapidly as p
46、ossible from room temperature to the desired test temperature 2)and subsequently from each test temperature step to the next. 1) Dielectric absorption in some cases may reduce the short-time value of resistance compared to the long-time value by a factor of as much as 100. 2) The test chamber should
47、 be controlled in such a manner that the temperature of the electrode backing plate does not exceed the desired test temperature.BS5823:1979 BSI 12-1999 3 When the temperature of the electrode backing plate is within 2 deg C or 1% (whichever is larger) of the desired test temperature, the voltage sp
48、ecified in the material specification shall be applied to the specimen for 1min (or for other times as specified) and the resistance shall then be measured. When the measurement is completed, the voltage shall be removed and the high voltage, measuring and guarded (if used) electrodes shall be conne
49、cted to each other (short-circuited). A sufficient number, but no less than five, test temperatures shall be selected to define adequately the relationship between temperature and resistance over the desired range of temperatures. At the lower temperatures, the temperature increments should be relatively small, e.g. 10 deg C. As the test temperature is increased, the temperature increments should also be increased. NOTEThe logarithm of resistance (or resistivity) is often plotted as a function of the reciprocal absolute temperature. 5.3 Precautions to be taken When the cur
