1、BRITISH STANDARD BS 4542:1970 Determination of Loss tangent and permittivity of electrical insulating materials in sheet form (Lynch method)BS 4542:1970 This British Standard, having been approved by the Electrical Industry Standards Committee, was published under the authorityof the Executive Board
2、on 30 January 1970 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference ELE/16/51/34 Draft for comment 66/25997 ISBN 580 05985 5 Co-operating organizations The Electrical Industry Standards Committee, under whose supervision this British Standard was prep
3、ared, consists of representatives from the following Government departments and scientific and industrial organizations: Associated Offices Technical Committee Association of Consulting Engineers Association of Mining Electrical and Mechanical Engineers Association of Supervising Electrical Engineer
4、s British Electrical and Allied Manufacturers Association* British Radio Equipment Manufacturers Association British Railways Board Crown Agents for Oversea Governments and Administrations Department of Employment and Productivity Electric Cable Makers Confederation Electric Lamp Industry Council El
5、ectric Light Fittings Association Electrical Contractors Association (Incorporated) Electrical Contractors Association of Scotland Electrical Research Association* Electricity Council, the Central Electricity Generating Board and the Area Boards in England andWales* Electronic Engineering Associatio
6、n Engineering Equipment Users Association Institution of Electrical Engineers Ministry of Defence Ministry of Defence, Army Department Ministry of Defence, Navy Department Ministry of Power Ministry of Public Building and Works Ministry of Technology Municipal Passenger Transport Association (Incorp
7、orated) National Inspection Council for Electrical Installation Contracting National Physical Laboratory (Ministry of Technology)* Oil Companies Materials Association Post Office* Public Transport Association (Incorporated) South of Scotland Electricity Board The Government departments and scientifi
8、c and industrial 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 Standard: British Plastics Federation Radio and Electronic Component Manufacturers Federation Amendments is
9、sued since publication Amd. No. Date CommentsBS4542:1970 BSI 12-1999 i Contents Page Co-operating organizations Inside front cover Foreword ii 1 Scope 1 2 Principle of method 1 3 Accuracy and range 1 4 Temperature of test specimen, and test frequency 1 5 Apparatus: the electrodes 1 6 Apparatus: the
10、bridge network 1 7 The specimen 2 8 Method 2 9 Calculation 2 Appendix A Bridge apparatus 3 Figure 1 General arrangement of electrode system 4 Figure 2 Method of introducing small variable conductance 5 Figure 3 Five-arm network 6BS 4542:1970 ii BSI 12-1999 Foreword This standard makes reference to t
11、he following British Standard: BS 2067, Determination of power-factor and permittivity of insulating materials (Hartshorn and Ward method). The method described in this British Standard for the determination of the losstangent and permittivity of electrical insulating materials at frequencies offrom
12、1 kHz to 100kHz is based on that described in the Proceedings of the Institution of Electrical Engineers,1966, Vol.112, pp.426431. The work of the Electrical Research Association in checking the accuracy and reproducibility of the results is acknowledged. The method given here is intended to supplem
13、ent BS2067, “Determination ofpower-factor and permittivity of insulating materials (Hartshorn and Wardmethod)”, and covers a slightly different range of frequency. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible fo
14、r their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 6 and a back cover. This standard has been updated (see copyright date)
15、and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS4542:1970 BSI 12-1999 1 1 Scope This British Standard describes the Lynch method for the determination of the loss tangent and the permittivity of insulating materials at frequencies o
16、f 1kHz to 100kHz at normal room temperatures. It gives details of the apparatus and of the procedure to be followed. The frequency range can be extended downward to50Hz unless the surface resistivity of the specimen is low (e.g. 10 107). It can be extended upward to 1MHz by taking the precautions su
17、ggested in Clause6 and inAppendix A. 2 Principle of method The specimen, which carries no electrodes of its own, is inserted in an electrode system in which theseparation of the electrodes is variable, and changes in capacitance and conductance are observed by using a bridge network. The loss tangen
18、t is calculated from the change in conductance which occurs when the specimen is inserted. The permittivity is calculated from the increase in the separation of the electrodes necessary to restore thecapacitance to its originalvalue. 3 Accuracy and range 3.1 Without special precautions, when the lar
19、ger ofthe two electrode systems described is used, the loss tangent (tan ) can be measured to an accuracy of 10% of itself, with a lower measurable limit of 0.000 03. With the precautions suggested in Clause6 however, the loss tangent can be measured within about0.02 tan 0.000005. Permittivity ( but
20、 it is difficult to measure very small loss tangents (0.0001 or less) with this size of specimen. 5.2 In order that the thickness may be measuredover the portion of the specimen which covers the effective area of electrode measurement (i.e. the guarded electrode), provision shall be made for locatin
21、g the specimen with respect to the guarded electrode. A convenient way of doing this is to make the specimen the same size as the upper electrode. 6 Apparatus: the bridge network 6.1 Any form of bridge network may be used in which direct or three-terminal capacitance is measured. The network must be
22、 adjustable, and thedetector sensitive, to changes of 0.0003 pF andf 10 15S where f is the frequency in Hz. Appendix Asuggests ways of meeting this requirement. 1) BS 2067, “Determination of power-factor and permittivity of insulating materials”.BS 4542:1970 2 BSI 12-1999 6.2 For the closer limits s
23、uggested in Clause3, the sensitivity must be f 10 16S. For this precision, and for use at frequencies above 100kHz, great care must be taken with the earthing of the apparatus. Each point intended to be earthed must be connected by its own separate wire to a single point, and these connections must
24、not be duplicated. Flexible cables should not be allowed to move unless it can be shown that their movement does not affect the measurement. The connections to the upper and lower electrodes should form as small a loop as possible, but the connection to the upper electrode must not affect freedom of
25、 movement. 7 The specimen 7.1 The specimen shall be a circular or rectangularsheet; the diameter of the circle, or thesmaller dimension of the rectangle, should be atleast 125mm 2)for the larger electrode system and at least50mm for the smaller electrode system. 7.2 The thickness of the specimen sha
26、ll be at least t(& 1)/h, where t is the uncertainty of measurement of thickness and h is the uncertainty tolerable in the measurement of permittivity. The thickness shall not exceed13mm for the larger electrode system or8mm for the smaller electrode system. Within the area which will be tested, the
27、specimen shall be of substantially uniform thickness: the maximum tolerable deviation is about0.005 of the thickness of the specimen. The specimen shall be substantially flat: the maximum tolerable deviation is about 0.1 of the thickness of the specimen, measured as a deviation from a straight edge
28、placed along a diameter or a diagonal. 8 Method 8.1 The electrode system is connected to the bridge network, the separation of the electrodes set to a convenient value, and the bridge balanced. The electrode separation is increased, the specimen is inserted between the electrodes, and the bridge reb
29、alanced by adjustment of the electrode separation and of the conductance contributed by the bridge network. The capacitance adjustment of the bridge network must not be altered. Unless the specimen is known to be satisfactorily flat, it is then removed, inverted, and replaced, and the bridge again b
30、alanced by the same method. 8.2 The measurement of thickness of flexible or compressible materials shall be made in such a manner that the material is not significantly distorted from its shape when in the electrode system. 9 Calculation 9.2 For measurements on a series of specimens, allwith the sam
31、e electrode system and at the same frequency, most of these quantities are constant, and the formula for tan can be put in the following form: tan = constant 9.2.1 If the specimens are of the same material and of roughly similar thickness, then (t sp t x ) may also be replaced by a constant. 9.2.2 I
32、n these expressions the working area A shall be calculated by assuming that the effective diameter of the electrode is its actual diameter plus the radial separation between it and the guard electrode. 2) Some commonly-used moulded specimens are approximately 100mm in diameter and of thickness not e
33、xceeding 4mm. These specimens may be used in the 125mm electrode system provided that the electrode separation does not exceed 4mm initially. 9.1 Lett a = initial separation of the electrodes t 1 = separation of electrodes with specimen in position t 2 = separation of electrodes with specimen in pos
34、ition after inverting t = or, if the specimen is flat and only one balance is made with the specimen in position, t = t 1 t = t p t a t s = mean thickness of working area of specimen A = working area of electrode G 0 = conductance reading of bridge network at initial balance G 1 , G 2 = conductance
35、reading at balance with specimen in position G = p G 0or, if the specimen is flat and only one balance is madewith the specimen in positionG = G 1p G 0 f = frequency (Hz) Then & = and tan = if G is in siemens (ohm 1 ) and dimensions are in millimetres. t 1 t 2 + () 2 - G 1 G 2 + () 2 - t s t s t x -
36、 G f - t a 2 t s t x - 2 A -9 10 12 G t s t x -BS4542:1970 BSI 12-1999 3 Appendix A Bridge apparatus Commercial bridge apparatus is available which is of adequate sensitivity to both capacitance and conductance as required in 6.1, but it may not be calibrated for the small conductance changes. To ov
37、ercome this difficulty, one or more additional decade dials can be introduced as shown inFigure 2. Commercial bridges may offer a choice of impedance ranges, and it is necessary to find by trial and error which setting of the range switches gives the best sensitivity. If it is necessary to assemble
38、a bridge network specially, this can most easily be done by using a “transformer bridge”, i.e., a network in which the ratio arms are coupled by mutual inductance. Theinfluence of transformer characteristics on the bridge balance can be minimized by using the circuit described in the Proc. I.E.E., V
39、ol. 112, pp. 426431. If great sensitivity is needed at the lower frequencies for the measurement of small loss tangents, it may be necessary to apply a voltage ofup to100V. BS 4542:1970 4 BSI 12-1999 NOTE 1The upper and the guard electrodes need not be circular, but they must each be large enough to
40、 enclose a circle of diameterC. NOTE 2The dimensions of the electrodes have been chosen so that the constantin 9.1 is 0.004 mm 2for the large electrodesand 0.02 mm 2for the small electrodes. Figure 1 General arrangement of electrode system 29 A -BS4542:1970 BSI 12-1999 5 In Figure 2 R 1and R 2have r
41、esistances of the order of 100 000 7 to 1 M7 each (they need not be equal) and may be Grade1 carbon or metal-oxide resistors. R vis a one- or two-decade resistance box, suitablefor the frequency at which the apparatus is used, of maximum resistance 107 or 1007. Theconnectionsshould be screened so th
42、at as little capacitance as possible appears across R 1and across R 2 . Theconductance between the specimen terminals is approximately(where R v , R 1 , R 2are resistances in ohms), which can easily be made variable in steps of 10 10 , 10 11 , or 10 12 . If R 2= R 1= R, the exact value of the conduc
43、tance G is R v /R(R + 2R v ): and the change of conductance G between two values R v , R v is: For frequencies above 100 kHz the five-arm network of Figure 3 is preferable. R 1 , R 2and R 3should thenbe 10 000 7 each, and R 4100 7 (or, better, 102 7). R 4may be a Grade 1 carbon or metal-oxide resist
44、or. Then the conductance between the specimen terminals is approximately R v 10 10S, where R vis the resistance in ohms. If R 1= R 2= R 3= R, R 4= mR, R v , = xR, the exact value of the conductance G is mx/R(1 + 2x + 2m + 3mx). The change of conductance G between two values x, x , is approximately:
45、provided that mx 1. Figure 2 Method of introducing small variable conductance R v R 1R 2 -S R v R v R 2R v +()R 2R v +() - mx x () R12m 2 x x + () + -BS 4542:1970 6 BSI 12-1999 Figure 3 Five-arm networkblankBS 4542:1970 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is t
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