1、BRITISH STANDARD BS 7663:1993 Methods of test for Determination of permittivity and dissipation factor of electrical insulating material in sheet or tubular form UDC |621.315.611-41 + 621.315.611-462|:621.317.33BS7663:1993 This British Standard, having been prepared under the directionof the Plastic
2、s and Rubber Standards Policy Committee, was published underthe authority of the Standards Board and comesintoeffect on 15July1993 BSI 01-2000 The following BSI references relate to the work on this standard: Committee reference PRM/25 Draft for comment 91/48847 DC ISBN 0 580 21798 1 Committees resp
3、onsible for this British Standard The preparation of this British Standard was entrusted by the Plastics and Rubber Standards Policy Committee (PRM/-) to Technical Committee PRM/25, upon which the following bodies were represented: British Floor Covering Manufacturers Association British Plastics Fe
4、deration British Rubber Manufacturers Association Ltd. EEA (Association of Electronics, Telecommunications and Business Equipment Industries) ERA Technology Ltd. Electrical and Electronic Insulation Association (BEAMA Ltd.) Federation of Resin Formulators and Applicators (Ferfa) Health and Safety Ex
5、ecutive RAPRA Technology Ltd. Amendments issued since publication Amd. No. Date CommentsBS7663:1993 BSI 01-2000 i Contents Page Committees responsible Inside front cover Foreword ii Introduction 1 1 Scope 1 2 References 1 3 Definitions 1 4 General 1 5 Test conditions 1 6 Number and handling of speci
6、mens 2 7 Measuring instruments 2 8 Method A: Air substitution technique 2 9 Method B: Two fluid immersion technique 5 10 Method C: Single fluid immersion technique 8 11 Precision 11 12 Test report 11 Annex A (informative) Modes of representation of capacitance 12 Annex B (informative) Liquids of kno
7、wn permittivity values 12 Figure 1 Example of electrode system for method A 3 Figure 2 Example of electrode system for method B: sheet specimens 6 Figure 3 Example of electrode system for method B: tubular specimens 7 Figure 4 Example of electrode system for method C 10 Figure A.1 Equivalence of ser
8、ies and parallel representations of a capacitor 12 List of references Inside back coverBS7663:1993 ii BSI 01-2000 Foreword This British Standard was prepared under the direction of the Plastics and Rubber Standards Policy Committee. Useful background information may be obtained from IEC250and from B
9、S2067both of which cover a wider frequency range than this standard. The resonance substitution methods described in BS2067have become obsolescent owing to the non-availability of suitable commercial equipment. The methods in this standard will, in due course, supersede those in BS 2067, except for
10、materials of very low dielectric loss or for measurements at high frequencies. A British Standard does 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 co
11、nfer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 12, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicat
12、ed in the amendment table on the inside front cover.BS7663:1993 BSI 01-2000 1 Introduction The methods described may be used for sheet materials in the thickness range0.3mm to5.0mm. The air substitution method is suitable for sheet materials of thickness1.0mm to5.0mm. The two immersion methods are c
13、apable of better precision for sheet materials of thickness0.3mm to1.0mm and have the advantage that accurate knowledge of the specimen thickness is not required. One of the immersion methods is suitable for measurements on tubular specimens but individually constructed electrodes may be needed for
14、specific sizes of tube. 1 Scope This British Standard describes three methods for the measurement of permittivity and of dissipation factor of electrical insulating materials in the form of sheets or rigid circular tubes at frequencies between50Hz and1MHz, under normal ambient temperatures and condi
15、tions. The methods described are applicable to sheet materials in the thickness range0.3mm to5.0mm and for tubes at least75mm long. The methods are: an air substitution method, commonly called the “Lynch” method (method A) a two fluid immersion method (method B) a single fluid immersion method (meth
16、od C). Methods A and B are suitable for materials of permittivity up to 10.0. For materials of dissipation factor below250 10 6the precision achieved by these methods may not be acceptable. Method A requires accurate knowledge of the specimen thickness and should be used in all cases when this infor
17、mation is available. If the thickness is not accurately known, methods B or C may be used subject to the limitation that method C is suitable for materials for which a liquid matching its permittivity to within0.1is available. Method C is suitable for measurement of polyolefin sheets whose permittiv
18、ity sufficiently closely matches that of silicone oil of kinematic viscosity of1cSt to2cSt 1) . Methods B and C are not suitable for materials with an open cell structure. Method B is suitable for measurements on straight cylindrical tubes of circular cross section. 2 References 2.1 Normative refere
19、nces This British Standard incorporates, by reference, provisions from specific editions of other publications. These normative references are cited at the appropriate points in the text and the publications are listed on the inside back cover. Subsequent amendments to, or revisions of, any of these
20、 publications apply to this standard only when incorporated in it by updating or revision. 2.2 Informative references This British Standard refers to other publications that provide information or guidance. Editions of these publications current at the time of issue of this standard are listed on th
21、e inside back cover, but reference should be made to the latest editions. 3 Definitions For the purposes of this standard the definitions given in BS 4727-1:Group 10:1991 apply. 4 General In the methods described, the electrode assembly is an integral part of the specimen holder into which the speci
22、men and appropriate insulating fluid(s) are introduced, the capacitance and dissipation factor of the assembly being measured. Such systems introduce smaller errors in measurement than intimately applied electrodes, and facilitate the provision of guard electrodes which eliminate electric field dist
23、ortions and stray capacitances. Suitable electrode systems for each of the methods are described in 8.2, 9.2 and 10.2. Suitable measuring instruments are described in clause 7. 5 Test conditions Unless otherwise specified in the materials specification, specimens shall be conditioned for (20 4) h un
24、der the following conditions: temperature (23 2) C; relative humidity (50 5)% r.h. Unless otherwise specified in the materials specification, measurements shall be carried out under the same conditions. The specimen, electrode system and immersion fluid(s) and their environment shall be in thermal e
25、quilibrium when the measurement is made, the temperature difference being less than1 C. 1) 1 cSt = 1 10 6 m 2 s 1BS7663:1993 2 BSI 01-2000 NOTEThe permittivity and dissipation factor of a dielectric may change considerably with frequency, temperature and relative humidity. Accordingly the measured v
26、alues should only be taken to indicate the dielectric properties of the specimen under conditions similar to those used for the test. 6 Number and handling of specimens In all three methods the test shall be carried out on three specimens unless otherwise specified. Each specimen comprises one test
27、piece for methods A and B, and two test pieces for method C. At all times the specimens shall be handled with stainless steel flat-faced forceps to minimize the likelihood of damage or contamination, taking particular care not to compress or distort flexible or soft materials. 7 Measuring instrument
28、s An instrument of adequate sensitivity 2)shall provide a minimum detectable change in capacitance of0.3fF (i.e. 0.3 10 15F) and a minimum detectable change in dissipation factor of0.00001(i.e. 10 10 6 ). NOTE 1A variety of modes of output is offered by commercial measuring equipment. Some of the mo
29、re sophisticated offer a variety of outputs from the same instrument thus enabling the user to select the appropriate output. This standard assumes that the output is in the form of capacitance (C, in pF) and dissipation factor (D). See Annex A for conversion of other forms of output to this format.
30、 NOTE 2The electrode systems described in methods A and B are of three terminal “guarded” design. This practically eliminates the influence of stray electric fields at the electrode edges and removes the need for “edge capacitance” corrections. In method C there is a close match in permittivity betw
31、een the material and the immersion fluid and thus there is little change in edge capacitance when the specimen is inserted or removed. NOTE 3Care should be taken to ensure that all measurement leads are screened and kept as short as possible, consistent with the manufacturers instructions. Some type
32、s of instrument require a “short” and “open” circuit calibration. The “short circuit” should be established between the electrodes of the electrode system i.e. in the position which the specimen would occupy. Care should be taken to ensure that the short circuit used is of low resistance and inducta
33、nce and that it does not damage the surfaces of the electrode. It is essential also to ensure the micrometer zero is not altered. A smooth metal disc, the diameter of which, is approximately75% that of the guarded electrode and1mm to3mm thick is suitable for use as a short circuit. The “open” circui
34、t is established by disconnection of the electrodes at the end of the cables furthest from the capacitance meter, i.e. so that allowance is again made for the effect of the measuring leads. Reference should be made to the manufacturers instructions to discover whether it is necessary to link the out
35、er connections of the coaxial cables during this calibration and whether the error introduced by omission of the electrode system is small and may be ignored. Accordingly it is to be preferred if a three terminal measuring instrument, with for example “high”, “low” and “guard” connections can be use
36、d. NOTE 4Many commercial instruments are now based on measurement of current, voltage and phase angle. These instruments are commonly of four (or five) terminal design. Reference should be made to the manufacturers instructions before connecting a three terminal electrode system to such an instrumen
37、t, since the preferred mode of connection may differ between instruments. 8 Method A: Air substitution technique 8.1 Principle The test piece is inserted into a guarded electrode system in which the electrode separation is variable. Small air gaps are left between the sample and electrodes to ensure
38、 that the test piece is not mechanically stressed. The capacitance and dissipation factor of the assembly are measured. The test piece is removed and the electrode separation adjusted so that the capacitance is restored to its original value. The electrode movement and the new value of dissipation f
39、actor are measured. The permittivity and dissipation factor of the test material are calculated, as shown in 8.5.2, from the test piece thickness, the change in electrode spacing and the change in observed values of dissipation factor. 8.2 Electrode system The electrode system shall be of rigid mech
40、anical design and of sufficient thermal capacity that rapid changes in ambient temperature do not significantly affect its dimensions. It shall comprise three parallel concentric electrodes, one of which is a guard. The electrode surfaces shall be flat and shall remain substantially parallel at all
41、times. Figure 1 illustrates a possible construction and means of connection to a three terminal measuring instrument. NOTE 1For connection to four or more terminal instruments, reference should be made to the manufacturers instructions. The system comprises a circular measuring electrode surrounded
42、by a concentric coplanar guard electrode, and a movable electrode whose separation from the measuring electrode is controlled by a micrometer head. Rotation of the drive mechanism should not be transmitted to the electrode. NOTE 2A more precise means of determining the changes in electrode spacing,
43、e.g. a displacement transducer, which will not disturb the electric field between the electrodes may be introduced. 8.3 Test pieces The test piece shall be flat and uniform in thickness and shall extend beyond the unguarded electrode by at least5mm. 2) For information on the availability of suitable
44、 instruments and electrode systems write to Customer Services Information, Services Group, BSI, Linford Wood, Milton Keynes MK14 6LE.BS7663:1993 BSI 01-2000 3 Where possible, test pieces shall be used as prepared by the manufacturer. For the electrode system shown the test piece shall be either: a)
45、a flat circular sheet (61 1) mm in diameter; or b) a flat rectangular sheet (61 1) mm by (100 1) mm. The thickness shall be between1.0mm and5.0mm. The thickness at any point shall not vary by more than1% from the mean value. NOTEIf possible the specimen should be of the same thickness prepared by th
46、e same process as the electrical insulating material under test. If it is necessary to reduce its thickness care should be taken to ensure that its surfaces are not contaminated during the process. The maximum tolerance deviation from a straight edge placed along a diameter or diagonal shall be less
47、 than10% of the thickness. If the test piece is warped, reject it at this stage and prepare another. Figure 1 Example of electrode system for method ABS7663:1993 4 BSI 01-2000 8.4 Procedure 8.4.1 Determination of test piece thickness Determine the test piece thickness with a micrometer conforming to
48、 BS 870:1950. Measure four values of thickness at points equally spaced around the periphery of the test piece, and a fifth value centrally. Calculate the arithmetic mean thickness of each test piece as t. NOTEWhilst absolute accuracy in measurement of thickness of the test piece is not important, a
49、nd the thickness and micrometer movement may be measured in arbitrary units, it is essential that all discrepancies of scale between the micrometer used for thickness measurement and that of the electrode system are minimized. Any such discrepancy will lead to erroneous results, the fractional error in result being generally greater than that in thickness measurement or electrode movement by a ratio dependent on the permittivity of the specimen. If the errors in t, and tan , expressed as fractions of values of t, and ta
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