1、BRITISH STANDARD BS 7737-1: 1995 IEC 377-1: 1973 Recommended methods for the determination of the dielectric properties of insulating materials at frequencies above300MHz Part 1: GeneralBS7737-1:1995 This British Standard, having been prepared under the directionof the Electrotechnical Sector Board,
2、 was published underthe authority of the Standards Board and comes intoeffect on 15October1995 BSI 11-1999 The following BSI references relate to the work on this standard: Committee reference GEL/15 Special announcement in BSI News April 1995 ISBN 0 580 24784 8 Committees responsible for this Briti
3、sh Standard The preparation of this British Standard was entrusted to Technical Committee GEL/15, Insulating material, upon which the following bodies were represented: British Ceramic Research Ltd. British Industrial Ceramic Manufacturers Association Electrical and Electronic Insulation Association
4、 (BEAMA Ltd.) Electricity Association Federation of the Electronics Industry Rotating Electrical Machines Association (BEAMA Ltd.) Transmission and Distribution Association (BEAMA Ltd.) Amendments issued since publication Amd. No. Date CommentsBS7737-1:1995 BSI 11-1999 i Contents Page Committees res
5、ponsible Inside front cover National foreword ii Introduction 1 1 Object and scope 1 2 Definitions 1 3 Factors influencing dielectric properties of dielectric materials 2 4 Survey on measuring methods 3 5 Testing procedure 6 6 Test report 7 Figure 1 A.C. measuring methods 8BS7737-1:1995 ii BSI 11-19
6、99 National foreword This Part of BS7737 has been prepared by Technical Committee GEL/15. It is identical with IEC377-1 Recommended methods for the determination of the dielectric properties of insulating materials at frequencies above 300 MHz Part1: General published by the International Electrotec
7、hnical Commission (IEC). 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 confer immunity from legal obligations. Summary of pages
8、 This document comprises a front cover, an inside front cover, pages i and ii, pages1to8 and a back cover. This standard 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.BS7737-1:1995 BSI 11-1999 1
9、 Introduction Methods for the determination of the dielectric properties of insulating materials may be divided roughly into two main groups: 1) Lumped-parameter methods can be used when the wavelength of the applied electromagnetic field is large compared with the dimensions of the specimen. These
10、relatively simple methods are dealt with in IEC Publication250, Recommended Methods for the Determination of the Permittivity and Dielectric Dissipation Factor of Electrical Insulating Materials at Power, Audio and Radio Frequencies Including Metre Wavelengths, covering the frequency range from powe
11、r frequencies up to about300MHz. 2) Distributed parameter methods shall be used when the spatial variation of the electromagnetic field over the specimen can no longer be ignored. Methods taking account of wave propagation are described in this recommendation, covering the frequency range from about
12、300MHz up to optical frequencies. In a narrow range of frequencies around the “critical” frequency of about300MHz (which is shown shadowed inFigure 1, page8), either one of the main methods may be used, depending mainly on the dimensions and permittivity of the specimen. 1 Object and scope This reco
13、mmendation applies to the procedures for the determination of relative permittivity and dielectric dissipation factor and of quantities related to them, such as loss index, of dielectric materials in the microwave frequency region (i.e.frequencies above about300MHz up to optical frequencies). Unlike
14、 the test methods employed at lower frequencies (see IEC Publication250), the test methods dealt with in this recommendation use test specimen and/or test set-up dimensions larger than or comparable to the wavelength of the electromagnetic field of the test frequency. In theory, the methods describe
15、d apply only to test materials having the permeability of absolute vacuum. Good approximation in general is obtained for dia- and paramagnetic materials (so-called non-magnetic materials) whereas with ferro- and ferrimagnetic materials special procedures have to be chosen to separate the dielectric
16、and magnetic properties. These latter methods, however, are beyond the scope of this recommendation. Note on magnetic properties. Specimens showing magnetic properties may be tested according to this recommendation if permeability is driven into saturation by a d.c. magnetic bias field of sufficient
17、 intensity. With special precautions and by the use of suitably designed measuring cells, liquids and fusible materials can be measured, as well as solid materials, by the methods described. The measured values are dependent on physical conditions such as frequency, temperature, moisture content, an
18、d in special cases on field strength as well. All measurements and calculations of this recommendation are based on a sinusoidal waveform of angular frequency = 2f. 2 Definitions NOTE 1All definitions apply only to dielectric materials having the permeability of absolute vacuum. NOTE 2For the defini
19、tions of terms related to wave propagation used in this recommendation, reference should be made to Groups05and62of the International Electrotechnical Vocabulary. 2.1 relative complex permittivity r * the relative complex permittivity r * of a dielectric material is: where C x * denotes the complex
20、capacitance of a small 1)capacitor in which the space between and around the electrodes is entirely and exclusively filled with the dielectric material in question, and C ois the capacitance of the same electrode configuration in absolute vacuum NOTEThe complex capacitance of a capacitor is defined
21、by: jC x * = Y x * = G x+ jC x where G xis the real part (a.c. conductance) and jC xthe imaginary part of the complex admittance Y x * of the said capacitor. as the wavelength of the applied electromagnetic field with increasing frequency approaches the dimensions of the specimen employed, the varia
22、tion of the electric (and magnetic) field parameters throughout the specimen can no longer be ignored. Therefore, for a proper interpretation of the measured data it is necessary to turn from lumped circuit analysis to wave analysis and transmission line theory. This means also growing sensitivity o
23、f results to inhomogeneity and anisotropy of specimens (1) 1) Small compared with the wavelength within the dielectric.BS7737-1:1995 2 BSI 11-1999 it follows that: the relative complex permittivity r * of a dielectric material is proportional to the square of the ratio of the complex propagation coe
24、fficient = +j of an electromagnetic wave in the dielectric material to that 0 =j 0in absolute vacuum: where 0is the wavelength in free space and cis the critical (or cut-off) wavelength of the mode used NOTE 1With plane waves or TEM waves c= Z. NOTE 2The relative permittivity rof ambient dry air fre
25、e from carbon dioxide at293K and normal atmospheric pressure equals1.00053, so that in practice measurements of C a , c aand ataken in air instead of C 0 , c 0and 0taken in absolute vacuum can be used to determine the relative permittivity rof solids and liquids with sufficient accuracy. NOTE 3The c
26、omplex (absolute) permittivity of a dielectric material is the product of its complex relative permittivity r * and the electric constant (or permittivity of absolute vacuum) 0 : * = 0 r . r * In the SI system, the absolute permittivity has the unit farad per metre (F/m); furthermore, the electric c
27、onstant 0has the following value: 2.2 relative permittivity r the relative permittivity rof a dielectric material is the real part of the complex relative permittivity, defined in Sub-clause2.1. According to equations (1) and (2): NOTEIf the dielectric quantities are noted as real numbers, i.e. rand
28、 tan (see Sub-clause2.4) instead of rand r , the prime is omitted: r= r 2.3 loss index r the loss index rof a dielectric material is the imaginary part of the relative complex permittivity defined in Sub-clause2.1. According to equations (1) and (2): 2.4 dielectric dissipation factor 2)tan the diele
29、ctric dissipation factor 2)tan of a dielectric material is the tangent of the phase angle (loss angle ) between the applied field strength E and the resulting dielectric displacement D within the insulating material, both varying sinusoidally with time at one and the same angular frequency =2f. as t
30、he field components E and D within the dielectric in general are not accessible to measurement, the dielectric dissipation factor of a given volume (e.g. of the dielectric material) is measured as the ratio of the electric energy dissipated to2 times that reversibly stored in that volume per one hal
31、f-period of oscillation. This ratio is also equivalent to: the reciprocal of the dissipation factor tan is called quality factor (Q-factor): 3 Factors influencing dielectric properties of dielectric materials The measured permittivity and dielectric dissipation factor of a given dielectric material
32、are determined by the resulting dielectric polarization of the test specimen. Various external and internal physical parameters such as frequency, temperature, electrical field strength, ionizing radiation, moisture and other impurities, chemical structure, homogeneity and isotropy (“physical and ch
33、emical structure”) etc., affect the measured data. Therefore to interpret consistently the results obtained from a test, it is necessary to know the state of the test specimen and to keep all the afore-mentioned parameters under control. In the following, the influences of frequency, temperature, mo
34、isture and other impurities, of physical and chemical structure and of electrical field strength on the measured dielectric properties are discussed separately. NOTEThe permittivity and dielectric dissipation factor measured within the frequency range covered by this recommendation mostly originate
35、from dipole polarization due to polar molecules and from atomic polarization. (2) (3) (4) (5) 2) Certain countries refer to “loss tangent” in preference to “dielectric dissipation factor” because the result of the measurement of the loss is reported as the tangent of the loss angle. (6) 1 tan -Q =BS
36、7737-1:1995 BSI 11-1999 3 3.1 Frequency As, for technical materials, rand tan are not constant over the wide frequency range over which they are used, it is necessary to measure the dissipation factor and the permittivity at those frequencies at which the dielectric material will be used. For accura
37、te interpolation between data measured at a few frequencies, it may sometimes be possible to obtain a Debye curve to fit over an absorption region; also, effective use may be made of a Cole-Cole plot. 3.2 Temperature The polarizability of a dielectric material depends also on its temperature. Theref
38、ore the frequencies of the loss index maxima (and correspondingly of the dielectric dissipation factor) vary with temperature. Accordingly, the temperature coefficient of loss index can be positive or negative depending on the position of the loss index maximum with respect to the measuring frequenc
39、y and the test temperature. Special attention is drawn to the fact that irreversible changes of the dielectric properties of the material investigated may occur in a short time, for example during a measurement at elevated temperatures. In this respect, see also Sub-clauses3.3 and3.4. 3.3 Moisture a
40、nd other impurities The polarizability is increased by absorption of water or by the formation of a water film on the surface of the dielectric, thus affecting the permittivity, the dissipation factor and the d.c. conductivity. Conditioning of test specimens is therefore of decisive importance and c
41、ontrol of the moisture content, both before and during testing, is imperative if test results are to be interpreted correctly. The polarizability is also subject to impurities introduced by physical contamination or chemical additives, for example solvents or plasticizers. Therefore care shall be ta
42、ken to ensure that the material to be tested is not affected or affected only in a controlled way by the sampling procedures or by subsequent treatments e.g. at elevated temperatures. 3.4 Physical and chemical structure The direction of polarization of the electromagnetic field relative to the struc
43、ture of the specimen under test strongly influences the result of the measurement. Different results may be obtained due to inhomogeneity (as in laminates) or to anisotropy, for example in crystals, unless all measurements on the specimens are made in the same relation to some identifiable feature o
44、f the material. NOTEMaterials showing some periodicity in their structure such as laminates may have a frequency response different from that of their constituents if the wavelength is comparable with the period of this structure. Specimens which have the same chemical composition but different chem
45、ical structures, e.g.curable resins subjected to different curing conditions or polymers of a different degree of polymerization, will also give different results. 3.5 A.C. Field strength In general, permittivity and dielectric dissipation factor are independent of field strength so long as no parti
46、al discharge occurs in the dielectric. With ferro-electric bodies, however, a field-dependent effect may still be observable at the lower microwave frequencies, but it rapidly vanishes as the frequency increases. 4 Survey on measuring methods 4.1 Principles of measuring methods 4.1.1 Introduction Th
47、e characteristic feature of methods for the determination of dielectric properties in the frequency range covered by this recommendation is that the electric and magnetic components of the field vary both in amplitude and phase from point to point of the specimen and of the measuring apparatus, beca
48、use the wavelength of the radiation is comparable with the dimensions of the specimen and the apparatus. In non-magnetic materials, this effect first becomes obvious in the tens-of-MHz region and can no longer be ignored from about600MHz upwards. The measuring apparatus, and often the measured quant
49、ities too, therefore differ from those used in the methods for lower frequencies (IEC Publication250). 4.1.2 Physical effects available for measurement The permittivity and loss govern the following effects: a) The propagation velocity of electromagnetic waves, and hence their wavelength within a given medium, is related inversely to the permittivity of the medium in question (seeSub-clause2.1). b) At any discontinuity of the permittivity of a medium transmitting a wave
