Recommended methods for the determination of the permittivity and dielectric ddissipation fator of electrical insulating materials at power, udio and radio frequencies including meter w
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
1 Scope
This standard applies to the procedures for determination of permittivity and dissipation factor and of quantities calculated from them, such as loss index, within the frequency range 15 Hz to 300 MHz approximately. Some of the methods described in this standard can, with special precautions, be used for measurements at frequencies considerably lower or higher than the given limits.
Liquids and fusible materials, as well as solid materials, can be measured by the methods described. The measured values are dependent on physical conditions such as frequency, temperature and moisture content, and in special cases, on field strength as well.
In some cases, tests at voltages exceeding 1,000V may introduce effects not related to permittivity and dielectric dissipation factor, and are not described here.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this standard. For dated references, subsequent amendments (excluding corrections) to, or revisions, of any of these publications do not apply to this standard. However parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies.
IEC 60247: 1978 Measurement of relative permittivity, dielectric dissipation factor and d.c. resistivity of insulating liquids
3 Terms and definitions
For the purposes of this standard, the following terms and definitions apply.
3.1
relative permittivity
εr
ratio of capacitance CX of a capacitor, in which the space between and around the electrodes is entirely and exclusively filled with the insulating material in question, to the capacitance C0 of the same configuration of electrodes in vacuum:
(1)
where,
εr——the relative permittivity;
CX——the capacitance of a capacitor which is filled with the insulating material in question;
C0——the capacitance of electrodes in vacuum.
The relative permittivity εr of dry air free from carbon dioxide, at normal atmospheric pressure, equals 1.000 53 so that in practice, the capacitance Ca of the configuration of electrodes in air can normally be used instead of C0 to determine the relative permittivity εr with sufficient accuracy.
The permittivity of an insulating material is, in a measurement system, the product of its relative permittivity εr and the electric constant (or permittivity of vacuum) ε0 in that measurement system.
In the SI system, the absolute permittivity is expressed in farad per metre (F/m); furthermore, in SI units, the electric constant ε0 has the following value:
ε0 = 8.854 × 1012 F/m ≈ × 109 F/m (2)
For the purpose of this standard, where picofarads and centimetres are used in calculating capacitance, the electric constant is:
ε0 = 0.088 54 pF/cm
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Uses and properties of electrical insulating materials
5 Form of specimen and electrode arrangement
6 Choice of measuring methods
7 Test procedures
8 Results
9 Test report
Annex A (Informative) Apparatus
Annex B (Informative) Comparison between clause/subclause numbers in this standard and those in IEC 60250: 1969
