GB/T 31838.8-2024 Solid insulating materials- Dielectric and resistive properties-Part 8 : Determination of dielectric properties (AC method) - Relative permittivity and dielectric dissipation factor (frequencies 1 MHz - 300 MHz)
1 Scope
This document specifies test methods (AC method) for the determination of permittivity and dissipation factor properties of solid insulating materials in a high frequency range from 1 MHz to 300 MHz.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
IEC 60212 Standard conditions for use prior to and during the testing of solid electrical insulating materials
Note: GB/T10580-2015 Standard conditions for use prior to and during the testing of solid electrical insulating materials (IEC 60212:2010, IDT)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
- ISO Online browsing platform: available at https://www.iso.org/obp
- IEC Electropedia: available at http://www.electropedia.org/
3.1
solid electrical insulating material
solid with negligibly low electric conductivity, used to separate conducting parts at different electrical potentials
Note: The term "electrical insulating material" is sometimes used in a broader sense to designate also insulating liquids and gases. Insulating liquids are covered by IEC 60247 [1].
3.2
dielectric properties
comprehensive behaviour of an insulating material measured with an alternating current comprising the capacitance, absolute permittivity, relative permittivity, relative complex permittivity, dielectric dissipation factor
3.3
absolute permittivity
ε
electric flux density divided by the electric field strength
3.4
vacuum permittivity
ε0
permittivity of a vacuum, which is related to the magnetic constant ε0 and μ0 to the speed of light in vacuum c0 by the relation ε0μ0c0 2 =1
3.5
relative permittivity
εr
ratio of the absolute permittivity to the permittivity of a vacuum ε0
3.6
relative complex permittivity
εr
permittivity in a complex number representation, under steady sinusoidal field conditions
3.7
dielectric dissipation factor tanδ
loss tangent
numerical value of the ratio of the imaginary to the real part of the complex permittivity
3.8
capacitance
C
property of an arrangement of conductors and dielectrics which permits the storage of electrical charge when a potential difference exists between the conductors
3.9
voltage application
application of a voltage between electrodes
Note: Voltage application is sometimes referred to as electrification
3.10
measuring electrodes
conductors applied to, or embedded in, a material to make contact with it to measure its dielectric or resistive properties
Note: The design of the measuring electrodes depends on the specimen and the purpose of the test.
4 Methods of test
4.1 Basic theory
Capacitance C is the property of an arrangement of conductors and dielectrics which permits the storage of electrical charge when a potential difference exists between the conductors.
C is the ratio of a quantity q of charge to a potential difference U. A capacitance value is always positive. The unit is farad when the charge is expressed in coulomb and the potential in volts.
The measured dielectric constant ε of an insulating material is the product of its relative permittivity ε, and the permittivity of a vacuum ε0:
This general method describes common values for general measurements. If a method for a specific type of material is described in this document, the specific method shall be used. The permittivity is expressed in farad per metre (F/m); the permittivity of vacuum ε0 has the following value:
Relative permittivity is the ratio of the absolute permittivity to the permittivity of a vacuum ε0
In the case of constant fields and alternating fields of sufficiently low frequency, the relative permittivity of an isotropic or quasi-isotropic dielectric is equal to the ratio of the capacitance of a capacitor, in which the space between and around the electrodes is entirely and exclusively filled with the dielectric, to the capacitance of the same configuration of electrodes in vacuum.
The relative permittivity εr, of dry air, at normal atmospheric pressure, equals 1.00059, so that in practice, the capacitances Ca of the configuration of electrodes in air can normally be used instead of C0 to determine the relative permittivity εr with sufficient accuracy.
Relative complex permittivity is permittivity in a complex number representation under steady sinusoidal field conditions expressed as
