Insulating liquids - Purpose and Scope,Normative References and Definitions

Purpose and Scope

This International Standard describes a method for the simultaneous measurement of the conductance G and the capacity C allow the calculation of the dissipation factor as of insulating liquids. The proposed method is applicable both new insulating liquids as insulating fluids in transformers and other service equipment.

This standard does not replace the IEC 60247, but instead complements it since it is particularly suitable for highly insulating fluids and recommends a method for the measurement of these liquids. This method allows to measure precision values ​​of the dissipation factor as low as 10-6 to power frequencies. Moreover, the range of ä such measures is 10-6 to 1 and can extend up to 200 in particular conditions.

Normative References

The (s) standard (s) which is then related to (n) contains provisions apply to this International Standard. In the time of publication (s) issue (s) indicated (s) was (were) in force. All standards are subject to revision, the parties to agreements based on this International Standard should consider applying the most recent edition of the (s) standard (s) (s) indicated below. Members of IEC and ISO maintain registers of international standards in force at the time.

IEC 60247:1978 - Measurement of relative permittivity, dielectric dissipation factor and resistivity in current continuous insulating liquids.

IEC 60475:1974 - Method of sampling liquid dielectrics.

ISO 5725-1:1994 - Accuracy (trueness and precision) of measurement methods and results. Part 1: General principles and their definitions.

ISO 5725-2:1994 - Accuracy (trueness and precision) of measurement methods and results. Part 2: Basic methods for the determination of repeatability and reproducibility of a standard measurement method.

ISO 5725-3:1994 - Accuracy (trueness and precision) of measurement methods and results. Part 3: intermediate measures days of the precision of a standard measurement method.

ISO 5725-4:1994 - Accuracy (trueness and precision) of measurement methods and results. Part 4: Basic methods to determine the veracity of a standardized measurement method.

Definitions

For purposes of this standard, the following definitions:
Conductivity (σ): Amount related to the intensity of the electric field E and current density j by

Resistivity (ρ): The inverse of the conductivity given by

Resistance (R): The resistance of the test cell filled with liquid is the relationship between the voltage V applied to the current cell and Fasei or R, and is given by

In the simplest case of parallel plate electrodes of area A and separation L,

Conductance (G): The inverse of the resistance, given by

Capacity (C): The ability of the test cell filled with liquid is the ratio of the charge Q electrodes and the voltage V applied to the test cell. For a plane capacitor,

Where
E is the permittivity of the liquid.

Dissipation factor: For a material subjected to sinusoidal voltage, as is the relation between the value of the absorbed active power and reactive power value. In the simple case of a capacitor C resulting in a resistance R,

Where
W= 2 f y f is the frequency of stress.

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Posted in: capacity,insulating liquids,resistance,resistivity

INTRODUCTION TO THE CONDUCTIVITY

The conductivity is a characteristic of a liquid only if measured in thermodynamic equilibrium.
To meet this requirement, avoid the application of high voltage electric or extended solicitations. This is not CIS is the case in 60,247 for the measurement of dc resistivity (electrical solicitations to 250 Vmm-1, electrification arbitrary conventional time 1 min).
There is a simple relationship between the dissipation factor as conductivity and permittivity a liquid with no (or negligible) losses dipole, which is the case with most liquid applications electronics:
So

Where

w= 2 f and f is the frequency of stress.
So far the much of any of themprovides the same information about the conduction properties the liquid. In fact, very often in practice there are major discrepancies between the calculated resistivity far from the much with conventional and DC resistivity measured by the recommendations of IEC 60247.
Currently there are new devices for measuring the conductivity in thermodynamic equilibrium. Are able to easily and accurately measure very low values of The characteristics of this new equipment allow measurement of insulating liquids new even at room temperature.

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Posted in: conductivity,thermodynamic equilibrium