RU2234075C2 - Non-contact method of determination of inductivity of the solid and liquid dielectrics - Google Patents

Abstract

FIELD: electrical measuring equipment.

SUBSTANCE: the invention is dealt with the field of electrical measuring equipment and may be used, for example, to check the quality of the solid and liquid insulating materials. The technical result is development of a rather simple and of high accuracy method to measure inductivity without destroying action. The method of determination of inductivity provides for action of an electromagnetic field on a specimen placed in the interelectrode space between a measuring flat electrode and a surface of a rotating metal disk, on which a polymeric film electric source of an electrical field is fixed. Then they determine the amplitude value of an inductive current of the measuring electrode in the case when the specimen is in the interelectrode space and the amplitude value of an inductive current without the dielectric placed in. The inductivity is determined by the given mathematical formula.

EFFECT: the invention offers a rather simple and of high accuracy method to measure inductivity without destroying action.

1 dwg

Description

The invention relates to electrical engineering and can be used, for example, to test the quality of solid and liquid insulating materials.

Known bridge and resonant methods for measuring the dielectric constant of solid and liquid dielectrics [1, 2], which allow the measurement of the dielectric constant of electrical insulation materials in a measuring cell with overhead or vacuum-sprayed metal measuring electrodes.

The disadvantage of the above measurement methods is that their implementation requires the use of overhead or vacuum-sprayed metal electrodes.

A known method of controlling the thickness and permittivity of a dielectric [3], which includes the simultaneous irradiation of the investigated dielectric on a metal base by radiation in the microwave and high frequency ranges. The frequency of the RF radiation is chosen from the condition that the thickness of the circuit layer is less than the thickness of the metal base, the measurement of changes in the values of the detected signals on the RF and microwave in the absence of the dielectric on the metal base and in its presence, and determination of the thickness.

A known method for determining the dielectric constant of the material [4]. The method includes exciting electromagnetic oscillations in a microstrip line with known complex dielectric permittivity parameters, measuring its impedance in idle and short circuit conditions when placing a microstrip line on the surface of the material sample under study and in the absence of the sample to be studied, and calculating the dielectric constant of the material sample under study.

The closest analogue is a method for determining the complex dielectric constant of a material [5]. The method consists in applying to the test sample an abruptly varying voltage of alternating polarity with a period of cyclic measurement frequency, integrating the polarization current and recording the magnitude of the polarization charge at equally spaced times. When calculating the real part of the complex permittivity, select the number of samples for a half-period of at least four, and when calculating the imaginary part, at least 32. Calculate the components of the complex permittivity by summing the values of the samples multiplied by the trigonometric functions of the phase angle (sine or cosine for real or imaginary part, respectively).

A disadvantage of the known methods and prototype is that they are quite difficult to use.

The objective of the invention is to provide a method for measuring the dielectric constant without damaging effects and achieve higher accuracy and quite easy to use.

The problem is achieved by the fact that in the known method for determining the dielectric constant by exposure to an electromagnetic field, the test sample is placed in the interelectrode space between the flat measuring electrode and the surface of a rotating metal disk on which a polymer film electret is mounted - an electric field source, the amplitude value of the induction current of the measuring electrode is determined in the case where the test sample is located in the interelectrode space I _x, s litudnoe induction current value I premises without dielectric _Sports, and the dielectric constant is calculated by the formula

where ε _x is the dielectric constant of the investigated dielectric material;

ε _air - dielectric constant of air;

h _x is the thickness of the investigated dielectric material;

h _air - the thickness of the air gap;

h is the distance from the surface of the measuring electrode to the surface of the rotating disk on which the thin-film electret is fixed - the source of the electric field;

I _x is the amplitude value of the induction current of the measuring electrode, measured using an oscilloscope, for the case when the investigated dielectric is in the interelectrode measuring gap;

I _air - the amplitude value of the induction current for the case when the interelectrode measuring gap is filled only with air.

A thin film electret made of a polytetrafluoroethylene (PTFE) capacitor film is used as an electric field source.

The method is as follows.

The drawing shows a diagram of a device for determining the dielectric constant.

On the surface of the rotating disk 1 is fixed pre-polarized electret 2 round in shape, with a diameter of d. The investigated solid dielectric 3 in the form of a cylinder with a diameter of D and a height of H, where D >> d, is placed in the gap between the measuring electrode 4 and the surface of the grounded rotating disk 1 with a fixed film electret 2.

If it is necessary to measure the dielectric constant - a liquid dielectric (for example, transformer oil), then a thin-walled cylindrical polyethylene vessel with a wall thickness - h, where h << N, is installed in the interelectrode gap. The wall thickness of the polyethylene vessel h is significantly less than the thickness of the liquid N.

A constant supply voltage from 0 to 30 V is supplied to the motor terminals. Depending on the supplied voltage, the rotational speed of the electric motor and, accordingly, the rotational speed of the disk 1 can vary from 0 to 3000 rpm.

The amplitude of the signal from electret 2 is measured using an electron beam oscilloscope. To determine the dielectric constant of solid and liquid dielectrics, two measurements of I _{i are} necessary.

The first I _air - is measured when the test dielectric is removed from the measuring interelectrode gap (only air is in the interelectrode gap). The second I _x - is measured when the investigated dielectric is placed in the measuring interelectrode gap.

The calculation of the dielectric constant of the investigated dielectric is produced by the formula

where h is the distance from the surface of the measuring electrode to the surface of the rotating disk; h _x - thickness of the investigated dielectric - the thickness of the air gap.

H = h _air + h _x

When the interelectrode gap is completely filled with the investigated dielectric (for example, taking measurements in transformer oil), the dielectric constant of the dielectric material is measured by the formula

where h _air = 0 and h _x = h.

Example 1

Measurement of dielectric constant of transformer oil.

Transformer oil is poured into a thin-walled glass made of polyethylene with a wall thickness of 0.05 mm (layer thickness 10 mm). The interelectrode distance in the measuring capacitor is set to 15 mm. It is checked that in this region of interelectrode gaps, the dependence of the amplitude of the measured signal on the reciprocal distance 1 / h I = f (1 / h) is almost linear and the contribution of the edge capacitance is minimal. The measurements use a PTFE film electret - h = 10 μm, polarized to an electret potential difference of V = 1000 V. Two measurements are made of the oscilloscope signal amplitude I _air - for an empty (filled with air) measuring capacitor and I _x - for a measuring capacitor with the test sample - transformer oil.

Two values of the signal amplitude I _air = 10.0 mm and I _x = 16.6 mm were measured on the scale of an electron beam oscilloscope. We believe that the dielectric constant of air ε _air = 1.

According to the formula, we calculate the dielectric constant of transformer oil

The calculated value of the dielectric constant for transformer oil is 2.5, which is in accordance with the reference data.

Example 2

In the measurements, a muscovite mica plate with a thickness of 10 mm is used. The interelectrode distance in the measuring capacitor is set to 15 mm. It is checked that in this region of interelectrode gaps, the dependence of the amplitude of the measured signal on the reciprocal of the distance 1 / h I _x = t (1 / h) is almost linear and the contribution of the edge capacitance is minimal. The measurements use a PTFE film electret - h = 10 μm, polarized to an electret potential difference of V = 1000 V. Two measurements are made of the oscilloscope signal amplitude I _air - for an empty (filled with air) measuring capacitor and I _x - for a measuring capacitor with the studied electrical insulation material (muscovite mica).

Two values of the signal amplitude I _air = 10.0 mm and I _x = 23.1 mm were measured on the scale of an electron beam oscilloscope. We believe that the dielectric constant of air ε _air = 1.

According to the formula, we calculate the dielectric constant of mica muscovite

The calculated value of the dielectric constant for mica muscovite is 6.7, which is in accordance with the reference data.

The proposed method can significantly simplify the measurement of dielectric constant without damaging effects.

Sources of information

1. Kazarnovsky D.M., Tareev B.M. Tests of electrical insulation materials. - M.-L .: Gosenergoizdat, 1963.

2. Emé F. Dielectric measurements. For quantitative analysis and to determine the chemical structure. Per. from German. Shtillera B.N. Ed. Zaslavsky I.I. - M.: Chemistry, 1967.

3. RF patent №2012871, G 01 N 22/00, 1994.

4. RF patent No. 2103673, G 01 N 22/00, G 01 R 27/26, 1998.

5. RF application No. 94012374, G 01 R 27/26, 1996 (prototype).

Claims (2)

1. A non-contact method for determining the dielectric constant of solid and liquid dielectrics by exposure to an electromagnetic field, characterized in that the test sample is placed in the interelectrode space between the measuring flat electrode and the surface of the rotating metal disk on which the polymer film electret is mounted - the source of the electric field, the amplitude value is determined induction current of the measuring electrode in the case when the test sample is in the interelectrode of the space, the amplitude of the induced current value without dielectric spaces, and the dielectric constant is calculated by the formula

where ε _x is the dielectric constant of the investigated dielectric material; ε _air - dielectric constant of air; h _x is the thickness of the investigated dielectric material; h _air -thickness of the air gap; h is the distance from the surface of the measuring electrode to the surface of the rotating disk on which the thin-film electret is fixed - the source of the electric field; I _x is the amplitude value of the induction current of the measuring electrode, measured using an oscilloscope, for the case when the investigated dielectric is in the interelectrode measuring gap; 1 _air - the amplitude value of the induction current for the case when the interelectrode measuring gap is filled only with air. 2. The method according to claim 1, characterized in that a thin film electret from a polytetrafluoroethylene capacitor film is used as the source of the electric field.