JPS6228655A - Diagnosing method for insulation deterioration - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for diagnosing insulation deterioration that can be widely applied to electrical equipment and equipment in general, such as electric motors and transformer cables.

[Prior art]

The insulation properties of electrical equipment and equipment deteriorate over time. Therefore, it should be periodically diagnosed, and if abnormal deterioration is observed or the deterioration has progressed to the extent that it exceeds the allowable limit, repair or replacement should be carried out.6 The conventional method for diagnosing insulation deterioration is dielectric loss tangent measurement and DC leakage current measurement. The former is a method in which a high commercial frequency voltage is applied to the diagnostic section to measure dielectric loss, and the latter is a method in which a high DC voltage is applied to determine leakage current, polarization index, etc.

[Problem that the invention seeks to solve]

In the conventional method described above, there is a problem in work safety because a high voltage is applied. Moreover, it takes a long time to prepare for a safe diagnosis.

In the case of solid insulators, cranks or trees occur. Then, the dielectric strength of this part is weak and partial discharge occurs here. If such a partial discharge occurs, it may interfere with the measurement of insulation properties, making it impossible to make a correct diagnosis.

Furthermore, both dielectric loss tangent measurement and leakage current measurement under high voltage are accompanied by fluctuations in measured values due to environmental conditions such as moisture absorption.

[Means for solving problems]

The present invention has been made to solve this problem, and reduces the applied voltage by applying a voltage with a frequency higher than the frequency of the electric field (generally commercial frequency) that is constantly applied to the diagnostic target. to be able to perform a diagnosis;
In addition to improving safety, the accuracy of measurement for diagnosis can be improved by preventing partial discharge in the crank and tree, and by improving measurement accuracy, we have developed an insulation deterioration diagnosis method that can use capacitance as a diagnostic element. The purpose is to provide.

A method for diagnosing insulation deterioration according to the present invention is a method for diagnosing deterioration of the insulation properties of an insulating material by applying a voltage to the insulating material. It is characterized by measuring capacitance and/or dielectric loss.

〔Example〕

Hereinafter, the present invention will be explained in detail based on the drawings showing the side numbers for implementing the invention.

Figure 1.2 is a schematic diagram showing the implementation state when the present invention is applied to a cable, Figure 1 is a wiring diagram for measuring capacitance, and Figure 2 is for measuring dielectric loss. It is a wiring diagram when carrying out.

In FIG. 1, a voltage at a frequency higher than the commercial frequency is applied between the inner and outer conductors 1a and lb of a cable 1 by a high frequency power supply 2, and the applied voltage E and leakage current I are measured by a voltmeter 3. Measured with ammeter 4.

The capacity 1c is calculated by the following equation (1).

C1/2π "E ... (1) In Fig. 2, a Schering bridge 5 is connected in place of the ammeter 4. With this Schering bridge, t
an δ (dielectric loss tangent) can be measured.

Then, the dielectric loss P is calculated using the following equation (2).

P = 2πs Cf E2 (Looking at formula 11, if the all-determining accuracy of the ammeter 4 is about the same as that of the conventional method and a certain amount of current ■ is to flow, the value of E required for this can be small. On the other hand, (2)
Regarding the equation, the value of E required to operate the galvanometer attached to the Schering bridge 5 to the same extent as in the conventional method can be small.

In other words, in the case of <1), the working voltage can be reduced in inverse proportion to the working frequency, and in the case of equation (2), the working voltage can be reduced in inverse proportion to the square of the working frequency.

〔effect〕

As described above, in the case of the present invention, work safety is increased by lowering the voltage used for diagnosis, and the time required for preparatory work can be reduced accordingly.

Furthermore, as the operating voltage is lowered, the electric field strength applied to the insulating part is reduced, making it difficult for cracks and partial discharges to occur in the first place, and by selecting an appropriate frequency and voltage, partial discharges can be completely eliminated. Is possible.

FIG. 3 shows an equivalent circuit of a deteriorated insulator.

In the figure, CO+RO indicates the capacitance and insulation resistance under normal conditions, and it is considered that a voltage is applied to these parallel circuits.

When insulation deterioration causes, for example, a crank, ], lee, etc., it is assumed that a series circuit of resistance r and capacitance C1 is added in parallel. When a high electric field strength is applied, a discharge gap G exists in parallel to the capacitance RCl. The decrease in insulation resistance due to geothermal deterioration is expressed by parallel resistance r'.

Therefore, in the case of the present invention, since no partial discharge occurs due to a decrease in the applied voltage E, there is no discharge gap G, and the capacitance C1 can be accurately determined as a++ (it is necessary to measure C6 at the beginning of use). (Of course there is).

As is clear from equation (1), when a discharge occurs in the discharge gap G, the value of I/)C with a large T is determined as a large value. Therefore, in the past, C1 could not be measured correctly and could not be used as an element for diagnosing insulation deterioration, but the present invention makes it possible. That is, according to the present invention, the increase in capacitance can also be used as a diagnostic index for insulation deterioration, and the present invention has excellent effects.

[Brief explanation of drawings]

1st. FIG. 2 is a schematic diagram showing the implementation state of the method of the present invention, and FIG. 3 is an equivalent circuit of a deteriorated insulator. 2...High frequency power supply 3...Voltmeter 4...Current δ
↑5... Schering Brisogi

Claims (1)

[Claims] 1. In a method of diagnosing deterioration of the insulation properties of an insulating material by applying a voltage to the insulating material, a voltage with a frequency higher than the frequency of the electric field that is constantly applied to the insulating material is applied to evaluate the capacitance and/or the dielectric material. An insulation deterioration diagnosis method characterized by measuring loss.