JPH0140956B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved DC leakage current testing method for electrical equipment (including cables).

As a method for diagnosing the insulation of electrical equipment, it is known to apply a DC high voltage to the electrical equipment and measure the leakage current under the applied voltage. When performing this measurement method, leakage current may be measured on the high voltage side.
FIG. 1 shows a method for measuring cable lines.

In FIG. 1, 1' indicates a cable, and the cable shielding layer is grounded by a grounding wire 2'.
31' and 32' are cable bushings, 4' is a DC high voltage power supply, 5' is an ammeter, and 6' is a current recorder. Guard electrodes 71' and 72' are respectively attached to the cable bushings 31' and 32', and these are connected by a guard wire 8'. 9' is a shield electrode that can surround the high voltage side of the bushing 32' at the far end of the cable.
10' is a shield electrode that surrounds the ammeter 5' and the current recorder 6', and the guard electrode 71' of the bushing 31' at the near end of the cable and the power lead wire 4.
0'. Therefore, the shield electrodes 9', 10' are maintained at the same voltage as the power supply voltage.

In the above, A'... is the bushing surface current flowing from the ground to the guard electrode of the bushing,
B′-・- indicate the currents flowing between the high voltage and the ground, and these currents are connected to the shield electrodes 9′ and 1.
0', the current does not enter the ammeter 5' and the current recorder 6', and the cable insulator current can be measured with high accuracy without being affected by these currents.

However, in the measuring method shown in FIG. 1, since the current measuring circuit is located on the high voltage side, it is difficult to operate the ammeter and recorder, and the circuit configuration is complicated.

The DC leakage current testing method for electrical equipment according to the present invention is a method that can eliminate the above-mentioned disadvantages, and conducts insulation diagnosis by applying a DC high voltage to the electrical equipment and measuring the leakage current under the applied voltage. In this method, an electric-to-optical converter is inserted on the high-voltage side to convert the amount of leakage current into a light amount, and the light amount is converted to a current amount by the optical-to-electrical converter via a light guide, and the amount of current is measured. This method is characterized by:

The present invention will be explained below with reference to the drawings.

In FIG. 2, 1 is a cable, and the shielding layer is grounded. 21 and 22 are bushings at both ends of the cable, and guard electrodes 31 and 32 are attached to each bushing 21 and 22, respectively. 4 is a DC high voltage power supply, which is connected to the cable conductor via a power supply lead wire 40. 5 is an electrical-to-optical converter inserted into the power supply lead wire 40; 6 is an optical-to-electrical converter; a light guide 7 (optical) is connected between the input end of the optical-to-electrical converter 6 and the electrical-to-optical converter 5; fiber cable). 8 is a current recorder, which is connected to the output end of the optical electric converter 6. A shield electrode 9 surrounds the opto-electrical converter 5 and is connected to the power supply lead wire 40 and the guard electrode 31 of the bushing 21 at the proximal end of the cable. A shield electrode 10 surrounds the high voltage side of the bushing 22 at the far end of the cable, and the shield electrode 10 and the shield electrode 9 are connected by a guard wire 11. Since this guard wire 11 is charged with a high power supply voltage, it is necessary to use a cable with excellent voltage resistance, and other cable lines other than those to be tested can be used.
A protective resistor 12 is used to prevent a large current from flowing in the event that the test cable 1 has a ground fault, and its impedance is sufficiently larger than the impedance of the electrical-to-optical converter 5. has been done.

In the above, the bushing surface current mentioned above,
It is clear from the above description that the high voltage-to-ground current does not enter the electrical-to-optical converter 5.

Therefore, only the cable insulator current (leakage current) flows through the electro-optical converter 5, and this amount of leakage current is converted into a light amount by the electro-optical converter 5, which passes through the light guide 7 and passes through the electro-optical converter 6. The converter 6 converts the leakage current into a leakage current amount, and this leakage current is recorded by the recorder 8.

In this case, since the measurement circuit system is isolated from the power supply voltage by the electrical-to-optical converter 5, it is possible to eliminate the complexity of the measurement circuit system and the difficulty of measurement operations caused by the power supply voltage.

Figure 3 shows a test circuit for simultaneously testing three phases of a cable line.
An element type opto-electrical converter is used. Also,
The recorder 8 used is one that can separate the leakage currents of the cable phases 1a, 1b, and 1c and simultaneously record each leakage current.

In FIG. 3, components having the same reference numerals as those in FIG. 2 indicate the same components as those in FIG. 2.

As described above, according to the DC leakage current testing method according to the present invention, the measurement circuit system is cut off from the test high voltage, and the leakage current can be measured without being affected by the bushing surface current or the high voltage-to-ground current. .

Therefore, highly accurate leakage current measurement can be performed with a stable and easy measurement operation.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional DC leakage current testing method, and FIGS. 2 and 3 are explanatory diagrams showing a test circuit used in the present invention. In the figure, 1, 1a, 1b, 1c are cables, 4 is a DC power supply, 5... is an electrical-to-optical converter, 7...
is a light guide, 6 is a photoelectric converter, and 8 is a current recorder.

Claims (1)

[Claims] 1 In a method of diagnosing insulation by applying DC high voltage to electrical equipment and measuring leakage current under the applied voltage, an electrical-to-optical converter is inserted on the high voltage side, and the amount of leakage current is measured by the amount of light. 1. A method for testing direct current leakage current of electrical equipment, which comprises converting the amount of light into an amount of current using a light guide and measuring the amount of current.