JPS61246671A - Dc leakage current measuring apparatus for power cable - Google Patents

Abstract

PURPOSE:To enable the measurement of true DC leakage current, by subtracting the detection current value of a current sensor on the far end side of a cable from the detection current value of a current sensor on the measuring end side thereof. CONSTITUTION:A voltage is caused with respect to a corona discharge current and a surface current respectively at both ends of each impedance element 31 at sensors 30-1 and 30-2 to be converted to digital light signals and then, applied to optical fiber cables 60-1 and 60-2. The light signals transmitted through the cables 60-1 and 60-2 are applied to a subtractor 80 after being converted into analog electrical signals with monitor sections 70-1 and 70-2 to execute a commutation of subtracting the output signal value of the monitor section 70-2 from the output signal value of the monitor section 70-1. A signal indicating the true DC leakage current i0 is outputted from the subtractor 80.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a device for measuring direct current leakage current in power cables, and in particular to a device for measuring direct current leakage current in power cables, and in particular to a device for measuring direct current leakage current in power cables, and in particular to a device for measuring direct current leakage current in power cables, and in particular to a device for measuring direct current leakage currents in power cables, and in particular, to remove the effects of corona discharge currents and surface currents at the far end of the cable. Regarding the same device.

[Technical Background of the Invention] FIG. 4 conceptually shows a DC leakage current measuring device that the present inventors have already proposed.

This measuring device includes a shield case 2 disposed at the measurement end of a cable to be measured 1 so as to cover a core wire 1a of the cable, and a case 2 disposed within the shield case 2.
and a current sensor 3 interposed between the cable core wire 1a, a power source 4 that applies a DC high voltage to the case 2, and the sensor 3.
It has a configuration in which a guard electrode 8 wound around the upper end of an insulator 7 is connected to the case 2. Note that the shielding layer 1b of the cable 1 is grounded.

According to this device, a high DC voltage is applied between the core 11Ala and the sheath lb of the cable 1 via the sensor 3. Therefore, if the insulator interposed between the core wire 1a and the sheath 1b is defective, a DC leakage current will flow between them, and this will be detected by the sensor 3.

[Problems with the Background Art] By the way, at the measurement end side of the cable l, a corona discharge (air discharge) as shown by the arrow occurs between the shield case 2 and the peripheral grounding part, and a corona discharge (air discharge) as shown by the arrow occurs on the insulator 7. A surface current flows in the direction.

Also, on the measurement end side of the cable 1, corona discharge occurs between the cable core wire 1a and the peripheral grounding section.

Also, a surface current flows through the insulator 9.

The current and surface current based on the corona discharge on the measurement end side flow directly into the power supply 4 without passing through the sensor 3, but both the corona discharge current and surface current on the far end side pass through the sensor 3 through the cable core 1a. will pass through.

For this reason, in the above-mentioned measuring device, the detection current of the sensor 3 includes the corona discharge current and surface current at the far end side, and as a result, the true DC leakage current cannot be accurately measured.

[Object of the Invention] In view of the above problems, the present invention seeks to provide a DC leakage current measurement device for power cables that can eliminate the influence of corona discharge current and surface current on the measurement results at the far end of the cable. It is.

[Summary of the Invention] In order to achieve the above object, the present invention covers the head at the far end of the cable to be measured with a shielding case.

A current sensor is interposed within this shield case between the case and the cable core termination.

Then, the true DC leakage current is obtained by subtracting the current value detected by the current sensor at the far end from the current value detected by the current sensor provided at the measurement end of the cable.

[Embodiments of the invention] The present invention will be described in detail below with reference to one drawing.

FIG. 1 shows an embodiment of a DC leakage current measuring device according to the present invention.

The measurement device according to this embodiment covers each head portion of the measurement end side and the far end side of the cable to be measured (A phase cable) 10 with shield cases 20-1 and 20-2, respectively, and conducts a current inside the cases. Sensors 30-1 and 30-
2 are installed.

The lower ends of the shield cases 20-1 and 20-2 are closely fitted to the upper surfaces of the insulators 40-1 and 40-2, and the cathode of the high voltage DC power supply 50 is connected to the case 20-1 on the measurement end side. It is connected.

As shown in FIG. 2, the sensor 30-1, 30-2 includes a detection impedance element 31 interposed between the conductor lead-out rod of the cable 10, that is, the core wire termination part 11, and the shield case.
An amplifier 32 for amplifying the terminal voltage of the element. An A/D converter 33 that converts the output signal of this amplifier into a digital signal.
The E10 converter 34 converts the output signal of the A/D converter into a corresponding optical signal. And sensor 3
The output of the sensor 30-1 is transmitted to the monitor section 70-1 on the ground via the optical fiber cable 60-1, and the output of the sensor 30-2 is transmitted to the monitor section 70 via the optical fiber cable 60-2.
-2.

As shown in FIG. 3, the monitor section 70-1, 70-2,
0/E converter 71 that converts optical signals into corresponding electrical signals
and a D/A converter that converts the output signal of this O/E converter into a D/A.
A converter 72. Then, the output of the monitor section 70-1 is added to the subtracter 80, and the output of the monitor section 70-1 is added to the subtracter 80.
-2 output is sent to the subtracter 80 via the B-phase cable 90.
added to.

The operation of this embodiment is as follows.

Since the DC high voltage of the power supply 50 is applied between the core wire termination portion 11 and the shielding layer 12 of the cable to be measured 10 via the sensor 30-1, if the insulation of the cable is defective, the core wire termination portion 11 and the shielding layer 12 are applied. Direct current leakage current i (1
flows, and this current i6 passes through the detection impedance element 31 of the sensor 30-1.

On the other hand, at the measurement end and the far end of the cable 10,
Corona discharge (air discharge) occurs between each of the cases 20-1 and 20-2 and the peripheral ground portion.

In addition, a surface current flows through the insulators 40-1 and 40-2.

The current and surface current based on the corona discharge on the measurement end side flow directly into the power supply 50 side without passing through the sensor 30-1, but the corona discharge current and surface current on the far end side flow directly into the sensor 30-1. 〇-2 detection impedance 31. Cable core wire terminal part 11 and sensor 30-1
Flows into the power supply 50 side through the detection impedance 31 .

Therefore, a current (i
Voltages corresponding to (1+i1 +12 ) and current (it +i2) are generated, and these voltages are converted into digital optical signals and then applied to fiber optic cables 60-1 and 60-2, respectively.

The optical signals transmitted by the cables 60-1 and 60-2 are converted into corresponding analog electrical signals by the monitor sections 70-1 and 70-2, respectively, and then added to the subtracter 80. The subtracter 80 calculates the current (i(1+i
An operation is performed to subtract the output signal value of the monitor section 70-2 indicating the current (it +i*) from the output signal value of the monitor section 70-1 indicating the current (it +i2), and thereby the subtracter 80 outputs the true A signal indicating DC leakage current i (1) is output.

Thus, according to this embodiment, the corona radiation at the far end of the cable is 1! A true DC current that is not affected by the current 11 and the surface current i can be measured.

In the embodiment described above, the output of the monitor section 70-2 is transmitted using the B-phase cable 90, but it may of course be transmitted using a dedicated cable.

In addition, in the embodiment, the monitor unit 70-1, 70-2 monitors the D/A
Although conversion is being performed, the digital output of the +ODE converter 71 may be directly input to the subtracter 80 and the subtracter 80 may perform digital calculations.

Note that the output of the subtracter 80 is stored in a recording means 0 (not shown).
Added to display devices, etc.

[Effects of the Invention] As is clear from the description of the above embodiments, according to the present invention, the corona discharge current and surface current at the far end of the cable to be measured can be determined from the current value detected at the measurement end side of the cable to be measured. Since the value is subtracted, the true DC leakage current of the cable under test can be measured.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram showing an embodiment of the DC leakage current measuring device according to the present invention, Fig. 2 is a block diagram showing an example of the configuration of the current sensor, and Fig. 3 is an example of the configuration of the monitor section. The block diagram and FIG. 4 are conceptual diagrams showing a conventional DC leakage current measuring device.

Claims (1)

[Claims] first and second shield cases respectively covering the head portions of the measurement end and the far end of the cable to be measured; a second current sensor interposed in the second shield case between the case and the cable core termination at the far end, and means for applying a DC high voltage to the first shield case. and means for subtracting the value of the current detected by the second current sensor from the value of the current detected by the first current sensor.