JPH0567191B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for testing the partial discharge of cables, and more particularly, to testing the partial discharge of cables such as CV cables having an extruded outer semiconducting layer. This invention relates to an improvement in the method of testing pinholes caused by manufacturing defects in high-voltage cables by continuously or intermittently measuring the entire length of the cable.

[Prior Art] In general, there are various types of partial discharge detection devices for cables of this type, in which a partial discharge measuring electrode is brought into electrical contact with the outer semiconducting layer of the cable under test, and this partial discharge measuring electrode is connected to ground. By detecting the partial discharge pulse generated at the partial discharge measuring electrode when applying a predetermined test voltage between the cables, it is possible to test the presence or absence of partial discharge in the cable and its degree.

By the way, in such a cable under test, partial discharge pulses are detected using the entire length of the cable as a sample, so that only the quality of the entire length of the cable can be determined.

For this purpose, a grounding electrode that is electrically contacted with the external semiconductive layer of the cable under test is provided at a predetermined distance from a partial discharge measuring electrode that is electrically contacted with the external semiconductive layer of the cable under test. A method that enables partial discharge measurement at any position on the cable under test by measuring partial discharge pulses generated at the partial discharge measurement electrode when a test voltage is applied to the partial discharge measurement electrode and the ground electrode. be.

[Problems to be solved by the invention] The detection sensitivity of partial discharge in the conventional cable partial discharge testing method tends to improve as the input impedance of the partial discharge measuring device connected to the partial discharge measuring electrode increases. be.

However, in addition to the input impedance between the partial discharge measuring electrode and the grounding terminal, the external semiconducting layer between the partial discharge measuring electrode and the grounding electrode is also connected in parallel, and the input impedance is low by this amount. Become. Therefore, in order to reduce the drop in input impedance, the distance at which the ground electrode is disposed may be increased, and the distance between the external semiconducting layer in contact with the ground electrode may be increased.

However, when this distance becomes longer, the charging current value increases in the longer part, which increases heat generation, and also causes noise and minute partial discharge pulses from this part. There is a risk of being masked. Note that the above noise is caused by contact noise (flicker noise) because the external semiconductive layer utilizes the contact resistance of carbon powder.

Of course, this contact noise depends on the properties of the partial discharge measuring electrode and the material of the external semiconducting layer, but generally the noise level is proportional to the charging current value.

Therefore, increasing the distance of the ground electrode and increasing the distance of the external semiconducting layer in contact therewith does not lead to an improvement in detection sensitivity.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a cable partial discharge testing method that can improve the detection sensitivity of partial discharge in a cable under test.

[Means for Solving the Problems] A partial discharge test method for a cable according to the present invention is a method for testing partial discharge of a cable having an extruded outer semiconducting layer continuously or intermittently over the entire length of the cable. A partial discharge measuring electrode is brought into electrical contact with the outer semi-conducting layer of the cable, and a grounding electrode is brought into electrical contact with the outer semi-conducting layer of the cable at a predetermined distance from the partial discharge measuring electrode. An auxiliary electrode is brought into electrical contact with the external semiconductive layer of the cable between the ground electrodes, a high frequency reactor is connected between the auxiliary electrode and the ground, and a test voltage is applied between the high voltage conductor of the cable and the ground. The present invention is characterized in that a partial discharge test is performed on the cable by measuring a partial discharge pulse generated at the partial discharge measuring electrode when the cable is heated.

[Function] An auxiliary electrode is brought into electrical contact with the external semiconducting layer between the partial discharge measuring electrode and the ground electrode, a high-frequency reactor is connected between the auxiliary electrode and the ground, and a high-frequency reactor is connected between the high-voltage conductor of the cable and the ground. Some devices improve detection sensitivity by bypassing the charging current flowing through the semiconductive layer when a test voltage is applied.

[Example] Hereinafter, the method of the present invention will be explained in detail using the drawings.

The figure is a longitudinal sectional view of a cable partial discharge measuring device applied to the test method of the present invention. In the figure, a test cable 1 has an internal high-voltage conductor 1a provided at its center, and an internal semiconducting layer 1b at its outer periphery.
is formed, an insulating layer 1c is formed on the outer periphery of the insulating layer 1c,
An external semiconducting layer 1d is formed around the outer periphery.

A partial discharge measuring electrode section 10 is disposed outside the cable 1 under test. That is, a partial discharge measuring electrode 12 is provided on the circumferential surface of the outer semiconducting layer 1d.
are electrically contacted, and two ground electrodes 11 are electrically contacted to the outer semiconducting layer 1d at a predetermined distance from the partial discharge measuring electrode 12.

This ground electrode 11 is grounded, and a partial discharge measuring device 20 is connected to the partial discharge measuring electrode 12.

Furthermore, auxiliary electrodes 13, 13 are provided between the partial discharge measuring electrode 12 and the ground electrodes 11, 11, respectively, to be in electrical contact with the external semiconducting layer 1d.

Further, high frequency reactors 14, 14 are connected between each of the auxiliary electrodes 13, 13 and the ground end.

When a commercial frequency high voltage is applied between the internal high voltage conductor 1a and the ground in the live test cable 1, the insulating layer 1C between the partial discharge measuring electrode 12 and the grounding electrodes 11, 11 is caused by the AC voltage application.
Charging current flows due to the capacitance of . This charging current also flows to the exposed portion of the outer semiconducting layer 1d, and this current flows in the length direction of the outer semiconducting layer 1d to the partial discharge measuring electrode 12, the grounding electrodes 11, 11
Diverge into.

Here, the detection sensitivity tends to improve as the input impedance of the partial discharge measuring device 20 connected to the partial discharge measuring electrode 12 increases as described above.

However, in addition to the input impedance between the partial discharge measuring electrode 12 and the grounding terminal, the external semiconducting layer 1d between the partial discharge measuring electrode 12 and the grounding electrode is also connected in parallel, and the input impedance is reduced by this amount. impedance becomes lower. Therefore, in order to reduce the drop in input impedance, the distance between the ground electrodes 11, 11 is increased, and the outer semiconducting layer 1d in contact with the ground electrodes 11, 11 is increased.
It is better to make the distance longer.

However, when this distance becomes longer, the charging current value increases in the long part, and as a result, heat generation increases.
There is a risk that noise will be generated from this portion and a minute partial discharge pulse will be masked. Note that the above noise is caused by contact noise (flicker noise) because the external semiconductive layer 1d utilizes the contact resistance of carbon powder.

Of course, this contact noise is caused by the partial discharge measurement electrode 1.
Although it depends on the properties of 2 and the material of the outer semiconducting layer,
Generally, the noise level is proportional to the charging current value.

Therefore, increasing the distance between the ground electrodes 11, 11 and the external semiconducting layer 1d in contact therewith does not lead to an improvement in detection sensitivity.

Therefore, in the cable partial discharge testing method according to the present invention, auxiliary electrodes 13, 13 are provided between the partial discharge measuring electrode 12 and the grounding electrodes 11, 11, and high frequency When a test voltage is applied between the internal high-voltage conductor 1a of the cable under test 1 and the ground, the detection sensitivity is increased by bypassing the charging current flowing to the external semiconductive layer 1d. It was designed to improve the situation.

Note that the high frequency reactors 14, 14 need to have sufficiently low reactance against applied commercial frequency voltage and sufficiently high reactance against high frequency components such as partial discharge pulses.

Therefore, by measuring the partial discharge pulse generated at the partial discharge measuring electrode 12 with the partial discharge measuring device 20 when a test voltage is applied between the internal high-voltage conductor 1a of the cable 1 under test and the ground, the cable 1 under test can be measured.
Partial discharge tests can be performed with high sensitivity.

It should be noted that the cable partial discharge testing method according to the present invention is not limited to the above-mentioned specific example, and it goes without saying that various modifications can be made without departing from the gist thereof.

For example, the high-frequency reactor is connected to each of the two auxiliary electrodes, but a large number of auxiliary electrodes may be provided, and a high-frequency reactor with a small capacity may be provided for each of the auxiliary electrodes.

Further, the high-frequency reactor may be shared by a plurality of auxiliary electrodes and connected to a high-capacity high-frequency reactor. In this case, it is desirable that the plurality of auxiliary auxiliary electrodes be arranged symmetrically.

Furthermore, a differential detection method may be used in which not only one but two partial discharge measuring electrodes are provided.

[Effects of the Invention] As described above, the cable partial discharge test method according to the present invention eliminates weak partial discharge pulses because the charging current flowing through the external semiconducting layer, which has been a problem in the past, is bypassed by the high-frequency reactor. The detection sensitivity of partial discharge can be greatly improved.

[Brief explanation of the drawing]

The figure is a vertical sectional view of a part of the cable partial discharge testing apparatus applied to the method of the present invention during actual use. 1...Test cable, 1a...Center conductor, 1b
...Inner semiconducting layer, 1c...Insulating layer, 1d...Outer semiconducting layer, 11...Grounding electrode, 12...Partial discharge measurement electrode, 13...Auxiliary electrode, 14...High frequency reactor, 20... ...Partial discharge measuring device.

Claims (1)

[Claims] 1. A method for continuously or intermittently testing the partial discharge of a cable having an extruded outer semiconducting layer over the entire length of the cable, comprising: providing a partial discharge measuring electrode on the outer semiconducting layer of the cable; bringing a ground electrode into electrical contact with the outer semi-conducting layer of the cable at a predetermined distance from the partial discharge measuring electrode, and contacting the outer semi-conducting layer of the cable between the partial discharge measuring electrode and the grounding electrode with a ground electrode; , an auxiliary electrode is brought into electrical contact, and a high-frequency reactor having a sufficiently low reactance against the applied commercial frequency voltage and a sufficiently high reactance against high-frequency components such as partial discharge pulses is connected between the auxiliary electrode and the ground. A portion of the cable characterized in that a partial discharge test is performed on the cable by measuring a partial discharge pulse generated at the partial discharge measuring electrode when a test voltage is applied between the high voltage conductor of the cable and the ground. Discharge test method.