JPH0644028B2 - Method for locating the position of partial discharge in power cable - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for locating a partial discharge occurrence position of a power cable.

[Technical background of the invention] When an insulation deteriorated portion is present in a power cable, discharge occurs in the insulation deteriorated portion when a high voltage is applied between the core wire and the sheath of the cable. A pulse wave is generated with the discharge, and the pulse wave propagates toward one end and the other end of the cable.

Therefore, by observing the pulse waves heading to one end and the other end of the cable, the propagation time difference between those pulse waves is measured,
Conventionally, a method of locating a partial discharge generation position based on the time difference has been implemented.

However, since the pulse wave is observed with many noises, it is often the case that the time difference cannot be accurately measured due to this noise, and as a result, the reliability of the orientation position is impaired. Has occurred.

[Object of the Invention] In view of such a situation, the present invention aims to provide a method capable of highly reliable orientation of a partial discharge occurrence position.

[Summary of the Invention] In order to achieve the above object, in the present invention, a discharge pulse generated in a power cable by applying a high voltage between a core wire and a sheath of the power cable is directed to one end of the power cable. The partial discharge occurrence frequency distribution in the length direction of the power cable is obtained by performing multiple measurements to locate the partial discharge occurrence position from the difference in the arrival time of the pulse and the pulse toward the other end to the measurement part. The position with the highest frequency of partial discharge occurrence is located as the true partial discharge occurrence position of the power cable.

Embodiments of the Invention Embodiments of the present invention will be described below with reference to the drawings.

When a high DC voltage is applied to the measurement end of the cable to be measured 1 shown in FIG. 1, partial discharge occurs in the insulation-deteriorated portion 1a of the cable. The pulse wave induced by this discharge propagates toward both the measurement end and the far end of the cable 1, and the pulse wave reaching the far end is passed through the coupling capacitor C ₁ and the amplifier 2 to return the pulse to the cable. After being injected at the far end of the cable 3, it propagates to the measuring end of the cable 3.

At the time when the pulse wave reaches the measurement end of the cable to be measured 1 and the time when it reaches the measurement end of the pulse return cable 3, there occurs a time difference ΔT based on the partial discharge occurrence position and the length of the pulse return cable 3. . Then, the following relationship is established between the partial discharge occurrence position with respect to the measurement end of the cable 1 and the time difference ΔT.

Where l _{1 is} the length of the cable 1 l _{2 is} the length of the cable 3 V _{P is} the propagation speed of the pulse wave In this embodiment, the signal wave output from the measurement end of the cable 1 is connected to the coupling capacitor C ₂ and the amplifier. The signal wave output from the measurement end of the cable 3 is input to the digital memory 5 via 4 and is input to the memory 5 via the coupling capacitor C ₃ and the amplifier 6. Then, based on the data stored in the memory 5, the microcomputer 7 is caused to measure the time difference ΔT, and the partial discharge occurrence position X is calculated using the above equation (1).

In FIG. 1, Z is an impedance element for signal detection.

By the way, since a large number of noises are included in the signal wave stored in the digital memory 5, the noise often causes an error in the measured value of the time difference ΔT. Therefore, the operation of generating partial discharge as described above is
It is difficult to obtain the true partial discharge occurrence position X by performing only once.

Therefore, in this embodiment, the above-mentioned partial discharge generation operation is repeated, and the true partial discharge generation position is determined by statistically processing a large number of partial discharge generation positions X obtained by this operation.

That is, first, the partial discharge occurrence frequency (number of occurrences) at each position of the cable 1 is obtained based on the obtained values of the large number of partial discharge occurrence positions X, and FIG. 2 shows a graph of this occurrence frequency distribution. It is illustrated in.

Incidentally, in FIG. 2, the partial discharge is at two places X of the power cable 1.
It is assumed that the a and Xb occur. As shown in the figure, the partial discharge occurrence position X obtained by multiple measurements
Indicates not only a specific position on the cable but also a distribution in the length direction. This suggests that random noise causes variations in the positions where partial discharges occur due to individual measurements.

Since the noise is randomly generated, it is assumed that the true partial discharge occurrence position X is at the position on the cable 1 corresponding to the vertices a and b of the distribution curve in FIG. Therefore, in this embodiment, the microcomputer 7 determines the maximum value of the partial discharge occurrence frequency based on the distribution of the partial discharge occurrence frequency as shown in the figure, and the position on the cable 1 corresponding to the maximum value. Xa and Xb are located as the partial discharge occurrence positions.

It is also possible to estimate the partial occurrence position based on the partial discharge occurrence frequency by using another statistical processing method.

Further, although the pulse return cable 3 is used in the embodiment, the present invention can be implemented even when the pulse return cable 3 is not used. In this case, the far end of the cable under test 1 is connected to the amplifier 6 and the following equation (2) is applied instead of the equation (1).

[Effects of the Invention] As is clear from the description of the above embodiment, in the present invention, the partial discharge occurrence position of the power cable is located a plurality of times to obtain the partial discharge occurrence frequency distribution in the length direction of the power cable. The partial discharge occurrence position is determined based on the discharge occurrence frequency. Therefore, the orientation error due to the influence of noise can be reduced as much as possible, and a highly accurate orientation result can be obtained.

[Brief description of drawings]

FIG. 1 is a conceptual diagram illustrating an embodiment of an orientation method according to the present invention, and FIG. 2 is a graph illustrating a distribution mode of partial discharge occurrence frequencies. 1 …… Cable to be measured 3 …… Pulse return cable 5 …… Digital memory 7 …… Microcomputer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasutaka Fujiwara 2-1-1 1-1 Oda Sakae, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Showa Electric Wire & Cable Co., Ltd. 2-1-1 No. 1 Showa Cable Electric Co., Ltd. (72) Inventor Akira Nagaoka 2-1-1 1-1 Oda Sakae, Kawasaki-ku, Kawasaki-shi, Kanagawa Kanagawa Prefecture (56) Reference: Japanese Patent Laid-Open No. 59-168376 (JP, A) JP 59-168377 (JP, A)

Claims (1)

[Claims] 1. A measurement of a pulse directed to one end of the power cable and a pulse directed to the other end of discharge pulses generated in the power cable by applying a high voltage between a core wire and a sheath of the power cable. The measurement for locating the partial discharge occurrence position from the difference in the arrival time to the part is performed multiple times to obtain the partial discharge occurrence frequency distribution in the length direction of the power cable, and the position of the maximum frequency of partial discharge occurrence from the distribution. Is located as the true partial discharge occurrence position of the power cable.