JPH06337280A - Method for detecting defect of power cable line - Google Patents

Abstract

PURPOSE:To provide a method for detecting the defect of power cable line by which the detection of defective part (foreign matter) in the insulator, void, protrusion on the surface of semiconductor layer, etc.) can be facilitated. CONSTITUTION:Damping vibration wave is applied one or a plurality of times in the first step and an ultralow frequency voltage is applied in the second step. The set of first and second steps is repeated one or a plurality of times to break down the cable and then the defective part of cable is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect portion (foreign matter in an insulator, void, etc.) that is harmful to the electric insulation performance of rubber and plastic insulated power cables (hereinafter referred to as power cables).
The present invention relates to a method for detecting defects in a power cable line, which detects protrusions on the surface of a semiconductive layer.

[0002]

2. Description of the Related Art Hitherto, as a method of detecting a defect such as a foreign substance or a void in an insulator, which is harmful to the electric insulation performance of a power cable used for long-distance power transmission, a DC voltage has been applied. However, the DC voltage has a low ability to detect such defects, and dielectric breakdown may occur from a defect not detected by the DC voltage immediately after starting operation at the commercial frequency voltage. Therefore, a detection method by applying a commercial frequency AC voltage, a damped oscillatory wave voltage, an ultra low frequency voltage (in the specification, an ultra low frequency means a frequency of 1 Hz or less), etc. has been proposed.

[0003]

However, the proposed detection method alone as described above has various problems when it is applied to a long-distance transmission line.

When the commercial frequency AC voltage is applied, the defect detection capability is excellent, but in the case of a long-distance power transmission line, the charging current becomes very large, so that the power supply device for power application is very huge. However, it is difficult to transport the device.

Further, in the case of a damped oscillatory wave voltage, application to a long distance line is sufficiently possible considering the size of the device,
Although the ability to generate a tree from a defective part is sufficiently high, the number of times the voltage is applied to finally detect the defective part (from the time the tree is made until it is destroyed) or the partial discharge measurement is not possible. Since it is difficult, the detection of the voltage waveform alone has many problems in its execution.

Further, in the case of applying an ultra low frequency voltage,
By lowering the frequency of charging, the charging current can be significantly reduced, so it can be applied to long-distance lines, and partial discharge can be measured. The voltage applied to detect a defective portion tends to be high, which causes operational problems and increases in the output voltage of the power applying device.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned problems and to provide a method of detecting a defect in a power cable line which can reliably and easily detect the defective portion of the power cable.

[0008]

In order to achieve the above-mentioned object, the present invention provides a method for detecting a defect in a power cable line, which detects a defect in a cable by applying a damped oscillatory wave voltage or an ultra-low frequency voltage. The damping vibration wave is applied one or more times in one step, the ultra low frequency voltage wave is applied in the second step, and the voltage application with the first step and the second step as one set is 1
Alternatively, it is repeated a plurality of times to break the cable by this voltage application and detect a defective portion of the cable. In addition, the charging with the combination of the first step and the second step is repeated one or more times, the partial discharge is measured in each second step, and the partial discharge signal accompanying the progress of the electrical tree is obtained. It is characterized by detecting and detecting a defective portion of the cable.

[0009]

According to the present invention, the damping vibration wave is applied once or a plurality of times in the first step, and the ultra low frequency voltage wave is applied in the second step. 1
Alternatively, since it is repeated a plurality of times, the electrical tree is generated from the defect portion with a damped oscillatory wave having a high ability to generate the electrical tree, and the generated electrical tree can be easily developed with an ultra-low frequency voltage. Reliably generate the electric tree that did not occur. Also, the first step and the second step
The partial discharge is easily performed because the partial discharge signal accompanying the progress of the electrical tree is detected by performing the partial charge measurement by repeating the step 1 and multiple times one or more times and measuring the partial discharge in each second step. Can be measured.

[0010]

EXAMPLES Examples of the present invention will be described in detail below. The power cable used in this example has an insulation thickness of 10 mm and a length of 2
This is a 0 m CV cable in which a metal needle is inserted into the insulator from the outside of the cable to a depth of 2 mm as a simulated protrusion at the center of the power cable.

As a first step, a damped oscillatory wave having a peak value of -400 kv as shown in FIG. 1 (a) was applied to this power cable 20 times, and then as a second step, as shown in FIG. 1 (b). The partial discharge is simultaneously measured by applying a triangular wave voltage having a repeating frequency of 0.1 Hz having a peak value of 130 kv. As a result, it was confirmed that the partial discharge was generated at the same time when the application of the triangular wave voltage was started. This indicates that the electrical tree was generated from the simulated protrusion portion of the power cable by the application of the damping vibration wave in the first step. Furthermore,
When the triangular wave was continuously applied, the partial discharge rapidly increased 11 minutes after the start of the application of the triangular wave, and the destruction occurred.

Next, another embodiment of the present invention will be described.
In the first step, a damped oscillatory wave having a peak value of −280 kv was applied to the power cable 10 times, and then in a second step, a repetition frequency of 0.
A triangular wave voltage of 1 Hz was applied for 10 minutes to measure partial discharge at the same time, and this charging cycle was repeated several times (Fig. 2).
reference). As a result, it was confirmed that partial discharge was generated at the same time when the triangular wave application was started for the fifth time of the charging cycle. This indicates that an electrical tree was generated from the defect due to the application of the damping oscillatory wave immediately before the occurrence of partial discharge. Further, when the triangular wave was continuously applied, dielectric breakdown occurred 9 minutes after the start of the triangular wave application.

As described above, according to the detection method of the present invention, it is possible to reduce the voltage application time, the number of times of application, and the peak value of the voltage wave. It can be seen that there is a remarkable effect in improving efficiency.

Next, a comparative example (conventional example) with the present invention will be described. The power cable used in the experiment is the above-mentioned 2 of the present invention.
It has the same structure and size as those used in the one embodiment. In the first comparative example, only a damped oscillatory wave is applied to detect a defect, and a waveform having a peak value of −400 kv (see FIG. 4) is repeatedly applied. As a result, dielectric breakdown occurred from the simulated protrusion at the 58th application. Therefore, we tried to detect the partial discharge, but could not measure it because of impulsive noise when the damped oscillatory wave was generated.

In the second comparative example, only a very low frequency is applied to detect a defect, and a triangular wave voltage having a peak value of 350 kv and a repetition frequency of 0.1 Hz (see FIG. 5) is applied. When the partial discharge was simultaneously measured while applying the triangular wave, a partial discharge occurred 15 minutes after the start of voltage application, and a dielectric breakdown occurred 37 minutes after the voltage application was continued.

As described above, not only is it difficult to measure partial discharge by the conventional detection method by applying a damped oscillatory wave alone, but the number of applications until dielectric breakdown increases, and the application of an ultra-low frequency alone is applied. It can be seen that the detection method according to (1) increases both the application time and the applied voltage until dielectric breakdown occurs, and there are many problems in reducing the voltage of the device, making it compact, and improving the efficiency of test operation.

In this embodiment, the ultra low frequency is 0.1.
I used a triangular wave of 1Hz, but as an ultra-low frequency, another 1Hz
Waveforms such as a triangular wave, a rectangular wave (see FIG. 3A), and a sine wave (see FIG. 3B) having the following frequencies can also be used. Also, although only the negative polarity was used for the charging voltage of the damped oscillatory wave, various combinations such as the method of using the positive polarity or the method of alternately using the negative polarity and the positive polarity are conceivable. Any of these may be applied. You can Further, the number of times the damping vibration wave voltage is applied, the application time of the ultra-low frequency voltage, and the like can be appropriately selected.

The vibration frequency of the damped vibration wave is 1 to 10 KH in terms of waveform uniformity with respect to the entire length of the power cable.
It is desirable to be included in the range of z. Further, the partial discharge measurement may be omitted if necessary.

[0019]

According to the defect detecting method of the power cable line of the present invention, the damping vibration wave is applied one or more times in the first step, and the ultra low frequency voltage wave is applied in the second step. Since the electric power application consisting of two steps is repeated one or more times, the electric tree is generated from the defective portion by the damped oscillatory wave having a high ability to generate the electric tree, and the generated electric tree is generated by the super low frequency voltage. Can be easily developed, and an electric tree that has not been generated at one time can be reliably generated. In addition, a partial discharge signal associated with the progress of the electric tree is obtained by performing the electric charging with the set of the first step and the second step once or a plurality of times and measuring the partial discharge in each second step. Is detected, the partial discharge can be easily measured. Therefore, the test voltage can be lowered, the device can be made compact, and the test operation can be efficiently performed.

[Brief description of drawings]

FIG. 1 is a waveform of a voltage applied in an embodiment of the present invention, in which (a) is a damping vibration wave and (b) is an extremely low frequency.

FIG. 2 is a diagram showing an applied waveform used in another embodiment of the present invention.

3A and 3B show modifications of an ultralow frequency used in the present invention, where FIG. 3A is a rectangular wave and FIG. 3B is a sine wave.

FIG. 4 shows a conventional waveform of a damped oscillatory voltage caused by charging.

FIG. 5 is a diagram showing a triangular waveform due to charging of a conventional ultra-low frequency voltage.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideo Tanaka 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Susumu Sakuma 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Osamu Fujii 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Teruyoshi Tanabe 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (2)

[Claims] 1. A defect detection method for a power cable line, which detects a defective portion of a power cable by applying a damped vibration wave voltage or an ultra-low frequency voltage, wherein the damped vibration wave is applied one or more times in a first step, In the second step, an ultra-low frequency voltage wave is applied, and the voltage application with the first step and the second step as one set is repeated one or more times, and the cable is destroyed by this voltage application, and the defective portion of the cable is removed. A method for detecting a defect in a power cable line, which is characterized by detecting. 2. A method in which the first step and the second step are electrically charged as one set is repeated one or more times, and partial discharge measurement is performed in each second step. The method for detecting a defect in a power cable line according to claim 1, wherein a defective portion of the cable is detected by detecting a discharge signal.