JPH07311236A - Method for detecting defect of power cable line - Google Patents

Abstract

PURPOSE:To provide the method for detecting the defect of a power cable line, which can readily detect the defective parts of the power cable (foreign matter and voids in an insulator, projections on the surface of a semiconductor layer and the like). CONSTITUTION:In the method for detecting the defect of a power cable line, a DC voltage is applied in the first step, a dumped oscillation wave is applied by once or a plurality of times in the second step, an ultra-lo-frequency voltage wave is applied at the third step, voltage application with the first step, the second step and the third step as one set is performed once or repeated by a plurality of times, the cable is broken by the voltage application and the defective part of the 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 Conventionally, 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 voltage is applied by a DC voltage. Although the power supply unit for the test is very compact, it often has a low ability to detect such defects at DC voltage, and from the defect that was not detected at DC voltage immediately after starting operation at commercial frequency voltage. Dielectric breakdown sometimes occurred. Therefore, commercial frequency AC voltage, damped oscillatory wave voltage, ultra-low frequency voltage (
A detection method by applying a voltage such as a frequency of less than Hz) is 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]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention provides a power cable with a defective vibration wave voltage,
In a defect detection method for a power cable line that is detected by applying an ultra-low frequency voltage, a DC voltage is applied in the first step, a damped oscillatory wave is applied one or more times in the second step, and an ultra-low voltage is applied in the third step. Frequency voltage wave is applied, and the first step, the second step, and the third step are electrically charged once or a plurality of times, and the cable is destroyed by this voltage application, and the defective portion of the cable is detected. It is characterized by

Further, the charging of the first step, the second step, and the third step as a set is repeated one or more times, and the partial discharge is measured in each of the third steps to develop the electric tree. Is detected to detect a defective portion of the cable.

[0010]

The present invention applies the DC voltage in the first step,
In the second step, the damped oscillatory wave is applied one or more times, in the third step, the ultra-low frequency voltage wave is applied, and in the first step, the second step, and the third step are combined into a single charge.
Alternatively, since it is repeated a plurality of times, it is possible to accelerate the generation of the space charge layer in the peripheral portion such as a defect shape where the electric field concentration is strong with a DC voltage that easily causes the accumulation of the space charge inside the insulator and to generate an electric tree. An electric tree is generated from a defect portion by a high damping vibration wave, the generated electric tree is easily developed by an ultralow frequency voltage, and an electric tree which is not generated at one time is surely generated.

Further, the charging of the first step, the second step, and the third step as a set is repeated one or more times, and the partial discharge is measured at each third step to develop the electric tree. Since the partial discharge signal associated with is detected, the partial discharge can be easily measured.

[0012]

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.

In this power cable, in the first step, -18
Apply a direct current voltage of 0 kv for 15 minutes, and from this state,
As a step, a damped oscillatory wave having a peak value of −180 kv was applied 10 times, and then, in the third step, a super low frequency triangular wave voltage having a repetition frequency of 0.1 Hz having a peak value of 130 kv was applied for 10 minutes to simultaneously perform partial The discharge was measured (see FIG. 1). As a result, it was confirmed that the partial discharge was generated at the same time when the triangular wave voltage was applied for the third time in the charging cycle. Furthermore, when the triangular wave was continuously applied, dielectric breakdown occurred 5 minutes after the start of the triangular wave application.

Next, another sample of the same size and size is
In step, apply DC voltage of -230kv for 15 minutes,
From this state, a damping vibration wave having a peak value of −230 kv is applied 10 times as a second step, and then a repetition frequency 0.1 having a peak value of 180 kv is applied in a third step.
The partial discharge was measured at the same time by applying a triangular wave voltage of ultra low frequency of Hz. As a result, partial discharge was generated at the same time when the first triangular wave application was started. 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. When the electricity was applied continuously, dielectric breakdown occurred within 5 minutes.

Therefore, paying attention to the relationship between the applied voltage and the number of charging cycles until breakdown, the DC voltage of the first step, the second
The effect of increasing the number of charging cycles by lowering the applied values of the damping vibration wave voltage of the step and the ultra low frequency voltage of the third step was verified. The samples used in the experiment were the same as those described above, the applied DC voltage and the voltage of the damped oscillatory wave were the same, and the above experiment was repeated by combining this with an ultra-low frequency until dielectric breakdown occurred. The results are shown in Table 1.

[0016]

[Table 1]

From the result, it is possible to detect a defect at a low voltage as compared with the case of each voltage waveform alone as shown below even in the state of one voltage application cycle, but the number of cycles is repeated a plurality of times. As a result, the test voltage can be further reduced, and the power-applying device can be made compact. However, if the number of power application cycles increases, the time required for the test becomes longer, which is not preferable. Therefore, it is desirable to set the number of times to 10 or less.

As described above, according to the detection method of the present invention, it is possible to reduce the voltage application time, the number of applications, 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. The first comparative example applies only a DC voltage, and is -5
A DC voltage of 50 kv was applied for 20 minutes. However, no dielectric breakdown of the sample was confirmed by applying this voltage.

In the second 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. 3) is repeatedly applied. This result is applied 58
Dielectric breakdown occurred from the simulated protrusion at the fourth time. Therefore, we tried to detect the partial discharge, but could not measure it because of impulsive noise when the damped oscillatory wave was generated.

Further, in the third 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. 4) is applied. When partial discharge was simultaneously measured while applying the triangular wave, partial discharge occurred 15 minutes after the start of voltage application, and dielectric breakdown occurred 37 minutes after the application of voltage continued.

In the fourth comparative example, a damped oscillatory wave having a peak value of −280 kv as shown in FIG. 5A was applied 20 times, and then a peak value of 130 kv as shown in FIG. 5B was applied. A triangular wave voltage having a repetition frequency of 0.1 Hz is applied to simultaneously measure partial discharge and the charging cycle is repeated several times. As a result, it was confirmed that the partial discharge occurred at the same time when the triangular wave voltage was applied for the fifth time of the charging cycle. This indicates that an electrical tree was generated from the simulated protrusion of the power cable due to the application of the damped oscillatory wave. Furthermore, when the triangular wave was continuously charged, the
In minutes, the partial discharge increased rapidly and destruction occurred.

As described above, the conventional application of the DC voltage alone does not cause the dielectric breakdown of the sample, and it is not only difficult to measure the partial discharge by the detection method by applying the damping vibration wave alone, but also the dielectric breakdown is caused. In addition, the detection time by applying the ultra-low frequency alone increases both the application time and the applied voltage until dielectric breakdown occurs, resulting in lower voltage of the device, downsizing, efficient test operation, etc. It turns out that there are many problems.

Further, it can be seen that the combination of the damped oscillatory wave and the ultra low frequency improves the defect detection capability as compared with the case of applying a single voltage.

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. 2A), and a sine wave (see FIG. 2B) 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.

[0027]

According to the method of detecting a defect in a power cable line of the present invention, a DC voltage is applied in the first step, a damped oscillatory wave is applied one or more times in the second step, and an ultra low frequency voltage is applied in the third step. Applying a wave and applying the first step, the second step, and the third step as a set repeatedly one or more times, the electric field is concentrated with a DC voltage that easily causes the accumulation of space charge inside the insulator. The generation of a space charge layer in the peripheral part of a strong defect shape, etc. is promoted, and an electrical tree is generated from the defect part by a damped oscillatory wave having a high ability to generate an electrical tree. Easily evolved and reliably generate electrical trees that did not occur at one time.

Further, the charging of the first step, the second step and the third step as one set is repeated one or more times, and the partial discharge measurement is performed at each third step to develop the electric tree. Since the partial discharge signal associated with 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 shows an applied waveform used in an embodiment of the present invention.

2A and 2B show modifications of an ultralow frequency used in the present invention, where FIG. 2A is a rectangular wave and FIG. 2B is a sine wave.

FIG. 3 shows a waveform of a conventional damped oscillatory voltage caused by charging.

FIG. 4 is a diagram showing a triangular waveform due to charging of a conventional ultra-low frequency voltage.

FIG. 5 is a waveform of charging voltage used in a conventional combination, (a)
Is a damped oscillatory wave, and (b) is an extremely low frequency.

 ─────────────────────────────────────────────────── ─── 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 method for detecting a defect in a power cable in which a defective portion of the power cable is detected by applying an oscillating wave voltage or an ultra-low frequency voltage, a direct current voltage is applied in the first step, and a damping is performed in the second step. Applying an oscillating wave one or more times, applying an ultra-low frequency voltage wave in the third step, and repeating the application of electricity by combining the first step, the second step, and the third step one or more times, A method of detecting a defect in a power cable line, characterized in that the cable is broken by this voltage application and a defective portion of the cable is detected. 2. The charging of the first step, the second step, and the third step as a set is repeated one or more times, and partial discharge measurement is performed at each third step to develop the electrical tree. 2. The method of detecting a defect in a power cable line according to claim 1, wherein a defective portion of the cable is detected by detecting a partial discharge signal associated with.