JP3083163B2 - Detecting method of defective part of cable insulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a defective insulator which causes a break in a power cable.

[0002]

2. Description of the Related Art Conventionally, in order to evaluate a defect of an insulator in a plastic power cable, a high voltage is applied to the cable to destroy a defective portion of the cable insulator. It has been evaluated whether or not defects such as certain foreign matter, voids, and conductive layer protrusions should be removed, and based on this, the cable manufacturing method has been improved to improve the electrical performance of the cable.

[0003]

As described above, in the conventional method for destroying a defective portion in a cable insulator,
In many cases, a large destruction hole is formed in the insulator due to heat or chemical change at the time of destruction of the insulator defect, and the defect is destroyed and burned.Therefore, the defect is examined to identify the cause of the insulator breakdown. It was difficult to do.

In order to improve this point, partial discharge measurement is performed at the same time as the AC power application test, and a tree-shaped tree-shaped destructive path called a tree which starts from a defective portion in the cable insulator is formed and progresses. By detecting the partial discharge that occurs immediately before the insulation defect is destroyed and stopping the application of electricity before the failure leads to complete breakdown, the insulator defect is not burned out A method has been developed that allows the detection of defective parts.

According to the above-mentioned method, it is possible to detect a defective portion of a cable insulator without burning it. However, this method detects a defective portion of the cable insulator which is harmful by a commercial frequency AC voltage. Other than the above, for example, a commercial frequency such as an impulse voltage generated by a lightning strike in a cable system, a high voltage including a high-frequency component in a voltage waveform, or a space charge accumulation. A harmful defect cannot be detected by a DC voltage including a factor different from the breakdown by an AC voltage.

In the case where a defective portion is detected by the above-described method at a commercial frequency, noise or the like may be generated if the voltage at the time of stopping the application of high voltage due to the occurrence of partial discharge is extremely high. In many cases, it is difficult to detect partial discharge because of the occurrence of electric discharge. The noise contained invades the partial discharge measurement system, leading to a significant deterioration in detection sensitivity, making the experiment difficult.

Therefore, the present invention solves the above problems,
It is an object of the present invention to provide a method for easily detecting a harmful defective portion in a cable insulator when detecting a defective portion in the cable insulator.

[0008]

In order to achieve the above object, a method for detecting a defective portion of a cable insulator according to the present invention comprises:
(1) High voltage is applied to the cable to cause dielectric breakdown in a part of the insulator, and then partial discharge is performed while applying a commercial frequency AC voltage to the non-destructive cable portion where no dielectric breakdown has occurred. To detect a partial discharge that signals the destruction of the insulator defect in the non-destructive cable part.
Absolute Entai by the voltage application stopped before the defect portion is destruction, is characterized in that it has to be detected without burn off insulator defect.

(2) In the method of (1),
Before the high voltage application that causes dielectric breakdown in a part of the cable insulator, the commercial frequency AC voltage is applied for a certain time so as not to cause the dielectric breakdown.

(3) In addition, before the high voltage application that causes a dielectric breakdown in a part of the cable insulator in the method (1), the commercial frequency AC voltage is applied to the cable so as not to cause the dielectric breakdown. The method is characterized in that the method (1) is carried out on a cable in which partial discharge measurement is performed simultaneously with the application of time and partial discharge is confirmed.

(4) The above (1), (2), (3)
In the method of (1), a voltage having a single-shot voltage waveform including a high-frequency component of 1 KHZ or more is applied as a high voltage for application that causes dielectric breakdown in a part of the cable insulator.

[0012]

When a high voltage is applied to a cable insulator, the defective portion may cause a dielectric breakdown, while the defective portion may cause a tree sprout from the defective portion without causing a dielectric breakdown. If a dielectric breakdown occurs, it is detected outside as a breakdown port. If tree sprouts occur without dielectric breakdown, the cable is apparently not destroyed because there is no breakage opening, but the occurrence of tree sprouts is a precursor to dielectric breakdown. In this case, the dielectric breakdown easily occurs when a high voltage is applied again. Therefore, its position needs to be detected.

In order to detect this position, partial discharge is measured while applying a commercial frequency AC voltage, and a signal in which the amount of partial discharge charge is generated or increased, that is, a bud of a tree previously generated in the cable, is detected. Detects signs that the defective part that has occurred will be destroyed. By detecting the occurrence or increase in the amount of partial discharge charge that is a precursor to the destruction of the insulator defect, and by interrupting the power application before the destruction,
It is possible to detect the position of the defect while avoiding the destruction and burning of the insulator defect.

The method of the present invention of the above (1) detects a partial discharge which is a precursor of the destruction of the insulator defect portion of the non-destructive cable portion in which the dielectric breakdown does not occur, and detects the insulator defect portion. By stopping the application of power before the breakdown, it is possible to detect the insulator defect without burning it.

The voltage at which the commercial frequency is recharged for detecting the partial discharge in the non-destructive cable portion is as follows:
Normally, if the cable is a sound insulator without any tree buds, it is 1/2 to 1/3 of the voltage applied when the high voltage was first applied to the cable to cause insulation breakdown. Voltage. Therefore, by confirming the partial discharge generation voltage due to the application of the commercial frequency, it is possible to check whether or not a tree bud has already been generated due to a high voltage causing dielectric breakdown.

Before applying a high voltage that causes dielectric breakdown to the cable, a commercial frequency AC voltage is applied for an appropriate voltage and time so that the cable does not cause dielectric breakdown, and at the same time, partial discharge is measured. If it is confirmed that there is no sprout of the tree, the sprout of the tree is that the sprout of the tree was generated in the defective part due to the high voltage that caused the dielectric breakdown, and the non-destructive part after the high voltage destruction By applying a commercial frequency AC voltage to the cable, it is possible to confirm that a partial discharge, that is, an electric tree has not occurred from the defective portion.

For this reason, the methods (2) and (3) require that a commercial frequency AC voltage be kept constant so as not to cause dielectric breakdown before a high voltage causing dielectric breakdown is applied to a part of the cable insulator. This is to apply power for a time and to measure partial discharge at the same time.

Most of the high voltage to which the cable is actually exposed when using the actual line is the impulse voltage at the time of lightning strike. Therefore, it is extremely important to detect a harmful defect in the insulation performance of the cable, especially in the lightning impulse voltage. . Therefore, in particular, insulation breakdown is caused in the cable using a single-shot voltage waveform including a high-frequency component of 1 KHZ or more. The method (4) applies such a voltage.

[0019]

Examples of the present invention will be described below with reference to the following (1) to (4).
This will be described with reference to an experimental example.

Experimental Example (1) As a plastic power cable of a sample, a 22 K VCV cable having an insulation thickness of 6 mm and a total length of 50 m was used, and a commercial frequency AC voltage of 200 KV was applied at room temperature for 10 minutes, and simultaneously a partial discharge was performed. Was measured, no occurrence of partial discharge was confirmed. This proved that the cable was perfectly sound. The dielectric breakdown voltage of this cable at a commercial frequency AC voltage at room temperature is 400 KV to 600 KV,
At about 00 KV, the voltage is not such that insulation breakdown occurs.

Next, the cable was maintained at 90 ° C., the impulse generator was charged so that a lightning impulse voltage could be generated at a maximum of −1000 KV, and a lightning impulse was applied only once to the cable. Breakdown occurred at -785 KV on the way to -1000 KV. After investigating the fracture opening after the impulse fracture, as shown in FIG.
A destruction hole (x mark) was found in b (2 is a terminal for applying a voltage).

The terminal was reassembled to the non-destructive cable portion 10 in which the dielectric breakdown did not occur, a commercial frequency AC voltage was applied at room temperature, and the partial discharge was measured at the same time. Was measured.
Since this voltage is lower than the commercial frequency AC voltage applied before the impulse voltage is applied, it can be seen that tree buds have occurred in the insulator with the application of the impulse voltage.

The application of power is stopped by detecting the partial discharge, the position where the partial discharge has occurred in the non-destructive cable portion 10 which has not been destroyed and burned is cut out, and the cable is cut out. Investigation revealed that the electrical tree extended from the protrusion having a height of about 20 μm and a width of about 15 μm existing on the outer semiconductive layer. This revealed that tree buds were generated by the impulse voltage.

Experimental Example (2): The same sample cable as that of Experimental Example (1) having a total length of 50 m was used as a sample, and a commercial frequency AC voltage of 200 KV was applied at room temperature for 10 minutes.
The measurement was performed for one minute, and at the same time, the partial discharge was measured. However, the occurrence of the partial discharge was not confirmed. This proved that the cable was perfectly sound. The dielectric breakdown voltage of this cable at a commercial frequency AC voltage at room temperature is 400 KV to 600 KV, and is not a voltage at which dielectric breakdown occurs at about 200 KV.

Next, the cable is kept at 90 ° C., and the lightning impulse voltage is first increased by −500 KV three times, and thereafter by −5 KV.
The voltage was increased by 0 KV, and an impulse voltage was applied three times at each voltage until the cable breakdown occurred.

As a result, when the cable was applied with -750 KV twice, dielectric breakdown occurred. When the fracture site was examined after the impulse breakdown, as shown in FIG. 2, the fracture site (x mark) was found at three places 4a, 4b, and 4c of the cable 1.

The non-destructive cable portion 10 that has not been subjected to dielectric breakdown was reassembled, and a commercial frequency AC voltage was applied at room temperature to measure the partial discharge.
The occurrence of partial discharge was measured when the voltage reached 0 KV. Since this voltage is lower than the commercial frequency AC voltage applied before the impulse voltage is applied, it can be seen that tree buds have occurred in the insulator with the application of the impulse voltage.

The application of power was stopped by the detection of the partial discharge, the position where the partial discharge occurred in the non-destructive cable portion 10 was located, the cable was cut out, and defects and electric trees were examined by a microscope. The electrical tree extended from a protrusion having a height of about 15 μm and a width of about 7 μm existing on the inner semiconductive layer. This revealed that tree buds were generated by the impulse voltage.

Experimental Example (3): A 22 K VCV cable having an insulation thickness of 6 mm and a total length of 30 m was used in the same manner as in the above Experimental Example (1), and a commercial frequency AC voltage of 200 KV was applied at room temperature for 10 minutes. The measurement was performed at the same time as the partial discharge, but no occurrence of the partial discharge was confirmed. This proved that the cable was perfectly sound. The dielectric breakdown voltage of this cable at a commercial frequency AC voltage at room temperature is 400 KV to 600 KV,
At about 00 KV, the voltage is not such that insulation breakdown occurs.

Then, at normal temperature, a positive DC voltage was applied to the cable at 200 KV for 5 minutes to 50 KV for 5 minutes, and the DC voltage was increased and applied until insulation breakdown of the cable.

As a result, the cable suffered dielectric breakdown when 650 KV was applied for 1 minute. After investigating the break point after DC breakdown, as shown in FIG.
Destruction holes (x marks) were found in a and 5b.

The terminal was reassembled to the non-destructive cable portion 10 in which the dielectric breakdown did not occur, a commercial frequency AC voltage was applied at room temperature, and the partial discharge was measured at the same time. Was measured.
Since this voltage is lower than the commercial frequency AC voltage applied before the application of the DC voltage, it can be seen that tree sprouts occurred in the insulator with the application of the DC voltage.

The application of power was stopped by the detection of the partial discharge, the position where the partial discharge occurred in the non-destructive cable portion 10 was located, the cable was cut out, and defects and electric trees were examined by a microscope. The electric tree extended from a foreign substance having a length of about 20 μm and a width of about 9 μm existing in the insulator. Thus, it was revealed that tree buds were generated by the DC voltage.

Experimental Example (4): As a plastic power cable of a sample, a 22 K VCV cable having an insulation thickness of 6 mm and a total length of 25 m was used, the cable was kept at 90 ° C., and a commercial frequency AC voltage was 200 KV for 10 minutes to 20 KV. ,
The pressure was increased every 10 minutes, and the power application was continued until the cable was broken down.

As a result, the cable suffered dielectric breakdown at 380 KV for 7 minutes. When the breaking point was inspected after this breaking, a breaking point (x mark) was found at one place 6a of the cable 1 as shown in FIG.

The non-destructive cable portion 10 in which the dielectric breakdown did not occur was reassembled into a terminal, a commercial frequency AC voltage was applied at room temperature, and the partial discharge was measured at the same time. Was measured. Since this voltage is lower than the voltage value destroyed by the first commercial frequency AC voltage, it can be seen that tree buds have been generated in the insulator with the application of the AC voltage that caused the dielectric breakdown. .

The application of power was stopped by the detection of the partial discharge, the position where the partial discharge occurred in the non-destructive cable portion 10 was located, the cable was cut out, and defects and electric trees were examined with a microscope. The electric tree extended from a foreign substance having a length of about 30 μm and a width of about 21 μm. As a result, it was revealed that the buds of the tree were generated by the commercial frequency AC voltage applied first.

Normally, when the partial discharge is measured when the cable is kept at a temperature higher than room temperature, such as 90 ° C., by an external electric heater or the like, noise included in the current supplied when the heater is heated penetrates. As a result, the sensitivity of the measurement may be significantly deteriorated. Therefore, under such conditions, it is extremely difficult to stop the application of electricity by detecting a partial discharge, but according to the present invention, it is possible to detect a defect very easily without such a failure. .

[0039]

As described above, according to the present invention, the cable
Causing insulation breakdown in a part of the insulator that can apply pressure,
Next, to the non-destructive cable part where insulation breakdown has not occurred
On the other hand, a commercial frequency AC voltage was applied and partial discharge was measured at the same time to detect signs of failure of the insulator defect, and the power application was stopped before the insulator defect was destroyed. Without destroying and burning the defective part, it is possible to detect harmful defects in various voltage waveforms such as high-frequency voltage represented by lightning impulse and DC voltage where space charge is a problem, The information for improving the characteristics of the cable is greatly increased, and the application of high-frequency high voltage such as impulse is a practical and direct performance improvement because this is a high voltage that penetrates the actual cable system. Because of the connection, the electrical performance of the cable can be improved. In addition, part of the insulator
Than the high voltage that is charged to cause dielectric breakdown
Partial discharge while applying low frequency commercial frequency AC voltage
Can be measured, and the voltage applied to cause dielectric breakdown
Noise is partially discharged even when the voltage is the commercial frequency AC voltage
Good measurement of partial discharge without risk of intrusion into the measurement system
And with high sensitivity.
Can be easily stopped and the cable insulation is defective
The part can be accurately detected.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a second embodiment of the present invention.

FIG. 3 is an explanatory view of a third embodiment of the present invention.

FIG. 4 is an explanatory view of a fourth embodiment of the present invention.

[Explanation of symbols]

1; cable 3a, 3b, 4a, 4b, 4c, 5a, 5b, 6a;

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-82374 (JP, A) JP-A-2-105070 (JP, A) JP-A-4-109179 (JP, A) JP-A-3- 202768 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01R 31/12

Claims (4)

(57) [Claims] A high voltage is applied to a cable to cause a dielectric breakdown in a part of a cable insulator, and then a commercial frequency AC voltage is applied to a non-destructive cable portion where no dielectric breakdown has occurred. By measuring the partial discharge while detecting the partial discharge which is a sign of the destruction of the insulator defect in the non-destructive cable part, the power application is stopped before the destruction of the insulator defect. A method for detecting a defective portion of an insulator. 2. The method according to claim 1, further comprising: applying a commercial frequency AC voltage for a predetermined time so as not to cause a breakdown before applying a high voltage causing a breakdown in a part of the cable insulator. A method for detecting defective parts in cable insulation. 3. A commercial frequency AC voltage is applied to a cable for a certain period of time so as not to cause insulation breakdown, and a partial discharge measurement is performed. A high voltage is applied to a cable in which no partial discharge occurs. By causing partial breakdown of the cable insulator and then measuring the partial discharge while applying a commercial frequency AC voltage to the non-destructive cable portion where no dielectric breakdown has occurred, the non-destructive cable portion is measured. A method for detecting a defective portion of a cable insulator, comprising detecting a partial discharge that is a precursor to the destruction of the defective insulator, and stopping the power application before the destruction of the defective insulator. 4. A single-shot waveform voltage containing a high-frequency component of 1 KHZ or more is applied as a high voltage to be applied to cause a dielectric breakdown in a part of the cable insulator. For detecting defective parts of cable insulators.