JPH0580112A - Failure diagnostic device for power cable - Google Patents

Abstract

PURPOSE:To provide a failure diagnostic device for a power cable, with which a failure generated at a junction of power cable after being laid can be sensed automatically. CONSTITUTION:A partial electric discharge sensor is composed of an electrode 2 arranged on the periphery of cable 1 and a coil 3 connected with this electrode 2. The signal emitted from the sensor is processed by a signal processing part 5 and given to a buffer memory 6. A data processing part 7 senses failure in the insulation part of the cable from the wave height increment of partial discharge pulses at a point near the zero-cross of the impressed voltage in the phi-q distribution (or phi-q-n distribution) of the partial discharge.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power cable abnormality diagnosing device for detecting a partial discharge occurring in a power cable after installation and detecting an abnormality in an insulating portion in a connection portion of the power cable based on the result.

[0002]

2. Description of the Related Art When a void or a crack is generated in an insulating portion at a connecting portion of a CV cable (cross-linked polyethylene insulated vinyl sheath cable) used as an electric power cable, a partial discharge occurs and the insulating portion is gradually removed. The phenomenon of deterioration is known. Understanding the state of deterioration of the insulation part of the CV cable is extremely important from the standpoint of preventive maintenance of the power cable.

Partial discharge characteristics (relationship between the phase φ of the applied voltage, the charge amount q of the partial discharge pulse and the number n of partial discharge pulses,
That is, the relationship between the time-dependent change of the φ-q distribution or the φ-q-n distribution) and the generation and progress of the tree (breakage path) has been examined using a sheet-shaped insulator sample (Tani et al. Journal A, Vol. 105, No. 7, page 357, published in 1985, Kitamura et al., The Institute of Electrical Engineers of Japan, Journal, Vol. 105, No. 7, page 365, Showa
60 years issued). Then, when the insulation deterioration is slight, a series of partial discharge pulses whose peak value gradually decreases is generated in each cycle of the applied voltage, but when the tree grows, the latter half of the partial discharge pulse generation phase is generated. It has been clarified that a partial discharge pulse having a large amount of electric charge is generated.

To observe such partial discharge, an automatic observation device for measuring partial discharge is used. This device has a function of removing periodic noise such as thyristor noise and background noise. In such an apparatus, the deterioration of the cable insulating portion can be detected by observing the partial discharge spectrum output on the recording paper or the CRT.

As a sensor suitable for detecting partial discharge, the inventors of the present invention have proposed a sensor composed of an electrode arranged on the peripheral surface of the cable and an inductance element connected to this electrode ( Japanese Patent Application No. 2-3110197, etc.). This sensor has an advantage that it can detect partial discharge in a cable in a live state. Further, in this sensor, partial discharge can be observed from a relatively low voltage of about 50% of the breakdown voltage depending on the defective portion. In this case, a method of differentially amplifying partial discharge and pulses other than partial discharge is usually used to reduce noise.

[0006]

However, in the prior art, if a skilled person observes the temporal change in the partial discharge characteristics, it is possible to determine whether or not it is related to the occurrence of trees. For that purpose, there is a problem that an expert always needs to compare and examine the data over time. That is, when conducting basic research on a sheet-shaped sample, etc., the experiment itself is completed in a relatively short time, so a researcher can constantly monitor the data and judge the deterioration state of the insulation part. However, it is practically impossible for a person to constantly monitor the data, such as by constantly monitoring the joint portion of the CV cable after installation.

The present invention has been made in view of the above problems, and can be applied to the constant monitoring of the installed power cable and can automatically detect the abnormality of the power cable. The purpose is to provide a device.

[0008]

A power cable abnormality diagnosing device according to the present invention comprises a partial discharge sensor composed of an electrode arranged on a peripheral surface of the cable and an inductance element connected to the electrode, and The partial discharge detection result by the partial discharge sensor for one cycle of the AC voltage applied to the cable is compared with the partial discharge detection result in the previous cycle, and the peak value of the partial discharge pulse in the specific phase of the applied voltage is compared. And an abnormality detecting means for detecting an abnormality based on the increase.

[0009]

In the present invention, the partial discharge characteristics (φ-q distribution and φ-q-n distribution) measured using the partial discharge sensor.
The time-dependent change of is compared with the data before that, instead of simply outputting it in time series. For example, the partial discharge characteristic data for each cycle of the applied voltage is compared with the immediately preceding cycle data. When the cable insulation part deteriorates and a tree is generated, and this tree grows, the peak value and the number of partial discharge pulses near the zero cross of the applied voltage in the φ-q distribution increase. In the present invention, the peak value of the partial discharge pulse in the vicinity of the zero cross of the applied voltage is increased, so that the abnormality of the insulating portion of the cable is automatically detected.

In this case, in order to compare the partial discharge detection result for one cycle of the AC voltage applied to the cable with the partial discharge detection result in the previous cycle, for example, the air corona generated from the end of the sample or the like. It is possible to reduce the effect of periodic noise due to.

For constant monitoring of joints after installation,
For example, the warning signal is output only when an abnormality is detected.

[0012]

Embodiments of the present invention will now be described with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a power cable abnormality diagnosis apparatus according to an embodiment of the present invention.

The partial discharge sensor is composed of an electrode 2 coated on the peripheral surface of the power cable 1 and a coil 3 connected to the electrode 2. This electrode 2 is a cable 1
A capacitor is formed by the outer conductive layer and the insulating coating portion of. Then, this capacitance forms a resonance circuit together with the coil 3, and selectively detects a high frequency signal caused by partial discharge. On the other hand, the zero-cross circuit 8, the phase counter 9 and the oscillator circuit 10 detect the phase of the AC voltage applied to the cable 1.

The signal detected by the partial discharge sensor is
It is sent to the signal processing unit 5 via the amplifier 4. The signal processing unit 5 removes signals (noise) equal to or lower than a threshold value, and performs processing such as polarity determination, peak hold and A / D conversion. The output of the signal processing unit 5 is stored in the buffer memory 6.

In the buffer memory 6, for example, a φ-q distribution as shown in FIG. 2 is stored. Even if the cable is not defective, as shown in FIG. 2, a signal (noise) due to the corona in the air is detected near the phase (90 ° and 270 °) where the applied voltage is maximum. When a partial discharge is generated due to a void or the like in the connection portion, a pulse signal based on the partial discharge is detected as shown in FIG. However, even if the partial discharge occurs, the insulation part is not destroyed when the φ-q distribution is stable. In the data processing unit 7, the φ-q distribution or the φ-q-n distribution and the previous φ-q distribution or the φ-q distribution for each cycle of the applied voltage.
-Compare with n distribution. That is, the difference between the φ-q distribution shown in FIG. 2 and the φ-q distribution shown in FIG. 3 is taken. FIG. 4 is a graph showing the difference between the φ-q distribution shown in FIG. 2 and the φ-q distribution shown in FIG. By taking the difference between these two data,
Periodic noise such as aerial corona can be removed.

When a tree is generated in the insulating layer and this tree grows, for example, the waveform shown in FIG. 5 is obtained. That is, as the tree advances, a relatively large pulse signal is generated near the zero cross (180 °) of the applied voltage. Φ of this waveform
7 is obtained by taking the difference between the -q distribution and the φ-q distribution of the partial discharge waveform when the same level voltage is applied to the normal cable shown in FIG. 6 or the partial discharge waveform before the tree progresses, for example. As described above, the noise due to the corona in the air can be removed. Then, the partial discharge due to the development of the tree can be detected in the vicinity of the zero cross. When the data processing unit 7 detects an increase in the peak value of the partial discharge pulse near the zero cross, it outputs a warning signal to the outside.

In this embodiment, each cycle of the applied voltage is compared with the signal in the previous one cycle, and the abnormality of the CV cable is detected based on the increase of the pulse peak value near the zero cross of the applied voltage. Output a warning signal.
Thereby, the abnormality of the CV cable, that is, the progress of the tree can be automatically detected. Further, by directly outputting the data from the data processing unit, the φ-q distribution and the φ-q
It is possible to measure changes in the q-n distribution over time, and it is also possible to study the occurrence and development of trees based on the results.

[0019]

As described above, according to the present invention,
The live condition of the cable after installation is constantly monitored, and the abnormality of the power cable is detected based on the increase of the peak value of the partial discharge pulse at the specific phase of the applied voltage, so that there is no need for humans to monitor the data. It is extremely useful for maintenance of power cables. Further, in the present invention, since the data for one cycle of the applied voltage is compared with the data for the previous cycle, it is possible to reduce the influence of noise such as air corona. Furthermore, since the CV cable can be constantly monitored, it is possible to store data after long-term tests and installation.

[Brief description of drawings]

FIG. 1 is a block diagram showing a power cable abnormality diagnosis device according to an embodiment of the present invention.

FIG. 2 is a graph showing a φ-q distribution when there is no defect.

[Fig. 3] φ-q when there is a relatively slight defect in the insulating part
It is a graph which shows distribution.

FIG. 4 is a graph showing a difference between the φ-q distribution shown in FIG. 2 and the φ-q distribution shown in FIG.

FIG. 5 is a photograph showing an output waveform of a partial discharge sensor when there is a defect in an insulating portion of a cable.

FIG. 6 is a photograph showing an output waveform of the partial discharge sensor when the cable is normal or when the tree does not progress.

7 is a graph showing the difference between the φ-q distribution of the waveform shown in FIG. 5 and the φ-q distribution of the waveform shown in FIG.

[Explanation of symbols]

 1; Cable 2; Electrode 3; Coil 4; Amplifier 5; Signal processing unit 6; Buffer memory 7; Data processing unit 8; Zero cross circuit 9; Phase counter 10; Oscillation circuit

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Hajime Takehana 1-5-1, Kiba, Koto-ku, Tokyo Inside Fujikura Electric Wire Co., Ltd.

Claims (1)

[Claims] 1. A partial discharge sensor composed of an electrode arranged on a peripheral surface of a cable and an inductance element connected to the electrode, and the partial discharge sensor for one cycle of an AC voltage applied to the cable. Comparing the partial discharge detection result by the partial discharge detection result in the previous period, and an abnormality detecting means for detecting an abnormality based on the increase of the peak value of the partial discharge pulse in the specific phase of the applied voltage. Characteristic power cable abnormality diagnostic device.