JPH09257849A - Diagnosing method for insulation of cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To diagnose deterioration in insulation of a cable and a defect of a shielding layer thereof in distinction. SOLUTION: An AC voltage of 50 or 60Hz and 6600V is connected to a conductor 3a of a cable 3 to be measured, from a reference AC power source 1 for testing through a transformer 2 and, moreover, a Gaussian noise signal of 0-50Hz and several volts is connected to the conductor 3a from a random noise generator 4. On other hand, a detecting circuit 5 is connected to a metallic shielding layer 3b of the cable 3 and an output of this detecting circuit 5 is connected to a data collecting circuit 6, to which an arithmetic circuit 7 such as a computer is connected. A detection signal from the metallic shielding layer 3b is inputted to the detecting circuit 5, a fundamental wave from the AC reference power source 1 is removed in this circuit and a signal corresponding to the Gaussian noise signal thus obtained is collected by the data collecting circuit 6 and stored therein in correspondence with time. Based on these data, a coherence function and a transfer function are determined in regard to a frequency of 0.1-20Hz by the arithmetic circuit 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable insulation diagnosis method capable of accurately measuring a state of insulation deterioration of a power cable.

[0002]

2. Description of the Related Art Conventionally, a pulsation detection method has been carried out for measuring the insulation deterioration state of a power cable by measuring a minute current flowing through a ground wire of a metal shield layer of a cable when a test voltage such as an AC high voltage is applied. However, this detection method is a measurement that takes into account the insulation abnormality of the shielding layer.

[0003]

Therefore, even if an abnormality is found, it is difficult to distinguish whether the cable insulating layer is deteriorated or the shielding layer is defective.

The object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a cable insulation diagnosis method capable of diagnosing cable insulation deterioration and shielding layer defects separately.

[0005]

In order to achieve the above object, a cable insulation diagnosis method according to the present invention comprises injecting a random noise signal into a conductor of a power cable to which a fundamental wave is applied to insulate the cable. The signal corresponding to the random noise signal is extracted by removing the fundamental wave from the signal obtained through the layer and the metal shielding layer, and the coherence function and the transfer function are calculated based on the signal, and the obtained coherence is obtained. A feature is that the insulation deterioration state of the power cable is diagnosed by evaluating the function and the transfer function.

The cable insulation diagnosis method having the above-mentioned structure is performed by injecting a random noise signal into the conductor of the cable,
Diagnosis is performed by finding the coherence function and the transfer function from the signal corresponding to the random noise signal obtained through the insulating layer and the metal shielding layer.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the illustrated embodiment. FIG. 1 is a circuit configuration diagram for implementing the present invention. The output from the test reference AC power supply 1 is connected to the conductor 3a of the power cable 3 to be measured via the transformer 2, and the output of the random noise generator 4 for generating a Gaussian noise signal is connected to the low voltage side of the transformer 2. To do. On the other hand, the detection circuit 5 is connected to the metal shielding layer 3b of the cable 3, the output of the detection circuit 5 is connected to the data collection circuit 6, and the data collection circuit 6 includes an arithmetic circuit 7 such as a computer.
Connect.

At the time of measurement, a fundamental wave is generated from the AC reference power source 1 through the transformer 2 and, for example, 50 Hz, 6
An AC voltage of 600 V is applied to the conductor 3a. In addition, for example, 0 to 50 from the random noise generator 4 is applied to this AC voltage.
A Gaussian noise signal signal of Hz and several V is superimposed.

Conductor 3a to insulating layer 3c, metal shield layer 3b
Is input to the detection circuit 5, the detection circuit 5 removes the fundamental wave from the AC reference power source 1 by a filter, etc., and a signal corresponding to the obtained Gaussian noise signal is amplified as necessary to obtain the data. The data is collected by the collecting circuit 6 and stored according to time. At the same time or at another time, this data is obtained by the arithmetic circuit 7 for the coherence function and the transfer function for the frequency of 0.1 to 20 Hz, for example.

The coherence function and the transfer function contain information on how the Gaussian noise signal is transferred from the conductor 3a of the cable 3 through the insulating layer 3c and the shielding layer 3b, and the waveform of the frequency vs. the output thereof. Therefore, the insulation state of the cable 3 can be diagnosed.

In addition to this, basic statistics (standard deviation,
We tried to calculate the skewness, kurtosis), Kurbag identification information criterion, power spectral density, wavelet transform, etc., but we could not obtain significant difference like coherence function and transfer function.

2A to 5A are coherence functions,
(b) shows the transfer function. FIG. 2 shows a case where both the insulating layer 3c and the shielding layer 3b are normal, the coherence function is 0.5 to 0.7 at 0.5 to 15 Hz, the transfer function has a peak at 1.0 Hz, and 0. It has a beautiful mountain shape of about 4 mm. In this case, since a linear transfer depending on the capacitance between the conductor 3a and the metal shielding layer 3b can be expected, the coherence function appears with a substantially constant correlation,
The characteristics of the filter in the previous stage appear in the transfer function.

FIG. 3 shows the case where the insulating layer 3c is normal, but the shield layer 3b is grounded, and the transfer function has a mountain-like shape. This is shown in the coherence function because the noise signal due to the grounding of the shielding layer 3b affects the low frequency region.

FIG. 4 shows the case where the insulating layer 3c is deteriorated and the shielding layer 3b is normal, and the coherence function is 10 to 20.
The output is rapidly decreasing at Hz. The noise signal caused by the deterioration appears in the high frequency region, and this appears in the coherence function. In addition, the transfer function is affected by the filter and has a small shape.

FIG. 5 shows that the insulating layer 3c has deteriorated and the shielding layer 3
The case where b is also grounded is shown. The coherence function is small over the entire target frequency, and the transfer function is also small in shape.

A table of these judgment criteria is as follows.

Coherence function Transfer function Insulating layer normal, shielding layer normal 0.5 to 15 Hz, peak at 1.0 Hz 0.5 or more 0.4 or more Insulating layer normal, shielding layer deterioration 5 to 15 Hz, peak at 1.0 Hz 0.5 Above 0.4 or more Insulation layer deterioration, normal shielding layer 1-10Hz 0.5 or more Peak at 1.0Hz 10-15Hz 0.2 or less 0.2 or less Insulation layer deterioration, shielding layer 0.5-15Hz 1.0Hz Peak 0.2 or less 0.2 or less

Although the test reference AC power supply 1 is used as the fundamental wave in the test in the embodiment, an actual commercial power supply may be used as it is.

[0019]

As described above, in the cable insulation diagnosis method according to the present invention, the random noise signal is injected into the conductor, the coherence function and the transfer function are obtained from the signal obtained from the shielding layer, and the combination of both is obtained. Diagnose the insulation deterioration condition from.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a measurement system.

FIG. 2 is a waveform diagram after signal processing.

FIG. 3 is a waveform diagram after signal processing.

FIG. 4 is a waveform diagram after signal processing.

FIG. 5 is a waveform diagram after signal processing.

[Explanation of symbols]

 1 Test reference AC power supply 2 Transformer 3 Cable 3a Conductor 3b Metal shielding layer 3c Insulating layer 4 Random noise generator 5 Detection circuit 6 Data collection circuit 7 Arithmetic circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mihaku Tsunoda 1008 Shinbori, Kumagaya-shi, Saitama Mitsubishi Cable Industries, Ltd. Kumagaya Manufacturing Co., Ltd. (72) Shigeto Nakamura 1008 Shinbori, Kumagaya-shi, Saitama Mitsubishi Cable Industries, Ltd. Kumagaya Works (72) Inventor Yujiro Mu, 1008 Shinbori, Kumagaya-shi, Saitama Mitsubishi Cable Industries, Ltd. Kumagaya Works

Claims (1)

[Claims] 1. A random noise signal is injected into a conductor of a power cable to which a fundamental wave is applied, and the fundamental wave is removed from the signal obtained through an insulating layer and a metal shielding layer of the cable to remove the random signal. A feature of diagnosing the insulation deterioration state of a power cable by extracting a signal corresponding to a noise signal, calculating a coherence function and a transfer function based on the signal, and evaluating the obtained coherence function and the transfer function Cable insulation diagnosis method.