JPH06249898A - Insulation diagnostic method for cv cable - Google Patents

Abstract

PURPOSE:To precisely diagnose the degree of insulation deterioration of a CV cable. CONSTITUTION:A power cable 1 to be tested is formed of a conductor 1a, a shielding layer 1b, an insulator 1c, and a sheathing 1d, and has an electrostatic capacity Ck in the insulator 1c between the conductor 1a and the shielding layer 1b earthed in its terminal. An AC power source S is connected to the conductor 1a of the power cable 1 to be tested. An impedance element 2 is inserted to the earthing conductor of the shielding layer 1b of the power cable 1 to be tested, and the voltage between both the ends of the impedance element 2 is connected to an indicator 6 through a low-pass filter 3, a resonator 4, and an amplifier 5. A switch 7 is ON/OFF, whereby the superposition signal of a voltage change of a determined magnitude is applied to the power cable 1 to be tested by a load 8, and the degree of insulation deterioration is diagnosed by means of pulsation detection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention uses a pulsation detection method to detect CV.
The present invention relates to a CV cable insulation diagnosis method for diagnosing the degree of cable insulation deterioration.

[0002]

2. Description of the Related Art In a power cable, insulation deterioration occurs due to aging after installation. Such insulation deterioration
If left unattended, it may progress and eventually lead to a large dielectric breakdown accident. Accurately grasp the deterioration state at an early stage,
It is necessary to take appropriate measures such as cable replacement.
Therefore, various methods for diagnosing insulation deterioration of electric power cables have been conventionally proposed.

The pulsation detection method targets the AC voltage applied to the cable conductor of the power cable to be measured and removes the commercial AC component from the obtained current, and then the specific low of the noisy pulsating current superimposed. It is intended to extract and measure only the frequency to perform insulation deterioration diagnosis of the power cable, and it has been attracting attention in recent years because it is not affected by the ground wire current.

[0004]

The pulsating current Δi flowing through the cable conductor is a admittance of a deteriorated portion inside the cable at a measurement frequency of 1 Hz, and the admittance locally increased by applying an AC voltage is Y, If the voltage change of the cable is ΔV, it is expressed by the following equation.

Δi = Y · ΔV (1) Various electrical loads are connected to the live cable, and if the fundamental frequency is removed as the load changes, the graph of FIG. As shown in, only noise due to load fluctuation remains. Therefore, it is possible to measure the pulsating current Δi by the pulsation detection method and diagnose the presence or absence of the portion where the admittance Y occurs in the insulation deterioration portion of the cable, but the voltage change ΔV
Is not constant, it is difficult to accurately diagnose the degree of deterioration.

The object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a CV cable insulation diagnosis method capable of accurately diagnosing not only the insulation deterioration of a cable but also the deterioration degree thereof.

[0007]

A method for diagnosing insulation of a CV cable according to the present invention for achieving the above object has a uniform size during operation when diagnosing insulation of a CV cable by a pulsation detection method. An electric load having a load characteristic that causes a periodic voltage change having a narrow width is connected to the cable, and a superimposed signal due to a voltage change of a predetermined magnitude is injected into the cable by turning the load on and off. It is characterized in that the insulation deterioration diagnosis of the cable is performed in a live state.

[0008]

In the insulation diagnosis method for a CV cable having the above-mentioned structure, when the insulation diagnosis of the cable is performed by the pulsation detection method, a load characteristic that causes a periodic voltage change of a uniform width during operation is obtained. By connecting and disconnecting an electrical load with a cable to the cable, a superimposed signal due to a voltage change of a certain magnitude is injected into the cable, and insulation deterioration diagnosis of the cable is performed in a live state.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail based on the illustrated embodiments. FIG. 1 is a block circuit configuration diagram according to the embodiment.
The test power cable 1 such as a CV cable to be measured is composed of a conductor 1a, a shield layer 1b, an insulator 1c, and an outer jacket 1d, and is provided as an insulator 1c between the conductor 1a and the shield layer 1b grounded at a terminal. It has a capacitance Ck. The conductor 1a of the test power cable 1 is connected to the AC power source S. Further, the impedance element 2 is inserted into the ground wire from the shield layer 1b of the power cable under test 1, and the voltage obtained at both ends of the impedance element 2 is low-pass filter 3, resonator 4, amplifier 5
Is connected to the display device 6 via. Further, the conductor 1a of the power cable 1 to be tested is connected through the switch 7 to an electric load having a load characteristic such that a periodical voltage change of a uniform width and a narrow width is generated during operation, for example, an electric load such as a heater. Load 8
Connect.

When a voltage of commercial frequency is applied from the AC power source S to the conductor 1a of the test power cable 1, the charging current i flows through the electrostatic capacitance Ck of the test power cable 1 without the insulation deterioration part. It will be. When an AC voltage is applied to the power cable under test 1, the conductor 1 is applied to the shielding layer 1b.
A charge corresponding to the applied AC voltage is induced by the electrostatic coupling with a, and a weak charging current i that fluctuates at a cycle similar to the frequency of the applied AC voltage flows through the ground line. Therefore, when the insulation 1c has an insulation deterioration portion, the pulsating current Δi is superimposed.

The load 8 automatically turns on and off the switch 7 so that the temperature due to its heat generation becomes constant, and as shown in FIG. 2, a superimposed signal having a uniform size and a repeated time is injected into the power cable 1 under test. . The superimposed signal due to the voltage change injected from the load 8 through the switch 7 should be sufficiently larger than the noise due to the load fluctuation of various loads connected to the power cable 1 under test, for example, one greater than one digit, Make the noise negligible. By doing so, the voltage change ΔV of the power cable under test 1 can be made substantially constant, so that the magnitude of the pulsating current Δi can be accurately obtained.

The impedance element 2 detects the charging current i, transmits it to the low-pass filter 3, and removes the basic AC component by the AC power source S from the charging current i generated by applying the AC voltage of the AC power source S to the cable conductor 1a. Then, only the pulsating component due to the load 8 is output. Normally, the frequency of the applied AC voltage is 50 Hz or 60 Hz, so for example 5
If the circuit of the low pass filter 3 is designed so that the frequency signal of less than 0 Hz or 60 Hz passes, the pulsating current Δi
Only the charging current i can be detected. The pulsating current Δi thus obtained is extracted by the narrow band type resonator 4 and only a specific low frequency from the pulsating flow component in the resonator 4. The frequency of the pulsating current Δi to be extracted is arbitrary, but the higher the frequency is, the more disadvantageous it is in terms of ground capacity. Therefore, the frequency is preferably about 5 Hz or less, and for example, 1 Hz is suitable. Further, this signal is amplified by the variable gain amplifier 5,
It is transmitted to the display 6 composed of a pen graph, an oscilloscope, etc., and its size and the like are measured.

With respect to the magnitude of the pulsating current Δi, the admittance Y increases as the degree of deterioration of the insulation-degraded portion increases, and the voltage fluctuation due to the load 8 is almost constant.
The degree of insulation deterioration can be quantitatively estimated to some extent by determining the magnitude of the.

[0014]

As described above, in the insulation diagnosis method for a CV cable according to the present invention, a superimposed signal due to a voltage change of a certain magnitude is injected into the cable conductor, so that the insulation deterioration of the cable can be prevented by the pulsation detection method. Not only with or without
The degree of deterioration can be accurately diagnosed in a live state.

[Brief description of drawings]

FIG. 1 is a block circuit configuration diagram of an embodiment.

FIG. 2 is a graph showing a voltage change obtained by removing the fundamental frequency of a cable in a live line state to which the insulation diagnosis method for a CV cable of the present invention is applied.

FIG. 3 is a graph showing a voltage change obtained by removing a fundamental frequency of a cable in a live state.

[Explanation of symbols]

 1 Test power cable 1a Conductor 1b Shielding layer 2 Impedance element 3 Low pass filter 4 Resonator 5 Amplifier 6 Indicator 7 Switch 8 Load S AC power supply

Claims (1)

[Claims] 1. When an insulation diagnosis of a CV cable is performed by a pulsation detection method, an electric load having a load characteristic that causes a periodical voltage change of a uniform width and a narrow width is connected to the cable during operation. Then, a superimposed signal due to a voltage change of a predetermined magnitude is injected into the cable by turning on / off the load, and insulation deterioration diagnosis of the cable is performed in a live line condition.