JP3176471B2 - Diagnosis method for insulation of CV cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a 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 evolve and eventually lead to a major dielectric breakdown accident.
It is necessary to take appropriate measures such as cable replacement.
For this reason, various methods of diagnosing insulation deterioration of power cables have been conventionally proposed.

The pulsation detection method targets an AC voltage applied to a cable conductor of a power cable to be measured, and removes a commercial AC component from an obtained current to remove a specific low noise pulsating current superimposed. It extracts and measures only the frequency and diagnoses the insulation deterioration of the power cable, and has recently attracted attention because of its advantages such as being unaffected by the ground line current.

[0004]

The pulsating current Δi flowing through the cable conductor is the 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 represented by Y, If the voltage change of the cable is ΔV, it is expressed by the following equation.

Δi = Y · ΔV (1) Various electric loads are connected to the cable in the live state. When the fundamental frequency is removed along with the load fluctuation of these loads, the graph of FIG. As shown in FIG. 7, only noise due to load fluctuation remains. Therefore, the pulsation current Δi is measured by the pulsation detection method to determine whether there is a portion where the admittance Y occurs in the cable insulation deteriorated portion.
However, there is a problem that it is difficult to accurately diagnose the degree of deterioration because the value is not constant.

An 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 that can accurately diagnose not only the presence or absence of cable insulation deterioration but also the degree of deterioration.

[0007]

The CV cable insulation diagnosis method according to the present invention for achieving the above object has a uniform size during operation when performing CV cable insulation diagnosis by a pulsation detection method. An electrical load having a load characteristic that causes a narrow periodic voltage change is connected to the cable, and a voltage fluctuation signal sufficiently larger than noise is injected into the cable by turning the load on and off,
The insulation deterioration diagnosis of the cable is performed in a live state.

[0008]

According to the insulation diagnostic method for a CV cable having the above-described structure, when performing insulation diagnosis of a cable by a pulsation detection method, a load characteristic such that a periodic voltage change having a uniform width and a small width is generated during operation. By connecting an electrical load having the following to the cable and turning it on and off, a superimposed signal due to a voltage change of a certain magnitude is injected into the cable, and the 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 with reference to the illustrated embodiments. FIG. 1 is a block diagram illustrating a configuration of a block circuit according to an embodiment.
A test power cable 1 such as a CV cable to be measured is composed of a conductor 1a, a shielding layer 1b, an insulator 1c, and a jacket 1d, and is connected to an insulator 1c between the conductor 1a and the shielding layer 1b grounded at a terminal. It has a capacitance Ck. The conductor 1a of the test power cable 1 is connected to an AC power supply S. In addition, an impedance element 2 is inserted into a ground line from the shielding layer 1b of the test power cable 1, and a voltage obtained at both ends of the impedance element 2 is a low-pass filter 3, a resonator 4, an amplifier 5
Is connected to the display 6 via the. Further, an electric load having a load characteristic such as a uniform periodic voltage change having a small width during operation, such as a heater or the like, is connected to the conductor 1a of the test power cable 1 via the switch 7. Load 8
Connect.

Here, when a voltage at a commercial frequency is applied to the conductor 1a of the test power cable 1 from the AC power supply S, the charging current i flows through the capacitance Ck of the test power cable 1 even without the insulation deterioration portion. Will be. When an AC voltage is applied to the test power cable 1, the conductor 1
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 period substantially equal to the frequency of the applied AC voltage flows through the ground line. Therefore, when the insulation degraded portion exists in the insulator 1c, the pulsating current Δi is superimposed.

The switch 8 is automatically turned on and off so that the temperature of the load 8 due to the heat generation becomes constant, and a superimposed signal having the same size and repetition time is injected into the test power cable 1 as shown in FIG. . The superimposed signal due to the voltage change injected from the load 8 through the switch 7 is sufficiently larger than the noise due to the load fluctuation of the various loads connected to the test power cable 1 by, for example, one or more digits. Make the noise negligible. By doing so, the voltage change ΔV of the test power cable 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 a basic AC component by the AC power supply S from the charging current i generated by applying the AC voltage of the AC power supply S to the cable conductor 1a. Then, only the pulsation component due to the load 8 is output. Usually, the frequency of the applied AC voltage is 50 Hz or 60 Hz.
If the circuit of the low-pass filter 3 is designed to pass a frequency signal of less than 0 Hz or 60 Hz, the pulsating current Δi
Only the charging current i can be detected. The obtained pulsating current Δi is used to extract only a specific low frequency from the pulsating flow component in the narrow-band resonator 4. The frequency of the pulsating current Δi to be extracted is arbitrary, but the higher the frequency, the more disadvantageous in terms of ground capacity. Therefore, the frequency is preferably about 5 Hz or less, for example, 1 Hz or the like. Further, this signal is amplified by the variable gain amplifier 5, and
The data is transmitted to the display 6 composed of a pen graph, an oscilloscope, and the like, and its size and the like are measured.

As the magnitude of the pulsating current Δi increases, the admittance Y increases as the degree of deterioration of the insulation-deteriorated portion increases, and the voltage fluctuation due to the load 8 is substantially constant.
The degree of insulation deterioration can be quantitatively estimated to a certain extent by obtaining the magnitude of.

[0014]

As described above, the insulation diagnosis method for a CV cable according to the present invention, by injecting a superimposed signal due to a voltage change of a certain magnitude into a cable conductor, reduces the insulation deterioration of the cable by a pulsation detection method. Not only the presence or absence,
The degree of the deterioration can be accurately diagnosed in the live state.

[Brief description of the drawings]

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

FIG. 2 is a graph showing a voltage change of a live cable to which a fundamental frequency has been removed, to which the CV cable insulation diagnostic method of the present invention has been applied.

FIG. 3 is a graph showing a voltage change in which a fundamental frequency of a cable in a live state is removed.

[Explanation of symbols]

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

Claims (1)

(57) [Claims] When performing an insulation diagnosis of a CV cable by a pulsation detection method, an electric load having a load characteristic that causes a narrow periodic voltage change having a uniform size during operation is connected to the cable. By turning on and off the load, a voltage sufficiently larger than noise is applied to the cable.
A method of diagnosing insulation of a CV cable, comprising injecting a fluctuation signal and performing insulation deterioration diagnosis of the cable in a live state.