JPH1078472A - Diagnosis method for deterioration of CV cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a CV cable deterioration diagnosis method capable of accurately measuring only a signal due to deterioration regardless of the magnitude of contact resistance between a metal shielding layer and an external semiconductive layer of a CV cable. SOLUTION: A DC voltage is applied by superimposing an AC voltage between a conductor and a shielding layer of a CV cable, and a degree of deterioration is determined based on a change in magnitude of a fundamental wave component or a harmonic component of a current flowing through the CV cable. I do.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for diagnosing deterioration of a CV cable due to water trees or the like under a live line.

[0002]

2. Description of the Related Art CV cables are subject to accelerated deterioration due to water trees or the like in a severe use environment, and may cause a dielectric breakdown accident within an expected life. Therefore, it is very important to diagnose the deterioration state of the cable and prevent an accident from occurring.

As one method of diagnosing deterioration of a CV cable, there is a dielectric loss tangent measurement method (tan δ method) as shown in, for example, Electric Cooperative Research Vol. The dielectric loss tangent measurement method is a method in which an AC voltage of a commercial frequency is generally applied to a cable to be measured, and a temperature characteristic and a voltage characteristic of tan δ are measured to determine an insulation state. In general, it is difficult to obtain a temperature characteristic of tan δ. Therefore, it is often the case that the voltage characteristic is usually measured and taken into consideration in conjunction with the results obtained by other measurement methods, thereby determining the insulation.

As a method for solving the problem of the dielectric loss tangent measurement method, for example, a deterioration diagnosis technique as disclosed in Japanese Patent Application Laid-Open No. 1-127968 has been proposed. This method is based on the capacitance component of the current flowing in the cable, that is, the in-phase current having the same phase as the applied AC voltage flowing through the resistance component of the cable, and the leading current that is 90 ° ahead of the AC voltage flowing through the capacitance component of the cable. The magnitude of the resistance component is measured by erasing the leading phase current and detecting only the in-phase current, thereby diagnosing the deterioration of the cable.

[0005]

However, according to the two methods for diagnosing deterioration described above, even if the cable insulator does not deteriorate, if the contact resistance between the metal shield layer and the external semiconductive layer of the cable is large, the former method is used. In the latter case, the value of tan δ becomes large and accurate deterioration diagnosis cannot be performed. In the latter case, a large resistance component current (loss current) is generated, and there is a possibility that water tree deterioration of the cable insulator cannot be detected.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and accurately measures only a signal caused by deterioration of a water tree or the like regardless of the magnitude of contact resistance between a metal shielding layer and an external semiconductive layer. The present invention provides a method for diagnosing deterioration of a CV cable which has been made possible.
An object of the present invention is to apply a DC voltage superimposed on the C voltage and determine the degree of deterioration based on a change in magnitude of the fundamental wave component or its harmonic component of the current flowing through the CV cable due to the application of the DC voltage.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a basic explanatory diagram of a deterioration diagnosis method according to the present invention. In the drawing, 1 is a CV cable, 1A is its conductor, 1B is a shielding layer, 2 is an AC power source, 3
Is a DC power supply, 4 is a switch, 5 is a capacitor, and 6 is a current detection device. First, as shown in the drawing, switch 4
1A of the CV cable 1 from the AC power supply 2
Applying an AC voltage between the shielding layers 1B and measuring the current I ₀ flowing through the CV cable 1; Next, the switch 4 is closed, the DC voltage is applied from the DC power supply 3 while being superimposed on the AC voltage, the current I ₁ flowing through the CV cable ₁ is measured, and the current change ΔI = I ₁ −I ₀ is calculated. Diagnose deterioration. In the above, the capacitor 5 is inserted as a bypass to prevent the current flowing through the CV cable 1 from flowing into the DC power supply.

In the above measurement, the change ΔI =
Since I ₁ -I ₀ is normally very small, as shown in FIG. 2A, C 1 in the case where the switch 4 is opened and no DC voltage is applied is applied.
The current I ₀ flowing through the V cables 1, the voltage of the external power supply 8 so that the output upsilon 'is upsilon' becomes = upsilon ₀ of the differential amplifier 7, to adjust the phase. Then, in this state, as shown in FIG. 2B, the switch 4 is closed, a DC voltage is applied, and υ ₁ −υ ′ = K (I ₁ −I ₀ ) is measured with the above υ ′ as it is.
Thereby, ΔI = I ₁ −I ₀ is measured. In addition, as a DC power supply, for example, ± 1 KV to 6 KV CV cable is used.
± 10 KV is appropriate.

FIG. 3A is a current-voltage characteristic diagram of the water tree of the CV cable. FIG. 3 (b) is a voltage characteristic diagram between the cable conductor and the shielding layer, and FIG. 3 (c) is a resistance component current (loss current).
B shows a case where a DC voltage is applied. As described above, it is considered that the voltage and the current change as shown in FIGS. 3B and 3C by applying the DC voltage superimposed on the AC voltage. At this time, since the contact resistance between the metal shielding layer and the external semiconductive layer of the CV cable is not related to the application of the DC voltage, only the deterioration of the water tree can be detected by measuring the change in the current.

[0010]

As described above, according to the method for diagnosing deterioration of a CV cable according to the present invention, the change in the current flowing through the CV cable due to the application of the DC voltage is measured, whereby the metal shield layer and the outer half are measured. It is possible to accurately measure only the signal due to deterioration regardless of the magnitude of the contact resistance of the conductive layer.

[Brief description of the drawings]

FIG. 1 is a basic explanatory diagram of a deterioration diagnosis method of the present invention.

FIGS. 2A and 2B are explanatory diagrams of a procedure for measuring a current change.

3 (a) is a current-voltage characteristic diagram of a water tree of a CV cable, FIG. 3 (b) is a voltage characteristic diagram between a cable conductor and a shielding layer, and FIG. 3 (c) is a resistance component current (loss current). It is a characteristic diagram.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 CV cable 1A Cable conductor 1B Shielding layer 2 AC power supply 3 DC power supply 4 Switch 5 Capacitor 6 Current detection device 7 Differential amplifier 8 External power supply

Claims (1)

[Claims] 1. A method for applying a DC voltage superimposed on an AC voltage between a conductor and a shielding layer of a CV cable, and changing a magnitude of the fundamental wave component or a harmonic component of the current flowing through the CV cable due to the application of the DC voltage. A method of diagnosing deterioration of a CV cable, characterized in that the degree of deterioration is determined by the method.