JPH0684979B2 - Insulation deterioration diagnosis method for power cables - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for diagnosing insulation deterioration of a power cable under hot line.

[Prior art and its problems]

A conventional insulation deterioration diagnosis method is shown in FIG. A power cable 13 to be diagnosed for insulation deterioration is connected to a high-voltage bus 12 charged by the main transformer 11. A grounding transformer 14 is connected to this three-phase circuit, and its neutral point is grounded by a grounding wire 15. On the other hand, the shield of the power cable 13 is also the ground wire 16
Grounded by.

When diagnosing, the neutral point ground wire 15 on the grounding transformer 14 side
Open, insert a low impedance 17 (capacitor or resistor) for the commercial frequency (50 or 60 Hz), and connect the measurement power supply 18 to both ends. At the same time, switches 19 and 20 are provided. On the other hand, insert a similar impedance 21 into the shield ground wire 16 on the power cable 13 side, and insert a current measuring device 22 at both ends.
Connect. At the same time, switches 23 and 24 are provided. In this state, a DC voltage is applied to the conductor of the power cable 13 by the measurement power supply 18, and the current flowing through the shield ground wire 16 through the insulator of the power cable 13 is measured by the current measuring device 22. The conventional method is to diagnose the degree of insulation deterioration based on the magnitude of this current.

However, in the conventional method, it is necessary to insert an impedance into the ground line, and it is dangerous to perform the wiring work under a live line, so that a temporary power outage is required. Therefore, there is a problem that the opportunity for diagnosis is limited. Although a direct current is generally used as a measurement power source, a method of using an alternating current power source having a frequency lower than a commercial frequency, which requires less charging current for a cable, is also known. However, when a low frequency power supply is used, it is difficult to separate the leakage current and the charging current, and it is not possible to diagnose the insulation deterioration with high sensitivity only by measuring the absolute value of the current.

[Means for solving problems and their effects]

The present invention provides a method for diagnosing insulation deterioration of a power cable that solves the above-mentioned problems of the prior art. The method is for a three-phase circuit to which a power cable whose insulation deterioration is to be diagnosed is connected. A clamp type voltage injection device is attached to the neutral point ground wire, and a clamp type current detection device is attached to the shield ground line of the power cable. While applying voltage, the leakage current is detected by the current detection device, and the waveform of the applied voltage and the waveform of the current based on the applied voltage extracted from the leakage current are analyzed to diagnose insulation deterioration of the power cable. It is characterized by that.

That is, in the present invention, by using a clamp type voltage injection device and a clamp type current detection device, it is possible to apply a low frequency voltage and to detect a current based on the low frequency voltage without opening the ground line, and to analyze sensitivity by waveform analysis. It enables high diagnosis.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to FIG.

In this method, first, a clamp type voltage injection device 25 is attached to the neutral point ground wire 15 of the ground transformer 14. This voltage injection device
25 is a clamp type (opening and closing type) core made of a magnetic material with a coil wound around it, which can be easily attached to and detached from the ground wire 15. The coil of the voltage injection device 25 is connected to the low frequency power source 26, and when a voltage having a frequency lower than the commercial frequency is applied from the coil, the low frequency voltage is induced in the closed circuit including the ground line 15.

On the other hand, a clamp-type current detector 27 is attached to the shield ground wire 16 of the power cable 13 to detect a leak current. The current detecting device 27 also has a structure in which a coil is wound around a clamp type core. The detected current is passed through the low frequency filter 28,
A current based on the low frequency voltage is extracted from the extracted current and input to the waveform analyzer 29. The waveform analyzer 29 includes the above low frequency power source.
26 voltage waveforms are also input.

In the waveform analyzer 29, from these inputs, the peak value of the current, the phase difference of the voltage / current (corresponding to the dielectric loss tangent),
Analyze and display the distortion of the current waveform (magnitude of harmonic component ratio).

With the above method, (a) degraded 6KV CV cable and (b)
When the insulation degradation diagnosis was performed on a new 6KV CV cable, 30m each, the peak value of the current was slightly higher in (a) than in (b), the phase difference was almost the same in both (a) and (b), As a result, it was obtained that the content of (a) was higher than that of (b).
In this way, the conventional method of measuring only the peak value of the current cannot diagnose the insulation deterioration with high sensitivity, but this method enables highly sensitive diagnosis by examining the waveform distortion.

Although the clamp type voltage injection device is attached to the neutral point ground wire of the grounding transformer in the above embodiment, for example, if the main transformer has a neutral point grounding line, the clamp type voltage injection device is attached to it. You may do it.

〔The invention's effect〕

As described above, according to the present invention, by using the clamp type voltage injection device and the clamp type current measuring device,
Without touching the ground wire from the outside, it is possible to diagnose the insulation deterioration of the power cable under uninterrupted power line. Also, by performing a waveform analysis of the measured voltage and current,
Insulation deterioration can be detected with high sensitivity.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an insulation deterioration diagnosis method for a power cable according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional insulation deterioration diagnosis method. 13 ~ power cable, 14 ~ grounding transformer, 15 ~ neutral grounding wire, 16 ~ shield grounding wire, 25 ~ clamp type voltage injection device,
26 ~ Low frequency power supply, 27 ~ Clamp type current detector, 28 ~ Low frequency filter, 29 ~ Waveform analyzer.

Claims (1)

[Claims] 1. A clamp type voltage injection device is attached to a neutral point ground wire of a three-phase circuit to which a power cable whose insulation deterioration is to be diagnosed is connected, and a clamp type current is connected to a shield ground wire of the power cable. A detection device is attached, a voltage lower than the commercial frequency is applied by the voltage injection device under the hot line, and a leakage current is detected by the current detection device, and extracted from the waveform of the applied voltage and the leakage current. A method for diagnosing insulation deterioration of a power cable, which comprises diagnosing insulation deterioration of the power cable by analyzing a waveform of a current based on the applied voltage.