JPH0618604A - Diagnostic method for insulation deterioration and defect detecting method for power cable - Google Patents

Abstract

PURPOSE:To determine the position of the deterioration in insulation by sequentially moving the heating position of a cable, measuring the thermally stimulated current, and detecting the change in current. CONSTITUTION:A sound cable and a deteriorated cable are used as the samples. A guard electrode 3 and a measuring electrode 4 of the cable 2 are connected to an ammeter 6 through lead wires 9 and 10. The cable 2 is moved at the speed of about 1m/h with moving rollers 5 through a cable heating device 1, and the current is measured. Meanwhile, a bias voltage Vb 8 is applied on the core conductor of the cable 2 for 10 minutes at ordinary temperature. Then, the cable is once grounded. A voltage (collecting bias Vc) 7 in the same polarity, which is smaller than Vb 8, is applied. The cable 1 is heated, and the thermally stimulated current flowing through the cable 2 is measured. As the value of the bias voltage Vb, 10kV/mm is sufficient. In actual detection, the sufficient detection can be performed when the detection is performed at the DC withstand voltage value of the cable to be detected. As the collecting bias Vc, about 1kV/mm, which does not give damage, is applied in order to improve the detecting sensitivity.

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 insulation deterioration and a method for testing initial performance of power cables, particularly polyethylene or crosslinked polyethylene insulated power cables.

[0002]

2. Description of the Related Art Polyethylene or cross-linked polyethylene power cables have so-called Vt characteristics in which the dielectric breakdown characteristics deteriorate with the passage of time, and it is an important subject to detect this insulation deterioration. As the insulation deterioration diagnosing method therefor, a tan δ method, a DC leakage current method, a residual voltage method, a method for detecting a DC component under AC voltage application,
Partial discharge detection methods have been used. A frame test (withstand pressure test, tan δ measurement) is performed as a test of initial performance.

[0003]

However, none of these methods has been able to diagnose insulation deterioration with 100% probability, and it is necessary to develop a new insulation deterioration diagnosis method with higher reliability. Was becoming. In particular, there has been a demand for the development of a method capable of evaluating a location where insulation deterioration has occurred.
Further, in the frame test of the initial performance test, the defect in the cable cannot be detected, and there has been a strong demand for the development of a new performance test method for detecting a serious defect in the power cable.

The object of the present invention was made in view of the above technical background, and a new method for diagnosing insulation deterioration of a power cable for preventing accidents due to insulation deterioration of the power cable, and an initial defect of the power cable. An object of the present invention is to provide a new test method with improved detection accuracy.

[0005]

According to the present invention, in a power cable using polyethylene or cross-linked polyethylene as an insulator, a direct current voltage is applied, the power cable is heated after grounding, and the current (thermally stimulated current) is measured. , In the method of diagnosing the insulation deterioration of the cable based on this current value, while sequentially moving the position to heat the cable, continuously measuring the current value during this, by detecting the change in this current value, A method for diagnosing insulation deterioration of a power cable, characterized in that the position of insulation deterioration can be evaluated. In addition, when measuring the thermal stimulation current, the current is measured while applying a DC voltage (collecting bias), and the deterioration of the cable insulation is detected based on this current value. Is the way.

Further, according to the present invention, the current value (thermal stimulation current) during this time is moved while sequentially moving the position for heating the cable.
Is continuously measured, and the position of the defect in the cable is evaluated by detecting the change in the current value. Further, when measuring the thermal stimulation current (TSC), the current is measured while applying a DC voltage (collecting bias), and a defect existing in the cable is detected based on this current value. This is a method for detecting a defect in a power cable.

[0007]

[Function] In a power cable using polyethylene and cross-linked polyethylene as an insulator, a method of applying a DC voltage, heating the cable after grounding, and measuring the current (thermally stimulated current) is the diagnosis of insulation deterioration and detection of defective cables. It was noted that it is effective for. Then, in the above-mentioned diagnostic method, it was found that the change in the current value can be detected by sequentially moving the heating position of the cable, and thereby the insulation deterioration position and the position where the defect exists in the cable can be evaluated. .

[0008]

[Examples] Degradation of a cross-linked polyethylene cable is often caused by voids existing in an insulator, foreign matter, a bowtie tree generated from protrusions on a semiconductive layer, and a water tree caused by external water immersion. A space charge is formed by the application of an electric field. The formation of this space charge is particularly remarkable when a DC voltage is applied, and the measurement of the thermal stimulation current detects the current caused by this space charge. When the insulator is polyethylene or crosslinked polyethylene, this thermally stimulated current has a peak at a temperature of around 60 ° C. Therefore, in the method of the present invention, it is necessary to move the heating part so that the temperature of each part of the cable exceeds 60 ° C. when moving the heating part of the cable. As a method of moving the heating portion, a portion to which the heater is fixed is provided, and this portion can be realized by passing the cable to be measured at a constant speed.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a detection device used in an experiment of a method for diagnosing insulation deterioration of a power cable and a method for detecting a defect according to the present invention. In this experiment, as an example, a cross-linked polyethylene insulation cable with an insulation thickness of 6 mm (hereinafter referred to as a deteriorated cable) in which the occurrence of bow tie tree is extremely high
And a sound cable was used as a sample. These cables 2
Lead wires 9 and 10 are connected to the guard electrode 3 and the measurement electrode 4, respectively, and are connected to an ammeter PA6. And
The cable 2 which is a sample is passed through the cable heating device 1 having a heater length of 1 m by a cable moving roller 5 to reach 1 m / m.
It is configured to move and measure at a speed of h.

On the other hand, a direct current voltage (bias voltage Vb) 8 was applied to the core conductor of the cable 2 at room temperature for 10 minutes.
Then, after grounding once, a voltage of the same polarity (collecting bias V
c) The thermal stimulation current (TSC) flowing in the cable 2 is measured while being heated by the cable heating device 1 while applying 7.

In this experiment, two kinds of bias voltage Vb of 60 kV and 180 kV were applied, and the collecting bias Vc was set to 6.0 kV. FIG. 2 shows the time-dependent change in the current value of the healthy cable during measurement, and FIG. 3 shows the time-dependent change in the deteriorated cable.

From this measurement result, the bias voltage Vb = 6
It can be seen that, in both cases of 0 kV and Vb = 180 kV, there is a change in the measurement result of the current value in the deteriorated cable. As seen in this example, the bias voltage V
About 10 kV is sufficient as the value of b, and it seems that sufficient detection can be actually performed by using the DC withstand voltage value of the cable to be diagnosed. Further, as the collecting bias Vc, the current value of the deteriorated cable changes even if this is not applied, but it is desirable to apply this for improving the detection sensitivity and does not affect the insulator. 1k
It is desirable to apply a collecting bias Vc of about V / mm.

An embodiment of the power cable defect detection method of the present invention will now be described with reference to the drawings. As an example, a model cable having an insulation pressure of 6 mm in which a large number of voids are mixed in a crosslinked polyethylene insulator was prepared, and the result was compared with the thermal stimulation current (TSC) of a normal cable, and the result is shown in FIG. It is a value when the bias voltage Vb = −60 kV and the collecting bias Vc = −8.6 kV. From this figure, it can be seen that the peak current of the thermal stimulation current (TSC) in the voided cable is considerably larger than that in the normal cable.

Similar to the previous example, a cross-linked polyethylene cable (hereinafter referred to as a deteriorated cable) having an insulation thickness of 6 mm in which a large number of voids are mixed in an insulator and a sound cable are used as samples, and a DC voltage (bias voltage) Vb is obtained at room temperature. = 60kV
Was applied for 10 minutes. Collecting bias Vc =-
The heating unit moving device 2 shown in FIG. 1 while applying 8.6 kV.
Was passed through the cable at a constant speed (1 m / h), and the thermal stimulation current (TSC) was measured during this period. The result is shown in FIG.

This figure also shows the measured values of the thermal stimulation current (TSC) of a normal sound cable and a deteriorated cable. It was confirmed that a peak of the TSC curve was found at the position where the void exists in the deteriorated cable containing the void.

As seen in this example, the bias voltage Vb
The value of 10 kV / mm is sufficient, and in practice, it can be detected sufficiently by using the DC withstand voltage value of the cable to be detected. As for the collecting bias Vc, the current value of the deteriorated cable changes even when this voltage is not applied, but to improve the detection sensitivity, the insulator is not damaged (Vc = 1 kV / m).
m) may be applied.

[0017]

As described above, according to the method for diagnosing the deterioration of the power cable and the method for detecting the defect of the power cable of the present invention, it is possible not only to determine the insulation deterioration of the power cable and the defective cable, but also It is now possible to assess the location of defects in the cable.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a heating device used in a method for diagnosing insulation deterioration of a power cable and a method for detecting defects according to the present invention;

FIG. 2 is a graph showing changes with time of thermally stimulated current in a sound cable,

FIG. 3 is a graph showing changes over time in thermally stimulated current in a deteriorated cable,

FIG. 4 is a graph showing thermal stimulation currents of a normal cable and a deteriorated cable,

FIG. 5 is a graph showing changes over time in thermally stimulated currents of a healthy cable and a deteriorated cable.

[Explanation of symbols]

 1 cable heating device 2 cable 3 guard electrode 4 measuring electrode 5 cable moving roller 6 ammeter 7 collecting voltage 8 bias voltage

Claims (4)

[Claims] 1. In a power cable using polyethylene or cross-linked polyethylene as an insulator, a DC voltage is applied, the cable is heated after grounding, the current (thermally stimulated current) is measured, and the current value of the cable is used as a basis. In the method of diagnosing insulation deterioration, while moving the position to heat the cable in sequence, continuously measure the current value during this period,
A method for diagnosing insulation deterioration of a power cable, characterized in that the position of insulation deterioration can be evaluated by detecting the change in the current value. 2. The current is measured while applying a DC voltage (collecting bias) at the time of measuring the thermally stimulated current,
The method for diagnosing insulation deterioration of a power cable according to claim 1, wherein deterioration of the cable insulation is detected based on the current value. 3. In a defect detection method for a power cable using polyethylene or crosslinked polyethylene as an insulator, a current value (thermally stimulated current) during this time is continuously measured while sequentially moving a heating position of the cable, and this current is measured. A method for detecting a defect in a power cable, characterized in that a defect position in the cable is evaluated by detecting a change in the value. 4. The current is measured while applying a DC voltage (collecting bias) at the time of measuring the thermal stimulation current,
The defect detecting method for a power cable according to claim 3, wherein a defect existing in the cable is detected based on the current value.