JPH05307061A - Degradation diagnosing method for power cable and its accessories - Google Patents

Abstract

PURPOSE:To provide possibility of diagnosing precisely the deterioration of a power cable and its accessories by irradiating them with a laser beam in the condition that AC or DC is impressed on them, measuring signals generated in the insulation, and determining the space charge distribution. CONSTITUTION:On a cable 3 a high voltage of commercial frequency is impressed from a transformer 1 for testing via a termination 2a. When a target 4 on the cable surface is irradiated with a laser beam 5a, a pressure wave is generated in the insulation and propagates, and if space charges exist in the insulation, pulse signals are produced which are due to vibration of the space charges. At measuring, a signal sensing part 6 removes the commercial frequency and takes out only the signal pulses. An amplifier 7 is of wide band type and amplifies good over to the high frequency range. The signal pulses flow to 6a, 6c, and the amplifier 7. The pulse signals due to the space charges generated in the insulation by the laser beam irradiation are sensed by the sensing part 6, amplified by the amplifier 7, and processed by the signal recording part 8a and waveform calculation processing computer 8b belonging to the measuring system 8, and thus diagnosis of deterioration can be executed precisely.

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 by measuring space charge distribution in an insulator of a power cable and its accessories.

[0002]

2. Description of the Related Art Conventionally, when measuring a space charge of an accessory such as a power cable or a connecting portion thereof, or when performing a deterioration diagnosis by measuring the space charge, a sample is disassembled and a toner attached to the charge is sprinkled. There is a method of measuring the space charge by using a method of measuring the space charge, or a method of measuring the space charge without applying a practical voltage.

[0003]

In all of the conventional techniques, since the measurement is performed in the state where the actual use voltage is not applied, the signal serving as the reference for judging the deterioration is the signal due to the accumulated space charge in the sample insulator. Is lost when the voltage is cut off, and there is a great risk that accurate measurement will not be possible.

Therefore, an object of the present invention is to make it possible to measure the space charge distribution existing in the insulator while applying a voltage to be actually used to the sample.

[0005]

In order to achieve the above object, the method of the present invention is for irradiating a laser beam on the outer periphery of a sample such as a cable or an accessory to be measured in order to detect space charge. A target is attached, and a pressure wave generator having a laser beam as a source irradiates the target with a laser beam to generate a pressure wave traveling in the cable insulator.

When space charge exists in the insulator, the space charge oscillates and is displaced by the progress of the pressure wave caused by the laser beam irradiation. The pulse accompanying this displacement reaches the center conductor of the cable. Since the displacement voltage pulse generated in the central conductor is a signal related to the space charge existing inside the insulator, the space charge can be measured by measuring the pulse generated in the conductor.

When a high voltage such as an actual operating voltage is applied to the cable, it is not possible to directly measure a minute pulse from the center conductor of the cable. Connect a coupling capacitor that extracts only the pulse of. By measuring the output of this coupling capacitor, the space charge can be measured while a high voltage is applied, and the deterioration diagnosis of the sample can be performed.

[0008]

The laser beam applied to the sample to be measured serves as a pressure wave source for oscillating the space charge accumulated inside the insulator. When the target on the outer surface of the sample is irradiated with the laser beam, a part of the target is vaporized, and a pressure wave is generated in the insulator due to the impact of the vaporization to proceed. As the pressure wave progresses, the insulator itself in the traveling path locally compresses and expands. Therefore, if space charge exists in the insulator, the space charge vibrates spatially. The vibration of the space charge becomes a displacement voltage and a current and reaches the cable conductor as a pulse. Since this pulse is a signal corresponding to the space charge inside the insulator, it can be converted into a space charge signal by appropriate computer processing.

In order to measure this high frequency pulse in the state where a low frequency DC or commercial frequency voltage is applied, it is necessary to perform the measurement with the measuring instrument at the ground potential. Therefore, the measuring device is protected from the high voltage by the coupling capacitor and only the high frequency pulse as the signal is taken out.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows one embodiment of the present invention, and FIG. 2 shows another embodiment. In the embodiment shown in FIG. 1, 1 is a test transformer for applying a voltage to a test cable, 2a and 2b are cable terminals, 3
Is a power cable, 3a is an exterior, and 3b is a conductor. Reference numeral 4 denotes a laser beam irradiation target provided on the surface of the cable, which is a metal electrode deposited on the outer circumference of the cable in a size of 15 mm × 15 mm. Reference numeral 5 denotes a laser light source, and 5a denotes the laser beam.

The cable 3 is connected from the test transformer 1 to the terminal 2
A commercial frequency high voltage is applied via a. When the laser beam 5a irradiates the target 4 on the surface of the cable, a pressure wave is generated and progresses in the insulator, and if space charge exists in the insulator, a pulse signal is generated by the vibration of the space charge.

Reference numeral 6 is a signal detecting portion connected to the cable terminal 2b, 6a is a coupling capacitor having a capacity of 2000 pF on the high voltage side, and 6b is an inductance of 10 mH on the low voltage side. In the meantime, the output section 6c has almost the ground potential with respect to the commercial frequency and has a high impedance with respect to the ground potential with respect to the high frequency pulse. The signal detection unit 6 removes the commercial frequency and takes out only the signal pulse during the measurement. The amplifier 7 is a wide band amplifier and can sufficiently amplify a high frequency signal. Signal pulse is 6a-6c-measurement signal amplifier 7
The pulse signal due to the space charge generated in the insulator due to the laser beam irradiation is detected by the signal detection unit 6, amplified by the amplifier 7, and is recorded by the signal recording unit 8a of the measurement system 8.
It is processed by the waveform calculation processing computer 8b.

The position where the laser beam irradiation target is attached to the outer circumference of the cable may be a position where the pressure wave propagates to the space charge in the cable insulator due to the laser beam irradiation, and the position of the cable may be adjusted as necessary. The laser beam is emitted by sequentially changing the mounting position in the length direction. Further, if the cable has a defective portion such as a water tree, space charge may be accumulated there. Therefore, if the cable of the pipeline has a submerged portion, it is attached to the outer circumference of the cable.

[0014] wherein the the test cable 3, about 1 year 3 months at test site, AC 50H _Z, a voltage of 12.7KV, 22KV of CV cable was flooded Division electrostatic test immersing the cable in water AC 50H _Z ,
The space charge was measured by the system of FIG. 1 while the voltage of 12.7 KV was applied. The space charge distribution obtained as a result was as shown in FIG. P1 in the horizontal axis of the figure
The position of is the conductor side, the position of P2 is the ground side, P1-P
Between 2 is an insulator region, and the vertical axis is space charge. According to this, it can be read that the presence of positive space charges is detected at a site approximately 1.7 mm from the outer peripheral portion of the insulator. Further, the space charge distribution obtained as a result of performing the same measurement while stopping the voltage application and cutting off the voltage is as shown in FIG. 4, and it can be seen that the space charge distribution is different from that during the voltage application. Therefore, it exists only during voltage application, and since the distribution of space charges changes when the voltage is cut off, it becomes possible to measure the true distribution of space charges during voltage application.

In the second embodiment of FIG. 2, 11 is a test transformer, 12a and 12b are cable terminals, and 13 is a sample CV cable. This is because the shield layer 13c on the outer periphery of the cable insulator is provided with an edge cut portion 19 to form a cable half portion 13a,
13b is electrically divided into two. The edging portion 19 is formed by cutting the shielding layer 13c in the circumferential direction and separating it to the left and right. Reference numeral 19a is a cable insulator portion while the shield layer 13c is separated into right and left. Reference numeral 14 is a target provided on the outer surface of the one cable half 13a from which the shielding layer 13c is cut off, 15 is a laser light source, and 15a is its laser beam. The cable halves 13a and 13b electrically divided by the edging portion 19 form a coupling capacitor of a circuit for detecting a pulse signal generated by the presence of space charge in the insulator by irradiating the target 14 with a laser beam. To do. One cable half 13b
Is grounded through a detection impedance 16 having an inductance of 10 mH, and a measurement amplifier 17 is connected to this portion,
The signal recording unit 18a of the measurement system 18 and the waveform calculation processing computer 18b are connected to the output side.

With the configuration of FIG. 2, the same measurement as in the embodiment of FIG. 1 can be performed. As a result of performing the same measurement as that of the first embodiment, the space charge distribution of FIG. It was confirmed that the space charge distribution shown in FIG.

The above-mentioned embodiment is an example of measurement on a cable sample, but the sample includes an extrusion mold joint of its accessory, and this accessory part is also irradiated with a laser beam as described above. Can measure the space charge distribution in the insulator. Also in the case of this connecting portion, although not shown, an intermediate portion of the metal sheath on the outer periphery thereof is cut off in the circumferential direction to provide an edge cutting portion similar to the edge cutting portion 19 of FIG. A laser beam irradiation target is attached to the metal sheath of this connecting portion, and a laser beam is irradiated in the same manner as described above to measure the space charge distribution in the insulator.

Even when the deterioration diagnosis is performed based on the presence or absence of space charge based on the above measurement results, the deterioration diagnosis is accurately performed during voltage application because the space charge distribution differs depending on the presence or absence of electric charge. be able to.

[0019]

As described above, according to the present invention, it is possible to accurately detect that the space charge distribution is different between when the electric charge is applied and when the electric charge is stopped. It is possible to accurately diagnose deterioration of the cable and its accessories.

[Brief description of drawings]

FIG. 1 is a circuit diagram of one embodiment of the method of the present invention.

FIG. 2 is a circuit diagram of another embodiment of the method of the present invention.

[Figure 3] Space charge distribution map during charging

[Figure 4] Space charge distribution map during interruption of voltage application

[Explanation of symbols]

 3, 13; Cables 5a, 15a; Laser beams 6a, 19a; Coupling capacitor 19; Edge cut portion

Claims (2)

[Claims] 1. A power cable having an insulator such as a plastic and its accessories are irradiated with a laser beam in a state in which an alternating current or a direct current is applied to generate a pressure wave in the insulator, thereby producing the insulator. A method for diagnosing deterioration of a power cable and its accessories, characterized in that a space charge distribution in an insulator is measured by measuring a signal generated therein through a coupling capacitor. 2. A method for diagnosing deterioration of a power cable and its accessories according to claim 1, wherein the cable shielding layer is provided with an edge cut portion to form a coupling capacitor.