JPH0616066B2 - Insulation defect detection method for power cable - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for detecting an insulation defect in a high-voltage power cable, a power cable mainly made by extrusion-coating a cross-linked polyethylene material (hereinafter referred to as a CV cable), and the like.

[Prior Art] Since CV cables are dry insulated, their maintenance is very easy and they are excellent in disaster prevention.
It has also come to be used for high voltage of 0 KV class.

The cause of the deterioration of the electrical performance of CV cable insulation is
Electrode irregularities in the internal and external electrostatic shield layers, voids in the insulator, foreign matter, and water trees generated in moisture-absorbed cables are considered. It is considered that if these defects are present, the local electric field at that portion becomes high, and if the applied voltage is increased, an electric tree is generated, which gradually progresses to eventually destroy the entire insulator. In order to improve the performance of the cable or reduce the insulation thickness, it is desirable to be able to directly confirm the defects that are the origin of these dielectric breakdowns.

As a method for clarifying the dielectric breakdown of this CV cable, it has been performed so far by detecting a residual defect portion due to suppression of burnout of the breakdown hole of the cable insulator due to high-speed cutoff. However, if the insulation of the cable insulator is destroyed, most of the defective portions are burned out, and the defect detection becomes almost impossible, and the cause cannot always be sufficiently clarified.

[Problems to be Solved by the Invention] As described above, in the prior art, even under the condition that the burnout energy of the breakage hole at the time of breaking the cable insulator is suppressed and the burnout of the defective part is reduced as much as possible. Since a certain degree of burnout that would cause dielectric breakdown of the cable insulator cannot be avoided, a very small defect could not be detected. Also,
Until now, a method for detecting the pre-breakdown discharge pulse and locating the defective portion has not been established.

Therefore, the present invention has been made in view of such a point, and if the electrical tree begins to extend to the insulator of the cable for test power and the portion can be detected immediately before the breakage, the problem of burnout of the cable insulator occurs. Is almost eliminated, and it is possible to clearly find the defect that is the starting point, so make sure that the cable insulator is degraded to some extent just before the dielectric breakdown and that the defect is obviously harmful. It is an object of the present invention to provide a novel method for detecting an insulation defect in a power cable or the like.

[Means and Actions for Solving Problems] According to the present invention, when a partial discharge detection device is connected to a cable for power under test to perform a voltage application test, the cable insulator is deteriorated to some extent by partial discharge, and the partial discharge is caused. By lowering the starting voltage, thereby reducing the energy of partial discharge and delaying the progress of insulation breakdown, the location of the partial discharge is located during this time and the insulation defect of the power cable is sampled and detected. This is a method for detecting insulation defects in cables.

[Embodiment] Hereinafter, an insulation defect detecting method for a power cable according to the present invention will be described with reference to the drawings.

FIG. 1 is an electric circuit diagram of a device for detecting a precursory partial discharge pulse according to the present invention and shutting off the power source based on the pulse to cause some damage to a defective portion. This circuit has the same principle as a circuit used for a general partial discharge detection measurement method.

That is, the precursory discharge interrupting device holds both ends of the power cable, for example, the CV cable 5 under test, by the cable air terminal 4 and the cable minikura terminal 8, and the cable air terminal 4 has a power breaker 1 and a high voltage. Connection is made so that a high voltage is applied via the transformer 2 and the coupling capacitor 3. A partial discharge detection resistor 6 is connected to the middle portion of the sample CV cable 5, both ends of this resistor 6 are connected to a partial discharge measuring instrument 7, and this measuring instrument 7 is connected to a power interruption control device 9. It is configured to control the power breaker 1 and sends a signal from the partial discharge measuring device 7 to the power cut-off control device 9 at a stage when it is apparent that the discharge is the precursor partial discharge, and automatically. The power is cut off.

The difference between the normal partial discharge and the precursor partial discharge lies in the discharge charge amount. That is, it is possible to determine whether or not the partial discharge is generated from the time when the partial discharge is larger than the normal partial discharge or is not discharged, and the discharge gradually increases. That is, when the partial discharge increases with time, it is determined to be the precursor partial discharge, and the power supply is shut off.

In this way, if the precursor partial discharge pulse of the sample CV cable 5 is detected and the power is cut off by the power breaker 1, the position of the position of the sample CV cable 5 at which partial discharge has occurred next Orientation is performed.

FIG. 2 is a partial discharge pulse polarity determination for locating a damaged portion of the insulator of the CV cable 5 to be tested, and subsequently recharging a low voltage to generate a slight partial discharge and examine it. It is an electric circuit diagram of an apparatus. That is, in the sample CV cable 5, the metal shielding layer on the outer semiconductive layer is cut off at the center by the dividing portion 11, and the sheath side electrodes 10 and 10 ′ made of this metal shielding layer are pulse transformers 12.
Are respectively connected to the primary side windings, and their centers are grounded. The secondary winding of the pulse transformer 12 is connected to the polarity discriminating device 13. Also, the cable aerial terminal 4
A series circuit of a coupling capacitor 14 and a voltage dividing capacitor 15 is connected to and is connected to a power supply terminal. The connection end of the coupling capacitor 14 and the voltage dividing capacitor 15 is connected to the input end of the polarity discriminating device 13.

Test CV including insulation defect where electrical tree occurred
When AC voltage is reapplied to the cable 5, partial discharge occurs in the electric tree portion. This partial discharge is generally much lower than the partial discharge before the generation of the electrical tree and the discharge start voltage. With the partial discharge regenerated, the phase of the power supply voltage is observed based on the voltage dividing capacitor 15, and the polarity of the partial discharge pulse is examined. Since the polarity of this pulse is reversed between the case where it occurs in one electrode part and the case where it occurs in the other half electrode part,
It is possible to determine in which electrode portion the partial discharge has occurred. If one half of the partly discharged can be identified, the part is further divided into two equal parts and the part where the partial discharge is generated is examined again. By repeating such an operation several times to ten or more times to gradually increase the length of the partial discharge occurrence portion, the position of the defective portion where the electrical tree has finally occurred in the insulator of the CV cable 5 under test. Can be located. After that, this defective portion is cut out and observed under a microscope, and it is possible to accurately detect what is the cause of the electrical tree generating portion which is just before the destruction.

The pulse transformer 12 of this partial discharge pulse polarity discrimination device
Alternatively, the detection resistors Rd and Rd ′ may be connected and the voltage across them may be differentially amplified to determine the pulse polarity.

Further, when the first partial discharge occurs and the progress of the electric tree is fast, the high speed power cutoff may be applied.

If it is difficult to distinguish from the partial discharge from the CV cable 5 under test due to a large amount of external noise, it is also good to use a normal partial discharge determination method.

If the range of partial discharge of the CV cable under test has been limited by the partial discharge pulse polarity discriminating apparatus shown in FIG. 2, the insulation may be broken down by the high-speed breaking method. Since it can be destroyed in the state where the applied voltage is low, the burnout of the sample CV cable insulator can be reduced, and the cause of the defect can be detected to some extent.

If the CV cable to be tested is cut only within a limited range and the destructive test is performed again, the sample length is short, so that the burnout can be reduced.

In addition, although the above-mentioned embodiment mainly explained the CV cable, it is needless to say that it can be applied to the detection of the insulation defect of the power cable other than the CV cable, the high voltage insulation system and the like.

[Effect of the Invention] The conventional partial discharge detection method merely measures the partial discharge, and can determine whether it is harmful or not, or locate the partial discharge part within a very limited range. could not.

According to the insulation defect detection method of the present invention, (1) a high voltage that causes a dielectric breakdown is applied, and a precursor partial discharge that causes a breakdown is detected and cut off, so that only a clearly harmful partial discharge is detected. be able to.

(2) Since a lower voltage value than before is recharged in a state where the insulator is damaged to some extent by the precursor partial discharge, a large partial discharge can be detected despite the low applied voltage, and further, damage re-progression due to it. Since there are few, it becomes possible to locate the damaged position relatively stably.

(3) There is little possibility of dielectric breakdown during measurement, and even if dielectric breakdown occurs, the applied voltage itself is low, so there is little damage to the measuring instrument, making it possible to measure with a high-grade measuring instrument and more accurate detection. You can

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of an apparatus for detecting a pre-partial discharge used in the method for detecting an insulation defect of a power cable of the present invention, shutting off the power source based on it, and damaging the defect to some extent, FIG. 2 is an electric circuit diagram of a partial discharge pulse polarity discriminating device for re-charging a low voltage to generate a slight partial discharge for locating a defective portion of the damaged test power cable. . 5 ... Test power cable 6 ... Partial discharge detection resistance 7 ... Partial discharge measuring instrument 10, 10 '... Sheath side electrode 12 ... Pulse transformer 13 ... Polarity discrimination device

Claims (1)

[Claims] 1. A high voltage is applied to a power cable to generate an electrical tree in an insulator to cause deterioration of charging, thereby detecting a partial discharge pulse, and then continuing charging. The partial discharge gradually increases, the power is cut off when it is understood that if the electrical tree extends the insulator of the power cable and continues to apply power as it is, dielectric breakdown will occur, and power will be applied again from a low voltage. First, gradually increasing the pressure to generate a partial discharge pulse, locating the generation position, extracting the defective part where the electrical tree is occurring, and detecting the insulation defective part of the part. A method for detecting insulation defects in a power cable.