JPH0210274A - Partial discharge detecting method for electric power cable - Google Patents

Abstract

PURPOSE:To facilitate the measurement of the position where partial discharge is generated and the estimation of the cause of the dielectric breakdown of a specimen cable by utilizing a part of the specimen cable as a coupling capacitor. CONSTITUTION:When a test voltage which is applied to the conductor of a specimen cable 1 from a power source 3 is close to a dielectric breakdown voltage, partial discharge is generated in the insulator of the cable 1. The signal is propagated along the entire length of the cable 1. Ring shaped parts 4a and 4b in the vicinities of both ends of the cable 1 face through the conductor and the insulator of the cable 1. The parts 4a and 4b serve the role of a coupling capacitor. Detecting parts 51 and 52 of a partial discharge detector 5 detect the partial discharge through the ring shaped parts 4a and 4b. Furthermore, a time difference operating part 53 captures the time difference between the partial discharges of the parts and can obtain the fact that at what position the discharge occurs relatively accurately. When the signal which is synthesized 54 from the detected signals of the detecting parts 51 and 52 exceeds a specified level, the power source 3 is cut 3a with a generated pulse.

Description

[Detailed Description of the Invention] (Technical Field of the Invention) The present invention relates to a method for detecting partial discharge of a power cable carried out in a destructive test of the power cable (Technical background of the invention and its problems) Characteristic test of a power cable There are destructive tests and non-destructive tests. In order to investigate the insulation characteristics of a power cable, a test voltage higher than its breakdown voltage is applied to actually cause breakdown, and the cause of the breakdown is investigated.

Usually, in this destructive test, after a test voltage is applied, a coupling capacitor is attached to the sample cable during the voltage application to measure partial discharge. After the insulation of the sample cable is completely destroyed, turn off the power circuit breaker.

However, in such conventional testing methods, even if the fracture point is investigated after the test is completed, the cause of the defect is often burned away along with the fracture, making it difficult to estimate the cause of the fracture.

Also, while it is possible to measure the size of partial discharge during energization, it is extremely difficult to find the location where it occurs.
In reality, the time difference between the partial discharge signal that directly reaches the detection end and the partial discharge signal that reaches the other end of the sample cable after being reflected, or the sample cable is actually cut in half. The method used is to cut ties with them while pushing them further.

However, when the partial discharge signal, which is originally extremely small, is reflected at the other end of the sample cable, it is further attenuated and detection is not easy.Also, the method of cutting the edge of the sample cable in half at a time is relatively complicated and difficult to work with. bad.

Also, for example, if both ends of the sample cable are sealed by a case such as a mini-clad, it is not easy to connect a coupling capacitor, and it is extremely difficult to detect partial discharge as is. There was also a drawback.

(Objective of the Invention) The present invention has been made with attention to the above points, and it detects partial discharges in power cables, which makes it easy to measure the location of partial discharge occurrence and to easily estimate the cause of dielectric breakdown of the sample cable. The purpose is to provide a method.

(Summary of the Invention) The method for detecting partial discharge in a power cable of the present invention involves dividing and cutting the metal sheath of the sample cable in the longitudinal direction near both ends of the sample cable to form an electrically independent annular portion. While a power supply is connected to the conductor of the sample cable and a test voltage is applied, a partial discharge generated inside the sample cable is detected through the annular portions at both ends, and when this partial discharge is detected, the The present invention is characterized in that the power supply is cut off and the position of occurrence of the partial discharge inside the sample cable is calculated from the detection time difference of the partial discharge detected through the annular portions at both ends of the sample cable.

(Example of the invention) Hereinafter, the present invention will be explained in detail using embodiments shown in the drawings.

FIG. 1 is a wiring diagram of a detection circuit that implements the method for detecting partial discharge in a power cable according to the present invention.

In the figure, both ends of the sample cable 1 are terminated by a bushing 2 or the like, and one end of the conductor is connected so that a test voltage is applied by a power source 3. or,
The metal sheath of the sample cable 1 is grounded at both ends and at the center. Near both ends of the sample cable 1, this metal sheath is longitudinally divided and edged to form electrically independent annular portions 4a and 4b.

In this way, the annular portions 1a and 4b that are electrically independent from the metal sheath of the sample cable 1 have a detection impedance Ra
, Rb are connected.

The other ends of the detection impedances Ra and Rb are grounded. Here, the detection impedances Ra and Rb are normal resistors. The annular portions 4a and 4b are electrically connected to detection terminals 5a and 5b of the partial discharge detector 5, respectively.

A pulse generator 6 is connected to the partial discharge detector 5 and generates a trigger pulse based on the partial discharge detection signal. The trigger pulse of the pulse generator 6 is supplied from the power supply 3.
The circuit breaker 3a is connected to the circuit breaker 3a built in the circuit breaker 3a.

The partial discharge detector 5 includes detection units 51 and 52 having a conventional partial discharge detection function, a time difference calculation unit 53 that calculates the detection time difference, and a pulse generator 6 that transmits the detection of partial discharge. It is composed of a notification section 54.

When the notification unit 54 notifies the partial discharge detection, the pulse generator 6 generates a predetermined trigger pulse that trips the circuit breaker 3a of the power supply 3. The circuit breaker 3a is composed of a trip coil (not shown), a disconnector, etc., which have been conventionally used to interrupt power circuits.

When the above connections are made, first, when a test voltage is applied to the conductor of the sample cable 1 by the power supply 3, if the test voltage is close to the breakdown voltage, partial discharge will occur inside the insulator of the sample cable 1. do. This partial discharge signal propagates over the entire length of the sample cable. On the other hand, the annular parts 4a and 4b provided near both ends of the sample cable are opposed to the conductor of the sample cable via the insulator, so they act as coupling capacitors, and the annular parts 4a and 4b Through the detection unit 5 of the partial discharge detector 5
1 and 52 detect the partial discharge. Rain detection section 51.5
The timing of detecting the partial discharge in step 2 differs depending on where on the sample cable 1 the partial discharge occurs.

The time difference calculation unit 53 in the partial discharge detector 5 captures the time difference between partial discharge detection and outputs the calculation result to a display device (not shown).If the propagation speed of the 0-part electric signal is known in advance, From the detection time difference, it is possible to relatively accurately determine at which position on the sample cable 1 the partial discharge has occurred.

On the other hand, the level of the partial discharge signal detected by the detection section 51 or the detection section 52 gradually increases as the destruction of the sample cable progresses.

For example, the notification unit 54 receives these two signals as is, combines them, and outputs the result to the pulse generator 6.

The pulse generator 6 outputs a trigger pulse that trips the circuit breaker 3a of the power supply 3 when the signal exceeds a predetermined threshold level. The pulse generator 6 can be configured, for example, by a conventionally known simple comparison circuit. The circuit breaker 3a receives this trigger pulse from the pulse generator 6 and immediately cuts off the power supply 3.

If the level of the partial discharge signal to generate the trigger pulse is appropriately set using the pulse generator 6,
It is possible to cut off the power supply 3 before the sample cable l is completely destroyed. In addition, in the detection units 51 and 52,
Since the partial discharge signal is captured directly rather than as a reflected wave, the signal level is relatively high, and by increasing the resolution of the time difference calculating section 53, it is possible to evaluate the partial discharge occurrence position with high accuracy.

The present invention is not limited to the above embodiments.

In the above example, partial discharge was detected only for the sample cable, but even if an accessory is connected to one end of the sample cable, a destructive test including the accessory can be performed. It is possible.

(Effects of the Invention) According to the method for detecting partial discharge in a power cable of the present invention described above, since a part of the sample cable is used as a coupling capacitor, the construction is easy, and both ends of the sample cable are sealed. This makes it possible to detect partial discharges even in cases where Furthermore, since the power supply is cut off before the sample cable is completely destroyed, it becomes easier to investigate the cause of the discharge. Furthermore, since partial discharge signals are extracted from both ends of the sample cable, there is also the advantage that the location where the partial discharge occurs can be accurately and quickly evaluated.

[Brief explanation of the drawing]

FIG. 1 is a wiring diagram of a detection circuit implementing the method for detecting partial discharge in a power cable according to the present invention. 1--------m-sample cable, 2----1--
---Terminal, 3---1--1--Power supply, 3a--1--1--Breaker, 4a, 4b--Circular part, 5----- --111 partial discharge detector, 6---
--------Pulse generator. I ----------KO4 cable 2----------One end 3----Power supply 3a ------------One cutoff [! JT device 4a4b---
---Instigation 5--Partial discharge detector 6-1--111--Pulse generation 8 Fig.

Claims (1)

[Claims] Near both ends of the sample cable, the metal sheath of the sample cable is longitudinally divided and edged to form an electrically independent annular portion, and a power source is connected to the conductor of the sample cable to apply a test voltage. On the other hand, a partial discharge generated inside the sample cable is detected through the annular portions at both ends of the sample cable, and when this partial discharge is detected, the power source is immediately cut off, and the partial discharge is detected through the annular portions at both ends of the sample cable. A method for detecting partial discharge in a power cable, characterized in that the position of occurrence of the partial discharge inside the sample cable is calculated from the detection time difference of the partial discharge.