JPH02227657A - Detector for partial discharge - Google Patents

Abstract

PURPOSE:To remove a noise signal regardless of the level size by comparing a DC reference signal obtained from the rectifying and smoothing of detected signals with the detected signals and interrupting the signals with the level lower than that of the DC reference signal among the detected signals. CONSTITUTION:A sensor 11 for detecting a partial discharge sound is arranged on the outer periphery of a cable connection part 10 so as be brought into contact therewith. When the detected signals (partial discharge signal S and noise signal N are mixed therein) 12 outputted from the sensor 11 are processed by a reference signal generating circuit 23, the DC reference signal 24 made by smoothing the signals 12 is obtained. The smoothness is made so that the DC signal including voltage variation with the degree corresponding to the envelope of the signal N is obtained. That is, the circuit constants of a smoothing device 23B in the circuit 23 are settled in the manner such as the above. When this signal 24 is supplied to a limiter circuit 22, the operation is made in the circuit 22 so that the signal levels with the absolute values lower than that of the signal 24 making the zero level of the signals 12 as the reference are interrupted. Then, only the signal S made by removing the signal N from the signals 12 is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a partial discharge detection device for detecting partial discharge generated inside an insulator or the like of an electric cable.

(Technical background of the invention and its problems) When a high voltage is applied to a dielectric (insulator), if there is an electrical defect such as a void inside the insulator, the electric field will concentrate in that part and cause electrical discharge.

For example, if such a partial discharge occurs in the insulator of a high-voltage cable for power transmission, the insulator will deteriorate from that part, and in the worst case, dielectric breakdown will occur.To prevent this, A method is known in which a partial discharge occurring in a cable insulator is acoustically detected in advance. This belongs to a type of non-destructive testing method called the acoustic emission method.

Generally, when a partial discharge occurs, a discharge sound is generated from the discharge location. This discharge sound propagates in the cable insulation as a sound wave. Therefore, by bringing an acoustic detection element such as an ultrasonic sensor into contact with the outer periphery of the cable insulator, the location and degree of partial discharge can be detected.

By the way, when performing such acoustic detection with high sensitivity, noise reduction measures become a particular problem. There are many types of noise, but it is also necessary to remove thermal noise generated by the ultrasonic sensor and its peripheral circuits, as well as other stationary noise. In particular, in a signal processing circuit, noise amplified to a high level may have an adverse effect at the stage of setting the optimum detection frequency.

Conventionally, in order to remove this type of noise, a limiter circuit in which a fixed removal level V is set has been used. This circuit operates as follows.

FIG. 3 is an explanatory diagram of the operation of a conventional limiter circuit.

In the figure, the detection signal l of the ultrasonic sensor, that is, the sensor for detecting partial discharge sound, includes an acoustic signal actually generated by partial discharge (hereinafter referred to as partial discharge signal S) and a steady noise signal N. It's mixed. When such a signal is input to the limiter circuit 2, the signal having a level below the removal level V set in the limiter circuit 2 is cut and output. As a result, only the partial discharge signal S is output to the output side of the limiter circuit 2.

However, when such a limiter circuit 2 is used, the following problems occur.

First, when the level of the partial discharge signal S is below this removal level V, even the partial discharge signal S is cut by the limiter circuit 2, making it impossible to obtain the necessary output.

On the other hand, as shown in FIG. 4, when the level of the noise signal N is higher than the removal level V set in the limiter circuit 2, the noise it number N' that could not be completely removed is present in the output signal of the limiter circuit 2. mixed in, making it impossible to obtain a sufficient noise removal effect.

(Object of the Invention) The present invention has been made with attention to the above points, and includes a part that can effectively remove the noise signal that occurs constantly as described above, regardless of the magnitude of the signal level. The object of the present invention is to provide a discharge detection device.

(Summary of the Invention) A partial discharge detection device of the present invention includes a partial discharge sound detection sensor and a signal processing circuit that processes a detection signal of the partial discharge sound detection sensor, and the signal processing circuit processes the detection signal of the partial discharge sound detection sensor. a reference signal generation circuit that rectifies and smoothes the signal to obtain a DC reference signal, and compares the detection signal and the DC reference signal;
The present invention is characterized in that it includes a limiter circuit that cuts signals of a level lower than the DC reference signal from among the detection signals.

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

FIG. 1 is a block diagram showing an embodiment of the partial discharge detection device of the present invention.

In the figure, a partial discharge sound detection sensor 11 is placed in contact with the outer circumferential portion of the cable connection portion 10 . The detection signal 12 of this partial discharge sound detection sensor 11 is
The signal is input to the signal processing circuit 20 and processed. This signal processing circuit 20 includes a preamplifier 21, a limiter circuit 22,
It has a reference signal generation circuit 23.

The preamplifier 21 is a circuit that receives and amplifies the detection signal 12 of the partial discharge detection sensor 11 and outputs the amplified signal to the limiter circuit 22 and the reference signal generation circuit 23. The reference signal generation circuit 23 is provided with a rectifier 23A and a smoother 23B made of diodes and the like. The reference signal generation circuit 23 is a circuit that receives the detection signal output from the preamplifier 21, rectifies it, and smoothes it with an appropriate time constant to obtain a DC reference signal 24. This DC reference signal 24 is output to the control terminal 22A of the limiter circuit 22. Note that this DC reference signal 24 is obtained by directly rectifying and smoothing the detection signal input to the reference signal generation circuit 23, and thus becomes a DC signal that fluctuates in response to fluctuations in the detection signal.

The limiter circuit 22 receives the amplified detection signal output from the preamplifier 21, and receives the amplified detection signal from the reference signal generation circuit 23.
This circuit compares the DC reference signal 24 outputted from the DC reference signal 24 with the detection signal, and cuts the signals of the detection signal whose level is lower than the DC reference signal 24. This circuit can be configured by, for example, a comparison amplifier circuit made of an operational amplifier or the like.

FIG. 2 is an explanatory diagram of the operation of the partial discharge detection device of the present invention shown in FIG. 1.

As shown in FIG. 2, the detection signal 12 output from the partial discharge detection sensor 11 shown in FIG. 1 includes a partial discharge signal S and a noise signal N mixed together. When this detection signal 12 is processed by the reference signal generation circuit 23, a DC reference signal 24 obtained by smoothing the detection signal 12 is obtained. In this case, the smoothness of the reference signal generation circuit 23 is optimally set to such a level that a DC signal including voltage fluctuations corresponding to the envelope of the noise signal N can be obtained. That is, the circuit constants of the smoother 23B of the reference signal generation circuit 23 shown in FIG. 1 are set in this way.

The DC reference signal 24 thus obtained is supplied to the limiter circuit 22. In this limiter circuit 22, the detection signal 12 “
With the 0° level as a reference, both the + side and the one side operate to cut signals whose absolute values are at a level below the DC reference signal. Then, as shown in the figure, only the partial discharge signal S obtained by removing the noise signal N from the detection signal 12 is output.

That is, in the device of the present invention, the removal level for operating the limiter circuit 22 is configured to change in accordance with the envelope of the noise signal actually included in the detection signal, so that the noise signal S is When the level is high, the level to be cut is high, and conversely, when the level of the noise signal S is low, the level to be cut is low, so that no noise signal remains in the output signal. In addition, when the noise signal level is relatively low, the partial discharge signal S with a relatively low level
can also be taken out to its output side.

The present invention is not limited to the above embodiments.

As mentioned above, it is desirable that the DC reference signal match the envelope of the noise signal N, but in reality, the noise signal changes in a relatively long period, and the partial discharge signal included in this signal changes in a relatively long period. Since the ratio is relatively small, even if the detection signal is rectified with a sufficiently large time constant, the effects of the device of the present invention described above can be achieved. Further, the signal processing circuit is not necessarily limited to the above-described block configuration, and may be a circuit having various equivalent functional configurations.

(Effects of the Invention) The partial discharge detection device of the present invention described above obtains a DC reference signal according to the noise signal level of the input detection signal,
Since the noise signal is removed from the detection signal, it can be completely removed whether the noise signal level is high or low.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the partial discharge detection device of the present invention, FIG. 2 is an explanatory diagram explaining its operation, and FIGS. 3 and 4 are operations of a limiter circuit in a conventional partial discharge detection device. FIG. 10-11---Connection part, 11-11---Partial discharge sound detection sensor, 12-
11-----Detection signal, 20-----11-1 Signal processing circuit, 21-----Preamplifier, 22-----m-Limiter circuit, 23-- -11--Reference signal generation circuit, 24-111--DC reference signal. (1 other person) 10---------One connection part 11-----Partial discharge'i! Detection sensor 1
2---------m-Detection signal 20---11---Signal processing circuit 21---11---Preamplifier 22---------Limiter circuit 23- 11------Reference signal generation circuit 24------
11---Direct Mll (No. 1i No.

Claims (1)

[Claims] The signal processing circuit includes a sensor for detecting partial discharge sound and a signal processing circuit for processing a detection signal of the sensor for detecting partial discharge sound, and the signal processing circuit rectifies and smoothes the detection signal to obtain a reference signal to obtain a DC reference signal. A partial discharge detection device comprising: a generation circuit; and a limiter circuit that compares the detection signal with the DC reference signal and cuts signals of a level lower than the DC reference signal among the detection signals.