JPH068842B2 - Partial discharge detection method for electrical equipment - Google Patents

Description

The present invention relates to a partial discharge detection for detecting partial discharge of an electric device covered with a metal container, such as a gas insulated switchgear, a gas insulated transformer and a gas insulated cable. It is about the method.

[Prior Art] As a method of detecting a partial discharge (corona discharge) generated in a container of an electric device such as a gas insulated switchgear, an electromagnetic wave generated by the partial discharge is detected by using an antenna arranged in the container of the electric device. There is a way to do it.

The antenna arranged in the container of the electric device is an electromagnetic wave generated by the partial discharge, an external radio wave included in a band such as a long wave and a medium wave received by the metal container of the electric device as an antenna, and the electric device. It also receives extraneous radio waves contained in the band such as short-wave and ultra-high-frequency waves that enter from cables that are drawn by. The weak electromagnetic waves generated by the partial discharge are detected in the form of being buried in these external radio waves, and therefore a detailed analysis of the detection signal is required to make the determination.

Therefore, in the conventional detection method of this type, the electromagnetic wave detected by placing the antenna in the container of the electric device is input to the spectrum analyzer, and the frequency spectrum obtained by this spectrum analyzer is used as the frequency spectrum when there is no partial discharge. Partial discharge was detected by comparison.

[Problems to be Solved by the Invention] In the conventional partial discharge detection method, since a spectrum analyzer is used, there is a problem that an apparatus for carrying out the detection method becomes expensive.

In the conventional method, a spectrum analyzer is used because radio waves coming in from cables connected to electrical equipment and radio waves received by the electrical equipment container acting as an antenna have a great influence on detection results. However, it was often difficult to accurately detect partial discharge.

Furthermore, when detecting an electromagnetic wave generated by a partial discharge using an antenna arranged in the container of an electric device, by limiting the detection frequency band, the detection sensitivity is increased, but conventionally, Since the detection frequency band was selected to be a band where the level of electromagnetic waves generated by partial discharge was high, external radio waves could be greatly affected even when the band was limited, and external radio waves and electromagnetic waves due to partial discharge could be clearly separated. In many cases, they could not be detected accurately.

An object of the present invention is to accurately detect a partial discharge by capturing an electromagnetic wave generated by the partial discharge without using an expensive device and being hardly affected by noise such as an external radio wave. Another object is to propose a partial discharge detection method for electric equipment.

[Means for Solving the Problems] The present invention provides a partial reception by receiving an electromagnetic wave generated by a partial discharge generated in an electric device covered with a metal container with a band limited by an antenna arranged in the container. The present invention relates to a partial discharge detection method for detecting discharge.

In the present invention, the signal received by the antenna is AM
After detection, it is converted into an audio signal to detect partial discharge.
When receiving, the lower limit frequency of the electromagnetic wave band to be received is set to 1 MHz or higher, and the upper limit frequency of the band is 6 MHz or more.
At a frequency of 0 MHz or less, and until the intensity of external radio waves radiated from the external circuit toward the antenna through the conductor portion of the electric device reaches the position of the antenna from the conductor portion is -2.
The frequency is set to be equal to or lower than the frequency that attenuates to 0 dB.

[Operation] When the antenna is arranged in the metal container of the electric device, the antenna includes an electromagnetic wave generated by the partial discharge and an external radio wave received by the metal container of the electric device as an antenna.
It receives external radio waves coming in from cables through the conductors of electrical equipment.

From the results of various experiments, the lower limit of the receiving band is 1MHz
With the above settings, when an external radio wave that has entered the inside due to the reception of the metal container of the electric device as an antenna is detected by the antenna arranged in the metal container and converted into a voice signal by AM detection, the external It has been clarified that the audio signal output of the radio wave can be reduced to a level at which it is hardly heard.

Further, from the result of the experiment, as described above, the frequency of the upper limit of the band is 60 MHz or less, and the intensity of the external radio wave radiated from the external circuit toward the antenna through the conductor portion of the electric device is higher than that of the antenna. If the frequency is set to -20 dB or less before reaching the position, the electromagnetic waves generated by the partial discharge can be detected easily and reliably without being affected by external radio waves entering through the main circuit conductor of the electric equipment. Can be done

Therefore, according to the present invention, the electromagnetic wave generated by the partial discharge can be detected without being affected by the external radio wave, and the received signal can be converted into the audio signal by the AM detection without using the spectrum analyzer. Discharge can be detected. In this way, if the received signal is converted into the audio signal by the AM detection to detect the partial discharge, it is possible to detect the partial discharge using an inexpensive AM receiver, and therefore, the partial discharge detection method is implemented. Therefore, the cost of the device used for this can be reduced.

Embodiments Embodiments of the present invention will be described below with reference to the accompanying drawings.

When the antenna is arranged in a metal container accommodating the electric device, an electromagnetic wave received by the antenna is an electromagnetic wave generated by the partial discharge when a partial discharge occurs in the electric device,
External radio waves contained in the band of long waves, medium waves, etc. received by the metal container as an antenna, and external waves contained in the bands of short waves, ultra-short waves, etc. that penetrate through the conductors of the electric devices from the cables drawn in by the electric devices. Is. Then, when a partial discharge occurs in an electric device, the electromagnetic waves generated by the partial discharge are distributed in a wide frequency band ranging from a long wave to an ultra-short wave similar to the external radio wave. Therefore, in order to accurately detect the partial discharge, it is necessary to prevent reception of these external radio waves as much as possible.

In a relatively low frequency band, high-frequency current that flows through the metal container that houses electrical equipment also flows through the inner surface of the wall, so the metal container acts as an antenna and external radio waves received directly from the outside enter the container to some extent. I cannot avoid doing it.
When the frequency of the external radio wave becomes high, the high frequency current comes to pass through the surface of the metal container due to the skin effect, so the electromagnetic wave received by the metal container itself enters the container at a rate of
It gradually becomes smaller as the frequency increases.

FIG. 4 shows the results confirmed by the inventor's experiment, and the curve A in FIG. 4 shows the sound detected by the antenna arranged inside the metal container when an external radio wave from the outside becomes an antenna. The level of audibility when converted into a signal is shown with respect to frequency. Dotted line C in FIG. 4 indicates that when an electromagnetic wave generated by a partial discharge of an electric device is detected by an antenna arranged in a metal container and converted into an audio signal, it can be reliably detected that the electromagnetic wave is a partial discharge. This is the minimum level of ease. From the curve A and the dotted line C, when the frequency of the external radio wave entering from the outside by the metal container acting as an antenna exceeds 1 MHz, the level A of the audibility of the external radio wave is easy to hear the electromagnetic wave generated by the partial discharge. It was confirmed that the value was smaller than the level C. Therefore, if the receiving band is limited to 1 MHz or more, the influence of external radio waves coming in by the metal container as an antenna can be almost eliminated.

In addition, radio waves that enter through a cable or the like drawn into the electric device are radiated into the container from the main circuit portion of the electric device arranged in the metal container and received by the antenna. The radio waves radiated from the main circuit part of this electric device are
Radio waves with a frequency of about 600 KHz or less that are radiated more strongly with higher frequencies cannot be detected unless the antenna is in contact with the main circuit part, but as the frequency increases, even if the distance between the antenna and the main circuit part increases Radio waves can be detected.

According to the experiment, the level of easiness of hearing when an external radio wave radiated from the main circuit part is detected by an antenna and converted into a voice signal becomes smaller as the frequency becomes lower, as shown by a curve B in FIG. It was confirmed that when the frequency is less than 60 MHz, it becomes less than the level C of the easiness of hearing the electromagnetic wave generated by the partial discharge. Therefore, it has been clarified that the influence of external radio waves coming from the main circuit portion can be almost eliminated by limiting the receiving band to 60 MHz or less.

From the above examination results, the reception frequency band of electromagnetic waves is set to 1 MH
It has been clarified that the influence of external radio waves can be substantially eliminated by limiting the range from z to 60 MHz.

Further, it has been known that the influence of external radio waves from the main circuit portion varies depending on the position of the antenna arranged inside the electric device. It is preferable that the intensity of external radio waves at the antenna position should be attenuated to -20 dB or less. Then, the distance (-20 dB attenuation distance) D from the main circuit portion required to attenuate the intensity of the external radio wave to -20 dB was calculated with respect to the frequency f, and the result of FIG. 2 was obtained. The upper limit of the electromagnetic wave reception frequency band is 6
At 0 MHz, the preferred distance from the main circuit portion to the antenna was 1 m.

Next, it was examined whether or not the electromagnetic waves generated by the partial discharge could be detected within the limited band as described above. FIG. 3 shows an example of an experimental result of measuring the frequency distribution of electromagnetic waves generated by partial discharge in an electric device. In FIG. 3, a partial discharge is not generated and a partial discharge is generated. Shows. As a result of many such experiments, it became clear that the electromagnetic waves generated by partial discharge are distributed in a wide band.
It was confirmed that the partial discharge can be sufficiently detected even when the signal is received by limiting the band from z to 60 MHz.

As described above, when electromagnetic waves are received with the band limited in the metal container, there is a clear difference between the electromagnetic waves generated by the partial discharge and the external electromagnetic waves, so that the electromagnetic waves generated by the partial discharge can be easily generated. Can be detected. Therefore, it is not necessary to analyze the frequency of the received signal, and the partial discharge can be detected only by converting the received signal into a voice signal by using an ordinary AM receiver.

Next, with reference to FIG. 1, a configuration example of an apparatus for carrying out the detection method of the present invention will be described. In FIG. 1, reference numeral 1 is a metal container that houses an electric device, for example, a device that constitutes a gas-insulated switchgear, and 2 is a main circuit conductor of the electric device housed in the container 1. Although only a single main circuit conductor is shown in the drawing for simplification of description, the type of electric equipment housed in the container 1 is arbitrary. The main circuit conductor 2 is a bushing 3
It is connected to the power transmission line 4 via.

Antennas 5 are arranged in the container 1 at a predetermined distance d. The antenna 5 is arranged at a position sufficiently distant from the electric device so as not to affect the insulation of the electric device in the container 1. The output of the antenna 5 is input to the high frequency amplifier 6, and the output of this amplifier 6 is input to the mixer 7. The output of the local oscillator 8 is also input to the mixer 7 through the amplifier 9, and the mixer 7 performs heterodyne detection of the signal received by the antenna. That is, a signal having an intermediate frequency f1 to f2 corresponding to the difference between the frequency f1 of the signal obtained from the high frequency amplifier 6 and the output frequency f2 of the local oscillator 8 is output to the output side of the mixer 7. This signal is amplified by the intermediate frequency amplifier 10 and then given to the AM detector 11 to be detected, and the output of this detector is amplified by the low frequency amplifier 12 and given to the speaker 13 as an audio signal. The gain of the low frequency amplifier 12 can be adjusted by the variable resistor V ₁ .

When the method of the present invention is carried out, the lower limit frequency of the reception band is set to 1 MHz or higher, the upper limit frequency of the band is 60 MHz or lower, and the external circuit is directed toward the antenna through the conductor portion of the electric device. The intensity of the radiated external radio wave is set to be equal to or lower than the frequency at which it is attenuated to -20 dB until it reaches the position of the antenna from the conductor portion.

As described above, when the reception band is limited in this way, the electromagnetic waves generated by the partial discharge and the external radio waves can be clearly distinguished when converted into an audio signal, so that the electromagnetic waves generated by the partial discharge can be easily generated. Can be detected.

The reception band may be limited by selecting the antenna 5, or a selection amplifier may be used as the high frequency amplifier 6, or
Alternatively, it may be performed by inserting a filter in the front stage or the output stage of the high frequency amplifier 6.

As described above, according to the present invention, the lower limit frequency of the reception band is set to 1 MHz or higher, and the upper limit frequency of the band is set to
At a frequency of 60 MHz or less, and until the intensity of the external radio wave radiated from the external circuit toward the antenna through the conductor portion of the electric device reaches the position of the antenna from the conductor portion-
By setting below the frequency that attenuates to 20 dB,
It has become possible to easily detect only the electromagnetic waves generated by the partial discharge by eliminating the influence of the external radio waves.

Further, according to the present invention, since it is possible to eliminate the influence of external radio waves, it is possible to detect a partial discharge by converting a received signal into a voice signal by AM detection. There is an advantage that discharge can be accurately detected.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of an apparatus for carrying out the method of the present invention, and FIG. 2 is a distance and frequency between a radio wave radiation source and an antenna necessary for attenuating radio wave intensity to −20 dB. 3 is a diagram showing an example of a frequency distribution of electromagnetic waves generated by partial discharge, and FIG. 4 is a diagram showing the relationship between the electromagnetic waves generated by partial discharge and external radio waves into voice signals. It is the diagram which showed the easiness of hearing in the case of doing with respect to frequency. DESCRIPTION OF SYMBOLS 1 ... Metal container, 2 ... Main circuit conductor of electric equipment, 4 ... Transmission line, 5 ... Antenna, 6 ... High frequency amplifier, 7 ... Mixer, 8
... local oscillator, 9 ... amplifier, 10 ... intermediate frequency amplifier, 1
1 ... Detector, 12 ... Low-frequency amplifier.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-55-149062 (JP, A) JP-A-53-66581 (JP, A) JP-B-45-40384 (JP, B1) Official technology number 80- 3635

Claims (1)

[Claims] 1. A partial discharge for detecting the partial discharge by receiving an electromagnetic wave generated by a partial discharge generated in an electric device covered with a metal container with a band limited by an antenna arranged in the container. In the detection method, the lower limit frequency of the band of the electromagnetic wave to be received is set to 1 MHz or higher, the upper limit frequency of the band is 60 MHz or lower, and is radiated from the external circuit toward the antenna through the conductor part of the electric device. Set the intensity of the external radio wave to a frequency below -20 dB until it reaches the position of the antenna from the conductor part, and detect the partial discharge by converting the received signal to an audio signal and converting it to an audio signal. A method for detecting partial discharge of an electric device, comprising: