JP6989232B2 - Partial discharge measuring device - Google Patents

Description

The present invention relates to a partial discharge measuring device for a ground wire or the like of the equipment to be measured.

Conventionally, in order to maintain high reliability of power transmission and distribution equipment and the like, it has been required to accurately monitor their status. Therefore, partial discharge (discharge that occurs only in a part of the insulating portion between conductors) generated in a power transmission / distribution facility or the like is measured.

As an example of a partial discharge measuring device for measuring such a partial discharge, a device that detects a high frequency current flowing through a ground wire with a high frequency current transformer is known. In such a partial discharge measuring device, various measures are taken against noise entering the ground wire (see, for example, Patent Document 1).

The partial discharge measuring device according to Patent Document 1 is provided with a filter in which a filter winding is wound around an iron core and the filter winding is blocked from passing a current in a specific frequency range. With such a configuration, of the magnetic flux generated in the iron core, a current that cancels the magnetic flux component due to the current other than the specific frequency range flows in the filter winding. As a result, only the current in a specific frequency range flows through the secondary winding wound around the iron core, and partial discharge can be detected with high sensitivity.

On the other hand, depending on the location where the partial discharge measurement is performed, a large commercial frequency current may flow in the ground wire due to three-phase imbalance or the like. In this case, a signal due to a commercial frequency current is superimposed on the output of the partial discharge measuring device. However, when the commercial frequency current becomes further large, there is a problem that the partial discharge measuring device is magnetically saturated, the dynamic range cannot be secured, and the measurement sensitivity is lowered.

The partial discharge measuring device according to Patent Document 1 has not been effective for such a problem. When trying to remove a signal due to a commercial frequency current as noise, it has an attenuation characteristic close to zero in the commercial frequency band (for example, 50 Hz or 60 Hz) and almost no attenuation in other frequency bands. This is because it is difficult to make a filter. Further, when a specific frequency range including the commercial frequency band is set, the commercial frequency current can be reduced, but the signal due to the partial discharge is also reduced, and the detection sensitivity of the partial discharge is lowered.

It should be noted that such a problem exists not only when a commercial frequency current flows through the ground wire but also when a current having a specific frequency flows.

Japanese Unexamined Patent Publication No. 9-15293

In view of such circumstances, it is an object of the present invention to provide a partial discharge measuring device capable of reducing a decrease in dynamic range due to a current flowing in a specific frequency and improving measurement sensitivity.

The first aspect for achieving the above object is an iron core in which a magnetic flux is generated by a current flowing through a lead wire connected to a power device of the equipment to be measured, a secondary coil around the iron core, and a canceling coil. The canceling means comprises a canceling means for supplying the canceling coil with a canceling current having a phase opposite to the current of the specific frequency flowing through the secondary coil, and the canceling means extracts the current of the specific frequency flowing through the secondary coil. The low-pass filter to be used and the AC signal from the low-pass filter are converted into a DC signal, and a signal is generated as the cancel current so that the AC signal output from the low-pass filter becomes zero based on the level of the DC signal. The partial discharge measuring apparatus is characterized by comprising an anti-phase generating unit.

In the first aspect, of the current output from the secondary coil, only a specific frequency is detected, and a canceling current that cancels this is supplied to the canceling coil. That is, since noise is not canceled over a wide range of frequencies, it is possible to avoid a decrease in the signal due to partial discharge as in the prior art, and it is possible to improve the detection sensitivity of partial discharge. More preferably, a cancellation current can be generated.

A second aspect of the present invention is in the partial discharge measuring device according to the first aspect, wherein the specific frequency is a commercial frequency.

In the second aspect, the influence of the commercial frequency can be reduced and the partial discharge can be detected with high sensitivity.

According to the present invention, there is provided a partial discharge measuring device capable of reducing a decrease in dynamic range due to a current flowing in at a specific frequency and improving measurement sensitivity.

It is a schematic diagram of a partial discharge measuring device. It is a block diagram of a partial discharge measuring apparatus. It is a graph which shows the current flowing through a ground wire, a canceling coil and a secondary coil in time series when the canceling current is not supplied. It is a graph which shows the current flowing through a ground wire, a canceling coil, and a secondary coil in time series when the cancellation current is supplied.

<Embodiment 1>
FIG. 1 is a schematic view of the partial discharge measuring device according to the present embodiment, and FIG. 2 is a block diagram of the partial discharge measuring device according to the present embodiment.

As shown in FIGS. 1 and 2, the partial discharge measuring device 1 removes noise due to the iron core 3, the secondary coil 4, the canceling coil 5, and the commercial frequency current that circulate around the ground wire 2 to be measured. The canceling means 10 and the like are provided.

The ground wire 2 is an example of a conducting wire electrically connected to the electric power device of the equipment to be measured. Examples of the electric power device include a transformer, a reactor, a capacitor, a rectifier, a circuit breaker, a switchgear, a switchboard, a power cable, and the like.

The iron core 3 is a general iron core used in a high-frequency current transformer, and is formed in an annular shape in the present embodiment. Of course, the iron core 3 is not limited to the annular shape, and may be, for example, a clamp shape.

Further, the ground wire 2 is inserted in the ring of the iron core 3, but the present invention is not limited to this mode. For example, the ground wire 2 may be wound around the iron core 3. In any case, the iron core 3 may be a structure / material in which a magnetic flux is generated by a current flowing through the ground wire 2.

The secondary coil 4 is a coil wound around the iron core 3. The number of turns of the secondary coil 4 is not particularly limited. The secondary coil 4 is connected to the distributor 13, and the current output from the secondary coil 4 is distributed to the output unit 14 and the canceling means 10 by the distributor 13.

The distributor 13 is a general signal distributor, and the output unit 14 is an oscilloscope or the like for displaying the current output from the secondary coil 4, but is not particularly limited.

The canceling coil 5 is a coil wound around an iron core 3. Further, the canceling coil 5 is supplied with a canceling current from the canceling means 10. The cancel current is a current having a phase opposite to the current of a specific frequency flowing through the secondary coil 4. Here, the specific frequency is a commercial frequency (50 Hz or 60 Hz). The generation of the cancel current will be described later.

The canceling means 10 is an electric circuit that generates the above-mentioned canceling current and supplies it to the canceling coil 5. Specifically, the canceling means 10 includes a low-pass filter 11 and an anti-phase generation unit 12.

The low-pass filter 11 takes the current output from the secondary coil 4 as an input, and extracts only the current of the commercial frequency. Such a low-pass filter can be realized by a known circuit configuration. The commercial frequency AC signal output from the low-pass filter 11 is input to the anti-phase generation unit 12.

The anti-phase generation unit 12 is an electric circuit that generates an anti-phase signal based on the AC signal extracted by the low-pass filter 11. As an example of such an electric circuit, a circuit provided with an AC / DC converter, a comparison unit, and a signal generation unit can be mentioned.

The AC / DC converter converts the AC signal from the low-pass filter 11 into a DC signal. The comparison unit outputs the level (potential) of the DC signal output by the AC / DC converter with the zero potential as a reference. The signal generation unit generates a signal such that the AC signal output from the low-pass filter 11 becomes zero based on the level of the DC signal output from the comparison unit. Then, this signal is supplied to the canceling coil 5 as a canceling current.

In this way, the canceling means 10 extracts the commercial frequency component from the current output from the secondary coil 4 and supplies the canceling current to the canceling coil 5 so as to cancel the commercial frequency component.

By supplying such a canceling current to the canceling coil 5, the magnetic flux generated from the canceling coil 5 cancels out the magnetic flux generated in the iron core 3 due to the current of the commercial frequency component. As a result, the current output from the secondary coil 4 is such that the current of the commercial frequency is removed or reduced.

Since the commercial frequency current is removed or reduced from the current output from the secondary coil 4, the decrease in the dynamic range in the partial discharge measurement can be reduced, and the measurement sensitivity of the partial discharge can be improved. ..

In the prior art, a low-pass filter allows a frequency component lower than the cutoff frequency f1 to flow in the filter winding provided with the filter, and a high-pass filter allows a current due to noise having a frequency higher than the cutoff frequency f2 to flow. As a result, among the magnetic flux generated in the iron core, the magnetic flux component due to the noise is canceled, the noise is not picked up by the secondary winding, and the detection sensitivity of the partial discharge is improved.

However, since the frequency of partial discharge is wide, as a result of removing noise in a wide frequency range as described above, the signal due to partial discharge is also reduced.

On the other hand, the partial discharge measuring device 1 of the present embodiment detects only the commercial frequency, which is a specific frequency, among the currents output from the secondary coil 4, and supplies the canceling current to the canceling coil 5 to cancel the current. Is. That is, since noise is not canceled over a wide range of frequencies, it is possible to avoid a decrease in the signal due to partial discharge as in the prior art, and it is possible to improve the detection sensitivity of partial discharge.

With reference to FIGS. 3 and 4, the current output from the secondary coil 4 will be described before and after applying the cancel current.

FIG. 3 is a graph showing the currents flowing through the ground wire 2, the canceling coil 5, and the secondary coil 4 in chronological order when the cancel current is not supplied. Reference numeral 30 indicates the current of the ground wire 2, reference numeral 31 indicates the current of the canceling coil 5, and reference numeral 32 indicates the current flowing through the secondary coil 4. The vertical axis of reference numerals 30 and 31 is the current value, the vertical axis of reference numeral 32 is the voltage value, and the horizontal axis is time.

A commercial frequency current (reference numeral 30) is flowing through the ground wire 2. Since the canceling current (reference numeral 31) is not supplied to the canceling coil 5, the current value is zero. In such a case, it can be seen that the current (reference numeral 32) of the secondary coil 4 has a commercial frequency current superimposed on the partial discharge current.

FIG. 4 is a graph showing the currents flowing through the ground wire 2, the canceling coil 5, and the secondary coil 4 in chronological order when the cancel current is supplied. Reference numeral 40 indicates a current of the ground wire 2, reference numeral 41 indicates a current of the canceling coil 5, and reference numeral 42 indicates a current flowing through the secondary coil 4. The vertical axis and the horizontal axis are the same as in FIG.

Similar to FIG. 3, a commercial frequency current (reference numeral 40) flows through the ground wire 2. On the other hand, the canceling coil 5 is supplied with a cancellation current (reference numeral 41) having a phase opposite to that of the commercial frequency current. In such a case, it can be seen that the current of the secondary coil 4 (reference numeral 42) does not overlap with the current of the commercial frequency, and only the current of the partial discharge appears.

1 ... Partial discharge measuring device, 2 ... Ground wire, 3 ... Iron core, 4 ... Secondary coil, 5 ... Canceling coil, 10 ... Canceling means, 11 ... Low-pass filter, 12 ... Opposite phase generator, 13 ... Distributor, 14 ... Output unit

Claims (2)

An iron core in which magnetic flux is generated by the current flowing through the conductor connected to the power equipment of the equipment to be measured,
The secondary coil that winds the iron core, the canceling coil, and
A canceling means for supplying a canceling current having a phase opposite to the current of a specific frequency flowing through the secondary coil to the canceling coil is provided .
The cancellation means is
A low-pass filter that extracts the current of a specific frequency flowing through the secondary coil,
An antiphase generator that converts an AC signal from the low-pass filter into a DC signal and generates a signal such that the AC signal output from the low-pass filter becomes zero based on the level of the DC signal as the cancel current. And, a partial discharge measuring device characterized by being provided. In the partial discharge measuring device according to claim 1,
A partial discharge measuring device characterized in that the specific frequency is a commercial frequency.

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