JPH09274063A - Partial-discharge measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a partial-discharge measuring device which has an excellent S/N ratio, by filtering out the component of periodic pulse-shaped noises. SOLUTION: This device comprise the following circuits: a comparing circuit 19 which outputs the trigger signal when the input signal including a partial- discharge signal and a noise signal exceeds a threshold vallue; a pulse generating circuit 23 which outputs the pulse signal based on the trigger signal; a period adjusting circuit 24 which adjusts the period of the pulse signal; a pulse-width adjusting circuit 25 adjusts the pulse width of the pulse signal; and a switching circuit 20 which uses the pulse signal, whose period and pulse width adjusted, as the control signal and blocks the passing of the periodic noise signal among the input signals. The partial-discharge signal is measured from the output signal of the switching circuit 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partial discharge measuring device used for measuring partial discharge of a power cable or the like,
In particular, it relates to a partial discharge device capable of easily measuring a partial discharge pulse by cutting periodic noise.

[0002]

2. Description of the Related Art A partial discharge measuring method is known as a method for diagnosing insulation of a power cable. In this partial discharge measurement method, for example, as disclosed in Japanese Patent Publication No. 6-7148, a detection impedance is connected to a sheath portion electrically insulated from each other by an insulating connection portion of a power cable via a foil electrode. In this state, the commercial cable high voltage is applied to the power cable.
When a partial discharge occurs in the insulator of the power cable, the high frequency pulse induced by this partial discharge flows through the detection impedance. The potential difference generated at both ends of the detection impedance at this time is detected by the partial discharge measuring device connected to this detection impedance, and the discharge pulse due to the partial discharge is measured.

However, since various noise components flow in the detected impedance in addition to the high frequency pulse induced by the partial discharge, a signal including this noise component can be captured by the partial discharge measuring apparatus. Therefore, S / N
Accurate partial discharge pulse measurements may be difficult due to the reduced ratio. Of such noise components, removal of noise components such as broadcast waves or sudden pulse noise has been conventionally performed. However, the periodic pulse noise of the noise component could not be sufficiently cut.

[0004]

Therefore, an object of the present invention is to remove the periodic pulse noise component to obtain S
An object of the present invention is to provide a partial discharge measuring device having an excellent / N ratio.

[0005]

The present invention adopts the following constitution in order to solve the above points. <Structure> The partial discharge measuring apparatus according to the present invention includes a cable,
A partial discharge measuring device for measuring a partial discharge signal generated from an insulator of an electric device or the like, which comprises a comparison means for outputting a trigger signal when an input signal including a partial discharge signal and a noise signal exceeds a threshold value, and a trigger. A pulse generating unit that outputs a pulse signal based on the signal, a period adjusting unit that adjusts the period of the pulse signal, a pulse width adjusting unit that adjusts the pulse width of the pulse signal, and a pulse whose period and pulse width are adjusted. A signal is used as a control signal, and a switching means for blocking passage of a periodic noise signal from among the input signal based on the control signal is provided, and the partial discharge signal is measured based on the output signal of the switching means. Is characterized by.

<Operation> The comparison means is S / S such as thermal noise.
A trigger signal corresponding to the periodic pulse noise having a large influence on the S / N ratio is generated from the noise components including low-level noise that does not substantially affect the N ratio. Since the trigger signal from the comparing means is used as a trigger for the pulse generating means, the pulse generating means produces a pulse signal which is synchronized with the periodic pulse noise. This pulse generating means, by the pulse width adjusting means,
A pulse signal having a pulse repetition length of the periodic pulse noise, that is, a pulse width slightly longer than each signal width of the periodic pulse noise can be generated, and the period of the pulse signal is variable by the period adjusting means. The switching means uses the pulse signal generated by the pulse generating means as a switch signal to open and close according to the pulse signal. By the opening / closing operation of the switching means, the sending of the output signal from the detected impedance to the display means is partially interrupted.

In the partial discharge measuring device according to the present invention, the period and pulse of the pulse signal are adjusted so that the pulse signal corresponding to the periodic pulse noise to be removed in advance can be sent from the pulse generating means to the switching means by the initial adjustment. By appropriately setting the width, a signal to the display means is provided so as to cut off the supply of the periodic pulse noise component from the detected impedance to the display means through the switching means to the display means. The route can be interrupted. By this initial adjustment, the supply of the set periodic pulse noise component to the display means is interrupted. Therefore, when the partial discharge measurement is started in the state of this initial adjustment, the output signal from the detection impedance is changed. Among them, the signal portion including the periodic pulse noise component included therein is partially cut. Therefore, the reduction of the S / N ratio due to the periodic pulse noise component is prevented, and the S / N ratio is improved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. <Specific Example> FIG. 1 is a block diagram schematically showing a partial discharge measuring apparatus according to the present invention. The partial discharge measuring apparatus 10 according to the present invention is used for measuring a partial discharge generated in an insulator of a power cable 11 such as a CV cable. A foil electrode 14 is formed on each of the sheath portions 13 electrically insulated from each other by the insulating connection portion 12 of the power cable 11. A detection impedance 15 is connected between both foil electrodes 14.

When a high voltage commercial frequency voltage is applied to the power cable 11 and a partial discharge occurs in one sheath portion 13 due to this voltage application, the other sheath portion 13 acts as a coupling capacitor, so Part 1
A slight voltage difference is generated between the three, and a current is induced. When this induced current flows through the detection impedance 15, a potential difference is generated across the detection impedance 15. In order to detect this potential difference as a discharge pulse, the partial discharge measuring device 10 is connected to the detection impedance 15. As is well known in the art, an amplifier 17 and a filter 18 for signal amplification are inserted in a signal bus 16 extending from the partial discharge measuring device 10 to the detection impedance 15.

The partial discharge measuring device 10 has a signal bus 1
6, a comparison circuit 19 inserted in the signal bus 6, a switching circuit 20 for opening and closing the signal bus 16, and a display means 2 such as an oscilloscope connected to the end of the signal bus 16.
1 is provided. A threshold setting circuit 22 is connected to the comparing circuit 19, and the comparing circuit 19 causes the pulse generating circuit 23 to generate a trigger pulse when the value of the signal flowing through the signal bus 16 exceeds the threshold set by the threshold setting circuit 22. To send.
The threshold level of the threshold setting circuit 22 is adjustable, and the level of the periodic pulse noise to be removed is selected by setting this threshold level to an appropriate value v (see FIG. 2 (A)). You can

The pulse generating circuit 23 includes a period adjusting circuit 24 for manually varying the period of the pulse generated when receiving the trigger pulse from the comparing circuit 19 and a pulse width adjusting circuit for manually varying the pulse width thereof. 25 are connected. In the initial adjustment, the comparison circuit 19 receives the first wave of the periodic pulse noise, and when a pulse is output from the comparison circuit 19 to the pulse generation circuit 23 in response to this, the pulse generation circuit 23 uses the pulse as a trigger. The signal is sent to the switching circuit 20. Since the period and pulse width of this pulse signal to the switching circuit 20 can be adjusted by the period adjusting circuit 24 and the pulse width adjusting circuit 25 in the initial adjustment, it is synchronous with the continuous signal width of the periodic pulse noise. Switching pulse signal 2
You can enter 0.

The switching circuit 20 opens and closes the signal bus 16 using the pulse signal from the pulse generating circuit 23 as a control signal. That is, of the binary signal from the pulse generating circuit 23, for example, a high level signal corresponding to the continuous signal width of the periodic pulse noise puts the signal bus 16 in the cutoff state, and a low level signal connects the signal bus 16. The switching circuit 20 operates so as to leave the state. As a result, of the signal from the detection impedance 15 flowing to the display means 21 via the signal bus 16, the predetermined periodic noise pulse portion set by the initial adjustment is cut, and the cut signal of this periodic noise pulse is obtained. It is sent to the display means 21.

<Operation of Specific Example> FIG. 2 is a timing chart showing the operation of the partial discharge measuring apparatus 10.
According to this timing chart, the partial discharge measuring device 10
Will be described. In the partial discharge measuring apparatus 10, prior to the partial discharge measurement of the power cable 11, initial adjustment for cutting periodic pulse noise is performed. FIG. 2 (A)
Shows the signal waveform of the noise component flowing through the signal bus 16 in this initial adjustment. Noise of a level lower than the threshold level v set by the threshold setting circuit 22 is a noise line segment that does not substantially affect the measurement, such as thermal noise, but is much higher than this low level noise. A high level of periodic pulse noise (a to f) is included in the noise component. In this example, each periodic pulse noise (a
~ F) has a period t of about 10 μsec, and a noise signal width Δt, which is a continuous repetition length of the high frequency pulse, is about 500 n.
Seconds.

When the pulse generation circuit 23 receives from the comparison circuit 19 the trigger signal output when the first wave of the periodic pulse noise shown in FIG. Using the corresponding pulse signal as a trigger, the period t set in the period adjusting circuit 24 and the pulse width adjusting circuit 2 are set.
The pulse signal having the pulse width Δt ′ set in 5 is sent to the switching circuit 20. Regarding the adjustment of the pulse width adjusting circuit 25, it is desirable to set the pulse width Δt ′ to be slightly larger than the noise signal width Δt so as to cope with the deviation of the period of the periodic pulse noise. This completes the initial adjustment work.

Note that the pulse adjustment by the period adjusting circuit 24 and the pulse width adjusting circuit 25 can be replaced by manual adjustment by automatic adjustment. In this case, pulse-like noises of different periods can be dealt with.

When the switching circuit 20 receives the pulse signal shown in FIG. 2B from the pulse generating circuit 23 as a control signal, the switching circuit 20 shuts off the signal bus 16 only when receiving a pulse having a pulse width Δt '. The signal bus 16 is brought into a conductive state by opening the contact point and closing the contact point in other cases. The open / closed state of the signal bus 16 by opening / closing the contacts of the switching circuit 20 is shown in FIG.
It is shown in the timing chart of (C). Therefore,
Due to the adjustment of the period adjusting circuit 24 and the pulse width adjusting circuit 25, from the signal sent to the display means 21 via the signal bus 16, as shown in FIG. Can be cut.

When the partial discharge measurement of the power cable 11 is started in this state, the periodic pulse noise component contained in the output signal sent from the detection impedance 15 to the display means 21 via the signal bus 16 is included. Since the signal portion including is partially cut, the discharge pulse due to the partial discharge to be measured is displayed in the waveform diagram shown in FIG. 2D that does not include the periodic pulse noise component. It will be different.

Therefore, the discharge pulse can be easily and accurately observed, and the discharge start voltage and the like can be measured with high accuracy without being affected by the periodic pulse noise. According to the partial discharge measuring apparatus 10 of the present invention,
It was confirmed that the noise level was reduced to 1/4 to 1/5 of the conventional level by removing the periodic pulse noise component.

[0019]

In the partial discharge measuring apparatus according to the present invention, the periodic pulse noise detected by the comparison circuit is used as a trigger to control the operation of the switching circuit for removing the periodic pulse noise. By removing this periodic pulse noise, it is possible to prevent the reduction of S / N due to the periodic pulse noise, and to improve the S / N ratio. Therefore, according to the present invention, S /
Since the partial discharge measuring device having a high N ratio is provided, the partial discharge pulse can be measured relatively easily and accurately, and thereby the deterioration state of the insulator of the power cable can be grasped more accurately. .

[Brief description of drawings]

FIG. 1 is a block diagram schematically showing a partial discharge measuring apparatus according to the present invention.

FIG. 2 is a timing chart showing the operation of the partial discharge measuring apparatus according to the present invention.

[Explanation of symbols]

 10 Partial Discharge Measuring Device 11 Power Cable 15 Detection Impedance 19 Comparison Circuit 20 Switching Circuit 21 Display Means 23 Pulse Generation Circuit

Claims (1)

[Claims] 1. A partial discharge measuring device for measuring a partial discharge signal generated from an insulator such as a cable or an electric device, wherein a trigger signal is generated when an input signal including a partial discharge signal and a noise signal exceeds a threshold value. Comparing means for outputting, pulse generating means for outputting a pulse signal based on the trigger signal, cycle adjusting means for adjusting the cycle of the pulse signal, pulse width adjusting means for adjusting the pulse width of the pulse signal A pulse signal whose period and pulse width are adjusted is used as a control signal, and based on this control signal, a switching means for blocking passage of a periodic noise signal from among the input signal is provided, A partial discharge measuring device characterized by measuring a partial discharge signal based on an output signal.