JP2001021607A - Device for detecting partial discharge generating position - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect only either vertical waves or horizontal waves included in an acoustic signal, and to accurately calculate a partial discharge position based on the detection signal in detecting the partial discharge position due to a defect of power cable connecting part or the like with an ultrasonic sensor. SOLUTION: In this partial discharge generating position detecting device, a pair of ultrasonic sensors 10a and 10b are arranged with a prescribed interval at arbitrary positions from the partial discharge position of an object, and either vertical wave or horizontal wave components are eliminated from each sensor signal by a signal processing part 11, and a distance until the discharge generating point is accurately calculated by an arithmetic part 12 based on any wave component signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a power cable,
The present invention relates to a partial discharge occurrence position detecting device that detects a partial discharge generated at a power cable connection portion or the like.

[0002]

2. Description of the Related Art It has been widely known that a partial discharge occurs due to a partial defect of a power cable, a power cable connection portion, and the like, and thus a dielectric breakdown occurs due to deterioration of the connection portion. As a method, a method of specifying a position by detecting a partial discharge with an electric position detecting means, a method of specifying a position by detecting an ultrasonic wave generated by the partial discharge, a method of using the above two methods together, or the like There is.

In particular, the position detection method using ultrasonic waves has an advantage of high identification accuracy because its propagation speed is much smaller than that of electric signals, and various methods have already been proposed. As one example, Japanese Patent Application Laid-Open No. 1-185458 discloses a partial discharge position locating method. In this method, a plurality of (at least five) ultrasonic sensors are arranged at arbitrary distances from the partial discharge position, the ultrasonic sensor at the shortest position is determined, and the distance and the detection time difference between the sensors are calculated. The sound wave velocity is determined, and the partial discharge position is specified.

[0004] A similar method using a plurality of ultrasonic sensors is described in IEEJ Transactions on Volumes 112, 10;
Detection of Partial Discharge of Prefabricated Connection Box for CV Cable by E Sensor ". In this detection method, a plurality of (four) ultrasonic sensors are attached to a prefabricated connection box, and a partial discharge position is specified based on a detection time difference between a discharge electric signal and an acoustic signal when a partial discharge occurs in each sensor. .

[0005]

By the way, when an acoustic signal due to partial discharge is detected by an ultrasonic sensor to specify the position of partial discharge, acoustic signals transmitted through a solid include longitudinal waves and transverse waves having different propagation speeds. It must be noted that In the conventional example of the method of detecting the acoustic signal described above,
The position is determined by the following formula using either the longitudinal wave or the transverse wave, or the intermediate velocity between them, without distinguishing between the longitudinal wave and the transverse wave. L = V × Δt L: distance from discharge point to sensor V: propagation velocity Δt: time difference between electric discharge signal and acoustic signal For this reason, a location error occurs. The detailed reason is as follows. Δt is measured at the rising edge of the acoustic signal as shown in FIG. However, a longitudinal wave generally has a greater distance attenuation than a transverse wave, and may or may not be detected depending on the sensor position. For this reason, it cannot be determined whether the rise of the detected acoustic signal is due to a longitudinal wave or a transverse wave. On the other hand, the propagation velocities of the longitudinal wave and the shear wave are about twice as large (for example, in the case of copper, the longitudinal wave is 5010 m / s,
(270 m / s, according to the science chronological table), if the type of the detected rising wave is wrong, a distance error occurs (the sensitivity increases if the averaging process is performed, but there is no effect in detecting the type of the wave). .

SUMMARY OF THE INVENTION The present invention is directed to a method and an apparatus for detecting a partial discharge position using a conventional ultrasonic sensor, and considers either a longitudinal wave or a transverse wave contained in an acoustic signal detected by an ultrasonic sensor. It is an object of the present invention to provide a detection device capable of accurately detecting a distance to a discharge occurrence point based on one of the waveforms.

[0007]

According to the present invention, as a means for solving the above-mentioned problems, a pair of acoustic sensors are arranged at predetermined intervals on an object to be measured for partial discharge. Either the longitudinal wave or the transverse wave component of one of the transmitted sensor signals is eliminated using the longitudinal wave or the transverse wave component of the other signal, and the signal processing is performed so that only the transverse wave or the longitudinal wave signal component is obtained. The partial discharge occurrence position detecting device includes a signal processing unit for calculating the discharge position from the propagation speed of any one of the signals obtained by the processing unit.

The detecting apparatus for detecting a partial discharge occurrence position according to the present invention having the above-described structure detects an acoustic signal of an ultrasonic wave transmitted through a solid object to be measured from the partial discharge occurrence position by an acoustic sensor. The distance to the point of occurrence is accurately detected. Although the above acoustic signal generally includes both longitudinal and transverse waves, this detection device eliminates either of them with the other wave component and detects only the longitudinal or transverse component to obtain the distance position. Perform orientation.

When erasing either a longitudinal wave or a transverse wave from a detected acoustic signal, for example, when erasing a longitudinal wave, 2
The distance between the two acoustic sensors is defined as a distance determined based on a predetermined calculation from the reference frequency signal and the propagation velocity of the longitudinal wave and the transverse wave, and the detection signal of the acoustic sensor near the discharge occurrence position is defined as the vertical distance of the set distance. A process of subtracting the detection signal of the acoustic sensor on the far side from the signal delayed by the wave propagation time is performed.

[0010] With this processing, the longitudinal wave components are eliminated because the longitudinal wave components are processed and subtracted from the detection signals of the two sensors based on the longitudinal waves. On the other hand, the transverse wave component has a different propagation speed from the longitudinal wave, so the waveform change at the same time in both sensors is different, so that it does not disappear even if a subtraction process is performed because of mismatch.
Only the transverse wave component is accurately detected. When only the longitudinal wave component is to be obtained, the reverse process may be performed.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic block diagram of a partial discharge occurrence position detecting device according to an embodiment. The measurement object is
For example, it is a prefabricated connection box used for a connection portion of a power cable. The partial discharge occurrence position detecting device includes the following members shown in FIG. First, a pair of ultrasonic sensors 10a, 10a,
0b is provided as an acoustic sensor. The detection signals of these ultrasonic sensors 10a and 10b are sent to the signal processing unit 11.

The signal processing unit 11 includes the ultrasonic sensor 10
a, 10b, one of the longitudinal and transverse wave components of one of the signals is erased using the longitudinal or transverse component of the other sensor signal, and the signal processing is performed so as to obtain only the transverse or longitudinal signal component. This is a processing unit. The obtained composite signal of the transverse wave or the longitudinal wave component is sent to the calculation unit 12, and the calculation unit 12 calculates the distance to the discharge position based on the rise time of the signal component and the propagation speed of the wave. The calculated distance of the discharge position is displayed on the display 13. Also, the signal processing unit 11
May be sent to the waveform measuring device 14 so that each waveform can be measured together with a pair of sensor signals.

In this embodiment, the signal processing unit 11
(B) As shown in the figure, a pair of amplifiers (amplifiers) 21
a, 21b, band pass filters (BPF) 22a, 2
2b, a delay circuit 23, and a differential circuit 24. The detection signals of the ultrasonic sensors 10a and 10b are supplied to the amplifier 21a,
21b, a band-pass filter (BPF) 22a after amplification,
At 22b, a signal of a required frequency is extracted. As the frequency, the center frequency of the band-pass filters 22a and 22b is set so that a frequency with good sensitivity can be selected depending on the object to be measured (for example, about 100 kHz or less in the case of a power cable connection part).

The distance .DELTA.L between the pair of ultrasonic sensors 10a and 10b is simply BPF (since the speed of the shear wave is generally about 1/2 of that of the longitudinal wave, and is assumed to be simplified for easy understanding). 1 / obtained from center frequency and longitudinal wave propagation velocity
The distance is two wavelengths λ (or a multiple thereof) (１ ／ λ of the shear wave when the shear wave propagation velocity is used). Specifically, it is set based on the following calculation. BPF center frequency: 100kHz Object: copper (longitudinal wave speed 5010m / s, horizontal wave speed
2270 m / s) Signal period T = 1/100 kHz = 10 μSec Signal wavelength λ = 5010 m / s × 10 μSec = 0.050 m λ / 2 = 0.050 m / 2 = 0.025 m → ΔL That is, the sensor distance ΔL is set to 25 mm. . However, since the calculation formula for determining the distance between sensors ΔL is strictly different, the exact solution will be described later.

Of the detection signals of the pair of ultrasonic sensors 10a and 10b, the sensor signal on the side closer to the discharge point is:
After passing through the BPF, the signal is delayed by 周期 cycle (5 μSec in the above example) by the delay circuit 23, and the difference between this signal and the sensor signal on the far side is obtained by the differential circuit 24. Then, the signal of the differential circuit 24 is sent to the next operation unit 12. The arithmetic unit 12 calculates the distance L to the discharge occurrence point based on the obtained propagation velocity of the longitudinal wave or the transverse wave, using the same formula as in the related art described in the section of the subject of the invention.

FIG. 2 shows the operation of the detection device having the above configuration.
This will be described with reference to FIG. In this example, ΔL is simply a distance of 波長 wavelength λ obtained by a predetermined calculation from the BPF center frequency and the longitudinal wave propagation velocity. As shown in FIG. 3, the ultrasonic waves generated by the discharge include longitudinal waves and transverse waves, and the sensor signals detected by the ultrasonic sensors 10 a and 10 b are detected as combined waveforms of the longitudinal waves and the transverse waves. You.
In general, a longitudinal wave has a higher propagation velocity than a transverse wave, so that the transverse wave has a time delay as shown in the figure, and the longitudinal wave attenuation waveform preceding the time-delayed transverse wave overlaps to form a composite waveform.

When a sensor signal having such a property is detected by each of the ultrasonic sensors 10a and 10b as an acoustic signal from the discharge generating point, as shown in FIG. Assuming that the waveform on the far side is b, even if the waveform b is an ultrasonic wave of the same sound source, it is detected with a delay of the distance ΔL as much as the distance of the ultrasonic sensor 10b. Since this distance ΔL is set to correspond to １ ／ of the wavelength λ at the propagation speed of the longitudinal wave, the waveform of the longitudinal wave component of the waveform b is detected with a delay corresponding to λ / 2. .

On the other hand, the ultrasonic sensor 10a closer to the sound source
Is detected by λ / 2 before the waveform b, but the sensor signal is delayed by a delay circuit 23 by a half (5 μsec) of the period based on the longitudinal wave propagation velocity and the difference is detected. Sent to the motion circuit 24. Therefore, in the waveform c obtained by taking the difference between the waveform a and the waveform b, the longitudinal wave components of the waveforms a and b coincide with each other, so that the longitudinal wave component is eliminated. However, since the transverse wave component has a different propagation velocity from that of the longitudinal wave, the waveforms a and b are subjected to a process of shifting ΔL = λ / 2 in position and T / 2 in time on the circuit as described above. However, the respective waveforms do not coincide with each other, so that the transverse wave component obtained by taking a difference is conversely obtained as a composite waveform having a larger amplitude than the single waveform a or b. That is, the waveform c is obtained as a composite waveform including only the transverse wave component.

Note that ΔL is short (several tens mm)
During this time, the attenuation when the waveform b proceeds is negligible. However, if the amount of attenuation cannot be neglected, it may be amplified by an amplifier (not shown) before input to the differential circuit 24 so that the amplitude becomes the same as the waveform a.

When the composite waveform c consisting only of the transverse wave component is obtained as described above, the arithmetic unit 12 calculates the distance L to the discharge position from the rise time of the waveform c and the transverse wave propagation velocity using the same formula as in the prior art. The result is displayed on the display 13. In order to calculate the time difference Δt between the electric discharge signal and the rising point of the acoustic signal when calculating the distance L, it is assumed that the electric discharge signal has been input to the calculation unit 12 (not shown).

In the above description, the procedure for erasing the waveform c so as not to include the longitudinal wave component has been described. On the contrary, the transverse wave component is eliminated, and the distance L to the discharge position is determined by the longitudinal wave component.
May be obtained. In this case, the interval ΔL between the ultrasonic sensors 10a and 10b and the delay time T / 2 in the delay circuit 23 may be set based on the shear wave propagation velocity.

Next, the above-mentioned pair of ultrasonic sensors 10
A case where the interval ΔL between a and 10b is set based on an exact solution will be described. First, the following symbols are defined as preconditions.

X = Vs / Vp: velocity ratio between shear wave and longitudinal wave (Vs: shear wave propagation velocity, Vp: longitudinal wave propagation velocity) f (period T = 1 / f): BPF center frequency ΔL: 2 pieces (A is closer to the discharge point and b is farther from the discharge point.) An optimal method for determining ΔL is to take the differential between the delay signal of the sensor 10a and the signal of the sensor 10b, eliminate longitudinal waves, and reduce transverse waves. The distance ΔL that can be maximized is selected. In this case, in the two sensor signals, the phases of the longitudinal waves a and b match, and the phases of the transverse waves a and b are (C / 2) · T (C:
(Odd number) It is assumed that it is shifted (if it is an even number, the transverse wave also disappears).
The procedure for calculating the optimum ΔL on the assumption as described above is as follows.

First, a detection time difference between the sensors 10a and 10b is obtained by the following equation. Δtp = L / Vp: detection time difference of longitudinal wave between sensors 10a and 10b Δts = L / Vs: detection time difference of transverse wave between sensors 10a and 10b From the above equation, Vp · Δtp = Vs · Δts → Δts = Δtp
/ X (from x = Vs / Vp). The signal of the sensor 10a is delayed by Δtp (matched in phase) to eliminate longitudinal waves. At that time, the phase shift φ of the transverse wave is as follows.

Φ = Δts−Δtp = Δtp / x−Δtp
= {(1-x) / x} .Δtp This transverse wave is most emphasized by the phase φ = (C / 2).
This is at the time of T (C: odd number). Therefore, {(1−x) / x} · Δtp = (c / 2) · T Therefore, Δtp = (C / 2) · T · {x / (1-x)} From the above, the optimal sensor interval ΔL is It is calculated by the formula.

ΔL = Vp · Δtp = Vp · (C / 2) · T · {x / (1-x)} (1) As can be seen from the above equation, ΔL is the propagation velocity of the longitudinal wave and the transverse wave, It is determined from the BPF center frequency. In the above formula,
When the speed ratio x of the transverse wave and the longitudinal wave is x = １ ／, ΔL is as follows. ΔL = Vp · (c / 2) · T (C: odd number) Further, when C = 1, ΔL = Vp · (1/2) · T is “half wavelength of longitudinal wave”.

The above is the procedure for setting the inter-sensor distance ΔL based on the exact solution. However, when the inter-sensor distance is set based on the exact solution, the setting of the delay time by the delay circuit 23 and the like are performed at a half wavelength. Perform in the same manner as described above.

FIG. 4 shows an ultrasonic sensor 10 according to the second embodiment.
The arrangement configuration of a and 10b is shown. The configuration other than the illustration is the same as that of the first embodiment, and is not shown. When the object has a complicated structure, the propagation path of the acoustic signal from the same discharge occurrence point is different for the two ultrasonic sensors 10a and 10b as shown in FIG. Alternatively, there is a case where it is difficult to perform the arrangement for detecting the distance between sensors ΔL based on the exact solution.

In order to deal with such practical difficulties,
(A) As shown in the drawing, a conductive member 10x is attached to an object by protruding, and a predetermined distance ΔL is attached to the conductive member 10x.
And a pair of ultrasonic sensors 10a and 10b are attached. Transmission of signals having different propagation paths to the ultrasonic sensors 10a and 10b by the conductive member 10x is restricted,
The predetermined distance can be secured.

FIG. 5 shows an arrangement of an ultrasonic sensor according to the third embodiment. This embodiment is also illustrated and described with a focus on differences from the first embodiment. In this embodiment, the conductive member 10x is a flat plate, and two ultrasonic sensors 10a and 10b are provided on both surfaces at a position apart from each other by the predetermined distance ΔL.
Is provided. The signal processing unit 11 ′ includes the addition circuits 25 a and 25 b of the sensor signals on both sides of the signal processing unit 11 ′.
a, It is inserted in the middle of each of the amplifiers 21b to BPF 22b.

Since the signals of the sensors provided on both sides of the flat plate are opposite in phase, they are added by the adding circuits 25a and 25b, so that the signal strength is doubled. On the other hand, the random noise is canceled and the detection sensitivity is improved. .

[0032]

As described above in detail, the partial discharge occurrence position detecting apparatus of the present invention detects an acoustic signal of a partial discharge of an object by an acoustic sensor, and detects one of a longitudinal wave and a transverse wave of the detected signal. A signal processing unit for erasing one of the components using the other signal component, and a calculation unit for calculating the discharge position based on the processed signal are provided. With this measurement, the position of the discharge occurrence can be located with higher accuracy using the propagation speed.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a partial discharge occurrence position detecting device according to an embodiment.

FIG. 2 is an explanatory diagram of an operation.

FIG. 3 is an explanatory diagram of an operation.

FIG. 4 is a configuration diagram of an ultrasonic sensor according to a second embodiment.

FIG. 5 is a configuration diagram of an ultrasonic sensor according to a third embodiment.

FIG. 6 is an explanatory diagram of a conventional discharge position calculation method.

[Explanation of symbols]

 10, 10a, 10b Ultrasonic sensor 11 Signal processing unit 12 Operation unit 13 Display unit 14 Waveform measuring device 23 Delay circuit 24 Differential circuit

Claims (4)

[Claims] A pair of acoustic sensors are disposed at predetermined intervals on an object to be measured for partial discharge, and a longitudinal wave and a transverse wave component of one of the sensor signals sent from these acoustic sensors are used to determine which of them. A signal processing unit for eliminating one of the signals using the longitudinal wave or the transverse wave component of the other signal and performing signal processing so as to obtain only the signal component of the transverse wave or the longitudinal wave, and any one of the signals obtained by the processing unit A partial discharge occurrence position detection device, comprising: a calculation unit that calculates a discharge position from the propagation speed of the partial discharge. 2. A band-pass filter for extracting a predetermined frequency signal from a detection signal of an acoustic sensor in the signal processing unit,
A delay circuit that delays a signal that has passed through the filter of the acoustic sensor closer to the discharge point, and a differential circuit that obtains a difference between a signal from the delay circuit and a filter pass signal of the sensor farther from the discharge point. Is provided, and the distance between the acoustic sensors is set to a distance obtained based on a predetermined calculation from the center frequency of the filter and the propagation speed of the longitudinal wave and the transverse wave. The delay circuit propagates the longitudinal wave or the transverse wave to be erased over the set distance. 2. The partial discharge occurrence position detecting device according to claim 1, wherein the partial discharge occurrence position detecting device is delayed by a time. 3. The partial discharge occurrence position detecting device according to claim 2, wherein a conductive member is provided on the object, and acoustic sensors are provided at the intervals on the conductive member. 4. The signal processing unit according to claim 1, wherein the conductive member is formed in a flat plate shape, a plurality of pairs of the acoustic sensors are provided on both surfaces thereof, and an addition circuit for adding sensor signals on both surfaces is provided in the signal processing unit. 3. The partial discharge occurrence position detecting device according to 3.