JPH08122397A - Method for locating partial discharge - Google Patents

Abstract

PURPOSE: To obtain a method for locating a partial discharge accurately by enhancing the time resolving power in digital transmission system thereby enhancing the revolving power in the location of partial discharge. CONSTITUTION: A measurement signal from a detector 11 is converted through a waveform processor 15 into a low frequency pulse which is then converted through an A/D converter 5 into a digital signal. On the other hand, a time counter 1 counts the time interval between the detection moment of the measurement signal and a moment when the delivery of digital data from a digital multiplex transmitter 2 is interrupted. These two pieces of information are multiplexed through the digital multiplex transmitter 2 and transmitted to a digital multiplex receiver 3. The digital multiplex transmitter counts the time difference between the interruptions of digital data transmitted from a plurality of positions and determines the time difference in the detection of partial discharge at a plurality of positions in combination with the time information from the time counter 1. This method can locate a partial discharge with high accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for locating a partial discharge generation position in an underground power transmission line or the like.

[0002]

2. Description of the Related Art If an insulator of a power cable has a defective portion, a high voltage applied to the cable causes a partial discharge from the defective portion, and if this is repeated for a long period of time, the insulator deteriorates and becomes insulated. May lead to destruction. Therefore,
When a power cable is used for a long period of time, it is important to know the location of partial discharge in order to prevent accidents such as dielectric breakdown from occurring.

As a method for locating the position of occurrence of partial discharge, for example, there is a characteristic that a high frequency component of a traveling signal wave generated by a discharge pulse generated in a cable and propagating in a conductive layer outside the cable resonates with a signal in a required frequency band. Japanese Patent Laid-Open No. 4-320977 discloses a method of detecting a time difference between a predetermined trigger point and detection of a partial discharge signal by two sensors and locating a partial discharge position based on this time difference. ing.

On the other hand, as a method of detecting mechanical vibrations generated during partial discharge by using an ultrasonic sensor, partial discharge generation by an acoustic emission method in which a generation point is calculated from delay time of elastic wave of vibration due to partial discharge A position locating method is known from JP-A-1-185458.

In any of the above methods, the partial discharge signal is transmitted and the partial discharge signals from a plurality of points are collectively monitored and measured. In such a centralized monitoring measurement method, as a method of locating the partial discharge position by focusing on the transmission method,
Conventionally, there are the following two methods.

One is a method in which a detection signal is largely modulated and analog-transmitted, as shown in FIG. Here, the underground transmission line is taken as an example of the measurement target. In this method, as shown in FIG. 4, the partial discharge position can be evaluated easily by measuring the time difference (ΔT) between the detection signals from a plurality of points.

In the figure, 11 is a partial discharge detector, and 12
Is an analog transmitter, 13 is an analog receiver, and 14 is a time difference measuring device.

The partial discharge occurrence position X is X = (L-ΔT
Vc) / 2. However, L is the measurement section length,
X is the distance to the discharge generation point, Vc is the pulse propagation speed in the cable, ΔT = T ₁ −T ₂ , T ₁ is the pulse propagation time from the discharge generation position to the measurement point 1, and T ₂ is the measurement point 2 The pulse transit time.

Another method is, as shown in FIG. 5, converting a detection signal into a low-frequency pulse that can be easily transmitted, and modulating the pulse such as frequency modulation, phase modulation, or digital modulation so that the transmission performance does not differ depending on the transmission distance. This is a method of transmission by a method (in FIG. 5, digital modulation is taken as an example). Also in this case, the partial discharge position can be located on the same principle as in FIG.

In the figure, 15 is a waveform processing device, 16 is a digital transmitting device, and 17 is a digital receiving device.

[0011]

However, in the above-described conventional method according to FIG. 4, since the transmission frequency band can be widened (for example, several tens of MHz), the rising edge of the detection pulse is sharp and the position location performance is good. However, there are disadvantages due to the analog transmission method such that the measurement dynamic range cannot be wide due to the restriction of the dynamic range of the analog transmission device, and the transmission performance depends on the transmission distance.

On the other hand, the method shown in FIG. 5 has the advantage that the same performance can be obtained regardless of where it is used and a wide dynamic range can be obtained because transmission is performed by a modulation method whose transmission performance does not depend on the transmission distance. . However, on the other hand, since it is necessary to convert the detection signal into a low-frequency pulse that is easy to transmit, there is a problem in that the time resolution when measuring the detection signal time difference is poor and the positioning accuracy is poor.

In consideration of the above-mentioned problems of the conventional partial discharge generation position locating method, the present invention provides time difference information while maintaining the advantages of digital transmission with a wide dynamic range and transmission performance independent of transmission distance. It is an object of the present invention to provide a partial discharge generation position locating method capable of accurately locating a partial discharge position by improving time resolution and position resolution by multiplexing and transmitting with a discharge pulse signal.

[0014]

As means for solving the above problems, the present invention detects a partial discharge pulse signal propagating from a partial discharge occurrence point at a plurality of measurement points by a detector,
These measurement signals are digitally converted and transmitted to the centralized monitoring measurement unit, and the discharge occurrence position is obtained from the partial discharge detection time difference.The measurement signal at the above measurement point is measured from the time of detection to the reference digital data break. The time is measured, and the time difference measurement result is transmitted to the centralized monitoring measurement unit together with the partial discharge signal, and the partial discharge detection time is calculated from the time difference between the digital data transmitted from a plurality of points and the time difference measurement result at each measurement point. The difference is determined, and the partial discharge occurrence position is determined from this partial discharge detection time difference.

In this method, it is preferable that the measurement signal detected by the detector is waveform-processed into a low-frequency pulse signal and digitally sampled to form a digital signal, which is transmitted.

When the measurement signal detected by the detector exceeds a predetermined threshold level, the time counter inputting the detection signal counts the clock wave number of the time difference until the break of the next digital data and discharges it as a time difference information signal. It may be transmitted with a signal.

[0017]

In the present invention using the above-described orientation method, when partial discharge occurs in the power cable, the discharge pulse propagates to a plurality of measuring points provided with detectors. The time to reach each measurement point varies depending on the distance, and if the time difference is known, the distance from the reference measurement point can be obtained and the partial discharge occurrence position can be known. In the present invention, the time difference is detected by each measurement, the measurement signal is converted into a digital signal and transmitted, and the centralized monitoring measurement section obtains it. Then, the position where the partial discharge occurs can be detected from this time difference ΔT by the following equation.

X = (L-ΔT · Vc) / 2, where L: measurement section length, Vc: discharge pulse propagation velocity, ΔT: time difference, X: distance from the reference measurement point. For example, if it is determined from the difference between the times when the discharge pulse reaches the two measurement points, the accuracy of ΔT is determined by the time resolution for the time until the discharge pulse reaches the measurement points. This time resolution is generally determined by the sampling cycle Ts in the transmission system for digital transmission, and the accuracy cannot be further improved.

On the other hand, in the present invention, the discharge pulse magnitude and the time difference information are digitally transmitted in order to obtain the time difference, and the time difference information from the instant when the discharge pulse reaches the measurement point to the break of the reference digital data. Is measured in finer time units, and the time difference is obtained by measuring the time difference information at the measuring point and the time difference between the breaks of the transmitted digital data in finer time units.

Therefore, the obtained time difference data is the time resolution Tc (<< Ts) in clock units for measuring the data.
Therefore, the distance resolution can be obtained with extremely high accuracy by locating the discharge generation position by obtaining this.

The measurement signal obtained at each measurement point is waveform-processed into a low-frequency pulse signal as in the second aspect of the invention and shaped into a waveform suitable for the sampling period when digitally transmitting this.

The digital signal thus transmitted contains the discharge pulse magnitude and the time difference information. When the measurement signal exceeds a predetermined threshold level, the number of clock waves of the time difference from the time of detection to the break of the sampling cycle of the next digital data is counted as in the third invention. The time difference thus obtained can be accurately measured in units of clock wave numbers.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall schematic block diagram of a system for measuring a partial discharge occurrence position of the embodiment. Measuring points 1 and 2
Are at appropriate positions on the left and right with respect to the partial discharge occurrence point as shown in the figure. However, the measurement points 1 and 2 do not necessarily have to be in such a position, and are located on the left side of the measurement point 1 or the measurement point 2
It may be a case where the partial discharge occurrence point exists on the right side.

L is the measurement section length, X is the distance from the measurement point 1 to the partial discharge occurrence point, T ₁ is the pulse propagation time until the partial discharge pulse reaches the measurement point 1, and T ₂ is the measurement point 2 The pulse transit time, ΔT, is the pulse transit time difference. Δ
T ₁ , ΔT ₂ , and ΔTx will be described later.

1 is a time counter, 2 is a digital multiplex transmitter, 3 is a digital multiplex receiver, 4 is a clock, 5 is an A / D converter, 11 is a detector, 14 is a time counter, and 15 is waveform processing. It is a device.

FIG. 2 shows a specific example of the above-mentioned partial discharge pulse measuring system.

As shown in the figure, the waveform processing device 15 is a waveform shaping device capable of converting the waveform of the measurement signal into a low frequency pulse containing only a component of fc = 50 KHz or less capable of digital transmission, and is an A / D converter. 5 is a sampling cycle 500
Convert the signal to a digital signal at KHz. As the time counter 1, an 8-bit counter and a clock of 32 MHz are used. 18 is a discharge magnitude output device, 19
Is a partial discharge position output device.

The above-mentioned measuring system detects the partial discharge generator from the partial discharge pulse as follows.

When the partial discharge pulse signal is generated at the partial discharge generation point, the pulse signal is propagated to the measurement points 1 and 2. At the measurement points 1 and 2, the detector 11 detects the measurement signal, the waveform processor 15 converts the measurement signal into a low-frequency pulse signal, and the A / D converter 5 converts the signal into a digital signal.

On the other hand, when the start signal is input, the time counter 1 counts the clock signal from the clock 4 and sends it to the digital multiplexing transmitter 2. The digital multiplexing transmitter 2 multiplexes the digitized signal of the measurement signal and the counted clock signal for transmission. This transmission signal is transmitted at a sampling cycle of Ts, as shown in FIG.

The sampling period Ts is 1/500 KHz = 2 μs in the embodiment, and in order to transmit the partial discharge signal at this sampling period, the waveform processor 15 outputs the discharge pulse to the low frequency pulse (the pulse width is smaller than Ts). It needs to be wide enough). Therefore, even if partial discharge orientation is performed using this discharge signal itself, a time resolution finer than Ts cannot be obtained in principle.

The start signal to the time counter 1 is
When the measurement signal exceeds a certain threshold level, the detection signal is given as a start signal, and the time counter 1 counts the wave number (time difference information) of the clock until the break of the next digital data. In Fig. 3, the time ΔT ₁ and ΔT ₂ from the time when the measured waveform (pulse waveform before waveform processing) after the measured waveform exceeds the threshold level at the measurement points 1 and 2 until the end of the next discharge magnitude data is taken as ΔT ₁ and ΔT _2. It is displayed. This time difference information is clock wave number (1 cycle T
can be easily obtained by counting with a counter IC, and it is easy to make the clock cycle Tc shorter than Ts.

In the illustrated example, ΔT ₁ = 100 × Tc, Δ
Assuming that T ₂ = 30 × Tc, 100 is displayed as the time difference information at measurement point 1 and 30 is displayed as the time difference information at measurement point 2. If there is no pulse exceeding the threshold level, the time difference information is 0. Note that here, the breaks of the discharge magnitude information and the time difference information are used as the breaks of the data, but it is of course possible to use other data breaks.

Here, the above certain threshold level is
Since the discharge pulse signal is attenuated according to the distance when the set measurement section length is long, the minimum signal that can be detected as a discharge pulse signal in the set section can be distinguished from the noise signal even if there is such attenuation. It is a level. In the signal transmission from each measurement point to the centralized monitoring point, the transmission delay time difference must be taken into consideration, but since the transmission delay is usually known or can be corrected, the transmission delay will be ignored for simplicity below. explain.

The above-mentioned transmission signal is received by the digital multiplex receiving apparatus 3, where it is returned to the original discharge magnitude information and time difference information. The data thus obtained is monitored at a centralized monitoring point, and from the time when significant data (a number other than 0 in this example) appears in any of the time difference information, significant data appears in the other time difference information. Until time ΔTx is measured. This ΔTx is also the counter IC of the time counter 14.
Can be easily calculated by counting the number of clock waves.

ΔT ₁ , ΔT ₂ , ΔT obtained from the above
The time difference ΔT obtained from x can be obtained as ΔT = ΔT ₁ −ΔT ₂ + ΔTx. This relationship is also displayed in FIG.

By the above method, the time resolution of the pulse time difference becomes Tc (<< Ts), and it becomes possible to measure the time difference more accurately than the resolution Ts when the present invention is not used. The partial discharge position is, as shown in FIG. 1, the partial discharge generation position X = (L−ΔT · Vc) / 2, where L is the measurement section length, and Vc is the pulse propagation speed in the cable. Improved resolution means improved resolution of the partial discharge position assessment.

The time resolution obtained in the specific example of the measurement system shown in FIG. 2 is as follows.

Sampling cycle Ts of A / D converter 5 =
Since (1/500 KHz) = 2 μs, the time resolution when position-locating using this waveform itself is at most 2 μs. Underground power transmission line pulse propagation velocity Vc = 18
Assuming 0 m / μs, the position localization resolution at this time is Δ
X = Vc × 2 μs = 360 m.

On the other hand, in this embodiment, the time difference information is counted with the clock of 32 MHz. The maximum value of ΔT ₁ and ΔT ₂ may be 2 μs, so the maximum count value of the time difference information is 2 μs / (1/32 MHz) = 2 μs / 31.25 ns.
= 64, and 6-bit time difference information bits are required. Therefore, in this embodiment, the time counter 1 has a margin of 8
It uses a bit counter.

The time resolution in this case is Tc = 31.25.
Therefore, the position orientation resolution is ΔX = Vc × 31.ns.
It can be seen that it is improved by an order of magnitude of 25 ns = 5.625 m.

[0042]

As described above in detail, in the partial discharge occurrence position locating method of the present invention, the measurement signal from the measurement point is sent to the centralized monitoring measurement section by digital transmission, and the measurement signal is detected as a reference digital data break from the detection time point. To obtain the distance from the reference measurement point to the discharge generation position by measuring the time difference between the time point and the break time of the digital data in units of the number of clock waves, so that the dynamic range can be wide and the transmission performance can be transmitted. The resolution of the partial discharge position locating can be improved while leaving the advantage of digital transmission that does not depend on the distance, and it has an advantage that it is extremely effective in maintaining the cable and ensuring safety.

[Brief description of drawings]

FIG. 1 is an overall schematic block diagram of a partial discharge position locating system according to an embodiment.

FIG. 2 is a block diagram of a specific example of a partial discharge measurement system.

FIG. 3 is an explanatory diagram of a method for measuring a time difference.

FIG. 4 is a block diagram of a conventional partial discharge position locating system.

FIG. 5 is a block diagram of another conventional partial discharge position locating system.

[Explanation of symbols]

 1 Time Counter 2 Digital Multiplexing Transmitter 3 Digital Multiplexing Receiver 4 Clock 5 A / D Converter 11 Detector 14 Time Counter 15 Waveform Processor

Claims (3)

[Claims] 1. A partial discharge pulse signal propagating from a partial discharge occurrence point is detected by a detector at a plurality of measuring points, and these measured signals are digitally converted and transmitted to a centralized monitoring measuring section. It consists of a method of obtaining the discharge occurrence position, measuring the time from the point of detection of the measurement signal at the above measurement point to the break of the reference digital data,
The time difference measurement result is transmitted to the centralized monitoring measurement unit together with the partial discharge signal, and the difference in the partial discharge detection time is obtained from the time difference between the digital data transmitted from a plurality of points and the time difference measurement result at each measurement point. A partial discharge occurrence position locating method for obtaining a partial discharge occurrence position from a partial discharge detection time difference. 2. The partial discharge occurrence position locating according to claim 1, wherein the measurement signal detected by the detector is waveform-processed into a low-frequency pulse signal and digitally sampled to be transmitted as a digital signal. Method. 3. The partial discharge generation position locating method according to claim 1, wherein the time point at which the measurement signal detected by the detector exceeds a predetermined threshold level is the time point at which the measurement signal is detected. .