JP2020003279A - Partial discharge detector and partial discharge detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a partial discharge detection device capable of detecting a partial discharge generated over a wide band and being able to be composed of relatively inexpensive parts. SOLUTION: A partial discharge detection device for detecting a partial discharge in a power cable is a first converter that converts an AC waveform analog signal flowing through the power cable into a digital signal, and an analog signal of the partial discharge current is a digital signal. It comprises a second converter that converts to, and a signal processing unit that processes the digital signal of the partial discharge current converted by the second converter, the second converter having a plurality of Nyquist frequency regions. The analog signal is converted into a digital signal, and the signal processing unit uses the phase of the AC waveform obtained from the digital signal of the AC waveform converted by the first converter in the second converter. The configuration is such that the digital signal of the changed partial discharge current is processed to reduce the amount of the signal. [Selection diagram] Fig. 1

Description

  The present invention relates to a partial discharge detection device and a partial discharge detection method.

  As a means for observing the signs of insulation deterioration of a power cable, it is common to measure the amount of partial discharge charge generated when a high voltage is applied to the insulator of the cable.

The middle junction box of the power cable has a ground wire connected to the cable insulation.
With respect to this ground line, a partial discharge due to insulation deterioration is measured by a current measuring device (CT) (for example, see Patent Document 1).

  It is known that the measured current value of the partial discharge is converted into a digital value by AD conversion, and the current value of the partial discharge is compared and evaluated according to the phase of the AC waveform flowing through the cable.

JP-A-9-96657

  In order to compare and evaluate the current value of the partial discharge, it is necessary to digitize the current value of the partial discharge measured by a current measuring device (CT) with an AD converter. Is an analog waveform.

In a baseband sampling method adopted for general AD conversion, the first Nyquist frequency band 0 to 1/2 Fs (sampling frequency) is an analog input band that can be digitized. Therefore, when analog input is performed in a Nyquist frequency band other than the first Nyquist frequency band, aliasing noise due to quantization is mixed in the first Nyquist frequency band.
Therefore, in order to remove mixed noise, a low-pass filter that allows only an analog input in the first Nyquist frequency band to pass is provided in a stage preceding the AD converter.

  If the analog input of the partial discharge is digitized by the baseband sampling method, the partial discharge becomes a high-frequency pulse, so that the sampling frequency Fs needs to be high. Therefore, there is a problem that the AD converter and the digital signal processing unit are required to have high performance and parts are expensive.

  On the other hand, in analog-to-digital conversion of an analog signal having a limited frequency band such as wireless communication, an under-sampling method is adopted. This method corresponds to an analog input in a higher frequency band than the sampling frequency, and specifies the second, third, and nth Nyquist frequency bands (n−1) / 2 to n / 2 · Fs other than the first. This is a sampling method limited to the Nyquist frequency band. Since an analog input other than the specific Nyquist frequency band becomes aliasing noise, a band-pass filter that passes only the specific Nyquist frequency band is provided in front of the AD converter so as to remove the aliasing noise. I have.

When the analog input of the partial discharge is digitized by the under-sampling method, when the analog input band of the partial discharge pulse deviates from a specific Nyquist frequency band, it is removed by a bandpass filter.
Since the signal of the partial discharge may be generated over a wide band of 1 MHz to several hundred MHz, the band to be detected becomes narrow only by detecting a specific Nyquist frequency band, and the generated partial discharge cannot be detected. Is possible.

In order to solve the above-described problem, the present invention provides a partial discharge detection device that can detect a partial discharge occurring over a wide band and can be configured with relatively inexpensive components. It is another object of the present invention to provide a partial discharge detection method capable of detecting a partial discharge occurring over a wide band and realizing it with relatively inexpensive components.
The above and other objects and novel features of the present invention will be apparent from the description of the present specification and the accompanying drawings.

  The partial discharge detection device according to the present invention is a partial discharge detection device that detects a partial discharge in a power cable. The power supply apparatus further includes a first converter that converts an analog signal having an AC waveform flowing through the power cable into a digital signal, and a second converter that converts an analog signal of a partial discharge current into a digital signal. In addition, a signal processing unit is provided for processing a digital signal of the partial discharge current converted by the second converter. The second converter converts a plurality of Nyquist frequency domain analog signals into digital signals. The signal processing unit obtains the phase of the AC waveform from the digital signal of the AC waveform converted by the first converter, and uses the obtained phase of the AC waveform to calculate the current of the partial discharge changed by the second converter. Is performed on the digital signal of (i).

  The partial discharge detection method of the present invention is a partial discharge detection method for detecting a partial discharge in a power cable. Then, an analog signal having an AC waveform flowing through the power cable is converted into a digital signal, and a plurality of Nyquist frequency domain partial discharge current analog signals are converted into digital signals. Further, the phase of the AC waveform is obtained from the digital signal of the AC waveform, and a process of reducing the signal amount is performed on the digital signal of the partial discharge current using the obtained phase of the AC waveform.

According to the present invention described above, a plurality of partial discharge currents in the Nyquist frequency domain are converted into analog signals from analog signals.
This makes it possible to detect a partial discharge that occurs over a wide band, and to realize the detection of the partial discharge with relatively inexpensive components.
Problems, configurations, and effects other than those described above will be apparent from the following description of the embodiments.

FIG. 1 is a schematic configuration diagram of one embodiment of a partial discharge detection system using a partial discharge detection device according to a first embodiment of the present invention. FIG. 2 is a diagram illustrating characteristics of a folded noise filter in the high-frequency analog input circuit of FIG. 1. FIG. 4 is a diagram illustrating a method for processing data of partial discharge in the first embodiment. 5 is a flowchart illustrating a method for processing partial discharge data according to the first embodiment. FIG. 8 is a diagram illustrating a detailed configuration of a digital signal processing unit for partial discharge detection of the partial discharge detection device according to the second embodiment of the present invention. 9 is a flowchart relating to counting of a phase of an AC waveform and detection of a partial discharge in the second embodiment. 10 is a flowchart relating to clearing of a partial discharge information table and transmission of partial discharge information to a communication unit in the second embodiment. FIG. 14 is a diagram illustrating a specific method of counting the phase of an AC waveform and detecting a partial discharge in the second embodiment. 9 is a time chart illustrating timings of clearing a partial discharge information table and transmitting partial discharge information according to a second embodiment. It is a flowchart in the 2nd Embodiment regarding the determination of the presence or absence of the insulation deterioration of the power cable in a host measuring device.

  Hereinafter, embodiments according to the present invention will be described with reference to text or drawings. However, the structure, material, other specific numerical values, and the like shown in the present invention are not limited to the embodiments described above, and can be appropriately combined or improved without changing the gist. In each of the drawings, the same or similar components are denoted by the same reference numerals, and repeated description will be omitted.

(First Embodiment)
First, a first embodiment of the present invention will be described.
FIG. 1 shows a schematic configuration diagram of one embodiment of a partial discharge detection system using a partial discharge detection device according to the first embodiment.

As shown in FIG. 1, an intermediate connection box 10 is provided so as to connect the power cables 30, and the intermediate connection box 10 is grounded by a ground wire. A current measuring device (CT) 40 for measuring a partial discharge is attached to the ground wire, and a Rogowski coil 20 for measuring an AC waveform is attached to the power cable 30.
The partial discharge detection device 1000 is connected to a current measuring device (CT) 40 and a Rogowski coil 20, respectively. The partial discharge detection device 100 is configured to exchange data with the higher-level measurement device 60 via the external network 50.
As described above, the Rogowski coil 20, the current measuring device 40, and the partial discharge detection device 1000 are provided for the power cable 30 and the intermediate connection box 10, and the partial discharge detection device 1000 and the higher-level measurement device 60 exchange data. A partial discharge detection system is configured to perform the above.
Analog signals output from the current measuring device 40 and the Rogowski coil 20 are input to the partial discharge detection device 1000. The analog signal output from the current measuring device 40 is a partial discharge analog signal.

  The partial discharge detection device 1000 includes a low-frequency analog input circuit 1100 and a low-speed AD converter 1110, a high-frequency analog input circuit 1200 and a high-speed AD converter 1210, a digital signal processing unit 1300 for partial discharge detection, and a communication unit 1400.

The low-frequency analog input circuit 1100 receives an analog signal having an alternating waveform output from the Rogowski coil 20.
The low-speed AD converter 1110 corresponds to a first converter that converts an analog signal of an AC waveform flowing through the power cable 30 into a digital signal. The low-speed AD converter 1110 converts the analog signal of the AC waveform input to the low-frequency analog input circuit 1100. Digitize the signal. The digital signal of the AC waveform digitized by the low-speed AD converter 1110 is input to the digital signal processing unit 1300 for detecting partial discharge.
The high-frequency analog input circuit 1200 receives an analog signal of the partial discharge current output from the current measuring device 40.
The high-speed AD converter 1210 corresponds to a second converter that converts an analog signal of a partial discharge current into a digital signal, and converts the analog signal of the partial discharge current input to the high-frequency analog input circuit 1200. Digitize. The digital signal of the partial discharge digitized by the high-speed AD converter 1210 is input to the digital signal processing unit 1300 for detecting the partial discharge.
The digital signal processing unit 1300 for partial discharge detection processes the digital signal of partial discharge for each phase of the digitized AC waveform. That is, the phase of the AC waveform is obtained from the digital signal of the AC waveform digitized in the low-speed AD converter 1110, and the digital signal of the partial discharge digitized in the high-speed AD converter 1210 is obtained using the obtained phase of the AC waveform. Process.
The communication unit 1400 outputs the detection result of the partial discharge to the external network 50.

Further, a plurality of partial discharge detection devices including one partial discharge detection device 1000 shown in FIG. 1 and other partial discharge detection devices are provided for the entirety of the large number of power cables 30 connected by the intermediate connection box 10. A detection device is provided.
Then, the host measurement device 60 comprehensively monitors the detection results of the plurality of partial discharge detection devices including the partial discharge detection device 1000 shown in FIG.

In the partial discharge detection device 1000 according to the first embodiment, the high-speed AD converter 1210 performs analog-to-digital conversion by using both the baseband sampling method and the undersampling method.
As described above, since the baseband sampling method and the undersampling method are used together, a wideband analog signal is input to the high-speed AD converter 1210.

Here, FIG. 2 shows a characteristic 1201 of a folded noise filter in the high-frequency analog input circuit 1200 in the partial discharge detection device 1000 according to the first embodiment.
As shown in FIG. 2, the characteristic 1201 of the aliasing noise filter has a wide frequency pass characteristic extending over a plurality of Nyquist regions from the first to the n-th (n is an integer of 2 or more). Thereby, digitization of the analog input of the broadband partial discharge pulse can be performed.

Although the number n of the Nyquist region of the characteristics 1201 of the aliasing noise filter is not particularly limited, it is preferable that n = about 4 to 10 because the frequency band of the partial discharge is about 1 MHz to several hundred MHz.
Then, the sampling frequency Fs may be selected according to the frequency band in which the signal of the partial discharge is desired to be detected, such that the number n of the Nyquist regions becomes this preferable level.

In general AD conversion, digital data after digital conversion is used, so it is necessary to remove aliasing noise. Therefore, the above-mentioned low-pass filter and band-pass filter are provided at the preceding stage of the AD conversion to remove aliasing noise only through a specific Nyquist frequency band.
On the other hand, in the present embodiment, it is sufficient to check the presence / absence of a partial discharge. Therefore, any data that can detect the presence / absence of a partial discharge is sufficient. As described in detail later, it is necessary to use all digital data. There is no. Therefore, in the present embodiment, it is not necessary to remove aliasing noise. Since aliasing noise is allowed in this way, no problem occurs even if a signal over a plurality of Nyquist frequency bands n is input to the high-speed AD converter 1210.

Next, a method of processing data of partial discharge in the first embodiment will be described with reference to FIGS. FIG. 3 shows a section of a specific phase interval of an AC waveform used for processing of partial discharge data, and an enlarged view of one section. FIG. 4 shows a flowchart of a method for processing data of partial discharge.
As shown in FIG. 3, in one section of a specific phase interval of the AC waveform 1310, the sum of the partial discharge pulse signal 1320 or the partial discharge The maximum value 1330 of the pulse signal 1320 is obtained. Then, in all the sections of the specific phase interval, similarly, the sum or the maximum value 1330 of the partial discharge pulse signals 1320 is obtained as the charge amount in each section.
The specific phase interval divides 360 ° of one cycle of a 50 Hz or 60 Hz AC waveform by a predetermined number. For example, one cycle of 360 ° is divided into 96 sections, and one section is set to a 3.75 ° phase interval. In FIG. 3, for convenience of illustration, one cycle of the AC waveform is divided into 20 sections, but the present invention is not limited to the 20 sections in FIG.
As the AC waveform 1310, a digital signal of an AC waveform, which is digitized from an analog signal of the AC waveform in the low-speed AD converter 1110, is used. Then, the phase of the AC waveform is obtained from the digital signal of the AC waveform, and is divided into specific phase intervals using the obtained phase of the AC waveform as shown in FIG.

As described above, the total or maximum value of the partial discharge pulse signal 1320 is obtained as the charge amount of the partial discharge in all the sections of the specific phase interval.
Then, the data of the obtained charge amount of the partial discharge is thinned out by signal processing in the digital signal processing unit 1300 for partial discharge detection.

The signal processing in the digital signal processing unit 1300 is performed during a predetermined period of the AC waveform, in the charge amount of the partial discharge (the sum or the maximum value of the partial discharge pulse signals 1320) of the partial discharge in the entire section of the specific phase interval. Extract and record only the amount. As a result, the digital data of a predetermined number of cycles in all sections of the phase interval is thinned out to one maximum charge amount. The predetermined period of the AC waveform is selected, for example, from a range of 5 to 20 periods.
For example, when the above-described one cycle of 360 ° is divided into 96 sections to determine the charge amount, and the predetermined period of the AC waveform is set to 10 periods, 96 × 10 = 960 partial discharge charge amount data are used. In other words, only the maximum value of the charge amount of the partial discharge, that is, only one data is thinned out.
As described above, even if the digital data of a predetermined number of cycles in the entire interval of the phase interval is thinned out to one maximum charge amount, the maximum charge amount after thinning changes according to the presence or absence of partial discharge. The presence or absence of partial discharge is reflected in the maximum charge amount. Therefore, the presence or absence of partial discharge can be detected based on the maximum charge amount.

  The data is thinned out in the digital signal processing unit 1300 for partial discharge detection, and the remaining data (data of the extracted maximum charge amount) is transmitted from the communication unit 1400 to the higher-level measuring device 60 via the external network 50.

The higher-level measurement device 60 monitors the transition of data (data of the maximum charge amount) received from the external network 50.
By monitoring the transition of the maximum amount of charge in the host measuring device 60, it is possible to monitor the signs of insulation deterioration of the power cable 30. In addition, the life of the power cable 30 can be estimated by checking the state of deterioration of the existing power cable 30.
Then, in the higher-level measuring device 60, the comparison between the received data of the maximum charge amount of the current partial discharge and the data of the maximum charge amount of the partial discharge received in the past is performed continuously. The progress of the deterioration of the entire power cables 30 can be grasped at any time.

FIG. 4 shows a flowchart of the above-described partial discharge data processing method.
In the flowchart of FIG. 4, first, in step S1, the maximum value or the sum of the current in each section of a specific phase interval of the AC waveform is obtained in all sections, and this is set as the charge amount in each section.
Next, in step S2, the maximum value of the charge amount in the section is extracted for each predetermined number of cycles of the AC waveform. As a result, (the number of sections in one cycle × the number of cycles) pieces of data are thinned out to one piece of data.
Next, in step S3, the data of the maximum value of the extracted charge amount is transmitted to the higher-level measuring device 60.
In this manner, the data thinned out by the extraction is transmitted to the higher-level measuring device 60, so that the amount of data to be transmitted to the higher-level measuring device 60 can be reduced.

The partial discharge detection device 1000 is always installed and monitors the state of the power cable 30.
By thinning out the data and reducing the amount of data to be sent, the cost and power consumption of the high-speed AD converter 1210 of the partial discharge detection device 1000 can be reduced. This makes it possible to realize the constant installation of the partial discharge detection device 1000.

In the first embodiment, the analog input circuits 1100 and 1200, the A / D converters 1110 and 1210, and the digital signal processing unit 1300 for detecting partial discharge in FIG. 1 can be configured by either hardware or computer software. is there.
When configured with hardware, it is configured with an integrated circuit or the like provided in the partial discharge detection device 1000.
When configured with computer software, a processor such as a microcomputer interprets the program using a program that realizes the functions of the analog input circuit, the AD converter, and the digital signal processing unit for partial discharge detection, Configure to run.
It is also possible to configure a part with hardware and the rest with computer software.

More preferably, the analog input circuits 1100 and 1200, the AD converters 1110 and 1210, and the digital signal processing unit 1300 for detecting partial discharge in FIG. 1 are configured by hardware.
When configured with computer software, a memory for storing calculation results and the like is required, and power for activating software and operating the memory is also required.
On the other hand, in the case of configuring with hardware, since power for starting software and operating the memory is not required, compared with the case of configuring with computer software, the operation of the partial discharge detection device 1000 is not required. The required power can be reduced. This makes it possible to install more partial discharge detection devices 1000 over the entire power cables 30.

According to the first embodiment described above, in the characteristics 1201 of the folded noise filter of the high-frequency analog input circuit 1200, a plurality of Nyquist frequency domain analog signals are passed. Then, the high-speed AD converter 1210 converts a plurality of Nyquist frequency domain analog signals into digital signals.
This converts a wideband analog signal of a plurality of Nyquist frequency regions into a digital signal, so that partial discharge occurring over a wide band can be detected.

  Further, since a plurality of analog signals in the Nyquist frequency domain are converted, the sampling frequency can be reduced as compared with the baseband sampling method for converting the analog signal in the first Nyquist frequency domain. Accordingly, it is not necessary to use expensive components for the high-speed AD converter 1210 and the digital signal processing unit 1300, and the high-speed AD converter 1210 and the digital signal processing unit 1300 can be configured with relatively inexpensive components. That is, the detection of partial discharge can be realized by relatively inexpensive components.

Further, the digital signal processing unit 1300 for partial discharge detection divides one cycle of the AC waveform into predetermined phase intervals, and charges the partial discharge charge (the maximum value of the partial discharge current) for all the sections of the predetermined phase interval. Or sum). As a result, since the entire digital signal of the partial discharge current digitally converted by the high-speed AD converter 1210 is converted into a signal of the amount of electric charge of the partial discharge (the maximum value or the sum of the current), the amount of the signal is reduced. You.
Further, the partial discharge detection digital signal processing unit 1300 extracts the maximum value of the amount of charge of the partial discharge at every predetermined number of cycles of the AC waveform in the entire section. As a result, (the number of sections × the predetermined number of cycles) charge amount signals are thinned out to one signal having the maximum charge amount, and the signal amount is reduced.

As described above, the digital signal processing unit 1300 for detecting partial discharge performs a process of reducing the amount of the signal of the partial discharge current that has been digitally converted in the high-speed AD converter 1210.
As a result, even if signals in a wide frequency range such as a plurality of Nyquist frequency ranges are handled, the amount of processed signals is reduced. Since the amount of signals is reduced, the configuration (memory and the like) for storing the signals is simplified, overflow is prevented from being transmitted from the communication unit 1400 to the external network 50, the power consumption of the partial discharge detection device 1000 is reduced, Etc. can be realized.
Further, the phase of the AC waveform is obtained from the digital signal of the AC waveform digitally converted by the low-speed AD converter 1110, and the phase of the AC waveform is divided into sections at predetermined phase intervals using the phase of the AC waveform to reduce the signal of the partial discharge. It is carried out. By using the phase of the AC waveform, it is possible to easily reduce the amount of signals from signals in a wide frequency range.

  Since overflow can be prevented when transmitting from the communication unit 1400 to the external network 50, the occurrence of partial discharge can be reliably grasped in real time in the higher-level measuring device 60.

  Since the power consumption of the partial discharge detection device 1000 can be reduced, it is possible to install more partial discharge detection devices 1000 over the entire power cables 30. In contrast to the conventional detection method, which mainly moves the partial discharge detection device to a position to be measured, a large number of partial discharge detection devices 1000 are installed stationary, and the partial The occurrence can be constantly monitored.

  Then, in the first embodiment, one of the maximum amount of electric charge is obtained for every predetermined number of cycles of the AC waveform from the entire digital signal of the partial discharge current digitally converted in the high-speed AD converter 1210. Since it is reduced to a signal, the amount of the signal is greatly reduced. As a result, the effect of simplifying the configuration (memory and the like) for storing signals and the effect of reducing the power consumption of the partial discharge detection device 1000 are increased, and the configuration of the partial discharge detection device 1000 is simplified and the component cost is reduced. Can be achieved.

  Further, the partial discharge detection device 1000 includes a communication unit 1400, and the communication unit is connected to the higher-level measurement device 60 via an external network, and configured to transmit data from the communication unit 1400. As a result, the degree of freedom of installation of the partial discharge detection device 1000 is increased as compared with the case where the partial discharge detection device and the higher-level measurement device are connected by wire, and more The discharge detection device 1000 can be installed.

(Second embodiment)
Next, a second embodiment of the present invention will be described.
In the second embodiment, in the configuration of the above-described first embodiment, a configuration for performing each process in the process of obtaining the charge amount of the partial discharge and the process of reducing the amount of the signal of the charge amount. And the details of each process are set more specifically.
Further, in the second embodiment, the maximum value of the partial discharge pulse signal 1320 in each section is adopted as the amount of charge of the partial discharge in each section of a specific phase interval.
In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description of the common components will be simplified or omitted.

Also in the second embodiment, similarly to the first embodiment, the partial discharge detection device 1000 and the partial discharge detection system shown in FIG. 1 are configured.
In the second embodiment, the digital signal processing unit 1300 for detecting partial discharge of the partial discharge detection device 1000 shown in FIG.

Also in the second embodiment, the charge amount of the partial discharge is obtained in all the sections obtained by dividing the phase of 360 ° of the AC waveform into 96 as described in the first embodiment, and the AC waveform is obtained. An example will be described in which the maximum value of the charge amount of the partial discharge is extracted every ten cycles.
In this example, the elapsed time of one section (phase 3.75 °) is about 208 μs when the AC waveform is 50 Hz. If the sampling frequency of the high-speed AD converter 1210 is 200 MHz, the sampling interval is 5 ns, and the number of times of data acquisition in one section is 208 μs / 5 ns = 41600 times.

FIG. 5 shows a detailed configuration of the digital signal processing unit 1300 for detecting partial discharge in the partial discharge detection device 1000 according to the second embodiment.
The digital signal processing unit 1300 for partial discharge detection shown in FIG. 5 includes a phase 0 detection unit 1301, a period counter 1302, a high-speed AD data input count counter 1303, a phase counter 1304, a partial discharge information table 1305, and a size determination unit 1306. Having.
The phase 0 detection unit 1301 detects the phase 0 (phase 0 °) of the AC waveform from the AC waveform sample data from the low-speed AD converter 1110.
The cycle counter 1302 counts the cycle of the AC waveform using the signal from the phase 0 detection unit 1301.
The high-speed AD data input number counter 1303 counts the number of times of partial discharge data input.
After being reset by a signal from the phase 0 detection unit 1301, the phase counter 1304 counts the phase of the AC waveform using a signal from the high-speed AD data input number counter 1303.
The partial discharge information table 1305 stores and stores information on partial discharge data, as will be described in detail later.
The magnitude determination unit 1306 compares the sample data of the partial discharge from the high-speed AD converter 1210 with the read data in the partial discharge information table 1305 to determine the magnitude of these data.

In the second embodiment, each of the units 1301 to 1306 of the digital signal processing unit 1300 for partial discharge detection in FIG. 5 can be configured by either hardware or computer software.
When it is configured by hardware, it is configured by an integrated circuit or the like.
When configured by computer software, a processor such as a microcomputer interprets and executes the program using a program that realizes the function of each of the units 1301 to 1306.
It is also possible to configure a part with hardware and the rest with computer software.

Next, a method of processing data of partial discharge in the second embodiment will be described with reference to FIG. 5 and FIGS.
FIG. 6 shows a flowchart relating to counting of the phase of the AC waveform and detection of the partial discharge. FIG. 7 shows a flowchart relating to clearing the partial discharge information table and transmitting the partial discharge information to the communication unit. FIG. 8 is a diagram illustrating a specific method of counting the phase of the AC waveform and detecting the partial discharge. FIG. 9 is a time chart for explaining the timing of clearing the partial discharge information table and transmitting the partial discharge information.

First, of the method of processing the data of the partial discharge, the counting of the phase of the AC waveform and the detection of the partial discharge will be described with reference to FIG. 5, FIG. 6, and FIG.
The counting of the phase of the AC waveform and the detection of the partial discharge are executed as shown in the flowchart of FIG.

First, as shown at the top of FIG. 6 (that is, at the start), the phase of the AC waveform 0 ° is detected from the data of the low-speed AD converter 1110 for acquiring the AC waveform of 50 Hz. That is, as shown in FIG. 5, the phase 0 detection section 1301 detects the phase 0 (phase 0 °) of the AC waveform from the AC waveform sample data from the low-speed AD converter 1110.
At this time, in FIG. 8, the AC waveform 1310 is the zero cross point at the left end.

Next, in step S11 of FIG. 6, the phase counter 1304 is initialized. That is, as shown in FIG. 5, when the phase 0 detector 1301 detects the phase 0 °, a reset pulse (initialization pulse) is output from the phase 0 detector 1301 to the phase counter 1304, and the phase counter is output. Initialize 1304.
At this time, in FIG. 8, an initialization pulse is input to the phase counter 1304, and the value of the phase counter 1304 becomes “0”.

Next, in step S12 of FIG. 6, the maximum detection value is acquired from the partial discharge information table 1305 with reference to the phase counter 1304. That is, as shown in FIG. 5, the phase of the phase counter 1304 is sent to the partial discharge information table 1305 as a reference address, and the detection maximum value (read data) corresponding to the reference address is acquired in the partial discharge table 1305. The acquired detection maximum value (read data) is sent to the magnitude determination unit 1306.
As shown in the lower right part of FIG. 8, the partial discharge information table 1305 detects the phase of each 3.75 ° phase (96 sections) and the detection of 10 cycles of the AC waveform in that phase. And the maximum value (the maximum value of the charge amount of the partial discharge for 10 cycles). Then, using the value of the phase (0, 3.75, 7.5,..., 356.25) of the phase counter 1304 as a reference address, the partial discharge information table 1305 obtains 10 cycles of the AC waveform in the phase section. To obtain the maximum detection value (read data).

Next, in step S13 of FIG. 6, the input value (charge amount) of the partial discharge is acquired from the high-speed AD converter 1210. That is, as shown in FIG. 5, sample data of the partial discharge is obtained from the high-speed AD converter 1210 and sent to the magnitude determining unit 1306. The magnitude determining unit 1306 inputs the partial discharge from the sample data of the partial discharge. Get the value (charge amount).
As shown in FIG. 8, the input value (charge amount) of the partial discharge is a partial discharge pulse signal 1320 sampled at a 200 MHz sampling interval (5 ns) of the high-speed AD converter 1210.

Next, in step S14 of FIG. 6, the detection maximum value of the partial discharge obtained from the partial discharge information table 1305 is compared with the input value (charge amount) of the partial discharge obtained from the high-speed AD converter 1210. That is, the magnitude determination unit 1306 in FIG. 5 compares the maximum detected value of the partial discharge with the input value (charge amount) of the partial discharge.
If the maximum value (detection maximum value of table 1305) <input value, the process proceeds to step S15. If the maximum value (detection maximum value of table 1305) ≧ input value, the process proceeds to step S16.

  In step S15 of FIG. 6, the maximum value (detection maximum value) of the partial discharge information table 1305 is updated to the input value, and the process proceeds to step S16.

Next, in step S16 of FIG. 6, it is checked whether or not the input value has been acquired from the high-speed AD converter 41,600 times (whether the phase has passed 3.75 °). That is, it is determined whether or not the high-speed AD data input number counter 1303 shown in FIG. 5 has acquired the input value 41600 times based on the elapsed time. Here, the number of input values = (elapsed time / sampling interval 5 ns), and as described above, the input value of 41600 times is about 208 μs. Therefore, every time 208 μs elapses, the number of high-speed AD data input A signal may be output from the counter 1303.
If the input value has been acquired 41,600 times, the process proceeds to step S17. If the input value has not been acquired 41600 times, the process returns to step S12.

  In this way, the steps S12 to S16 are repeated until the input value is acquired 41,600 times. This means that the maximum value 1330 of the input value (charge amount) of the partial discharge pulse signal 1320 shown in FIG. 8 is compared with the detected maximum value in the partial discharge information table 1305. If the maximum value 1330 of the input value is larger, the detected maximum value of the partial discharge information table 1305 is updated to the maximum value 1330 of the input value.

Next, in step S17, the phase counter is advanced by + 3.75 °, and the flow proceeds to step S12. That is, as shown in FIG. 5, a signal of 3.75 ° elapse increment is output from the high-speed AD data input number counter 1303 to the phase counter 1304.
At this time, in FIG. 8, the phase counter 1304 moves to the section of the next phase. For example, the phase shifts from the section of 3.75 to the section of 7.5. Then, for the next phase section, the acquisition of the input value of the partial discharge and the comparison between the input value and the detected maximum value of the partial discharge information table 1305 are executed.

  In this way, by performing the phase counting of the AC waveform and the detection of the partial discharge, the input value (charge amount) of the partial discharge is detected for each section of the predetermined phase interval of the AC waveform. The maximum value of the charge amount of the partial discharge is extracted.

Next, the clearing of the partial discharge information table and the transmission of the partial discharge information to the communication unit in the processing method of the partial discharge data will be described with reference to FIGS. 5, 7, and 9. FIG.
Clearing of the partial discharge information table and transmission of the partial discharge information to the communication unit are executed as shown in the flowchart of FIG.

First, in step S21 of FIG. 7, the AC waveform cycle counter is initialized. That is, the cycle counter 1302 shown in FIG. 5 is initialized.
At this time, the cycle counter 1302 is initialized to a value “0” as shown in FIG.

  Next, in step S22 of FIG. 7, the partial discharge information table 1305 is cleared. That is, in FIG. 5, a table clear signal is sent from the cycle counter 1302 to the partial discharge information table 1305. Then, as shown in FIG. 9, a signal for clearing the partial discharge information table is input, and the partial discharge information table 1305 is cleared.

Next, it is confirmed whether or not the phase 0 ° of the AC waveform is detected in step S23 of FIG. That is, it is confirmed whether the phase 0 ° is detected by the phase 0 detection unit 1301 shown in FIG. This step S23 is the same process as the detection of the phase 0 ° described at the top (at the start) of the flowchart in FIG.
When the phase 0 ° is detected, the process proceeds to step S24, and when the phase 0 ° is not detected, the process returns to before step S23.

Next, in step S24 of FIG. 7, it is checked whether the cycle counter is at the tenth cycle. That is, the cycle counter 1302 shown in FIG. 5 checks whether the cycle is the 10th cycle.
If it is the tenth cycle, the process proceeds to step S25. If it is not the tenth cycle, the process proceeds to step S26.

If the cycle counter 1302 is in the tenth cycle, in step S25 in FIG. 7, all data of the partial discharge information table is transmitted to the communication unit, and the process returns to step S21. That is, from the partial discharge information table 1305 shown in FIG. 5, all data of the partial discharge information table 1305 is transmitted to the communication unit 1400, and thereafter, the cycle counter 1302 is initialized.
At this time, in FIG. 9, the value of the cycle counter 1302 is “9” corresponding to the tenth cycle, and the value of the cycle counter 1302 is set to “0” corresponding to the first cycle by initialization of the cycle counter 1302 thereafter. Return.
In addition, all data of the partial discharge information table 1305 transmitted to the communication unit 1400 is transmitted from the communication unit 1400 to the higher-level measuring device 60 before the cycle counter 1302 is initialized and the partial discharge information table 1305 is cleared.
Then, when the period counter 1302 is initialized, the partial discharge information table 1305 is also cleared.

If the cycle counter 1302 is not at the tenth cycle, the AC waveform cycle counter is incremented in step S26 in FIG. 7 and the process returns to before step S23. That is, the signal of the AC cycle increment from the phase 0 detection unit 1301 in FIG. 5 is input to the cycle counter 1302, and the cycle counter 1302 is incremented.
At this time, in FIG. 9, the value of the cycle counter 1302 increases by one, such as 0 to 1, 1 to 2, 2 to 3, and shifts to the next cycle of the AC waveform.

  As described above, the steps S23 to S26 are repeated until ten cycles have elapsed. Thereby, the cycle of the AC waveform is measured starting from the phase 0 ° of the AC waveform, and every time 10 cycles of the AC waveform elapse, all data from the partial discharge information table 1305 is transmitted to the communication unit 1400. Then, the cycle counter 1302 is initialized, the partial discharge information table 1305 is cleared, and the process proceeds to the next ten cycles.

Next, monitoring of data transition in the higher-level measuring device 60 will be described.
The upper measurement device 60 compares the data of the partial discharge information table 1305 received from the communication unit 1400 of the partial discharge detection device 1000 with reference to the partial discharge information table received in the past. Then, it is determined that the data of the current partial discharge information table 1305 received from the communication unit 1400 has a large increase in the maximum value of the detected partial discharge as compared with the data of the referenced partial discharge information table received in the past. If it does, it warns that there are signs of insulation degradation.
The time when the partial discharge information table received in the past, which is referred to by the higher-level measuring device 60, can be arbitrarily selected, such as one day ago, one month ago, one year ago, etc., according to the user setting. preferable.
As a criterion for judging that the increase in the maximum value of the detection of the partial discharge is large, a predetermined criterion is selected such that the maximum value of the detection is twice or more.

Next, a method of determining the presence or absence of insulation deterioration of the power cable will be described.
FIG. 10 is a flowchart illustrating the determination of the presence / absence of insulation deterioration of the power cable in the upper level measurement device 60.

  First, as shown at the top of FIG. 10 (that is, at the start), the partial discharge information table 1305 is received. That is, all data of the partial discharge information table 1305 transmitted from the communication unit 1400 is received by the higher-level measuring device 60.

  Next, in step S31, the partial discharge information table 1305 received in the past is referred to.

Next, in step S32, the table received in the past and the table currently received are compared for each phase of the AC waveform.
If it is determined in step S33 that the increase in the maximum value of the partial discharge detection is greater than in the past, the process proceeds to step S34, and a warning that "there is a sign of insulation deterioration" is output.
On the other hand, if it is determined that the increase in the partial discharge detection maximum value is not large compared to the past, the process proceeds to step S35, and no warning is issued as “no indication of insulation deterioration”.

  In this way, when the higher-level measuring device 60 determines that there is a sign of insulation deterioration, a warning is output and the sign of insulation deterioration can be made known.

According to the above-described second embodiment, similarly to the first embodiment, the digital signal processing unit 1300 for detecting partial discharge uses the charge amount of the partial discharge at every predetermined number of cycles of the AC waveform of the entire section. Extract the maximum value of. As a result, (the number of sections × the predetermined number of cycles) charge amount signals are thinned out to one signal having the maximum charge amount, and the signal amount is reduced.
As described above, since the digital signal processing unit 1300 for partial discharge detection performs the process of reducing the amount of the partial discharge current signal digitally converted in the high-speed AD converter 1210, the signal in a wide frequency range is provided. , The amount of signal after processing is reduced. Therefore, it is possible to simplify the configuration (memory and the like) for storing the signal, prevent overflow when transmitting from the communication unit 1400 to the external network, reduce the power consumption of the partial discharge detection device 1000, and the like. become.
Further, the phase of the AC waveform is obtained from the digital signal of the AC waveform digitally converted by the low-speed AD converter 1110, and the phase of the AC waveform is divided into sections at predetermined phase intervals using the phase of the AC waveform to reduce the signal of the partial discharge. It is carried out. By using the phase of the AC waveform, it is possible to easily reduce the amount of signals from signals in a wide frequency range.

  Since overflow can be prevented when transmitting from the communication unit 1400 to the external network, the occurrence of partial discharge can be reliably grasped in real time in the higher-level measuring device 60.

  Since the power consumption of the partial discharge detection device 1000 can be reduced, it is possible to install more partial discharge detection devices 1000 over the entirety of a large number of power cables. In contrast to the conventional detection method, which mainly moves the partial discharge detection device to a position to be measured, a large number of partial discharge detection devices 1000 are installed stationary, and the partial The occurrence can be constantly monitored.

  In the second embodiment, as in the first embodiment, one of the maximum amount of charge is determined from the entire digital signal of the partial discharge current every predetermined number of cycles of the AC waveform. , The amount of signal is greatly reduced. As a result, the effect of simplifying the configuration (memory and the like) for storing signals and the effect of reducing the power consumption of the partial discharge detection device 1000 are increased, and the configuration of the partial discharge detection device 1000 is simplified and the component cost is reduced. Can be achieved.

In each of the above-described first and second embodiments, the specific phase interval of the AC waveform 1310 is set to a section of 96 divided phases of 3.75 °, and the AC waveform 1310 for extracting the maximum value of the charge amount is set. The description has been given with an example in which the predetermined period is set to 10 periods.
The number of divisions of a specific phase interval of the AC waveform and the number of periods of the AC waveform for extracting the maximum value of the charge amount are not limited to this example, and may be other numbers.
The two numbers may be configured as a parameter by a computer program or the like that controls such that the setting can be arbitrarily changed.
Further, the number of periods of the AC waveform for extracting the maximum value of the charge amount is, for example, in accordance with the range of the Nyquist frequency region where partial discharge is detected, as one period when only the first Nyquist region is used. (n × 2) periods may be used when confirming the n Nyquist region.

(Modification)
In each of the above-described embodiments, the process of obtaining the charge amount of the partial discharge from the partial discharge pulse signal 1320 shown in FIGS. 3 and 8 is performed in the entire section of the AC waveform 1310 at a specific phase interval (for example, 96 divisions). All sections).

  On the other hand, it is also possible to perform a process of obtaining the charge amount of the partial discharge in a part of the specific phase interval of the AC waveform. By calculating the charge amount of the partial discharge for some sections in this way, it is possible to reduce the amount of data in advance compared to obtaining the charge amount of the partial discharge for all sections.

However, when the charge amount of the partial discharge is obtained for some sections, when the partial discharge occurs in the section where the process of obtaining the charge amount of the partial discharge is not performed, the generated partial discharge cannot be detected. .
Therefore, a section in which the process of obtaining the charge amount of the partial discharge is selected according to the actual occurrence frequency of the partial discharge.
The frequency of occurrence of partial discharge is high near the zero cross (zero point where the sign of the current amount changes, the phase is 0 °, 180 °, 360 °) of the AC waveform of 50 Hz or 60 Hz, and the partial discharge is distributed before and after the zero cross. I do. Therefore, for example, a predetermined number (for example, 50 or 70) of the 96 sections obtained by dividing the 96 sections, in which the partial discharge occurrence frequency before and after the zero cross is higher, is selected, and the selected section is selected. , The charge amount of the partial discharge may be obtained.

  As described above, for a part of the specific phase interval of the AC waveform, even when performing the process of obtaining the amount of charge of the partial discharge, the phase of the AC waveform is obtained from the digital signal of the AC waveform. It is divided into specific phase intervals using the phase of the AC waveform.

In each of the above-described embodiments and modifications, the process of calculating the charge amount of the partial discharge is performed for all or a part of the specific phase interval of the AC waveform, and the maximum value of the charge amount is determined every predetermined number of cycles. By extracting, the amount of signal was reduced.
The method of processing for reducing the amount of the signal with respect to the digital signal of the partial discharge is not limited to the method of the above-described embodiment and the modified example, and other methods can be adopted. Even if other methods are adopted, the phase of the AC waveform is obtained from the digital signal of the AC waveform, and the process of reducing the amount of the signal is performed on the digital signal of the partial discharge using the obtained phase of the AC waveform. . As a result, the digital signal of the partial discharge can be made to correspond to the phase of the AC waveform, so that the amount of the digital signal of the partial discharge can be reduced while more reliably detecting the partial discharge that is likely to occur near the specific phase of zero crossing. It becomes possible to reduce.

  Reference Signs List 10 Intermediate junction box, 20 Rogowski coil, 30 cable, 40 current measuring device (CT), 50 external network, 60 host measuring device, 1000 partial discharge detection device, 1100 low frequency analog input circuit, 1110 low speed AD converter, 1200 High-frequency analog input circuit, 1210 high-speed AD converter, 1300 digital signal processing unit for partial discharge detection, 1301 phase 0 detection unit, 1302 cycle counter, 1303 high-speed AD data input number counter, 1304 phase counter, 1305 partial discharge information table, 1306 Size judgment unit, 1400 communication unit

Claims (5)

A partial discharge detection device that detects partial discharge in a power cable,
A first converter that converts an analog signal of an AC waveform flowing through the power cable into a digital signal;
A second converter for converting an analog signal of the partial discharge current into a digital signal;
A signal processing unit that processes a digital signal of the current of the partial discharge converted by the second converter,
The second converter converts a plurality of Nyquist frequency domain analog signals into digital signals,
The signal processing unit obtains the phase of the AC waveform from the digital signal of the AC waveform converted by the first converter, and uses the obtained phase of the AC waveform to calculate the phase of the AC waveform. A partial discharge detection device that performs a process of reducing a signal amount of a changed digital signal of the partial discharge current.   The partial discharge detection device according to claim 1, further comprising a communication unit configured to output a signal processed by the signal processing unit to an external network.   The signal processing unit divides one cycle of the AC waveform into a predetermined phase interval, and, for all or some of the sections of the predetermined phase interval, calculates a current of the partial discharge as a charge amount of the partial discharge. A process of obtaining a maximum value or a sum, and extracting a maximum value of the charge amount of the partial discharge in every predetermined number of cycles of the AC waveform in the entire section or the partial section, thereby reducing a signal amount. The partial discharge detection device according to claim 1, which performs the following. A partial discharge detection method for detecting partial discharge in a power cable,
Convert the analog signal of the AC waveform flowing through the power cable into a digital signal,
For the analog signal of the current of the partial discharge in a plurality of Nyquist frequency domain, perform conversion to a digital signal,
A phase of the AC waveform is obtained from the digital signal of the AC waveform, and a process of reducing a signal amount is performed on the digital signal of the partial discharge current using the obtained phase of the AC waveform. Method.   One cycle of the AC waveform is divided into predetermined phase intervals, and a maximum value or a sum of the currents of the partial discharges is obtained as a charge amount of a partial discharge for all or a part of the predetermined phase intervals. 5. A process for reducing a signal amount by extracting a maximum value of a charge amount of the partial discharge at every predetermined number of cycles of the AC waveform in the entire section or the partial section. 4. The partial discharge detection method according to claim 1.

Images