JP2020101491A - Partial discharge detector and partial discharge detection method - Google Patents

Abstract

To provide a low-cost partial discharge detector with which it is possible to observe a high-frequency current flowing on the surface of a container that stores an electric apparatus and efficiently detect a signal caused by a partial discharge with good sensitivity.SOLUTION: A partial discharge detector 10 comprises: a sensor 11 for detecting the surface current of an object; a filter unit 12 for limiting the output signal of the sensor 11 to a set frequency band; a RF detector 20 for measuring the energy of the output signal of the filter unit 12 and outputting a signal that corresponds to the strength of the energy; a recording unit 15 for sampling and recording the output signal of the RF detector 20; and an analysis unit 16 for analyzing the signal recorded by the recording unit 15. The analysis unit 16 includes a level determination unit for detecting a signal of a defined threshold or greater, a noise rejection unit for removing a signal of other than a defined cycle, a continuity determination unit for determining the continuity of a signal of the defined cycle, and a partial discharge determination unit for determining a partial discharge upon receiving the result of the continuity determination unit.SELECTED DRAWING: Figure 1

Description

The present invention relates to a partial discharge detection device and a partial discharge detection method for detecting the occurrence of partial discharge inside an electric facility/apparatus.

Partial discharge is a precursor to dielectric breakdown, and the deterioration of the insulation performance of electrical equipment can be diagnosed by measuring and evaluating the partial discharge generated from electrical equipment in operation (such as transformers and switchgear). It is being appreciated.

As a method of detecting partial discharge, there is a method of using a sensor that senses light emission, heat generation, pulse current, electromagnetic waves, ultrasonic waves, etc. associated with partial discharge. For example, Patent Document 1 discloses a sensor that detects a high-frequency current flowing on the surface of a container that stores an electric device. The sensor disclosed in this document has a structure in which noise from the outside does not easily enter by covering the detection electrode with a shield metal container, and reduces the influence of so-called environmental noise to improve the detection sensitivity of surface current. Is being attempted.

However, even if the sensitivity of the sensor is improved by specializing on the surface current, it is still necessary to determine whether the detected signal is the surface current caused by partial discharge or the surface current caused by other noise. There is a problem that it is difficult. In addition, if the signals for partial discharge detection are widely distributed in a high frequency band, in order to record and analyze those signals, a high-performance element with high sampling speed and high sensitivity or analysis Since it is necessary to use a high-speed signal processing processor, the cost of the measuring device becomes high.

JP, 10-170594, A

INDUSTRIAL APPLICABILITY The present invention observes a high-frequency current flowing on the surface of a container that stores electric equipment, efficiently detects a signal caused by partial discharge with high sensitivity, and can reduce the cost of measurement. An object is to provide an apparatus and a partial discharge detection method.

The present invention adopts the following means in order to solve the above problems.
That is, the partial discharge detection device of the present invention, a sensor that detects the surface current of the object, a filter unit that limits the output signal of the sensor to a set frequency band, and measures the energy of the output signal of the filter unit. An RF detector that outputs a signal corresponding to the intensity of the energy, a recording unit that samples and records the output signal of the RF detector, and an analysis unit that analyzes the signal recorded in the recording unit, The analysis unit includes a level determination unit that extracts a signal having a predetermined threshold value or more, a noise removal unit that removes a signal other than a predetermined period, and a continuity that determines continuity of the signal of the predetermined period. It is characterized by comprising a determination unit and a partial discharge determination unit that determines a partial discharge based on a result of the continuity determination unit.
According to such a configuration, the signal obtained from the surface current can be analyzed by removing the noise component and extracting the signal caused by the partial discharge, so that the detection sensitivity when the partial discharge occurs can be improved. it can.

In one aspect of the present invention, the predetermined threshold value of the partial discharge detection device of the present invention is set at each time.
According to such a configuration, the threshold value is set based on the change of noise with time, so that erroneous signal detection can be reduced.

In one aspect of the present invention, the continuity determination unit of the partial discharge detection device of the present invention has a plurality of determination criteria, the partial discharge determination unit, the partial discharge by each number of occurrences of the plurality of determination criteria. It is characterized by judging.
According to such a configuration, the partial discharge is determined based on a plurality of criteria, so that it is possible to determine the occurrence of the partial discharge corresponding to various modes of the partial discharge, and when the partial discharge occurs. The detection sensitivity of can be improved.

In one aspect of the present invention, the partial discharge detection device of the present invention is characterized in that the sensor is a surface current sensor.

Further, the partial discharge detection method of the present invention limits the signal detected by the sensor that detects the surface current of the object to the set frequency band, and measures the energy of the signal limited to the set frequency band. , Sampling and recording a signal corresponding to the intensity of the energy, analyzing the recorded signal, the analysis, extracting a signal equal to or more than a predetermined threshold, the signal other than a predetermined period Removing, determining the continuity of the signal of the defined period, and determining partial discharge based on the result of the determination of continuity.
According to such a configuration, the signal obtained from the surface current can be analyzed by removing the noise component and extracting the signal caused by the partial discharge, so that the detection rate of occurrence of the partial discharge can be improved.

According to the present invention, it is possible to observe a high-frequency current flowing on the surface of a container that stores an electric device, efficiently detect a signal caused by partial discharge with high sensitivity, and reduce the cost of measurement. A discharge detection device and a partial discharge detection method can be provided.

It is a functional block diagram which shows the structure of the partial discharge detection apparatus which concerns on embodiment of this invention. 2 is a functional block diagram showing a configuration of an analysis unit in FIG. 1. FIG. It is a figure which shows the signal obtained by observing the surface current at the time of partial discharge generation. It is a figure which shows the output signal of the RF detector of the partial discharge detection apparatus which concerns on embodiment of this invention. FIG. 4 is a spectrum analysis diagram in which a signal obtained by observing a surface current is converted into a frequency and a frequency component intensity, and a waveform when environmental noise and partial discharge occur is shown. It is a figure which shows the signal recorded on the recording part of the partial discharge detection apparatus which concerns on embodiment of this invention. It is a figure which shows the signal recorded on the recording part of the partial discharge detection apparatus which concerns on embodiment of this invention.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
(First embodiment)
FIG. 1 is a functional block diagram showing the configuration of the partial discharge detection device according to the first embodiment of the present invention, and FIG. 2 is a functional block diagram of the analysis unit shown in FIG.
As shown in FIG. 1, the partial discharge detection device 10 includes a sensor 11, a bandpass filter 12, an amplifier 13, an RF detector 20, an A/D converter 14, a recording unit 15, an analysis unit 16, a display unit 17, and The recording unit 15 and the analysis unit 16 are provided with memories 18 and 19, respectively. As shown in FIG. 2, the analysis unit 16 includes a level determination unit 50, a noise removal unit 51, a continuity determination unit 52, and a partial discharge determination unit 53.

The sensor 11 is attached to the surface of a container or the like that stores electric equipment (for example, a transformer or a switchgear) in order to detect a partial discharge, senses a current flowing on the surface of the container, and corresponds to the current intensity. Output the signal. The signal output from the sensor 11 is input to the bandpass filter 12. The bandpass filter 12 filters the signal in a predetermined frequency band and outputs the signal to the amplifier 13. The signal input to the amplifier 13 is amplified and input to the RF detector 20. The RF detector 20 measures the energy of the input RF signal and outputs a signal having an output level corresponding to the energy intensity to the A/D converter 14. The A/D converter 14 converts the input signal intensity into an analog amount into a digital amount so that digital signal analysis can be performed, and transmits the data to the recording unit 15.

The data transmitted to the recording unit 15 is recorded in the memory 18 in time series. At this time, the data recorded in the memory 18 is recorded in association with the information necessary for the analysis of the analysis unit 16, such as the sampling date and time and the sampling period designated in advance by the control unit (not shown). The analysis unit 16 calls the data in the memory 18 through the recording unit 15 and analyzes the presence or absence of partial discharge according to the analysis procedure described later. The analyzed result is displayed on the display unit 17.

Here, the operation of the RF detector will be described. FIG. 3 is a diagram showing the output a (solid line) of the sensor 11 and the power supply voltage b (dotted line) of 50 Hz applied to the electric device when the partial discharge occurs, and the horizontal axis represents time (msec), The vertical axis represents the signal strength. FIG. 4 shows the output c (solid line) of the RF detector 13 to which the sensor output a in FIG. 3 is input. The signal due to the partial discharge is generated every 10 msec from 0 msec to 60 msec, but the RF detector measures the RF energy of a mass of amplitude signal like the sensor output a in FIG. 3, and as shown in FIG. Outputs a one-shot pulse signal.

As described above, by using the RF detector, it is possible to treat a group of high-frequency signal amplitudes as a group, and to use a sampling clock for detecting partial discharge and a signal processor clock for analysis with a relatively low speed. Things can be used. That is, since it is less necessary to use a high-grade IC chip, the cost can be reduced as compared with the conventional analysis device. In addition, since the sampling clock has a low speed, it is possible to save a memory space for recording a signal, which is a preferable effect.

Further, the partial discharge detection device 10 will be described in detail with reference to FIGS. 3 and 4.
As shown in FIG. 3, a relatively large sensor output occurs at 0 msec, 20 msec, 40 msec, and 60 msec, and a small sensor output occurs at 10 msec, 30 msec, and 50 msec. As can be seen from FIGS. 3 and 4, the partial discharge tends to occur at the rise and fall of the power supply voltage. Therefore, it is considered that the sensor output signal generated in the same cycle as the power supply frequency is closely related to the partial discharge. This property is taken into consideration when removing noise in the analysis unit 16 described later. That is, a signal that does not occur in the same cycle as the power supply frequency can be removed as a signal that is not related to partial discharge.

FIG. 5 is a graph showing the frequency (MHz) on the horizontal axis and the frequency component intensity on the vertical axis, and is a spectrum analysis diagram in which the sensor output signal a shown in FIG. 3 is converted into frequency and frequency component intensity. FIG. 5 shows an environmental noise waveform c drawn by a solid line in which no partial discharge occurs and a waveform d drawn by a double line when a partial discharge occurs. As can be seen from FIG. 5, in the regions near 10 to 30 MHz, 40 MHz, 55 MHz, and 70 to 90 MHz, the signal at the time of partial discharge occurrence is sufficiently larger than the environmental noise. That is, it is considered from FIG. 5 that there is a region having a good S/N ratio depending on the frequency band.

The partial discharge detection device 10 sets the pass band of the band filter 12 to a frequency band in which the signal at the time of occurrence of partial discharge is larger than environmental noise, in other words, to a frequency band with a good S/N ratio. , It becomes possible to detect the partial discharge signal with high sensitivity. Further, in the present embodiment, the recorded signal is the output of the RF detector that receives the high-frequency signal from the sensor 11 and outputs a signal based on the energy, so that the energy band of the RF detector can be measured. For example, signals in a wide band from several MHz to several GHz can be converted and recorded for analysis. Therefore, the frequency band set in the bandpass filter 12 can be arbitrarily set in a portion having a good S/N ratio of the signal when the partial discharge occurs, without changing the internal clock speed for sampling. It is possible to provide a partial discharge detection device which has a sufficient detection sensitivity while suppressing the cost.

Next, the operation of the analysis unit 16 will be described with reference to FIGS. 6 and 7. 6 and 7 are graphs showing the time (msec) on the horizontal axis and the signal intensity on the vertical axis, showing the output of the RF detector 20 when partial discharge occurs in different situations. The data shown in FIG. 6 and FIG. 7 shows data for a sampling period of 100 msec for 5 cycles when the power supply frequency is 50 Hz.

The analysis unit 16 shown in FIGS. 1 and 2 first reads the data as shown in FIGS. 6 and 7 recorded in the memory 18 through the recording unit 15. Next, the level determination unit 50 of the analysis unit 16 extracts a signal having a level equal to or higher than the threshold T drawn by the dotted line in FIGS. 6 and 7 as an analysis target.
The threshold T used for determining the signal analysis target is preset in the memory 19. The level determination unit 50 refers to the value of the threshold T in the memory 19 and extracts the signal. Here, the threshold value T may be a constant value or a different value may be set for each time. For example, when the environmental noise level is relatively low at midnight or early morning, a lower threshold may be set. On the other hand, when the level of environmental noise is relatively high during the daytime, a higher threshold value may be set. In this way, by changing the threshold value T in response to the change of the environmental noise of the partial discharge observed for each time, it is possible to prevent erroneous detection and improve the detection sensitivity of the partial discharge.

Next, the noise removal unit 51 of the analysis unit 16 checks whether or not each of the signals extracted by the level determination unit 50 is generated every 20 msec corresponding to the power supply frequency. Each of the groups indicated by A and B in FIG. 6 is a signal group determined to occur every 20 msec. At this time, when confirming the occurrence of every 20 msec, the fluctuation of the value in a certain range is taken into consideration rather than making the determination exactly at 20 msec. For example, if it is 20 msec+-0.5 msec, it is determined that the power cycle is 20 msec. In FIG. 6, since the signal group indicated by C is not generated in the cycle of 20 msec, the noise removing unit 51 determines that it is noise and excludes it from the analysis target. That is, in FIG. 6, the signal groups of group A and group B are to be analyzed.
In this way, signals other than those generated in conjunction with the power supply cycle are removed as noise for analysis, so signals related to partial discharge are efficiently extracted, erroneous detection is prevented, and detection sensitivity for partial discharge is improved. be able to.

Next, the continuity determination unit 52 of the analysis unit 16 checks how often the signal group generated in the cycle of 20 msec occurs in the sampling period. Since the signal groups of the group A and the group B shown in FIG. 6 are generated 5 times in 5 cycles, both are determined to have an occurrence frequency of 5/5. In the case of the group D shown in FIG. 7, since it occurs 3 times in 5 cycles, it is determined to be 3/5.
The continuity determination unit 52 sequentially analyzes a plurality of sets of data that are continuously acquired, with one set of data for a period of 100 msec corresponding to five power supply cycles of 50 Hz. Here, if the periodic data of 5 times in 5 cycles of the power supply frequency of one set of data is observed, it is determined that the event of 5/5 has occurred. Each time a partial discharge occurrence event, which is expressed as 5/5, 4/5, 3/5, 2/5, is determined, the counter provided for each event is incremented by 1 to The number of occurrences is recorded in the memory 19. The meaning of the event represented by n/5 (n=2 to 5) shown here indicates that a signal conforming to a cycle of 20 msec was observed n times in 5 cycles.

The partial discharge determination unit 53 of the analysis unit 16 monitors the value of the counter for each event counted by the continuity determination unit 52, and when it is confirmed that each event has occurred a predetermined number of times or more, partial discharge occurs. Is determined to have occurred. For example, for each of the events 5/5, 4/5, 3/5, and 2/5, it is determined that the partial discharge occurs when the value is 100 times, 100 times, 500 times, or 1000 times or more.
By such means, the partial discharge detection device 10 efficiently extracts the signal caused by the partial discharge by utilizing the property of the partial discharge generation, reduces the erroneous detection, and improves the detection sensitivity of the partial discharge. be able to.

In the partial discharge detection device, the sensor 11 that is attached to the surface of a container or the like that stores electrical equipment and that senses a current flowing on the surface of the container can physically sense the surface current if it is a capacitance. However, a sensor specialized as a surface current sensor may be used. Further, although the case where the power supply frequency is 50 Hz is described in the present embodiment, it can be implemented by changing the periodicity determination from 20 msec to 16.6 msec even when the power supply frequency is 60 Hz. This periodicity determination cycle can be arbitrarily changed according to the observation environment. In the present embodiment, an example of a power supply frequency of 5 cycles (100 msec in the case of a power supply frequency of 50 Hz) is also described for one set of sampling periods. Then, an appropriate sampling period may be set. At this time, an appropriate value may be set for the partial discharge determination count number for each partial discharge occurrence event.

In the present embodiment, the sensor 11 that is attached to the surface of a container or the like that stores electrical equipment and that senses the current flowing through the surface of the container is used, and only signals that depend on the power supply frequency are selected for analysis. When a partial discharge occurs in any of the devices related to the three-phase AC power supply, regardless of which phase of the three-phase AC power supply caused the partial discharge, a signal expected to be caused by the partial discharge Sensitive with one sensor. Then, the sensed signal can be subjected to continuity determination analysis to determine whether or not partial discharge occurs in any of the three phases.

10 Partial Discharge Detection Device 11 Sensor 12 Bandpass Filter 15 Recording Section 16 Analyzing Section T Threshold 20 RF Detector 50 Level Determination Section 51 Noise Removal Section 52 Continuity Determination Section 53 Partial Discharge Determination Section

Claims (5)

A sensor that detects the surface current of the object,
A filter unit that limits the output signal of the sensor to a set frequency band,
An RF detector that measures the energy of the output signal of the filter unit and outputs a signal corresponding to the intensity of the energy,
A recording unit for sampling and recording the output signal of the RF detector;
An analysis unit for analyzing the signal recorded in the recording unit,
The analysis unit is
A level determination unit that extracts a signal equal to or higher than a predetermined threshold,
A noise removal unit that removes signals other than the specified period,
A continuity determination unit that determines the continuity of the signal of the predetermined cycle,
A partial discharge detection device comprising: a partial discharge determination unit that determines a partial discharge in response to a result of the continuity determination unit. The partial discharge detection device according to claim 1, wherein the determined threshold value is set for each time. The part according to claim 1 or 2, wherein the continuity determination unit has a plurality of determination criteria, and the partial discharge determination unit determines a partial discharge based on the number of times each of the plurality of determination criteria occurs. Discharge detection device. The partial discharge detection device according to any one of claims 1 to 3, wherein the sensor is a surface current sensor. Limit the signal detected by the sensor that detects the surface current of the object to the set frequency band,
Measuring the energy of the signal limited to the set frequency band,
Sampling and recording a signal corresponding to the energy intensity,
Analyzing the recorded signal,
The analysis is
Extracting signals above a defined threshold,
Removing signals outside the defined period,
Determining the continuity of the signal of the defined period,
Determining partial discharge in response to the result of determining the continuity,
A partial discharge detection method comprising:

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