Partial discharge detection method and partial discharge detection device

Abstract

To provide a partial discharge detection method capable of separating aerial discharge and partial discharge to suitably detect the partial discharge under a condition where the aerial discharge and the partial discharge coexist.SOLUTION: A partial discharge detection method comprises: detecting a transient ground voltage in order to detect the presence or absence of partial discharge in a device installed inside a tank; obtaining two time signals from two TEV sensors, one being a grounded first TEV sensor and the other being an ungrounded second TEV sensor; transforming the two time signals into two frequency signals by Fourier transform; obtaining a frequency signal of a difference component based on the two frequency signals; transforming the frequency signal of the differential component into a time signal of the differential component by inverse Fourier transform; and obtaining a partial discharge signal based on the time signal of the difference component.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a partial discharge detection method and device that suitably separates air discharge from discharge occurring inside high-voltage equipment (hereinafter sometimes referred to as "partial discharge") in high-voltage equipment. [Background technology]

[0002] High-voltage equipment such as distribution boards, switchgears, transformers, and switches are used for a long period of time after installation, and as a result, deterioration over time, such as a decline in insulation performance (insulation abnormality), occurs. It is generally known that partial discharge occurs inside high-voltage equipment when the insulation performance declines. In particular, repeated partial discharges inside high-voltage equipment can lead to insulation breakdown, which may lead to disasters such as fires. Therefore, it is important to detect partial discharges in order to operate high-voltage equipment safely.

[0003] Background art in this technical field includes, for example, Japanese Patent Application Laid-Open No. 09-068556 (hereinafter referred to as Patent Document 1) and Japanese Patent Application Laid-Open No. 10-210647 (hereinafter referred to as Patent Document 2).

[0004] Patent Document 1 describes an electrical equipment insulation diagnostic device that detects electromagnetic waves generated by partial discharges that occur due to insulation abnormalities in electrical equipment and determines whether or not there is an insulation abnormality. The electrical equipment described is targeted at polyphase AC electrical equipment, and the electrical equipment insulation diagnostic device has detection means that is installed in each phase of the electrical equipment and detects electromagnetic waves of each phase, and determination means that monitors and compares the output levels of the detection means for each phase, and determines that an insulation abnormality has occurred if the output level of one or more of the multiple phases exceeds a reference level and only one of the multiple phases has a uniquely high output level (see the abstract of Patent Document 1).

[0005] Furthermore, Patent Document 2 describes an insulation abnormality diagnosis device for electrical equipment that distinguishes between electromagnetic waves due to partial discharge and external noise, detecting external noise using a noise antenna, selecting a predetermined number of frequencies with little external noise within a diagnostic frequency band of 300 to 1000 MHz, determining these as diagnostic frequencies, and using detection signals of the diagnostic frequencies from among signals detected by the abnormal electromagnetic wave detection antenna during diagnostic processing, the device has a judgment unit that judges whether or not there is an insulation abnormality (see the abstract of Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 09-068556 [Patent Document 2] Japanese Patent Application Publication No. 10-210647 Summary of the Invention [Problem to be solved by the invention]

[0007] Patent Document 1 describes an insulation diagnostic device for electrical equipment that detects electromagnetic waves generated by partial discharge without being affected by external noise, and Patent Document 2 describes an insulation abnormality diagnostic device for electrical equipment that distinguishes between electromagnetic waves generated by partial discharge and external noise.

[0008] However, Patent Document 1 and Patent Document 2 do not describe a partial discharge detection method or partial discharge detection device that separates and appropriately detects partial discharge in a situation in which air discharge and partial discharge are mixed.

[0009] Therefore, the present invention provides a partial discharge detection method and a partial discharge detection device that separates aerial discharge from partial discharge and appropriately detects partial discharge in a situation in which aerial discharge and partial discharge coexist. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, the partial discharge detection method of the present invention detects whether or not partial discharge has occurred in equipment installed inside a tank by detecting a transient ground voltage, obtaining two time signals from two TEV sensors, one of which is a grounded first TEV sensor and the other is an ungrounded second TEV sensor, converting the two time signals into two frequency signals by Fourier transform, obtaining a differential component frequency signal based on the two frequency signals, converting the differential component frequency signal into a differential component time signal by inverse Fourier transform, and obtaining a partial discharge signal based on the differential component time signal.

[0011] In addition, the partial discharge detection device of the present invention is characterized by having two TEV sensors, one of which is a grounded first TEV sensor and the other is an ungrounded second TEV sensor, which detect transient ground voltages to detect the presence or absence of partial discharge in equipment inside the tank, and a signal detection device which acquires two time signals from the two TEV sensors, converts the two time signals into two frequency signals by Fourier transform, acquires a differential component frequency signal based on the two frequency signals, converts the differential component frequency signal into a differential component time signal by inverse Fourier transform, and acquires a partial discharge signal based on the differential component time signal. Effect of the Invention

[0012] According to the present invention, it is possible to provide a partial discharge detection method and a partial discharge detection device that can separate aerial discharge and partial discharge and appropriately detect partial discharge in a situation in which aerial discharge and partial discharge coexist.

[0013] Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is an explanatory diagram for explaining a schematic diagram of the partial discharge detection device described in the first embodiment. [Diagram 2]4 is an explanatory diagram illustrating detection signals of the TEV sensor 1a and the TEV sensor 1b detected in the tank 4 described in the first embodiment. FIG. [Diagram 3] FIG. 4 is an explanatory diagram illustrating a frequency signal obtained by Fourier transform of a detection signal. [Figure 4] 10 is an explanatory diagram illustrating a calculation result obtained by arithmetic processing of a frequency signal. FIG. [Diagram 5] FIG. 11 is an explanatory diagram for explaining a time signal obtained by inverse Fourier transform of the calculation result. [Figure 6] FIG. 4 is an explanatory diagram illustrating a flow of signal processing in the signal detection device 3 described in the first embodiment. [Figure 7] FIG. 4 is an explanatory diagram for explaining calibration data for identifying the charge amount of partial discharge described in the first embodiment. [Figure 8] 2 is an explanatory diagram for explaining a metal plate 2 described in Example 1. FIG. [Figure 9] FIG. 11 is an explanatory diagram for explaining a schematic diagram of a partial discharge detection device according to a second embodiment. [Figure 10] FIG. 11 is an explanatory diagram for explaining a schematic diagram of a partial discharge detection device according to a third embodiment. [Figure 11] FIG. 11 is an explanatory diagram for explaining a schematic diagram of a partial discharge detection device described in a fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In each drawing, substantially the same or similar configurations will be described using the same reference numerals. When the description of each drawing is repeated, the repeated description may be omitted. EXAMPLES

[0016] First, a partial discharge detection device according to a first embodiment will be described.

[0017] FIG. 1 is an explanatory diagram for explaining a schematic diagram of the partial discharge detection device described in the first embodiment.

[0018] In Example 1, the high-voltage device typically includes a tank 4 having therein equipment for which it is desired to detect the occurrence of partial discharge 12, and an external power source 7 that supplies high voltage to the equipment inside the tank 4 via an application line 13 and a high-voltage bushing 6, and the equipment inside the tank 4 includes an insulator 5 and an object to be insulated 9 that is insulated by the insulator 5.

[0019] One end of the object to be insulated 9 is connected to the high-voltage bushing 6, and the other end of the object to be insulated 9 is grounded.

[0020] A high voltage is supplied to the equipment inside the tank 4 from an external power source 7 via an application line 13 and the high-voltage bushing 6. At this time, aerial discharges 11 frequently occur from the high-voltage bushing 6 in the air portion of the high-voltage bushing 6.

[0021] On the other hand, when the equipment inside the tank 4 is used for a long period of time, aging degradation such as a decrease in insulating performance occurs in the insulator 5. That is, voids 10 occur inside the insulator 5, and the insulating performance of the insulator 5 decreases. Then, when a high voltage is supplied to the equipment inside the tank 4, partial discharges 12 occur from the insulator 5 inside the tank 4 due to the voids 10 that have occurred inside the insulator 5.

[0022] Generally, air discharge 11 and partial discharge 12 occur at almost the same time, so when detecting discharge signals using a normal antenna, the air discharge signal and the partial discharge signal overlap, making it difficult to detect only the partial discharge signal.

[0023] Therefore, in the first embodiment, two Transient Earth Voltage (TEV) sensors 1 (TEV sensor 1a and TEV sensor 1b) for detecting a TEV are used.

[0024] The TEV sensor 1a and the TEV sensor 1b are each provided with a metal plate 2. The TEV sensor 1a and the TEV sensor 1b each detect a surface current induced on the surface of the metal plate 2 as a voltage signal (detection signal), and output the surface current.

[0025] Both the TEV sensor 1a having the metal plate 2 and the TEV sensor 1b having the metal plate 2 are installed outside (on the outside) of the tank 4, and are installed around the equipment in which partial discharge is desired to be detected (around the tank 4).

[0026] A ground wire 8 is connected to the metal plate 2 of one of the TEV sensors, for example, TEV sensor 1a having the metal plate 2, while a ground wire 8 is not connected to the metal plate 2 of the other of the TEV sensors, for example, TEV sensor 1b having the metal plate 2. The ground wire 8 is connected to a ground wire that connects the other of the insulation object 9 to the ground and to the tank 4.

[0027] That is, TEV sensor 1a is at ground potential, and TEV sensor 1b is at floating potential.

[0028] The TEV sensor 1a detects partial discharge signals generated from the insulator 5 via a ground wire 8 that connects the ground wire connected to the tank 4 and the metal plate 2 of the TEV sensor 1a. At the same time, the TEV sensor 1a detects air discharge signals as an antenna.

[0029] The TEV sensor 1a detects the air discharge signal and the partial discharge signal simultaneously. However, since the air discharge signal reaches the TEV sensor 1a as an electromagnetic wave, it is detected earlier than the partial discharge signal that arrives via the ground wire 8.

[0030] On the other hand, the TEV sensor 1b detects an air discharge signal propagating through the air portion as an antenna.

[0031] The TEV sensors 1a and 1b are each connected to a signal detection device 3 via a measurement line 14. The signal detection device 3 is also connected to a display device 15. The signal detection device 3 stores the arrival time and signal strength of the voltage signals detected by the TEV sensors 1a and 1b. The detection timing of the voltage signals of the TEV sensors 1a and 1b is synchronized. The display device 15 also displays Figures 2, 3, 4, 5, 7, etc., which will be described later.

[0032] Next, the detection signals of the TEV sensor 1a and the TEV sensor 1b detected in the tank 4 described in the first embodiment will be described.

[0033] FIG. 2 is an explanatory diagram illustrating detection signals of the TEV sensor 1a and the TEV sensor 1b detected in the tank 4 described in the first embodiment.

[0034] FIG. 2 shows the relationship between time (eg, μsec) and signal strength (eg, mV). The signal strength is the detection signal detected by TEV sensor 1a and TEV sensor 1b, and is a voltage signal.

[0035] 2 shows the detection signal (ungrounded) detected by the TEV sensor 1b, and the lower part of FIG. 2 shows the detection signal (grounded) detected by the TEV sensor 1a.

[0036] 2, the detection signal (output signal) of TEV sensor 1a and the detection signal (output signal) of TEV sensor 1b detected in tank 4 are different. The detection signal of TEV sensor 1a (lower stage) contains an air discharge signal component and a partial discharge signal component, so the signal strength is large, while the detection signal of TEV sensor 1b (upper stage) contains only an air discharge signal component, so the signal strength is small.

[0037] The TEV sensor 1a detects the air discharge signal and the partial discharge signal simultaneously. The air discharge signal arrives at the TEV sensor 1a as an electromagnetic wave, and is therefore detected earlier than the partial discharge signal that arrives via the ground wire 8.

[0038] Next, a frequency signal obtained by Fourier transform of the detection signal will be described.

[0039] FIG. 3 is an explanatory diagram for explaining a frequency signal obtained by Fourier transform of a detection signal.

[0040] Figure 3(a) is a diagram similar to Figure 2, Figure 3(b) is a diagram (grounded) obtained by Fourier transforming the lower part of Figure 3(a), and Figure 3(c) is a diagram (ungrounded) obtained by Fourier transforming the upper part of Figure 3(a). Figures 3(b) and 3(c) show the relationship between frequency (e.g., Hz) and signal strength (e.g., dimensionless: relative energy ratio).

[0041] The time domain signals of the detection signal (grounded) of the TEV sensor 1a and the detection signal (ungrounded) of the TEV sensor 1b are converted into respective frequency domain signals by Fourier transform. In other words, the time signals (detection signals) of the grounded and ungrounded are converted into respective frequency signals of the grounded and ungrounded by Fourier transform.

[0042] As shown in Figures 3(b) and 3(c), the frequency spectrum (including air discharge signal components and partial discharge signal components) of the TEV sensor 1a at ground potential contains many low-frequency components, while the frequency spectrum (including only air discharge signal components) of the TEV sensor 1b at floating potential contains many high-frequency components.

[0043] This is because the detection signal of the TEV sensor 1a includes a superimposed air discharge signal and a partial discharge signal, while the detection signal of the TEV sensor 1b includes only the air discharge signal.

[0044] In other words, since the detection signal of the TEV sensor 1a is detected via the ground wire 8, when the detection signal propagates through the ground wire 8, an effect equivalent to a low-pass filter occurs due to the influence of the ground capacitance of the ground wire 8, resulting in an increase in low-frequency components.

[0045] Next, the results of the calculation performed on the frequency signal will be described.

[0046] FIG. 4 is an explanatory diagram for explaining the calculation results obtained by arithmetic processing of the frequency signal.

[0047] FIG. 4(a) is a view similar to FIG. 3(b), and FIG. 4(b) is a view similar to FIG. 3(c).

[0048] Then, based on the grounded frequency spectrum (frequency signal) shown in FIG. 4(a) and the non-grounded frequency spectrum (frequency signal) shown in FIG. 4(b), an arithmetic operation (logical operation) is performed to extract an AND component and a difference component.

[0049] In other words, the frequency spectrum of air discharge is extracted by extracting the AND component (the spectrum obtained by calculation of the AND component) from the frequency signals in the two frequency spectra, and the frequency spectrum of partial discharge is extracted by extracting the difference component (the spectrum obtained by calculation of the difference component).

[0050] The calculation of the AND component is an operation that compares the grounded frequency signal with the non-grounded frequency signal and extracts the smaller frequency signal, and the calculation of the differential component is an operation that subtracts the non-grounded frequency signal from the grounded frequency signal and extracts the absolute value of the subtracted frequency signal.

[0051] Next, the time signal obtained by inverse Fourier transform of the calculation result will be described.

[0052] FIG. 5 is an explanatory diagram for explaining a time signal obtained by inverse Fourier transform of the calculation result.

[0053] Figure 5(a) is a diagram similar to Figure 4(c), and Figure 5(b) is a diagram similar to Figure 4(d). Figure 5(c) is a diagram (air discharge) obtained by inverse Fourier transform of Figure 5(a), and Figure 5(d) is a diagram (partial discharge) obtained by inverse Fourier transform of Figure 5(b). Figures 5(c) and 5(d) show the relationship between time (e.g., μsec) and signal strength (e.g., mV).

[0054] In this way, the frequency domain signal is converted to a time domain signal by inverse Fourier transform. In other words, the frequency signals of the AND component and the difference component are converted to time signals of the air discharge and partial discharge by inverse Fourier transform.

[0055] In this way, a time signal of the air discharge and a time signal of the partial discharge are detected.

[0056] Then, based on the relationship between time and signal intensity during partial discharge (FIG. 5(d)), it is possible to detect the occurrence of partial discharge 12 in the equipment inside the tank 4, which is caused by voids 10 occurring inside the insulator 5. In other words, the insulation state of the equipment inside the tank 4 can be grasped.

[0057] Next, a flow of signal processing in the signal detection device 3 according to the first embodiment will be described.

[0058] FIG. 6 is an explanatory diagram illustrating a flow of signal processing in the signal detection device 3 described in the first embodiment.

[0059] (1) In S101, a ground detection signal and a non-ground time signal (signal of signal strength against time) are obtained using a TEV sensor 1a (first TEV sensor) and a TEV sensor 1b (second TEV sensor) (see FIG. 2).

[0060] (2) In S102, the time signal of the detection signal (grounded) of the TEV sensor 1a is converted into a frequency signal by Fourier transform, and the time signal of the detection signal (ungrounded) of the TEV sensor 1b is converted into a frequency signal (signal of signal strength versus frequency) by Fourier transform (see FIG. 3).

[0061] (3) In S103, an arithmetic process is performed based on the grounded frequency signal and the ungrounded frequency signal to obtain an AND component frequency signal and a difference component frequency signal (see FIG. 4). In other words, the common signal component (AND component) of the two frequency signals is regarded as an aerial discharge component, and the remaining signal component (difference component) of the two frequency signals is regarded as a partial discharge component.

[0062] (4) In S104, the frequency signal of the AND component is converted into a time signal of the AND component by inverse Fourier transform, and the frequency signal of the difference component is converted into a time signal of the difference component by inverse Fourier transform (see FIG. 5).

[0063] (5) In S105, an air discharge signal is acquired based on the time signal of the AND component, and a partial discharge signal is acquired based on the time signal of the difference component (see FIG. 5).

[0064] In this way, the partial discharge detection method described in Example 1 detects the occurrence or non-occurrence of partial discharge 12 in equipment installed inside the tank 4 by acquiring two time signals from two TEV sensors 1, one of which is a grounded TEV sensor 1a (first TEV sensor) and the other is an ungrounded TEV sensor 1b (second TEV sensor), which are installed around the tank 4 to detect transient ground voltages, converting these two time signals into two frequency signals by Fourier transform, acquiring a differential component frequency signal based on these two frequency signals, converting this differential component frequency signal into a differential component time signal by inverse Fourier transform, and acquiring a partial discharge signal based on the differential component time signal.

[0065] Moreover, the partial discharge detection device described in the first embodiment has two TEV sensors 1, one of which is a grounded TEV sensor 1a (first TEV sensor) and the other of which is an ungrounded TEV sensor 1b (second TEV sensor), that are installed around the tank 4 in order to detect the occurrence of partial discharge 12 in equipment installed inside the tank 4 and detect transient ground voltages, and a signal detection device 3 that acquires two time signals from the two TEV sensors 1, converts these two time signals into two frequency signals by Fourier transform, acquires a frequency signal of a difference component based on these two frequency signals, converts this frequency signal of a difference component into a time signal of a difference component by inverse Fourier transform, and acquires a partial discharge signal based on the time signal of the difference component.

[0066] This allows the detection of an air discharge signal and a partial discharge signal, making it possible to detect the occurrence of partial discharge 12 in the equipment inside the tank 4. Then, based on the partial discharge signal, the insulation state of the equipment inside the tank 4 can be grasped.

[0067] Thus, according to the first embodiment, when detecting a partial discharge 12, an air discharge 11 (including external electromagnetic noise such as radio waves) generated at a location exposed to the air, such as a high-voltage bushing 6, is superimposed on a partial discharge 12 generated in the equipment to be detected, but only this partial discharge 12 can be detected.

[0068] Furthermore, according to the first embodiment, when using the TEV sensor 1 to detect partial discharge 12, there is no need to select a predetermined number of frequencies, and there is no need to determine a diagnostic frequency, and only partial discharge 12 can be detected.

[0069] In other words, according to Example 1, two TEV sensors 1, one grounded and one ungrounded, are used, and the output signals from these two TEV sensors 1 are signal processed, so that in a situation in which air discharges 11 and partial discharges 12 coexist, the air discharges 11 and partial discharges 12 can be separated, and partial discharges 12 can be suitably detected even in an environment with a large amount of external noise.

[0070] Next, the calibration data for identifying the charge amount of partial discharge described in the first embodiment will be described.

[0071] FIG. 7 is an explanatory diagram for explaining calibration data for identifying the charge amount of partial discharge described in the first embodiment.

[0072] Here, the magnitude of the charge of the detected partial discharge 12 is identified.

[0073] First, calibration data is acquired to identify the magnitude of the charge of the detected partial discharge 12.

[0074] In the calibration data shown in FIG. 7, the horizontal axis represents the detection signal strength (mV) and the vertical axis represents the calibration signal strength (pC).

[0075] This calibration data is obtained by the following procedure. (1) First, a discharge generating device or a signal generating device with a known discharge charge amount is connected to the equipment, and a discharge or a signal is generated. (2) Next, the TEV sensor 1a and the TEV sensor 1b are used to obtain a ground detection signal and a non-ground time signal, and a partial discharge signal is obtained according to the signal processing flow described above. (3) This is carried out with several different amounts of discharge charge to obtain a characteristic curve (calibration data) between the detection signal strength and the calibration signal strength. (4) Then, using this calibration data, the magnitude of the charge amount of the detected partial discharge 12 (calibration signal strength) is identified based on the signal strength of the partial discharge 12 (detection signal strength) at a certain time.

[0076] This makes it possible to identify the magnitude of the charge of the detected partial discharge 12.

[0077] Next, the metal plate 2 described in the first embodiment will be described.

[0078] FIG. 8 is an explanatory diagram for explaining the metal plate 2 described in the first embodiment.

[0079] Here, the metal plate 2 made of, for example, aluminum or stainless steel and installed in the TEV sensor 1a and the TEV sensor 1b has a bowtie antenna shape. That is, the metal plate 2 is made of two isosceles triangular plates of the same shape, and is installed so that the apex angles of the isosceles triangular plates face each other.

[0080] Since the aerial discharge 11 is often in the GHz band, it is preferable to set the antenna length and the antenna opening angle so that the center frequency in the frequency characteristics of the bowtie antenna is in the GHz band, and it is particularly preferable to set the antenna length to 10 cm or more and the antenna opening angle to 30 degrees or more. In Example 1, the antenna length is 10 cm and the antenna opening angle is 30 degrees.

[0081] This makes it possible to achieve wideband frequency characteristics and improve reception sensitivity. EXAMPLES

[0082] Next, a partial discharge detection device according to a second embodiment will be described.

[0083] FIG. 9 is an explanatory diagram for explaining a schematic diagram of the partial discharge detection device described in the second embodiment.

[0084] In the second embodiment, the TEV sensor 1a is directly installed on the metal portion on the side surface of the tank 4. This makes it possible to obtain the same effect as in the first embodiment.

[0085] Partial discharge 12, which is a radial electromagnetic wave generated inside tank 4, is induced in the metal part of the wall of tank 4, generating a surface current.

[0086] According to the second embodiment, the signal strength of the partial discharge can be increased by detecting the surface current induced in the metal portion.

[0087] In the second embodiment, the metal plate 3 is not provided on the TEV sensor 1a. EXAMPLES

[0088] Next, a partial discharge detection device according to a third embodiment will be described.

[0089] FIG. 10 is an explanatory diagram for explaining a schematic diagram of the partial discharge detection device described in the third embodiment.

[0090] In the third embodiment, three TEV sensors 1a are directly installed at three locations on the metal portion of the side surface of the tank 4. This makes it possible to obtain the same effects as those of the first embodiment.

[0091] The three locations to be installed on the metal portion of the side surface of the tank 4 are spaced apart from one another. Specifically, for example, one is installed on the side surface of the tank 4, one is installed on the upper end of the side surface opposite the side surface of the tank 4, and one is installed on the lower end of the side surface opposite the side surface of the tank 4.

[0092] When the TEV sensors 1a are installed at three locations spaced apart from each other, the arrival times of the electromagnetic waves of the partial discharge 12 differ. Then, the arrival times of the first wave of the detection signals of the three TEV sensors 1a are compared.

[0093] The shorter the distance from the partial discharge source to the TEV sensor 1a, the faster this arrival time.

[0094] In addition, since the speed of the electromagnetic waves of the partial discharge 12 is constant, the distance between the partial discharge source and each TEV sensor 1a can be obtained from the arrival time of the electromagnetic waves of the partial discharge 12 at each TEV sensor 1a.

[0095] According to the third embodiment, the TEV sensors 1a are installed at three locations, so that the location of the partial discharge source can be identified. That is, the distance from each TEV sensor 1a to the partial discharge source is taken as the radius of the circle centered on each TEV sensor 1a, and the overlapping portion of these circles is the location of the partial discharge source.

[0096] In the third embodiment, the three TEV sensors 1a are installed at three locations, but three or more TEV sensors 1a may be installed at three or more locations.

[0097] In the third embodiment, the metal plate 3 is not provided on the three TEV sensors 1a. EXAMPLES

[0098] Next, a partial discharge detection device according to a fourth embodiment will be described.

[0099] FIG. 11 is an explanatory diagram for explaining a schematic diagram of the partial discharge detection device described in the fourth embodiment.

[0100] In the fourth embodiment, a changeover switch 16 is installed on the metal plate 2 installed on the TEV sensor 1. One end of the changeover switch 16 is connected to the metal plate 2, and the other end of the changeover switch 16 is connected to the ground wire 8, and the TEV sensor 1 is switched between grounded (ON) and ungrounded (OFF) by turning the changeover switch 16 ON and OFF. In other words, two TEV sensors 1 are realized with one TEV sensor 1 by the changeover switch 16 installed on the metal plate 2. This makes it possible to obtain the same effects as in the first embodiment.

[0101] According to the fourth embodiment, one TEV sensor can be switched between grounded and ungrounded to obtain grounded and ungrounded detection signals. That is, when the selector switch 16 is grounded, a partial discharge signal and an air discharge signal are obtained, and when the selector switch 16 is ungrounded, only an air discharge signal is obtained.

[0102] The present invention is not limited to the following examples, and includes various modified examples. For example, the following examples are specifically described in order to explain the present invention in an easily understandable manner, and the present invention is not necessarily limited to those having all of the described configurations.

[0103] Also, a part of the configuration of one embodiment can be replaced with a part of the configuration of another embodiment. Also, the configuration of another embodiment can be added to the configuration of one embodiment. Also, a part of the configuration of each embodiment can be deleted, and a part of another configuration can be added or replaced with a part of another configuration. [Explanation of symbols]

[0104] 1...TEV sensor 2…Metal plate 3. Signal detection device 4. Tank 5…Insulator 6…High voltage bushing 7…External power supply 8…Ground wire 9…Insulation target 10…Void 11...Air discharge 12…partial discharge 13...Applying wire 14…Measurement line 15...Display device 16...Selector switch

Claims

1. A partial discharge detection method for detecting the occurrence of partial discharge in a device that is installed inside a tank having a metal part and is completely covered by the tank, comprising: using a first TEV sensor and a second TEV sensor that detect electromagnetic waves generated by the partial discharge as a transient ground voltage, the first TEV sensor is grounded together with the tank to obtain a first time signal including an air discharge signal component and a partial discharge signal component, and obtaining a second time signal including an air discharge signal component but not including a partial discharge signal component from an ungrounded second TEV sensor; converting the first time signal and the second time signal into a first frequency signal including an air discharge signal component and a partial discharge signal component and a second frequency signal including the air discharge signal component but not the partial discharge signal component by a Fourier transform; obtaining a frequency signal of a difference component based on the first frequency signal and the second frequency signal; converting the frequency signal of the difference component into a time signal of the difference component by an inverse Fourier transform; A partial discharge detection method, comprising: acquiring a partial discharge signal based on the time signal of the difference component.

2. 2. A partial discharge detection method according to claim 1, comprising: A partial discharge detection method, comprising providing a metal plate on at least the detection surface of the non-grounded second TEV sensor.

3. 3. A partial discharge detection method according to claim 2, comprising: The partial discharge detection method according to claim 1, wherein the metal plate is shaped like a bowtie antenna.

4. 2. A partial discharge detection method according to claim 1, comprising: A partial discharge detection method, comprising: installing the first TEV sensor directly on the metal portion of the side of the tank.

5. A partial discharge detection method according to claim 4, comprising: A partial discharge detection method comprising: installing at least three or more first TEV sensors; obtaining the distance between a partial discharge source and each of the first TEV sensors from the arrival time of a partial discharge at each of the first TEV sensors; and identifying the position of the partial discharge source.

6. 3. A partial discharge detection method according to claim 2, comprising: A partial discharge detection method, characterized in that the first TEV sensor and the second TEV sensor are realized by a changeover switch installed on the metal plate.

7. A device for detecting the occurrence of partial discharge in equipment installed inside a tank having a metal part and completely covered by the tank, comprising a first TEV sensor and a second TEV sensor which detect electromagnetic waves generated by the partial discharge as a transient ground voltage, wherein the first TEV sensor is grounded together with the metal part of the tank and acquires a first time signal which includes an air discharge signal component and a partial discharge signal component, and the second TEV sensor is not grounded and acquires a second time signal which does not include a partial discharge signal component but includes an air discharge signal component; a signal detection device that acquires the first time signal and the second time signal from the first TEV sensor and the second TEV sensor, converts the first time signal and the second time signal by Fourier transform into a first frequency signal including an air discharge signal component and a partial discharge signal component and a second frequency signal including the air discharge signal component but not the partial discharge signal component, acquires a frequency signal of a difference component based on the first frequency signal and the second frequency signal, converts the frequency signal of the difference component into a time signal of a difference component by inverse Fourier transform, and acquires the partial discharge signal based on the time signal of the difference component; A partial discharge detection device comprising:

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