Discharge detection device and discharge detection method

Abstract

To appropriately detect discharge.SOLUTION: A discharge detection device includes a discharge detection portion, a waveform extension circuit, and a determination circuit. The discharge detection portion has a metal electrode that detects discharge between an electrode and a sliding body being in contact with and slidable on the electrode. The waveform extension circuit extends a discharge waveform output from the discharge detection portion in a time direction. The determination circuit determines that discharge has occurred in the sliding body when a signal value exceeds a first threshold and the time during which the signal value exceeds the first threshold is held for a time longer than the first time, for output of the waveform extension circuit.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to an electric discharge detection device and an electric discharge detection method. [Background technology]

[0002] Sliding current-carrying mechanisms, which bring two different electrical components into contact with each other and conduct electricity between them, are used in a wide variety of electrical products in a wide range of fields as a method of conducting electricity in electrical machines with moving parts, as typified by the brushes and collector rings (slip rings) of rotating electrical machines. In such sliding current-carrying mechanisms, the electrical components gradually wear out due to the sliding, and maintenance work such as inspection and replacement is required.

[0003] However, the wear state of electrical parts varies greatly depending on the operating conditions of the electric machine, the surrounding environment, and the state of the contact cross section of the sliding contact part, and the rate of wear varies depending on the magnitude of the current flowing through each part. If this sliding current-carrying mechanism stops functioning, the flow of current will be interrupted, which will cause the electric machine to stop, and this could lead to a serious accident. It has also been revealed that when the sliding current-carrying mechanism stops functioning and the flow of current begins to be interrupted, spark discharges occur where two different electrical parts are in contact with each other, and abnormalities can be detected by monitoring the condition of the electrical machine's sliding parts and detecting spark discharges.

[0004] It is desirable for a detection device to automatically detect spark discharges that occur in a very short time with high accuracy and early detection. For this reason, it is desirable for the detection device to quickly and accurately detect impulse waves caused by spark discharges, but in order to configure a detection device that operates at high speed, electronic components capable of high-speed sampling are required, which increases the cost of the device. Furthermore, in order to detect spark discharges, the occurrence of which cannot be predicted, a large-capacity storage device is required to store the results of sampling performed at high speed, and securing this storage capacity also increases the cost. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-054575 A Summary of the Invention [Problem to be solved by the invention]

[0006] One embodiment proposes an apparatus for appropriately detecting electrical discharges. [Means for solving the problem]

[0007] According to one embodiment, the discharge detection device includes a discharge detection unit, a waveform expansion circuit, and a determination circuit. The discharge detection unit has a metal electrode that detects a discharge between an electrode and a sliding body that is in contact with the electrode and can slide. The waveform expansion circuit expands the discharge waveform output from the discharge detection unit in the time direction. The determination circuit determines that a discharge has occurred in the sliding body when the signal value of the output of the waveform expansion circuit exceeds a first threshold value and the time during which the signal value exceeds the first threshold value is maintained longer than a first time. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating a generator using a rotating electric machine according to an embodiment. [Diagram 2] 1 is a block diagram illustrating a discharge detection device according to an embodiment; [Diagram 3] FIG. 2 is a diagram illustrating an example of waveform stretching according to an embodiment. [Figure 4] FIG. 13 is a diagram illustrating an example of a clear state of an expanded wavelength by a clearing circuit according to an embodiment. [Diagram 5] FIG. 2 is a diagram illustrating an example of an overall path of the electric discharge detection device according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment will be described with reference to the drawings. In this disclosure, the terms "greater than" and "less than" may be used, but these terms may be interpreted as "greater (higher)" and "smaller (lower)" respectively, to the extent that they are not inconsistent. Also, they may be interpreted in the opposite manner.

[0010] Fig. 1 is a schematic diagram showing a generator using a rotating electric machine according to an embodiment. Fig. 1 is shown as a non-limiting example, and the discharge detection in the present disclosure is not limited to the rotating electric machine of this configuration, but can be used for a device that has a sliding mechanism and is likely to generate discharge or spark discharge.

[0011] The generator 1 comprises a stator 10, a rotor 12, a rotating portion 14, and a stationary portion 16.

[0012] The stator 10 is fixedly installed in the generator 1. The rotor 12 is installed between the stators 10 or within the stators 10 so as to be rotatable. When the rotor 12 is excited, the rotor 12 rotates around its axis inside the stator 10. When the rotor 12 rotates within the rotating part 14, a current is generated in the stator 10, and appropriate AC is output. Furthermore, when a permanent magnet is used for the stator 10, when the rotor 12 rotates within the rotating part 14, a current is generated in the rotor 12, and the current is output via the rotating part 14.

[0013] The rotating part 14 rotates together with the rotor 12. The rotating part 14 is, for example, a slip ring.

[0014] The stationary portion 16 is an electrode that is installed in contact with the electrode portion 14a of the rotating portion 14. The electrodes are in sliding contact with each other between the rotating portion 14 and the stationary portion 16. The stationary portion 16 is, for example, a brush-type electrode, and when an excitation current flows through the electrode portion 14a via the stationary portion 16, the rotor 12 is excited and a magnetic flux (electromagnet) is formed.

[0015] Discharges may occur at the sliding electrical conductive portion between the rotating portion 14 and the stationary portion 16. The discharge detection device of the present disclosure appropriately detects these discharges.

[0016] 2 is a block diagram showing a schematic diagram of a discharge detection device according to an embodiment. The discharge detection device 2 includes a discharge detection unit 200, a filter circuit 202, a rectifier circuit 204, a waveform expansion circuit 206, a clear circuit 208, a voltmeter 210, a determination circuit 212, and a clear time setting circuit 214. The discharge detection device 2 detects a discharge at a location of sliding contact. The discharge detection device 2 detects, for example, a spark discharge at a location of sliding contact.

[0017] Among these, the filter circuit 202, the rectifier circuit 204, the clear circuit 208, and the clear time setting circuit 214 are circuits that can be provided optionally. In other words, the discharge detection device 2 may be provided with, as a minimum configuration, the discharge detection unit 200, the waveform expansion circuit 206, the voltmeter 210, and the determination circuit 212.

[0018] (First embodiment) As a first embodiment, a discharge detection device 2 including the discharge detection unit 200, which is the minimum configuration among the above, a waveform stretching circuit 206, a voltmeter 210, and a determination circuit 212 will be described. In this case, the filter circuit 202, the rectifier circuit 204, the clearing circuit 208, and the clearing time setting circuit 214 in Fig. 2 are omitted. That is, the waveform stretching circuit 206 is connected to the output of the discharge detection unit 200, the voltmeter 210 is connected to the output of the waveform stretching circuit 206, and the determination circuit 212 is connected to the output of the voltmeter 210. In the following embodiments, detailed explanations of the connections may be omitted, but appropriate components are connected to each other based on Fig. 2 etc.

[0019] The discharge detection unit 200 has a metal electrode that detects discharge at a sliding contact portion between the electrode portion 14a of the rotating unit 14 in FIG. 1 and the stationary unit 16 (sliding unit) that is in sliding contact with the electrode portion 14a (i.e., is in contact with and can slide with the electrode portion 14a). The discharge detection unit 200 is disposed, for example, at a distance that allows it to capture discharge from the sliding contact portion. When detecting a spark discharge, the discharge detection unit 200 is disposed, for example, at a position where sparks generated at the sliding contact portion scatter onto the metal electrode. Furthermore, when a discharge detection unit 200 having a physically large shape is used, it is disposed at a distance that allows it to capture discharge at a location (outside the generator 1) that is distant from the housing of the generator 1 that has the sliding contact portion between the electrode portion 14a of the rotating unit 14 in FIG. 1 and the stationary unit 16 that is in sliding contact with the electrode portion 14a.

[0020] The waveform expansion circuit 206 is a circuit that expands in the time direction the discharge waveform output from the discharge detection unit 200. The waveform expansion circuit 206 may be configured as a so-called integration circuit. By configuring it as an integration circuit, it is possible to expand only the waveform in the time direction without destroying the frequency characteristics.

[0021] 3 is a diagram showing an example of the input / output waveforms of the waveform expansion circuit 206. When an impulse-shaped waveform signal is input, the waveform expansion circuit 206 outputs a signal having a waveform obtained by expanding the waveform in the time direction. Such waveform expansion can be achieved by an integrating circuit having a predetermined time constant set.

[0022] The figure below is a comparative example using a bandpass filter (or lowpass filter), which shows that when an impulse-shaped waveform signal is input, the bandpass filter outputs a certain band of frequency components. With a bandpass filter, as shown in the figure, for example, frequency components other than a set frequency are removed, making it impossible to maintain the waveform. In addition, removing frequency components other than the set frequency components generates negative values ​​in the waveform, as shown in the figure.

[0023] For this reason, by using a waveform expansion circuit to expand the waveform of a signal without removing high frequency components, it is possible to expand the waveform in the time direction while appropriately maintaining the amplitude and waveform. The waveform expansion circuit 206 may include a voltage holding time constant circuit that accumulates a voltage for a predetermined time. Based on this time constant, the waveform expansion circuit 206 accumulates the voltage and appropriately expands the waveform in the time direction before outputting it.

[0024] Returning to Fig. 2, the voltmeter 210 is connected to the output of the waveform stretching circuit 206, and measures and outputs the voltage of the waveform output by the waveform stretching circuit 206. This measurement result is output to the determination circuit 212. The voltmeter 210 may include a sampling type voltmeter that detects and holds the discharge waveform with a sampling time that is equal to or less than 1 / 2 the voltage holding time constant of the waveform stretching circuit 206.

[0025] The determination circuit 212 is a circuit that determines whether or not a discharge has occurred based on the waveform output by the waveform expansion circuit 206. For example, the determination circuit 212 uses the output waveform of the waveform expansion circuit 206, which is output as voltage information by the voltmeter 210, for the determination. The determination circuit 212 measures the time during which the absolute value of the voltage of the signal exceeds a first threshold value. If the time during which the voltage exceeds the first threshold value is longer than the first time, the determination circuit 212 determines that a discharge has occurred at the sliding contact portion.

[0026] As described above, according to this embodiment, when a discharge (e.g., a spark discharge) occurs at a sliding contact portion, the signal output from the detection portion near the sliding contact portion is expanded in the time direction, and the magnitude of the amplitude of this expanded signal and the length of time during which the amplitude is large are determined, thereby making it possible to appropriately detect the discharge without being affected by other factors such as noise. Furthermore, the circuit described above can be implemented without using expensive elements with a high sampling speed. This makes it possible to reduce the cost of the discharge detection device 2 without reducing the accuracy of discharge detection.

[0027] In an electrical installation environment in which an electrical sliding component is provided, noise is generated due to the operation of other electrical equipment or high-power devices. The generated noise may propagate to the discharge detection unit 200 by radiation or conduction, and in this case, it affects the waveform captured by the discharge detection unit 200. The signal values ​​of the discharge from the sliding contact part and the influence of these noises are significantly different. Therefore, even in such a case, by having at least the above-mentioned configuration, the discharge detection device 2 can properly detect the discharge from the sliding contact part.

[0028] Second Embodiment The discharge detection device 2 may include a rectifier circuit 204 in addition to the minimum configuration of the first embodiment.

[0029] The rectifier circuit 204 is provided with an insulating section that provides physical insulation between the discharge detection section 200 and the waveform stretching circuit 206. In other words, the rectifier circuit 204 is a rectifier that outputs the signal output from the discharge detection section 200 to the waveform stretching circuit 206 with a connection end on the input side of the waveform stretching circuit 206 being physically insulated from the internal electric circuit of the waveform stretching circuit 206.

[0030] The rectifier circuit 204 receives a signal, for example, by differential input, extracts the absolute value of the amplitude of this differentially input signal, and outputs it to the waveform expander circuit 206. An example of a specific circuit configuration will be described later.

[0031] As described above, according to this embodiment, the waveform to be input to the waveform stretching unit can be converted to a positive component and input. By using a waveform with a positive component, even if the signal output from the discharge detection unit 200 has a waveform that changes in both positive and negative directions, it is possible to stretch the waveform that changes in only one direction in the waveform stretching circuit 206, and by holding the voltage with a predefined time constant, it is possible to convert the impulse-shaped discharge detection signal into a low-frequency electrical signal.

[0032] (Third embodiment) The discharge detection device 2 may include a filter circuit 202 in addition to the configuration of each of the above-described embodiments.

[0033] The filter circuit 202 may be a circuit that selectively passes a signal portion having a component larger than a second threshold value with respect to the signal output from the discharge detection unit 200. The waveform expansion circuit 206 expands, in the time direction, the signal having a component larger than the second threshold value.

[0034] By using such a filter circuit 202, it becomes possible to detect discharge from the sliding contact portion while removing small amplitude noise components more accurately than in the above-mentioned embodiments. The second threshold value may be the same as the first threshold value, or may be smaller or larger than the first threshold value.

[0035] Furthermore, the filter circuit 202 may include an amplitude limiting circuit that removes waveforms having amplitudes equal to or greater than a predetermined amplitude, from the viewpoint of avoiding damage to elements included in the circuits of the waveform stretching circuit 206 and the voltmeter 210. For example, the filter circuit 202 may saturate and output amplitudes equal to or greater than a predetermined amplitude to a predetermined amplitude. The filter circuit 202 that achieves this amplitude limiting may be disposed, as another example, in the preceding stage of the waveform stretching circuit 206 or in the preceding stage of the voltmeter 210, rather than being connected to the output of the discharge detection unit 200 as shown in FIG. 2.

[0036] By providing such a filter circuit 202, it becomes possible to detect discharges using elements that do not have a high withstand voltage, and as a result, the cost of the discharge detection device 2 can be further reduced.

[0037] As another example, the filter circuit 202 may include a band-pass filter circuit that selectively passes electrical signals in a predetermined frequency band in order to remove noise components.

[0038] The circuits given as examples above may be configured in appropriate combination. As an example, the filter circuit 202 may be configured as a circuit that increases the amplitude above the second threshold and saturates the amplitude to a predetermined amplitude that is higher than the second threshold.

[0039] (Fourth embodiment) The discharge detection device 2 may include a clear circuit 208 in addition to the configuration of each of the above-described embodiments.

[0040] The clear circuit 208 is connected between the waveform stretching circuit 206 and the voltmeter 210. The clear circuit 208 is a circuit that clears the voltage signal held in the waveform stretching circuit 206 to an initial value, for example, ground voltage, after a second time has elapsed since the voltage signal detected by the voltmeter exceeded the first threshold value.

[0041] 4 is a diagram showing an example of detection based on a threshold value from an expanded waveform in a case where the clear circuit 208 is provided and in a case where the clear circuit 208 according to the embodiment described above is not provided. By providing the clear circuit 208 according to this embodiment, the determination circuit 212 can properly detect the occurrence of multiple discharges even when a voltage value exceeding the first threshold value occurs consecutively.

[0042] The clear circuit 208 may clear the output of the waveform stretching circuit 206 at a time interval longer than the first time. As another example, the discharge detection device 2 may further include a clear time setting circuit 214. The clear circuit 208 performs signal processing so that the output is not superimposed on the next waveform, for example, by discharging a capacitor that determines a time constant provided in the waveform stretching circuit 206.

[0043] The clear time setting circuit 214 sets a clear time from the sampling time of the voltmeter 210 and transmits it to the clear circuit 208. When the sampling time of the voltmeter 210 is fixed, the clear time setting circuit 214 is not an essential component. On the other hand, there are cases where the sampling time of the voltmeter 210 is variable, or where the sampling time of the voltmeter 210 fluctuates.

[0044] Even in such a case, it is possible to appropriately clear the expanded wavelength by having the clear time setting circuit 214 acquire the sampling time of the voltmeter 210. The clear time setting circuit 214 sets, for example, a second time that is longer than the first time and shorter than the sampling time of the voltmeter 210, and outputs a timing signal to the clear circuit 208 to clear the expanded wavelength at the timing when the second time has elapsed since the first predetermined value was exceeded.

[0045] The clear time setting circuit 214 may measure the sampling time of the voltmeter 210, and transmit the timing to clear to the clear circuit 208 based on the timing of receiving a determination signal indicating that a discharge has been detected from the determination circuit 212. Based on the second time acquired from the clear time setting circuit 214, the clear circuit 208 sets the voltage value in the signal output by the waveform stretching circuit 206 to the ground voltage at the timing of the second time after the signal exceeds the first threshold value.

[0046] As shown in the right diagram of Figure 4, when discharges occur continuously, the waveform caused by new discharges may be superimposed on the decaying signal in the stretched waveform. In such a case, as shown in the bottom right diagram, when the signal waveforms are compared and output at a certain threshold value (first threshold value), they are extracted as a continuous large waveform, rather than as individual waveforms.

[0047] As in this embodiment, by issuing an instruction to clear the stretched waveform by the clear circuit 208, it becomes possible to appropriately separate and extract consecutively generated discharges one by one. As described above, the discharge from the sliding contact portion is, for example, a spark discharge, and such spark discharges often occur consecutively. For this reason, by providing the clear circuit 208 according to this embodiment and separating and judging consecutive sparks one by one, it becomes possible to detect discharges with higher accuracy.

[0048] Therefore, the determination circuit 212 can more accurately detect discharges based on at least one of the number of times discharges have occurred and the interval between discharge occurrences, in addition to the presence or absence of discharge occurrence.

[0049] Fifth embodiment In the above-described embodiments, a description has been given of the circuit configuration in the discharge detection device 2. In the present embodiment, the overall connections of this circuit will be described.

[0050] FIG. 5 is a diagram showing a schematic diagram of the overall path of the discharge detection device 2 according to one embodiment.

[0051] The discharge detection unit 200 may have a pair of balanced metal electrodes as the metal electrodes. One balanced metal electrode is disposed at a position where the electrode can appropriately capture the discharge from the discharge in the sliding contact portion. In this case, when the discharge detection unit 200 captures a discharge at one or both electrodes, the discharge detection unit 200 propagates the captured signal through the balanced line as a path.

[0052] When the path is a balanced line, the balanced line may be provided with a shield downstream of the discharge detection unit 200, for example, so that noise signals other than from the sliding contact portion are not superimposed on the propagating signal. When used in the generator 1 of Fig. 1, for example, the shield may be appropriately provided inside the generator 1. Of course, this does not exclude the provision of a shield from the outside of the generator 1 to a part of the inside of the discharge detection device 2.

[0053] The signal propagated by the balanced line is input to a filter circuit 202. At this timing, the signal may be processed as a signal having positive and negative signals centered around the ground voltage.

[0054] The rectifier circuit 204, which has a physically isolated region, extracts the absolute values ​​of positive and negative signal values, for example, by connecting an electromagnetic transformer as shown in the figure. The operation of this rectifier circuit 204 is similar to that of a general rectifier circuit, so a detailed description will be omitted.

[0055] This signal is input to the waveform expansion circuit 206. The waveform expansion circuit 206 expands the waveform, which is expressed as an absolute value signal, in the time axis direction and outputs it.

[0056] Thereafter, the signal converted into a voltage by the voltmeter 210 is judged by the determination circuit 212, which then executes discharge detection output. The determination circuit 212 notifies an appropriate external device or the like of the discharge detection result as necessary.

[0057] If necessary, the expanded waveform is cleared by the clear time setting circuit 214 and the clear circuit 208 before the determination is performed.

[0058] In one embodiment, the path can thus be a balanced line.

[0059] Sixth embodiment Although each of the above-described embodiments has one of each of the configurations, the present invention is not limited to this.

[0060] The discharge detection device 2 may include a plurality of discharge detection units 200. Signals output from the plurality of discharge detection units 200 are connected to each component circuit by appropriate lines. At least one of the plurality of discharge detection units 200 may have the balanced metal electrode described in the fifth embodiment, and in this case, the line connected to the balanced metal electrode may be a balanced line.

[0061] By referring to the outputs from multiple discharge detection units 200, it is possible to detect bias in the position of the discharge, or to cover discharges that cannot be detected by one discharge detection unit 200 using other discharge detection units 200.

[0062] As another example, the discharge detection device 2 may branch the output of the discharge detection unit 200 into multiple branches and compare the results of signal processing in each branch to detect the occurrence of a discharge. For example, each branch may be provided with a circuit from the filter circuit 202 to the determination circuit 212. Parameters of these circuits may be changed for each branch.

[0063] In this way, it is possible to appropriately detect discharges in different situations by using a plurality of lines. At least one of the plurality of determination circuits 212 provided for each branch may acquire outputs from the other determination circuits 212 and determine whether or not a discharge has been detected based on the determination results of the plurality of determination circuits 212. This determination may be based on a rule base, or may be based on a trained model that has been appropriately machine-learned.

[0064] Furthermore, a plurality of electric discharge detectors 200 may be branched out into a plurality of lines having different parameters.

[0065] Naturally, the contents of the present disclosure also include discharge detection methods using the configurations described in the above embodiments.

[0066] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0067] 1: Generator, 10: Stator, 12: Rotor, 14: Rotating part, 16: Stationary part, 2: Discharge detection device, 200: Discharge detection unit, 202: filter circuit, 204: Rectifier circuit, 206: Waveform expansion circuit, 208: Clear circuit, 210: Voltmeter, 212: Judgment circuit, 214: Clear time setting circuit

Claims

1. a discharge detection unit having a metal electrode that detects discharge between an electrode and a sliding body that is in contact with the electrode and is slidable; A rectifier circuit that rectifies a discharge waveform output from the discharge detector; a waveform expansion circuit that integrates the output from the rectification circuit and expands it in the time direction; a voltmeter that measures the voltage of the waveform output by the waveform expansion circuit; a determination circuit that determines that a discharge has occurred in the slide when a state in which a signal value of an output of the waveform stretching circuit exceeds a first threshold value is maintained for a period longer than a first time based on the voltage measured by the voltmeter; and Equipped with the waveform expansion circuit is an integration circuit having a predetermined time constant and integrating an output voltage of the rectification circuit, the voltmeter measures and holds the output voltage of the waveform stretching circuit at a sampling time equal to or less than half the predetermined time constant; Discharge detection device.

2. a clear circuit that clears the voltage of the voltage signal held at the predetermined time constant to an initial value after a second time has elapsed since the voltage signal measured by the voltmeter exceeded the first threshold value; The discharge detection device of claim 1 further comprising:

3. a filter connected between the discharge detection unit and the waveform expansion circuit, for selectively transmitting a portion of the waveform of the discharge signal captured by the discharge detection unit that has a component greater than a second threshold value; Further equipped with The waveform expansion circuit processes the output of the discharge detection unit via the filter.

3. The discharge detection device according to claim 1 or 2.

4. an amplitude limiting circuit that limits the discharge signal captured by the discharge detection unit to an electrical signal having a predetermined amplitude; provided in front of the waveform expansion circuit or in front of the voltmeter. The discharge detection device according to any one of claims 1 to 3.

5. a band-pass filter circuit connected to the discharge detection unit and configured to selectively extract a signal in a predetermined frequency band from the discharge signal captured by the discharge detection unit; The discharge detection device according to any one of claims 1 to 4, comprising:

6. The discharge detection unit has a pair of balanced metal electrodes as the metal electrodes. The discharge detection device according to any one of claims 1 to 5.

7. A plurality of the discharge detection units are provided, detecting the occurrence of a discharge by comparing detection results based on signals output from the plurality of discharge detection units; The discharge detection device according to any one of claims 1 to 5.

8. At least one of the plurality of discharge detection units has a pair of balanced metal electrodes, and a balanced line is used to connect the output of the discharge detection unit having the pair of balanced metal electrodes and a circuit connected to the output of the discharge detection unit. The discharge detection device according to claim 7.

9. The output of the discharge detection unit is branched into a plurality of branches, and the results of signal processing in each branch are compared to detect the occurrence of a discharge. The discharge detection device according to any one of claims 1 to 6.

10. an insulating section, at an input side of the waveform stretching circuit, having a connection end that is physically insulated from an internal electric circuit of the waveform stretching circuit and transmits an electric signal; The discharge detection device according to any one of claims 1 to 9, comprising:

11. a discharge detection unit having a metal electrode detects a discharge between the electrode and a sliding body that is in contact with the electrode and is slidable; a waveform expansion circuit that expands the rectified discharge waveform output from the discharge detection unit in a time direction and outputs the expanded waveform; a voltmeter for measuring a voltage of the waveform output by the waveform expansion circuit; a determination circuit that determines, based on the voltage measured by the voltmeter, that a discharge has occurred in the slide body when a state in which the waveform output by the waveform stretching circuit exceeds a first threshold value is maintained for a period longer than a first time. A discharge detection method, comprising: the waveform expansion circuit is an integration circuit having a predetermined time constant and integrating the rectified output voltage, The voltmeter measures and holds the output voltage of the waveform stretching circuit at a sampling time equal to or less than half of the predetermined time constant. Discharge detection method.

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