Partial discharge measuring device and partial discharge measuring method

Abstract

To improve an effect of removing noise superimposed on a partial discharge signal such as partial discharge sound.SOLUTION: A partial discharge measuring device includes: a first sensor that detects a partial discharge signal, on which noise is superimposed, to output a first electric signal according to the partial discharge signal; a second sensor that detects the noise to output a second electric signal according to the noise; and a difference detection unit that detects a difference between the first electric signal and the second electric signal to output a third electric signal according to the difference.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a partial discharge measuring device and a partial discharge measuring method. [Background technology]

[0002] A partial discharge detection device is known that splits a sound wave signal caused by a partial discharge detected by an AE sensor into two, inputs one of the split signals to a signal filter, and inputs the other split signal to a noise filter. This partial discharge detection device calculates the difference between the output signal of the signal filter and the output signal of the noise filter, and outputs only the signal caused by the discharge (see, for example, Patent Document 1).

[0003] Also known is a method of obtaining a second measurement signal by applying a low-pass filter to a first measurement signal detected by an acoustic sensor attached to the outer surface of the object to be inspected, obtaining a third measurement signal by removing noise components caused by mechanical vibrations of the object to be inspected from the second measurement signal, and determining whether or not partial discharge has occurred in the object to be inspected based on the time waveform of the third measurement signal (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-320356 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-114185 Summary of the Invention [Problem to be solved by the invention]

[0005] The occurrence of partial discharges can be indirectly measured by detecting partial discharge signals such as partial discharge sounds generated by partial discharges. However, with conventional techniques, it can be difficult to remove noise superimposed on the partial discharge signals from the partial discharge signals.

[0006] An object of the present disclosure is to improve the effect of removing noise superimposed on partial discharge signals, such as partial discharge sounds. [Means for solving the problem]

[0007] The partial discharge measuring device according to the present disclosure comprises: a first sensor that detects a partial discharge signal on which noise is superimposed and outputs a first electrical signal corresponding to the partial discharge signal; a second sensor that detects the noise and outputs a second electrical signal corresponding to the noise; The device further includes a difference detector that detects a difference between the first electrical signal and the second electrical signal and outputs a third electrical signal according to the difference. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to improve the effect of removing noise superimposed on partial discharge signals, such as partial discharge sound. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram showing an example of the configuration of a partial discharge measuring device according to a first embodiment. [Figure 2] 1 is a flowchart illustrating an example of a partial discharge measurement method. [Figure 3] FIG. 2 is a diagram illustrating an example of the configuration of a first sensor. [Figure 4] FIG. 4 is a diagram illustrating an example of the configuration of a second sensor. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment will be described below.

[0011] In high-voltage power equipment enclosed in a metal case (such as transformers, circuit breakers, switchboards, motors, etc.), electric fields can concentrate locally inside the equipment, causing partial discharges. If partial discharges continue to occur, they may lead to dielectric breakdown, so there is a demand for technology to measure partial discharges that occur as a precursor to dielectric breakdown.

[0012] Partial discharge is a small discharge that occurs locally inside a device due to the concentration of electric field stress. Partial discharge accelerates corrosion of the surrounding insulation structure, degrading the insulation performance of the device and potentially leading to dielectric breakdown.

[0013] For example, with the trend toward higher voltages in devices such as inverters using SiC semiconductors, there is a demand for technology to measure the occurrence of partial discharges in power electronics devices or automotive devices, where problems have not previously been apparent. The possibility of insulation breakdown or frequent equipment failures occurring in a short period of time due to repeated partial discharges is greater at high voltages (e.g., voltages above 600V) than at low voltages (e.g., voltages below 600V).

[0014] The SiC semiconductors in these devices can switch high voltages such as 1200V, 1700V, and 3300V at high frequencies. This means that partial discharges can occur on the circuit boards on which the SiC semiconductors are mounted, or inside the motors driven by the SiC semiconductors. Regarding the repetition frequency of partial discharges, the number of repetitions of partial discharges that occur in typical high-voltage devices operating at 50Hz or 60Hz is equivalent to the peak frequency, at around 50 to 100 times per second. However, because SiC semiconductors reverse polarity at a high frequency of several tens of kHz, the number of repetitions of partial discharges can reach several thousand times per second.

[0015] Conventional discharge detection and sensing technologies use filters to separate noise of several hundred kHz superimposed on 50 Hz or 60 Hz signals, making noise separation relatively easy. However, it is difficult to separate surge noise (electromagnetic waves and / or conducted noise) caused by the switching of SiC semiconductors from partial discharge signals. Therefore, there is a new need to measure partial discharges while performing high-frequency switching using SiC semiconductors.

[0016] The present disclosure provides a partial discharge measuring device and a partial discharge measuring method that improve the effect of removing noise superimposed on partial discharge signals such as partial discharge sounds. In particular, the present disclosure provides a partial discharge measuring device and a partial discharge measuring method that can remove high-frequency noise superimposed on partial discharge signals and measure partial discharges with high accuracy under conditions where high-frequency noise such as inverter surges occurs.

[0017] Fig. 1 is a diagram showing an example of the configuration of a partial discharge measuring device according to one embodiment. The partial discharge measuring device 101 shown in Fig. 1 is a device that measures partial discharges that occur in a source 32 inside high-voltage equipment 2 that is surrounded by a grounded metal wall 31. The partial discharge measuring device 101 indirectly measures the occurrence of partial discharges by detecting partial discharge signals such as partial discharge sounds that are generated on the surface of the metal wall 31 due to partial discharges that occur in the source 32 inside the metal wall 31.

[0018] The high-voltage equipment 2 has a bushing 33 electrically connected to the high-voltage power supply 1 via a lead wire 35. The bushing 33 is an example of a high-voltage introduction section that introduces the high voltage HV supplied from the high-voltage power supply 1 to the high-voltage equipment 2. The high-voltage equipment 2 has an internal conductor to which the high voltage HV introduced via the bushing 33 is applied. The high voltage HV is, for example, a voltage that simulates an inverter surge.

[0019] The high-voltage equipment 2 is power equipment that handles high power, and specific examples thereof include a switchboard, a transformer, a circuit breaker, etc. The high-voltage equipment 2 is not limited to these specific examples. The high-voltage equipment 2 may also be a load such as a motor.

[0020] The high-voltage equipment 2 has a metal wall 31. The metal wall 31 is part of the metal housing of the high-voltage equipment 2. The metal wall 31 is not limited to the wall of a metal housing, but may be the wall of a metal door, etc. The metal wall 31 may have a dielectric coating film. The metal wall 31 is an example of a metal part to be grounded. If the high-voltage equipment 2 is a motor, the metal part to be grounded may be a stator coil, a motorette, etc.

[0021] The partial discharge measuring device 101 includes sensors 3 a and 3 b and a difference detecting unit 7 .

[0022] The sensors 3a and 3b are detection devices that are attached to the outer surface 31a of the grounded metal wall 31. The sensors 3a and 3b may be attached anywhere on the outer surface 31a of the metal wall 31. It is also advisable to attach the sensors 3a and 3b electrically insulated from the ground to reduce the influence of noise currents from the ground.

[0023] The sensor 3a is an example of a first sensor that detects a partial discharge signal on which noise is superimposed and outputs a first electrical signal corresponding to the detected partial discharge signal (partial discharge signal on which noise is superimposed). The sensor 3a detects, for example, a partial discharge sound that reaches the metal wall 31 due to a partial discharge generated inside the metal wall 31 using a piezoelectric element, outputs a first electrical signal E1 corresponding to the detected partial discharge signal, and inputs it to the difference detection unit 7 via the cable L1.

[0024] The sensor 3a is, for example, an acoustic emission sensor (AE sensor) that detects partial discharge sound, which is an elastic wave. However, the sensor 3a is not limited to a sensor that detects partial discharge sound generated by partial discharge. In addition to partial discharge sound, partial discharge signals generated by partial discharge include discharge pulse current, electromagnetic waves, partial discharge light, etc. The sensor 3a may also be a sensor that detects partial discharge signals other than partial discharge sound.

[0025] The partial discharge signal detected by the sensor 3a contains frequency components in a frequency band originating from the partial discharge signal emitted from the source 32. For example, the partial discharge sound detected by the sensor 3a contains frequency components between 10 kHz and 3 MHz. Meanwhile, at sites where high-voltage equipment 2 is in operation, environmental noise such as broadcast waves, inverter surges, and switching surges may occur. Such environmental noise induces noise N of a predetermined noise frequency component (for example, 30 MHz or less) in the metal wall 31.

[0026] In this case, noise N may be superimposed on the partial discharge signal in a frequency band that overlaps with the partial discharge signal. If the frequency of the noise N superimposed on the partial discharge signal is included in the detection band of the sensor 3a, the noise N will be superimposed on the partial discharge signal detected by the sensor 3a and on the first electrical signal E1 output from the sensor 3a in response to the detected partial discharge signal. The sensor 3a detects not only the original partial discharge signal but also the noise N superimposed on the partial discharge signal, resulting in a reduced signal-to-noise ratio.

[0027] Therefore, the partial discharge measuring device 101 is provided with a sensor 3b that can detect only noise N in a frequency band that overlaps with the frequency band of the partial discharge signal.

[0028] The sensor 3b is an example of a second sensor that detects noise N and outputs a second electrical signal corresponding to the detected noise N. The sensor 3b detects the noise N using, for example, a capacitor or a resistor, outputs a second electrical signal E2 corresponding to the detected noise N, and inputs the second electrical signal E2 to the difference detection unit 7 via the cable L2. The second electrical signal E2 includes a frequency component of the noise N.

[0029] The difference detection unit 7 performs a detection process (differential processing) to calculate the difference Δ between the first electrical signal E1 and the second electrical signal E2, and outputs a third electrical signal E3 corresponding to the calculated difference Δ. By performing differential processing between the first electrical signal E1 and the second electrical signal E2, the third electrical signal E3 corresponding to the partial discharge signal from which the noise N has been removed is output. This improves the effect of removing the noise N superimposed on the partial discharge signal, and the third electrical signal E3 that is a result of measuring the partial discharge with high accuracy is obtained.

[0030] The difference detection unit 7 includes, for example, a first amplifier 4a that amplifies the first electrical signal E1, a second amplifier 4b that amplifies the second electrical signal E2, a first discriminator 5a to which an output signal A1 of the first amplifier 4a is input, and a second discriminator 5b to which an output signal A2 of the second amplifier 4b is input. In this case, the difference Δ detected by the difference detection unit 7 may be the difference between the output signal D1 of the first discriminator 5a and the output signal D2 of the second discriminator 5b.

[0031] The first amplifier 4a amplifies the first electrical signal E1 and outputs an amplified output signal A1. The second amplifier 4b amplifies the second electrical signal E2 and outputs an amplified output signal A2. The first amplifier 4a may be provided in the sensor 3a. The second amplifier 4b may be provided in the sensor 3b.

[0032] The first discriminator 5a discriminates between the output signal A1 and a noise signal contained in the output signal A1. The first discriminator 5a removes the noise signal from the output signal A1 and outputs an output signal D1. The second discriminator 5b discriminates between the output signal A2 and the noise contained in the output signal A2. The second discriminator 5b removes the noise signal from the output signal A2 and outputs an output signal D2.

[0033] The difference detection unit 7 includes, for example, a measuring device 6 that performs a detection process (differential process) to calculate a difference Δ between the output signal D1 and the output signal D2, and outputs a third electrical signal E3 corresponding to the calculated difference Δ.

[0034] The measuring device 6 measures the magnitude of partial discharges occurring inside the metal wall 31 based on the difference Δ between the first electrical signal E1 and the second electrical signal E2 (the difference Δ between the output signal D1 and the output signal D2). The measuring device 6 outputs a third electrical signal E3 representing the measurement results of the magnitude of partial discharges to the outside, thereby allowing the user to understand the measurement results. For example, the measuring device 6 may output an alarm notifying the user of deterioration due to partial discharge when the difference Δ or the third electrical signal E3 exceeding a predetermined level is detected a predetermined number of times or more. This allows the user to take preventive measures, such as replacing parts, before actual insulation breakdown occurs. The measuring device 6 may be a measuring device itself, such as a data logger or an oscilloscope, or a control device equipped with a measuring device.

[0035] Furthermore, externally generated noise may be picked up by the cable L1 connecting the sensor 3a and the amplifier 4a, and this noise may be superimposed on the first electrical signal E1 output from the sensor 3a to the amplifier 4a. In this case, the first electrical signal E1 is a partial discharge signal that includes noise that has entered from the cable L1, and the electrical signal E2 is a signal that includes noise that has entered from the cable L2. The third electrical signal E3 obtained by the difference detection unit 7 is the difference Δ between the first electrical signal E1 and the second electrical signal E2 (the difference Δ between the output signal D1 and the output signal D2), and therefore a signal from which the noise signal that has entered from the cable L1 has been removed can be obtained.

[0036] Here, it is preferable that the cable L1 and the cable L2 have the same impedance, for example, by using the same material or the same length. If the impedance of the cable L1 and the impedance of the cable L2 are the same, the detection accuracy of the difference Δ between the first electrical signal E1 and the second electrical signal E2 is improved. However, the impedances of the cables L1 and L2 may be different as long as the detection accuracy of the difference between the first electrical signal E1 and the second electrical signal E2 is ensured.

[0037] The measuring instrument 6 is, for example, an oscilloscope that detects the difference Δ between the output signal D1 and the output signal D2 and displays a waveform corresponding to the third electrical signal E3 that represents the difference Δ, thereby allowing the user to visually grasp the magnitude of the partial discharge that has occurred.

[0038] In this disclosure, the measuring device 6 is an electronic circuit such as a central processing unit (CPU), a field programmable gate array (FPGA), or an application specific integrated circuit (ASIC), or a device equipped with such an electronic circuit. The measuring device 6 may also be a computer having a memory and a processor. The measuring device 6 performs the various control operations described in this specification by executing a program such as instruction code stored in the memory, or by being a circuit designed for a specific application.

[0039] FIG. 2 is a flowchart showing an example of a partial discharge measuring method.

[0040] In step S10, the partial discharge signal on which noise N is superimposed is detected by the sensor 3a, and the noise N is detected by the sensor 3b. A first electrical signal E1 corresponding to the partial discharge signal is output from the sensor 3a to the first amplifier 4a, and a second electrical signal E2 corresponding to the noise N is output from the sensor 3b to the second amplifier 4b.

[0041] In step S20, the first electrical signal E1 is amplified by the first amplifier 4a, and the second electrical signal E2 is amplified by the second amplifier 4b. The amplified output signal A1 is output from the first amplifier 4a to the first discriminator 5a, and the amplified output signal A2 is output from the second amplifier 4b to the second discriminator 5b.

[0042] In step S30, the first discriminator 5a and the second discriminator 5b each include a bandpass filter in which the frequency band of partial discharges lies between a minimum cutoff frequency and a maximum cutoff frequency. The first discriminator 5a performs bandpass filtering on the output signal A1 to narrow the frequency of the output signal A1 to the same band as the frequency band of partial discharges, thereby generating an output signal D1 having the same frequency components as the partial discharges. The second discriminator 5b performs bandpass filtering on the output signal A2 to narrow the frequency of the output signal A2 to the same band as the frequency band of partial discharges, thereby generating an output signal D2 having the same frequency components as the partial discharges.

[0043] In step S40, the difference between the output signal D1 and the output signal D2 is detected by the difference detection unit 7. Even if noise is superimposed on the partial discharge signal detected by the sensor 3a or if a noise signal enters from the cable L1, by performing difference processing, it is possible to obtain an accurate measurement result of the partial discharge with the noise signal removed.

[0044] Fig. 3 is a diagram showing an example of the configuration of the first sensor, showing the internal structure when sensor 3a is an AE sensor, and Fig. 4 is a diagram showing an example of the configuration of the second sensor, showing the internal structure when sensor 3b is an AE sensor.

[0045] The sensor 3a shown in Fig. 3 includes a first wave receiving plate 11 that receives a partial discharge signal, and a first conversion unit 12 that converts the partial discharge signal received by the first wave receiving plate 11 into a first electric signal E1. The first wave receiving plate 11 is attached to the outer surface 31a of a grounded metal wall 31, and receives partial discharge sound, which is a partial discharge signal. The first conversion unit 12 includes a piezoelectric element 12a that converts the partial discharge sound received by the first wave receiving plate 11 into the first electric signal E1.

[0046] In contrast, the sensor 3b shown in Fig. 4 includes a second wave receiving plate 21 that receives noise N and a second conversion unit 22 that converts the noise N received by the second wave receiving plate 21 into a second electrical signal E2. The second wave receiving plate 21 is attached to the outer surface 31a of a grounded metal wall 31 and receives the noise N. The second conversion unit 22 includes a conversion element 22a that converts the noise N received by the second wave receiving plate 21 into the second electrical signal E2. The conversion element 22a may be a capacitor, a resistor, or an element including both a capacitor and a resistor. The conversion element 22a is not a piezoelectric element (it is not an element having piezoelectricity).

[0047] The material of the piezoelectric element 12a shown in Fig. 3 is, for example, PZT (lead zirconate titanate ceramic). When the piezoelectric element 12a is distorted by the partial discharge sound, which is an elastic wave, dielectric polarization occurs, generating a voltage that outputs an electrical signal. Therefore, the sensor 3a has a piezoelectric element and can detect the partial discharge sound, but the sensor 3b does not have a piezoelectric element and cannot detect the partial discharge sound.

[0048] 3, the sensor 3a has a signal line 13, a connector 14, and a shield case 15. A signal output from the piezoelectric element 12a of the first conversion unit 12 is output as a first electrical signal E1 from the connector 14 via the signal line 13.

[0049] The first wave receiving plate 11 is made of an insulating material such as alumina, and serves to transmit elastic waves (partial discharge noise) generated by the high-voltage equipment 2. For this reason, it is preferable that the wave receiving surface of the first wave receiving plate 11 be in contact with the surface of the high-voltage equipment 2. The transmitted elastic waves are transmitted to the piezoelectric element 12a via the first wave receiving plate 11, converted into an electrical signal, and sent to the connector 14. Connecting a cable to the connector 14 enables signal transmission to the outside. The shielding case 15 has a cylindrical structure and is made of a conductor such as aluminum or stainless steel. The first conversion unit 12 and the piezoelectric element 12a are shielded by the shielding case 15 to prevent electrical noise from entering from the outside.

[0050] 4, the sensor 3b has a signal line 23, a connector 24, and a shield case 25. A signal output from the conversion element 22a of the second conversion unit 22 is output as a second electrical signal E2 from the connector 24 via the signal line 23.

[0051] The second wave receiving plate 21 is made of an insulating material such as alumina and has the role of transmitting elastic waves (partial discharge noise) generated from the high-voltage equipment 2. For this reason, it is preferable that the wave receiving surface of the second wave receiving plate 21 be in contact with the surface of the high-voltage equipment 2. The noise N that has transmitted through the second wave receiving plate 21 is transmitted to the conversion element 22a via the second wave receiving plate 21, where it is converted into an electrical signal and sent to the connector 24. Connecting a cable to the connector 24 enables signal transmission to the outside. The shielding case 25 has a cylindrical structure and is made of a conductor such as aluminum or stainless steel. The second conversion unit 22 and the conversion element 22a are shielded by the shielding case 25 to prevent electrical noise from entering from the outside.

[0052] If the impedance of the second conversion unit 22 or the conversion element 22a is the same as the impedance of the first conversion unit 12 or the piezoelectric element 12a, the detection accuracy of the difference Δ between the first electrical signal E1 and the second electrical signal E2 is improved. However, the impedances may be different as long as the detection accuracy of the difference between the first electrical signal E1 and the second electrical signal E2 is ensured.

[0053] Although the embodiments have been described above, they are presented as examples and the present invention is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

[0054] For example, the partial discharge measuring device may be a device that measures partial discharge occurring in stationary equipment, or a device that measures partial discharge occurring in equipment mounted on a mobile object such as a vehicle. [Explanation of symbols]

[0055] 1 High voltage power supply 2. High-voltage equipment 3a First sensor 3b Second sensor 4a, 4b amplifier 5a,5b Discriminator 6 Measuring instruments 7 Difference detection section 11,21 Wave receiving plate 12,22 Conversion unit 12a Piezoelectric element 13,23 signal line 14,24 connector 15,25 Shield case 22a Conversion element 31 metal wall 31a External surface 32 Source 33 Bushing 35 lead wire 36 Ground wire 101 Partial discharge measuring device

Claims

1. a first sensor that detects a partial discharge signal having noise superimposed thereon and outputs a first electrical signal corresponding to the partial discharge signal; a second sensor that detects the noise and outputs a second electrical signal corresponding to the noise; a difference detection unit that detects a difference between the first electrical signal and the second electrical signal and outputs a third electrical signal according to the difference.

2. 2. The partial discharge measuring device according to claim 1, wherein the second sensor includes a second wave receiving plate that receives the noise, and a second conversion unit that converts the noise received by the second wave receiving plate into the second electrical signal.

3. The partial discharge measuring device according to claim 2 , wherein the second conversion unit includes a capacitor or a resistor that converts the noise received by the second wave receiving plate into the second electric signal.

4. the first sensor includes a first wave receiving plate that receives the partial discharge signal, and a first conversion unit that converts the partial discharge signal received by the first wave receiving plate into the first electric signal, The partial discharge measuring device according to claim 3 , wherein the impedance of the second conversion unit is the same as the impedance of the first conversion unit.

5. the first wave receiving plate receives a partial discharge sound that is the partial discharge signal, the first conversion unit includes a piezoelectric element that converts the partial discharge sound received by the first wave receiving plate into the first electric signal, The partial discharge measuring device according to claim 4 , wherein the impedance of the second conversion unit is the same as the impedance of the piezoelectric element.

6. The difference detection unit a first amplifier that amplifies the first electrical signal; a second amplifier that amplifies the second electrical signal; a first discriminator to which the output signal of the first amplifier is input; a second discriminator to which the output signal of the second amplifier is input, The partial discharge measuring device according to claim 1 , wherein the difference is a difference between an output signal of the first discriminator and an output signal of the second discriminator.

7. The partial discharge measuring device according to claim 6 , wherein the difference detecting section includes an oscilloscope that detects the difference and displays a waveform corresponding to the third electrical signal.

8. A partial discharge measurement method comprising: detecting a difference between a first electrical signal output from a first sensor that detects a partial discharge signal on which noise is superimposed in response to the partial discharge signal; and a second electrical signal output from a second sensor that detects the noise in response to the noise; and outputting a third electrical signal that corresponds to the difference.

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