Partial discharge detection circuit, partial discharge detector, and partial discharge measuring device

Abstract

To acquire the fundamental frequency of the partial discharge of a measurement target that is compatible with high-frequency operation, without being affected by noise generated from electrical equipment. [Solution] A partial discharge detection circuit that extracts a high-frequency partial discharge signal and a low-frequency reference signal from a target to be measured via a vacuum capacitor VC, comprising an inductance L, resistors R1 and R2, a high-pass filter HPF, and a low-pass filter LPF. The vacuum capacitor VC is connected to the inductance L. Resistor R1 is connected in series with the inductance L. Resistor R2 is connected in series with resistor R1. The high-pass filter HPF extracts the partial discharge signal from the output side of the inductance L. The low-pass filter LPF extracts the reference signal from the output side of resistor R1. The value of resistors R1 / R2 is between 0.2 and 7.

Description

Technical Field

[0001] The present invention relates to the field of insulation deterioration diagnosis technology for detecting partial discharges generated from electrical equipment (low-voltage and high-voltage).

Background Art

[0002] The partial discharge measurement system of Patent Document 1 includes two sensors, and extracts a high-frequency partial discharge signal (hereinafter referred to as a PD signal) and a low-frequency reference signal from separate independent sensors, respectively.

[0003] The partial discharge measurement apparatus of Patent Document 2 includes one sensor (a vacuum capacitor), and extracts a PD signal and a reference signal from this single sensor. In order to separate the PD signal and the reference signal, the circuit configuration is such that a signal line is branched, and a high-pass filter HPF and a low-pass filter LPF are connected in parallel.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0005]

Non-Patent Document 1

[0006] One possible method for operating motors is to convert the high voltage of commercial power (50 / 60Hz), such as that used in high-frequency inverter-driven motors, to a frequency exceeding the commercial power frequency (50Hz to several hundred Hz) via an inverter. However, in this case, noise is generated due to the switching of the inverter's power semiconductors and surrounding circuits, making it difficult to detect partial discharges.

[0007] In the partial discharge measurement system described in Patent Document 1, the size of the sensor affects the measurement sensitivity, so a larger area is better. However, if, for example, two sensors of the same area are required, the installation area for one sensor is halved.

[0008] While the partial discharge measuring device described in Patent Document 2 can be integrated into a single unit, it was revealed that a portion of the high-frequency PD signal leaks to the ground wire through the internal circuitry of the LPF, causing the PD signal obtained from the HPF to be attenuated.

[0009] In view of the above circumstances, the present invention aims to acquire the fundamental frequency of a partial discharge of a measurement target that is compatible with high-frequency operation without being affected by noise generated from electrical equipment. [Means for solving the problem]

[0010] One aspect of the present invention is a partial discharge detection circuit that extracts a high-frequency partial discharge signal and a low-frequency reference signal from a target to be measured via a vacuum capacitor, comprising an inductance to which the vacuum capacitor is connected, a first resistor connected in series with the inductance, a second resistor connected in series with the first resistor, a high-pass filter that extracts the partial discharge signal from the output side of the inductance, and a low-pass filter that extracts the reference signal from the output side of the first resistor, wherein the value of the first resistor / the second resistor is 0.2 or more and 7 or less.

[0011] In one aspect of the present invention, in the partial discharge detection circuit, the value of the first resistor is 0.33 kΩ or more and 1.75 kΩ or less, and the value of the second resistor is 0.25 kΩ or more and 1.67 kΩ or less.

[0012] In one aspect of the present invention, in the partial discharge detection circuit, the sum of the first resistor and the second resistor is 2 kΩ.

[0013] In one aspect of the present invention, the partial discharge detection circuit has a capacitance of 40 pF or less.

[0014] One aspect of the present invention provides, in the partial discharge detection circuit, a second inductance that can be connected in parallel with the inductance when reducing the value of the inductance, and can be connected in series with the inductance when increasing the value of the inductance.

[0015] One aspect of the present invention comprises, in the partial discharge detection circuit: a third resistor that can be connected in parallel with the first resistor when reducing the value of the first resistor; and a fourth resistor that can be connected in parallel with the second resistor when reducing the value of the second resistor.

[0016] One aspect of the present invention is configured such that, in the partial discharge detection circuit, when increasing the resistance value, the input side and the output side of the first resistor and the second resistor are short-circuited, and a third resistor and a fourth resistor can be sequentially connected in series to an output side of the second resistor.

[0017] One aspect of the present invention is the partial discharge detection circuit, wherein the high-pass filter has a cutoff frequency of 300 MHz to 500 MHz.

[0018] One aspect of the present invention provides a partial discharge measurement device comprising: the partial discharge detection circuit described above; and a measurement unit that obtains a partial discharge pattern of the measurement object based on the partial discharge signal and the reference signal.

[0019] One aspect of the present invention is a partial discharge detector that extracts a high-frequency partial discharge signal and a low-frequency reference signal via vacuum capacitors from an electrical device that outputs a pulse voltage waveform with a rise time of 200 ns or less, comprising: a first vacuum capacitor, a second vacuum capacitor and a third vacuum capacitor respectively connected to the U-phase, V-phase and W-phase feeder lines of the electrical device; a first inductance connected to the first vacuum capacitor; a first resistor connected in series with the first inductance; a second resistor connected in series with the first resistor; a first high-pass filter that extracts the partial discharge signal from the output side of the first inductance; a low-pass filter that extracts the reference signal from the output side of the first resistor; a second inductance connected to the second vacuum capacitor; a third resistor connected in series with the second inductance; a second high-pass filter that extracts the partial discharge signal from the output side of the second inductance; a third inductance connected to the third vacuum capacitor; a fourth resistor connected in series with the third inductance; and a third high-pass filter that extracts the partial discharge signal from the output side of the third inductance, wherein the capacitance of the first vacuum capacitor, the second vacuum capacitor and the third vacuum capacitor is 40 pF or less, and the cut-off frequency of the first high-pass filter, the second high-pass filter and the third high-pass filter is 300 MHz to 500 MHz.

[0020] One aspect of the present invention is the partial discharge detector, wherein the first vacuum capacitor, the second vacuum capacitor and the third vacuum capacitor are connected to the feeder lines via antennas.

[0021] One aspect of the present invention is the partial discharge detector, wherein the antenna is connected to each of the U-phase, V-phase and W-phase feeder lines.

[0022] One aspect of the present invention provides a partial discharge measurement apparatus characterized by comprising the aforementioned partial discharge detector. Advantageous Effects of the Invention

[0023] According to the present invention described above, the fundamental frequency of the partial discharge of the target to be measured can be obtained without being affected by noise generated from electrical equipment, and is compatible with high-frequency operation. [Brief explanation of the drawing]

[0024] [Figure 1] A diagram showing the configuration of a partial discharge detection circuit in a partial discharge measuring device according to Embodiment 1 of the present invention. [Figure 2] Circuit configuration when the inductance L value is reduced. [Figure 3] Circuit configuration when increasing the value of inductance L. [Figure 4] Circuit configuration when reducing the values ​​of resistors R1 and R2. [Figure 5] Circuit configuration when the resistance value is increased in the detection impedance Z. [Figure 6] (a) Circuit configuration of the detection impedance related to the standard, (b) Circuit configuration of the detection impedance related to the comparative example, (c) Circuit configuration of the detection impedance related to the example. [Figure 7] Relationship between the values ​​of resistors R1 / R2 and the magnitude of the calibration signal. [Figure 8] The relationship between the values ​​of resistors R1 / R2 and the magnitude of the reference signal. [Figure 9] A diagram showing the configuration of a partial discharge measuring device related to an experiment that serves as a premise for Embodiment 2 of the present invention. [Figure 10] (a) PD signal (partial discharge signal) showing the effect of removing switching noise by a high-pass filter (HPF) (cutoff frequency 80 MHz) for the partial discharge detection circuit in Figure 9 under energization condition 1, (b) FFT analysis results showing the said removal effect. [Figure 11] Reference voltage signal, U-phase, V-phase, and W-phase PD signals demonstrating the switching noise reduction effect under power application condition 1. [Figure 12] Figure 9 shows the switching noise rejection effect of the partial discharge detection circuit under energization condition 2, including the reference voltage signal, U-phase, V-phase, and W-phase PD signals. [Figure 13]Reference voltage signal, U-phase, V-phase, and W-phase PD signals demonstrating the switching noise reduction effect during inverter operation under power application condition 3 of the partial discharge detection circuit in the comparative example. [Figure 14] Under power application condition 3 of the partial discharge detection circuit in the comparative example, the reference voltage signal, U-phase, V-phase, and W-phase PD signals demonstrate the switching noise reduction effect while the inverter is stopped. [Figure 15] A diagram showing the configuration of a partial discharge detection circuit according to Embodiment 2 of the present invention. [Figure 16] (a) Detection results of partial discharge in an embodiment of the second embodiment of an elevator hoisting machine while the inverter is stopped, (b) Detection results of the partial discharge while the inverter is in operation. [Figure 17] A cross-sectional view of an example of a power supply line according to Embodiment 2 of the present invention. [Figure 18] A cross-sectional view of an example of a power supply line according to Embodiment 2 of the present invention. [Modes for carrying out the invention]

[0025] Embodiments of the present invention will be described below with reference to the drawings.

[0026] [Embodiment 1] Figure 1 shows a partial discharge detection circuit of a partial discharge measuring device 1 according to an embodiment of the present invention. The power supply line connecting the inverter 2 and the motor 3 is for three phases, but for the sake of explanation, only one phase is shown in the figure.

[0027] The partial discharge measuring device 1 is applied to each of the three phases of the power supply line and includes a detection impedance Z, a high-pass filter (HPF), a low-pass filter (LPF), and an oscilloscope 4 to measure the partial discharge of the target.

[0028] In this embodiment, the input terminal In of the detection impedance Z is connected to the inverter 2 and motor 3, which are the objects of measurement, via a vacuum capacitor VC.

[0029] While there are no restrictions on the capacitance value of the vacuum capacitor VC, it is sufficient to use one with a capacitance of 40pF or less so that partial discharge at frequencies above the switching noise frequency band of inverter 2 (below 40MHz) can be measured.

[0030] The detection impedance Z corresponds to one embodiment of the partial discharge detection circuit of the present invention, and comprises an inductance L, resistors R1 and R2, and a diode D for preventing overvoltage application. Resistors R1 and R2 correspond to the first and second resistors of the present invention, respectively.

[0031] At the detection impedance Z, the inductance L and resistors R1 and R2 are connected in series between the input terminal In and the ground terminal GND. The input side of inductance L is connected to the input terminal In and the output terminal Out1. The output side of inductance L is connected to the output terminal Out2 and the input sides of resistor R1 and diode D. The output side of resistor R1 is connected to the output terminal Out3 and the input side of resistor R2. The output side of resistor R2 is connected to the output side of diode D, the ground terminal GND, and the output terminal Out4. Output terminal Out2 is connected to oscilloscope 4 (measurement unit) via a high-pass filter HPF. Output terminal Out3 is connected to oscilloscope 4 via a low-pass filter LPF.

[0032] Diode D is connected in parallel with resistors R1 and R2, and limits the upper limit of the applied voltage to a voltage (25V) compliant with the Japan Electrical Association's "Guidelines for Ground Fault Protection in Low-Voltage Circuits."

[0033] The inductance L prevents the signal input from the vacuum capacitor VC via the input terminal In from oscillating significantly for extended periods. If the specifications of the vacuum capacitor VC make the inductance L unnecessary, output terminals Out1 and Out2 are short-circuited.

[0034] Here, when the value of inductance L is reduced, an inductance L' of an appropriate value can be connected in parallel with inductance L to output terminals Out1 and Out2 as a second inductance, as shown in Figure 2.

[0035] On the other hand, when increasing the value of inductance L, an appropriate inductance L' can be connected in series with inductance L to input terminal In, as shown in Figure 3. A new input terminal In' is connected to the input side of inductance L'. A vacuum capacitor VC can then be connected to this input terminal In'.

[0036] Furthermore, when reducing the value of resistor R1, a third resistor R1' of an appropriate value can be connected in parallel with resistor R1 to output terminals Out2 and Out3, as shown in Figure 4.

[0037] On the other hand, if the value of resistor R2 is reduced, a resistor R2' of an appropriate value can be connected in parallel with resistor R2 to output terminals Out3 and Out4 as a fourth resistor, as shown in the figure.

[0038] The grounding terminal GND is connected to the ground wire. However, if the wiring connected to the output terminals Out2 and Out3 is removed from the oscilloscope 4 when a high voltage is applied to the vacuum capacitor VC, there is a risk that a voltage exceeding the maximum clamping voltage of 25V limited by the diode D may be applied to the output terminals Out2 and Out3, so the values ​​of resistors R1 and R2 are usually limited. Specifically, as illustrated in Table 1, it is preferable that resistors R1 and R2 are limited to 2kΩ, and the combined resistance of resistors R1 and R2 is limited to 4kΩ. As an exception, when the resistance value is increased in the detection impedance Z, as shown in Figure 5, the output terminals Out2, Out3, and Out4 are all short-circuited, and a new circuit with large value resistors R1', R2' and diode D' is connected to the grounding terminal GND. Resistors R1' and R2' are connected in series sequentially between the grounding terminal GND and the grounding terminal GND'. Diode D' is connected in parallel with resistors R1' and R2' to the grounding terminals GND and GND'.

[0039] Table 1 shows the parameters for inductance L, resistors R1 and R2, and diode D (the numerical ranges marked with *1 exclude the condition where the combined resistance of resistors R1 and R2 is 0 kΩ).

[0040] [Table 1]

[0041] The high-pass filter (HPF) extracts a high-frequency PD signal (partial discharge signal) from the signal received at output terminal Out2 and outputs it to oscilloscope 4. The cutoff frequency of the high-pass filter (HPF) is set to, for example, 9kHz or higher, and the input impedance Zin2 is set to, for example, 50Ω. Depending on the specifications of the high-pass filter (HPF), it may be better to set the input impedance Zin2 of oscilloscope 4 to 1MΩ, but this is undesirable because it shifts the frequency bandwidth of the vacuum capacitor VC to the lower frequency side.

[0042] The low-pass filter (LPF) extracts a low-frequency reference signal from the signal received at output terminal Out3 and outputs it to oscilloscope 4. The cutoff frequency of the low-pass filter (LPF) is set to, for example, 50kHz or less, and the input impedance Zin1 of oscilloscope 4 is set to 1MΩ.

[0043] The oscilloscope 4 obtains the partial discharge pattern of the object to be measured based on the PD signal from the high-pass filter (HPF) and the reference signal from the low-pass filter (LPF). For example, the waveform observation and calculation device described in Patent Document 2 is used as the oscilloscope 4.

[0044] An example of the partial discharge measuring device 1 of this embodiment will be described below.

[0045] In Figure 6, (a) shows the circuit configuration for the detection impedance related to the reference, (b) shows the circuit configuration for the detection impedance related to the comparative example, and (c) shows the circuit configuration for the detection impedance Z related to the embodiment.

[0046] The circuit configuration of the above embodiment is the same as the circuit configuration of the partial discharge measuring device 1 in Figure 1.

[0047] The circuit configuration of the above standard is the same as that of the above embodiment, except that it has a single resistor R but does not have a low-pass filter LPF.

[0048] The circuit configuration of the comparative example is the same as that of the embodiment, except that it has a single resistor R and a low-pass filter LPF and a high-pass filter HPF connected to the output side of the inductance L.

[0049] The specifications of each component of the detection impedance in the above standard, the above comparative example, and the above embodiment are shown below. • Low-pass filter (LPF): Thorlabs, model EF110 • High-pass filter (HPF): Thorlabs, model EF123 • Oscilloscope 4: Tektronix MSO44 (Frequency bandwidth: 1GHz) • Input impedance of Oscilloscope 4: Low-pass filter (LPF) output (reference signal) is 1MΩ, HPF (PD signal) is 50Ω Inductance L: 19μH • Value of resistor R, combined resistance of resistors R1 and R2: 2kΩ In particular, the value of resistor R and the combined resistance of resistors R1 and R2 should be set so that the magnitude of the voltage output from Out2 and Out3 does not exceed the maximum input voltage of a typical oscilloscope (5Vrms if the input impedance is 50Ω). In this example, considering the balance with the impedance of the vacuum capacitor VC, the value of resistor R and the combined resistance of resistors R1 and R2 were set to 2kΩ.

[0050] Table 2 shows the peak voltage when a PD calibration signal (10nC) simulating a partial discharge signal is applied using a calibrator, with a vacuum capacitor VC connected to the input terminal In of the detection impedance Z of the standard, comparative example, and embodiment. It also shows the measurement results of the reference signal voltage when a high voltage (1000Hz, 3.81kVrms) is actually applied to the high-voltage side of the vacuum capacitor VC. A vacuum capacitor manufactured by Meidensha (SCF-300.25H48C, capacitance: 25pF) was used for the vacuum capacitor VC. A Partial discharge Calibrator, model PPG-0010, manufactured by Sparks Instruments was used for the calibrator. The table also shows the peak voltage and reference signal voltage for embodiments 1 to 11 when the values ​​of resistors R1 and R2 are changed.

[0051] [Table 2]

[0052] [Peak voltage] When a 10nC calibration signal is applied, the peak voltage of the PD signal through the high-pass filter (HPF) is significantly attenuated to 268mV in the comparative example compared to 620mV in the reference example. In contrast, the peak voltages of Examples 1 to 11 are higher than the peak voltage of the comparative example (268mV), indicating a reduction in attenuation. Here, if we set the measurement limit to a value 10% lower than the reference peak voltage of 620mV (which is set to 1), then as shown in Figure 7, the value of resistor R1 / resistor R2 is 0.2, and the value of resistor R1 + resistor R2 is 2kΩ, resulting in a lower limit of resistor R1 of 0.33kΩ and an upper limit of resistor R2 of 1.67kΩ.

[0053] [Reference signal voltage] While the reference signal voltage in the comparative example was 42.9 mVrms, it was confirmed that the reference signal voltage in Examples 1 to 11 decreased as the value of resistor R1 / resistor R2 increased. If we set the comparative example's 42.9 mV as 1 and reduce it by 10% to set the measurement limit, as shown in Figure 8, the value of resistor R1 / resistor R2 becomes 7, and the value of resistor R1 + resistor R2 becomes 2 kΩ, resulting in an upper limit of resistor R1 of 1.75 kΩ and a lower limit of resistor R2 of 0.25 kΩ.

[0054] From the results in Figures 7 and 8, In the detection impedance Z of Figure 1, The value of resistor R1 / resistor R2 is between 0.2 and 7. The value of resistor R1 is between 0.33kΩ and 1.75kΩ. The value of resistor R2 is between 0.25kΩ and 1.67kΩ. The sum of the values ​​of resistors R1 and R2 is 2kΩ. By setting resistors R1 and R2, low-frequency reference signals and high-frequency PD signals can be measured with attenuation of 10% or less.

[0055] According to the partial discharge measuring device 1 of the above embodiment, the fundamental frequency of the partial discharge of the target to be measured, which is compatible with high-frequency operation, can be obtained without being affected by noise generated from electrical equipment.

[0056] In particular, by applying the circuit configurations shown in Figures 2-5 to the detection impedance Z, the parameters of the detection impedance Z (inductance L, resistance R1, R2 values) can be arbitrarily set according to the specifications of the vacuum capacitor VC.

[0057] Furthermore, in the detection impedance Z, by connecting the diode D in parallel with resistors R1 and R2, the voltage of the detection impedance Z can be limited to a voltage compliant with the low-voltage circuit ground fault protection guidelines.

[0058] Furthermore, by connecting a vacuum capacitor VC with a capacitance of 40 pF or less to the input terminal In of the detection impedance Z, it is possible to measure partial discharges at frequencies above the switching noise frequency band of inverter 2.

[0059] [Embodiment 2] Embodiment 1 is intended for inverter-driven electrical equipment that outputs a relatively slow pulse voltage waveform with a rise time of 200 ns or more.

[0060] However, in recent years, inverter-driven electrical equipment has emerged that uses power semiconductors (high-speed type Si semiconductors, SiC semiconductors, GaN semiconductors) that operate with a rise time of 200 ns or less. The inverters of this high-speed electrical equipment generate very high-frequency and large switching noise. There is a need for a partial discharge detector (PD sensor) that can perform insulation degradation diagnosis even under such operating conditions (online).

[0061] Therefore, Embodiment 2 provides a partial discharge detector 5 using a vacuum capacitor VC that can be used in high-voltage and high-frequency environments.

[0062] The partial discharge measuring instrument described in Patent Document 2 is not compatible with inverter-driven electrical equipment using power semiconductors (high-speed type Si semiconductors, SiC semiconductors, GaN semiconductors) intended for high-speed switching operation with a rise time of 200 ns or less. As a result, the influence of switching noise generated during inverter operation is very large, making it impossible to measure partial discharge. Patent Document 1 (paragraphs 0024-0029) suggests that a filter with a cutoff frequency of 300-500 MHz can be used. However, the partial discharge measuring system described in Patent Document 2 requires at least two sensors (first sensor and second sensor) to accommodate a cutoff frequency of 300-500 MHz, which increases the number of components.

[0063] The following experiment was conducted to determine that the aforementioned partial discharge could not be measured.

[0064] As shown in Figure 9, the inverter 2 and motor 3 were connected by power lines 5U, 5V, and 5W, and the partial discharge detector 5 was connected to the terminal block 31 of the motor 3 to operate the inverter 2. The partial discharge detector 5 is a three-phase specification for U, V, and W phases, and the resistor R of the U phase is divided into resistors R1 and R2, with a circuit configuration that simultaneously acquires the reference voltage and PD signal. Since the acquisition of the reference voltage for the remaining two phases (V and W phases) is not required, there is only one resistor R, and only the PD signal is acquired. A high-pass filter (HPF) with a cutoff frequency of 80 MHz (model CHPFL-0080) was selected from those listed in Table 3. This high-pass filter (HPF) is the same as the one used in Patent Document 3. The low-pass filter (LPF) used was the same as the model shown in Table 4 as in Embodiment 1. A vacuum capacitor (VC) of model SCF-300.25H48C (withstand voltage 18 kVp, capacitance 25 pF) was selected from those listed in Table 5. Inverter 2 was a SiC three-phase inverter (using SiC semiconductors, pulse voltage rise time 120 ns) as shown in Table 6. Motor 3 was a three-phase induction motor as shown in Table 7. Switching noise was observed when inverter 2 was operated under the power supply condition 1 (voltage at which PD does not occur) shown in Table 8.

[0065] [Table 3]

[0066] [Table 4]

[0067] [Table 5]

[0068] [Table 6]

[0069] [Table 7]

[0070] [Table 8]

[0071] Figure 10 shows the voltage waveform of the PD signal acquired from the terminals of motor 3 while inverter 2 is operating, and the results of the FFT analysis of that waveform. It was confirmed that the HPF (high-pass filter) with a cutoff frequency of 80 MHz was unable to remove switching noise (maximum 200 mV) present in the frequency band of 50 MHz to 300 MHz.

[0072] In Embodiment 2, the cutoff frequency of the high-pass filter (HPF) is adjusted as follows in the partial discharge measuring instrument described in Patent Documents 2 and 3.

[0073] In Embodiment 1, as described above, the high-pass filter (HPF) extracts a high-frequency PD signal (partial discharge signal) from the signal received from the output terminal Out2 and outputs it to the oscilloscope 4. The cutoff frequency of the high-pass filter (HPF) is set to, for example, 9kHz or higher.

[0074] The partial discharge measuring instrument described in Patent Document 2 (paragraph 0027) extracts only the partial discharge waveform using a high-pass filter (HPF), and the cutoff frequency is adjusted according to the surrounding noise environment (for example, a cutoff frequency of 5 MHz or higher).

[0075] The partial discharge measuring instrument disclosed in Patent Document 3 (Claim 3) comprises a capacitor with a capacitance of 40 pF or less and a cutoff frequency of 80 MHz or higher connected to the object to be measured; a detection impedance with one end connected to the other end of the capacitor and the other end grounded; a low-pass filter with one end connected to the connection point between the capacitor and the detection impedance; a high-pass filter with one end connected to the connection point between the capacitor and the detection impedance; and a measuring unit connected to the other end of the low-pass filter and the other end of the high-pass filter to measure the partial discharge. The high-pass filter consists of two filters: a first high-pass filter and a second high-pass filter. The cutoff frequency of the first high-pass filter is adjusted to 9 kHz or higher, and the cutoff frequency of the second high-pass filter is adjusted to 50 MHz or higher.

[0076] The partial discharge measurement circuits of Embodiment 1 and Patent Documents 2 and 3 described above include frequency bands that cannot remove switching noise for inverters using SiC semiconductors with a rise time of 200 ns or less, and are therefore unsuitable.

[0077] Conventionally, PD sensors that detect high-frequency PD signals have used antennas, high-frequency CTs (current transformers), PMTs (photomultiplier tubes), and Rogowski coil current probes.

[0078] However, the aforementioned PD sensor has the following problems from the standpoint of electrical insulation. The antenna requires an insulation distance appropriate to the voltage class; the greater the insulation distance, the lower the measurement sensitivity. Because high-frequency current transformers (CTs) use conductive magnetic materials, they must be installed on ground wires where no voltage is applied, and are therefore far from the high-voltage partial discharge site. Consequently, the high-frequency components of the PD signal are attenuated as the PD signal propagates from the high-voltage partial discharge site to the ground-side high-frequency CT, resulting in reduced measurement sensitivity. While there are methods to enhance electrical insulation and install them on high-voltage cables, these require measures such as thickening the insulating material to ensure sufficient insulation distance, making them very large. • PMTs must be installed inside the motor to directly observe photoelectrons generated from the discharge site, but due to the structure of PMTs, they lack mechanical and thermal durability. Like high-frequency CTs, Rogowski coils also require a certain insulation distance to enhance electrical insulation, resulting in inferior measurement sensitivity.

[0079] Furthermore, there are no precedents in Non-Patent Documents 1-8 for using a vacuum capacitor VC as a PD sensor.

[0080] Therefore, the partial discharge measuring device 1 of Embodiment 2 shown in Figure 9 is applied to the power supply line connecting the inverter 2 and the motor 3, and comprises a partial discharge detector 5 having a detection impedance Z, a high-pass filter HPF, a low-pass filter LPF, and an oscilloscope 4.

[0081] The partial discharge detector 5 detects partial discharges generated from a motor 3 driven by an inverter 2 that outputs a pulse voltage waveform with a rise time of 200 ns or less.

[0082] The partial discharge detector 5 is The first vacuum capacitor VC1, the second vacuum capacitor VC2, and the third vacuum capacitor VC3 are connected to the U-phase, V-phase, and W-phase power supply lines 5U, 5V, and 5W, respectively, which connect the inverter 2 and the motor 3. The first vacuum capacitor VC1, the second vacuum capacitor VC2, and the third vacuum capacitor VC3 are connected to the first inductance L1, the second inductance L2, and the third inductance L3, respectively. The first inductance L1 and the first resistor R1 connected in series, The second resistor R2 is connected in series with this first resistor R1, The second inductor L2 connected to the second vacuum capacitor VC2, This second inductance L2 is connected in series with a third resistor R3, The third inductor L3 connected to the third vacuum capacitor VC3, The fourth resistor R4 is connected in series with this third inductance L3, A first high-pass filter HPF1 extracts the partial discharge signal from the output side of the first inductance L1, A low-pass filter (LPF) that extracts the reference signal from the output side of the first resistor R1, A second high-pass filter HPF2 extracts the partial discharge signal from the output side of the second inductance L2, A third high-pass filter HPF3 extracts the partial discharge signal from the output side of the third inductance L3, It holds.

[0083] For the first vacuum capacitor VC1, the second vacuum capacitor VC2, and the third vacuum capacitor VC3, for example, in the 6.6kV voltage class, examples of vacuum capacitors VC with a capacitance of 40pF or less, as exemplified in Table 5, can be used. Although an example of PD detection using SCF-300.2H48C is not provided, it is clear that PD detection is possible because it has similar specifications to the other two vacuum capacitors VC.

[0084] There are no specific requirements for the first high-pass filter HPF1, the second high-pass filter HPF2, and the third high-pass filter HPF3. Specifically, among the high-pass filters HPF with cutoff frequencies of 300MHz to 500MHz exemplified in Table 3, for example, model: CHPFL-0300 (fc=300MHz) or CHPFL-0500 (fc=500MHz) may be used.

[0085] For example, a low-pass filter with fc = 2kHz, as shown in Table 4, can be applied.

[0086] With the partial discharge detector 5 described above, by using a high-pass filter (HPF) with a cutoff frequency of 300 MHz or 500 MHz, switching noise (frequency band 50 MHz to 300 MHz) propagating from the inverter 2 and mixed into the PD signal can be greatly attenuated. On the other hand, the frequency band below the cutoff frequency of the PD signal is also greatly attenuated, but generally the frequency band of the PD signal contains frequency components above the cutoff frequency of the high-pass filter (HPF), so the presence or absence of the PD signal can be observed.

[0087] Furthermore, the first vacuum capacitor VC1, the second vacuum capacitor VC2, and the third vacuum capacitor VC3 are connected to the motor 3 via a flat antenna 6, as shown in Figure 15, for example. The antenna 6 may be installed away from the motor 3. However, to prevent a decrease in measurement sensitivity, the distance between the antenna 6 and the motor 3 should be set to 1 m or less.

[0088] In the configuration shown in Figure 15, the PD is detected collectively from the U, V, and W phase feed lines between the inverter 2 and the motor 3. However, as illustrated in Figure 17, a configuration in which the PD is detected from semicircular antennas 6 placed in close proximity to each of the U, V, and W phase feed lines 5U, 5V, and 5W may also be adopted.

[0089] The power supply lines 5U, 5V, and 5W may have a structure in which a conductor 51 is wrapped around the surface of the insulation of the power supply lines 5U, 5V, and 5W, as shown in the figure. Furthermore, an installation method for power supply lines 5U, 5V, and 5W that do not have a shielded structure is shown in Figure 18. As shown in the figure, after wrapping the conductor 51 around the insulating surface of the power supply lines 5U, 5V, and 5W to achieve a predetermined capacitance, the conductor 51 is connected to the high-voltage side of the vacuum capacitor VC, thereby electrically connecting the partial discharge detector 5 to the insulating insulation 52 of the power supply lines 5U, 5V, and 5W.

[0090] The partial discharge detector 5 can also measure partial discharges that occur inside electrical equipment. Examples of such electrical equipment include DC power supplies equipped with inverters 2, AC stabilized power supplies and generators, as well as substations (transformers, switchboards, control panels) and power transmission equipment (wires and insulators) located near inverters 2.

[0091] Furthermore, the voltage categories are defined as low voltage (DC 750V or less or AC 600V or less) and high voltage (DC over 750V to 7000V or AC over 600V to 7000V). This means that in the future, if vacuum capacitors VC and inverter 2 capable of withstanding extra-high voltage (over 7000V) become available, extra-high voltage (over 7000V) will also be within the scope of application.

[0092] An example of the partial discharge detector 5 of this embodiment is shown below.

[0093] The first high-pass filter HPF1, the second high-pass filter HPF2, and the third high-pass filter HPF3 used high-pass filters from Table 3 (U-phase: CHPFL-0225, V-phase: CHPFL-0300, W-phase: CHPFL-0500 were selected). The low-pass filter LPF used low-pass filters from Table 4. The first vacuum capacitor VC1, the second vacuum capacitor VC2, and the third vacuum capacitor VC3 used vacuum capacitors from Table 5 (SCF-300.25H48C was selected). The SiC three-phase inverter from Table 6 was used for inverter 2. The three-phase induction motor from Table 7 was used for motor 3. Then, inverter 2 was operated under the power supply condition 1 from Table 8 (no PD occurs in any of the U-phase, V-phase, or W-phase).

[0094] Figure 11 shows the reference voltage signal, U-phase, V-phase, and W-phase PD signals demonstrating the switching noise reduction effect under power application condition 1. A low-pass filter (LPF) with a cutoff frequency (fc) of 2kHz was able to acquire a reference voltage signal (voltage at the fundamental frequency). • A high-pass filter (HPF) with a cutoff frequency (fc) of 225 MHz failed to remove switching noise (maximum 12 mV). • A high-pass filter (HPF) with a cutoff frequency (fc) of 300MHz was able to remove switching noise (maximum 2mV). A high-pass filter (HPF) with a cutoff frequency (fc) of 500MHz was able to remove switching noise (maximum 2mV).

[0095] Next, inverter 2 was operated under the power supply condition 2 shown in Table 9 (voltages at which PD is known to occur in the V and W phases).

[0096] [Table 9]

[0097] Figure 12 shows the reference voltage signal and the PD signals for the U, V, and W phases, illustrating the switching noise reduction effect under power application condition 2. It was demonstrated that the PD signal can be detected without the influence of switching noise by using a high-pass filter (HPF) with a cutoff frequency (fc) of 300 MHz (maximum 15 mV). It was demonstrated that the PD signal can be detected without the influence of switching noise by using a high-pass filter (HPF) with a cutoff frequency (fc) of 500 MHz (maximum 4 mV).

[0098] As a comparative example, the inverter 2 was operated using the motor shown in Table 10 for motor 3 and the antenna shown in Table 11 for antenna 6, under the power supply condition 3 shown in Table 12 (voltage at which PD is known to occur in the V and W phases).

[0099] [Table 10]

[0100] [Table 11]

[0101] [Table 12]

[0102] Antenna 6 was installed near the terminal box of motor 3, approximately 10 cm away from the surface of the terminal box. The terminal box of motor 3 has holes for wire routing, and electromagnetic waves caused by PD generated inside the motor propagate through the gaps in these holes or the wires themselves. The distance between the surface of the terminal box and antenna 6 was determined considering the directivity, reception strength, and insulation distance of antenna 6.

[0103] During operation of the comparative example inverter 2 shown in Figure 13 and during shutdown of the same comparative example inverter 2 shown in Figure 14, it was confirmed that there was a slight difference in the output signal of antenna 6 between operation (maximum 1100mV) and shutdown (maximum 950mV). This difference was insufficient to clearly determine whether or not a PD signal was being generated in the V-phase and W-phase.

[0104] In contrast, the partial discharge detector 5 according to the present invention observes PD at the same frequency as the switching frequency of the inverter 2 (10 kHz) in the V phase, clearly indicating that PD occurs each time a pulse voltage is applied. In the W phase, although the frequency is less than in the V phase, it is clear that PD is occurring.

[0105] In the following examples, we did not use inverter 2 which outputs a pulse voltage waveform with a rise time of 200 ns or less, but we verified the observation of PD using a combination of a vacuum capacitor VC and a high-pass filter HPF (CHPFL-0300) with a cutoff frequency of 300 MHz.

[0106] (1) Using a sample that simulates slot discharge with an insulation configuration for an isolation voltage of 6kV, the PD was observed using the U-phase only circuit shown in Figure 9 and an HPF (CHPFL-0300) with a cutoff frequency of 300MHz, under sine wave, 1kHz, and 6kVrms energization conditions (voltages at which slot discharge is known to occur). As shown in Table 13, it was confirmed that both VCs (SCF-300.1H48C, SCF-300.25H48C) shown in Table 5 were capable of measuring PD.

[0107] [Table 13]

[0108] (2) A partial discharge detector 5 equipped with the antenna 6 shown in Figure 15 was installed, and the PD generated from the motor 3 of the elevator hoisting machine while the inverter 2 was operating was observed under the energization conditions shown in Table 14. The vacuum capacitor VC was selected as SCF-300.25H48C. The antenna 6 was a flat electrode as described in Patent Document 2 (Claim 3), with dimensions of (W)300mm × (H)200mm, and was installed approximately 1m away from the terminal block 31 of the motor 3.

[0109] [Table 14]

[0110] Figure 16(a) shows the detection results of the PD signal in the second embodiment of the elevator hoisting machine when inverter 2 is stopped. Figure 16(b) shows the detection results of the PD signal in the same embodiment when inverter 2 is in operation. As is clear from the comparison of the results in (a) and (b) of the same figure, it was confirmed that the PD signal can be observed during operation. [Explanation of symbols]

[0111] 1...Partial discharge measuring device 2…Inverter 3...motor, 31...terminal block 4…Oscilloscope (measurement unit) 5…Partial discharge measuring device 6… Antenna VC...Vacuum capacitor, VC1...First vacuum capacitor, VC2...Second vacuum capacitor, VC3...Third vacuum capacitor Z...Detection impedance (partial discharge detection circuit) L...Inductance, L'...Inductance (Second Inductance), L1...First Inductance, L2...Second Inductance, L3...Third Inductance R1...Resistance (first resistance), R2...Resistance (second resistance), R1'...Resistance (third resistance), R2'...Resistance (fourth resistance), R1...First resistance, R2...Second resistance, R3...Third resistance, R4...Fourth resistance LPF... Low-pass filter HPF...High-pass filter, HPF1...First high-pass filter, HPF2...Second high-pass filter, HPF3...Third high-pass filter

Claims

1. A partial discharge detection circuit that extracts a high-frequency partial discharge signal and a low-frequency reference signal from the object to be measured via a vacuum capacitor, The inductance to which the vacuum capacitor is connected, This inductance and the first resistor connected in series, This first resistor is connected in series with a second resistor, A high-pass filter that extracts the partial discharge signal from the output side of the inductance, A low-pass filter that extracts the reference signal from the output side of the first resistor, Equipped with, The value of the first resistor / second resistor shall be between 0.2 and 7. A partial discharge detection circuit characterized by the following.

2. The value of the first resistor is between 0.33 kΩ and 1.75 kΩ. The value of the second resistor shall be between 0.25 kΩ and 1.67 kΩ. A partial discharge detection circuit according to claim 1, characterized by the following:

3. The partial discharge detection circuit according to claim 2, characterized in that the sum of the first resistor and the second resistor is 2 kΩ.

4. The partial discharge detection circuit according to claim 1, characterized in that the capacitance of the vacuum capacitor is 40 pF or less.

5. The partial discharge detection circuit according to claim 1, further comprising a second inductor that can be connected in parallel with the inductor when the value of the inductance is reduced, and that can be connected in series with the inductor when the value of the inductance is increased.

6. When the value of the first resistor is reduced, a third resistor can be connected in parallel with the first resistor, When the value of the second resistor is reduced, a fourth resistor can be connected in parallel with the second resistor. The partial discharge detection circuit according to claim 1, further comprising:

7. In the partial discharge detection circuit according to claim 1, when the value of the resistance is increased, the input and output sides of the first and second resistors are short-circuited, and the third and fourth resistors can be sequentially connected in series to the output side of the second resistor. A partial discharge detection circuit characterized by the following.

8. The partial discharge detection circuit according to claim 1, characterized in that the high-pass filter has a cutoff frequency of 300 MHz to 500 MHz.

9. A partial discharge detection circuit according to claim 1, A measurement unit that obtains the partial discharge pattern of the target to be measured based on the partial discharge signal and the reference signal. A partial discharge measuring device characterized by being equipped with the following features.

10. A partial discharge detector that extracts a high-frequency partial discharge signal and a low-frequency reference signal via a vacuum capacitor from an electrical device that outputs a pulse voltage waveform with a rise time of 200 ns or less, A first vacuum capacitor, a second vacuum capacitor, and a third vacuum capacitor are connected to the U-phase, V-phase, and W-phase power supply lines of the aforementioned electrical equipment, respectively. The first inductance connected to the first vacuum capacitor, This first inductance and the first resistor connected in series, This first resistor is connected in series with a second resistor, A first high-pass filter that extracts the partial discharge signal from the output side of the first inductance, A low-pass filter that extracts the reference signal from the output side of the first resistor, The second inductance connected to the second vacuum capacitor, This second inductance is connected in series with a third resistor, A second high-pass filter that extracts the partial discharge signal from the output side of the second inductance, The third inductance connected to the third vacuum capacitor, This third inductance is connected in series with a fourth resistor, A third high-pass filter that extracts the partial discharge signal from the output side of the third inductance, It has, The first vacuum capacitor, the second vacuum capacitor, and the third vacuum capacitor have a capacitance of 40 pF or less. The first high-pass filter, the second high-pass filter, and the third high-pass filter have a cutoff frequency of 300 MHz to 500 MHz. A partial discharge detector characterized by the following features.

11. The partial discharge detector according to claim 10, characterized in that the first vacuum capacitor, the second vacuum capacitor, and the third vacuum capacitor are connected to the feed line via an antenna.

12. The partial discharge detector according to claim 11, characterized in that the antenna is connected to each of the U-phase, V-phase, and W-phase feed lines.

13. A partial discharge measuring device characterized by comprising the partial discharge detector described in claim 10.

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