JP2013036884A - Insulation monitoring method and insulation monitor - Google Patents

Abstract

An object of the present invention is to obtain a resistance component current in a leakage current with high accuracy by digital filter processing and calculation of an effective part and an ineffective part without monitoring a large amount of data, and monitor an insulation deterioration state in a live line state.
A leakage current flowing through a ground line is detected when a low-frequency monitoring signal is superimposed on a distribution circuit, and a resistance component current and a capacitance component current are separated and extracted, respectively, and the electric circuit is calculated from the magnitude of the resistance component current. In the method of monitoring the insulation deterioration state of the leakage current and the commercial frequency component of the leakage current flowing through the ground line and the commercial frequency component of the voltage of the ground line are respectively removed by an analog filter to extract the monitoring signal frequency component of the leakage current and voltage, These monitor signal frequency components are converted into digital signals and digital filtered, and the output is used to determine the effective and ineffective portions of the monitor signal frequency components. The effective component is the resistance component current and the ineffective component is the capacitance. The insulation deterioration state of the electric circuit is monitored as a component current.
[Selection] Figure 1

Description

  The present invention superimposes a monitoring signal having a frequency lower than the commercial frequency on the grounding line of the distribution circuit to be monitored, and measures the leakage current flowing back through the grounding point and the electric circuit at that time, thereby measuring the electric circuit (the electric circuit). The present invention relates to an insulation monitoring method and an insulation monitoring device for monitoring an insulation deterioration state of a load (including a connected load).

  In this type of insulation monitoring device, focusing on the fact that the resistance component current (current having the same phase as the monitoring signal voltage) Igr of the measured leakage current Ig corresponds to the insulation deterioration current, the capacitance component current is determined from the leakage current Ig. There is known an Igr type insulation monitoring device that monitors the insulation deterioration state of the electric circuit based on the magnitude of the resistance component current Igr obtained by removing Igc (current whose phase is advanced by 90 degrees from the monitoring signal voltage). This Igr type insulation monitoring device is widely used to monitor the insulation deterioration state of various electric circuits regardless of the phase wire type such as three-phase four-wire, three-phase three-wire, single-phase three-wire, single-phase two-wire, etc. ing.

For example, in Patent Document 1, the first low-frequency and second low-frequency monitoring signals are injected into the low-voltage side electric circuit of the transformer via the ground line, and the first of the leakage currents returned to the ground line is returned. The active portion and the ineffective portion are obtained from the low frequency component of the current line, and a predetermined calculation is performed using the effective portion, the ineffective portion, and the second low frequency component of the leakage current, so that the electric circuit in the live state An insulation resistance measurement method is described in which the insulation resistance is measured.
In Patent Document 2, a leakage current having the same frequency as a low-frequency monitoring signal injected into an electric circuit is detected, and a resistance component current and a capacitance component current are separated and extracted, and these components are generated using the monitoring signal voltage and the like. An insulation monitoring device is described that detects the amount of suppression required to cancel the resistance component current as an insulation resistance value by canceling each component with the suppressed current.
In Patent Document 3, the primary signal of a zero-phase current transformer is disclosed in order to improve the detection signal level and the characteristics of the zero-phase current transformer (ZCT) when detecting a leakage current having the same frequency component as a low-frequency monitoring signal. An insulation state monitoring device is described in which a correction signal having a frequency different from that of the monitoring signal is superimposed on the side, and the detection signal is corrected by the amount of change in the correction signal detected from the secondary side of the zero-phase current transformer. ing.

Furthermore, Patent Document 4 discloses an insulation monitoring device that enables highly accurate insulation monitoring using a low-power insulation monitoring signal.
Here, FIG. 4 is a block diagram of the insulation monitoring device described in Patent Document 4, wherein 1 is a transformer, 2 is a load, 3 and 5 are secondary-side electric circuits of the transformer 1, and 4 is a class B ground. Lines 10 and 10 are insulation monitoring devices, 30 is a superposition transformer, 50 is ZCT, C is a ground capacitance of the electric circuit, and R is a ground insulation resistance.

  Briefly describing the configuration and operation of the insulation monitoring device 10, the monitoring signal generation unit 20 including the oscillator 21 and the amplifier 22 generates a monitoring signal W having a frequency lower than the commercial frequency, and the B of the transformer 1 through the superimposing transformer 30. Superimpose on the seed grounding wire 4. The ZCT 50 detects a leakage current flowing back to the B-type ground line 4 via the ground impedance of the electric circuit and the ground, and this leakage current (measurement signal M) is converted into a head amplifier 61, a low-pass filter (LPF) 62, and an A / D. The signal is processed by the measurement signal detection means 60 comprising the converter 63 and converted into a digital signal.

In the reference signal detection means 40, unnecessary components such as a commercial frequency and its harmonics are generated by a switched capacitor filter (SCF) 46 through a commercial component removal unit 41 to which the voltage of the class B ground line 4 is applied as a reference input b. The reference signal B is obtained by removing. Reference numeral 42 denotes an anti-aliasing filter (AAF), 43 denotes an attenuator (ATT), 44 denotes a band elimination filter (BEF), and 45 denotes an amplifier.
The reference signal B is sent to the suppression signal generation unit 80 and is also input to the synchronization signal generation unit 70, and the synchronization signal S is sent to the arithmetic processing unit 90.

The arithmetic processing unit 90 performs a DFT (Discrete Fourier Transform) operation using the measurement signal M for n cycles of the reference signal in synchronization with the predetermined phase of the reference signal B, and the resistance component current Igr and capacitance included in the measurement signal M The component current Igc is separated and extracted.
The suppression signal generation unit 80 adjusts the amplitude of the reference signal B based on the capacitance component current Igc output from the arithmetic processing unit 90, and adds the suppression current signal P to the suppression unit of the ZCT 50 in the opposite phase, thereby measuring the measurement signal. Feedback control is performed so that the capacitance component current Igc in M is magnetically canceled.
For this reason, the arithmetic processing unit 90 calculates only the resistance component current Igr having the frequency of the monitoring signal with high accuracy by performing the calculation using the measurement signal M in a state where the capacitance component current Igc is sufficiently suppressed. Is possible. In FIG. 4, 101 is a display unit, 102 is an operation unit, and 103 is an alarm output unit.

JP-A-63-289465 (page 2, lower right column, lines 1 to 17, FIG. 1, etc.) JP-A-9-318684 (paragraphs [0027] to [0040], FIG. 1, etc.) Japanese Patent Laying-Open No. 2003-215196 (paragraphs [0015] to [0022], FIG. 1, FIG. 2, etc.) Japanese Patent Laying-Open No. 2010-66162 (paragraphs [0043] to [0047], FIG. 1, FIG. 2, etc.)

As described above, in the device for monitoring the insulation deterioration state by injecting the monitoring signal having a frequency different from the commercial frequency into the electric circuit, the magnitude of the resistance component current to be detected and the other capacitance component current are as follows. It becomes a relationship.
That is, the frequency (commercial frequency) of the rated circuit voltage is 50 [Hz], the effective value is 200 [V], the capacitance of the circuit is 1 [μF], the insulation resistance of the circuit is 1 [MΩ], and the frequency of the monitoring signal Is 20 [Hz] and the effective value is 0.5 [V],
(1) Commercial frequency component in leakage current:
Resistance component current: 200 [V] / 1 [MΩ] = 0.2 [mA]
Capacitance component current: 200 [V] / {1 / (2 · π · 50 [Hz] · 1 × 10 ⁻⁶ )} = 62.83 [mA]
(2) Monitor signal frequency component in leakage current:
Resistance component current: 0.5 [V] / 1 [MΩ] = 0.5 [μA]
Capacitance component current: 0.5 [V] / {1 / (2 · π · 20 [Hz] · 1 × 10 ⁻⁶ )} = 62.83 [μA]
It becomes.

As is clear from the above example, the ratio of the commercial frequency component to the monitoring signal frequency component in the leakage current is about 1000 to 1, so how to remove the commercial frequency component from the detected leakage current is one. It is an issue.
Furthermore, when focusing only on the monitoring signal frequency component in the leakage current, the ratio of the resistance component current to the capacitance component current is 1: 100, and in order to accurately detect the resistance component current to be obtained, the capacitance component current is Reliable removal is also a major issue.
In order to realize these, it is necessary to detect the resistance component current with high accuracy by appropriately combining hardware and software. Even in the above-described Patent Documents 1 to 4, problems are caused by various filters and Fourier transform processing. We are trying to solve this problem.

Here, for example, when a specific frequency component is extracted by Fourier transform such as DFT calculation as described in Patent Document 4, if the analysis frequency interval is set roughly, a target frequency (frequency of the monitoring signal) component Not only that, but also the surrounding frequency components are detected, which become noise and the measurement accuracy is significantly reduced. Therefore, in order to increase the measurement accuracy, it is desirable to make the analysis frequency interval as short as possible, for example, 1 [Hz] interval. To measure the waveform for one period at this frequency interval, data for 1 second is required. It is necessary to accumulate, and the shorter the analysis frequency interval, the longer the data accumulation target time.
In addition, for the frequency component to be extracted or removed, since the waveform is sampled at a frequency several times that frequency, a certain fine sampling period and a time width for suppressing the influence of the surrounding frequency are required. As a result, several hundreds to several thousand points of data must be accumulated, and a large-capacity memory must be prepared.

  In addition, when calculating the resistance component current from the data after Fourier transform, a method of performing a trigonometric function calculation using the phase value of the leakage current is conceivable. However, when the phase value is used, the phase is close to 0 degrees and 90 degrees. Since the influence of the error becomes extremely large, it can be said that calculation of the resistance component current by such a method should be avoided as much as possible.

  Therefore, the problem to be solved by the present invention is that a large amount of data is not required as in the Fourier transform, and the resistance component current and the capacitance component current, which are vector components of the leakage current, are digitally filtered and effective / ineffective calculations are performed. It is an object to provide an insulation monitoring method and an insulation monitoring apparatus which can monitor an insulation deterioration state with high accuracy by digital calculation and can test the quality of a monitoring operation as necessary.

In order to solve the above-described problem, an insulation monitoring method according to claim 1 is configured to flow through a ground line of the electric circuit when a monitoring signal having a frequency lower than a commercial frequency is superimposed on a live distribution circuit that is an object of insulation monitoring. A leakage current is detected, and the component of the leakage current has a frequency of the monitoring signal and has a resistance component current corresponding to the ground insulation resistance of the circuit and a capacitance component current corresponding to the ground capacitance of the circuit In the insulation monitoring method for separating and extracting each, and monitoring the insulation deterioration state of the electric circuit based on the extracted magnitude of the resistance component current,
The commercial frequency component of the leakage current flowing through the ground line and the commercial frequency component of the voltage of the ground line are respectively removed by an analog filter to extract the monitoring signal frequency component of the leakage current and voltage, and these monitoring signal frequency components are extracted. The digital signal is converted into a digital signal and digital filter processing is performed, and the effective and ineffective components of the monitoring signal frequency component are obtained by using the output of the digital filter by the digital calculation of the arithmetic processing means, and the effective component is determined as the resistance component. The reactive component is identified as the capacitance component current.

  The insulation monitoring method according to claim 2 is the insulation monitoring method according to claim 1, wherein the arithmetic processing means generates a suppression current having the same magnitude and opposite phase with respect to the identified capacitance component current. The capacitance component current is canceled by injecting the suppression current into the electric circuit.

  The insulation monitoring method according to claim 3 is the insulation monitoring method according to claim 2, wherein the suppression current and the resistance test current generated by the arithmetic processing means are added to a vector and injected into the electric circuit, The capacitance component current is canceled, and the total value of the resistance component test current and the resistance component current is compared with a predetermined insulation monitoring level to test whether the monitoring operation is good.

  The insulation monitoring method according to claim 4 is the insulation monitoring method according to claim 2, wherein the suppression current and the resistance test current generated by the arithmetic processing means are added to a vector and injected into the electric circuit, The capacitance component current is canceled, and the total value of the resistance component test current and the resistance component current is compared with a predetermined insulation monitoring level to determine whether the monitoring accuracy is good or bad.

  The insulation monitoring method according to claim 5 is the insulation monitoring method according to claim 3 or 4, wherein the monitoring output is obtained when a total value of the resistance test current and the resistance component current exceeds a predetermined insulation monitoring level. Is generated to check the quality of the monitoring operation or the quality of the monitoring accuracy.

The insulation monitoring apparatus according to claim 6 superimposes a monitoring signal having a frequency lower than the commercial frequency on a live-line power distribution circuit to be insulated.
Means for detecting a leakage current flowing through a ground line of the electric circuit when the monitoring signal is superimposed on the electric circuit;
A commercial frequency component is removed from the detected leakage current, and a resistance component current having the frequency of the monitoring signal as the leakage current component and corresponding to the ground insulation resistance of the circuit and the ground of the circuit Separation / extraction means for separating and extracting each of the capacitance component currents corresponding to the electric capacity,
In an insulation monitoring device that monitors the insulation deterioration state of the electric circuit based on the extracted magnitude of the resistance component current,
The separation / extraction means is
An analog filter that removes the commercial frequency component of the leakage current flowing through the ground line and the commercial frequency component of the voltage of the ground line, and
AD conversion means for converting the output of the analog filter into a digital signal;
A digital filter for digitally processing the output of the AD conversion means to extract the monitor signal frequency component of the leakage current and voltage;
An effective component calculating means and an invalid component calculating means for obtaining an effective component and an invalid component of the monitoring signal frequency component from the output of the digital filter, respectively,
The effective component is identified as the resistance component current, and the ineffective component is identified as the capacitance component current.

  The insulation monitoring device according to claim 7 is the insulation monitoring device according to claim 6, wherein the capacitance component current is the same in magnitude and generates an antiphase suppression current, and the capacitance component Means for injecting the suppression current into the electric circuit in order to cancel the current.

An insulation monitoring apparatus according to an eighth aspect is the insulation monitoring apparatus according to the seventh aspect, wherein a unit for generating a resistance test current having a predetermined magnitude, and the resistance test current and the suppression current are added in vector. Means for injecting a vector addition result of the resistance test current and the suppression current into the electric circuit,
The total value of the resistance component current identified as the effective component of the monitoring signal frequency component and the resistance test current is detected from the electric circuit, and the total value is compared with a predetermined insulation monitoring level to determine whether the monitoring operation is good or bad. Are to be tested.

  The insulation monitoring device according to claim 9 is the insulation monitoring device according to claim 8, wherein the means for injecting the vector addition result of the resistance test current and the suppression current into the electric circuit includes the suppression current in the electric circuit. It is also characterized by the fact that it also serves as a means for injecting into the liquid.

  The insulation monitoring device according to claim 10 is the insulation monitoring device according to any one of claims 6 to 9, wherein a total value of the resistance component current and the resistance test current exceeds the insulation monitoring level. Sometimes, the contact output or alarm output as the monitoring operation is locked.

  The insulation monitoring apparatus according to claim 11 is the insulation monitoring apparatus according to any one of claims 6 to 10, wherein an amplification unit is provided on an output side of the analog filter, and an output of the amplification unit is converted to the AD conversion unit. And the effective component calculating means via the digital filter.

  The insulation monitoring apparatus according to a twelfth aspect is the insulation monitoring apparatus according to any one of the sixth to eleventh aspects, wherein the digital filter is an FIR filter.

The present invention combines an analog filter and a digital filter without using a Fourier transform process that requires a large amount of data accumulated over a relatively long time as in Patent Document 4 or a trigonometric function operation. The resistance component current and the capacitance component current are respectively separated and extracted by calculating the effective / ineffective portion of the monitoring signal frequency component.
For this reason, a large-capacity memory is not required, the cost can be reduced, and the responsiveness can be improved.
Further, since the monitoring signal frequency component is extracted from only the target resistance component current by sufficiently suppressing the capacitance current component from the leakage current, the full scale of the input signal to the AD conversion means can be minimized. It is possible to calculate the resistance component current as an index of the insulation deterioration state with high accuracy.
Furthermore, a resistance test current is superimposed on the extracted resistance component current and injected into the electric circuit, and it is detected whether or not an actual monitoring output can be obtained when the total value thereof exceeds a predetermined insulation monitoring level. Thus, it is possible to confirm whether the monitoring operation as the insulation monitoring device is good or bad and the monitoring accuracy is good.

It is a block diagram which shows embodiment of this invention. It is a vector diagram of voltage and current showing the operation of the embodiment. It is a vector diagram of voltage and current at the time of an operation check test in the embodiment. It is a block diagram which shows the prior art described in patent document 4.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of this embodiment. In FIG. 1, a load 2 is connected to secondary-side electric circuits 3 and 5 of a transformer 1 in which a primary-side electric circuit is connected to a distribution system.
A B-type ground wire 4 is connected to the electric circuit 3, and the insulation monitoring device according to the present embodiment has the electric circuits 3, 5, and 5 when the insulation monitoring signal having a frequency lower than the commercial frequency is superimposed on the B-type ground line 4. The resistance component current Igr is extracted from the leakage current flowing back through the ground potentials E _d and E _b, and the insulation deterioration state of the electric circuit (including the load connected to the electric circuit) is monitored based on the magnitude. .

Next, the configuration and operation of the insulation monitoring apparatus main body 200 will be described.
The monitoring signal data generated by the first waveform generation unit 211 in the CPU 210 is converted into an analog signal by the D / A converter 221. This analog signal is smoothed by a band-pass filter (BPF) 222 to become an insulation monitoring signal having a low frequency (for example, 20 [Hz]), and is injected into the B-type ground line 4 via the superposition transformer 30.

The voltage of the B type ground line 4 is input to the A / D converter 225 via the LPF 223 and the BPF 224 as a reference voltage, converted into a digital signal, and input to the CPU 210. Further, a leakage current flowing through the B-type grounding wire 4 is detected by a zero-phase current transformer (ZCT) 50. This leakage current is converted into a digital signal by the A / D converter 229 from the secondary side of the ZCT 50 via the LPF 226 and the BPF 227 and input to the CPU 210, and after being amplified by the amplifier 228, the A / D conversion is performed. It is input to the CPU 210 via the device 230.
Here, the LPFs 223 and 226 are for removing harmonics from the measured current / voltage.
Further, the BPFs 224 and 227 reduce the commercial frequency components to about −60 to −80 [dB] with the frequency of the monitoring signal as a cutoff frequency in order to remove the commercial frequency components from the outputs of the LPFs 223 and 226, respectively. Therefore, the commercial frequency component is reduced to about 1/1000 to 1/10000 of the conventional frequency component. In order to remove commercial frequency components, a normal active filter (BPF, LPF, HPF, etc.) may be used in multiple stages, or an SCF described in Patent Document 4 may be used.

  The voltage / current converted into digital signals by the A / D converters 225, 229, and 230 is input to finite impulse response filters (FIR filters) 212, 213, and 214 in the CPU 210, and digital filter processing is performed. These FIR filters 212, 213, and 214 allow the monitoring signal frequency component to pass and remove the commercial frequency component almost completely. With the above configuration, for example, a commercial frequency component of 50 [Hz] or 60 [Hz] can be selectively removed from a monitoring signal of 20 [Hz], as in DFT computation or FFT computation. A Fourier transform process using a large amount of data becomes unnecessary.

By using the instantaneous value of the reference voltage between the B-type ground line 4 and the ground potential _Ed and the monitoring signal frequency component of the leakage current thus obtained, the effective component calculating unit 216 and the invalid component calculating unit 215 For example, the calculations of Formulas 1 and 2 are performed.
In these equations, V _ne is the instantaneous value of the reference voltage, I ₀ is the leakage current (= Ig), n is the current sampling point, and n-90 ° is the sampling point 90 ° before the electrical angle.
[Equation 1]
I _gr (n) = {V _ne (n) · I ₀ (n) + V _ne (n-90 °) · I ₀ (n-90 °)} / √ {V _ne (n) ² + V _ne ( n-90 °) ² }
[Equation 2]
I _gc (n) = {V _ne (n) · I ₀ (n-90 °) −V _ne (n-90 °) · I ₀ (n)} / √ {V _ne (n) ² + V _ne ( n-90 °) ² }

As shown in Equations 1 and 2, the resistance component current Igr and the capacitance component current Igc can be calculated as an effective component and an ineffective component of the monitor signal frequency component, respectively, by a simple product-sum operation using the reference voltage and the leakage current. .
The resistance component current Igr calculated by the effective component calculating means 216 indicates the insulation deterioration state of the electric circuit to be monitored, and the value is digitally displayed by the display unit 240 and exceeds a predetermined insulation monitoring level. In this case, the monitoring output unit 250 is operated to perform contact output or alarm output.

  Further, the capacitance component current Igc calculated by the ineffective component calculation means 215 is input to the second waveform generation means 217 together with the reference voltage output from the FIR filter 212. This waveform generation means 217 reproduces the capacitance component current waveform shifted to the 90 ° advance phase using the magnitude of the capacitance component current Igc and the zero cross timing of the reference voltage, and this is reproduced with respect to the actual capacitance component current Igc. Then, a signal to be superimposed on the primary side of the ZCT 50 is generated so as to flow in an opposite phase.

The output signal of the waveform generating means 217 is converted into an analog signal by the D / A converter 231 and further supplied to the primary side of the ZCT 50 via the BPF 232. Thereby, a suppression current for canceling the capacitive component current Igc is passed, and the capacitive component current Igc can be reliably removed from the leakage current detected by the ZCT 50.
Here, the BPF 232 has a function of smoothing the waveform after DA conversion, like the BPF 222. Instead of the DA converter 231 (the same applies to the DA converter 221), the output waveform of the waveform generation means 217 (and the waveform generation means 211) may be given to the BPF 232 (and BPF 222) as a square wave.

  2 shows the reference voltage V (reference V) and leakage current Ig (electric circuit Ig) detected via the B-type grounding wire 4, and the leakage current Ig by the above-described effective component calculation means 216 and invalid component calculation means 215. Resistance component current Igr (electric circuit Igr) and capacitance component current Igc (electric circuit Igc) calculated as vector components of the signal, and suppression current Igc (suppression Igc) generated by the waveform generation means 217 to cancel the capacitance component current Igc FIG.

In FIG. 1 again, reference numeral 218 denotes a test signal generating means. The test signal generation means 218 generates a resistance test current Igr ′ having a predetermined magnitude in phase with the resistance component current Igr detected by the effective component calculation means 216, and the resistance test current Igr ′ is generated. The vector is added to the suppressing capacitance component current Igc generated by the waveform generating means 217 and injected into the ZCT 50.
As a result, the total value of the resistance component Igr detected by the effective component calculating means 216 and the resistance component test current Igr ′ generated by the test signal generating means 218 as a result of the capacitance component current Igc being canceled in the B-type ground line 4. Only will flow. Therefore, whether or not the monitoring output unit 250 operates when the value of the resistance test current Igr ′ is set to be greater than or equal to the difference between the insulation monitoring level in the monitoring output unit 250 and the resistance component current Igr detected by the effective component calculation means 216. By detecting this, the quality of the insulation monitoring function, that is, the operation confirmation can be performed.

FIG. 3 is a vector diagram at the time of the above test, and Igr ′ is generated by the test signal generating means 218 and superimposed so that the total value (Igr + Igr ′) of Igr and the resistance test current Igr ′ exceeds the insulation monitoring level. Shows the case.
In this case, the monitoring output unit 250 is operated to perform contact output or the like, but at the time of a test using the test signal generation means 218, a setting such as locking the output of the monitoring output unit 250 is added. This makes it possible to check the operation of the device without affecting the operating status.

As described above, according to the present embodiment, the LPF 226 and the BPF 227 can reduce the commercial frequency component of the leakage current to 1/1000 to 1/10000 of the conventional one, with a ratio of about 1: 1 or more, It is possible to make the monitoring signal frequency component larger than the commercial frequency component.
Therefore, by selecting the gain of the amplifier 228 in FIG. 1 as a predetermined value and inputting it to the AD converter 230, the AD conversion full scale can be reduced to near the maximum measured value of the resistance component current Igr. The detection accuracy of the resistance component current Igr can be improved.

Further, if the analog input signals of the AD converters 229 and 230 are converted into digital values that do not saturate the inputs of the subsequent FIR filters 213 and 214, the commercial frequency components are further selectively selected by these FIR filters 213 and 214. In addition, the response speed can be increased.
For example, if the frequency of the monitoring signal is 20 [Hz], the commercial frequency component of the leakage current can be completely removed by using the FIR filter of the arithmetic expression expressed by the following formulas 3 and 4. .
[Formula 3] (When the commercial frequency is 50 [Hz])
I (n) = i (n) + i (n−72 °)
[Formula 4] (When commercial frequency is 60 [Hz])
I (n) = i (n) + i (n−60 °)
In these mathematical expressions, n is the current sampling time point, and “n−72 °” and “n−60 °” indicate the sampling time points 72 ° and 60 ° before the electrical angle, respectively.
Although the values of 72 ° and 60 ° described above vary depending on the monitoring signal frequency, the phase angle θ can be expressed by a general formula θ = 180 ° / (commercial frequency / monitoring signal frequency), and is obtained here. If AD conversion is performed at a sampling interval several times larger than the phase angle, calculation by the FIR filter can be easily performed.

  Furthermore, each arithmetic processing in the present embodiment does not need to perform Fourier transform processing such as DFT arithmetic and FFT arithmetic, and if there is sampling data for approximately 0.5 cycles, both the resistance component current and the capacitance component current are effective. An operation result corresponding to the value is obtained. For this reason, the memory capacity can be reduced and the responsiveness is excellent as compared with the Fourier transform that can be realized by accumulating a large number of data over many cycles.

  In addition, the resistance test current is vector-added to the suppression current and injected into the electric circuit, so that the total value of the resistance test current and the resistance component current is compared with the insulation monitoring level while canceling the capacitance component current. Since it is possible to test whether or not the monitoring output can be obtained, a highly reliable insulation monitoring device can be realized.

1: Transformer 2: Load 3, 5: Secondary side circuit 4: Class B ground wire 30: Superposition transformer 50: Zero-phase current transformer (ZCT)
200: Insulation monitoring device body 210: CPU
211, 217: Waveform generating means 212, 213, 214: Finite impulse response filter (FIR filter)
215: Effective component calculating means 216: Invalid component calculating means 218: Test signal generating means 221, 231: D / A converter 222, 224, 227, 232: Band pass filter (BPF)
223, 226: Low-pass filter (LPF)
225, 229, 230: A / D converter 228: Amplifier 240: Display unit 250: Monitor output unit C: Ground capacitance R: Ground insulation resistance

Claims (12)

When a monitoring signal having a frequency lower than the commercial frequency is superimposed on a live distribution circuit that is subject to insulation monitoring, a leakage current flowing through the ground line of the circuit is detected, and the component of the monitoring signal is detected as a component of the leakage current. A resistance component current having a frequency and corresponding to a ground insulation resistance of the circuit and a capacitance component current corresponding to a ground capacitance of the circuit are separated and extracted, respectively, and the extracted resistance component current is obtained. In an insulation monitoring method for monitoring an insulation deterioration state of the electric circuit based on:
The commercial frequency component of the leakage current flowing through the ground line and the commercial frequency component of the voltage of the ground line are respectively removed by an analog filter to extract the monitoring signal frequency component of the leakage current and voltage, and these monitoring signal frequency components are extracted. The digital signal is converted into a digital signal and digital filter processing is performed, and the effective and ineffective components of the monitoring signal frequency component are obtained by using the output of the digital filter by the digital calculation of the arithmetic processing means, and the effective component is determined as the resistance component. An insulation monitoring method characterized in that the current is used and the ineffective portion is identified as the capacitance component current. In the insulation monitoring method according to claim 1,
For the identified capacitance component current, the calculation processing means generates a suppression current having the same magnitude and opposite phase, and canceling the capacitance component current by injecting the suppression current into the electric circuit. A characteristic insulation monitoring method. In the insulation monitoring method according to claim 2,
By adding the vector of the suppression current and the resistance test current generated by the arithmetic processing unit and injecting it into the electric circuit, the capacitance component current is canceled and the sum of the resistance test current and the resistance component current is calculated. An insulation monitoring method comprising testing a quality of a monitoring operation by comparing a value with a predetermined insulation monitoring level. In the insulation monitoring method according to claim 2,
By adding the vector of the suppression current and the resistance test current generated by the arithmetic processing unit and injecting it into the electric circuit, the capacitance component current is canceled and the sum of the resistance test current and the resistance component current is calculated. An insulation monitoring method comprising: comparing a value with a predetermined insulation monitoring level to determine whether the monitoring accuracy is good or bad. In the insulation monitoring method according to claim 3 or 4,
Insulation monitoring characterized in that when a total value of the resistance test current and the resistance component current exceeds a predetermined insulation monitoring level, a monitoring output is generated to check the quality of the monitoring operation or the quality of the monitoring accuracy. Method. Means for superimposing a monitoring signal of a frequency lower than the commercial frequency on a live distribution circuit that is subject to insulation monitoring;
Means for detecting a leakage current flowing through a ground line of the electric circuit when the monitoring signal is superimposed on the electric circuit;
A commercial frequency component is removed from the detected leakage current, and a resistance component current having the frequency of the monitoring signal as the leakage current component and corresponding to the ground insulation resistance of the circuit and the ground of the circuit Separation / extraction means for separating and extracting each of the capacitance component currents corresponding to the electric capacity,
In an insulation monitoring device that monitors the insulation deterioration state of the electric circuit based on the extracted magnitude of the resistance component current,
The separation / extraction means is
An analog filter that removes the commercial frequency component of the leakage current flowing through the ground line and the commercial frequency component of the voltage of the ground line, and
AD conversion means for converting the output of the analog filter into a digital signal;
A digital filter for digitally processing the output of the AD conversion means to extract the monitor signal frequency component of the leakage current and voltage;
An effective component calculating means and an invalid component calculating means for obtaining an effective component and an invalid component of the monitoring signal frequency component from the output of the digital filter,
The insulation monitoring apparatus, wherein the effective component is identified as the resistance component current, and the ineffective component is identified as the capacitance component current. In the insulation monitoring device according to claim 6,
Means for generating an anti-phase suppression current of the same magnitude and opposite phase with respect to the identified capacitive component current;
Means for injecting the suppression current into the electrical path to cancel the capacitive component current;
An insulation monitoring device comprising: In the insulation monitoring device according to claim 7,
Means for generating a resistance test current of a predetermined magnitude;
Means for vector addition of the resistance test current and the suppression current;
Means for injecting a vector addition result of the resistance test current and the suppression current into the electric circuit,
The total value of the resistance component current identified as the effective component of the monitoring signal frequency component and the resistance test current is detected from the electric circuit, and the total value is compared with a predetermined insulation monitoring level to determine whether the monitoring operation is good or bad. Insulation monitoring device characterized by testing. In the insulation monitoring device according to claim 8,
The means for injecting a vector addition result of the resistance test current and the suppression current into the electric circuit also serves as means for injecting the suppression current into the electric circuit. In the insulation monitoring apparatus according to any one of claims 6 to 9,
An insulation monitoring device that locks a contact output or an alarm output as the monitoring operation when a total value of the resistance component current and the resistance test current exceeds the insulation monitoring level. In the insulation monitoring apparatus according to any one of claims 6 to 10,
An insulation monitoring apparatus, comprising: an amplifying unit provided on an output side of the analog filter; and the output of the amplifying unit being input to the effective component calculating unit via the AD converting unit and the digital filter. In the insulation monitoring apparatus according to any one of claims 6 to 11,
An insulation monitoring apparatus, wherein the digital filter is an FIR filter.

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