JP2019152495A - Insulation monitoring system - Google Patents

Abstract

To provide an insulation monitoring system with which it is possible to perform highly accurate monitoring of insulation based on a weak zero-phase current without being affected by a residual current.SOLUTION: Provided is an insulation monitoring system 1 for monitoring the insulation state of an electrical circuit, in which a current detection unit 11 includes an annular core penetrating through a load electric wire 300 for sending a load current Il from an AC power supply to a load and a suppression electric wire 400 for sending a suppression current Is, and detects a residual current Id from the load current Il flowing to the load electric wire 300, and a suppression current output unit 12 generates a suppression current Is of the same phase and same level as the detected residual current Id, and sends a suppression current Is in a direction opposite the residual current Id to the suppression electric wire 400 so that the suppression current Is cancels out the residual current Id, whereby the problem is resolved.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an insulation monitoring system. More specifically, the present invention relates to an insulation monitoring system that performs accurate insulation monitoring based on a weak zero-phase current without being affected by a residual current.

  Poor insulation of electrical circuits and electrical equipment can cause serious accidents such as electric fires and electric shocks. For this reason, there are various methods for the purpose of examining the insulation state of the electric circuit and the electric equipment. For example, there is a method to check the insulation state of electrical circuits and electrical equipment using an insulation resistance meter. However, it is necessary to operate the electrical circuit and electrical equipment to be temporarily interrupted for measurement. It cannot cope with the modern system that becomes.

  In order to deal with such a problem, a technique for examining the insulation state of electric circuits and electric devices without a power failure has been generally used. For example, a technique using an insulation monitoring device proposed in Patent Document 1 is a technique that is generally used as a means for examining the insulation state of electric circuits and electrical devices without a power failure. The insulation monitoring device used in this method detects the phase of the voltage of the electric circuit and the current flowing through the ground line (hereinafter referred to as “leakage current”), and from this leakage current, the same component as the phase of the voltage of the transmission line Only the component (hereinafter referred to as “resistance component”) is taken out, and the insulation state of the electric circuit and the electric device is determined based on this resistance component.

  In other words, a conventional insulation monitoring device uses a zero-phase current transformer to detect leakage current. The leakage current detected by the zero-phase current transformer is a vector sum of a resistance component and a component whose phase advances by 90 ° with respect to the voltage of the electric circuit (hereinafter referred to as “capacitance component”). The capacitance component does not affect the insulation state of the electric circuit, and only the resistance component affects the insulation state of the electric circuit. In other words, the conventional insulation monitoring device determines the insulation state by detecting only the resistance component from the leakage current detected by the zero-phase current transformer.

JP 2008-8823 A

  However, the conventional insulation monitoring device including the technique proposed in Patent Document 1 cannot detect a weak zero-phase current. For example, when the insulation resistance value is 1 MΩ (mega ohms), it is necessary to detect a weak zero-phase current of about 200 μA (microamperes). However, in a conventional insulation monitoring device, such a weak zero current is required. The phase current cannot be detected. This is not related to insulation monitoring because the zero-phase current transformer is affected by the permeability of the core material, the magnetic saturation of the core, the position of the primary conductor, the winding and arrangement of the secondary conductor, etc. This is because a zero-phase current called a residual current may flow, and such a residual current becomes an obstacle when performing accurate insulation monitoring.

  On the other hand, in the present age when electronic devices are becoming smaller and finer, some of the electronic devices on the market require accurate insulation monitoring that can detect such a weak zero-phase current. There are many things to do.

  An object of the present invention is to provide an insulation monitoring system capable of performing accurate insulation monitoring based on a weak zero-phase current without being affected by a residual current.

  In order to solve the above problems, an insulation monitoring system according to the present invention is an insulation monitoring system for monitoring an insulation state of an electric circuit, including a load wire for flowing a load current from an AC power source to a load, and a suppression for flowing a suppression current An annular core that penetrates the electric wire, and a current detecting means for detecting a residual current from a load current flowing through the penetrated load electric wire, and generating a suppression current in phase and at the same level as the detected residual current And a suppression current output means for causing the suppression current to flow in the direction opposite to the residual current to the suppression piezoelectric wire so that the suppression current cancels the residual current.

  According to the present invention, a suppression current having the same phase and level as the residual current detected by the current detection means is generated, and the generated suppression current cancels the residual current. Therefore, it is possible to prepare a suitable monitoring environment in which the residual current is reduced.

  In the insulation monitoring system according to the present invention, it is preferable that the AC power source is a three-phase AC power source, the load is a three-phase load, and the current detection means is a zero-phase current transformer. According to the present invention, the zero-phase current transformer detects a zero-phase current obtained by adding the currents flowing through the respective phases of the three-phase load cable as a residual current, and generates a suppressed current having the same phase and the same level as the residual current. Since the suppressed current is made to flow in the direction opposite to the residual current so as to cancel out the residual current, a suitable monitoring environment in which the residual current is reduced can be prepared.

  In the insulation monitoring system according to the present invention, the current detection means further detects a zero-phase current from a load current flowing through the load wire, and based on the detected value of the zero-phase current, the insulation state of the electric circuit It is preferable to further include an insulation state determination means for determining whether or not the resistance is good. According to the present invention, accurate insulation monitoring based on a weak zero-phase current can be performed without being affected by the residual current under a suitable monitoring environment in which the residual current is reduced.

  According to the present invention, accurate insulation monitoring based on a weak zero-phase current can be performed without being affected by a residual current.

It is a figure which shows the structure of the electrical circuit containing the insulation monitoring system which concerns on 1st Embodiment of this invention. It is a figure which shows the content and result of a residual current reduction test using the insulation monitoring system of FIG. It is a figure which shows the structure of the high voltage electric circuit containing the insulation monitoring system which concerns on 2nd Embodiment and 3rd Embodiment of this invention. It is a block diagram which shows the structure of the insulation monitoring system of FIG. It is a vector diagram which shows the phase difference of the voltage signal measured by the insulation monitoring system of FIG. 4, and leakage current. It is a block diagram which shows the structure of the insulation monitoring system which concerns on 3rd Embodiment of this invention.

  Hereinafter, an insulation monitoring system according to the present invention will be described with reference to the drawings. The present invention is not limited to the illustrated embodiment.

[First Embodiment]
The insulation monitoring system 1 according to the first embodiment of the present invention is a system that monitors the insulation state of a three-phase electric circuit. As shown in FIG. 1, a CPU (Central Processing Unit) 10, a current detection unit 11, and The suppression current output unit 12 and the insulation state determination unit 13 are provided. The insulation monitoring system 1 detects the residual current Id from the three-phase load cable 300, generates a suppression current Is having the same phase and level as the detected residual current Id, and the suppression current Is cancels the residual current Id. In addition, a suppression current Is having a direction opposite to the residual current Id is passed through the suppression piezoelectric wire 400. Then, the insulation monitoring system 1 detects the zero-phase current Iz from the load current Il flowing through the load wire 300, and determines whether or not the insulation state of the electric circuit is good based on the detected value of the zero-phase current Iz. .

  Hereinafter, each component of the insulation monitoring system 1 will be described in detail.

(CPU)
The CPU 10 controls various processes executed by the current detection unit 11, the suppressed current output unit 12, and the insulation state determination unit 13.

(Current detector)
The current detection unit 11 in the present embodiment includes an annular core (not shown), a conductor wound around the core (not shown), and an outer case (not shown) that houses the core and the conductor. It is a zero-phase current transformer (also referred to as ZCT) and detects the current flowing through the load wire 300. The core constituting the current detection unit 11 penetrates the three-phase load wire 300 for flowing the load current Il from the three-phase AC power source to the three-phase load 200 and the suppression piezoelectric wire 400 for flowing the suppression current Is. When the load current Il flows through the load wire 300 penetrating through the core of the current detection unit 11, the zero-phase current Iz obtained by adding the load currents Il flowing through the three-phase load wires 300 flows through the conductor. That is, in the normal state, the magnitudes of the load currents I1 flowing through the respective phases are the same and are in a balanced state, and thus the magnitude of the zero-phase current Iz is zero. For this reason, for example, current (zero-phase current Iz) does not flow through the conductor in a normal state where no abnormality such as ground fault or electric leakage occurs.

  However, the current detection unit 11 has a zero current called a residual current that is not related to insulation monitoring due to the influence of the magnetic permeability of the core material, the magnetic saturation of the core, the position of the load wire 300, the manner in which the conductor is wound and the arrangement, etc. Phase current may flow. Such a residual current Id becomes an obstacle when performing accurate insulation monitoring. For this reason, the insulation monitoring system 1 cancels the residual current Id using the suppression current Is generated by the suppression current output unit 12 described later. Thereby, the residual current Id can be reduced. A specific method for reducing the residual current Id using the suppression current Is will be described later.

  The magnitude | size of the core of the electric current detection part 11 will not be specifically limited if it is a magnitude | size which can penetrate the load electric wire 300 and the suppression piezoelectric wire 400. FIG. The material of the core is not particularly limited, and those generally used as the core material, such as Permalloy (registered trademark) and Finemet (registered trademark), can be employed. In the present embodiment, the core is formed by laminating permalloy flat plates. The conductor is a conductor wound around the core. In addition, the material of a conductor is not specifically limited, The insulation coating copper wire etc. which are generally used as a conductor can be used.

(Suppression current output part)
The suppression current output unit 12 includes a synchronization signal detection jig 121, a sine wave generator 122, a power amplifier 123, and a phase difference meter 124. The suppression current output unit 12 generates a suppression current Is having the same phase and the same level as the residual current Id detected by the current detection unit 11, and the residual current Id in the suppression piezoelectric wire 400 so that the suppression current Is cancels the residual current Id. A suppression current Is in the direction opposite to Id is supplied. That is, since the suppression current Is passed through the suppression piezoelectric wire 400 works so as to cancel the residual current Id, it is possible to prepare a suitable monitoring environment in which the residual current is reduced.

  The synchronization signal detection jig 121 includes a filter, an amplifier, and an SCF (switched capacitor filter). The filter (not shown) detects the voltage signal Va generated in the electric circuit shown in FIG. 1, and removes a noise component from the detected voltage signal Va. An amplifier (not shown) amplifies the voltage signal Va output from the filter. The SCF has a function as a low-pass filter that reduces a component having a frequency higher than the cutoff frequency while hardly attenuating a component having a frequency lower than the cutoff frequency in the voltage signal Va, and has a predetermined clock. Based on the frequency, the phase of the voltage signal Va output from the amplifier is adjusted.

  The sine wave generator 122 adjusts the level and phase of the voltage signal Va output from the SCF of the synchronization signal detection jig 121 to generate a sine wave.

  The power amplifier 123 amplifies the sine wave generated by the sine wave generator 122 to generate a suppression current Is having the same phase and level as the residual current Id, and the suppression current Is cancels the residual current Id. A suppression current Is in the direction opposite to the residual current Id is passed through the suppression piezoelectric wire 400. Thereby, in the current detection part 11, only the residual current Id remaining as a result of cancellation is detected, so that the residual current can be reduced. As a result, a suitable monitoring environment in insulation monitoring can be prepared.

  The phase difference meter 124 is an instrument that measures the phase of the load current Il and the phase of the suppression current Is and detects the difference between the two. Since the phase difference meter 124 detects the difference between the phase of the load current Il and the phase of the suppression current Is, the power amplifier 123 can generate the suppression current Is in phase with the residual current Id.

(Insulation state determination unit)
The insulation state determination unit 13 includes a residual current measuring device 131 and a measured value display terminal 132. The insulation state determination unit 13 determines whether or not the insulation state of the electric circuit shown in FIG. 1 is good based on the value of the zero-phase current Iz detected by the current detection unit 11.

  The residual current measuring device 131 measures the value of the zero-phase current Iz detected by the current detector 11, and when the value of the zero-phase current Iz exceeds a preset threshold value, the insulation state of the electric circuit has deteriorated. Judgment is made and a warning is issued. Thereby, it is possible to promptly notify the operator of the deterioration of the insulation state.

  The measured value display terminal 132 displays the value of the zero-phase current Iz detected by the current detector 11 on a display (not shown). The operator can recognize the insulation state of the electric circuit shown in FIG. 1 by viewing this display.

When the insulation monitoring system 1 of FIG. 1 is used, a test was performed under the following conditions as to how much the residual current is reduced.
[Test 1]
(Content)
When the load current is the R phase (100 A), the S phase (100 A), and the T phase (100 A) and the residual current Id is 845 μA (the phase difference is 67.8 deg), the suppression current Is of the same level and the same phase And the change in the residual current Id is confirmed when the suppression current Is is supplied. The test was performed four times under the same conditions.

(result)
As a result of flowing the suppression current, the residual current remaining is 2.09 μA for the first time, 3.81 μA for the second time, 3.12 μA for the third time, 4 for the fourth time. 72 μA. That is, by flowing the suppression current, the residual current of 845 μA could be dramatically reduced to about 2.09 μA to 4.72 μA.

[Test 2]
(Content)
When the load current is the R phase (100 A), the S phase (130 A), and the T phase (100 A) and the residual current Id is 845 μA (the phase difference is 67.8 deg), the suppression current Is of the same level and the same phase And the change in the residual current Id is confirmed when the suppression current Is is supplied. The test was performed four times under the same conditions.

(result)
As a result of flowing the suppression current, the remaining residual current was 242 μA for the first average, 243 μA for the second time, 244 μA for the third time, 243 μA for the fourth time, and 243 μA for the fourth time. Although the residual current Id can be reduced by flowing the suppression current Is, a dramatic reduction like the result of Test 1 has not occurred. That is, it was found that when the load current in a specific phase (S phase) fluctuates from 100 A to 130 A, the residual current Id changes in both level and phase.

[Test 3]
(Content)
When the load current is the R phase (130 A), the S phase (100 A), and the T phase (130 A), and the residual current Id is 845 μA (the phase difference is 67.8 deg), the suppression current Is of the same level and the same phase And the change in the residual current Id is confirmed when the suppression current Is is supplied. The test was performed four times under the same conditions.

(result)
As a result of flowing the suppression current, the remaining residual current was 127 μA for the first average, 125 μA for the second time, 122 μA for the third time, 121 μA for the fourth time, and 121 μA for the fourth time. Although the residual current Id can be reduced by flowing the suppression current Is, as in the case of the test 2, the dramatic reduction like the result of the test 1 did not occur. That is, it was found that when the load current in a specific phase (R phase and T phase) fluctuates from 100 A to 130 A, the residual current Id changes in both level and phase.

[Test 4]
(Content)
With respect to the residual current Id remaining as a result of the test 2, it was confirmed what kind of change occurs in the residual current Id by generating and flowing a readjusted suppression current Is. The test was performed four times under the same conditions.

(result)
As a result of flowing the readjusted suppression current Is, the remaining residual current Id is 7.16 μA for the first average, 6.57 μA for the second, 6.96 μA for the third, and 4.96 μA for the third. The average value was 6.95 μA. That is, it was found that the residual current Id can be reduced by flowing the readjusted suppression current Is.

[Test 5]
(Content)
As to the residual current Id remaining as a result of the test 3, it was confirmed what kind of change occurs in the residual current Id by generating and flowing the readjusted suppression current Is. The test was performed four times under the same conditions.

(result)
As a result of flowing the readjusted suppression current Is, the remaining residual current Id is 1.30 μA for the first average, 3.70 μA for the second, 2.85 μA for the third, and 4.85 μA for the fourth. The average value was 2.28 μA. That is, it was found that the residual current Id can be reduced by flowing the readjusted suppression current Is.

[Second Embodiment]
The insulation monitoring system 2 according to the second embodiment of the present invention is a system that monitors the insulation state of the high-voltage electric circuit W. As shown in FIG. 3, the high-voltage electric circuit W includes a transformer TR1 that transforms a high voltage (for example, 6600V) received from a high-voltage power receiving line into a commercial voltage (for example, 110V). Is connected to the load 200 via power transmission lines 500 and 501. The power transmission path 501 is grounded via a B-type ground line (hereinafter referred to as “ground line”) 600. Between the power transmission path 500 and the ground, there exists a ground impedance Z0 obtained by combining the ground insulation resistance R0 and the ground capacitance (floating capacitance) C0. For this reason, the same current as the current flowing through the ground impedance Z0 flows through the ground line 600. As shown in FIG. 3, the insulation monitoring system 2 is disposed in a state where it penetrates the ground line 600 and is connected to the power transmission paths 500 and 501.

  As shown in FIG. 4, the insulation monitoring system 2 includes a CPU 20, a current detection unit 21, a leakage current amplification unit 22, a suppression current output unit 23, and an information presentation unit 60. The insulation monitoring system 2 is configured to suppress the suppression current Is that is equal to and opposite to the leakage current I0 flowing through the ground line 600 with the ground wire 600 and the suppression wire 700 passed through the current detection unit 21. Flow to 700. Then, when the zero-phase current Iz detected by the current detector 21 becomes zero, a component (hereinafter referred to as “in-phase component”) that is in phase with the voltage signal Va among the components constituting the suppression current Is is recognized. Then, based on this in-phase component, it is determined whether or not the insulation state of the high voltage electric circuit W is good.

  Hereinafter, each component of the insulation monitoring system 2 will be described in detail.

(CPU 20)
The CPU 20 in this embodiment controls various processes executed by the current detection unit 21, the leakage current amplification unit 22, the suppression current output unit 23, and the information presentation unit 60. For example, the CPU 20 obtains the phase angle θ of the current I0 based on the reference signal generated by the reference signal adjustment unit 37 and the leakage current I0 detected by the current detection unit 21, as shown in FIG. The CPU 20 obtains a resistance component I0r of the current I0 and a capacitance component I0c of the current I0 based on the phase angle θ. The CPU 20 generates an Ir adjustment signal and an Ic adjustment signal based on the resistance component I0r and the capacitance component I0c, and outputs these adjustment signals to the Ir suppression signal generator 38 and the Ic suppression signal generator. 40 and output respectively. That is, the CPU 20 functions as a phase detection unit that detects the phase of the voltage generated between the power transmission lines 500 and 501.

  The CPU 20 generates an Ir adjustment signal and an Ic adjustment signal so that the resistance component I0r of the leakage current I0 detected by the current detection unit 21 and the capacitance component I0c are both zero, and the resistance component I0r. Then, the Ir adjustment signal when both the electrostatic capacitance component I0c becomes zero is recognized as the resistance component I0r of the leakage current I0. That is, the CPU 20 determines whether the insulation state of the power transmission lines 500 and 501 is good based on the in-phase component when the current value detected by the current detection unit 21 becomes zero by flowing the suppression current Is. It also functions as an insulation state determination means for determining whether or not.

(Current detector)
The current detection unit 21 according to the present embodiment includes an annular core (not shown), a conductor wound around the core (not shown), and an outer case (not shown) that houses the core and the conductor. Zero phase current transformer (ZCT). The current detection unit 21 penetrates the ground wire 600 and a suppression wire 700 described later. Since the core constituting the current detection unit 21 penetrates the ground line 600 and the suppression wire 700, the current detection unit 21 includes the leakage current I 0 flowing through the ground line 600 and the suppression current Is flowing through the suppression wire 700. Can be detected. Note that the characteristics such as the size and material of the core constituting the current detection unit 21 and the characteristics such as the material of the conductor are the same as those in the first embodiment, and thus the description thereof is omitted.

(Leakage current amplifier)
The leakage current amplification unit 22 includes a head amplifier 32 and a filter 33. The head amplifier 32 amplifies the leakage current I0 detected by the current detection unit 21. The filter 33 removes a noise component from the leakage current I0 amplified by the head amplifier 32, and supplies the leakage current I0 from which the noise component has been removed to the CPU 20.

(Suppression current output part)
The suppression current output unit 23 includes a filter 34, an amplifier 35, an SCF (switched capacitor filter) 36, a reference signal adjustment unit 37, an Ir suppression signal generator 38, a phase shift circuit 39, and Ic suppression. A signal generator 40 and a power amplifier 41 are included.

  The filter 34 detects the voltage signal Va generated between the two power transmission lines 500 and 501, and removes a noise component from the detected voltage signal Va. The amplifier 35 amplifies the voltage signal Va output from the filter 34. The SCF 36 functions as a low-pass filter and adjusts the phase of the voltage signal Va output from the amplifier 35 based on a predetermined clock frequency. The reference signal adjustment unit 37 performs level adjustment on the voltage signal Va output from the SCF 36 to generate a reference signal. The Ir suppression signal generator 38 generates an Ir suppression signal which is a signal in phase with the voltage signal Va output from the SCF 36 and which is a level determined based on the Ir adjustment signal. The phase shift circuit 39 advances the phase of the voltage signal Va output from the SCF 36 by 90 °. The Ic suppression signal generator 40 generates an Ic suppression signal that is a signal having a phase advanced by 90 ° by the phase shift circuit 39 and a signal having a level determined by the Ic adjustment signal. The power amplifier 41 generates and generates a suppression current Is obtained by combining and amplifying the Ir suppression signal generated by the Ir suppression signal generator 38 and the Ir suppression signal generated by the Ic suppression signal generator 40. The suppression current Is is supplied to the suppression wire 700. That is, the power amplifier 41 converts the current I0 detected by the current detector 21 into a component in phase with the phase detected by the CPU 20 (in-phase component) and a component whose phase is advanced by 90 ° (hereinafter “phase advance component”). And generating a suppression current Is composed of these two components, and causing the suppression current Is to flow in the suppression wire 700 so as to be opposite to the current flowing in the ground line 600. Function as.

(Information presentation part)
The information presentation unit 60 provides various types of information to the operator of the insulation monitoring system 2. The information presentation unit 60 includes a display 51 and an alarm device 52. The display 51 displays various information such as the insulation state of the power transmission paths 500 and 501. The alarm device 52 issues an alarm when it is determined that the insulation resistance has deteriorated.

  In the insulation monitoring system 2 having the above-described configuration, the current detection unit 21 passes through the ground wire 600 and the suppression wire 700, and the leakage current I0 detected by the current detection unit 21 is zero. The suppression current Is flowing through the electric wire 700 is controlled. Then, the Ir adjustment signal when the leakage current I0 detected by the current detection unit 21 becomes zero is recognized as the resistance component I0r of the leakage current I0, and the threshold value for which the resistance component I0r is set in advance is recognized. If it exceeds, it is determined that the insulation state of the transmission lines 500 and 501 has deteriorated, and an alarm is issued to the operator. As a result, the operator can quickly know the deterioration of the insulation state of the power transmission paths 500 and 501.

  In the present embodiment, the suppression current Is that cancels the leakage current I0 is generated, and the resistance component of the suppression current Is is detected as the resistance component I0r of the leakage current I0. Therefore, the detection accuracy of the current detection unit 21 varies. Even in the case where a magnetic field is generated in the surroundings, it is possible to monitor the insulation state of the transmission lines 500 and 501 by measuring the resistance component I0r with high accuracy.

[Third Embodiment]
As shown in FIG. 6, the insulation monitoring system 3 according to the third embodiment of the present invention does not include the Ir suppression signal generator 38 as compared with the insulation monitoring system 2 according to the second embodiment described above. The CPU 20 is different in that it does not generate an Ir adjustment signal to be supplied to the Ir suppression signal generator 38. The CPU 20 of the insulation monitoring system 3 according to the third embodiment separates the leakage current I0 detected by the current detection unit 21 into a resistance component I0r and a capacitance component I0c, and sets the capacitance component I0c to zero. An Ic adjustment signal is generated and output. Then, the resistance component I0r when the capacitance component I0c becomes zero is recognized as the resistance component I0r of the leakage current I0. Since the other configuration is the same as that shown in FIG. 4, the same reference numerals are given and description of the configuration is omitted.

  In the insulation monitoring system 3 having the above-described configuration, the ground line 600 and the suppression wire 700 are passed through the current detection unit 21 so that the capacitance component I0c of the leakage current I0 detected by the current detection unit 21 becomes zero. Thus, the current (suppression current Is) flowing through the suppression wire 700 is controlled. Then, the resistance component I0r when the capacitance component of the current detected by the current detection unit 21 becomes zero is recognized as the resistance component I0r of the leakage current I0, and the threshold value set in advance by the resistance component I0r. Is exceeded, it is determined that the insulation state of the transmission lines 500 and 501 has deteriorated, and an alarm is issued to the operator. As a result, the operator can quickly know the deterioration of the insulation state of the power transmission paths 500 and 501.

1,2,3 Insulation monitoring system 10,20 CPU
11, 21 Current detection unit 12 Suppressed current output unit 13 Insulation state determination unit 22 Leakage current amplification unit 23 Suppressed current output unit 32 Head amplifier 33, 34 Filter 35 Amplifier 36 SCF (switched capacitor filter)
37 Reference signal adjustment unit 38 Ir suppression signal generator 39 Phase shift circuit 40 Ic suppression signal generator 41 Power amplifier 51 Display 52 Alarm device 60 Information presentation unit 121 Synchronization signal detection jig 122 Sine wave generator 123 Power amplifier 124 Phase difference Total 131 Residual current measuring device 132 Measured value display terminal 200 Load 300 Load electric wire 400 Suppression piezoelectric wire 500,501 Transmission line 600 Ground wire 700 Suppression wire C0 Floating capacitance I0 Leakage current I0c Capacitance component I0r Resistance component Id Residual current Il Current Is Suppressed current Iz Zero phase current TR1 Transformer R0 Ground insulation resistance R phase S phase T phase Va Voltage signal W High voltage circuit Z0 Impedance

Claims (3)

An insulation monitoring system for monitoring an insulation state of an electric circuit,
Current detection for detecting a residual current from the load current flowing through the load wire that has passed through the load wire for flowing a load current from the AC power source and a piezoelectric wire for passing the suppression current through the load core. Means,
A suppression current that generates a suppression current having the same phase and level as the detected residual current, and causes the suppression current to flow in the direction opposite to the residual current through the suppression piezoelectric line so that the suppression current cancels the residual current. Output means;
An insulation monitoring system comprising: The AC power supply is a three-phase AC power supply, the load is a three-phase load, and the current detection means is a zero-phase current transformer.
The insulation monitoring system according to claim 1. The current detection means further detects a zero-phase current from a load current flowing through the load wire,
Further comprising an insulation state determination means for determining whether or not the insulation state of the electric circuit is good based on the detected value of the zero-phase current.
The insulation monitoring system according to claim 1 or 2.

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