Monitoring device and monitoring method

Abstract

To accurately detect leakage currents occurring in each of the multiple phase circuits included in the power system. [Solution] A monitoring device comprising: a derivation unit that derives leakage current components of each order generated by the fundamental wave and harmonics constituting the voltage of the circuit, based on the insulation resistance value to ground of each of the multiple phase circuits included in the system and the capacitance value to ground of each of the multiple phase circuits; and an output unit that outputs an insulation monitoring result or a leakage current monitoring result for the system according to the magnitude of the leakage current including the leakage current components of each order derived for each of the multiple phases by the derivation unit.

Description

[Technical Field]

[0001] This disclosure relates to a monitoring device and monitoring method capable of counteracting the counteracting phenomenon. [Background technology]

[0002] As an insulation monitoring method for low-voltage power systems, the leakage current (leakage current I) caused by capacitance to ground is calculated from the detected zero-sequence current I0. 0c ) is separated, and leakage current (ground fault current I) caused by the insulation resistance to ground is separated. 0r I detects 0r The method is known. Conventional I 0r The method involves extracting the current component that is in phase with the system's voltage to ground from the detected zero-sequence current I0, thereby determining the ground fault current I caused by the insulation resistance to ground. 0r It detects. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 5494929 [Overview of the project] [Problems that the invention aims to solve]

[0004] When insulation degradation occurs in each of the multiple phase circuits included in a power system, the leakage currents generated in each of the multiple phase circuits may cancel each other out with the ground or PE wire (protective earthing wire), resulting in a phenomenon called cancellation where only the canceled-out current flows through the earthing wire. The leakage currents generated in each of the multiple phase circuits cancel each other out due to the phase relationship, leading to erroneous detection. Therefore, conventional methods that extract the current component in phase with the power system's voltage to ground from the detected zero-sequence current are ineffective. 0r In this method, a leakage current smaller than the actual leakage current occurring in each of the multiple phase circuits may be detected, or leakage current may not be detected at all.

[0005] For example, FIG. 1 is a vector diagram illustrating a case where insulation degradation occurs in each of two lines (two phases) of a single-phase three-wire system. In a single-phase three-wire system where the phases of the ground voltages V1 and V2 are different by 180°, the ground fault current I 0r1 that occurs in the same phase as the ground voltage V1 in the circuit of the ground voltage V1 0r2 is different in phase by 180° from the ground fault current I 0r that occurs in the same phase as the ground voltage V2 in the circuit of the ground voltage V2. Therefore, in the conventional I 0r1 method, a small ground fault current I 0r2 corresponding to the difference between the actually occurring ground fault currents I 0r in each of the two circuits is detected. This is the same for the leakage current I 0c as well.

[0006] The present disclosure provides a monitoring device and a monitoring method capable of correctly detecting leakage currents generated in each of a plurality of phases of circuits included in a system.

Means for Solving the Problem

[0007] In one aspect of the present disclosure, <o000183>a derivation unit that derives leakage current components of each order generated by each of the fundamental wave and harmonic waves constituting the voltage of the circuit for each of the plurality of phases of the circuits included in the system, based on the ground insulation resistance value of each of the plurality of phases of the circuits and the ground capacitance value of each of the plurality of phases of the circuits; an output unit that outputs an insulation monitoring result or a leakage monitoring result of the system according to the magnitude of the leakage current including the leakage current components of each order derived for each of the plurality of phases by the derivation unit, is provided.

[0008] In another aspect of the present disclosure, leakage current components of each order generated by each of the fundamental wave and harmonic waves constituting the voltage of the circuit are derived for each of the plurality of phases of the circuits included in the system, based on the ground insulation resistance value of each of the plurality of phases of the circuits and the ground capacitance value of each of the plurality of phases of the circuits, A monitoring method is provided that outputs an insulation monitoring result or a leakage current monitoring result for the system according to the magnitude of the leakage current, including the leakage current component of each order derived for each phase of the multiple phases. [Effects of the Invention]

[0009] According to this disclosure, leakage currents occurring in each of the multiple phase circuits included in the power system can be accurately detected. [Brief explanation of the drawing]

[0010] [Figure 1] This is a vector diagram illustrating a case where insulation degradation occurs in each of the two wires (two phases) of a single-phase three-wire system. [Figure 2] This figure shows a first configuration example of an insulation monitoring device according to the first embodiment. [Figure 3] This figure illustrates the filter characteristics of the first analog filter. [Figure 4] This figure illustrates the filter characteristics of the second analog filter. [Figure 5] This is a vector diagram illustrating a case where insulation degradation occurs in each of the two wires (two phases) of a single-phase three-wire system. [Figure 6] This is a system configuration diagram illustrating a scenario where insulation degradation occurs in each of the two wires (two phases) of a single-phase three-wire system. [Figure 7] This figure shows an example of a leakage current waveform in which a third harmonic with a phase difference of 180° from the fundamental wave (phase 0°) is superimposed. [Figure 8] This figure shows an example of a leakage current waveform in which a third harmonic with a phase difference of 0° is superimposed on the fundamental wave (phase 0°). [Figure 9] This figure shows an example of selecting harmonic voltage components to derive the magnitude of leakage current. [Figure 10] This is a vector diagram illustrating a case where insulation degradation occurs in each of the three wires (three phases) of a three-phase four-wire system. [Figure 11]This is a system configuration diagram illustrating a scenario where insulation degradation occurs in each of the three (three phases) of the electrical circuits included in a three-phase four-wire system. [Figure 12] This figure shows an example configuration of a ground fault circuit breaker according to the second embodiment. [Figure 13] This figure shows an example configuration of a ground fault relay according to the third embodiment. [Modes for carrying out the invention]

[0011] Several embodiments will be described below with reference to the drawings.

[0012] <Insulation monitoring device according to the first embodiment> Figure 2 shows an example configuration of an insulation monitoring device according to the first embodiment. The insulation monitoring device 101 shown in Figure 2 monitors the insulation status or leakage current status of two circuits (circuit 1 of phase P1 and circuit 2 of phase P2) included in a single-phase three-wire system 10, and outputs the insulation monitoring result or leakage current monitoring result to the outside of the insulation monitoring device 101. For example, the insulation monitoring device 101 detects the ground-to-ground insulation resistance of the system 10, or detects the ground fault current flowing to the ground due to the deterioration of the insulation resistance of the system 10, and outputs the detection result to the outside of the insulation monitoring device 101 as the insulation monitoring result or leakage current monitoring result.

[0013] The insulation monitoring device 101 may also be a device called a ground fault monitoring device or a ground fault alarm device. An insulation monitoring device, ground fault monitoring device, or ground fault alarm device is an example of a monitoring device that monitors the insulation or ground fault of a multi-phase circuit included in a system and outputs the monitoring results.

[0014] System 10 includes circuit 1 for the P1 phase, circuit 2 for the P2 phase, and neutral wire 5 for the N phase. Circuits 1 and 2 each include electric wires. Grounding wire 4 electrically connects neutral wire 5 to the earth.

[0015] The insulation monitoring device 101 includes an output section 20 and an output section 30.

[0016] The derivation unit 20 includes, for example, an electronic circuit such as a CPU (Central Processing Unit), GPU (Graphics Processing Unit), FPGA (Field Programmable Gate Array), or ASIC (Application Specific Integrated Circuit). Part or all of the derivation unit 20 may be a microcomputer having memory and a processor. Part or all of the derivation unit 20 performs the various control operations described in this specification by executing a program such as instruction code stored in memory, or by being circuit-designed for a specific application.

[0017] The derivation unit 20 includes a circuit that derives the magnitude of the leakage current generated in the system 10 for each phase (each circuit) based on the respective ground insulation resistance values ​​R1 and R2 of circuits 1 and 2 and the respective ground capacitance values ​​C1 and C2 of circuits 1 and 2. In this example, the derivation unit 20 derives the leakage current I generated in circuit 1. 01 The size and leakage current I generated in circuit 2 02 Derive the size of [the variable].

[0018] The output unit 20 includes voltage acquisition circuits 41, 42, current acquisition circuit 43, AD converters 51, 52, 53, memory 60, and processor 70.

[0019] The voltage acquisition circuit 41 acquires the ground voltage V1 with reference to the N-phase neutral wire 5 and outputs waveform data of the acquired ground voltage V1. The ground voltage V1 includes fundamental wave components and harmonic components. The voltage acquisition circuit 41 may include an analog filter AF that extracts the fundamental wave components and harmonic components. In order to accurately detect harmonic components smaller than the fundamental wave component, the voltage acquisition circuit 41 may also include a high-pass filter that extracts the harmonic components of the ground voltage V1 and an amplification circuit that amplifies the harmonic components of the ground voltage V1.

[0020] The voltage acquisition circuit 41 includes, for example, a first analog filter AF1 that extracts the fundamental wave component of the voltage V1 to ground, and a second analog filter AF2 that extracts the harmonic components of the voltage V1 to ground. The first analog filter AF1 is, for example, a low-pass filter 41a that extracts the fundamental wave component of the voltage V1 to ground. The second analog filter AF2 is, for example, a band-pass filter 41b (a filter that combines a low-pass filter and a high-pass filter) that extracts the harmonic components of the voltage V1 to ground.

[0021] The voltage acquisition circuit 42 acquires the ground voltage V2 with reference to the N-phase neutral wire 5 and outputs waveform data of the acquired ground voltage V2. The ground voltage V2 includes fundamental wave components and harmonic components. The voltage acquisition circuit 42 may include an analog filter AF that extracts the fundamental wave components and harmonic components. In order to accurately detect harmonic components smaller than the fundamental wave component, the voltage acquisition circuit 42 may also include a high-pass filter that extracts the harmonic components of the ground voltage V2 and an amplification circuit that amplifies the harmonic components of the ground voltage V2.

[0022] The voltage acquisition circuit 42 includes, for example, a first analog filter AF1 that extracts the fundamental wave component of the voltage V2 to ground, and a second analog filter AF2 that extracts the harmonic components of the voltage V2 to ground. The first analog filter AF1 is, for example, a low-pass filter 42a that extracts the fundamental wave component of the voltage V2 to ground. The second analog filter AF2 is, for example, a band-pass filter 42b (a filter that combines a low-pass filter and a high-pass filter) that extracts the harmonic components of the voltage V2 to ground.

[0023] When a waveform composed of a fundamental wave and harmonics is converted using analog-to-digital (AD) conversion, and the harmonic components are extracted from the resulting data, the resolution of the AD-converted data is low, making it difficult to accurately detect the harmonics. By using different analog filters for fundamental wave extraction and harmonic extraction, harmonics can be accurately detected before AD conversion.

[0024] Figure 3 illustrates the filter characteristics of the first analog filter. The first analog filter AF1 is, for example, a low-pass filter having a cutoff frequency f1.

[0025] Figure 4 illustrates the filter characteristics of the second analog filter. The second analog filter AF2 is a bandpass filter formed by combining, for example, a low-pass filter with a cutoff frequency f3 and a high-pass filter with a cutoff frequency f2. The cutoff frequency f3 is set to a higher frequency than the cutoff frequency f2. The cutoff frequency f2 is higher than the cutoff frequency f1 (Figure 3) and is set, for example, in the frequency band of the second harmonic.

[0026] In Figure 2, the current acquisition circuit 43 acquires the zero-sequence current I0 detected by the sensor 6 and outputs waveform data of the acquired zero-sequence current I0. The zero-sequence current I0 includes a fundamental wave component and harmonic components. The current acquisition circuit 43 may include an analog filter AF that extracts the fundamental wave component and harmonic components. In order to accurately detect harmonic components smaller than the fundamental wave component, the current acquisition circuit 43 may also include a high-pass filter that extracts the harmonic components of the zero-sequence current I0 and an amplifier circuit that amplifies the harmonic components of the zero-sequence current I0.

[0027] Sensor 6 is, for example, a zero-sequence current transformer (ZCT) that monitors circuits 1 and 2 and the neutral wire 5. Instead of a ZCT, sensor 6 may also be a current transformer (CT) that detects the zero-sequence current I0 flowing through the ground wire 4.

[0028] The AD converter 51 samples the analog data of the voltage to ground V1 acquired by the voltage acquisition circuit 41 at a constant period and converts it into digital data. The AD converter 51 includes a first AD converter 51a that converts the analog data of the fundamental wave component of the voltage to ground V1 into digital data, and a second AD converter 51b that converts the analog data of the harmonic components of the voltage to ground V1 into digital data. The digital data output from the AD converter 51 is stored in the memory 60.

[0029] The AD converter 52 samples the analog data of the voltage to ground V2 acquired by the voltage acquisition circuit 42 at a fixed period and converts it into digital data. The AD converter 52 includes a first AD converter 52a that converts the analog data of the fundamental wave component of the voltage to ground V2 into digital data, and a second AD converter 52b that converts the analog data of the harmonic components of the voltage to ground V2 into digital data. The digital data output from the AD converter 52 is stored in the memory 60.

[0030] The AD converter 53 samples the analog data of the zero-sequence current I0 acquired by the current acquisition circuit 43 at regular intervals and converts it into digital data. The digital data output from the AD converter 53 is stored in the memory 60.

[0031] Memory 60 stores multiple digital data (multiple voltage data and multiple current data) for a certain period of time, supplied from each of the AD converters 51, 52, and 53, for the processor 70 to perform a Fourier transform. Memory 60 is, for example, RAM.

[0032] The processor 70 uses multiple digital data (multiple voltage data and multiple current data) stored in the memory 60 to derive the magnitude of the leakage current occurring in the system 10 for each phase (each circuit). In this example, the processor 70 derives the magnitude of the leakage current I occurring in circuit 1. 01 The size and leakage current I generated in circuit 2 02 Derive the size of [the variable].

[0033] The processor 70 performs a Fourier transform using the voltage data (digital data of the voltage to ground V1) within a predetermined time window in the memory 60, and determines the amplitude A of the fundamental and harmonic components of the voltage to ground V1. n and absolute phase α np We derive the following (n=1,3,5,7,9,···). Absolute phase α np The angular frequency ω of the voltage V1 to ground is nf This corresponds to the product of n=1 and time t. Here, n=1 represents the fundamental wave component, and n=3, 5, 7, 9, ... represents the 3rd, 5th, 7th, 9th, ... harmonics (the same applies below).

[0034] The processor 70 performs a Fourier transform using the voltage data (digital data of the voltage to ground V2) within a predetermined time window in the memory 60, and determines the amplitude B of the fundamental and harmonic components of the voltage to ground V2. n and absolute phase β np Derive the following (n=1,3,5,7,9,···). Absolute phase β np The angular frequency ω of the voltage V2 to ground is nf The product of time t and the phase angle θ n It is equivalent to the sum of the two.

[0035] The processor 70 performs a Fourier transform using current data (digital data of zero-sequence current I0) within a predetermined time window in the memory 60, and determines the amplitude C of the fundamental and harmonic components of the zero-sequence current I0. n and absolute phase γ np Derive the following (n=1,3,5,7,9,···). Absolute phase γ np The angular frequency ω of the zero-sequence current I0 is nf The product of time t and the phase angle φ n It is equivalent to the sum of the two.

[0036] The processor 70, for example, uses either the Discrete Fourier Transform (DFT) or the Fast Fourier Transform (FFT) as the Fourier transform.

[0037] Processor 70 is absolute phase α np and absolute phase β np Using "θ" n =β np -α np The calculation of " results in the relative phase (i.e., phase angle θ) of the voltage V2 relative to the voltage V1 relative to the ground. n ) is derived. Processor 70 has absolute phase α np and absolute phase γ np Using "φ n =γ np -α np The calculation of " determines the relative phase (i.e., phase angle φ) of the zero-sequence current I0 with respect to the voltage V1 relative to ground. n Derive ).

[0038] The processor 70 uses the known components derived as described above (ground voltage V1, ground voltage V2, zero-sequence current I0, phase angle θ, and phase angle φ) to perform the derivation method described later and derives the unknown components, which are system constants (ground insulation resistance values ​​R1, R2 and ground capacitance values ​​C1, C2). The processor 70 uses the derived system constants (ground insulation resistance values ​​R1, R2 and ground capacitance values ​​C1, C2) to perform the derivation method described later and derives the leakage current I generated in circuit 1. 01 The size and leakage current I generated in circuit 2 02 Derive the size of [the variable].

[0039] The output unit 30 outputs the leakage current (in this example, leakage current I) that has been derived for each phase (for each circuit) by the derivation unit 20. 01 and leakage current I 02 The insulation monitoring result or leakage current monitoring result of system 10 is output according to the size of the system. The output unit 30 outputs the insulation monitoring result or leakage current monitoring result to the outside of the insulation monitoring device 101 by output format such as display, light emission, sound, contact output or communication. By outputting the insulation monitoring result or leakage current monitoring result to the outside by the output unit 30, the insulation monitoring device 101 can notify the user or external equipment of the insulation monitoring result or leakage current monitoring result. The external equipment is, for example, a higher-level device such as a server. The output unit 30 may include, for example, one or more of the following: display, lamp, buzzer, speaker, relay, and communication circuit.

[0040] The output unit 30 outputs, for example, the insulation monitoring results or leakage current monitoring results from the derivation unit 20 for each of the multiple phases. This allows the insulation monitoring device 101 to notify the user or external equipment of the insulation monitoring results or leakage current monitoring results for each of the multiple phases.

[0041] The output unit 30 outputs, for example, the leakage current (in this example, leakage current I) derived for each of the multiple phases by the derivation unit 20. 01 and leakage current I 02 If any one of the magnitudes of the two values ​​exceeds the first threshold, an alarm representing the leakage current monitoring result is output. As a result, the insulation monitoring device 101 detects a relatively large leakage current I in the circuit 1. 01Is this occurring, or is there a relatively large leakage current I in circuit 2? 02 It can notify the user or external devices if an issue is occurring.

[0042] The output unit 30 may output the ground-to-ground insulation resistance values ​​(in this example, ground-to-ground insulation resistance values ​​R1 and R2) for each of the multiple phases of the circuit detected by the derivation unit 20. This allows the insulation monitoring device 101 to notify the user or external equipment of the detected ground-to-ground insulation resistance values ​​for each of the multiple phases.

[0043] The output unit 30 outputs an alarm indicating the insulation monitoring result if, for example, one of the ground-to-ground insulation resistance values ​​(in this example, ground-to-ground insulation resistance values ​​R1, R2) of the multiple phase circuits detected by the derivation unit 20 falls below the second threshold. This allows the insulation monitoring device 101 to notify the user or external equipment whether relatively large insulation degradation has occurred in circuit 1 or in circuit 2.

[0044] <Method for deriving system constants in the case of a single-phase three-wire system> Next, we will explain how to derive the system constants in the case of a single-phase three-wire system.

[0045] Figure 5 is a vector diagram illustrating the case where insulation degradation occurs in each of the two wires (two phases) of a single-phase three-wire system. When deriving the system constants, as shown in Figure 5, the phase difference between the voltage to ground V2 and the voltage to ground V1 does not have to be 180°.

[0046] Figure 6 is a system configuration diagram illustrating the case where insulation degradation occurs in each of the two wires (two phases) of the single-phase three-wire system 10a. The insulation resistance value to ground R1 is the insulation resistance value between circuit 1 of the ungrounded phase P1 and the ground. The insulation resistance value to ground R2 is the insulation resistance value between circuit 2 of the ungrounded phase P2 and the ground. The capacitance value to ground C1 is the capacitance value between circuit 1 of the ungrounded phase P1 and the ground. The capacitance value to ground C2 is the capacitance value between circuit 2 of the ungrounded phase P2 and the ground.

[0047] The processor 70 uses the known components (ground insulation resistance values ​​R1, R2 and ground capacitance values ​​C1, C2) derived as described above to derive the unknown components, which are system constants (ground insulation resistance values ​​R1, R2 and ground capacitance values ​​C1, C2).

[0048] The leakage current (zero-sequence current I0) flowing through grounding wire 4 is expressed by the following equation 1. Note that the "·" above each component represents a vector (the same applies hereafter).

[0049]

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[0050] Ground fault current I 0r1 This is the leakage current caused by the ground insulation resistance value R1. Ground fault current I 0r2 This is the leakage current caused by the ground insulation resistance value R2. Leakage current I 0c1 This is the leakage current caused by the capacitance value to ground C1. Leakage current I 0c2 This is the leakage current caused by the capacitance value to ground C2. Ground fault current I 0r1 Ground fault current I 0r2 , leakage current I 0c1 and leakage current I 0c2 This can be expressed by the following equations 1A, 1B, 1C, and 1D.

[0051]

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[0052] Substituting equations 1A, 1B, 1C, and 1D into equation 1 yields equation 2.

[0053]

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[0054] The voltages to ground V1, V2, and zero-sequence current I0 are expressed by equations 2A, 2B, and 2C.

[0055]

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[0056] If we express the zero-sequence current I0 shown in Equation 2 for each of the 3rd, 5th, 7th, and 9th harmonics, for example, we obtain Equations 3, 4, 5, and 6.

[0057]

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[0058] I 0 nf V represents the nth-order frequency component of the zero-sequence current I0. 1 nf V represents the nth-order frequency component of the voltage V1 to ground. 2 nf This represents the nth-order frequency component of the voltage V2 to ground.

[0059] Equations 3, 4, 5, and 6 are a system of four linear equations with four unknown variables (R1, R2, C1, C2). When expressed in terms of determinants, we obtain equation 7.

[0060]

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[0061]

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[0062]

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[0063]

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[0064]

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[0065]

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[0066] According to equations 8A, 8B, 8C, and 8D, the four unknown variables (R1, R2, C1, C2) can be determined from the known components. In other words, the processor 70 can derive the unknown components, which are system constants (insulation resistance values ​​R1, R2 and capacitance values ​​C1, C2), by substituting the known components (voltage to ground V1, voltage to ground V2, zero-sequence current I0, phase angle θ, and phase angle φ) into equations 8A, 8B, 8C, and 8D.

[0067] As described above, the derivation unit 20 of this disclosure obtains multiple harmonic voltage components (Equation 7A) from the voltage waveforms of the multi-phase circuit and multiple harmonic current components (Equations 3, 4, 5, 6) from the zero-sequence current waveform of the system 10a. Based on these obtained multiple harmonic voltage components (Equation 7A) and multiple harmonic current components (Equations 3, 4, 5, 6), the derivation unit 20 derives the insulation resistance values ​​R1, R2 and the capacitance values ​​C1, C2 to ground. Although an example using Cramer's rule is shown for solving the simultaneous equations, other methods may be used for this solution.

[0068] <Leakage current I in the case of a single-phase three-wire system 01 ,I 02 A first method for deriving the respective sizes of > Next, the processor 70 uses the system constants (ground insulation resistance values ​​R1, R2 and ground capacitance values ​​C1, C2) derived by the method described above to determine the leakage current I generated in circuit 1. 01 The size and leakage current I generated in circuit 2 02 Derive the size of [the variable].

[0069] Leakage current I generated in circuit 1 01 And leakage current I generated in circuit 2 02 When expressed as vectors, it can be represented by the following equations 20A and 20B.

[0070]

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[0071] Based on the known components derived as described above, the processor 70 uses the following equations 21A, 22A, 23A, 24A, and 25A to determine the multiple leakage current components I that occur in the circuit 1 of system 10a. 01 nf Derive the following.

[0072]

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[0073] Leakage current component I 01 nf This is the leakage current I generated in circuit 1. 01 This represents the nth-order frequency component of the sequence. 01 1f This is the primary leakage current component (leakage current I) generated by the fundamental wave that constitutes the voltage to ground V1. 01 It represents the fundamental wave component. 01 3f This is the third-order leakage current component (leakage current I) generated by the third-order harmonic that constitutes the voltage to ground V1. 01 This represents the third harmonic component of the current. The same applies to leakage current components of other orders.

[0074] The processor 70 has multiple leakage current components I derived using equations 21A, 22A, 23A, 24A, and 25A. 01 nf The root of the sum of the squares of the following equation 26 can be used to calculate the leakage current I generated in circuit 1. 01 The effective value representing the magnitude |I 01 Derive |.

[0075]

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[0076] Similarly, based on the known components derived as described above, the processor 70 uses the following equations 21B, 22B, 23B, 24B, and 25B to determine the multiple leakage current components I occurring in the circuit 2 of system 10a. 02 nf Derive the following.

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[0078] Leakage current component I 02 nf is the leakage current I generated in circuit 2 02 and represents the nth harmonic component of I. I 02 1f is the fundamental leakage current component (fundamental wave component of leakage current I 02 ) generated by the fundamental wave constituting the ground voltage V2. I 02 3f is the third harmonic leakage current component (third harmonic component of leakage current I 02 ) generated by the third harmonic constituting the ground voltage V2. The same applies to leakage current components of other orders.

[0079] The processor 70 calculates the root mean square of the sum of the squares of a plurality of leakage current components I 02 nf derived using equations 21B, 22B, 23B, 24B, 25B, and uses the following equation 27 to derive the effective value |I 02 | representing the magnitude of the leakage current I generated in circuit 2. 02 |.

[0080]

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[0081] Leakage current I 01 and leakage current I 02 are vector - synthesized as in the prior art, and the magnitude of the synthesized leakage current is detected to be smaller than the actual leakage current due to the cancellation phenomenon. In contrast, in the insulation monitoring device 101 according to the first embodiment of the present disclosure, the processor 70 represents the magnitude of the leakage current generated in the system 10a not by a single effective value, but by a plurality of effective values (in this example, two effective values |I 01 |, |I 02 |) derived for each phase. As a result, the insulation monitoring device 101 can correctly detect the magnitude of each of the leakage currents I 01 , I 02 generated in each of the plurality of - phase circuits included in the system 10a.

[0082] <Leakage current I in the case of a single-phase three-wire system 01 , I 02 >Second method for deriving the magnitude of each of The leakage current I derived using Equations 26 and 27 01 , I 02 The magnitude of each of does not take into account the phase of the fundamental wave component and harmonic components included in the leakage current. In an actual power distribution system, each harmonic does not necessarily have the same phase as the fundamental wave. Due to the difference in the phase of each superimposed harmonic, the waveform of the leakage current is not uniform. Therefore, the effective value derived using Equations 26 and 27 may not correctly represent the magnitude of the leakage current in each phase.

[0083] FIG. 7 is a diagram showing an example of a leakage current waveform in which a third harmonic having a phase difference of 180° with respect to the fundamental wave (phase 0°) is superimposed. FIG. 8 is a diagram showing an example of a leakage current waveform in which a third harmonic having a phase difference of 0° with respect to the fundamental wave (phase 0°) is superimposed. As shown in FIGS. 7 and 8, when the phase of the third harmonic superimposed on the fundamental wave is different, even if the amplitude of the third harmonic is the same, the area of the leakage current waveform after superposition may be different.

[0084] Therefore, in the second method for deriving the magnitude of the leakage current I 01 , I 02 the processor 70 obtains the area of the leakage current waveform considering the phase of each superimposed harmonic instead of obtaining the effective value, thereby deriving the magnitude of each of the leakage currents I 01 , I 02 of each. z

[0085] The leakage current generated in Circuit 1 of System 10a can be expressed using trigonometric functions such as the following Equations 31A, 32A, 33A, 34A, and 35A. Based on the known components derived as described above, the processor 70 uses the following Equations 31A, 32A, 33A, 34A, and 35A to derive a plurality of leakage current components I 01 nf in Circuit 1 of System 10a.

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[0087] The processor 70 has multiple leakage current components I derived using equations 31A, 32A, 33A, 34A, and 35A. 01 nf By combining (summing) these using the following equation 36A, the leakage current I generated in circuit 1 is calculated. 01 Derive the waveform.

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[0089] The processor 70 calculates the leakage current I generated in circuit 1 using the following equation 37, based on the combined waveform of multiple leakage current components derived using equation 36A. 01 Area S represents the size of the area. I01 Derive the following.

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[0091] For the value of 'a' used in Equation 37, for example, we can set a = 2π, which represents a period that is an integer multiple of one cycle of the fundamental wave. By setting a = 2π, each superimposed harmonic will contain a waveform with the same number of cycles as its order multiple, and the duration of the extracted waveform will be an integer multiple of one cycle of the fundamental wave. Therefore, the waveform is not cut off midway, and the deterioration of calculation accuracy is suppressed.

[0092] Similarly, the leakage current occurring in circuit 2 of system 10a can be expressed using trigonometric functions such as those shown in the following equations 31B, 32B, 33B, 34B, and 35B. Based on the known components derived as described above, the processor 70 uses the following equations 31B, 32B, 33B, 34B, and 35B to express the multiple leakage current components I occurring in circuit 2 of system 10a. 02 nf Derive the following.

[0093]

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[0094] The processor 70 has multiple leakage current components I derived using equations 31B, 32B, 33B, 34B, and 35B. 02 nf By combining (summing) these using the following equation 36B, the leakage current I generated in circuit 2 is obtained. 02 Derive the waveform.

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[0096] The processor 70 calculates the leakage current I generated in circuit 2 using the following equation 38, based on the combined waveform of multiple leakage current components derived using equation 36B. 02 Area S represents the size of the area. I02 Derive the following.

[0097]

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[0098] For the value of 'a' used in equation 38, for example, a = 2π, which represents a period that is an integer multiple of one cycle of the fundamental wave. By setting a = 2π, each superimposed harmonic will contain a waveform with the same number of cycles as its order multiple, and the duration of the extracted waveform will be an integer multiple of one cycle of the fundamental wave. Therefore, the waveform is not cut off midway, and the deterioration of calculation accuracy is suppressed.

[0099] In the insulation monitoring device 101 according to the first embodiment of this disclosure, the processor 70 does not represent the magnitude of the leakage current occurring in the system 10a with a single area, but rather with multiple areas derived for each phase (in this example, two areas S I01 ,S I02 This is expressed as follows: The insulation monitoring device 101 then detects the leakage current I generated in each of the multiple phase circuits included in the system 10a. 01 ,I 02 It can correctly detect the size of each element.

[0100] <Regarding the order of harmonics used in Fourier analysis> As described above, when deriving insulation resistance and capacitance values, or leakage current, the equations are based on harmonics contained in the voltage component. Therefore, the technology disclosed hereby requires selecting the optimal order of the voltage harmonics. In the above explanation, fixed 3rd, 5th, 7th, and 9th harmonics are used, but these harmonics are not necessarily present in the system. In actual operation, the magnitude and phase of each harmonic fluctuate, making it difficult to determine in advance which harmonic component is large.

[0101] The processor 70 of this disclosure performs harmonic analysis each time the magnitude of the leakage current is derived, and selects harmonics in order from the largest order component. This allows the harmonics with the largest order component to be used in deriving the magnitude of the leakage current, thereby improving the accuracy of correctly detecting the magnitude of the leakage current.

[0102] Figure 9 shows an example of selecting harmonic voltage components used to derive the magnitude of leakage current. In the example in Figure 9, the processor 70 uses, for example, the 3rd, 7th, 9th, and 11th harmonics. In this way, the derivation unit 20 selects the harmonics used to derive the magnitude of leakage current such that the orders of the multiple harmonic voltage components and multiple harmonic current components are different from the order of the smallest frequency component among the multiple frequency components obtained from the voltage waveform. The derivation unit 20 selects the harmonics used to derive the magnitude of leakage current such that the orders of the multiple leakage current components are different from the order of the smallest frequency component among the multiple frequency components obtained from the voltage waveform.

[0103] <Method for deriving system constants in the case of a three-phase four-wire system> Next, we will explain how to derive the system constants in the case of a three-phase four-wire system. In the case of a three-phase four-wire system, if two or three wires deteriorate in insulation simultaneously, the same cancellation phenomenon as in a single-phase three-wire system can occur.

[0104] Figure 10 is a vector diagram illustrating the case where insulation degradation occurs in each of the three (three phases) circuits included in a three-phase four-wire system. When deriving the system constants, as shown in Figure 10, the phases of the voltages to ground V1, V2, and V3 do not need to be 180° apart from each other.

[0105] Figure 11 is a system configuration diagram illustrating the case where insulation degradation occurs in each of the three wires (three phases) of the three-phase four-wire system 10b. The insulation resistance value R1 to ground is the insulation resistance value between circuit 1 of the ungrounded phase P1 and the ground. The insulation resistance value R2 to ground is the insulation resistance value between circuit 2 of the ungrounded phase P2 and the ground. The insulation resistance value R3 to ground is the insulation resistance value between circuit 3 of the ungrounded phase P3 and the ground. The capacitance value C1 to ground is the capacitance value between circuit 1 of the ungrounded phase P1 and the ground. The capacitance value C2 to ground is the capacitance value between circuit 2 of the ungrounded phase P2 and the ground. The capacitance value C4 to ground is the capacitance value between circuit 3 of the ungrounded phase P3 and the ground.

[0106] The processor 70 uses the known components derived as described above (ground voltage V1, ground voltage V2, zero-sequence current I0, phase angle θ, and phase angle φ) to derive the unknown components, which are system constants (ground insulation resistance values ​​R1, R2, R3 and ground capacitance values ​​C1, C2, C3).

[0107] The leakage current (zero-sequence current I0) flowing through grounding wire 4 is expressed by the following equation 1. Note that the "·" above each component represents a vector (the same applies hereafter).

[0108]

number

[0109] Ground fault current I 0r1 This is the leakage current caused by the ground insulation resistance value R1. Ground fault current I 0r2 This is the leakage current caused by the insulation resistance to ground R2. Ground fault current I 0r3 This is the leakage current caused by the ground insulation resistance value R3. Leakage current I 0c1This is the leakage current caused by the capacitance value to ground C1. Leakage current I 0c2 This is the leakage current caused by the capacitance value to ground C2. Leakage current I 0c3 This is the leakage current caused by the capacitance value to ground C3. Ground fault current I 0r1 Ground fault current I 0r2 Ground fault current I 0r3 , leakage current I 0c1 , leakage current I 0c2 and leakage current I 0c3 This can be expressed by the following equations 41A, 41B, 41C, 41D, 41E, and 41F.

[0110]

number

[0111] The ground voltages V1, V2, V3, and zero-sequence current I0 are expressed by equations 42A, 42B, 42C, and 42D.

[0112]

number

[0113] If we express the zero-sequence current I0 shown in Equation 41 for each of the 3rd, 5th, 7th, 9th, 11th, and 13th harmonics, we obtain Equations 43, 44, 45, 46, 47, and 48.

[0114]

number

[0115] I 0 nf V represents the nth-order frequency component of the zero-sequence current I0. 1 nf V represents the nth-order frequency component of the voltage V1 to ground. 2 nf V represents the nth-order frequency component of the voltage V2 to ground. 3 nf This represents the nth-order frequency component of the voltage V3 to ground.

[0116] Equations 43, 44, 45, 46, 47, and 48 are a system of six linear equations with six unknown variables (R1, R2, R3, C1, C2, C3). When expressed in terms of determinants, we obtain equation 57.

[0117]

number

[0118]

number

[0119]

number

[0120]

number

[0121]

number

[0122]

number

[0123]

number

[0124]

number

[0125] According to equations 58A, 58B, 58C, 58D, 58E, and 58F, the six unknown variables (R1, R2, R3, C1, C2, C3) can be determined from the known components. In other words, the processor 70 can derive the unknown components, which are system constants (insulation resistance values ​​R1, R2, R3 and capacitance values ​​C1, C2, C3), by substituting the known components (ground voltage V1, ground voltage V2, ground voltage V3, zero-sequence current I0, phase angle θ1, phase angle θ2, and phase angle φ) into these equations.

[0126] As described above, the derivation unit 20 of this disclosure obtains multiple harmonic voltage components (Equation 57A) from the voltage waveforms of the multi-phase circuit and multiple harmonic current components (Equations 43, 44, 45, 46, 47, 48) from the zero-sequence current waveform of the system 10b. Based on these obtained multiple harmonic voltage components (Equation 57A) and multiple harmonic current components (Equations 43, 44, 45, 46, 47, 48), the derivation unit 20 derives the insulation resistance values ​​to ground R1, R2, R3 and the capacitance values ​​to ground C1, C2, C3. Although an example using Cramer's rule is shown for solving the simultaneous equations, other methods may be used for this solution.

[0127] Leakage current I in the case of a three-phase four-wire system 01 ,I 02 ,I 03 How to derive the respective sizes of > The processor 70 calculates the leakage current I generated in circuit 1, similar to the derivation method described above for the single-phase three-wire system. 01 The size and leakage current I generated in circuit 2 02 The size and leakage current I generated in circuit 3 03 The magnitude is derived. The explanation of the derivation method for a three-phase four-wire system is omitted by referring to the explanation of the derivation method for a single-phase three-wire system described above.

[0128] <Summary of the insulation monitoring device according to the first embodiment> The insulation monitoring device 101 according to the first embodiment includes a derivation unit 20 and an output unit 30, as shown in Figure 2. The derivation unit 20 calculates the leakage current components of each order I generated by the fundamental wave and harmonics that constitute the voltage of the circuit 1, based on the insulation resistance value R1 of the circuit 1 to ground and the capacitance value C1 of the circuit 1 to ground. 01 nf The following is derived. Similarly, the derivation unit 20 derives the leakage current components I of each order generated by the fundamental wave and harmonics that constitute the voltage of circuit 2, based on the insulation resistance value R2 of circuit 2 to ground and the capacitance value C2 of circuit 2 to ground. 02 nf The following is derived. The output unit 30 outputs the leakage current components I of each order derived by the derivation unit 20. 01 nf Leakage current I 01 The size and the leakage current components I of each order derived by the derivation section 20 02 nf Leakage current I 02 Depending on the magnitude, the system 10 outputs either insulation monitoring results or leakage current monitoring results. The derivation unit 20 derives the magnitude of the leakage current for each phase in a form that includes the detected values ​​of the leakage current components of each order, as shown in the above equations 26, 27, 36A, 37, 36B, and 38, so that the magnitude of the leakage current for each phase can be correctly detected. This makes it possible to take measures against false detections caused by cancellation phenomena.

[0129] <Earth leakage circuit breaker according to the second embodiment> Figure 12 shows an example configuration of a ground fault circuit interrupter according to the second embodiment. In the second embodiment, the description of the configuration, operation, and effects similar to those of the first embodiment will be omitted by referring to the above description. The ground fault circuit interrupter 102 shown in Figure 12 monitors the insulation state or ground fault state of two electrical circuits 1 and 2 included in a single-phase three-wire system 10, and outputs the insulation monitoring result or ground fault monitoring result as an output signal. Note that the ground fault circuit interrupter 102 can also be applied to a three-phase four-wire system.

[0130] The earth leakage circuit breaker 102 may also be a device called a circuit breaker. An earth leakage circuit breaker or circuit breaker is an example of a monitoring device that monitors the insulation or earth leakage of multi-phase circuits included in a system and outputs the monitoring results.

[0131] The earth leakage circuit breaker 102 comprises an output section 20, an output section 30, and a tripping means 200. The tripping means 200 trips the circuits 1 and 2 connecting the power supply 7 and the load 8 based on the output signal (insulation monitoring result or earth leakage monitoring result) output from the output section 30.

[0132] For example, the interruption means 200 outputs leakage currents (in this example, leakage current I) derived from each of the multiple phases by the derivation section 20. 01 and leakage current I 02 If the magnitude of any one of the leakage currents (1, 2) exceeds the first threshold, the circuit breaker (1, 2) is interrupted. The interruption means (200) interrupts the circuit breaker (1, 2) when it receives an output signal from the output unit (30) indicating that the magnitude of any one of the leakage currents (1, 2) derived for each of the multiple phases by the derivation unit (20) exceeds the first threshold. As a result, the earth leakage circuit breaker (102) can interrupt the flow of leakage current.

[0133] For example, the interruption means 200 interrupts circuits 1 and 2 if any one of the ground-to-ground insulation resistance values ​​(in this example, ground-to-ground insulation resistance values ​​R1 and R2) of the multiple phase circuits detected by the derivation unit 20 falls below a second threshold. When the interruption means 200 receives an output signal from the output unit 30 indicating that any one of the ground-to-ground insulation resistance values ​​of the multiple phase circuits detected by the derivation unit 20 has fallen below a second threshold, it interrupts circuits 1 and 2. As a result, the earth leakage circuit breaker 102 can interrupt the flow of leakage current.

[0134] An example of the interruption means 200 is an actuator that operates to interrupt circuits 1 and 2 in accordance with the output signal output from the output unit 30. The interruption means 200 may include an electromagnetic contactor or the like that opens and closes circuits 1 and 2. The interruption means 200 may also be an electronic circuit or the like that includes a semiconductor switching element that interrupts circuits 1 and 2. The configuration of the interruption means 200 is not limited to these.

[0135] <Earth leakage relay according to the third embodiment> Figure 13 shows an example configuration of a ground fault relay according to the third embodiment. In the third embodiment, a description of the configuration, operation, and effects similar to those of the first or second embodiment will be omitted by referring to the above description. The ground fault relay 103 shown in Figure 13 monitors the insulation state or ground fault state of the two electrical circuits 1 and 2 included in the single-phase three-wire system 10, and outputs the insulation monitoring result or ground fault monitoring result as an output signal. Note that the ground fault relay 103 can also be applied to a three-phase four-wire system.

[0136] A ground fault relay is an example of a monitoring device that monitors the insulation or ground fault of multiple phase circuits included in a power system and outputs the monitoring results.

[0137] The leakage relay 103 comprises a lead-out section 20, an output section 30, and a relay 201. The lead-out section 20 and the output section 30 may be the same as in the embodiment described above. The relay 201 makes a contact output when an output signal (insulation monitoring result or leakage monitoring result) is output from the output section 30. For example, the relay 201 emits a contact output to the outside of the leakage relay 103 based on the output signal from the output section 30. The interruption means 200 provided outside the leakage relay 103 interrupts the circuits 1 and 2 when it receives the contact output.

[0138] As described above, embodiments have been explained, but these embodiments are presented as examples only, and the present invention is not limited by these embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, and modifications are possible without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

[0139] For example, the above embodiment uses odd-order harmonics as harmonics, but at least one or more even-order harmonics may also be used. [Explanation of Symbols]

[0140] 1,2,3 electric circuit 4 Ground wire 5 Neutral line 6 sensors 7 Power supply 8 loads 10,10a,10b system 20 Derivation part 30 Output section 41,42 Voltage acquisition circuit 41a, 42a Low-pass filters 41b, 42b bandpass filter 51, 52, 53 AD converters 51a, 52a First AD Converter 51b,52b 2nd AD converter 60 memory 70 processors 101 Insulation monitoring device 102 Earth leakage circuit breaker 103 Leakage Relay 200 Blocking means 201 Relay AF Analog Filter AF1 First Analog Filter AF2 Second Analog Filter

Claims

1. A derivation unit that derives, for each of the multiple phases, the leakage current components of each order generated by the fundamental wave and harmonics that constitute the voltage of the circuit, based on the ground-to-ground insulation resistance value of each of the multiple phases included in the system and the ground-to-ground capacitance value of each of the multiple phases, The system includes an output unit that outputs an insulation monitoring result or a leakage current monitoring result for the system according to the magnitude of the leakage current, including the leakage current component of each order, which is derived for each phase of the multiple phases by the derivation unit, The magnitude of the leakage current is the area of ​​the waveform of the leakage current, according to the monitoring device.

2. A derivation unit that derives, for each of the multiple phases, the leakage current components of each order generated by the fundamental wave and harmonics that constitute the voltage of the circuit, based on the ground-to-ground insulation resistance value of each of the multiple phases included in the system and the ground-to-ground capacitance value of each of the multiple phases, The system includes an output unit that outputs an insulation monitoring result or a leakage current monitoring result for the system according to the magnitude of the leakage current, including the leakage current component of each order, which is derived for each phase of the multiple phases by the derivation unit, The derivation unit is a monitoring device that derives the ground-to-ground insulation resistance value and ground-to-ground capacitance value of each of the multiple phase circuits based on multiple harmonic voltage components obtained from the voltage waveforms of the multiple phase circuits and multiple harmonic current components obtained from the zero-sequence current waveform of the system.

3. The monitoring device according to claim 2, wherein the output unit outputs the ground-to-ground insulation resistance value of each of the multiple phase circuits.

4. The monitoring device according to claim 2, wherein the output unit outputs an alarm when any one of the multiple phase circuits' ground-to-ground insulation resistance values ​​falls below a threshold.

5. The monitoring device according to claim 2, wherein if any one of the insulation resistance values ​​to ground of the multiple phases of the circuit falls below a threshold value, the circuit is shut off.

6. The monitoring device according to claim 2, wherein the orders of the plurality of harmonic voltage components and the plurality of harmonic current components are different from the order of the frequency component with the smallest magnitude among the plurality of frequency components obtained from the voltage waveform.

7. A derivation unit that derives, for each of the multiple phases, the leakage current components of each order generated by the fundamental wave and harmonics that constitute the voltage of the circuit, based on the ground-to-ground insulation resistance value of each of the multiple phases included in the system and the ground-to-ground capacitance value of each of the multiple phases, The system includes an output unit that outputs an insulation monitoring result or a leakage current monitoring result for the system according to the magnitude of the leakage current, including the leakage current component of each order, which is derived for each phase of the multiple phases by the derivation unit, A monitoring device wherein the order of the leakage current component is different from the order of the frequency component with the smallest magnitude among the multiple frequency components obtained from the voltage waveform of the multi-phase circuit.

8. A derivation unit that derives, for each of the multiple phases, the leakage current components of each order generated by the fundamental wave and harmonics that constitute the voltage of the circuit, based on the ground-to-ground insulation resistance value of each of the multiple phases included in the system and the ground-to-ground capacitance value of each of the multiple phases, A monitoring device comprising: an output unit that outputs insulation monitoring results or ground fault monitoring results for the system for each of the multiple phases according to the magnitude of the leakage current including the leakage current component of each order derived for each of the multiple phases by the derivation unit.

9. A derivation unit that derives, for each of the multiple phases, the leakage current components of each order generated by the fundamental wave and harmonics that constitute the voltage of the circuit, based on the ground-to-ground insulation resistance value of each of the multiple phases included in the system and the ground-to-ground capacitance value of each of the multiple phases, The system includes an output unit that outputs an insulation monitoring result or a leakage current monitoring result for the system according to the magnitude of the leakage current, including the leakage current component of each order, which is derived for each phase of the multiple phases by the derivation unit, The output unit is a monitoring device that outputs an alarm when the magnitude of any one of the leakage currents derived for each of the multiple phases by the derivation unit exceeds a threshold.

10. A derivation unit that derives, for each of the multiple phases, the leakage current components of each order generated by the fundamental wave and harmonics that constitute the voltage of the circuit, based on the ground-to-ground insulation resistance value of each of the multiple phases included in the system and the ground-to-ground capacitance value of each of the multiple phases, The system includes an output unit that outputs an insulation monitoring result or a leakage current monitoring result for the system according to the magnitude of the leakage current, including the leakage current component of each order, which is derived for each phase of the multiple phases by the derivation unit, A monitoring device that shuts off the circuit if the magnitude of any one of the leakage currents derived for each of the multiple phases by the derivation unit exceeds a threshold.

11. The monitoring device according to any one of claims 7 to 10, wherein the derivation unit derives the magnitude of the leakage current for each of the multiple phases by calculating the square root of the sum of the squares of the leakage current components of each order derived for each of the multiple phases.

12. Based on the ground-to-ground insulation resistance value of each of the multiple phase circuits included in the system and the ground-to-ground capacitance value of each of the multiple phase circuits, the leakage current components of each order generated by the fundamental wave and harmonics that constitute the voltage of the circuit are derived for each of the multiple phases. A monitoring method that outputs an insulation monitoring result or a leakage current monitoring result for the system according to the magnitude of the leakage current including the leakage current component of each order derived for each of the multiple phases, A monitoring method in which the magnitude of the leakage current is the area of ​​the waveform of the leakage current.

13. Based on the ground-to-ground insulation resistance value of each of the multiple phase circuits included in the system and the ground-to-ground capacitance value of each of the multiple phase circuits, the leakage current components of each order generated by the fundamental wave and harmonics that constitute the voltage of the circuit are derived for each of the multiple phases. A monitoring method that outputs an insulation monitoring result or a leakage current monitoring result for the system according to the magnitude of the leakage current including the leakage current component of each order derived for each of the multiple phases, A monitoring method for deriving the ground-to-ground insulation resistance value and ground-to-ground capacitance value of each of the multiple phase circuits based on multiple harmonic voltage components obtained from the voltage waveforms of the multiple phase circuits and multiple harmonic current components obtained from the zero-sequence current waveform of the system.

14. Based on the ground-to-ground insulation resistance value of each of the multiple phase circuits included in the system and the ground-to-ground capacitance value of each of the multiple phase circuits, the leakage current components of each order generated by the fundamental wave and harmonics that constitute the voltage of the circuit are derived for each of the multiple phases. A monitoring method that outputs an insulation monitoring result or a leakage current monitoring result for the system according to the magnitude of the leakage current including the leakage current component of each order derived for each of the multiple phases, A monitoring method wherein the order of the leakage current component is different from the order of the frequency component with the smallest magnitude among the multiple frequency components obtained from the voltage waveform of the multi-phase circuit.

15. Based on the ground-to-ground insulation resistance value of each of the multiple phase circuits included in the system and the ground-to-ground capacitance value of each of the multiple phase circuits, the leakage current components of each order generated by the fundamental wave and harmonics that constitute the voltage of the circuit are derived for each of the multiple phases. A monitoring method that outputs insulation monitoring results or leakage current monitoring results for the system for each of the multiple phases, according to the magnitude of the leakage current including the leakage current component of each order derived for each of the multiple phases.

16. Based on the ground-to-ground insulation resistance value of each of the multiple phase circuits included in the system and the ground-to-ground capacitance value of each of the multiple phase circuits, the leakage current components of each order generated by the fundamental wave and harmonics that constitute the voltage of the circuit are derived for each of the multiple phases. A monitoring method that outputs an insulation monitoring result or a leakage current monitoring result for the system according to the magnitude of the leakage current including the leakage current component of each order derived for each of the multiple phases, A monitoring method that outputs an alarm if any one of the magnitudes of the leakage currents derived for each of the multiple phases exceeds a threshold.

17. Based on the ground-to-ground insulation resistance value of each of the multiple phase circuits included in the system and the ground-to-ground capacitance value of each of the multiple phase circuits, the leakage current components of each order generated by the fundamental wave and harmonics that constitute the voltage of the circuit are derived for each of the multiple phases. A monitoring method that outputs an insulation monitoring result or a leakage current monitoring result for the system according to the magnitude of the leakage current including the leakage current component of each order derived for each of the multiple phases, A monitoring method that shuts off the circuit if the magnitude of any one of the leakage currents derived for each of the multiple phases exceeds a threshold.

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