Insulation monitoring device and method for detecting electric leakage thereof

Abstract

To explicitly indicate whether a leakage current is generated in an R phase or a T phase in an electric circuit of a three-phase three-wire system, regardless of whether a temporary or continuous electric leakage occurs.SOLUTION: An insulation monitoring device calculates a fundamental leakage current (Io) based on a leakage current measured by a leakage current measurement circuit, calculates a phase difference between a current and a voltage of a three-phase AC electric path based on the leakage current measured by the leakage current measurement circuit and a voltage measured by a voltage measurement circuit, and calculates an effective leakage current (Ior) based on the fundamental leakage current (Io) and the phase difference between the current and the voltage of the three-phase AC electric path. The insulation monitoring device determines that electric leakage occurs in a phase whose phase is within a predetermined threshold when the effective leakage current (Ior) is equal to or greater than a predetermined threshold value, and the phase of the effective leakage current (Ior) and the phase of the voltage of each phase are within a predetermined threshold.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to an insulation monitoring device and a leakage current detection method, and more particularly to an insulation monitoring device and a leakage current detection method suitable for detecting whether a leakage current has occurred in any of the phases in a three-phase, three-wire system. [Background technology]

[0002] In electrical equipment, a so-called earth leakage phenomenon can occur, in which a current that deviates from a normal electrical path (leakage current) flows due to deterioration of the equipment or other causes.

[0003] Since leakage current can cause fires, sudden power outages, and electric shock accidents, countermeasures against leakage current are an important issue in the maintenance of electrical equipment.

[0004] An insulation monitoring device is a device that detects such leakage current and notifies maintenance personnel. The relationship between leakage current in a three-phase three-wire system and the insulation monitoring device will be described below with reference to Figs. 8 and 9.

[0005] For example, consider a system as shown in Figure 8, in which a consumer load 2 is connected to the secondary side (low voltage side) of a transformer 1 in a three-phase, three-wire system, and which monitors leakage current between the secondary side of transformer 1 and the circuit of load 2.

[0006] In this leakage current monitoring system, a zero-phase current transformer (hereinafter simply referred to as "ZCT") 10 detects leakage current and transmits it to an insulation monitoring device 100. The ZCT 10 is designed to pass three-phase electric wires through it all at once. The insulation monitoring device 100 is a type of device for protecting electric circuits from leakage current such as ground faults and short circuits, and constantly monitors whether the electric circuit is maintaining a normal insulation state.

[0007] The leakage current (fundamental wave leakage current) Io measured by the ZCT10 is the vector sum of the resistive leakage current (active leakage current) Ior and the capacitive leakage current (capacitive leakage current) Ioc, as shown in Figure 9. Here, θ in Figure 9 is the phase difference between the leakage current and the reference voltage. The resistive leakage current Ior can cause fires and electric shocks, and the capacitive leakage current Ioc can cause equipment failures due to harmonics.

[0008] Conventional insulation monitoring devices used the so-called Io method, which measures leakage current Io, but in recent years, the so-called Ior method (fundamental wave effective component method), which excludes capacitor leakage current Ioc and detects resistive leakage current Ior, has become mainstream.

[0009] An insulation monitoring device using the Ior method is disclosed, for example, in Patent Document 1. In the insulation monitoring device described in Patent Document 1, a sine wave signal is extracted from a square wave voltage signal using a low-pass filter, and the active leakage current (Ior) is calculated from the phase difference obtained based on the voltage rising zero cross point of the extracted sine wave signal and the fundamental wave leakage current obtained based on the current signal of a zero-phase-sequence current transformer. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2018-128270 A Summary of the Invention [Problem to be solved by the invention]

[0011] Ior in a three-phase, three-wire system is calculated as the vector sum of the R phase and T phase, and when leakage current occurs, a larger contribution of Ior will flow to the R phase or T phase where the leakage current occurred.

[0012] However, in the conventional insulation monitoring device of the Ior method as described in Patent Document 1, it was not possible to distinguish whether the leakage current was occurring in the R phase or the T phase. Therefore, when a leakage current was generated and the insulation monitoring device notified, a maintenance worker had to investigate on-site to determine in which phase, the R phase or the T phase, the leakage current was occurring. In addition, when the leakage current was generated temporarily, there was also a problem that it was difficult to investigate if no leakage was occurring during the on-site investigation.

[0013] The object of the present invention is to provide an Ior type insulation monitoring device and a leakage current detection method thereof that can explicitly indicate in which phase, R phase or T phase, a leakage current is occurring in an electrical circuit of a three-phase, three-wire system, regardless of whether the leakage current is temporary or continuous. [Means for solving the problem]

[0014] The configuration of the insulation monitoring device of the present invention is preferably an insulation monitoring device that detects leakage current in a three-phase AC electric circuit, and has a leakage current measurement circuit that inputs a leakage current output from a zero-phase current transformer installed in the three-phase AC electric circuit and measures the leakage current, and a voltage measurement circuit that measures the voltage of the three-phase AC electric circuit, and calculates a fundamental leakage current (Io) based on the leakage current measured by the leakage current measurement circuit, calculates a phase difference between the current and voltage of the three-phase AC electric circuit based on the leakage current measured by the leakage current measurement circuit and the voltage measured by the voltage measurement circuit, calculates an effective leakage current (Ior) based on the fundamental leakage current (Io) and the phase difference between the current and voltage of the three-phase AC electric circuit, and determines whether or not leakage current has occurred in each phase of the three-phase AC based on the effective leakage current (Ior).

[0015] More specifically, in the above-mentioned insulation monitoring device, when the magnitude of the active leakage current (Ior) is equal to or greater than a predetermined threshold and the phase of the active leakage current (Ior) and the phase of the voltage of each phase are within a predetermined threshold, it is determined that a leakage current has occurred in a phase whose phase is within the predetermined threshold. Effect of the Invention

[0016] According to the present invention, it is possible to provide an Ior type insulation monitoring device and a leakage current detection method thereof that can explicitly indicate in which phase, R phase or T phase, a leakage current is occurring in an electrical circuit of a three-phase three-wire system, regardless of whether the leakage current is temporary or continuous. [Brief description of the drawings]

[0017] [Figure 1] 1 is a configuration diagram showing an example of an insulation monitoring device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a functional configuration diagram of an insulation monitoring device according to an embodiment. [Figure 3A] This is an example of a coordinate axis representing a symmetrical three-phase AC voltage with 0V as the reference. [Figure 3B] 1 is an example of coordinate axes representing a symmetrical three-phase AC voltage with respect to the S phase. [Figure 4A] This is a vector that shows the relationship between the components of each phase of Ior on the coordinate axes that represent a symmetrical three-phase AC voltage. [Figure 4B] This is a vector that indicates the relationship between the components of each phase of Ioc on the coordinate axes that represent a symmetrical three-phase AC voltage. [Figure 4C] This is a vector that shows the relationship between Io, Ioc, and Ior on the coordinate axes that represent a symmetrical three-phase AC voltage. [Figure 5A] FIG. 1 is a diagram for explaining a state where a leakage current occurs in an R phase on coordinate axes representing a symmetrical three-phase AC voltage with respect to an S phase. [Figure 5B] FIG. 1 is a diagram illustrating a state where a leakage current occurs in a T-phase on coordinate axes representing a symmetrical three-phase AC voltage with respect to an S-phase. [Figure 6] 4 is a flowchart showing the process of the insulation monitoring device of the present embodiment. [Figure 7] FIG. 13 is a diagram showing an example of a display panel showing the measurement results of leakage current in a display device. [Figure 8] FIG. 1 is a diagram showing an example of the configuration of a three-phase, three-wire system in which an insulation monitoring device is disposed. [Figure 9] 1 is a vector diagram relating to leakage current. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] An insulation monitoring device according to one embodiment will be described below with reference to Figs.

[0019] First, a configuration of an example of an insulation monitoring device according to the present embodiment will be described with reference to FIG. In the following description, current and voltage are basically expressed as vector quantities having a magnitude and a phase, and when the magnitude of current or voltage is meant, they are explicitly described as scalars.

[0020] The insulation monitoring device 100 of this embodiment is a device that monitors leakage current in a three-phase, three-wire electric circuit 20. As shown in Fig. 8, the three-phase, three-wire electric circuit 20 is an electric circuit in which three-phase AC flows between, for example, a transformer and a consumer load using three wires, and the individual phases are generally called the R phase, the S phase, and the T phase.

[0021] As shown in FIG. 1, the insulation monitoring device 100 comprises a voltage measuring circuit 101, a leakage current measuring circuit 102, an AD conversion circuit 103, a CPU (Central Processing Unit) 110, a main memory 120, a non-volatile memory 130, and a display 140.

[0022] The voltage measurement circuit 101 is a circuit that receives voltage from, for example, an R-phase line and an S-phase line of a three-phase three-wire circuit 20 and measures the voltage in a time series manner.

[0023] The leakage current measuring circuit 102 is a circuit that measures the leakage current from the current input from the ZCT 10. As already described, the ZCT 10 is a device that detects the currents obtained collectively from the electric wires for three phases.

[0024] The AD conversion circuit 103 is a circuit that converts the analog data output from the voltage measurement circuit 101 and the leakage current measurement circuit 102 into digital data.

[0025] The CPU 110 is a processor that performs processing based on the digital data output from the AD conversion circuit 103 in accordance with a program.

[0026] The main memory 120 is a volatile semiconductor storage device that holds work data and programs accessed by the CPU 110. The non-volatile memory 130 is a non-volatile semiconductor storage device such as a flash memory that holds programs.

[0027] In the non-volatile memory 130, a fundamental wave leakage current calculation program 131, a phase difference detection program 132, an active leakage current calculation program 133, an individual phase leakage occurrence determination program 134, and a leakage measurement result display program 135 are written as firmware.

[0028] The fundamental wave leakage current calculation program 131, the phase difference detection program 132, the active component leakage current calculation program 133, the individual phase leakage current occurrence determination program 134, and the leakage current measurement result display program 135 are programs which respectively realize the functions of the fundamental wave leakage current calculation unit 161, the phase difference detection unit 162, the active component leakage current calculation unit 163, the individual phase leakage current occurrence determination unit 164, and the leakage current measurement result display unit 165. Details of each unit will be described later.

[0029] The display 140 is a liquid crystal display device that displays information such as the measurement results of the leakage current of the insulation monitoring device 100 .

[0030] Next, the functional configuration of the insulation monitoring device according to one embodiment will be described with reference to FIG. As shown in FIG. 2 , the insulation monitoring device 100 has the following functional components: a fundamental wave leakage current calculation unit 161, a phase difference detection unit 162, an active leakage current calculation unit 163, an active leakage current calculation unit for each phase 164, an electric leakage occurrence determination unit for each phase 164, and an electric leakage measurement result display unit 165.

[0031] The fundamental wave leakage current calculation unit 161 is a functional unit that calculates the current input from the ZCT 10 and measured by the leakage current measurement circuit 102 and the fundamental wave leakage current Io.

[0032] The phase difference detection section 162 is a functional section that determines the phase difference between the waveform of the current input from the ZCT 10 and measured by the leakage current measurement circuit 102 and the waveform of the voltage detected by the voltage measurement circuit 102 .

[0033] The active leakage current calculation unit 163 is a functional unit that calculates the active leakage current Ior from the fundamental leakage current Io calculated by the fundamental leakage current calculation unit 161 and the phase difference between the leakage current detected by the phase difference detection unit 162 and the voltage of the electrical path.

[0034] The each-phase leakage current determination unit 164 is a functional unit that determines the presence or absence of leakage current in each phase.

[0035] The leakage current measurement result display unit 165 is a functional unit that displays information on the measurement results relating to leakage current measured by the insulation monitoring device 100 to a maintenance worker.

[0036] Next, coordinate axes representing a symmetrical three-phase AC voltage will be described with reference to FIG. 3A and FIG. 3B. As is well known, a symmetrical three-phase AC voltage is a voltage that fluctuates according to a three-phase sinusoidal waveform in which the voltage magnitude of each phase, designated R phase, S phase, and T phase, is the same and the voltages are shifted by a phase difference of 120° (2π / 3).

[0037] Here, if we take the voltage coordinate axis on the complex plane with 0V as the reference, it will be as shown in Figure 3A (the voltage axis of the R phase is v R , the axis of the S-phase current, v S , the axis of the T-phase current, v T (It was decided that.)

[0038] Here, if the voltage coordinate axis is taken based on the S phase, it will be as shown in FIG. 3B (the voltage axis of the R phase is V R , the axis of the T-phase current, V T (It was decided that.)

[0039] That is, in comparison with FIG. 3A, the vector operation is V R =v R -v S, v S , V T =v T -v S And V R and V T The respective axes have a phase difference of 60° (π / 3).

[0040] Next, the relationship of leakage currents on coordinate axes representing a symmetrical three-phase AC voltage with respect to the S phase will be described with reference to Figs. 4A to 4C. The phase of the voltage of each phase and the leakage current of the resistance are in phase. Therefore, if the R component of Ior is expressed as Ior-R and the T component of Ior is expressed as Ior-T, the resultant vector of Ior-R and Ior-T becomes Ior, as shown in Figure 4A. In Figures 4A to 4C, the current is superimposed on the axis representing the voltage.

[0041] If the R component of Ioc is represented by Ioc-R and the T component of Ioc is represented by Ioc-T, then the resultant vector of Ioc-R and Ioc-T becomes Ioc, as shown in Fig. 4B. Here, in the R phase, Ioc-R lags behind Ior-R by 90° (π / 2), and in the S phase, Ioc-S lags behind Ior-S by 90° (π / 2).

[0042] As already explained, as shown in FIG. 4C, Io is the vector sum of the resistive leakage current Ior and the capacitive leakage current Ioc.

[0043] Next, a method for detecting leakage current in each phase from Ior will be described with reference to Figs. 5A and 5B.

[0044] Ior is calculated by taking the vector difference between Io and Ioc. At this time, as shown in FIG. 5A, when Ior is below a certain threshold (Th Leak ) and the Ior and R phase voltage (V R ) and the angle θ Rmeets the following (Equation 1) (i.e., is greater than or equal to -α and less than or equal to +α), it is determined that a voltage is generated in the R phase. Here, α is the angle threshold for determining that a leakage current is occurring in each of the R phase and the T phase.

[0045] This is because, as shown in Figure 5A, the voltage of Ior and the R phase (V R ) and the angle θ R When Ior is greater than -α and less than +α, most of Ior is thought to be caused by leakage current in the R phase. R ) and the angle θ R When the phase of the active leakage current is greater than or equal to -α and less than or equal to +α, the voltage (V R ) phase and within a specified range.

[0046] Similarly, as shown in FIG. 5B, when Ior is below a certain threshold (Th Leak ) or more, and Ior and the T-phase voltage (V T ) and the angle θ T When it meets the following (Equation 2) (i.e., when it is -α or more and +α or less), it is determined that a voltage is generated in the T phase. The interpretation of this is the same as that of the R phase described above.

[0047] In addition, in (Equation 2), when the R phase is used as the reference, θ T This is equivalent to determining that a voltage is generated in the T phase when the angle is greater than 60°-α and less than 60°+α.

[0048]

number

[0049] Based on the above, the processing of the insulation monitoring device of this embodiment will be described with reference to FIG. First, the insulation monitoring device 100 measures the leakage current input from the ZCT 10 by the leakage current measuring circuit 102 (S01).

[0050] Next, the insulation monitoring device 100 detects the voltage between two phases of the three-phase AC (the voltage between the R phase and the S phase in FIG. 1) by the voltage measurement circuit 101 (S02).

[0051] Next, the insulation monitoring device 100 performs Fourier expansion on the time-series data of the leakage current to extract the fundamental leakage current (Io) from which the harmonic components have been removed (S03).

[0052] Next, the insulation monitoring device 100 obtains the fundamental leakage current (Io) and the phase difference θ between the current and the three-phase AC voltage, and obtains the effective leakage current (Ior) by the following (Equation 3) (S04).

[0053]

number

[0054] Next, the insulation monitoring device 100 checks whether the magnitude of the effective leakage current (Ior) is equal to or exceeds a threshold value (Th Leak ) or more (the following (Equation 4) is satisfied) (S05). Then, the magnitude of the effective leakage current (Ior) is judged to be equal to or greater than the threshold value (Th Leak ) or more (S05: YES), go to S07 and set the threshold value (Th Leak ) (S05: NO), it is determined that no leakage current has occurred (S06), and the process proceeds to S12.

[0055]

number

[0056] The magnitude of the effective leakage current (Ior) is the threshold value (Th Leak ), as shown in Figure 5A, the active leakage current (Ior) and the R phase voltage (V R ) and the angle θ R is judged to be equal to or larger than -α and equal to or smaller than +α (S07), and RIf θ is within this range (S07: YES), it is determined that a leakage current is occurring in the R phase (S08), and the process proceeds to S12. R If it is not within this range (S07: NO), go to S09.

[0057] Active leakage current (Ior) R phase voltage (V R ) and the angle θ R When the value is not greater than -α or less than +α, the magnitude of the active leakage current (Ior) is determined as a function of the active leakage current (Ior) and the T-phase voltage (V T ) and the angle θ T is judged to be equal to or larger than -α and equal to or smaller than +α (S09), and T If θ is within this range (S09: YES), it is determined that a leakage current is occurring in the T phase (S10), and the process proceeds to S12. T If it is not within this range (S09: NO), it is determined that leakage current has occurred in both the R phase and the T phase (S11), and the process proceeds to S12.

[0058] Then, the insulation monitoring device 100 causes the display 140 to display the measurement results of the leakage current in each phase (R phase, T phase) (S12).

[0059] Next, the user interface for displaying the measurement results of leakage current on the display device will be described with reference to FIG. As shown in FIG. 7, a leakage current display area 210 and a command area 220 are displayed on a display panel 200 of the display device 140.

[0060] The leakage current display area 210 is an area for displaying information related to the leakage current measured by the insulation monitoring device 100. In the leakage current display area 210, the active leakage current (Ior), the R-phase active leakage current (Ior-R), and the T-phase active leakage current (Ior-T) are displayed as respective pieces of information.

[0061] The leakage current display area 210 displays a label display area 211, a leakage current value 212, and a warning lamp 213. The label display area 211 displays a character string indicating whether the leakage current is active (Ior), the R-phase active leakage current (Ior-R), or the T-phase active leakage current (Ior-T). The leakage current value 212 displays the value of the leakage current in mA. The warning lamp 213 is a lamp that is turned on to alert a maintenance person when the leakage current value 212 exceeds a specified threshold value.

[0062] The command area 220 is an area for inputting system monitoring setting values ​​and commands for resetting the device, and can be operated by a maintenance technician using a touch panel.

[0063] As described above, the insulation monitoring device of this embodiment can detect whether leakage current is occurring in the R phase or T phase in an electrical circuit of a three-phase, three-wire system, regardless of whether a load motor or the like is operating, and can directly notify maintenance personnel, enabling them to quickly respond to leakage current in each phase. [Explanation of symbols]

[0064] 1...Transformer, 2...Load, 10...Zero-phase current transformer (ZCT), 20...Three-phase three-wire electrical circuit, 100...insulation monitoring device, 101...voltage measurement circuit, 102...leakage current measurement circuit, 103...AD conversion circuit, 110...CPU, 120...main memory, 130...non-volatile memory, 140...display

Claims

1. An insulation monitoring device for detecting leakage current in a three-phase AC circuit, a leakage current measuring circuit that measures the leakage current by inputting a leakage current output from a zero-phase current transformer installed in the three-phase AC circuit; A voltage measurement circuit that measures the voltage of a three-phase AC circuit, Calculating a fundamental wave leakage current (Io) based on the leakage current measured by the leakage current measuring circuit; Calculating a phase difference between a current and a voltage in the three-phase AC circuit based on the leakage current measured by the leakage current measuring circuit and the voltage measured by the voltage measuring circuit; Calculating an effective leakage current (Ior) based on the fundamental wave leakage current (Io) and a phase difference between the current and voltage of the three-phase AC circuit; An insulation monitoring device characterized in that it is determined whether or not a leakage current is occurring in each phase of the three-phase AC based on the effective leakage current (Ior).

2. 2. An insulation monitoring device as claimed in claim 1, characterized in that when the magnitude of the active leakage current (Ior) is equal to or greater than a predetermined threshold and the phase of the active leakage current (Ior) and the phase of the voltage of each phase are within the predetermined threshold, it is determined that a leakage current has occurred in a phase whose phase is within the predetermined threshold.

3. 3. An insulation monitoring device according to claim 2, wherein when it is determined that a ground fault has occurred in each phase, a display is provided to indicate that a ground fault has occurred in that phase.

4. A leakage current detection method for an insulation monitoring device that detects leakage current in a three-phase AC electric circuit, comprising: The insulation monitoring device includes: a leakage current measuring circuit that measures the leakage current by inputting a leakage current output from a zero-phase current transformer installed in the three-phase AC circuit; A voltage measurement circuit that measures the voltage of a three-phase AC circuit, A step in which the insulation monitoring device calculates a fundamental wave leakage current (Io) based on the leakage current measured by the leakage current measuring circuit; a step in which the insulation monitoring device calculates a phase difference between a current and a voltage in the three-phase AC circuit based on the leakage current measured by the leakage current measuring circuit and the voltage measured by the voltage measuring circuit; The insulation monitoring device calculates an effective leakage current (Ior) based on the fundamental wave leakage current (Io) and a phase difference between the current and voltage of the three-phase AC circuit; The insulation monitoring device calculates an effective leakage current in each phase of the three-phase AC based on the effective leakage current (Ior); determining whether the magnitude of the effective leakage current (Ior) is equal to or greater than a predetermined threshold; determining that a leakage current occurs in a phase whose phase is within a predetermined threshold when the phase of the effective leakage current (Ior) and the phase of the voltage of each phase are within a predetermined threshold; and when it is determined that a ground fault has occurred in each phase, the insulation monitoring device displays a message indicating that a ground fault has occurred.

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