Insulation monitoring device and insulation monitoring method

Abstract

To calculate a fundamental wave leakage current Io without performing Fourier expansion processing with software in an insulation monitoring device.SOLUTION: A first zero phase current transformer ZCT1 and a second zero phase current transformer ZCT2 are provided in a power line, test wiring 108 for flowing a test current is laid in the second zero phase current transformer ZCT2, and a test current of an arbitrary effective leakage current Ior is caused to flow from an Ior test current output part 105 in the time of measurement. In this state, a calculation part 110 compares output in ZCT1 in which the test current does not flow with output in ZCT2 in which the test current flows and calculates a fundamental wave leakage current Io by performing vector calculation processing with software. Measurement of the fundamental wave leakage current Io is performed all the time and the measurement result is stored in a memory 111 of the calculation part 110.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an insulation monitoring device and insulation monitoring method for measuring and monitoring leakage current in a power line. [Background technology]

[0002] Conventional insulation monitoring devices measure leakage current by installing a zero-phase current transformer (ZCT) in a three-phase circuit (e.g., 50 Hz, 60 Hz). One known insulation monitoring device uses the fundamental active component method (Ior method). This method detects the commercial frequency current (Io) and circuit voltage using a zero-phase current transformer, and then calculates the current (Ior) flowing through the insulation resistance based on that voltage. The Ior method calculates leakage current using a zero-phase current transformer (hereinafter referred to as ZCT), and then calculates the fundamental leakage current Io and the active component leakage current Ior. To calculate the fundamental leakage current Io, a Fourier expansion process is performed using software in a processor (e.g., a microcomputer) included in the insulation monitoring device. Furthermore, to calculate the active component current Ior, the fundamental leakage current Io is subjected to vector calculations using software. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-128270 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional insulation monitoring devices use software to perform Fourier expansion and vector calculations, but the large amount of calculation required means that the process takes a long time to complete. In particular, when software processing in insulation monitoring devices is implemented using a built-in microcomputer, the microcomputer's own processing power limitations can make real-time insulation monitoring impossible. Furthermore, the time required for software processing means that it is not possible to calculate the effective leakage current (Ior) for all of the continuous waveforms being monitored.

[0005] The present invention has been made to solve the above problems, and an object of the present invention is to provide an insulation monitoring device that can continuously measure the active leakage current Ior. Another object of the present invention is to quickly calculate the active leakage current Ior by passing a test current of any active leakage current Ior from an insulation monitoring device and comparing the vector value difference between the measured value of the active leakage current Ior when the test current is not flowing and the measured value when the test current is flowing. [Means for solving the problem]

[0006] According to one aspect of the present invention, an insulation monitoring device includes a zero-phase current transformer (ZCL) installed on a power line, an amplifier that amplifies the output from the zero-phase current transformer, and a filter circuit that passes the fundamental signal band of the signal output from the amplifier. The signal filtered by the filter circuit is input to a calculation unit, which calculates the fundamental active leakage current. The insulation monitoring device includes two combinations of a zero-phase current transformer, an amplifier, and a filter circuit, and the outputs of the two combinations are input to one calculation unit. Furthermore, a test wire is placed in the penetration of the second set of zero-phase current transformers (ZCL2) along with the power line, so that measurement can be performed using the zero-phase current transformer (ZCL2) while a test current is passed through the test wire from the Io test current output unit. The calculation unit acquires the output from the zero-phase current transformer (ZCL1) when no test current is applied and the output from the zero-phase current transformer (ZCL2) when the test current is applied, and calculates the active leakage current (Ior) by performing vector calculations to compare these outputs. [Effects of the Invention]

[0007] According to the present invention, the software processing of the active leakage current Ior executed by the insulation monitoring device is reduced, so the value of the active leakage current Ior can be determined more quickly. Furthermore, since measurement and calculation processing are completed for each waveform, there is an advantage that no waveform to be measured is missed. Furthermore, although the test current It is supplied to the penetration of the zero-phase current transformer ZCL during measurement, there is an advantage that there is no effect on the power line (field). [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a configuration diagram of an insulation monitoring device 100 according to an embodiment of the present invention. [Figure 2] FIG. 2 is a vector diagram of leakage current Io measured by the insulation monitoring device 100. [Figure 3] FIG. 1 is a vector diagram of leakage current Io measured by insulation monitoring device 100 when test current It is passed. [Figure 4] 3 is a flowchart showing a processing procedure for calculating an active leakage current Ior by the insulation monitoring device 100 of FIG. 1. [Figure 5] FIG. 10 is a configuration diagram of an insulation monitoring device 100A according to a second embodiment of the present invention. [Figure 6] 6 is a flowchart showing a processing procedure for calculating an active leakage current Ior by the insulation monitoring device 100A of FIG. 5. DETAILED DESCRIPTION OF THE INVENTION [Example]

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following drawings, the same parts are given the same reference numerals and repeated explanations will be omitted.

[0010] FIG. 1 is a configuration diagram of an insulation monitoring device 100 according to an embodiment of the present invention. The insulation monitoring device 100 monitors the insulation of an inductive load, such as a motor, and is installed midway along a power line 11 extending from a power supply, such as a transformer 10, to a load 20. The power line 11 is a three-phase, three-wire AC system consisting of three electric wires (R phase, S phase, and T phase). The inductive load 20, such as an electric motor, is grounded, and if the insulation deteriorates, a leakage current flows through the ground wire 21. The insulation monitoring device 100 monitors fluctuations in the insulation state of the load 20 based on the magnitude of the measured voltage and leakage current (also referred to as leakage current). Although not shown in FIG. 1, the voltages of the three electric wires (R phase, S phase, and T phase) are also input to a calculation unit 110 of the insulation monitoring device 100 via a voltage input unit (not shown) and monitored by a microcomputer in the calculation unit 110.

[0011] Two zero-phase current transformers (ZCT1, ZCT2) are installed in the path of the three electric wires (R phase, S phase, T phase). The zero-phase current transformer ZCT is a widely used and well-known measuring device, and by passing all three electric wires (R phase, S phase, T phase) through a penetration, it is possible to extract the current for one phase to the secondary side of the current transformer. Under normal conditions when no earth fault occurs, no current flows through the secondary side of the zero-phase current transformer ZCT, but if an earth fault occurs, the balance of the current flowing through the zero-phase current transformer is disrupted, and current begins to flow through the secondary side of the zero-phase current transformer ZCT.

[0012] The first zero-phase current transformer (ZCT1) is also provided in conventional insulation monitoring devices. The amplifier 101 amplifies the output from the secondary output line 106, allowing the calculation unit 110 to measure the normal leakage current Io. The calculation unit 110 includes a central processing unit (CPU), which can be implemented using a general-purpose microcomputer. The calculation unit 110 includes volatile and nonvolatile memory 111. A band-pass filter circuit 103 is provided between the amplifier 101 and the calculation unit 110. The band-pass filter circuit 103 is a typical hardware filter circuit. This circuit extracts sine wave signals by passing signals in a band including a frequency of 50 Hz or 60 Hz. Signals in other frequency bands are attenuated by this circuit. The signal passing through the band-pass filter circuit 103 becomes the fundamental leakage current Io and is input to the calculation unit 110. The calculation unit 110 calculates the effective leakage current Ior from the input signal (fundamental leakage current Io). In this case, the software processing for Fourier expansion that has conventionally been performed by the calculation unit 110 can be eliminated and replaced with a simple calculation method described below.

[0013] In this embodiment, a second zero-phase-sequence current transformer (ZCT2) is provided in addition to a first zero-phase-sequence current transformer (ZCT1). The first zero-phase-sequence current transformer (ZCT1) and the second zero-phase-sequence current transformer (ZCT2) can be identically configured, and both are installed so that three electric wires (R phase, S phase, T phase) pass through a penetration on the primary side. However, in the second zero-phase-sequence current transformer (ZCT2), in addition to the three power lines 11 (R phase, S phase, T phase), one test electric wire 108 connected to an Ior test current output unit 105 is also arranged to pass through the penetration of the second zero-phase-sequence current transformer (ZCT2). That is, in addition to the three electric wires of R-, S-, and T-phases of the power line 11, the test electric wire 108 is positioned in the penetration part of the second zero-phase current transformer (ZCT2) so as to extend in the same direction as the three electric wires of R-, S-, and T-phases, for a total of four electric wires. The test electric wire 108 is placed parallel to the power line 11 in a partial range near the second zero-phase current transformer (ZCT2), and current is passed through the penetration part of ZCT2.

[0014] The secondary output line 107 of the second zero-phase current transformer (ZCT2) is amplified by an amplifier 102. The amplifier 102 may have the same configuration as the amplifier 101. The output of the amplifier 102 passes through a band-pass filter circuit 104 before being output to a calculation unit 110. The band-pass filter circuit 104 is identical to the band-pass filter circuit 103. The calculation unit 110 detects a combined current of an active leakage current Ior due to the three electric wires (R phase, S phase, and T phase) and an active leakage current Ior' obtained by adding an arbitrary test current It added by the test current output unit 105. The insulation monitoring device 100 can apply an arbitrary test current It from the Ior test current output unit 105. The test current It is applied by the Ior test current output unit 105 in accordance with a control signal sent from the calculation unit 110 of the insulation monitoring device 100 via a control line 112. Since the value of the test current It is determined in advance, the calculation unit 110 knows what the arbitrary value is. As described above, in this embodiment, two sets of combinations of a zero-phase-sequence current transformer, an amplifier, and a filter circuit are provided, and the outputs of these two sets are input to one calculation unit 111, respectively.

[0015] 2 is a vector diagram showing the leakage current Io200 measured by the insulation monitoring device 100 and passed through the bandpass filter circuit 103. The horizontal axis represents the measured voltage V of the R phase input from a voltage input unit (not shown). R 201 and the voltage V S Voltage V with 202 as the reference potential R 201. If we take this horizontal axis line as the reference, the vector of the active leakage current Ior203 is the voltage V S 202 and V R 201. On the other hand, the leakage current Ioc of the capacitor component theoretically has a phase difference of 90° with Ior. The fundamental leakage current Io200 is a value obtained by combining Ior and Ioc, and therefore becomes a vector of the fundamental leakage current Io200. This fundamental leakage current Io200 is input to the calculation unit 110, which then recognizes the length of this vector.

[0016] Figure 3 is a vector diagram of the leakage current measured by the insulation monitoring device when a test current is applied. Figure 3 is obtained when a test current It305 is applied to the fundamental leakage current Io300. The vector of the test current It305 of the insulation monitoring device is the voltage V R 301 and voltage V S 302. This test current It305 is output from the insulation monitoring device 100, so the calculation unit 110 recognizes the length of the vector corresponding to the test current It305. When this test current It305 is applied, the test current It306 is combined with the fundamental leakage current Io300 (theoretically the same magnitude as the fundamental leakage current Io200 detected by the first zero-phase current transformer (ZCT1)), so the vector changes from the original fundamental leakage current Io300 to the fundamental leakage current Io307. The fundamental leakage current Io307 is input to the calculation unit 110 via the amplifier unit 102 and band-pass filter unit 104, so the calculation unit 110 can recognize the length of the vector 307.

[0017] Next, the effective leakage current Ior303 is calculated from the difference between the fundamental wave leakage currents Io300 and 307. First, the angle θ3 is calculated using the cosine theorem. The formula for the cosine theorem is as follows: Io3002 =Io307 2 +It306 2 -2×Io307×It306×Cosθ3 The above formula is expanded to the following formula: Cosθ3=(Io307 2 +It306 2 -Io300 2 )÷2×Io307×It306

[0018] From the above, the angle can be calculated as follows: ArcCosθ3=angle θ3° Once angle θ3 is known, angles θ1 and θ2 can be calculated. θ1°=90°-θ3° θ2°=180°-90°-(90°-θ3°)

[0019] Once the angle θ2 is known, the active current Ior303 can be calculated using trigonometric functions. Ior303+It305=Io307×Cosθ2 From the above, the active current Ior303 can be calculated as follows: Ior303=Io307×Cosθ2-It305 If the template for the above calculation formula is included in the software executed by the microcomputer, the active current Ior303 can be calculated by a short calculation process using the calculation unit 110.

[0020] Next, the calculation procedure performed by the insulation monitoring device 100 will be described using the flowchart in Figure 4. Once the device is started, the insulation monitoring device 100 begins to continuously detect the fundamental wave leakage current Io in the three-phase electric wires (R phase, S phase, and T phase). First, the Ior test current output unit 105 flows a predetermined test current It through the penetration of the second zero-phase current transformer (ZCT2) via the test electric wire 108 (step 61). This test current It is then allowed to flow continuously thereafter. Next, ZCT1 and ZCT2 of the insulation monitoring device 100 output signals corresponding to the leakage currents to secondary outputs 106 and 107, respectively. The secondary outputs 106 and 107 are amplified by amplifiers 101 and 102, and are input to the calculation unit 110 after passing through filter circuits 103 and 104, respectively (step 62). Next, the calculation unit 110 of the insulation monitoring device 100 detects the fundamental leakage current Io200 (=fundamental leakage current Io300) from the output amplified by the amplifier unit 101, and detects the combined value Io307 of the fundamental leakage current Io300 and the test current It306 from the output amplified by the amplifier unit 102 (step 63).

[0021] Next, the calculation unit 110 calculates the active component current Ior303 using the method described in FIG. 3 and stores it in a storage device (not shown) within the calculation unit 110 (step 64). Next, the calculation unit 110 determines whether the detected active component current Ior303 exceeds a threshold (step 65). If it does exceed the threshold, an alarm is displayed on the display screen, an alarm sounds, an alarm lamp is activated, or an alarm is displayed to notify a supervisor (step 66). One or more thresholds may be set, and if the active component current Ior303 is large enough to shut off the power line, shutoff measures are taken in accordance with regulations. Alternatively, an alarm may be issued not immediately when the threshold is exceeded only once, but only if the threshold continues to be exceeded for a certain period of time. If the active component current Ior303 is less than the threshold in step 65, the process proceeds to step 67.

[0022] In step 67, the detected active current Ior303 is sent to the external control device 150 (see FIG. 1). If the measurement results by the insulation monitoring device 100 are sent to the external control device 150 such as a server device, the power line 11 can be remotely monitored. 7 The transmission in step 6 does not necessarily have to be in real time, but may be configured to be transmitted at predetermined time intervals. 6 When an alarm is to be outputted by the external control device 150 (see FIG. 1), it is advisable to immediately send the alarm to the external control device 150 (see FIG. 1).

[0023] Although the present invention has been described above using the embodiments, the present invention is not limited to the above configuration and may be configured in other ways. For example, the number of zero-phase current transformers ZCTs used may be three or more instead of two. Furthermore, it may be only one, as in conventional insulation monitoring devices. In this case, the insulation monitoring device 100A of the second embodiment has the same configuration as the insulation monitoring device 100 of FIG. 1, except that the ZCT1, amplifier unit 101, and bandpass filter unit 103 have been removed. This configuration is shown in FIG. 5. [Example]

[0024] FIG. 5 is a diagram of an insulation monitoring device 100A according to a second embodiment of the present invention. Identical components are designated by the same reference numerals, and redundant description will be omitted. Note that the term "identical" as used herein does not necessarily mean "completely identical" but also encompasses components that perform equivalent functions. In the insulation monitoring device 100A of the second embodiment, a single test wire 108 connected to an Ior test current output unit 105 is arranged so that it passes through a single zero-phase current transformer ZCT. The secondary output 107 measured with no test current It flowing through this test wire 108 is compared with the secondary output 107 measured with the test current It flowing through it. Because these two outputs cannot be measured simultaneously, calculations are performed by alternating between measurements with and without the test current It flowing through the zero-phase current transformer ZCT for each measurement unit and measurement section. For example, in odd-numbered measurements, the leakage current Io200 (see FIG. 2) is measured without passing the test current It through the test electric wire 108, and the value is temporarily stored in the memory 111 of the calculation unit 110. This storage is temporary and is performed only for the purpose of performing calculations during the next measurement, so the memory 111 used may be a non-volatile memory area such as a buffer memory. In the next measurement interval (even-numbered measurement), the leakage current Io300 (see FIG. 3) is measured with the test current It passing through the test electric wire 108. In this way, the active current Ior303 (see FIG. 3) can be calculated using the previous measurement result (stored in memory 111) and the current measurement result during the measurement interval, using the same method as described with reference to FIG. 3.

[0025] FIG. 6 is a flowchart showing the calculation processing procedure of the insulation monitoring device 100A. This procedure includes two measurement steps: steps 71 to 73, in which the calculation unit 110 selects the odd-numbered leakage current Io200 (see FIG. 2), and steps 74 to 76, in which the calculation unit 110 selects the even-numbered leakage current Io300 (see FIG. 3). First, the secondary output 107 of the zero-phase current transformer ZCT is continuously input to the calculation unit 110 of the insulation monitoring device 100A. The leakage currents Io200 and Io300 are acquired from the signals input to the calculation unit 110 at predetermined measurement intervals. First, the calculation unit 110 measures the leakage current Io200 from the secondary output 107 of the zero-phase current transformer ZCT (steps 71 and 72). The measured value of the leakage current Io200 is temporarily stored in the memory 111 included in the calculation unit 110 (step 73).

[0026] Next, during the next measurement interval (even-numbered measurement), the calculation unit 110 passes the test current It through the test wire 108 for a certain period of time (step 74). This certain period of time is approximately the time required for the zero-phase-sequence current transformer ZCT to detect the secondary output 107, and while the test current It is flowing, the calculation unit 110 measures the leakage current Io300 (steps 75 and 76). Here, the test current It is controlled so that it returns to zero at the start of the next measurement interval (odd-numbered measurement). Next, the calculation unit 110 reads out the leakage current Io200 temporarily stored in the memory 111, and calculates the active current Ior303 by taking the difference between the calculated leakage current Io200 and the leakage current Io300, and stores this value in the memory 111 (step 77).

[0027] Next, the calculation unit 110 determines whether the detected active component current Ior303 exceeds a threshold for determining whether to issue an alarm (step 78), and if it exceeds the threshold, an alarm is displayed to notify a supervisor or a person near the device (step 79). One or more thresholds may be set, and if the active component current Ior303 is large enough to cut off the power line, cut-off measures or the like are taken in accordance with regulations. If the active component current Ior303 is less than the threshold in step 78, the process proceeds to step 80.

[0028] The value of active component current Ior303 detected in step 77 is sent continuously or intermittently to external control device 150 (see FIG. 1) (step 80). As described above, even if insulation monitoring device 100A is provided with only one zero-phase current transformer ZCT, by providing Ior test current output unit 105 and test wire 108, it is possible to calculate active component leakage current Ior303 with a simple calculation without performing complex calculations such as Fourier transformation, by configuring the ZCT to measure the sum of normal leakage current Io and test current It.

[0029] As described above in the two embodiments, the insulation monitoring devices 100 and 100A of the present invention are capable of calculating the active leakage current Ior using vector calculations without using software to perform Fourier expansion processing. Furthermore, the time required for calculations by the CPU of the calculation unit 100 is significantly reduced, making it possible to detect the active leakage current Ior for all or most of the power waveforms, and thus monitor the active leakage current Ior with high accuracy. The present invention is not limited to the configurations of the above-described embodiments, and various modifications are possible within the spirit and scope of the invention. [Explanation of symbols]

[0030] 10. Transformers 11 Power Lines 20 Load 21 Ground wire 100, 100A insulation monitoring device 101, 102 Amplification section 103, 104 Bandpass filter circuit 105 Ior test current output section 106, 107 (ZCT) secondary output wire 110 CPU 111 memory 150 External control device 160 External alarm 200 Fundamental wave leakage current Io 201 Voltage V R Vector 202 Voltage VS standard 203 Active leakage current Ior 204 Capacitor component leakage current Ioc 300 Fundamental wave leakage current Io 301 Voltage V R Vector 302 Voltage V S standard 303 Active leakage current Ior 304 Capacitor component leakage current Ioc 305, 306 Test current It 307 Fundamental leakage current Io and effective leakage current Ior are combined components of the test current θ1, θ2, θ3 angles ZCT, ZCT1, ZCT2 zero phase current transformer

Claims

1. An insulation monitoring device that calculates a fundamental wave active leakage current based on a leakage current taken from a zero-phase current transformer installed in a power line and a voltage signal taken from the power line, a first zero-phase current transformer and a second zero-phase current transformer are provided on the power line as the zero-phase current transformers; a test wire is provided through the penetration portion of the second zero-phase current transformer together with the power line; a test current output unit for passing a test current through the test electric wire, a first amplifier unit for amplifying an output from the first zero-phase current transformer, and a second amplifier unit for amplifying an output from the second zero-phase current transformer, The calculation unit is a first detection value output from the first amplifier; a second detection value output from the second amplifier unit, which is detected while a test current is flowing from the test current output unit, is input; an insulation monitoring device for calculating the fundamental wave effective leakage current of the power line by performing a vector operation using a trigonometric function from the first detected value and the second detected value;

2. 2. The insulation monitoring device according to claim 1, wherein the calculation unit determines whether the calculated fundamental wave effective leakage current exceeds a predetermined threshold, and issues an alarm using an alarm if the calculated fundamental wave effective leakage current exceeds the threshold.

3. a first filter circuit is provided between the first amplifier unit and the calculation unit, the first filter circuit passing a fundamental signal band of 50 Hz or 60 Hz of the signal output from the first zero-phase current transformer; 3. An insulation monitoring device according to claim 2, characterized in that a second filter circuit is provided between the second amplifier section and the calculation section, which passes a fundamental signal band of 50 Hz or 60 Hz of the signal output from the second zero-phase current transformer.

4. The calculation unit calculates the fundamental wave active leakage current (I ＯＲ )of, I ＯＲ =I Ｏ２ ×Cosθ ２ -I ｔ However, I ＯＲ : Fundamental wave effective leakage current I Ｏ２ : Second (current) detected value θ ２ : Current value I Ｏ２ and voltage V Ｒ The angle between I ｔ : Test current value 4. The insulation monitoring device according to claim 3, wherein the calculation is performed using the following formula:

5. a storage device for storing the measurement value of the fundamental wave effective leakage current calculated by the calculation unit; the calculation unit stores the calculated measurement values ​​in the storage device continuously or discretely; 5. The insulation monitoring device according to claim 4, wherein the calculation unit outputs the measured value stored in the storage device to an external control device using a communication means.

6. An insulation monitoring device that calculates a fundamental wave effective leakage current by a calculation unit based on a current detection value obtained by amplifying a leakage current taken in from a zero-phase current transformer provided in a power line by an amplifier unit and a voltage detection value taken in from the power line, a test wire disposed so as to pass through the penetration portion of the zero-phase current transformer together with the power line; and a test current output portion for causing a test current to flow through the test wire; The calculation unit performs the following steps a) to d): a) acquiring and storing a first detection value from the amplifier when no test current is flowing through the test wire; b) obtaining a second detection value from the amplifier when a test current is applied to the test wire by the test current output unit; c) calculating the fundamental wave effective leakage current by performing a vector operation of a trigonometric function using the first detection value stored in step a) and the second detection value detected in step b); d) issuing an alarm using an alarm when the fundamental wave effective leakage current is equal to or greater than a predetermined threshold; The insulation monitoring method is characterized by the fact that the above steps are repeated in order to continuously monitor the insulation of the power line.

7. a filter circuit is provided between the amplifier and the calculator, which passes a fundamental signal band of 50 Hz or 60 Hz among the signals output from the zero-phase current transformer; 7. The insulation monitoring method according to claim 6, wherein the calculation unit executes step c) using the first detection value and the second detection value that have passed through the filter circuit.

8. The calculation unit calculates the fundamental wave active leakage current (I ＯＲ )of, I ＯＲ =I Ｏ２ ×Cosθ ２ -I ｔ However, I ＯＲ : Fundamental wave effective leakage current I Ｏ２ : Second (current) detected value θ ２ : Current value I Ｏ２ and voltage V Ｒ The angle between I ｔ : Test current value 8. The insulation monitoring method according to claim 7, wherein the calculation is performed using the following formula:

9. A calculation unit; a first zero-phase current transformer provided on the power line; and a first amplifier for amplifying an output of the first zero-phase current transformer; a second zero-phase-sequence current transformer provided on the power line; and a second amplifier that amplifies an output of the second zero-phase-sequence current transformer, a test wire is provided through the penetration portion of the second zero-phase current transformer together with the power line; An insulation monitoring method for an insulation monitoring device including a test current output unit for supplying a test current to the test wire under the control of the calculation unit, comprising: The calculation unit performs the following steps a) to c): a) acquiring a first detection value from the first amplifier and acquiring a second detection value from the second amplifier when a test current is passed through the test wire; b) calculating a fundamental wave effective leakage current by performing a vector calculation using a trigonometric function from the first detection value and the second detection value; c) if the fundamental wave effective leakage current is equal to or greater than a predetermined threshold, an alarm is issued using an alarm when the threshold is exceeded; The insulation monitoring method is characterized by the fact that the above steps are repeated in order to continuously monitor the insulation of a live power line.

10. 10. The insulation monitoring method according to claim 9, wherein the calculation unit stores the calculated value of the fundamental wave effective leakage current in a readable storage device and sends it to an external control device.

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