Leakage current measurement method and leakage current measurement device

Abstract

This invention provides an inexpensive leakage current measuring device with a relatively simple configuration, without requiring high-speed processing components suitable for fast Fourier transforms. [Solution] The processing means 15 of the leakage current measuring device 1 performs, in parallel, a first calculation process that calculates the effective leakage current Ior of the insulation resistance using the average value S_ave of instantaneous multiplication values ​​obtained by synchronously multiplying the combined leakage current Io_d for one period from an arbitrary change point of the sampling start clock U_clk with the sinusoidal data Sin_d, and a second calculation process that calculates the effective leakage current Ior of the insulation resistance using the average value S_ave of instantaneous multiplication values ​​obtained by synchronously multiplying the combined leakage current Io_d for one period from a change point of the sampling start clock U_clk that is 1 / 2 period delayed from the change point of the sampling start clock U_clk.

Description

Technical Field

[0001] The present invention relates to a leakage current measurement method for measuring the leakage current Ior of insulation resistance (hereinafter also referred to as "effective leakage current") in a measured distribution line, where the low-voltage side three-phase winding of a transformer is connected in a triangle, and the S-phase of the three-phase three-wire distribution line among the S-phase, T-phase, and R-phase is grounded and used as the measured distribution line to be measured, and a leakage current measurement device applying this method.

Background Art

[0002] As a leakage current measurement device applying a method for measuring the leakage current of a three-phase three-wire distribution line, there is a leakage current measurement device proposed by the applicant of this application (see Patent Document 1). In the leakage current measurement device described in this Patent Document 1, voltage measurement means sequentially inputs and measures the line voltage generated between the non-grounded phases (from the T-phase to the R-phase) of the three-phase three-wire distribution line system (S-phase grounded), and the zero-phase current measurement means measures the zero-phase current, which is the leakage current to the ground flowing through the distribution line from the power source and electrical equipment as a load facility connected to this distribution line, and obtains the analysis window width from the line voltage, and calculates the effective leakage current Ior flowing through the ground insulation resistance of the distribution line and electrical equipment from the real part and imaginary part of the fundamental wave of the line voltage obtained using the fast Fourier transform, and the real part and imaginary part of the fundamental wave of the synthesized leakage current Io.

[0003] In the case of the leakage current measuring device described in Patent Document 1 above, when an effective leakage current Ior flows through the ground insulation resistance due to insulation deterioration of the power distribution line under test, the combined value of this current and the current flowing through the ground capacitance (hereinafter also referred to as "reactive leakage current") Ioc is measured as a combined leakage current Io, which is a zero-sequence current. However, in a three-phase three-wire power distribution line with S-phase grounding where ground capacitance exists in the balanced voltage, the effect of reactive leakage current Ioc can be removed by calculating the analysis window width from the line voltage and using the fundamental wave real and imaginary parts of the line voltage obtained using the Fast Fourier Transform, as well as the fundamental wave real and imaginary parts of the combined leakage current Io. Therefore, only the effective leakage current Ior can be calculated with high accuracy. Accordingly, the above-described leakage current measuring device can safely detect leakage current flowing through the ground insulation resistance of a three-phase three-wire power distribution line with the S-phase grounded and the electrical equipment connected thereto, while the power is still on. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 6240918 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, in the leakage current measuring device described in Patent Document 1, since the Fast Fourier Transform is used to determine the fundamental wave real and imaginary parts of the line voltage, and the fundamental wave real and imaginary parts of the combined leakage current Io, even if the nominal frequency of the commercial power supply fluctuates, it is necessary to accurately divide one period of the power supply voltage by 2 to the power of n (where n is an arbitrary natural number) and measure it. Furthermore, in monitoring devices that constantly measure leakage current Ior, it is necessary to simultaneously sample the line voltage and the combined leakage current Io, and to continuously perform calculations using the Fast Fourier Transform and the fundamental wave real and imaginary parts, thereby determining the insulation state of the power distribution line being measured while continuously determining the effective leakage current Ior.

[0006] To perform these processes simultaneously and at high speed, the system must be configured using FPGAs (Field Programmable Gate Arrays) or DSPs (Digital Signal Processors) capable of high-speed parallel processing, Flah for storing calculation data, SDRAM, a CPU for interface control processing, etc. This makes the processing complex, and in order to ensure measurement accuracy, a certain amount of measurement data (for example, 200ms (10 cycles for 50Hz, 12 cycles for 60Hz)) must be subjected to a Fast Fourier Transform. Including other calculation times, there is a problem that it takes more than 400ms of processing time to determine the effective leakage current Ior (for example, a high-speed leakage relay needs to physically shut off the circuit within 100ms). In addition, there is a problem that the product cost will be high because a large number of expensive components are used.

[0007] Therefore, the present invention aims to provide a leakage current measurement method that can accurately and seamlessly detect leakage current flowing from a power distribution line under test at short time intervals without using the Fast Fourier Transform. Furthermore, by applying this leakage current measurement method, the present invention aims to provide a relatively simple and inexpensive leakage current measurement device that does not require high-speed processing components and can perform all calculations using the processing power of a standard CPU. [Means for solving the problem]

[0008] To solve the above problems, the leakage current measurement method according to the present invention is a three-phase three-wire distribution line to be measured, in which the low-voltage side three-phase windings of a transformer are connected in a triangular shape and the S phase is grounded among the S phase, T phase, and R phase, and the effective leakage current Ior of the insulation resistance in this distribution line to be measured is measured, and the zero-crossing point where the waveform of the added line voltage Ust+Usr, obtained by adding the line voltage Ust between the S phase and the T phase and the line voltage Usr between the S phase and the R phase in the distribution line to be measured, becomes 0 volts is detected and the sampling start clock U_ A sampling start clock generation step that generates clk; a current detection step that detects the combined leakage current Io flowing through the power distribution line under measurement; a combined leakage current Io data generation step that starts sampling the combined leakage current Io detected in the current detection step in synchronization with the change point of the sampling start clock U_clk, and converts it into digital data combined leakage current Io_d while sampling at a required sampling period; a sine wave data generation step that generates sine wave data Sin_d of an arbitrary RMS value of digital data at the same period as the sampling start clock U_clk, and in synchronization with the change point of the sampling start clock U_clk, and at the same sampling period as the sampling period in the combined leakage current Io data generation step; a first calculation process that takes the average value S_ave of the instantaneous multiplication value obtained by synchronously multiplying the combined leakage current Io_d and the sine wave data Sin_d for one period from an arbitrary change point of the sampling start clock U_clk, and calculates the effective leakage current Ior of the insulation resistance based on equation (1); and the standard S_ave that serves as the basis for calculating the effective leakage current Ior. The method is characterized by performing, in parallel, a second calculation process to determine the effective leakage current Ior of the insulation resistance at half a period of the sampling start clock U_clk, by taking the average value S_ave of the instantaneous multiplication obtained by synchronously multiplying the combined leakage current Io_d and the sine wave data Sin_d for one period from the change point of the pulling start clock U_clk which is 1 / 2 period delayed or 1 / 2 period advanced from the change point of the pulling start clock U_clk, and determining the effective leakage current Ior of the insulation resistance based on equation (1).

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[0009] Furthermore, in the above configuration, in the processing step, either the effective leakage current Ior of the insulation resistance obtained in the first calculation process for each cycle, or the effective leakage current Ior of the insulation resistance obtained in the second calculation process for each cycle, may be presented as a measured value.

[0010] To solve the above problems, the leakage current measuring device according to the present invention measures a three-phase three-wire distribution line in which the low-voltage side three-phase windings of a transformer are connected in a triangle and the S phase is grounded among the S phase, T phase, and R phase, and measures the leakage current Ior of the insulation resistance in this distribution line under measurement. The device detects the zero-crossing point where the waveform of the sum of the line voltages Ust+Usr, obtained by adding the line voltages Ust between the S phase and the T phase and Usr between the S phase and the R phase of the distribution line under measurement, becomes 0 volts, and sets the sampling start clock U_clk. : A sampling start clock generation means to generate a sampling start clock; a current detection means to detect the combined leakage current Io flowing through the power distribution line under measurement; a combined leakage current Io data generation means that starts sampling the combined leakage current Io detected by the current detection means in synchronization with the change point of the sampling start clock U_clk, and converts it into digital data combined leakage current Io_d while sampling at a required sampling period; a sine wave data generation means that generates sine wave data Sin_d of an arbitrary RMS value of digital data at the same period as the sampling start clock U_clk, and in synchronization with the change point of the sampling start clock U_clk, and at the same sampling period as the sampling period of the combined leakage current Io data generation means; a first calculation process that takes the average value S_ave of the instantaneous multiplication value obtained by synchronously multiplying the combined leakage current Io_d and the sine wave data Sin_d for one period from an arbitrary change point of the sampling start clock U_clk, and calculates the effective leakage current Ior of the insulation resistance based on equation (1); and the sample that serves as the reference for calculating the effective leakage current Ior The system is characterized by comprising: a processing means for determining the effective leakage current Ior of the insulation resistance at half a period of the sampling start clock U_clk, by performing in parallel a second calculation process which involves taking the average value S_ave of an instantaneous multiplication of the combined leakage current Io_d and the sine wave data Sin_d in synchronous multiplication for one period from a change point of the sampling start clock U_clk that is 1 / 2 period delayed or 1 / 2 period advanced from the change point of the ring start clock U_clk, and determining the effective leakage current Ior of the insulation resistance based on equation (1); and a second calculation process which involves performing in parallel a second calculation process which involves determining the effective leakage current Ior of the insulation resistance at half a period of the sampling start clock U_clk.

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[0011] Furthermore, in the above configuration, the processing means may present either the effective leakage current Ior of the insulation resistance obtained for each cycle in the first calculation process, or the effective leakage current Ior of the insulation resistance obtained for each cycle in the second calculation process, as a measured value.

[0012] Furthermore, in the above configuration, the sampling start clock generation means may generate the sampling start clock U_clk with reference to a point obtained by advancing the phase by 90 degrees from the zero-crossing point where the waveform of the line voltage Utr between the T phase and the R phase of the power distribution line under measurement becomes 0 volts.

[0013] Furthermore, in the above configuration, the sampling start clock generation means may generate the sampling start clock U_clk with reference to a point obtained by advancing the phase by 30 degrees from the zero-crossing point where the waveform of the line-to-line voltage Usr between the S phase and the R phase of the power distribution line under measurement becomes 0 volts.

[0014] Furthermore, in the above configuration, the sampling start clock generation means may generate the sampling start clock U_clk with reference to a point that is 30 degrees behind the zero-crossing point where the waveform of the line-to-line voltage Ust between the S phase and the T phase of the power distribution line under measurement becomes 0 volts.

[0015] Furthermore, in the above configuration, the system may be provided with a combined leakage current phase error identification means capable of identifying a phase error θ occurring in the combined leakage current Io detected by the current detection means due to the influence of the phase characteristics inherent in the current detection means, and the sinusoidal data generation means may generate phase error corrected sinusoidal data Sin_d by correcting the phase of the sinusoidal waveform so as to cancel out the phase error θ occurring in the combined leakage current Io identified by the combined leakage current phase error identification means.

[0016] Furthermore, the above configuration may include insulation state determination means for determining the insulation state of the power distribution line under test based on comparing the effective leakage current Ior of the insulation resistance measured by the processing means with a predetermined insulation state determination standard value.

[0017] Furthermore, in the above configuration, the processing means may include an insulation resistance acquisition function that determines the resistance value of the insulation resistance based on the effective leakage current Ior of the insulation resistance measured by the processing means and the voltage value applied to the power distribution line under measurement. [Effects of the Invention]

[0018] According to the leakage current measurement method of the present invention, a first calculation process is performed in parallel to determine the effective leakage current Ior of the insulation resistance based on equation (1). This is done by taking the average value S_ave of the instantaneous multiplication of the combined leakage current Io_d for one period and the sine wave data Sin_d synchronously from an arbitrary change point of the sampling start clock U_clk generated by the sampling start clock generation process, and calculating the effective leakage current Ior of the insulation resistance based on equation (1). A second calculation process is performed in parallel to determine the effective leakage current Ior of the insulation resistance based on equation (1). This is done by taking the average value S_ave of the instantaneous multiplication of the combined leakage current Io_d for one period and the sine wave data Sin_d synchronously from a change point of the sampling start clock U_clk that is 1 / 2 period delayed or 1 / 2 period advanced from the change point of the sampling start clock U_clk.

[0019] Also, according to the current measurement device of the present invention, an average value S_ave of instantaneous multiplication values obtained by multiplying the synthetic leakage current Io_d for one cycle and the sine wave data Sin_d in synchronization from an arbitrary change point of the sampling start clock U_clk generated by the sampling start clock generation means is taken, and based on Equation (1), a first arithmetic process for obtaining the effective leakage current Ior of the insulation resistance is performed. A second arithmetic process for obtaining the effective leakage current Ior of the insulation resistance is performed by taking the average value S_ave of the instantaneous multiplication values obtained by multiplying the synthetic leakage current Io_d for one cycle and the sine wave data Sin_d in synchronization from the change point of the sampling start clock U_clk that is delayed or advanced by half a cycle from the change point of the sampling start clock U_clk. By performing these two processes in parallel, the effective leakage current Ior of the insulation resistance can be obtained every half cycle of the sampling start clock U_clk. Therefore, not only can the effective leakage current Ior be obtained at shorter time intervals than when using the fast Fourier transform, but also no arithmetic components for high-speed processing are required, and the overall arithmetic process can be performed with the arithmetic capabilities of a standard CPU, resulting in a relatively simple configuration and a low-cost device.

Brief Description of the Drawings

[0020] [Figure 1] It is a schematic configuration diagram of a leakage current measurement device to which the leakage current measurement method according to the present invention is applied, connected to a measured distribution line. [Figure 2] It is a vector diagram for explaining the measurement principle of the effective leakage current Ior. [Figure 3] It is an explanatory diagram showing an overview of the procedure from the line-to-line voltages and the synthetic leakage current Io in a three-phase three-wire distribution line to obtaining the effective leakage current Ior. [Figure 4] It is a characteristic diagram showing an example of the phase characteristics of a current detection probe.

Embodiments for Carrying Out the Invention

[0021] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Figure 1 shows a schematic configuration in which a leakage current measuring device 1 to which the leakage current measuring method of the present invention is applied is connected to the distribution line of a three-phase three-wire AC power supply 2.

[0022] The leakage current measuring device 1 comprises at least a sampling start clock generation means 11, a current detection means 12, a combined leakage current Io data generation means 13, a sine wave data generation means 14, a processing means 15, a storage means 16, and a display means 17. For example, the device measures three distribution lines Lr, Ls, and Lt connected to the three-phase terminals R, S, and T of an AC power supply 2, where the low-voltage side three-phase winding 21 of a transformer is connected in a triangle and the S terminal is grounded, and measures the effective leakage current Ior for these distribution lines.

[0023] In this example, AC power supply 2 generates a commercial frequency three-phase AC voltage (line voltages Usr, Ust, Utr) and outputs the generated line voltages Usr, Ust, Utr from the three-phase terminals R, S, T. Thus, AC power supply 2 outputs line voltages Usr, Ust, Utr between the three-phase terminals R, S, T to which the distribution lines Lr, Ls, Lt are connected, and can supply phase currents Ir, Is, It to the load 3 connected between the distribution lines Lr, Ls, Lt. In addition, as shown in Figure 1, there are ground capacitances Cr, Ct and ground leakage resistances Rr, Rt between the distribution lines Lr, Lt of AC power supply 2 and the ground.

[0024] The zero-crossing point detection function of the sampling start clock generation means 11 can be configured with three voltage detection probes 18a, 18b, and 18c, and, for example, a pair of low-pass filters and a comparator. The sampling start clock generation means 11 generates a sampling start clock U_clk, which is defined as the rising or falling edge of a pulse at the zero-crossing point (the point on the time axis where the voltage changes from positive to negative, or from negative to positive) in the waveform of the added line voltage Ust+Usr, which is obtained by adding the line voltages Ust of the distribution lines Ls and Lt detected via the voltage detection probes 18a, 18b, and 18c, and the line voltages Usr of the distribution lines Ls and Lr, or at the point advanced by 90 degrees from the zero-crossing point in the waveform of the line voltage Utr of the distribution lines Lt and Lr, or at the point advanced by 30 degrees from the zero-crossing point in the waveform of the line voltage Usr of the distribution lines Ls and Lr, or at the point delayed by 30 degrees from the zero-crossing point in the waveform of the line voltage Ust of the distribution lines Ls and Lt, and outputs it to the processing means 15.

[0025] The current detection means 12 detects the combined leakage current Io, which consists of phase currents Ir, Is, It flowing through the distribution lines Lr, Ls, Lt, reactive leakage currents Iocr, Ioct flowing to ground via the capacitances Cr, Ct, and effective leakage currents Iorr, Iort flowing to ground via the leakage resistances Rr, Rt, and converts it into a combined leakage current conversion voltage signal Io_u, which is then output to the combined leakage current Io data generation means 13. Furthermore, the phase currents Ir, Is, and It flowing through load 3 flow in opposite directions in each of the distribution lines Lr, Ls, and Lt, as shown by the dotted lines in Figure 1 (they flow in opposite directions within the current detection probe 4). Therefore, when detecting current with the current detection probe 4, the phase currents Ir, Is, and It flowing through each of the distribution lines Lr, Ls, and Lt cancel each other out, and only the combined leakage current Io, which is the sum of the two reactive leakage currents Iocr and Ioct and the two active leakage currents Iorr and Iort, is detected by the current detection probe 4.

[0026] The combined leakage current Io data generation means 13 can consist of, for example, one comparator, one anti-aliasing filter, and one A / D converter. That is, the combined leakage current Io data generation means 13 outputs the zero-crossing point (a point on the time axis where the voltage changes from positive to negative, or from negative to positive) in the voltage waveform of the combined leakage current conversion voltage signal Io_u supplied from the current detection means 12 to the processing means 15 as the combined leakage current reference clock Io_clk. At the same time, the conversion process of the A / D converter is started based on the change point of the sampling start clock U_clk supplied from the sampling start clock generation means 11 via the processing means 15, and the current conversion voltage signal Io_u is converted into digital data combined leakage current Io_d and output to the processing means 15.

[0027] The sine wave data generation means 14 is provided as one function within the CPU that constitutes the processing means 15, and generates sine wave data Sin_d for at least one period from the change point of the sampling start clock U_clk supplied from the sampling start clock generation means 11, with a resolution synchronized with the sampling of the composite leakage current Io_d, and stores it in the storage means 16.

[0028] The processing means 15 can be configured, for example, with a CPU, and does not require the use of many expensive components such as FPGAs and DSPs, resulting in a relatively simple and inexpensive device. The processing means 15 outputs the sampling start clock U_clk supplied from the sampling start clock generation means 11 to the combined leakage current Io data generation means 13, thereby obtaining the combined leakage current Io_d supplied from the combined leakage current Io data generation means 13 and the corresponding sine wave data Sin_d from the storage means 16. Furthermore, as will be described in detail later, the processing means 15 performs a first calculation process in which it calculates the average value S_ave based on the change point of the sampling start clock U_clk and determines the effective leakage current Ior of the insulation resistance using the following equation (1), and a second calculation process in which it calculates the average value S_ave based on the change point of the sampling start clock U_clk that is 1 / 2 cycle delayed or 1 / 2 cycle advanced from the change point of the sampling start clock U_clk and determines the effective leakage current Ior of the insulation resistance using the following equation (1).

[0029]

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[0030] Here, assuming that the combined leakage current Io_d and the sinusoidal data Sin_d have the same angular frequency ω (=2πf) and differ in phase by a phase difference θ, if we take the effective value (signal strength) of the sinusoidal data Sin_d as 1 and the effective value of the combined leakage current Io_d as S0, then the respective digital data can be expressed by the following equations (2) and (3).

[0031] Equivalent leakage current Io_d = S0 × sin(ωt + θ) ... (2)

[0032] Sine wave data Sin_d=sin(ωt) ···(3)

[0033] Furthermore, from equations (2) and (3) above, the product of the combined leakage current Io_d and the sinusoidal data Sin_d can be expressed by equation (4) below.

[0034] S0×sin(ωt+θ)×sin(ωt)=S0×(-1 / 2)×{cos(ωt+ωt+θ)-cos(ωt-ωt+θ)}=(S0 / 2)×{cos(θ)-cos(2ωt)} ···(4)

[0035] By averaging the multiplicative value obtained by equation (4) above over one period and removing the frequency component (the component containing ω), the average value S_ave of the DC component can be obtained. This average value S_ave can be expressed by equation (5) below.

[0036] Average value S_ave = S0 / 2 × cosθ ... (5)

[0037] When the combined leakage current Io_d and the sinusoidal data Sin_d have the same phase angle (θ=0), the average value S_ave is given by equation (6) below.

[0038] Average value S_ave = S0 / 2 × 1 = S0 / 2 ... (6)

[0039] When the combined leakage current Io_d and the sinusoidal data Sin_d have a phase difference of 90 degrees (θ=90 degrees), the average value S_ave is given by equation (7) below.

[0040] Average value S_ave = S0 / 2 × 0 = 0 ... (7)

[0041] Furthermore, the processing means 15 performs calculation processing (first calculation processing and second calculation processing) to calculate the effective leakage current Ior (combined current of effective leakage currents Iorr and Iort) of the insulation resistance of the power distribution lines Lr and Lt based on the equation (1) described above.

[0042] Next, we will explain the basis for the calculation of equation (1) above, referring to Figure 2.

[0043] First, in a power distribution configuration where the low-voltage side three-phase winding 21 is connected in a triangle and the S terminal is grounded, and AC voltage is supplied via a distribution line from an AC power source 2, it is empirically known that when an insulation failure occurs, the insulation of one of the distribution lines connected to the three-phase terminals R and T is significantly deteriorated, while the other distribution line is almost always sound. Therefore, in the configuration of the distribution line under test shown in Figure 1, if an insulation failure occurs, it is considered that the insulation of either distribution line Lr or distribution line Lt is significantly deteriorated, while the other distribution line is sound.

[0044] Therefore, when an insulation failure occurs (or the insulation condition deteriorates) in two distribution lines Lr and Lt, the effective leakage current Ior can be considered to be caused by either the effective leakage current Iorr of distribution line Lr or the effective leakage current Iort of distribution line Lt.

[0045] On the other hand, the capacitances Cr and Ct to ground of the distribution lines Lr and Lt are considered to exist in a balanced state regardless of whether or not insulation failures occur. In other words, the reactive leakage currents Iocr and Ioct are considered to have the same current value.

[0046] First, we will explain the case where only the effective leakage current Iorr is generated due to insulation failure in the distribution line Lr, referring to Figures 2(a) and (b). For ease of understanding, the line voltages Usr, Ust, Utr, and the added line voltage Ust+Usr (the sum of line voltages Ust and Usr) are shown as dashed lines in Figure 2. In the following explanation, the angles of each vector will be expressed as the angle when the line voltage Utr is used as the reference (0 degrees) and rotated counterclockwise with respect to the plane of the paper.

[0047] The reactive leakage current Iocr for distribution line Lr is 90 degrees ahead in phase of the effective leakage current Iorr (in phase with line voltage Usr (60 degrees)), and the reactive leakage current Ioct for distribution line Lt is 90 degrees ahead in phase of the effective leakage current Iort (in phase with line voltage Ust (120 degrees)). Furthermore, as mentioned above, the current values ​​of both reactive leakage currents Iocr and Ioct are the same. Therefore, the combined reactive leakage current Ioc, which is the sum of both reactive leakage currents Iocr and Ioct, is in opposite phase (180 degrees) to the line voltage Utr.

[0048] Here, the combined leakage current Io of each leakage current Iocr, Iorr, Ioct, and Iort can be expressed as a vector sum Io = Ioc + Iorr, since the effective leakage current Iort is zero and the combined reactive leakage current of each reactive leakage current Iocr and Ioct is Ioc. As mentioned above, the effective leakage current Iorr lies at the same angle (60 degrees) as the line voltage Usr, so the combined leakage current Io lies within a 120-degree range from 60 degrees to 180 degrees relative to the line voltage Utr, as shown in Figures 2(a) and (b).

[0049] Here, the length (average value S_ave) that overlaps with the vector of the summing line voltage Ust+Usr (or the phase of Utr advanced by 90 degrees, or the phase of Usr advanced by 30 degrees, or the phase of Ust delayed by 30 degrees) is equal to the length of the perpendicular a drawn from the tip of the combined leakage current Io to the phase voltage Utr (in Figure 2(b), the combined reactive leakage current Ioc with opposite phase), and the length of the perpendicular b drawn from the tip of the effective leakage current Iorr to the phase voltage Utr are the same (average value S_ave=a=b). In addition, the angle between the effective leakage current Iorr and the phase voltage Utr is 60° (sin60°=√3 / 2=b / Iorr). Therefore, the length (current value) of the effective leakage current Iorr is expressed by the following equation (8).

[0050]

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[0051] Furthermore, since there is no insulation defect in the distribution line Lt and the effective leakage current Iort for the distribution line Lt is zero, the effective leakage current Iorr becomes the effective leakage current Ior of the insulation resistance for the distribution lines Lr and Lt. Therefore, if we use equation (8), which calculates the current value of the effective leakage current Iorr, as the equation for calculating the effective leakage current Ior of the insulation resistance for the distribution lines Lr and Lt, then equation (1) above will hold.

[0052] Next, we will explain the case where only the effective leakage current Iort is generated due to an insulation failure in the distribution line Lt, referring to Figure 2(c). For ease of understanding, the line voltages Usr, Ust, Utr, and the added line voltage Ust+Usr (the sum of line voltages Ust and Usr) are shown as dashed lines in Figure 2. In the following explanation, the angles of each vector will be expressed as the angle obtained by rotating the line voltage Utr as the reference (0 degrees) and the vector counterclockwise with respect to the plane of the paper.

[0053] The combined reactive leakage current Ioc of each reactive leakage current Iocr and Ioct exists in the same state as in Figures 2(a) and (b) (out of phase with the line voltage Utr). Therefore, the combined leakage current Io, which is obtained by combining this combined reactive leakage current Ioc with the effective leakage current Iort (in phase with the line voltage Ust (120 degrees)), exists within a 60-degree range from 120 degrees to 180 degrees relative to the line voltage Utr, as shown in Figure 2(c).

[0054] Here, the length (average value S_ave) that overlaps with the vector of the summing line voltage Ust + Usr (or the phase of Utr advanced by 90 degrees, or the phase of Usr advanced by 30 degrees, or the phase of Ust delayed by 30 degrees), the length of the perpendicular a drawn from the tip of the combined leakage current Io to the combined reactive leakage current Ioc which is in the opposite phase to the inter-phase voltage Utr, and the length of the perpendicular c drawn from the tip of the effective leakage current Iort to the combined reactive leakage current Ioc which is in the opposite phase to the inter-phase voltage Utr are the same (average value S_ave = a = c). In addition, the angle between the effective leakage current Iort and the inter-phase voltage Utr is 120° (sin120° = √3 / 2 = c / Iort). Therefore, the length (current value) of the effective leakage current Iort is expressed by the following equation (9).

[0055]

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[0056] Furthermore, since there is no insulation defect in the distribution line Lr and the effective leakage current Iorr is zero, the effective leakage current Iort becomes the effective leakage current Ior of the insulation resistance for the distribution lines Lr and Lt. Therefore, if we use equation (9), which calculates the current value of the effective leakage current Iort, as the equation for calculating the effective leakage current Ior of the insulation resistance for the distribution lines Lr and Lt, then equation (1) above will hold.

[0057] Thus, the processing means 15 calculates the effective leakage current Iorr and the effective leakage current Iort as the effective leakage current Ior by performing the calculation in equation (1).

[0058] Next, with reference to Figure 3, the principle of acquiring the effective leakage current Ior and the processing operation by the processing means 15 will be explained.

[0059] The sampling start clock U_clk generated by the sampling start clock generation means 11 changes its potential level at the zero-crossing point of the summing line voltage Ust+Usr. Figure 3 shows the combined leakage current Io_d obtained by starting sampling of the combined leakage current Io from the point where the sampling start clock U_clk changes, the sinusoidal data Sin_d with an effective value of 1 stored in the storage unit 16 as an example, and the calculation timing of the effective leakage current Ior.

[0060] By performing a first calculation operation in which the average value S_ave of the instantaneous multiplication obtained by synchronously multiplying the combined leakage current Io_d for one period from the earliest change point of the sampling start clock U_clk with the sine wave data Sin_d is applied to the aforementioned equation (1), the effective leakage current Ior of the insulation resistance can be obtained for each period of the sampling start clock U_clk.

[0061] In other words, the effective leakage current Ior for the current period can be determined from the range 1 of the sine wave Sin_d and the range 1 of the combined leakage current Io_d, which represent one period from the earliest change point of the sampling start clock U_clk. The effective leakage current Ior for the current period can be determined from the range 3 of the sine wave Sin_d and the range 3 of the combined leakage current Io_d for the second period. The effective leakage current Ior for the current period can be determined from the range 5 of the sine wave Sin_d and the range 5 of the combined leakage current Io_d for the third period. The effective leakage current Ior for the current period can be determined from the range 7 of the sine wave Sin_d and the range 7 of the combined leakage current Io_d for the fourth period. In this way, the effective leakage current Ior of the insulation resistance can be determined for each period of the summing line voltage Ust+Usr waveform.

[0062] Furthermore, by performing a second calculation process that applies the average value S_ave of the instantaneous multiplication obtained by synchronously multiplying the combined leakage current Io_d for one period with the sine wave data Sin_d from a change point that is 1 / 2 period delayed from the earliest change point of the sampling start clock U_clk to equation (1), the effective leakage current Ior of the insulation resistance is obtained for each period from a change point that is 1 / 2 period delayed from the earliest change point of the sampling start clock U_clk.

[0063] In other words, the effective leakage current Ior for this period can be determined from the range 2 of the sine wave Sin_d and the range 2 of the combined leakage current Io_d, which is one period from the earliest change point of the sampling start clock U_clk that is 1 / 2 period delayed. The effective leakage current Ior for this period can be determined from the range 4 of the sine wave Sin_d and the range 4 of the combined leakage current Io_d for the second period that follows. The effective leakage current Ior for this period can be determined from the range 6 of the sine wave Sin_d and the range 6 of the combined leakage current Io_d for the sixth period that follows. The effective leakage current Ior for this period can be determined from the range 8 of the sine wave Sin_d and the range 8 of the combined leakage current Io_d for the fourth period that follows.

[0064] The effective leakage current Ior of the insulation resistance obtained by these second calculation processes is obtained with a delay of 1 / 2 cycle compared to the effective leakage current Ior obtained by the first calculation process. Therefore, by performing the first and second calculation processes in parallel, the effective leakage current Ior of the insulation resistance can be obtained every 1 / 2 cycle of the summing line voltage Ust+Usr waveform. For example, if a 50Hz commercial AC is supplied from the wire under test, one cycle is 20ms, so the leakage current measuring device 1 can determine the effective leakage current Ior every 10ms. Note that the phase difference from the earliest change point of the reference sampling start clock U_clk is not limited to a delay of 1 / 2 cycle; if the change point is advanced by 1 / 2 cycle, the effective leakage current Ior can be determined 1 / 2 cycle earlier than the effective leakage current Ior based on the change point of the reference sampling start clock U_clk.

[0065] As described above, if a leakage current measurement method is used, which involves performing a processing step to determine the effective leakage current Ior of the insulation resistance every 1 / 2 period, based on the first calculation process using the combined leakage current Io_d of the digital data generated in the combined leakage current Io data generation process and the sine wave data Sin_d of the digital data generated in the sine wave data generation process, based on the earliest change point of the sampling start clock U_clk synchronized with the zero-crossing point generated in the sampling start clock generation process, and the combined leakage current Io_d of the digital data generated in the combined leakage current Io data generation process and the sine wave data Sin_d of the digital data generated in the sine wave data generation process, based on the change point of the sampling start clock U_clk that is 1 / 2 period delayed or 1 / 2 period advanced from the earliest change point of the sampling start clock U_clk, then the leakage current flowing from the power distribution line under test can be accurately detected at short time intervals without using the Fast Fourier Transform. Furthermore, a current measuring device to which this leakage current measurement method is applied does not require a high-speed processing component, and the entire calculation process can be performed with the processing power of a standard CPU, so it can be provided as a relatively simple and inexpensive device. In addition, if it is not necessary to acquire the effective leakage current Ior of the insulation resistance every 1 / 2 period, the processing means 15 may present either the effective leakage current Ior of the insulation resistance obtained by the first calculation process or the effective leakage current Ior of the insulation resistance obtained by the second calculation process as the measured value for each period.

[0066] In the processing means 15 described above, the effective leakage current Ior is determined by assuming that the phase of the combined leakage current Io detected by the current detection probe 4 is synchronized with the zero-crossing point detected by the sampling start clock generation means 11. However, due to the influence of the phase characteristics inherent in the current detection probe 4, a phase error θ that cannot be ignored may occur. Therefore, with reference to Figure 4, the phase correction of the current detection probe 4 will be explained.

[0067] While high-precision current detection probes 4 exhibit good phase characteristics, general-purpose probes have different phase characteristics depending on the frequency, and their phase also changes depending on the magnitude of the leakage current being measured. Figure 4 shows an example of the effect of the phase characteristics of the current detection probe 4 on the combined leakage current Io_d, for each frequency and current phase characteristic. Furthermore, because the phase characteristics differ depending on the type of current detection probe 4, the phase difference between the combined leakage current Io_d and the sinusoidal data Sin_d becomes apparent, making it impossible to obtain the correct effective leakage current Ior.

[0068] As an example, the effect of a phase error θ occurring between the combined leakage current Io_d and the sinusoidal data Sin_d due to the phase characteristics of the current detection probe 4 can be shown by equation (10) below.

[0069]

number

[0070] Thus, the phase error θ of the combined leakage current Io_d caused by the phase characteristics of the current detection probe 4 occurs as a measurement error of the effective leakage current Ior. To solve this, the processing means 15 first determines the effective value of the combined leakage current Io from the combined leakage current Io_d supplied by the combined leakage current Io data generation means 13, and at the same time determines the phase error θ from the combined leakage current reference clock Io_clk and the sampling start clock U_clk supplied by the sampling start clock generation means 11, and the power supply voltage frequency from the sampling start clock U_clk, and stores the effective value of the combined leakage current Io, the power supply frequency, and the corresponding phase error θ in the storage means 16. In other words, the processing means 15 is equipped with the function of a combined leakage current phase error identification means that can identify the phase error θ (phase error θ corresponding to the effective value of the combined leakage current Io and the power supply frequency) that occurs in the combined leakage current Io_d due to the influence of the phase characteristics inherent in the current detection probe 4.

[0071] Then, when actually measuring the effective leakage current Ior, the sinusoidal data generation means 14 reads from the storage means 16 the phase error θ (phase error occurring in the combined leakage current Io_d) corresponding to the effective value of the measured combined leakage current Io and the power supply frequency, and generates sinusoidal data Sin_d by delaying or advancing this phase error θ. In other words, the sinusoidal data generation means 14 generates phase error corrected sinusoidal data Sin_d by correcting the phase of the sinusoidal waveform so as to cancel out the phase error θ occurring in the combined leakage current Io identified by the combined leakage current phase error identification means.

[0072] As described above, by using the phase error corrected sine wave data Sin_d generated by the sine wave data generation means 14, the phase error θ with the combined leakage current Io_d caused by the phase characteristics of the current detection probe 4 is corrected to zero (cos(0°)=1). Applying this to equation (10) above, equation (1) above is obtained as the equation for determining the effective leakage current Ior of the insulation resistance for the distribution lines Lr and Lt.

[0073] In other words, even when detecting the combined leakage current Io using a current detection probe 4 with relatively poor phase characteristics, the correct effective leakage current Ior can be obtained by correcting the phase error θ.

[0074] The processing means 15 may also be equipped with a function as an insulation state determination means that determines the insulation state of the power distribution line under test based on a comparison between the effective leakage current Ior of the insulation resistance measured by the processing means 15 as described above and a predetermined insulation state determination standard value Iref. Alternatively, the processing means 15 may be equipped with an insulation resistance acquisition function that determines the resistance values ​​of the insulation resistances Rr and Rt for the power distribution lines Lr and Lt based on the effective leakage current Ior of the insulation resistance measured by the processing means 15 and the voltage value applied to the power distribution line under test (determined by a measurement means not shown). The resistance values ​​of the insulation resistances Rr and Rt obtained by the insulation resistance acquisition function of the processing means 15 may be displayed to the user by the display means 17.

[0075] Returning to Figure 1, the storage means 16 of the leakage current measuring device 1 can be composed of semiconductor memory such as ROM, RAM, or Flash, and stores the operation program for the processing means 15 described above, the sine wave data Sin_d generated by the sine wave data generation means 14, the phase error θ between the sampling start clock U_clk and the combined leakage current reference clock Io_clk, etc., and reads them out as needed. In addition, the storage means 16 may be provided with a function to store the effective leakage current Ior obtained by the processing means 15 in chronological order and recall it as needed.

[0076] The display means 17 may consist of a display device such as an LCD, or it may consist of an analog meter or a segment-type digital display. The display means 17 visually displays the measured leakage current and the insulation status determination results obtained by the processing means 15. Alternatively, a function to output the measured values ​​and determination results as voice using speech synthesis may be provided separately, or an alarm device may be provided instead of the display means 17 to issue an alarm for insulation abnormalities using sound, light, etc.

[0077] Next, the operation of the leakage current measuring device 1 with the above configuration will be explained. It should be assumed that, in order to perform measurements using the leakage current measuring device 1, three voltage detection probes 18a, 18b, and 18c are connected to the power distribution lines Lr, Ls, and Lt, and the current detection probe 4 is attached to the power distribution lines Lr, Ls, and Lt in a predetermined orientation.

[0078] In the operating state of the leakage current measuring device 1, the sampling start clock generation means 11 detects the line voltages Usr of the distribution lines Ls and Lr, Ust of the distribution lines Ls and Lt, and Utr of the distribution lines Lt and Lr via three voltage detection probes 18a, 18b, and 18c. It then detects the zero-crossing point in the waveform of the added line voltage Ust+Usr (obtained by adding the detected line voltages Usr and Ust), or a point advanced 90 degrees from the zero-crossing point in the waveform of the line voltage Utr of the distribution lines Lt and Lr, or a point advanced 30 degrees from the zero-crossing point in the waveform of the line voltage Usr of the distribution lines Ls and Lr, or a point delayed 30 degrees from the zero-crossing point in the waveform of the line voltage Ust of the distribution lines Ls and Lt, and generates a sampling start clock U_clk, which is output to the processing means 15. Furthermore, the current detection means 12 detects the combined leakage current Io flowing through the power distribution lines Lr and Lt via the current transformer type current detection probe 4, and converts it into a combined leakage current conversion voltage signal Io_u, which is then output to the combined leakage current Io data generation means 13. The combined leakage current Io data generation means 13 receives the combined leakage current conversion voltage signal Io_u as input, and at the same time, at each change point of the sampling start clock U_clk from the processing means 15, it starts the process of converting the current conversion voltage signal Io_u into a combined leakage current Io_d and outputs it to the processing means 15.

[0079] The sine wave data generation means 14 operates as one function of the processing means 15 and generates sine wave data Sin_d for at least one period from the change point of the sampling start clock U_clk, with the same sampling period as the sampling period of the combined leakage current Io_d, and stores it in the storage means 16.

[0080] The processing means 15 obtains the effective value of the combined leakage current Io from the combined leakage current Io_d supplied from the combined leakage current Io data generation means 13, and at the same time obtains the power supply voltage frequency from the sampling start clock U_clk, and obtains the phase error θ and sine wave data Sin_d corresponding to the effective value of the combined leakage current Io and the power supply frequency from the storage means 16. Furthermore, by performing in parallel a first calculation process that calculates the average value S_ave of the DC component by averaging the multiplication value of the combined leakage current Io_d and the sine wave data Sin_d over one period, based on the change point of the sampling start clock U_clk, and then calculating the effective leakage current Ior of the insulation resistance using the calculation in equation (1), and a second calculation process that calculates the average value S_ave of the DC component by averaging the multiplication value of the combined leakage current Io_d and the sine wave data Sin_d over one period, based on the change point of the sampling start clock U_clk which is 1 / 2 period delayed or 1 / 2 period advanced from the change point of the sampling start clock U_clk, and then calculating the effective leakage current Ior of the insulation resistance using the calculation in equation (1), the effective leakage current Ior of the insulation resistance can be calculated every 1 / 2 period of the sampling start clock U_clk.

[0081] Furthermore, in a leakage current measuring device 1 in which the processing means 15 functions as an insulation state determination means, the measured effective leakage current Ior is compared with a predetermined insulation state determination standard value Iref, and the result of this comparison, the insulation state determination result, is displayed on the display means 17, thereby allowing the user of the leakage current measuring device 1 to be reliably and easily informed of the quality of the insulation state of the power distribution lines Lr and Lt. Even in a leakage current measuring device 1 that does not have an insulation state determination means function and only displays the measured effective leakage current Ior on the display means 17, the user can determine the insulation state of the power distribution lines Lr and Lt by comparing the measured effective leakage current Ior with the insulation state determination standard value Iref.

[0082] Furthermore, by displaying the insulation resistance values ​​for power distribution lines Lr and Lt on the display means 17 based on the effective leakage current Ior of the insulation resistance measured by the processing means 15 and the voltage value applied to the power distribution line under test (determined by a measurement means not shown), the user of the leakage current measuring device 1 can quantitatively determine whether the insulation condition of power distribution lines Lr and Lt is good or bad, thereby numerically determining the degree of deterioration of the two power distribution lines.

[0083] Furthermore, if leakage current relays are separately provided on the power distribution lines Lr, Ls, and Lt, and the leakage current relays can be shut off by an external control signal line, then by connecting the control signal line of the leakage current relay to the leakage current measuring device 1, performing a leakage current inspection with the leakage current measuring device 1, and if the insulation state determination result of the processing means 15 indicates insulation deterioration, then outputting an operation command to the leakage current relay via the control signal line and promptly executing the shutdown operation of the leakage current relay, the leakage current relay control function of the processing means 15 can be equipped with a leakage current relay control function that can reliably prevent accidents caused by leakage current. For example, a high-speed leakage current relay needs to physically shut off the circuit within 100ms, but the leakage current measuring device 1 of this embodiment can measure the effective leakage current Ior every 1 / 2 cycle of the power supply voltage (10ms for 50Hz, and approximately 8.3ms for 60Hz), so it is possible to perform the detection of a leakage current abnormality and the operation of the high-speed leakage current relay within 100ms.

[0084] The leakage current measurement method according to the present invention and embodiments of a leakage current measurement device to which the same is applied have been described above with reference to the attached drawings. However, the present invention is not limited to these embodiments, and may be implemented by adapting known and existing equivalent technical means without changing the configuration described in the claims. [Explanation of symbols]

[0085] 1. Leakage current measuring device 11. Sampling start clock generation means 12 Current detection means 13. Means for generating composite leakage current Io data 14. Sine wave data generation means 15 Processing means 16 Memory means 17 Display means 2 AC power supply 3 load 4 Current detection probe

Claims

1. A leakage current measurement method for measuring the effective leakage current Ior of the insulation resistance in a three-phase three-wire distribution line, in which the low-voltage side three-phase windings of a transformer are connected in a triangular configuration and the S phase of the S phase is grounded among the S phase, T phase, and R phase, is used as the distribution line to be measured. A sampling start clock generation step involves detecting a zero-crossing point where the waveform of the summed line voltage Ust + Usr, obtained by adding the line voltage Ust between the S phase and the T phase and the line voltage Usr between the S phase and the R phase in the distribution line under measurement, becomes 0 volts, and generating a sampling start clock U_ck. A current detection step for detecting the combined leakage current Io flowing through the power distribution line under measurement, A composite leakage current Io data generation step is performed in synchronization with the change point of the sampling start clock U_ck, to start sampling the composite leakage current Io detected in the current detection step, and to convert it into a composite leakage current Io_d digital data while sampling at a required sampling period. A sine wave data generation step generates sine wave data Sin_d, which is an arbitrary RMS value, with the same period as the sampling start clock U_ck and synchronized with the change point of the sampling start clock U_ck, and with the same sampling period as the sampling period in the composite leakage current Io data generation step. A processing step to determine the effective leakage current Ior of the insulation resistance by performing the following in parallel: a first calculation process to determine the effective leakage current Ior of the insulation resistance at half a period of the sampling start clock U_ck, by taking the average value S_ave of the instantaneous multiplication of the combined leakage current Io_d and the sine wave data Sin_d for one period from an arbitrary change point of the sampling start clock U_ck, and calculating the effective leakage current Ior of the insulation resistance based on equation (1); and a second calculation process to determine the effective leakage current Ior of the insulation resistance by taking the average value S_ave of the instantaneous multiplication of the combined leakage current Io_d and the sine wave data Sin_d for one period from a change point of the sampling start clock U_ck that is 1 / 2 period delayed or 1 / 2 period advanced from the change point of the sampling start clock U_ck that serves as the reference for determining the effective leakage current Ior, by taking the average value S_ave of the instantaneous multiplication of the combined leakage current Io_d and the sine wave data Sin_d for one period from an arbitrary change point of the sampling start clock U_ck, and calculating the effective leakage current Ior of the insulation resistance based on equation (1); A leakage current measurement method characterized by performing the following. [Math 1]

2. The leakage current measurement method according to claim 1, characterized in that, in the processing step, either the effective leakage current Ior of the insulation resistance obtained in the first calculation process for each cycle, or the effective leakage current Ior of the insulation resistance obtained in the second calculation process for each cycle, is presented as a measured value.

3. A leakage current measuring device measures the leakage current Ior of the insulation resistance in a three-phase, three-wire distribution line, where the low-voltage side three-phase windings of a transformer are connected in a triangular configuration, and the S phase is grounded among the S phase, T phase, and R phase. A sampling start clock generation means that detects a zero-crossing point where the waveform of the summed line voltage Ust + Usr, obtained by adding the line voltage Ust between the S phase and the T phase of the distribution line under measurement and the line voltage Usr between the S phase and the R phase, becomes 0 volts, and generates a sampling start clock U_ck. A current detection means for detecting the combined leakage current Io flowing through the power distribution line under measurement, Synchronized with the change point of the sampling start clock U_ck, the sampling of the composite leakage current Io detected by the current detection means is started, and composite leakage current Io data generation means converts the sampled data into a composite leakage current Io_d digital data while sampling at a required sampling period, A sine wave data generation means generates sine wave data Sin_d of digital data which is an arbitrary RMS value, with the same period as the sampling start clock U_ck and synchronized with the change point of the sampling start clock U_ck, and with the same sampling period as the sampling period of the composite leakage current Io data generation means, A processing means for determining the effective leakage current Ior of the insulation resistance by performing, in parallel, a first calculation process that takes the average value S_ave of instantaneous multiplication obtained by synchronously multiplying the composite leakage current Io_d and the sine wave data Sin_d for one period from an arbitrary change point of the sampling start clock U_ck, and determining the effective leakage current Ior of the insulation resistance based on equation (1); and a second calculation process that takes the average value S_ave of instantaneous multiplication obtained by synchronously multiplying the composite leakage current Io_d and the sine wave data Sin_d for one period from a change point of the sampling start clock U_ck that is 1 / 2 period delayed or 1 / 2 period advanced from the change point of the sampling start clock U_ck that serves as the reference for determining the effective leakage current Ior, and determining the effective leakage current Ior of the insulation resistance based on equation (1); A leakage current measuring device characterized by comprising the following features. [Math 2]

4. The leakage current measuring device according to claim 3, characterized in that the processing means presents either the effective leakage current Ior of the insulation resistance obtained for each cycle in the first calculation process, or the effective leakage current Ior of the insulation resistance obtained for each cycle in the second calculation process, as a measured value.

5. The leakage current measuring device according to claim 3 or 4, characterized in that the sampling start clock generation means generates a sampling start clock U_CLK with reference to a point obtained by advancing the phase by 90 degrees from the zero-crossing point where the waveform of the line voltage Utr between the T phase and the R phase of the power distribution line to be measured becomes 0 volts.

6. The leakage current measuring device according to claim 3 or 4, characterized in that the sampling start clock generation means generates a sampling start clock U_CLK with reference to a point obtained by advancing the phase by 30 degrees from the zero-crossing point where the waveform of the line voltage Usr between the S phase and the R phase of the power distribution line to be measured becomes 0 volts.

7. The leakage current measuring device according to claim 3 or 4, characterized in that the sampling start clock generation means generates a sampling start clock U_ck with reference to a point that is 30 degrees behind in phase from the zero-crossing point where the waveform of the line-to-line voltage Ust between the S phase and the T phase of the power distribution line under measurement becomes 0 volts.

8. The system includes a combined leakage current phase error identification means capable of identifying the phase error θ occurring in the combined leakage current Io detected by the current detection means, based on the influence of the phase characteristics inherent in the current detection means. The leakage current measuring device according to claim 3 or 4, characterized in that the sinusoidal data generation means generates phase error corrected sinusoidal data Sin_d, which corrects the phase of the sinusoidal waveform so as to cancel out the phase error θ occurring in the composite leakage current Io identified by the composite leakage current phase error identification means.

9. The leakage current measuring device according to claim 3 or 4, further comprising insulation state determination means for determining the insulation state of the power distribution line to be measured based on comparing the effective leakage current Ior of the insulation resistance measured by the processing means with a predetermined insulation state determination standard value.

10. The leakage current measuring device according to claim 3 or 4, characterized in that the processing means includes an insulation resistance acquisition function that determines the resistance value of the insulation resistance based on the effective leakage current Ior of the insulation resistance measured by the processing means and the voltage value applied to the power distribution line to be measured.

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