JP7587213B2 - Inspection device, inspection method, and inspection program - Google Patents

Description

The present invention relates to an inspection device, an inspection method, and an inspection program for inspecting or monitoring a three-phase delta power line.

The insulation performance of an electrical system, including the load equipment of electrical equipment, is extremely important in preventing electric shock, fire, etc., but the insulation performance can be impaired due to aging deterioration of electrical equipment or construction work, etc., and leakage current (hereinafter referred to as "Io") can occur in the electric line. It is important to predict the occurrence of Io or detect Io that has actually occurred, and prevent accidents before they occur, or at an early stage.

For this reason, the receiving transformer is provided with an inspection device that inspects Io on the ground wire of the secondary circuit. Here, Io includes leakage current due to capacitance to earth (hereinafter referred to as "Ioc") and leakage current due to insulation resistance to earth, which is directly related to insulation resistance (hereinafter referred to as "Ior").

For example, in Patent Document 1, there is provided a zero-phase current detection means for detecting a zero-phase current in a three-phase electric circuit, a voltage detection means for detecting the voltage of the electric circuit, a specified frequency component extraction means for extracting first and second frequency components from the zero-phase current and voltage, the first frequency component being a harmonic component other than the fundamental wave or a harmonic component of an integer multiple of the third order, and the second frequency component being a harmonic component other than the harmonic component of an integer multiple of the third order and different from the first frequency component, and a specified frequency component extraction means for converting the second frequency component in the zero-phase current into a specified correction current and converting the extracted zero-phase current The present disclosure discloses an insulation monitoring device equipped with a leakage current calculation means that calculates the leakage current due to the earth insulation resistance of two of the three phases based on the first frequency component in the zero-phase current, the correction current, the phase difference between the first and second frequency components in the zero-phase current and the frequency of the first and second frequency components in the zero-phase current relative to the reference voltage, using the voltage of any one of the three phases as a reference voltage, and the predetermined correction current is a current obtained by converting the second frequency component in the zero-phase current to a value when the second frequency component in the voltage is equal to the first frequency component in the voltage.

JP 2004-317466 A

Here, Ior is expressed as the scalar sum of the two phases. However, if it is not known what proportion of Ior is occurring in the two phases, it is difficult to identify the problem areas of Ior (such as the location where Ior is occurring), the cause of occurrence, and changes during regular inspections. The two phases are the R phase and T phase, the T phase and S phase, or the S phase and R phase.

The objective of this disclosure is to provide an inspection device, inspection method, and inspection program that can calculate the Ior values occurring in each of the two phases in the Ior measurement results by assuming changes in Ioc, and can inspect or monitor a delta-connected electric line under test.

In order to achieve the above object, the present invention is configured as follows.
(1) An inspection device comprising: a leakage current detection unit that detects a leakage current flowing in a measured electric line in which a first phase, a second phase, and a third phase are delta-connected; a voltage detection unit that detects a voltage applied to the measured electric line; a phase angle detection unit that detects a phase angle based on the leakage current detected by the leakage current detection unit and the voltage detected by the voltage detection unit; a first calculation unit that calculates a possible range of a capacitive component leakage current caused by earth capacitance included in the leakage current flowing in the measured electric line, based on the leakage current detected by the leakage current detection unit and the phase angle detected by the phase angle detection unit; and a second calculation unit that calculates a possible range of a resistive component leakage current caused by earth insulation resistance included in the leakage current flowing in the measured electric line, based on the possible range of the capacitive component leakage current calculated by the first calculation unit, the phase angle detected by the phase angle detection unit, and the leakage current detected by the leakage current detection unit.
(2) The inspection device described in (1), wherein the second calculation unit calculates the resistive component leakage current based on a value selected from a range in which the capacitive component leakage current can be, the phase angle detected by the phase angle detection unit, and the leakage current detected by the leakage current detection unit.
(3) The inspection device described in (1), wherein the second calculation unit calculates the resistive component leakage current based on the median of the capacitive component leakage current calculated by the first calculation unit, the phase angle detected by the phase angle detection unit, and the leakage current detected by the leakage current detection unit.
(4) An inspection method comprising: a leakage current detection step of detecting a leakage current flowing in a measured electric line having a first phase, a second phase, and a third phase connected in a delta connection; a voltage detection step of detecting a voltage applied to the measured electric line; a phase angle detection step of detecting a phase angle based on the leakage current detected by the leakage current detection step and the voltage detected by the voltage detection step; a first calculation step of calculating a possible range of a capacitive component leakage current caused by earth capacitance, which is included in the leakage current flowing in the measured electric line, based on the leakage current detected by the leakage current detection step and the phase angle detected by the phase angle detection step; and a second calculation step of calculating a possible range of a resistive component leakage current caused by earth insulation resistance, which is included in the leakage current flowing in the measured electric line, based on the possible range of the capacitive component leakage current calculated by the first calculation step, the phase angle detected by the phase angle detection step, and the leakage current detected by the leakage current detection step.
(5) An inspection program for causing a computer to execute the following steps: a leakage current detection step for detecting a leakage current flowing in a measured electric line having a first phase, a second phase, and a third phase connected in a delta connection; a voltage detection step for detecting a voltage applied to the measured electric line; a phase angle detection step for detecting a phase angle based on the leakage current detected by the leakage current detection step and the voltage detected by the voltage detection step; a first calculation step for calculating a possible range of a capacitive component leakage current caused by earth capacitance, which is included in the leakage current flowing in the measured electric line, based on the leakage current detected by the leakage current detection step and the phase angle detected by the phase angle detection step; and a second calculation step for calculating a possible range of a resistive component leakage current caused by earth insulation resistance, which is included in the leakage current flowing in the measured electric line, based on the possible range of the capacitive component leakage current calculated by the first calculation step, the phase angle detected by the phase angle detection step, and the leakage current detected by the leakage current detection step.

According to the present invention, it is possible to calculate the Ior values occurring in each of the two phases in the Ior measurement results by assuming changes in Ioc, and to inspect or monitor the Δ-connected electric line under test.

FIG. 1 is a diagram showing the configuration of an inspection device. FIG. 2 is a diagram illustrating the possible range of Ioc. FIG. 3 is a diagram that illustrates a vector diagram when the expected value of Ioc is set to the minimum value (Ioc(rt)MIN). FIG. 4 is a diagram that illustrates a vector diagram when the expected value of Ioc is set to the maximum value (Ioc(rt)MAX). FIG. 5 is a diagram that illustrates a vector diagram when the expected value of Ioc is set to the median value (Ioc(rt)CEN). FIG. 6 is a flow chart illustrating the procedure of the inspection method. FIG. 7 is a block diagram showing a first configuration example of a computer. FIG. 8 is a block diagram showing a second configuration example of the computer.

The present embodiment will be described below. Note that the present embodiment described below does not unduly limit the content of the present invention described in the claims. Furthermore, not all of the configurations described in the present embodiment are necessarily essential components of the present invention.

Figure 1 is a diagram showing the configuration of the inspection device 1. The inspection device 1 includes a leakage current detection unit 11, a voltage detection unit 12, a phase angle (phase) detection unit 13, a first calculation unit 14, and a second calculation unit 15.

The leakage current detection unit 11 detects the leakage current flowing in the electric line under test in which the first, second, and third phases are connected in a Δ (delta) configuration. In the following, the first phase is referred to as the R phase, the second phase is referred to as the T phase, and the third phase is referred to as the S phase, but these names are not limited to these. In the following, the leakage current measured by the leakage current detection unit 11 is referred to as "Io", but these names are not limited to these.

In addition, the inspection device 1 is described as having the S phase of the three phases (R phase, S phase, T phase) grounded, but the ground phase may be the R phase or the T phase.

A zero-phase current transformer (ZCT) 10 is connected to the leakage current detection unit 11. The zero-phase current transformer 10 is configured to clamp the electric line all at once. For example, the zero-phase current transformer 10 is configured as a handy type through-hole split type zero-phase current transformer, so that workers can easily install it on the electric line at the site.

The leakage current detection unit 11 detects (calculates) the Io flowing through the measured electric line from the signal measured by the zero-phase current transformer 10.

The voltage detection unit 12 detects the voltage applied to the electric line being measured.

The phase angle detection unit 13 detects a phase angle (θ) based on the leakage current (Io) detected by the leakage current detection unit 11 and the voltage detected by the voltage detection unit 12. Specifically, the phase angle detection unit 13 detects the phase angle (θ) based on the effective value of the leakage current (Io) detected by the leakage current detection unit 11 and the effective value of the voltage (e.g., reference voltage V _T-R ) detected by the voltage detection unit 12. For example, the phase angle detection unit 13 detects the phase angle (θ) between the reference voltage V _T-R and the leakage current (Io) based on the zero crossing points of the reference voltage V _T-R and the zero crossing points of the leakage current (Io).

The first calculation unit 14 calculates the possible range of the capacitive component leakage current (Ioc) caused by the earth capacitance contained in the leakage current flowing through the measured electric line based on the leakage current detected by the leakage current detection unit 11 and the phase angle detected by the phase angle detection unit 13.

Here, we explain the possible range of Ioc. Figure 2 is a diagram used to explain the possible range of Ioc.

When the voltage detection unit 12 detects the voltage between the R phase and the T phase and determines the reference point from the detected voltage, as shown in Figure 2, the R phase axis is at a position 60° from the reference point, and the T phase axis is at a position 120° from the reference point. Furthermore, since the phase difference between the R phase Ior (hereinafter referred to as Ior(r)) and the reference point is 60°, Ior(r) appears on the R phase axis. Since the phase difference between the T phase Ior (hereinafter referred to as Ior(t)) and the reference point is 120°, Ior(t) appears on the T phase axis.

In addition, Ior (hereinafter referred to as Ior(rt)), which is the vector synthesis of Ior(r) and Ior(t), occurs between the R-phase axis and the T-phase axis (in the range of 60° to 120° from the reference point).

Furthermore, the Ioc of the R phase (hereinafter referred to as Ioc(r)) occurs at a position 90° from the axis of the R phase. The Ioc of the T phase (hereinafter referred to as Ioc(t)) occurs at a position 90° from the axis of the T phase. When Ioc(r) and Ioc(t) are in equilibrium, the Ioc (hereinafter referred to as Ioc(rt)), which is the combination (vector combination) of Ioc(r) and Ioc(t), occurs in the 180° direction of the reference axis (the "-X" direction in Figure 2).

Io is the composition (vector composition) of Ior(rt) and Ioc(rt). If Io detected by the leakage current detection unit 11 is at the position shown in Figure 2, Ior(rt) will occur on line L (parallel to the line on which the reference point is located) to which the end point P1 of Io belongs, in the range of 60° to 120° from the reference point (R1 in Figure 2).

If a perpendicular line is drawn from the end point P1 of Io to the line on which Ioc(rt) is generated and the intersection point is "P2", then the point P3 from the origin 0 is the maximum value of Ioc(rt) (hereinafter referred to as Ioc(rt)MAX). The angle between points P1, P3, and P2 is 60°. The point P4 from the origin 0 is the minimum value of Ioc(rt) (hereinafter referred to as Ioc(rt)MIN). The angle between points P1, P4, and P2 is 60°.

Note that Ioc(rt)MAX and Ioc(rt)MIN occur in the 180° direction (-X direction) of the reference axis, but are shown in different positions in Figure 2 for the sake of explanation.

When Ioc(rt)MIN, "Ior(rt) = Ior(t)" (Ior(r) = 0). When Ioc(rt)MAX, "Ior(rt) = Ior(r)" (Ior(t) = 0).

The first calculation unit 14 therefore calculates Ioc(rt)MIN and Ioc(rt)MAX based on Io detected by the leakage current detection unit 11 and the phase angle (θ) detected by the phase angle detection unit 13. The range of Ioc(rt) is the range between Ioc(rt)MIN and Ioc(rt)MAX (R2 in FIG. 2).

The second calculation unit 15 calculates the possible range of the resistive component leakage current caused by the earth insulation resistance contained in the leakage current flowing through the measured electric line based on the possible range of the capacitive component leakage current calculated by the first calculation unit 14, the phase angle detected by the phase angle detection unit 13, and the leakage current detected by the leakage current detection unit 11.

By configuring in this manner, the inspection device 1 calculates the possible range of Ioc from Io and the phase angle (θ), and calculates the possible range of Ior based on this possible range of Ioc, Io, and the phase angle (θ). This possible range of Ior can then be used to inspect or monitor the Δ-connected electric line under test.

(Operation of the second calculation unit)
The second calculation unit 15 may be configured to calculate the resistive component leakage current based on a value selected from the range that the capacitive component leakage current (Ioc) can take, the phase angle detected by the phase angle detection unit 13, and the leakage current detected by the leakage current detection unit 11.

The configuration may be such that a user selects a value from within the range of possible values for Ioc. For example, the inspection device 1 includes a display unit that displays information and an operation unit that accepts operations by the user. The user operates the operation unit to input an arbitrary value from within the range of Ioc displayed on the display unit.

The second calculation unit 15 may be configured to calculate the resistive component leakage current based on the median (IocCEN) of the capacitive component leakage current (Ioc) calculated by the first calculation unit 14, the phase angle detected by the phase angle detection unit 13, and the leakage current detected by the leakage current detection unit 11. Note that the calculated resistive component leakage current is not limited to the median, and may be the maximum value of Ioc or the minimum value of Ioc.

Here, by assuming an Ioc value within the possible range of Ioc calculated by the first calculation unit 14, the composite vector of Ior (Ior(rt)) is determined, and Ior(r) and Ior(t), which are elements of Ior(rt), can be calculated.

Specifically, Ior(rt) in a delta-connected circuit can be calculated using equation (1).
Ior(rt)=Io×sin(θ)/cos30°...(1)

Ior(t) can be calculated by equation (2).
Ior(t)=Ior(rt)-Ioc-(Io×sin(120°-θ/cos30°)...(2)

Moreover, Ior(r) can be calculated by the formula (3).
Ior(r)=Ior(rt)-Ior(t)...(3)

For example, let us take the case where the leakage current (Io) detected by the leakage current detection unit 11 is "50.00 (mA)" and the phase angle (θ) detected by the phase angle detection unit 13 is "110°". Here, Ior in a delta-connected circuit can be calculated using formula (1).

Ior is calculated by substituting Io and θ into equation (1).
Ior(rt)=50× ^10-3 ×sin110°/cos30°=54.253(mA)

In addition, when "Io = 50.00 (mA)" and "θ = 110°", the minimum value of Ioc(rt) (Ioc(rt)MIN) is "-10.026 (mA)", the maximum value of Ioc(rt) (Ioc(rt)MAX) is "44.228 (mA)", and the median value of Ioc(rt) (Ioc(rt)CEN) is "((-10.026 + 44.228)/2 =) 17.101 (mA)".
When Ioc(rt) is a negative value, Ioc(rt)MIN is set to "0 (mA)."

(When the expected value of Ioc is set to the minimum value (Ioc(rt)MIN))
Here, a case where the expected value of Ioc is set to the minimum value (Ioc(rt)MIN) will be considered. Fig. 3 is a diagram that shows a schematic vector diagram when the expected value of Ioc is set to the minimum value (Ioc(rt)MIN). As described above, Ioc(rt)MIN is "0 (mA)", so "Io = Ior(rt)".

Ior(t) is calculated from equation (2) as follows:
Ior(t)=44.23(mA)

Moreover, Ior(r) is calculated from equation (3) as follows:
Ior(r)=10.02(mA)

(When the expected value of Ioc is set to the maximum value (Ioc(rt)MAX))
Next, the case where the expected value of Ioc is set to the maximum value (Ioc(rt)MAX) will be considered. Fig. 4 is a diagram that shows a schematic vector diagram when the expected value of Ioc is set to the maximum value (Ioc(rt)MAX). As described above, Ioc(rt)MAX is "44.228 (mA)".

Ior(t) is calculated from equation (2) as follows:
Ior(t)=0 (mA)

Moreover, Ior(r) is calculated from equation (3) as follows:
Ior(r)=54.253 (mA)

(When the expected value of Ioc is set to the median value (Ioc(rt)CEN))
Next, the case where the expected value of Ioc is set to the median value (Ioc(rt)CEN) will be considered. Fig. 5 is a diagram that shows a schematic vector diagram when the expected value of Ioc is set to the median value (Ioc(rt)CEN). As described above, Ioc(rt)CEN is "17.101 (mA)".

Ior(t) is calculated from equation (2) as follows:
Ior(t)=27.13 (mA)

Moreover, Ior(r) is calculated from equation (3) as follows:
Ior(r)=27.13 (mA)

(Inspection method)
Here, a description will be given of an inspection method using the inspection device 1. Fig. 6 is a flow chart illustrating the procedure of the inspection method.

In step ST1, the leakage current detection unit 11 detects the leakage current flowing in the measured electric line in which the first, second, and third phases are delta-connected (leakage current detection process).

In step ST2, the voltage detection unit 12 detects the voltage applied to the electric line to be measured (voltage detection process).

In step ST3, the phase angle detection unit 13 detects the phase angle based on the leakage current detected by the leakage current detection process and the voltage (reference voltage) detected by the voltage detection process (phase angle detection process).

In step ST4, the first calculation unit 14 calculates the possible range of the capacitive leakage current caused by the earth capacitance contained in the leakage current flowing through the measured electric line based on the leakage current detected by the leakage current detection process and the phase angle detected by the phase angle detection process (first calculation process).

In step ST5, the second calculation unit 15 calculates the possible range of the resistive component leakage current caused by the earth insulation resistance contained in the leakage current flowing through the measured electric line based on the possible range of the capacitive component leakage current calculated in the first calculation process, the phase angle detected in the phase angle detection process, and the leakage current detected in the leakage current detection process (second calculation process).

In this way, the inspection method calculates the possible range of Ioc from Io and the phase angle (θ), and calculates the possible range of Ior based on this possible range of Ioc, Io, and the phase angle (θ). This possible range of Ior can then be used to inspect or monitor the Δ-connected electric line under test.

(About the inspection program)
The inspection program, which calculates the possible range of Ior based on the possible range of Ioc, Io and the phase angle (θ) and inspects or monitors the Δ-connected electric line under test, is mainly composed of the following steps and is executed by a computer 500 (hardware).

Step 1: A step of detecting a leakage current flowing in a measured electric line having a first, second and third phases connected in a delta connection. Step 2: A step of detecting a voltage applied to the measured electric line. Step 3: A step of detecting a phase angle based on the leakage current detected in step 1 and the voltage (reference voltage) detected in step 2. Step 4: A step of calculating a possible range of a capacitive component leakage current caused by earth capacitance included in the leakage current flowing in the measured electric line based on the leakage current detected in step 1 and the phase angle detected in step 3. Step 5: A step of calculating a possible range of a resistive component leakage current caused by earth insulation resistance included in the leakage current flowing in the measured electric line based on the possible range of the capacitive component leakage current calculated in step 4, the phase angle detected in step 3 and the leakage current detected in step 1.

Here, the configuration and operation of computer 500 will be described with reference to the diagram. As shown in FIG. 7, computer 500 is configured with processor 501, memory 502, storage 503, input/output I/F 504, and communication I/F 505 connected on bus A, and these components work together to realize the functions and/or methods described in this disclosure.

The input/output I/F 504 is connected to, for example, a display that displays various information, and a touch panel that accepts user operations. The touch panel is located in front of the display. Thus, the user can perform intuitive operations by touching icons displayed on the display with his/her finger. The touch panel does not have to be located in front of the display. Also, instead of or together with the touch panel, a keyboard and a pointing device such as a mouse may be connected to the input/output I/F 504. Also, a speaker that outputs sound to the outside and a microphone that inputs sound from the outside may be connected to the input/output I/F 504.

The display is configured with a liquid crystal display or an organic EL (Electro Luminescence) display, and displays various information under the control of the processor 501.

Memory 502 is composed of RAM (Random Access Memory). The RAM is composed of volatile memory or non-volatile memory.

Storage 503 is composed of ROM (Read Only Memory). ROM is composed of non-volatile memory, and is realized, for example, by HDD (Hard Disc Drive) or SSD (Solid State Drive). Storage 503 stores various programs such as the inspection programs realized in steps 1 to 5 described above.

For example, the processor 501 controls the overall operation of the computer 500. The processor 501 is an arithmetic device that loads an operating system and various programs that realize various functions from the storage 503 into the memory 502 and executes the instructions contained in the loaded programs.

Specifically, when processor 501 receives a user operation, it reads a program (e.g., an inspection program) stored in storage 503, expands the read program in memory 502, and executes the program. In addition, by processor 501 executing the inspection program, the functions of leakage current detection unit 11, voltage detection unit 12, phase angle detection unit 13, first calculation unit 14, and second calculation unit 15 are realized.

Here, the configuration of the processor 501 will be described. The processor 501 is realized, for example, by a CPU (Central Processing Unit), an MPU (Micro Processing Unit), a GPU (Graphics Processing Unit), various other arithmetic devices, or a combination of these.

Furthermore, in order to realize the functions and/or methods described in this disclosure, some or all of the functions of the processor 501, memory 502, storage 503, etc. may be configured in a processing circuit 601, which is dedicated hardware, as shown in FIG. 8. The processing circuit 601 is, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination of these.

Although the processor 501 has been described as a single component, the present invention is not limited to this and may be configured as a collection of multiple physically separate processors. In this specification, a program or instructions included in the program described as being executed by the processor 501 may be executed by a single processor 501, or may be distributed and executed by multiple processors. Furthermore, a program or instructions included in the program executed by the processor 501 may be executed by multiple virtual processors.

The communication I/F 505 is an interface that complies with a specific communication standard and communicates with external devices via wired or wireless communication.

In this way, the inspection program is executed by the computer 500 to calculate the possible range of Ioc from Io and the phase angle (θ), and calculate the possible range of Ior based on this possible range of Ioc, Io, and the phase angle (θ). This possible range of Ior can then be used to inspect or monitor the Δ-connected electric line under test.

REFERENCE SIGNS LIST 1 Inspection device 10 Zero-phase current transformer 11 Leakage current detection unit 12 Voltage detection unit 13 Phase angle detection unit 14 First calculation unit 15 Second calculation unit

Claims (4)

a leakage current detection unit for detecting a leakage current flowing through a test electric line having a first phase, a second phase, and a third phase connected in a delta configuration;
A voltage detection unit that detects a voltage applied to the electric line under test;
a phase angle detection unit that detects a phase angle based on the leakage current detected by the leakage current detection unit and the voltage detected by the voltage detection unit;
a first calculation unit that calculates a possible range of a capacitive leakage current caused by an earth capacitance included in the leakage current flowing through the electric line under test, based on the leakage current detected by the leakage current detection unit and the phase angle detected by the phase angle detection unit;
a second calculation unit that calculates a possible range of a resistive component leakage current caused by an insulation resistance to ground, which is included in the leakage current flowing through the electric line under test, based on a possible range of the capacitive component leakage current calculated by the first calculation unit, the phase angle detected by the phase angle detection unit, and the leakage current detected by the leakage current detection unit ,
The second calculation unit calculates the resistive component leakage current based on the median of the capacitive component leakage current calculated by the first calculation unit, the phase angle detected by the phase angle detection unit, and the leakage current detected by the leakage current detection unit . The inspection device according to claim 1, wherein the second calculation unit calculates the resistive component leakage current based on a value selected from a range that the capacitive component leakage current can take, the phase angle detected by the phase angle detection unit, and the leakage current detected by the leakage current detection unit. a leakage current detection step of detecting a leakage current flowing in a test electric line in which a first phase, a second phase, and a third phase are delta-connected;
a voltage detection step of detecting a voltage applied to the electric line to be measured;
a phase angle detection step of detecting a phase angle based on the leakage current detected by the leakage current detection step and the voltage detected by the voltage detection step;
a first calculation step of calculating a possible range of a capacitive leakage current caused by an earth capacitance included in the leakage current flowing through the electric line under test, based on the leakage current detected in the leakage current detection step and the phase angle detected in the phase angle detection step;
and a second calculation step of calculating a resistive component leakage current caused by ground insulation resistance, which is included in the leakage current flowing through the measured electric line, based on the median of the capacitive component leakage current calculated in the first calculation step, the phase angle detected in the phase angle detection step, and the leakage current detected in the leakage current detection step. On the computer,
a leakage current detection step of detecting a leakage current flowing in a test electric line in which a first phase, a second phase, and a third phase are delta-connected;
a voltage detection step of detecting a voltage applied to the electric line to be measured;
a phase angle detection step of detecting a phase angle based on the leakage current detected by the leakage current detection step and the voltage detected by the voltage detection step;
a first calculation step of calculating a possible range of a capacitive leakage current caused by an earth capacitance included in the leakage current flowing through the electric line under test, based on the leakage current detected in the leakage current detection step and the phase angle detected in the phase angle detection step;
and a second calculation step of calculating a resistive component leakage current caused by ground insulation resistance contained in the leakage current flowing through the measured electric line based on the median value of the capacitive component leakage current calculated in the first calculation step, the phase angle detected in the phase angle detection step, and the leakage current detected in the leakage current detection step.

Images