Insulation resistance measuring device and insulation resistance measuring method

Abstract

To provide an insulation resistance measuring device capable of appropriately measuring insulation resistance.SOLUTION: The insulation resistance measuring device includes a first terminal, a second terminal, a voltage measuring unit for measuring the voltage between the first terminal and the second terminal, a voltage applying circuit for applying an applied voltage between the first terminal and the second terminal, and a control circuit which, in a first state where the impedance between the first terminal and the second terminal is set to a first value, acquires a first voltage value between the first terminal and the second terminal from the voltage measurement unit, in a second state where the impedance is set to a second value different from the first value, acquires a second voltage value between the first terminal and the second terminal from the voltage measurement unit, and when the absolute value of the difference between the first voltage value and the second voltage value is equal to or greater than a first threshold, measures the insulation resistance between the first terminal and the second terminal in a third state where the voltage applying circuit applies an applied voltage, and when the absolute value is smaller than the first threshold, does not measure the insulation resistance.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to an insulation resistance measuring device and an insulation resistance measuring method. [Background technology]

[0002] An insulation resistance measuring device is known that measures the insulation resistance between an earth terminal and a line terminal (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-82501 Summary of the Invention [Problem to be solved by the invention]

[0004] If the insulation resistance of the system being measured is measured without turning off the breaker, the insulation resistance measuring device may be damaged. Therefore, it is possible to avoid measuring the insulation resistance when a voltage is applied between the terminals. However, if the device determines that a voltage is applied between the terminals due to noise, it will be unable to measure the insulation resistance.

[0005] An object of the present disclosure is to provide an insulation resistance measuring device and an insulation resistance measuring method that are capable of appropriately measuring insulation resistance. [Means for solving the problem]

[0006] According to an embodiment of the present disclosure, an insulation resistance measuring device includes a first terminal, a second terminal, a voltage measurement unit that measures a voltage between the first terminal and the second terminal, a voltage application circuit that applies an application voltage between the first terminal and the second terminal, and a control circuit that, in a first state in which an impedance between the first terminal and the second terminal is set to a first value, acquires a first voltage value between the first terminal and the second terminal from the voltage measurement unit, and, in a second state in which the impedance is set to a second value different from the first value, acquires a second voltage value between the first terminal and the second terminal from the voltage measurement unit, and, in a third state in which the voltage application circuit applies an application voltage, measures the insulation resistance between the first terminal and the second terminal when the absolute value of the difference between the first voltage value and the second voltage value is equal to or greater than a first threshold, and does not measure the insulation resistance when the absolute value is smaller than the first threshold.

[0007] According to an embodiment of the present disclosure, an insulation resistance measurement method includes measuring a first voltage value between a first terminal and a second terminal in a first state in which an impedance between the first terminal and a second terminal is set to a first value, measuring a second voltage value between the first terminal and the second terminal in a second state in which the impedance is set to a second value different from the first value, measuring an insulation resistance between the first terminal and the second terminal in a third state in which an applied voltage is applied between the first terminal and the second terminal when the absolute value of the difference between the first voltage value and the second voltage value is equal to or greater than a first threshold, and not measuring the insulation resistance when the absolute value is smaller than the first threshold. [Effects of the Invention]

[0008] According to the present disclosure, insulation resistance can be measured appropriately. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram of a system under test in which the first embodiment is used. [Figure 2] FIG. 2 is a block diagram of the insulation resistance measuring device according to the first embodiment. [Figure 3]FIG. 3 is a flowchart showing the operation of the control circuit in the insulation resistance measuring device according to the comparative example. [Figure 4] FIG. 4 is a flowchart showing the operation of the control circuit in the insulation resistance measuring device according to the first embodiment. [Figure 5] FIG. 5 is a flowchart showing the operation of the control circuit in the insulation resistance measuring device according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The following embodiments are examples for embodying the technical ideas of the invention, and the present disclosure is not limited to the described configurations and numerical values. In each drawing, the same components are denoted by the same reference numerals, and duplicate explanations may be omitted as appropriate.

[0011] (First embodiment) Fig. 1 is a block diagram of a system under test in which the first embodiment is used. As shown in Fig. 1, the system under test 110 includes a power receiving facility 20 and a load 25. The power receiving facility 20 includes a transformer 21 and a breaker 22. The transformer 21 converts the voltage of a high-voltage distribution line 26 into the voltage of a low-voltage distribution line 27. The breaker 22 connects or disconnects the low-voltage distribution line 27 and a distribution line 28. The distribution line 28 supplies commercial power to the load 25.

[0012] The high-voltage distribution line 26 is, for example, a three-phase 6.6 kV system. The low-voltage distribution line 27 and the distribution line 28 are, for example, a three-phase three-wire 200 V system, a single-phase three-wire 200 / 100 V system, or a single-phase two-wire 100 V system. The high-voltage distribution line 26, the low-voltage distribution line 27, and the distribution line 28 are not limited to the above systems. The load 25 is, for example, a motor or a transformer. The insulation resistance R is the resistance between the distribution line 28 and the ground. For example, in a motor, the insulation resistance is the resistance between the distribution line 28 and the exterior, and in a transformer, the insulation resistance is the resistance between the distribution line 28 and the exterior or the resistance between the primary distribution line 28 and the secondary distribution line. The load 25 is not limited to a motor or a transformer.

[0013] 2 is a block diagram of the insulation resistance measuring device according to the first embodiment. The insulation resistance measuring device 100 includes a voltage application circuit 11, a voltage measurement unit 12, a discharge circuit 13, a switch 14, a current measurement unit 15, a control circuit 16, an input unit 18, an output unit 19, and terminals T1 and T2.

[0014] In FIG. 2, terminal T1 (first terminal) is grounded, and terminal T2 (second terminal) is connected to a power distribution line 28 (see FIG. 1). A voltage application circuit 11 applies an application voltage Va between terminals T1 and T2. The voltage of terminal T2 is, for example, positive relative to terminal T1. A voltage measurement unit 12 measures the voltage value between terminals T1 and T2. For example, the voltage measurement unit 12 has a resistor Rm. The voltage value measured by resistive division of the resistor Rm is output to the control circuit 16. The resistance value of the resistor Rm is, for example, 10 MΩ to 500 MΩ, and is 10 MΩ as an example.

[0015] The discharge circuit 13 is electrically connected between terminals T1 and T2. The discharge circuit 13 has a resistor Rd having one end connected to terminal T1 and the other end connected to terminal T2. The resistance value of the resistor Rd is, for example, 100 kΩ to 1 MΩ, and is, for example, 500 kΩ. The resistance value of the resistor Rd is lower than the resistance value of the resistor Rm. The switch 14 electrically connects the discharge circuit 13 between terminals T1 and T2 or electrically disconnects the discharge circuit 13 from terminal T1 based on a control signal from the control circuit 16. The switch 14 may be provided between the discharge circuit 13 and terminal T2.

[0016] In FIG. 2 , the current measurement unit 15 measures the current flowing between terminal T1 and terminal T2. For example, the current measurement unit 15 measures the current value of the current flowing from the voltage application circuit 11 to terminal T1. The current measurement unit 15 outputs the measured current value to the control circuit 16. The control circuit 16 acquires the voltage value measured by the voltage measurement unit 12 and the current value measured by the current measurement unit 15. For example, the outputs of the voltage measurement unit 12 and the current measurement unit 15 are analog signals. The control circuit 16 converts the analog signals output by the voltage measurement unit 12 and the current measurement unit 15 into digital signals and acquires the converted signals as voltage and current values, respectively. The control circuit 16 controls the voltage application circuit 11 and the switch 14 based on the acquired voltage and current values. The control circuit 16 calculates the insulation resistance based on the voltage and current values. At least some of the functions of the control circuit 16 may be executed by a processor such as a CPU (Central Processing Unit) in cooperation with software. At least some of the functions of the control circuit 16 may be executed by a dedicated hardware circuit.

[0017] The voltage measured by the voltage measurement unit 12 may be either an AC voltage or a DC voltage. The voltage measurement unit 12 may include an AC / DC determination circuit and a rectifier circuit. For example, the AC / DC determination circuit includes a comparator. The comparator compares a reference voltage with the resistively divided voltage. The AC / DC determination circuit determines the measured voltage as an AC voltage if the output of the comparator alternates between high and low levels for a predetermined period of time. The AC / DC determination circuit determines the measured voltage as a DC voltage if the output of the comparator remains high or low for a predetermined period of time. If the measured voltage is determined to be an AC voltage, the rectifier circuit rectifies the measured voltage. The rectifier circuit may be a full-wave rectifier circuit or a half-wave rectifier circuit. The voltage measurement unit 12 does not necessarily have to include the AC / DC determination circuit and the rectifier circuit. In this case, the control circuit 16 may convert the analog signal output by the voltage measuring unit 12 into a digital signal, and use the digital signal to determine whether the output signal of the voltage measuring unit 12 is AC or DC.

[0018] The input unit 18 is a switch, button, or key, and a user operates the input unit 18 when measuring insulation resistance using the insulation resistance measuring device 100. The output unit 19 is an interface with a display device or external device, and outputs the resistance value of the measured insulation resistance and error information.

[0019] 1, when measuring insulation resistance R, the user turns off breaker 22. Then, the user uses a voltage detector or voltmeter to check whether or not voltage is being supplied to distribution line 28. After checking that no voltage is being supplied to distribution line 28, the user grounds terminal T1 of insulation resistance measuring device 100, connects terminal T2 to one of distribution lines 28, and measures insulation resistance R.

[0020] In this case, if the user connects terminals T1 and T2 of insulation resistance measuring device 100 to ground and power line 28, respectively, and measures insulation resistance R without turning off breaker 22 and checking the voltage, insulation resistance R cannot be measured accurately. In addition, insulation resistance measuring device 100 may be damaged. Therefore, in the comparative example, when a voltage is applied between terminals T1 and T2, insulation resistance measuring device 100 does not measure the insulation resistance and notifies the user of an error.

[0021] (Flowchart in Comparative Example) 3 is a flowchart showing the operation of the control circuit in the insulation resistance measuring device according to the comparative example. As shown in FIG. 3, the control circuit 16 starts measurement (step S10). For example, a user grounds the terminal T1 and connects the terminal T2 to the power distribution line 28. Next, the control circuit 16 enters the first state (step S11). Specifically, the voltage application circuit 11 does not generate the application voltage Va, and the switch 14 is turned off. Next, the control circuit 16 acquires the voltage value V1 from the voltage measurement unit 12 (step S12).

[0022] Next, the control circuit 16 determines whether the acquired voltage value V1 is equal to or greater than the threshold value Th2 (step S22). If the result is No, the control circuit 16 changes the first state to the third state (step S16). Specifically, the switch 14 remains off, and the voltage application circuit 11 generates the applied voltage Va. Next, the control circuit 16 measures the insulation resistance R (step S17). Specifically, the control circuit 16 calculates the resistance value of the insulation resistance R from the voltage value V of the voltage measurement unit 12 and the current value I of the current measurement unit 15. Next, the control circuit 16 outputs the calculated resistance value of the insulation resistance R to the output unit 19 (step S18). Next, the control circuit 16 ends the measurement (step S19). Then, the process ends.

[0023] If the answer is Yes in step S22, the control circuit 16 ends the measurement (step S20). Next, the control circuit 16 outputs error information to the output unit 19 (step S21). Then, the process ends. When the user recognizes the error, the user turns off the breaker 22 and checks whether there is voltage in the distribution line 28, and then presses the measurement key again.

[0024] In the comparative example, even if the user presses the measurement key, if a voltage equal to or greater than the threshold value Th2 is applied between terminals T1 and T2, the measurement of insulation resistance is not started and the measurement is terminated. This prevents the measurement of insulation resistance from being started when a voltage is applied to the power distribution line 28 in FIG. 1.

[0025] In FIG. 1, if a live distribution line 30 is present near the distribution line 28, stray capacitance Cf between the distribution lines 28 and 30 may cause induced noise on the distribution line 28. In addition to the distribution line 30, noise 32 may also be generated due to radiation noise from adjacent equipment. For example, if the voltage of the distribution line 30 is 6.6 kV, noise 32 with an effective value of approximately 100 V may be applied to the distribution line 28 depending on the stray capacitance Cf. In particular, if the internal impedance between terminals T1 and T2 is high, the voltage of the noise 32 will be high. When noise 32 is applied to the distribution line 28, the insulation resistance measuring device 100 may determine that a voltage is applied between terminals T1 and T2, failing to measure the insulation resistance and informing the user of an error.

[0026] Therefore, in the first embodiment, the internal impedance between terminals T1 and T2 is varied and the voltage between terminals T1 and T2 is measured. When a commercial power supply voltage is supplied to distribution line 28, the impedance between distribution line 28 of the commercial power supply is low, so that the AC voltage between terminals T1 and T2 remains almost unchanged even when the internal impedance is varied.

[0027] When noise 32 is applied to the power distribution line 28, the AC voltage between terminals T1 and T2 is a voltage divided by the impedance between terminals T1 and T2 and stray capacitance Cf. Therefore, the AC voltage between terminals T1 and T2 varies depending on the impedance between terminals T1 and T2. Therefore, in the first embodiment, the AC voltage between terminals T1 and T2 is measured using different internal impedances, and if the measured voltages differ, it is determined to be induced noise and the insulation resistance measurement continues. This will be explained in detail below.

[0028] (Flowchart in the first embodiment)

[0029] 4 is a flowchart showing the operation of the control circuit in the insulation resistance measuring device according to the first embodiment. As shown in FIG. 4, the control circuit 16 starts measurement (step S10). For example, the user grounds terminal T1 and connects terminal T2 to the power distribution line 28. Then, the user presses the measurement key. When the measurement start key is pressed, the control circuit 16 starts measurement.

[0030] As shown in FIG. 4, the control circuit 16 is set to the first state (step S11). Specifically, the control circuit 16 does not generate the applied voltage Va to the voltage application circuit 11, and sets the voltage application circuit 11 to a high impedance. The control circuit 16 turns off the switch 14, electrically disconnecting the discharge circuit 13 from the terminal T2. In the first state, the impedance between the terminals T1 and T2 is the internal resistance Rm of the voltage measurement unit 12. Next, the control circuit 16 acquires a voltage value V1 from the voltage measurement unit 12 (step S12). The voltage value V1 is an AC voltage value, for example, an effective value.

[0031] Next, the control circuit 16 switches to the second state (step S13). Specifically, the control circuit 16 does not generate the applied voltage Va in the voltage application circuit 11, turns on the switch 14, and electrically connects the discharge circuit 13 to the terminal T2. In the second state, the impedance between the terminals T1 and T2 is the resistance Rd of the discharge circuit 13. Next, the control circuit 16 acquires a voltage value V2 from the voltage measurement unit 12 (step S14). The voltage value V2 is an AC voltage value, for example, an effective value.

[0032] Next, the control circuit 16 determines whether the absolute value |V1-V2| of the difference between the voltage values ​​V1 and V2 is equal to or greater than the threshold value Th1 (step S15). If the determination is Yes, the control circuit 16 sets the second state to the third state (step S16). Specifically, the control circuit 16 turns off the switch 14 and causes the voltage application circuit 11 to generate an application voltage Va. The application voltage Va is, for example, a DC voltage. Next, the control circuit 16 measures the insulation resistance R (step S17). Specifically, the control circuit 16 acquires the voltage value V and the current value I from the voltage measurement unit 12 and the current measurement unit 15, respectively. The control circuit 16 calculates the resistance value of the insulation resistance R from the voltage value V and the current value I. For example, the control circuit 16 calculates V / I as the resistance value of the insulation resistance R.

[0033] Next, the control circuit 16 outputs the calculated resistance value of the insulation resistance R (step S18). Specifically, if the output unit 19 is a display unit, the resistance value of the insulation resistance R is displayed on the display unit. Alternatively, if the output unit 19 is an interface with an external device, the resistance value of the insulation resistance R is output to the external device. Next, the control circuit 16 ends the measurement (step S19). Specifically, it causes the voltage application circuit 11 to end the application of the application voltage Va. For example, when the user confirms the measured value of the insulation resistance R and presses the measurement key, the control circuit 16 ends the measurement. Then, the process ends.

[0034] If the result in step S15 is No, the control circuit 16 ends the measurement (step S20). Specifically, the control circuit 16 turns off the switch 14 and ends the application of the applied voltage Va to the voltage application circuit 11. Next, the control circuit 16 outputs error information (step S21). Specifically, if the output unit 19 is a display unit, an error is displayed on the display unit. Alternatively, if the output unit 19 is an interface with an external device, the error information is output to the external device. Then, the process ends. When the user recognizes the error, the user turns off the breaker 22 and checks whether or not there is voltage in the distribution line 28, and then presses the measurement key again.

[0035] According to the first embodiment, the control circuit 16 sets the impedance between the terminal T1 (first terminal) and the terminal T2 (second terminal) to a first value R1 as in step S11 of FIG. 4 . In the first state, the control circuit 16 acquires a voltage value V1 (first voltage value) between the terminals T1 and T2 from the voltage measurement unit 12 as in step S12. In the second state, the control circuit 16 sets the impedance between the terminals T1 and T2 to a second value R2 as in step S13. In the second state, the control circuit 16 acquires a voltage value V2 (second voltage value) between the terminals T1 and T2 from the voltage measurement unit 12 as in step S14. When the absolute value |V1-V2| of the difference between the voltage values ​​V1 and V2 is equal to or greater than a threshold value Th1 (first threshold value) as in step S15 (Yes), the control circuit 16 sets the voltage application circuit 11 to a third state in which the application voltage Va is applied as in step S16. The control circuit 16 measures the insulation resistance R between the terminals T1 and T2 as in step S17. The control circuit 16 does not measure the insulation resistance R when |V1-V2| is smaller than the threshold value Th1 as in No in step S15.

[0036] This allows the device to determine whether the voltage applied between terminals T1 and T2 is a commercial power supply or induced noise, and if it is determined to be induced noise, it can measure the insulation resistance.

[0037] A resistor Rd (first resistor) is connected between terminals T1 and T2. The control circuit 16 electrically disconnects the resistor Rd from at least one of the terminals T1 and T2 when the first state is selected. The control circuit 16 connects the resistor Rd between the terminals T1 and T2 when the second state is selected. This allows the first value R1 and the second value R2 to be different from each other.

[0038] The first resistor is a resistor Rd for discharging between terminals T1 and T2. This allows the insulation resistance measuring device to be made smaller and less expensive. The first resistor may be provided separately from the discharge circuit 13.

[0039] The first value of the impedance in the first state is set to the internal impedance of the voltage application circuit 11. This allows the insulation resistance measuring device to be made smaller and less expensive. A resistor may be provided to set the impedance to the first value in the first state.

[0040] Induction noise often occurs as an AC component in the power distribution line 28. Therefore, the voltage values ​​V1 and V2 are set to AC voltage values. This makes it possible to determine whether the voltage between terminals T1 and T2 is the AC voltage of the commercial power supply or the AC voltage of induction noise. The voltage values ​​V1 and V2 may also be DC voltage values.

[0041] When the applied voltage Va supplied by the voltage application circuit 11 is a DC voltage, the measurement accuracy of the insulation resistance does not decrease even if AC induction noise occurs. Therefore, it is preferable that the applied voltage Va is a DC voltage. However, the applied voltage Va may also be an AC voltage.

[0042] As in step S21, the control circuit 16 outputs error information, which allows the user to recognize that voltage is being supplied to the power distribution line 28. The user can confirm that the breaker 22 is disconnected and the voltage between the power distribution lines 28.

[0043] From the viewpoint of differentiating the voltage values ​​V1 and V2 of the induced noise, the first impedance value is preferably at least twice or at most half the second impedance value. The larger of the first and second impedance values ​​is, for example, 1 MΩ to 100 MΩ, and the smaller of the first and second impedance values ​​is, for example, 100 kΩ to 1 MΩ.

[0044] From the viewpoint of not determining that commercial power is induced noise, it is preferable that threshold value Th1 be, for example, 1 / 10 or more of the voltage of the commercial power (effective value in the case of AC). If threshold value Th1 is too large, the induced noise will be determined to be commercial power. Therefore, from the viewpoint of not determining that induced noise is commercial power, threshold value Th1 is preferably 1 / 2 or less of the voltage of the commercial power. Since commercial power is 100V or more, threshold value Th1 is preferably 10V or more. It is preferable that threshold value Th1 (effective value in the case of AC) be 50V or less.

[0045] The threshold value Th1 may be changed depending on the voltage values ​​V1 and V2. For example, when the voltage value V1 is large, the threshold value Th1 can be increased, and when the voltage value V1 is small, the threshold value Th1 can be decreased. For example, the threshold value Th1 may be determined by multiplying a predetermined value by the voltage value V1. The threshold value Th1 may be determined by multiplying a predetermined value by |V1-V2|. The threshold value Th1 may be set based on the rate of change between V1 and V2, |V1-V2| / V1. For example, the threshold value Th1 may be set so that |V1-V2| / V1 is a predetermined value (e.g., 0.1).

[0046] (Second embodiment) Fig. 5 is a flowchart showing the operation of the control circuit in the insulation resistance measuring device according to the second embodiment. As shown in Fig. 5, after step S12, the control circuit 16 determines whether the acquired voltage value V1 is equal to or greater than the threshold value Th2 (step S22). If the result is Yes, the process proceeds to step S13. If the result is No in step S22, the process proceeds to step S16. The subsequent flow is the same as that shown in Fig. 4 of the first embodiment.

[0047] According to the second embodiment, when the voltage value V1 is equal to or greater than the threshold value Th2 (second threshold value) as in step S22 (Yes), the control circuit 16 acquires the voltage value V2 in the second state as in steps S13 and S14. When the voltage value V1 is smaller than the threshold value Th2 as in step S22 (No), the control circuit 16 does not acquire the voltage value V2 and measures the insulation resistance in the third state as in step S17.

[0048] When the voltage value V1 is equal to or less than the threshold value Th2, it can be determined that the commercial power supply voltage is not being applied to the power distribution line 28 without acquiring the voltage value V2. Therefore, when the voltage value V1 is equal to or less than the threshold value Th2, the insulation resistance is measured without measuring the voltage value V2. This simplifies the flow.

[0049] For example, threshold value Th2 is preferably 1 / 10 or more of the commercial power supply voltage (effective value in the case of AC), and more preferably 1 / 20 or more. If threshold value Th2 is too large, it may be determined that commercial power is not being applied even when it is actually being applied. From this perspective, threshold value Th2 is preferably 9 / 10 or less of the commercial power supply voltage, and more preferably 8 / 10 or less. Since commercial power supplies are 100V or more, threshold value Th2 is preferably 10V or more, and more preferably 20V or more. Threshold value Th2 is preferably 90V or less, and more preferably 80V or less.

[0050] Although the embodiments have been described above, they are presented as examples and the present invention is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims. [Explanation of symbols]

[0051] 11: Voltage application circuit 12: Voltage measurement section 13:Discharge circuit 14: Switch 15: Current measurement section 16: Control circuit 18: Input section

Claims

1. A first terminal; A second terminal; a voltage measurement unit that measures a voltage between the first terminal and the second terminal; a voltage application circuit that applies a voltage between the first terminal and the second terminal; acquiring a first voltage value between the first terminal and the second terminal from the voltage measurement unit in a first state in which an impedance between the first terminal and the second terminal is set to a first value; In a second state in which the impedance is set to a second value different from the first value, a second voltage value between the first terminal and the second terminal is acquired from the voltage measurement unit; When an absolute value of a difference between the first voltage value and the second voltage value is equal to or greater than a first threshold value, in a third state in which the voltage application circuit applies an application voltage, the insulation resistance between the first terminal and the second terminal is measured; a control circuit that does not measure the insulation resistance when the absolute value is smaller than the first threshold value; An insulation resistance measuring device comprising:

2. a first resistor connected between the first terminal and the second terminal; 2. The insulation resistance measuring device according to claim 1, wherein the control circuit electrically disconnects the first resistor from at least one of the first terminal and the second terminal when the device is in the first state, and connects the first resistor between the first terminal and the second terminal when the device is in the second state.

3. 3. The insulation resistance measuring device according to claim 2, wherein the first resistor is a resistor for discharging between the first terminal and the second terminal.

4. 4. The insulation resistance measuring device according to claim 2, wherein the first value is an internal impedance of the voltage measuring unit.

5. The insulation resistance measuring device according to claim 1 , wherein the first voltage value and the second voltage value are AC voltage values.

6. 6. The insulation resistance measuring device according to claim 5, wherein the applied voltage is a DC voltage.

7. 4. The insulation resistance measuring device according to claim 1, wherein the control circuit outputs error information without measuring the insulation resistance when the absolute value is greater than the first threshold value.

8. The control circuit When the first voltage value is equal to or greater than a second threshold, the second voltage value is acquired in the second state; 4. The insulation resistance measuring device according to claim 1, wherein when the first voltage value is smaller than a second threshold value, the second voltage value is not acquired and the insulation resistance is measured in the third state.

9. measuring a first voltage value between the first terminal and the second terminal in a first state in which an impedance between the first terminal and the second terminal is set to a first value; measuring a second voltage value between the first terminal and the second terminal in a second state in which the impedance is set to a second value different from the first value; measuring an insulation resistance between the first terminal and the second terminal in a third state in which an applied voltage is applied between the first terminal and the second terminal when an absolute value of a difference between the first voltage value and the second voltage value is equal to or greater than a first threshold value; When the absolute value is smaller than the first threshold value, the insulation resistance is not measured.

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