Insulation resistance meter

Abstract

To enhance the measurement accuracy of capacitance while shortening the measurement time in an insulation resistance meter.SOLUTION: The insulating resistance meter 1 includes a voltage generation part 10 for generating a voltage to be applied to the measuring object 2, a voltage detection part 30 for detecting the voltage of the DC voltage, and a processing part 70 for calculating the resistance Rx of the insulating resistance 2A of the measuring object 2 by using the voltage of the DC voltage and the detected leakage current. An insulation resistance meter 1 includes a discharge resistor 40 for discharging a measuring object 2, a switch 50 for making a discharge current flow from the measuring object 2 to the discharge resistor 40, and a control part 80 for switching the switch 50 from a non-conductive state to a conductive state so that the discharge current is output from the measuring object 2. The processor 70 calculates the capacitance Cx of the electrostatic capacitance V1 in the target 2 based on the discharge time Tc, the resistance Rc of the discharge resistor 40, and the resistance Rx of the insulating resistance V2 in the target 2, the discharge time Tc being the time required for the voltage detected by the voltage detector 30 to decrease from the first reference voltage 2A to the second reference voltage 2B while the switch 50 is in the conductive state.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an insulation resistance meter that measures leakage current from a measurement object represented by an equivalent circuit in which insulation resistance and capacitance are connected in parallel with each other while a DC voltage is applied to the measurement object. [Background technology]

[0002] Patent Document 1 discloses a technique for charging a capacitor with a constant current for a predetermined time and measuring the capacitance of the capacitor from the constant current value, the charging time, and the differential voltage between the initial voltage of the capacitor and the final voltage at the end of charging. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-197308 Summary of the Invention [Problem to be solved by the invention]

[0004] Some objects to be measured by insulation resistance meters can be represented by an equivalent circuit in which capacitance is connected in parallel to the insulation resistance. Therefore, the above-mentioned technology can also be applied to insulation resistance meters. However, when the above-mentioned technology is applied, if the measurement method measures the capacitance after measuring the insulation resistance of the object to be measured, the object to be measured must first be discharged and then charged again, which takes time to measure the capacitance.

[0005] Furthermore, it is possible that the resistance of the insulation resistor connected in parallel to the capacitance of the object being measured by the insulation resistance meter may be lower than the resistance of the discharge resistor inside the insulation resistance meter. In such cases, a charging current will be more likely to flow through the insulation resistor of the object being measured, which will reduce the final voltage of the object being measured and reduce the accuracy of the capacitance measurement.

[0006] The present invention has been made in view of these problems, and has as its object to improve the measurement accuracy of capacitance while shortening the measurement time in an insulation resistance tester. [Means for solving the problem]

[0007] According to one aspect of the present invention, an insulation resistance meter detects a leakage current flowing through an object to be measured, the object being represented by an equivalent circuit in which an insulation resistance and a capacitance are connected in parallel, while a DC voltage is applied to the object to be measured. The insulation resistance meter includes: a voltage generator that generates a voltage to apply the DC voltage from the output terminals of the insulation resistance meter to the object to be measured; a voltage detector that detects the voltage value of the DC voltage; and a processor that calculates the resistance value of the insulation resistance of the object to be measured using the voltage value of the DC voltage and a detected value of the leakage current. The insulation resistance meter also includes a discharge resistor that discharges the object to be measured, a switch that causes a discharge current to flow from the object to be measured to the discharge resistor, and a controller that switches the switch from a non-conductive state to a conductive state after the detected value of the leakage current is obtained so that the discharge current is output from the object to be measured. The processing unit calculates the capacitance value of the capacitance of the object to be measured based on the discharge time until the voltage value detected by the voltage detection unit while the switch is in the conductive state drops from the first threshold value to the second threshold value, the resistance value of the discharge resistor, and the resistance value of the insulation resistor of the object to be measured. [Effects of the Invention]

[0008] According to this aspect, after measuring the insulation resistance of the object to be measured, the switch of the discharge resistor is switched from a non-conductive state to a conductive state to discharge the object to be measured, thereby measuring the capacitance of the object to be measured. Therefore, compared to a general process in which the capacitance of the object to be measured is measured while the object to be measured is being charged, there is no need to charge the object to be measured, and therefore the measurement time can be shortened.

[0009] Furthermore, when calculating the capacitance value of the capacitance to be measured, the resistance value of the insulation resistor connected in parallel to the capacitance to be measured is used in addition to the discharge time until the voltage value of the DC voltage drops from the first threshold to the second threshold and the resistance value of the discharge resistor.

[0010] For example, when the resistance value of the insulation resistance of the object to be measured is lower than the resistance value of the discharge resistor of the insulation resistance meter, the discharge current output from the capacitance of the object to be measured is more likely to flow to the insulation resistance of the object to be measured than when the insulation resistance is higher than the discharge resistor, and the discharge current flowing to the discharge resistor of the insulation resistance meter decreases.

[0011] As a countermeasure, when measuring the capacitance of the object to be measured, the resistance value of the insulation resistor of the object to be measured is used in addition to the discharge resistance of the insulation resistance meter, which makes it possible to take into account the decrease in discharge current in the discharge resistor caused by the insulation resistance of the object to be measured, thereby preventing a decrease in the measurement accuracy of the capacitance of the object to be measured.

[0012] Therefore, according to this aspect, it is possible to shorten the measurement time in the insulation resistance meter while improving the measurement accuracy of the capacitance. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a circuit diagram showing the circuit configuration of an insulation resistance tester according to the first embodiment. [Figure 2] FIG. 2 is an explanatory diagram showing the operation of the insulation resistance meter. [Figure 3] FIG. 3 is a circuit diagram showing the circuit configuration of an insulation resistance tester according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In this specification, the same or equivalent elements are designated by the same reference numerals throughout.

[0015] (First embodiment) FIG. 1 is a circuit diagram showing the circuit configuration of an insulation resistance tester 1 according to the first embodiment.

[0016] The insulation resistance meter 1 is a measuring device for measuring the insulation resistance of, for example, a household distribution board, power receiving equipment in buildings and factories, a transformer, a motor, and the like.

[0017] Insulation resistance meter 1 detects leakage current flowing from object to be measured 2 to detection terminal T2 while outputting output voltage Vout, which is a DC voltage, from output terminal T1 and applying it to object to be measured 2. Insulation resistance meter 1 then calculates the insulation resistance of object to be measured 2 by dividing the voltage value of output voltage Vout by the detected value of the leakage current.

[0018] A pair of cables with probes at the tips are connected to the output terminal T1 and the detection terminal T2, respectively, and the pair of probes are brought into contact with both ends of the object 2 to be measured by the measurer.

[0019] The insulation resistance meter 1 of the first embodiment performs constant current control to keep the leakage current flowing through the object to be measured 2 constant when the output voltage Vout is less than a predetermined voltage value, and performs constant voltage control to keep the output voltage Vout constant when the output voltage Vout reaches the predetermined voltage value.

[0020] The insulation resistance meter 1 may be configured to perform constant current control to keep the leakage current flowing through the object to be measured 2 constant when the insulation resistance 2A of the object to be measured 2 is less than a predetermined resistance value, and to perform constant voltage control to keep the output voltage Vout constant when the insulation resistance 2A of the object to be measured 2 is equal to or greater than the predetermined resistance value.

[0021] The object to be measured 2 of the insulation resistance meter 1 in the first embodiment can be represented by an equivalent circuit in which an insulation resistance 2A and a capacitance 2B are connected in parallel to each other. Therefore, the insulation resistance meter 1 in the first embodiment measures not only the insulation resistance 2A of the object to be measured 2, but also the capacitance 2B connected in parallel to the insulation resistance 2A.

[0022] The insulation resistance meter 1 of the first embodiment performs at least a first measurement process (resistance measurement process) to measure the insulation resistance 2A of the object to be measured 2 by performing constant voltage control, and then performs a second measurement process (capacity measurement process) to measure the capacitance 2B of the object to be measured 2 by performing discharge control to discharge the object to be measured 2.

[0023] The insulation resistance meter 1 includes a voltage generating unit 10, a limiting resistance element 20, a voltage detecting unit 30, a discharge resistor 40, a switch 50, a leakage current detecting unit 60, a processing unit 70, and a control unit 80.

[0024] The voltage generating unit 10 generates an output voltage Vout to be applied to the device under test 2. The voltage generating unit 10 includes an AC source 11, a rectifying element 12, a capacitive element 13, and a switch 14.

[0025] The AC source 11 is a generating circuit that generates an AC voltage. The AC source 11 is composed of, for example, a battery of several volts, a transformer for boosting the battery voltage, and a switching element for supplying and cutting off the battery voltage to the primary winding of the transformer.

[0026] The rectifying element 12, together with the capacitance element 13, is an element that converts the AC voltage of the AC source 11 into a DC voltage. In the first embodiment, a diode is used as the rectifying element 12, and the anode of the rectifying element 12 is connected to one end of the AC source 11, and the cathode of the rectifying element 12 is connected to one end of the capacitance element 13.

[0027] The capacitance element 13, together with the rectifying element 12, is an element that converts the AC voltage of the AC source 11 into a DC voltage, and is a so-called smoothing capacitor. The capacitance value of the capacitance element 13 is designed to be, for example, within a range from several tens of nF to several hundreds of nF.

[0028] One end of the capacitance element 13 is connected to the cathode of the rectifier element 12 , and the other end of the capacitance element 13 is connected to the other end of the AC source 11 .

[0029] Switch 14 is a switching device that protects limiting resistor element 20 when an external voltage is applied between output terminal T1 and detection terminal T2 of insulation resistance meter 1. Switch 14 is connected between the other end of AC source 11 and the other end of capacitive element 13 and ground potential G. Ground potential G is a reference potential that serves as a reference when insulation resistance meter 1 operates.

[0030] The internal state of switch 14 is switched between a conductive state and a non-conductive state in response to an instruction from control unit 80. When constant current control and constant voltage control are performed by control unit 80, switch 14 is switched to a conductive state, after which voltage output to output terminal T1 is stopped and discharge control is performed. Switch 14 remains in a conductive state while measurement object 2 is being discharged, and when capacitance measurement is completed and output voltage Vout drops to a non-hazardous low voltage, control unit 80 switches switch 14 to a non-conductive state.

[0031] The limiting resistor 20 is a resistor that limits the current input to the output terminal T1 of the insulation resistance meter 1 when an external voltage is applied to the output terminal T1 of the insulation resistance meter 1. The resistance value Ro of the limiting resistor 20 is designed to be, for example, within a range of up to several hundred kΩ. In the first embodiment, the resistance value Ro of the limiting resistor 20 is designed to be 100 kΩ.

[0032] The limiting resistor 20 is connected between one end of the capacitive element 13 and the output terminal T1 of the insulation resistance meter 1. Specifically, one end of the limiting resistor 20 is connected to one end of the capacitive element 13, and the other end of the limiting resistor 20 is connected to the output terminal T1 of the insulation resistance meter 1.

[0033] The voltage detection unit 30 detects the voltage value of the connection line L1 extending between the other end of the limiting resistance element 20 and the connection point of the discharge resistor 40. The voltage detection unit 30 of the first embodiment is connected between the connection line L1 and the ground potential G.

[0034] The voltage detection unit 30 of the first embodiment is a voltage dividing circuit configured by voltage dividing resistor elements 31 and 32 connected in series to each other. The resistance values ​​of the voltage dividing resistor elements 31 and 32 are designed to be, for example, several hundred MΩ, and in the first embodiment, are designed to be, for example, approximately 300 MΩ.

[0035] In the voltage detection unit 30, one end of the voltage dividing resistor element 31 is connected to the connection line L1, the other end of the voltage dividing resistor element 31 is connected to one end of the voltage dividing resistor element 32, and the other end of the voltage dividing resistor element 32 is connected to the ground potential G.

[0036] The voltage detection unit 30 outputs a divided voltage signal generated at the connection point between the voltage dividing resistor elements 31 and 32 as a detection signal of the output voltage Vout to the processing unit 70. The output signal of the voltage detection unit 30 is used by the control unit 80 for constant voltage control.

[0037] Discharge resistor 40 is a resistor for discharging the charge accumulated in capacitance 2B of measurement object 2. Discharge resistor 40 of the first embodiment is made up of discharge resistance elements 41 and 42 that can be connected in series.

[0038] The resistance value of the discharge resistance element 41 is designed to be, for example, several hundred kΩ, and in the first embodiment, is designed to be, for example, 600 kΩ. On the other hand, the resistance value of the discharge resistance element 42 is designed to be several hundred Ω, and in the first embodiment, is designed to be, for example, 100 Ω.

[0039] The discharge resistance element 42 is installed to detect failures in the discharge resistance element 41 and the switch 50. Specifically, the voltage of the discharge resistance element 42 is output to the processing unit 70 via a signal line (not shown), and the processing unit 70 determines whether or not a failure has occurred.

[0040] One end of the discharge resistance element 41 is connected to the connection line L1, and the other end of the discharge resistance element 41 is connected to one end of the switch 50. The other end of the switch 50 is connected to one end of the discharge resistance element 42, and the other end of the discharge resistance element 42 is connected to the ground potential G.

[0041] The switch 50 is a switching device for passing a discharge current from the capacitance 2B of the object to be measured 2 to the discharge resistor 40. The internal state of the switch 50 is switched between a conductive state and a non-conductive state according to instructions from the control unit 80. When the control unit 80 executes discharge control, the switch 50 is switched to the conductive state.

[0042] Leakage current detection unit 60 detects the magnitude of the leakage current flowing through measurement object 2. Specifically, leakage current detection unit 60 detects the magnitude of the leakage current flowing in from detection terminal T2 of insulation resistance meter 1.

[0043] The leakage current detection unit 60 is configured by, for example, an IV conversion circuit and an AD conversion circuit. The leakage current detection unit 60 outputs a detection signal indicating the magnitude of the detected leakage current to the processing unit .

[0044] The processing unit 70 is a computer that includes a processing unit such as a CPU, a storage device, a display device, an input device, a network connection device, and the like.

[0045] The processing unit 70 calculates a measured amount of insulation resistance 2A of the object to be measured 2 using the output signal of the voltage detection unit 30 and the output signal of the leakage current detection unit 60 while executing constant voltage control on the voltage generation unit 10. Thereafter, the processing unit 70 calculates a measured amount of capacitance 2B of the object to be measured 2 using the output signal of the voltage detection unit 30 while executing discharge control on the object to be measured 2.

[0046] The processing unit 70 of the first embodiment includes a calculation unit 71 and a display unit 72.

[0047] The calculation unit 71 uses the detection value of the leakage current detected by the leakage current detection unit 60 and the voltage value of the output voltage Vout to calculate the resistance value Rx of the insulation resistance 2A of the object to be measured 2. The voltage value of the output voltage Vout may be the detection value of the output voltage Vout detected by the voltage detection unit 30 or the set value of the output voltage Vout set in the control unit 80.

[0048] In addition, the calculation unit 71 calculates the capacitance value of the electrostatic capacitance 2B of the object to be measured 2 based on the discharge time of the object to be measured 2 measured while the switch 50 is in a conductive state, the resistance value of the discharge resistor 40, and the resistance value of the insulation resistor 2A of the object to be measured 2.

[0049] The discharge time of the object to be measured 2 is the time required for the voltage value detected by the voltage detection unit 30 to decrease from the first threshold value to the second threshold value during the discharge of the object to be measured 2. The first threshold value and the second threshold value are values ​​determined so as to have a relatively small effect on the measurement accuracy of the capacitance 2B.

[0050] In this regard, the inventor has found that it is preferable to set the first threshold value and the second threshold value sufficiently low relative to the output voltage Vout in order to suppress the influence of the limiting resistance element 20, while it is preferable to set them close to the output voltage Vout in order to suppress the influence of the capacitance element 13.

[0051] For this reason, in the first embodiment, the first threshold value and the second threshold value are determined in advance based on the limiting resistor 20 and the capacitor 13 so as to avoid a range in which the measurement accuracy of the capacitance 2B is affected, particularly by the resistance value Ro of the limiting resistor 20 and the capacitance value Cs of the capacitor 13. For example, the first threshold value is set to approximately 160 [V], and the second threshold value is set to approximately 120 [V].

[0052] Specifically, the calculation unit 71 calculates the capacitance value Cx of the capacitance 2B using the discharge time Tc of the object to be measured 2, the resistance value Rc of the discharge resistor 40, and the resistance value Rx of the insulation resistor 2A of the object to be measured 2, as shown in the following equation (1).

[0053] [Number 1] Tc = -Cx×Rt×ln(V1 / V2) ···(1)

[0054] Here, the combined resistance value Rt in the above formula (1) is the combined value (Rc / / Rx) of the resistance value Rc of the discharge resistor 40 and the resistance value Rx of the insulation resistor 2A connected in parallel to the discharge resistor 40. The resistance value Rc of the discharge resistor 40 is the sum of the resistance values ​​of the discharge resistor element 41 and the discharge resistor element 42.

[0055] As described above, the discharge time Tc is the time from when the voltage value of the output voltage Vout reaches the first threshold V1 to when it reaches the second threshold V2, and the first threshold V1 and the second threshold V2 are predetermined values.

[0056] Next, when the above equation (1) is solved for the capacitance value Cx of the electrostatic capacitance 2B, the following equation (2) is derived.

[0057] [Number 2] Cx = -Tc / {Rt×ln(V1 / V2)} ···(2)

[0058] The calculation unit 71 calculates the capacitance value Cx of the capacitance 2B using the above formula (2). Specifically, the calculation unit 71 calculates a composite value (Rc / / Rx) of the pre-stored resistance value Rc of the discharge resistor 40 and the calculated resistance value Rx of the insulation resistor 2A, and substitutes the calculated composite value (Rc / / Rx) for the composite resistance value Rt in the above formula (2).

[0059] Furthermore, the calculation unit 71 monitors the output signal of the voltage detection unit 30, measures the time from when the output voltage Vout reaches the first threshold value V1 to when it reaches the second threshold value V2, and substitutes the measured time for the discharge time Tc in the above equation (2).

[0060] As a result, calculation unit 71 obtains capacitance value Cx of capacitance 2B of object to be measured 2. In calculating capacitance value Cx of capacitance 2B, the above equation (2) takes into account the effect of a portion of the discharge current output from capacitance 2B of object to be measured 2 toward discharge resistor 40 in insulation resistance meter 1 being diverted to insulation resistor 2A.

[0061] In addition, the influence of capacitance element 13 in insulation resistance meter 1, which is connected in parallel to capacitance 2B of object to be measured 2, may be taken into consideration. In this case, instead of capacitance value Cx of capacitance 2B in equation (2) above, a combined capacitance value Ct (=Cx+Cs) of capacitance value Cx of capacitance 2B and capacitance value Cs of capacitance element 13 is used.

[0062] Therefore, the calculation unit 71 calculates the capacitance value Cx of the capacitance 2B by further using the capacitance value Cs of the capacitance element 13, as shown in the following equation (3). As a result, the effect of the capacitance element 13 is taken into account in the calculation result.

[0063] [Number 3] Cx = -Tc / {Rt×ln(V1 / V2)}-Cs (3)

[0064] That is, the calculation unit 71 corrects the capacitance value Cx of the capacitance 2B of the object 2 under test using the capacitance value Cs of the capacitive element 13 as a parallel capacitance connected in parallel to the capacitance 2B of the object 2 under test.

[0065] Furthermore, the influence of voltage detection section 30 having voltage dividing resistors 31 and 32 in insulation resistance meter 1 connected in parallel to capacitance 2B of object 2 to be measured may be taken into consideration.

[0066] In this case, the calculation unit 71 calculates a composite value (Rc / / Rx / / Rd) of the resistance value Rc of the discharge resistor 40, the resistance value Rx of the calculated insulation resistor 2A, and the resistance value Rd of the voltage detection unit 30, which is the sum of the resistance values ​​of the voltage dividing resistor elements 31 and 32. The resistance value Rc of the discharge resistor 40 and the resistance value Rd of the voltage detection unit 30 are stored in advance in the processing unit 70, for example.

[0067] The calculation unit 71 then substitutes the calculated combined value (Rc / / Rx / / Rd) into the combined resistance value Rt in the above equation (2) or (3), thereby taking into account the influence of the voltage detection unit 30 in the calculation result.

[0068] That is, the calculation unit 71 corrects the capacitance value Cx of the capacitance 2B of the object to be measured 2 using the resistance value Rd of the voltage detection unit 30 as a parallel resistor within the insulation resistance meter 1 connected in parallel to the capacitance 2B of the object to be measured 2.

[0069] In this way, by using the constant of the capacitance element 13 in the insulation resistance meter 1 connected in parallel to the capacitance 2B of the object to be measured 2 and at least one passive element of the voltage detection unit 30, the measurement accuracy of the capacitance 2B of the object to be measured 2 can be improved.

[0070] The calculation unit 71 then records the calculated capacitance value Cx of the electrostatic capacitance 2B in a storage unit (not shown) or outputs it to the display unit 72.

[0071] The capacitance 2B of the object to be measured 2 may have characteristics that depend on the magnitude of the output voltage Vout applied to the object to be measured 2. In such a case, the calculation unit 71 may record the calculated capacitance value Cx of the capacitance 2B and the voltage value of the output voltage Vout in a storage unit or output them to the display unit 72 in association with each other.

[0072] The display unit 72 is a display device that displays the results of calculations performed by the calculation unit 71. The display unit 72 displays, for example, the resistance value Rx of the insulation resistance 2A of the object to be measured 2 and the capacitance value Cx of the electrostatic capacitance 2B of the object to be measured 2, together with the voltage value of the output voltage Vout applied to the object to be measured 2.

[0073] The control unit 80 controls the operations of the AC source 11 and the switch 14 of the voltage generating unit 10 , as well as the switch 50 .

[0074] In order to measure the insulation resistance 2A of the object 2 to be measured, the control unit 80 performs PWM control of the switching element of the AC source 11 to perform constant current control and constant voltage control.

[0075] Specifically, the control unit 80 executes constant current control until the output voltage Vout increases to the set value, and controls the operation of the AC source 11 so that the leakage current is constant based on the output signal of the leakage current detection unit 60. When the output voltage Vout reaches the set value, the control unit 80 executes constant voltage control, and controls the operation of the AC source 11 so that the output voltage Vout is constant at the set value based on the output signal of the voltage detection unit 30.

[0076] After the measurement of the insulation resistance 2A of the object to be measured 2 is completed, the control unit 80 controls the voltage generating unit 10 to stop voltage generation, and executes discharge control of the object to be measured 2 to control the operation of each of the switches 14 and 50 in order to measure the capacitance 2B of the object to be measured 2.

[0077] Specifically, the control unit 80 maintains the conductive state of the switch 14 and switches the switch 50 from the non-conductive state to the conductive state, which stops the charging of the object under test 2 by the voltage generating unit 10 and starts discharging the object under test 2.

[0078] In this way, after the control unit 80 obtains a detection value of the leakage current flowing through the object to be measured 2 while the output voltage Vout applied to the object to be measured 2 is maintained constant, it switches the switch 50 from a non-conductive state to a conductive state so that a discharge current is output from the object to be measured 2.

[0079] Next, the operation of measuring capacitance 2B by insulation resistance meter 1 will be described with reference to FIG.

[0080] 2 is a diagram for explaining a method for measuring the capacitance 2B of the object to be measured 2. The horizontal axis in FIGS. 2(a) to 2(d) is a common time axis.

[0081] Figure 2(a) shows the signal level of the control signal of switch 14, Figure 2(b) shows the signal level of the control signal of switch 50, and Figure 2(c) shows the change in output voltage Vout obtained by the output signal of voltage detection unit 30.

[0082] 2(d) shows the signal levels of the output signals of the first comparator and the second comparator provided in the calculation unit 71. The first comparator compares the output signal of the voltage detection unit 30 with a first threshold value V1, and the second comparator compares the output signal of the voltage detection unit 30 with a second threshold value V2.

[0083] Measurement of the discharge time Tc starts when the output signal level of the first comparator switches from high level Hi1 to low level Lo1, and ends when the output signal level of the second comparator switches from high level Hi2 to low level Lo2.

[0084] As shown in FIG. 2(c), until time T11 has passed, the insulation resistance measurement process is performed, the control unit 80 executes constant voltage control, and the output voltage Vout is maintained at the set value Vset.

[0085] Around time T11, as shown in FIG. 2(a), the control unit 80 controls the voltage generating unit The voltage generation of 10 is stopped, and the application of the output voltage to the object under test 2 is thereby stopped.

[0086] 2(b), the control unit 80 executes discharge control, and the control signal level of the switch 50 is set to the high level On. This switches the switch 50 from a non-conductive state to a conductive state, and a discharge current is output from the capacitance 2B of the object to be measured 2 toward the discharge resistor 40. At this time, a current also flows from the capacitive element 13 toward the discharge resistor 40.

[0087] Then, a discharge current flows from the capacitance 2B toward the discharge resistor 40, and as shown in FIG. 2(c), the voltage value of the output voltage Vout gradually decreases from time T11 to time T12.

[0088] At time T12, as shown in FIG. 2(d), the output voltage Vout drops to the first threshold V1, so the output signal level of the first comparator switches to the low level Lo1, and the calculation unit 71 starts measuring the discharge time Tc.

[0089] At this time, the calculation unit 71 newly sets the first threshold value V1 to a predetermined value greater than the first threshold value V1. The new first threshold value V1 is changed to, for example, approximately 180 V. This prevents the output signal level of the voltage detection unit 30 from switching to the high level Hi1 and terminating measurement of the discharge time Tc even if the output signal level of the voltage detection unit 30 suddenly rises.

[0090] Thereafter, as shown in FIG. 2(c), the voltage value of the output voltage Vout gradually decreases from time T12 to time T13 compared to the time change of the output voltage Vout from time T11 to time T12.

[0091] At time T13, as shown in FIG. 2(d), the output voltage Vout drops to the second threshold V2, so the output signal level of the second comparator switches to the low level Lo2, and the calculation unit 71 stops measuring the discharge time Tc.

[0092] At this time, the calculation unit 71 newly sets a specific value greater than the second threshold value V2 as the second threshold value V2. The new second threshold value V2 is changed to, for example, approximately 140 V. This prevents the output signal level of the voltage detection unit 30 from being switched to the high level Hi2 and continuing to measure the discharge time Tc even if the output signal level of the voltage detection unit 30 suddenly increases.

[0093] In this way, the discharge time Tc is measured by the first comparator and the second comparator of the calculation unit 71. Then, the calculation unit 71 substitutes at least the discharge time Tc, the resistance value Rx of the insulation resistance 2A acquired immediately before the execution of discharge control, and the first threshold value V1 and the second threshold value V2 before the change into the constants of the above formula (2) or (3), and calculates the capacitance value Cx of the capacitance 2B of the object to be measured 2.

[0094] After time T13 has elapsed, when the output voltage Vout drops to the low voltage Vs as shown in Fig. 2(c), the control unit 80 sets the control signal level of the switch 14 to the low level Off as shown in Fig. 2(a). The low voltage Vs is preset to a sufficiently low voltage value that is not dangerous, for example, 30 [V].

[0095] In this way, when the voltage of object 2 under test has dropped to a sufficiently low voltage value, switch 14 switches from the conductive state to the non-conductive state, and voltage generation by voltage generating unit 10 stops.

[0096] Next, the effects of the first embodiment will be described.

[0097] In the first embodiment, insulation resistance meter 1 detects leakage current flowing through object to be measured 2, which is represented by an equivalent circuit in which insulation resistance 2A and capacitance 2B are connected in parallel, while applying output voltage Vout, which is a DC voltage, to object to be measured 2. Insulation resistance meter 1 includes voltage generating unit 10 that applies output voltage Vout from output terminal T1 of insulation resistance meter 1 to object to be measured 2, voltage detecting unit 30 that detects the voltage value of output voltage Vout, and processing unit 70 that calculates resistance value Rx of insulation resistance 2A of object to be measured 2 using the voltage value of output voltage Vout and the detected value of the leakage current.

[0098] The insulation resistance meter 1 further includes a discharge resistor 40 that discharges the object to be measured 2, a switch 50 that passes a discharge current from the object to be measured 2 to the discharge resistor 40, and a control unit 80 that switches the switch 50 from a non-conductive state to a conductive state so that a discharge current is output from the object to be measured 2 after a detection value of the leakage current has been obtained.

[0099] The processing unit 70 calculates the capacitance value Cx of the capacitance 2B of the object to be measured 2 based on the discharge time Tc required for the voltage value detected by the voltage detection unit 30 to drop from the first threshold value V1 to the second threshold value V2 while the switch 50 is in a conductive state, the resistance value Rc of the discharge resistor 40, and the resistance value Rx of the insulation resistor 2A of the object to be measured 2.

[0100] With this configuration, insulation resistance meter 1 measures insulation resistance 2A of object to be measured 2, and then measures capacitance 2B of object to be measured 2 by switching switch 50 of discharge resistor 40 from a non-conductive state to a conductive state to discharge object to be measured 2. Therefore, compared to a process in which capacitance 2B of object to be measured 2 is measured while the object to be measured 2 is being charged, insulation resistance meter 1 does not need to charge object to be measured 2, and therefore measurement time can be shortened.

[0101] Furthermore, when calculating the capacitance value Cx of the capacitance 2B of the object to be measured 2, in addition to the discharge time Tc until the voltage value of the output voltage Vout drops from the first threshold V1 to the second threshold V2 and the resistance value Rc of the discharge resistor 40, the resistance value Rx of the insulation resistor 2A connected in parallel to the capacitance 2B of the object to be measured 2 is also used.

[0102] For example, when the resistance value Rx of insulation resistance 2A of object to be measured 2 is lower than the resistance value Rc of discharge resistor 40 in insulation resistance meter 1, the discharge current output from capacitance 2B of object to be measured 2 is more likely to be shunted to insulation resistance 2A of object to be measured 2 than when insulation resistance 2A is higher than discharge resistance 40. As a result, the discharge current flowing from capacitance 2B of object to be measured 2 to discharge resistor 40 in insulation resistance meter 1 decreases, resulting in a larger measurement error for capacitance 2B.

[0103] To address this issue, by calculating capacitance 2B of object to be measured 2 using the resistance value Rx of insulation resistance 2A of object to be measured 2 in addition to discharge resistor 40 in insulation resistance meter 1, it becomes possible to take into account the decrease in discharge current at discharge resistor 40 caused by insulation resistance 2A of object to be measured 2. This makes it possible to prevent a decrease in the measurement accuracy of capacitance 2B of object to be measured 2.

[0104] Therefore, in the insulation resistance meter 1, the measurement time for the capacitance 2B can be reduced while the measurement accuracy of the capacitance 2B can be improved.

[0105] In the first embodiment, the insulation resistance tester 1 further includes a limiting resistor 20 connected between the output end of the voltage generating unit 10 and the output terminal T1 of the insulation resistance tester 1. The limiting resistor 20 serves to limit the current input to the output terminal T1 of the insulation resistance tester 1 when an external voltage is applied to the output terminal T1 of the insulation resistance tester 1. In this circuit configuration, the voltage range from the first threshold value V1 to the second threshold value V2 is determined in advance based on the resistance value Ro of the limiting resistor 20.

[0106] According to this configuration, the first threshold V1 and the second threshold V2 are set to avoid a voltage range in which the measurement accuracy of the capacitance 2B is affected by the resistance value Ro of the limiting resistor element 20, thereby suppressing a decrease in the measurement accuracy of the capacitance 2B.

[0107] Furthermore, the processing unit 70 of the first embodiment corrects the capacitance value Cx of the capacitance 2B of the object to be measured 2 using the capacitance value of the parallel capacitance in the insulation resistance meter 1 connected in parallel to the capacitance 2B of the object to be measured 2.

[0108] According to this configuration, the effect of the parallel capacitance arranged in insulation resistance meter 1 is taken into account in the calculation result, so that capacitance 2B of object to be measured 2 can be measured with high accuracy.

[0109] For example, voltage generating unit 10 includes, as a parallel capacitance, capacitive element 13 that functions as a smoothing capacitor connected in parallel to the secondary winding of the transformer. In this case, the capacitance value of capacitive element 13 corresponds to the capacitance value of the parallel capacitance in insulation resistance meter 1 that is connected in parallel to capacitance 2B of object to be measured 2, and affects the measurement accuracy of capacitance 2B.

[0110] According to this configuration, when measuring the capacitance 2B of the object to be measured 2, the influence of the capacitance element 13, which smooths the output voltage of the voltage generating unit 10 in the insulation resistance measurement, is taken into account, so that the decrease in the measurement accuracy of the capacitance 2B caused by the capacitance element 13 can be suppressed.

[0111] Furthermore, the processing unit 70 of the first embodiment corrects the capacitance value Cx of the capacitance 2B of the object to be measured 2 using the resistance value of a parallel resistor in the insulation resistance meter 1 connected in parallel to the capacitance 2B of the object to be measured 2.

[0112] According to this configuration, the effect of the parallel resistance placed in insulation resistance meter 1 is taken into account in the calculation result, so that capacitance 2B of object to be measured 2 can be measured with high accuracy.

[0113] For example, the voltage detection unit 30 is a voltage dividing circuit having a plurality of voltage dividing resistor elements 31 and 32 connected in series, and the resistance value of this voltage dividing circuit corresponds to the resistance value of a parallel resistor used in the correction process of the capacitance value Cx.

[0114] According to this configuration, when measuring the capacitance 2B of the object to be measured 2, the influence of the voltage divider circuit that constitutes the voltage detection unit 30 is taken into account, thereby suppressing a decrease in the measurement accuracy of the capacitance 2B caused by the voltage divider circuit.

[0115] In the first embodiment, when the voltage value detected by the voltage detection unit 30 falls below the first threshold value V1, the processing unit 70 sets a new first threshold value V1 to a predetermined value greater than the first threshold value V1. Furthermore, when the voltage value detected by the voltage detection unit 30 falls below the second threshold value V2, the processing unit 70 sets a new second threshold value V2 to a specific value greater than the second threshold value V2.

[0116] This configuration can suppress hunting that can occur in measuring the discharge time Tc. Therefore, it is possible to stably measure the discharge time Tc even when sudden noise is mixed into the output signal of the voltage detection unit 30. Therefore, the need to measure the discharge time Tc again is suppressed, and the measurement time can be shortened.

[0117] Furthermore, the capacitance 2B of the object to be measured 2 may have a characteristic that changes depending on the voltage value of the output voltage Vout applied to the object to be measured 2, and the control unit 80 can arbitrarily set the voltage value of the output voltage Vout. Therefore, the processing unit 70 displays or records the voltage value of the output voltage Vout applied by the voltage generating unit 10 and the capacitance value Cx of the capacitance 2B of the object to be measured 2 in association with each other.

[0118] With this configuration, insulation resistance meter 1 arbitrarily sets the voltage value of output voltage Vout, charges object of measurement 2, which has voltage dependency, at that set value, and then measures capacitance 2B of object of measurement 2 by discharging object of measurement 2. Processing unit 70 then displays or records the voltage value of output voltage Vout applied to object of measurement 2 and capacitance value Cx of capacitance 2B of object of measurement 2, associating them with each other.

[0119] This allows the measurer to grasp the measurement results of the capacitance 2B for each charging voltage, and therefore allows the measurer to evaluate the capacitance 2B of the measurement object 2 taking the charging voltage into consideration.

[0120] Second Embodiment The circuit configuration of the insulation resistance meter 1 is not limited to the circuit configuration shown in Fig. 1, and the measurement method of the first embodiment can be applied to other circuit configurations as well. Therefore, below, an embodiment having another circuit configuration will be referred to as a second embodiment and will be briefly described with reference to Fig. 3.

[0121] FIG. 3 is a circuit diagram showing the circuit configuration of an insulation resistance tester 1A according to the second embodiment.

[0122] In addition to the components of the insulation resistance tester 1 of the first embodiment, the insulation resistance tester 1A also includes a feedback voltage detection unit 90. The other components of the insulation resistance tester 1A are the same as or equivalent to the components of the insulation resistance tester 1 shown in Fig. 1, so the same reference numerals as those of the insulation resistance tester 1 are used and redundant explanations will be omitted.

[0123] The feedback voltage detection unit 90 is a voltage detection unit different from the voltage detection unit 30, and detects the voltage value of the voltage of the connection line L2 extending between the output terminal of the voltage generation unit 10 and one end of the limiting resistance element 20. The feedback voltage detection unit 90 of the second embodiment is connected between the connection line L2 and the ground potential G.

[0124] The feedback voltage detection unit 90 of the second embodiment is another voltage dividing circuit configured by voltage dividing resistor elements 91 and 92 connected in series with each other. The resistance values ​​of the voltage dividing resistor elements 91 and 92 are designed to be, for example, several hundred MΩ, and in the second embodiment, are designed to be, for example, approximately 300 MΩ.

[0125] In the feedback voltage detection unit 90, one end of the voltage-dividing resistor element 91 is connected to the connection line L2, the other end of the voltage-dividing resistor element 91 is connected to one end of the voltage-dividing resistor element 92, and the other end of the voltage-dividing resistor element 92 is connected to the ground potential G.

[0126] The feedback voltage detection unit 90 outputs a divided voltage signal generated at the connection point between the voltage dividing resistor elements 91 and 92 to the control unit 80 as a detection signal of the output voltage Vout.

[0127] In the second embodiment, the capacitive element 13 and the limiting resistive element 20 form a low-pass filter to remove inductive noise entering from the output terminal T1. Therefore, the inductive noise superimposed on the voltage-divided signal of the feedback voltage detector 90 is removed by the low-pass filter.

[0128] In this way, by disposing the feedback voltage detection unit 90 between the capacitance element 13 and the limiting resistance element 20, a voltage division signal in which the influence of induced noise is suppressed is output from the feedback voltage detection unit 90 to the control unit 80. The control unit 80 performs constant voltage control based on the output signal of the feedback voltage detection unit 90. The calculation unit 71 then calculates the resistance value Rx of the insulation resistance 2A of the object to be measured 2 using the output signal of the voltage detection unit 30 and the output signal of the leakage current detection unit 60.

[0129] Thereafter, the control unit 80 executes discharge control to maintain the conductive state of the switch 14 and switch the switch 50 from the non-conductive state to the conductive state.

[0130] The calculation unit 71 uses the output signal of the voltage detection unit 30 to measure the time it takes for the output voltage Vout to drop from the first threshold V1 to the second threshold V2, and substitutes the measured time, for example, into the discharge time Tc in the above equation (3), and also substitutes the pre-stored capacitance value of the capacitance element 13 into the electrostatic capacitance value Cs in equation (3).

[0131] The calculation unit 71 then calculates a composite value (Rc / / Rx / / Rd / / Rf) of the calculated resistance value Rx of the insulation resistor 2A, the pre-stored resistance value Rc of the discharge resistor 40, the resistance value Rd of the voltage detection unit 30, and the resistance value Rf of the feedback voltage detection unit 90. The resistance value Rf of the feedback voltage detection unit 90 is the sum of the resistance values ​​of the voltage dividing resistance elements 91 and 92.

[0132] Furthermore, the calculation unit 71 substitutes the calculated combined value (Rc / / Rx / / Rd / / Rf) for the combined resistance value Rt in the above equation (3). As a result, the calculation unit 71 calculates the capacitance value Cx of the electrostatic capacitance 2B of the object to be measured 2. The calculation result takes into account the effects of the capacitive element 13, the voltage detection unit 30, and the feedback voltage detection unit 90.

[0133] In this way, the calculation unit 71 corrects the capacitance value Cx of the capacitance 2B of the object to be measured 2 using the constants (Cs, Rd, and Rf) of the capacitance element 13, voltage detection unit 30, and feedback voltage detection unit 90 in the insulation resistance meter 1, which are connected in parallel to the capacitance 2B of the object to be measured 2.

[0134] Next, the effects of the second embodiment will be described.

[0135] The insulation resistance meter 1A in the second embodiment has the same or equivalent configuration as the insulation resistance meter 1 in the first embodiment, and these configurations can achieve the same effects as those of the first embodiment described above.

[0136] In addition, in the second embodiment, the insulation resistance meter 1A includes a limiting resistance element 20 connected between the voltage generating unit 10 and the output terminal T1 of the insulation resistance meter 1A, and a feedback voltage detecting unit 90 which is another voltage detecting unit connected between the voltage generating unit 10 and the limiting resistance element 20.

[0137] Feedback voltage detection unit 90 is another voltage divider circuit having multiple voltage-dividing resistor elements 91 and 92 connected in series, and the resistance value Rf of this voltage divider circuit corresponds to the resistance value of the parallel resistor in insulation resistance meter 1 that is connected in parallel to capacitance 2B of object to be measured 2. For this reason, the resistance value Rf of feedback voltage detection unit 90 is added to the combined resistance value Rt of the parallel resistors in equations (2) and (3) above that are used to calculate capacitance value Cx of capacitance 2B of object to be measured 2.

[0138] According to this configuration, when measuring the capacitance 2B of the measurement object 2, the influence of the other voltage divider circuits that constitute the feedback voltage detection unit 90 is taken into account, so that a decrease in the measurement accuracy of the capacitance 2B caused by the resistance value Rf of the feedback voltage detection unit 90 can be suppressed.

[0139] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments.

[0140] In the above embodiment, the limiting resistance element 20 is provided in the insulation resistance meters 1 and 1A, but the limiting resistance element 20 may be omitted. Even in this case, the effects of the above embodiment can be obtained. [Explanation of symbols]

[0141] 1. 1A insulation resistance tester 2. Measurement Object 2A insulation resistance 2B capacitance 10 Voltage generation unit 20 Limiting resistor element 30 Voltage detection section 40 Discharge resistor 50 Switch 70 Processing section 80 Control Unit 90 Feedback voltage detector (other voltage detector)

Claims

1. 1. An insulation resistance meter that detects leakage current flowing through a measurement object represented by an equivalent circuit in which insulation resistance and capacitance are connected in parallel with each other while a DC voltage is applied to the measurement object, a voltage generating unit that generates a voltage to be applied from an output terminal of the insulation resistance meter to the object to be measured; a voltage detection unit that detects a voltage value of the DC voltage; a processing unit that calculates a resistance value of the insulation resistor to be measured using the voltage value of the DC voltage and the detected value of the leakage current; a discharge resistor that discharges the object to be measured; a switch for causing a discharge current to flow from the object to be measured to the discharge resistor; a control unit that switches the switch from a non-conductive state to a conductive state so that the discharge current is output from the measurement object after the detection value of the leakage current is acquired, the processing unit calculates a capacitance value of the capacitance of the object to be measured based on a discharge time required for a voltage value detected by the voltage detection unit to decrease from a first threshold value to a second threshold value while the switch is in the conductive state, a resistance value of the discharge resistor, and a resistance value of the insulation resistor of the object to be measured. Insulation resistance tester.

2. 2. The insulation resistance meter according to claim 1, a limiting resistor element connected between the voltage generating unit and an output terminal of the insulation resistance meter, the limiting resistor element limiting a current input to the output terminal of the insulation resistance meter when a voltage is applied to the output terminal of the insulation resistance meter from an external source; a voltage range from the first threshold to the second threshold is predetermined based on the limiting resistor element; Insulation resistance tester.

3. 2. The insulation resistance meter according to claim 1, the processing unit corrects the capacitance value of the capacitance of the measurement target using a capacitance value of a parallel capacitance connected in parallel to the capacitance of the measurement target. Insulation resistance tester.

4. 4. The insulation resistance meter according to claim 3, The capacitance value of the parallel capacitance is the capacitance value of a smoothing capacitor of the voltage generating unit. Insulation resistance tester.

5. 2. The insulation resistance meter according to claim 1, correcting the capacitance value of the capacitance of the object to be measured using a resistance value of a parallel resistor connected in parallel to the capacitance of the object to be measured; Insulation resistance tester.

6. 6. The insulation resistance meter according to claim 5, the voltage detection unit is a voltage dividing circuit having a plurality of resistor elements connected in series, The resistance value of the parallel resistor is the resistance value of the voltage divider circuit. Insulation resistance tester.

7. 7. The insulation resistance meter according to claim 5 or 6, a limiting resistor element connected between the voltage generating unit and an output terminal of the insulation resistance meter; another voltage detection unit connected between the voltage generation unit and the limiting resistance element; the other voltage detection unit is another voltage dividing circuit having a plurality of resistor elements connected in series, The resistance value of the parallel resistor is the resistance value of the other voltage divider circuit. Insulation resistance tester.

8. 2. The insulation resistance meter according to claim 1, The processing unit When the voltage value detected by the voltage detection unit falls below the first threshold value, a predetermined value greater than the first threshold value is newly set as the first threshold value; When the voltage value detected by the voltage detection unit falls below the second threshold, a specific value greater than the second threshold is newly set as the second threshold. Insulation resistance tester.

9. 2. The insulation resistance meter according to claim 1, the capacitance of the object to be measured has a characteristic that changes depending on the voltage value of a DC voltage applied to the object to be measured, the control unit can arbitrarily set a voltage value of the DC voltage, the processing unit displays or records a voltage value of the DC voltage applied by the voltage generating unit and a capacitance value of the capacitance to be measured in association with each other. Insulation resistance tester.

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