INSULATION DETECTOR AND ELECTRIC APPARATUS

• US 20160377670A1
• Filed: 10/28/2014
• Published: 12/29/2016
• Est. Priority Date: 11/22/2013
• Status: Active Grant

• Current Assignee: Mitsubishi Electric Corporation
• Original Assignee: Mitsubishi Electric Corporation
• Inventors: UEMATSU, Masayuki, TSUJIKAWA, Kosuke, TAMIDA, Taichiro, TANABE, Akira, HAYASHI, Yoshitomo, TSUTSUMISHITA, Yoji
• Granted Patent: US 10,416,224 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01R 27/025 Measuring very high resistances, e.g. isolation resistances, i.e. megohm-meters
• CPC Class Codes: G01R 27/18 Measuring resistance to earth , i.e. line to ground
• CPC Class Codes: G01R 31/12 Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing G01R31/08, G01R31/327 and G01R31/72 take precedence; measuring in plasmas G01R19/0061; measuring dielectric constants G01R27/2617; ESD, EMC or EMP testing of circuits G01R31/002
• CPC Class Codes: G01R 31/34 Testing dynamo-electric machines
• CPC Class Codes: G01R 31/343 in operation
• CPC Class Codes: G01R 31/52 Testing for short-circuits, leakage current or ground faults

Abstract

An insulation detector for highly accurately detecting or measuring, with a simple configuration, insulation resistance of a load or an apparatus to a ground or a housing and connected to an electric apparatus including one or both of an intra-apparatus capacitor and a battery, the insulation detector including an intra-insulation detector capacitor, a voltage detecting unit that detects a voltage of the intra-insulation detector capacitor, and a current-path forming switch for connecting the ground or the housing, the intra-apparatus capacitor, and the intra-insulation detector capacitor in series and forming a current path including insulation resistance of the electric apparatus. The insulation detector measures the insulation resistance by measuring a time constant of a change in the voltage of the intra-insulation detector capacitor. A capacitance value of the intra-insulation detector capacitor is a value negligible in the measurement of the insulation resistance compared with a capacitance value of the intra-apparatus capacitor.

Claims

1. An insulation detector connected to an electric apparatus including an intra-apparatus capacitor, the insulation detector comprising:

an intra-insulation detector capacitor;

a voltage detecting unit to detect a voltage of the intra-insulation detector capacitor; and

a current-path forming switch to connect a ground or a housing, the intra-apparatus capacitor, and the intra-insulation detector capacitor in series and form a current path including insulation resistance of the electric apparatus, wherein

the insulation detector measures the insulation resistance by measuring, with the voltage detecting unit, a time constant of a change in the voltage of the intra-insulation detector capacitor, and

a capacitance value of the intra-insulation detector capacitor is a value negligible in the measurement of the insulation resistance compared with a capacitance value of the intra-apparatus capacitor.

3. The insulation detector according to claim 1, wherein

the electric apparatus includes a configuration for driving a load with an inverter, and

the insulation detector comprises a load-side path guide switch for connecting one end of the intra-apparatus capacitor and an output line to the load.

5. The insulation detector according to claim 3, wherein one of inverter elements in the inverter is also used as the load-side path guide switch.

11. The insulation detector according to claim 1, wherein the insulation detector calculates stray capacitance of a measurement system from a change in a voltage waveform immediately after a measurement start of the time constant and calculates a resistance value of the insulation resistance from a calculated value of the stray capacitance and a measured value of the time constant.

12. The insulation detector according to claim 1, wherein the intra-insulation detector capacitor has a configuration in which two capacitance elements are connected in parallel.

13. The insulation detector according to claim 1, wherein the voltage detecting unit includes a resistance element having a known resistance value smaller than an input of impedance of a measurement system of the voltage detecting unit, the resistance element being connected to an input of the measurement system in parallel.

14. The insulation detector according to claim 1, comprising a memory to record a detection value of the voltage detecting unit, wherein

the insulation detector can record a temporal change of the detection value.

20. An electric apparatus comprising the insulation detector according to claim 1.

2. An insulation detector connected to an electric apparatus including a battery, the insulation detector comprising:

an intra-insulation detector capacitor;

a voltage detecting unit to detect a voltage of the intra-insulation detector capacitor; and

a current-path forming switch to connect a ground or a housing, the battery, and the intra-insulation detector capacitor in series and form a current path including insulation resistance of the electric apparatus, wherein

the insulation detector measures the insulation resistance by measuring, with the voltage detecting unit, a time constant of a change in the voltage of the intra-insulation detector capacitor.

4. The insulation detector according to claim 2, wherein

the electric apparatus includes a configuration for driving a load with an inverter, and

the insulation detector comprises a load-side path guide switch for connecting one pole of the battery and an output line to the load.

21. The insulation detector according to claim 4, wherein one of inverter elements in the inverter is also used as the load-side path guide switch.

25. The insulation detector according to claim 2, wherein the insulation detector calculates stray capacitance of a measurement system from a change in a voltage waveform immediately after a measurement start of the time constant and calculates a resistance value of the insulation resistance from a calculated value of the stray capacitance and a measured value of the time constant.

26. The insulation detector according to claim 2, wherein the intra-insulation detector capacitor has a configuration in which two capacitance elements are connected in parallel.

27. The insulation detector according to claim 2, wherein the voltage detecting unit includes a resistance element having a known resistance value smaller than an input of impedance of a measurement system of the voltage detecting unit, the resistance element being connected to an input of the measurement system in parallel.

28. The insulation detector according to claim 2, comprising a memory to record a detection value of the voltage detecting unit, wherein

the insulation detector can record a temporal change of the detection value.

33. An electric apparatus comprising the insulation detector according to claim 2.

6. An insulation detector connected to an electric apparatus including an intra-apparatus capacitor, the insulation detector comprising:

an intra-insulation detector capacitor;

a voltage detecting unit to detect voltages of the intra-apparatus capacitor and the intra-insulation detector capacitor connected in series; and

a current-path forming switch to connect a ground or a housing, the intra-apparatus capacitor, and the intra-insulation detector capacitor in series and form a current path including insulation resistance of the electric apparatus, wherein

the insulation detector measures the insulation resistance by measuring, with the voltage detecting unit, a time constant of a change in the voltage of the intra-insulation detector capacitor, and

a capacitance value of the intra-insulation detector capacitor is a value negligible in the measurement of the insulation resistance compared with a capacitance value of the intra-apparatus capacitor.

8. The insulation detector according to claim 6, comprising discharge resistance connected to both ends of the intra-insulation detector capacitor.

9. The insulation detector according to claim 6, wherein

a switch for short circuit and a low resistance element having a resistance value lower than the insulation resistance connected in series are connected in parallel to the intra-insulation detector capacitor, and

a resistance value of the low resistance element is a value for enabling, in measuring a time constant of the insulation resistance, the intra-insulation detector capacitor to be discharged in an interval of the measurement.

10. The insulation detector according to claim 9, wherein the insulation detector closes, when starting the measurement of the time constant, the current-path forming switch in a state in which the switch for short circuit is closed and opens the switch for short circuit after accumulation of charges in a stray capacitor.

29. The insulation detector according to claim 6, comprising a memory to record a detection value of the voltage detecting unit, wherein

the insulation detector can record a temporal change of the detection value.

34. An electric apparatus comprising the insulation detector according to claim 6.

7. An insulation detector connected to an electric apparatus including a battery, the insulation detector comprising:

an intra-insulation detector capacitor;

a voltage detecting unit to detect voltages of the battery and the intra-insulation detector capacitor connected in series; and

a current-path forming switch to connect a ground or a housing, the battery, and the intra-insulation detector capacitor in series and form a current path including insulation resistance of the electric apparatus, wherein

the insulation detector measures the insulation resistance by measuring, with the voltage detecting unit, a time constant of a change in the voltage of the intra-insulation detector capacitor.

22. The insulation detector according to claim 7, comprising discharge resistance connected to both ends of the intra-insulation detector capacitor.

23. The insulation detector according to claim 7, wherein

a switch for short circuit and a low resistance element having a resistance value lower than the insulation resistance connected in series are connected in parallel to the intra-insulation detector capacitor, and

a resistance value of the low resistance element is a value for enabling, in measuring a time constant of the insulation resistance, the intra-insulation detector capacitor to be discharged in an interval of the measurement.

24. The insulation detector according to claim 23, wherein the insulation detector closes, when starting the measurement of the time constant, the current-path forming switch in a state in which the switch for short circuit is closed and opens the switch for short circuit after accumulation of charges in a stray capacitor.

30. The insulation detector according to claim 7, comprising a memory to record a detection value of the voltage detecting unit, wherein

the insulation detector can record a temporal change of the detection value.

35. An electric apparatus comprising the insulation detector according to claim 7.

15. An insulation detector connected between one of a P bus and an N bus of an electric apparatus and an output line, the electric apparatus including a rectifier circuit that is disposed between an alternating-current power supply and a load and converts an alternating-current voltage from the alternating-current power supply into a direct-current voltage and an inverter that is connected to a post stage of the rectifier circuit and drives the load, and the output line connecting the inverter and the load, wherein

the insulation detector includes a resistor configured by a series-connected detection resistor and a voltage dividing resistor, a capacitor connected in parallel to the resistor, and a voltage detector to detect a resistance value of the measurement resistor, the voltage of which being divided by the voltage dividing resistor to measure a voltage value across both ends of the insulation detector, and

the insulation detector detects insulation resistance between the load and a ground or a housing from the voltage value measured by the voltage detector.

18. The insulation detector according to claim 15, wherein the insulation detector estimates a value of the insulation resistance according to voltage values across both ends of the insulation detector measured three or more times in a state in which a voltage across both the ends of the insulation detector transiently changes and a time interval between times when the voltage values across both the ends of the insulation detector are measured.

19. The insulation detector according to claim 15, wherein the insulation detector estimates stray capacitance of the load from amplitude of an alternating-current fluctuation component of a voltage across both the ends of the insulation detector.

36. An electric apparatus comprising the insulation detector according to claim 15.

16. An insulation detector connected between one of a P bus and an N bus of an electric apparatus and an output line via a switch, the electric apparatus including a rectifier circuit that is disposed between an alternating-current power supply and a load and converts an alternating-current voltage from the alternating-current power supply into a direct-current voltage and an inverter that is connected to a post stage of the rectifier circuit and drives the load, and the output line connecting the inverter and the load, wherein

the insulation detector includes a resistor configured by a series-connected detection resistor and a voltage dividing resistor, a capacitor connected in parallel to the resistor, and a voltage detector to detect a resistance value of the measurement resistor, the voltage of which being divided by the voltage dividing resistor to measure a voltage value across both ends of the insulation detector, and

the insulation detector detects insulation resistance between the load and a ground or a housing from the voltage value measured by the voltage detector.

17. The insulation detector according to claim 16, wherein

one end of the insulation detector is connected to one of the P bus and the N bus,

during operation of the inverter, the other end of the insulation detector is connected to the other of the P bus and the N bus via the switch, and

when stopping the inverter and performing detection of the insulation resistance, the insulation detector switches the switch and switch the other end of the insulation detector to the output line of the inverter.

31. The insulation detector according to claim 16, wherein the insulation detector estimates a value of the insulation resistance according to voltage values across both ends of the insulation detector measured three or more times in a state in which a voltage across both the ends of the insulation detector transiently changes and a time interval between times when the voltage values across both the ends of the insulation detector are measured.

32. The insulation detector according to claim 16, wherein the insulation detector estimates stray capacitance of the load from amplitude of an alternating-current fluctuation component of a voltage across both the ends of the insulation detector.

37. An electric apparatus comprising the insulation detector according to claim 16.