Insulation state detecting device

1. An insulation state detecting device comprising:

a positive side input terminal connected to a positive side power line of a high voltage DC power supply;

a negative side input terminal connected to a negative side power line of the high voltage DC power supply;

a ground electrode;

a controller that detects insulation states between the positive side power line and the negative side power line and the ground electrode based on a charge voltage of a flying capacitor; and

an equilibrium state forming circuit that promotes an operation of transiting a charge state of an electrostatic capacitance of a positive side capacitor between the positive side power line and the ground electrode and a charge state of an electrostatic capacitance of a negative side capacitor between the negative side power line and the ground electrode from non-equilibrium states to equilibrium states,

wherein in the non-equilibrium states, amounts of electricity charges on the positive side capacitor and the negative side capacitor fluctuate; and

wherein in the equilibrium states, the amounts of electricity charges on the positive side capacitor and the negative side capacitor are not changed.

2. The insulation state detecting device according to claim 1 , wherein the equilibrium state forming circuit includes:

control resistors which are connected to the positive side power line and the negative side power line respectively, and resistance values of the control resistors being much smaller than resistance values of ground fault resistances to be detected; and

control switches adapted to be opened and closed to temporarily connect the control resistors to electrodes having constant electric potentials according to control signals.

3. The insulation state detecting device according to claim 1 , wherein the equilibrium state forming circuit includes:

a positive side control resistor having one end which is connected to the positive side power line:

a negative side control resistor having one end which is connected to the negative side power line: and

control switches adapted to be opened and closed to temporarily connect the other end of the positive side control resistor and the other end of the negative side control resistor to the ground electrode according to control signals;

wherein a resistance value of the positive side control resistor is larger than a value for which an instant drop of insulation state is permitted when the control switches are closed and is much smaller than resistance values of ground fault resistances to be detected; and

wherein the resistance value of the negative side control resistor is larger than a value for which an instant drop of insulation state is permitted when the control switches are closed and is much smaller than resistance values of the ground fault resistances to be detected.

4. The insulation state detecting device according to claim 2 , further comprising:

a control signal generator that automatically generates timings of the control signals, which are given to the control switches, in synchronous with the change of a control cycle of charging and discharging of the flying capacitor.

5. The insulation state detecting device according to claim 4 , wherein the control signal generator includes selecting switches which change generation conditions of the control signals.

6. The insulation state detecting device according to claim 4 , further comprising:

a positive side Y condenser connected between the positive side power line and the ground electrode; and

a negative side Y condenser connected between the negative side power line and the ground electrode,

wherein the control signal generator automatically generates the timings of the control signals based on a relation between the control timings of the control switches and sizes of electrostatic capacitances of the positive side Y condenser and the negative side Y condenser.

7. The insulation state detecting device according to claim 4 , wherein the control signal generator generates the control signals to close the control switches in synchronous with timings in which the flying capacitor is charged with a course which does not pass through both of a positive side ground fault resistance formed between the positive side input terminal and the ground electrode and a negative side ground fault resistance formed between the negative side input terminal and the ground electrode.

8. The insulation state detecting device according to claim 2 , further comprising:

a control signal generator that generates the control signals to close the control switches except timings in which the flying capacitor is charged with a course which passes through a positive side ground fault resistance formed between the positive side input terminal and the ground electrode or a negative side ground fault resistance formed between the negative side input terminal and the ground electrode.

9. The insulation state detecting device according to claim 3 , further comprising:

a control signal generator that automatically generates timings of the control signals, which are given to the control switches, in synchronous with the change of a control cycle of charging and discharging of the flying capacitor.

10. The insulation state detecting device according to claim 9 , wherein the control signal generator includes selecting switches which change generation conditions of the control signals.

11. The insulation state detecting device according to claim 9 , further comprising:

a positive side Y condenser connected between the positive side power line and the ground electrode; and

a negative side Y condenser connected between the negative side power line and the ground electrode,

wherein the control signal generator automatically generates the timings of the control signals based on a relation between the control timings of the control switches and sizes of electrostatic capacitances of the positive side Y condenser and the negative side Y condenser.

12. The insulation state detecting device according to claim 9 , wherein the control signal generator generates the control signals to close the control switches in synchronous with timings in which the flying capacitor is charged with a course which does not pass through both of a positive side ground fault resistance formed between the positive side input terminal and the ground electrode and a negative side ground fault resistance formed between the negative side input terminal and the ground electrode.

13. The insulation state detecting device according to claim 3 , further comprising:

a control signal generator that generates the control signals to close the control switches except timings in which the flying capacitor is charged with a course which passes through a positive side ground fault resistance formed between the positive side input terminal and the ground electrode or a negative side ground fault resistance formed between the negative side input terminal and the ground electrode.