Earth fault detector

1. A earth fault detector connected to a non-ground high voltage battery and detecting an earth fault of a system in which the high voltage battery is provided, the earth fault detector comprising:

a controller;

a detection capacitor operating as a flying capacitor;

a positive side first resistance connected to a positive side of the high voltage battery;

a negative side first resistance connected to a negative side of the high voltage battery;

a positive side second resistance of which one end is grounded and a voltage of another end is measured by the controller;

a negative side second resistance of which one end is grounded;

a positive side C contact switch alternatively switching a connection destination of a first end of the detection capacitor to either a path including the positive side first resistance or a path including the positive side second resistance based on an instruction of the controller; and

a negative side C contact switch alternatively switching a connection destination of a second end of the detection capacitor to either a path including the negative side first resistance or a path including the negative side second resistance based on the instruction of the controller.

2. The earth fault detector according to claim 1 , wherein the controller, when simultaneously operating and switching the positive side C contact switch and the negative side C contact switch, controls, so that either the positive side C contact switch or the negative side C contact switch is switched in advance and that opportunities for switching first are equalized.

3. The earth fault detector according to claim 2 , wherein the positive side C contact switch and the negative side C contact switch are constructed by a mechanical relay or a reed relay.

4. The earth fault detector according to claim 1 , wherein the positive side C contact switch and the negative side C contact switch are formed as twin relays in which interlocking relays are connected in parallel.

5. The earth fault detector according to claim 4 , wherein equal value shunt resistances are connected in series to a detection capacitor connecting side in each of the twin relays.

6. The earth fault detector according to claim 5 , wherein the positive side C contact switch and the negative side C contact switch are constructed by a mechanical relay or a reed relay.

7. The earth fault detector according to claim 4 , wherein

the positive side first resistance is formed by connecting in series an equal value resistance at a high voltage battery connecting side of each of the twin relays forming the positive side C contact switch,

the negative side first resistance is formed by connecting in series an equal value resistance at the high voltage battery connecting side of each of the twin relays forming the negative side C contact switch, and

equal value shunt resistances are connected in series to a positive side second resistance connecting side of each of the twin relays forming the positive side C contact switch and a negative side second resistance connecting side of each of the twin relays forming the negative side C contact switch.

8. The earth fault detector according to claim 7 , wherein the positive side C contact switch and the negative side C contact switch are constructed by a mechanical relay or a reed relay.

9. The earth fault detector according to claim 4 , wherein the positive side C contact switch and the negative side C contact switch are constructed by a mechanical relay or a reed relay.

10. The earth fault detector according to claim 1 , wherein the positive side C contact switch and the negative side C contact switch are constructed by a mechanical relay or a reed relay.