Over-voltage protection system and method

1. An over-voltage protection system comprising:

an electronic valve connected across two terminals of a circuit, the electronic valve having a plurality of semiconductor devices connected in series;

an over-voltage detection circuit connected across one of the plurality of semiconductor devices for detecting an over-voltage across the circuit, the over-voltage detection circuit comprising:

a voltage divider circuit connected to a break-over diode in a way to provide a representative low voltage to the break-over diode, the representative low voltage representing a voltage across the one semiconductor device;

an optocoupler configured to receive a current from the break-over diode when the representative low voltage exceeds a threshold voltage of the break-over diode indicating an over-voltage condition; and

a plurality of self-powered gate drive circuits connected to the plurality of semiconductor devices, wherein the plurality of self-powered gate drive circuits receive over-voltage triggering pulses from the optocoupler during the over-voltage condition and switch on the plurality of semiconductor devices to bypass the circuit.

2. The over-voltage protection system of claim 1 further comprising a mechanical switch to bypass the circuit for a long duration after the circuit has been bypassed by the plurality of semiconductor devices in the electronic valve.

3. The over-voltage protection system of claim 2 , wherein the electronic valve and the mechanical switch are open circuited during a non-fault condition.

4. The over-voltage protection system of claim 1 , wherein the semiconductor devices include thyristors, insulated gate bipolar transistors (IGBT) or controllable semiconductor devices.

5. The over-voltage protection system of claim 1 , wherein the break-over diode includes a low voltage break-over diode.

6. The over-voltage protection system of claim 1 , wherein the over-voltage detection circuit is connected across about a center switching device of the plurality of switching devices.

7. The over-voltage protection system of claim 1 , wherein the break-over diode is connected in series with a low-pass filter to form a break-over diode branch, the low pass filter configured to block a displacement current of the break-over diode.

8. The over-voltage protection system of claim 7 further comprising a snubber circuit connected in parallel to the break-over diode branch to filter out high frequency noises.

9. The over-voltage protection system of claim 8 comprising a filtering network connected between the optocoupler and the break-over diode branch and configured to drive the optocoupler.

10. The over-voltage protection system of claim 1 , wherein the self-powered gate drive circuit of each of the semiconductor switches includes a power generation circuit which generates a voltage from a storage capacitor in parallel with a super capacitor.

11. The over-voltage protection system of claim 10 , wherein the storage capacitor and the super capacitor are charged by a ballast resistor of the power generation circuit.

12. The over-voltage protection system of claim 11 , wherein the power generation circuit includes a voltage clamper to clamp the voltage across the storage capacitor.

13. The over-voltage protection system of claim 11 , wherein the power generation circuit receives energy from the respective open-circuited semiconductor device during a non-fault condition.

14. A method of bypassing a circuit during an over-voltage, the method comprising:

connecting an electronic valve across two terminals of a circuit, the electronic valve formed by connecting a plurality of semiconductor devices in series;

providing an over-voltage detection circuit across one of the plurality of semiconductor devices to detect an over-voltage across the circuit, wherein detecting the over-voltage includes:

providing a representative low voltage representing a voltage across the one semiconductor device to a break-over diode by connecting a voltage divider circuit across the semiconductor device;

receiving a current at an optocoupler from the break-over diode when the representative low voltage exceeds a threshold voltage of the break-over diode indicating an over-voltage condition; and

utilizing the optocoupler for providing over-voltage triggering pulses to self-powered gate drive circuits of the plurality of semiconductor devices for turning on the plurality of semiconductor devices of the electronic valve to bypass the circuit during the over-voltage condition.

15. The method of claim 14 further comprising switching on a mechanical switch connected across the circuit to bypass the circuit for a long duration after initial bypass by the electronic valve.

16. The method of claim 14 , wherein providing an over-voltage detection circuit includes connecting the over-voltage detection circuit across about a center switching device of the plurality of switching devices.

17. The method of claim 15 further comprising connecting a low-pass filter in series with the break-over diode to form a break-over diode branch and to block a displacement current of the break-over diode.

18. The method of claim 17 further comprising connecting a snubber circuit in parallel to the break-over diode branch to filter out high frequency noises.

19. The method of claim 14 , wherein the self-powered gate drive circuit of each of the semiconductor switches includes a power generation circuit which generates a voltage from a storage capacitor in parallel with a super capacitor.

20. The method of claim 19 comprising charging the storage capacitor and the super capacitor by a ballast resistor of the power generation circuit.