Electrical apparatus

1. An electrical apparatus comprising:

first and second terminals for connection to an electrical circuit;

a chain-link converter connected between the first and second terminals, the chain-link converter including a plurality of chain-link modules, each chain-link module including at least one switching element and at least one energy storage device, the or each switching element and the or each energy storage device of each chain-link module combining to selectively provide a voltage source; and

a protection device connected in parallel with an electrical block that includes at least two of the plurality of chain-link modules, the protection device including a plurality of series-connected semiconductor devices, wherein the protection device selectively provides a current-conductive path to allow at least part of a current flowing in the electrical apparatus to fully bypass the electrical block.

2. An electrical apparatus according to claim 1 wherein the plurality of series-connected semiconductor devices is any one of:

a plurality of series-connected passive semiconductor devices;

a plurality of series-connected active semiconductor devices; or

at least one active semiconductor device connected in series with at least one passive semiconductor device.

3. An electrical apparatus according to claim 1 wherein the protection device is switched, in use, to a reverse-biased state when at least one chain-link module of the electrical block is configured to provide a non-zero voltage in a non-bypassed mode, and a forward-biased state when all of the chain-link modules of the electrical block are configured to provide a zero voltage in a bypassed mode and the direction of current in the electrical block allows switching of the protection device to a forward-biased state.

4. An electrical apparatus according to claim 3 further including a switching control unit, wherein the switching control unit controls the switching of the chain-link modules of the electrical block to selectively configure at least one chain-link module of the electrical block in the non-bypassed mode so as to maintain the protection device in the reversed-biased state during normal operation of the electrical apparatus.

5. An electrical apparatus according to claim 1 wherein the plurality of series-connected semiconductor devices includes: at least one passive semiconductor device, and the protection device includes a switching element to selectively inhibit or allow conduction of the or each passive semiconductor device.

6. An electrical apparatus according to claim 1 wherein the protection device includes at least one control circuit and at least one active semiconductor device, the or each control circuit being connected across a control electrode and an anode of the active semiconductor device or a respective one of the active semiconductor devices, wherein an impedance of the or each control circuit is variable to selectively allow a non-zero voltage to be applied across the control electrode and a cathode of the corresponding active semiconductor device in order to switch that active semiconductor device to an on-state.

7. An electrical apparatus according to claim 6 wherein the control circuit includes a resistive element with a non-linear voltage-current characteristic.

8. An electrical apparatus according to claim 6 wherein the impedance of the or each control circuit varies to allow a non-zero voltage to be applied across the control electrode and a cathode of the corresponding active semiconductor device when the or each control circuit has a voltage thereacross that matches or exceeds a predetermined voltage threshold.

9. An electrical apparatus according to claim 8 wherein the predetermined voltage threshold corresponds to a fault operating condition of the electrical apparatus.

10. An electrical apparatus according to claim 8 wherein the predetermined voltage threshold is below a safety voltage level which corresponds to failure of one or more components of the electrical block.

11. An electrical apparatus according to claim 1 further including a reactor connected in series with the plurality of chain-link modules, wherein the electrical block includes at least part of the reactor.

12. An electrical apparatus according to claim 11 wherein the protection device is connected to a tap on the reactor such that the electrical block includes part of the reactor.

13. An electrical apparatus according to claim 11 wherein the reactor is split into a plurality of reactor elements, and the protection device is connected to a junction between two of the plurality of the reactor elements such that the electrical block includes at least one of the reactor elements.

14. An electrical apparatus according to claim 1 including a plurality of protection devices and a plurality of electrical blocks, wherein each protection device is connected across a respective one of the electrical blocks, each electrical block including at least two of the plurality of chain-link modules, each protection device including a plurality of series-connected semiconductor devices, wherein each protection device selectively provides a current-conductive path to allow current flowing in the electrical apparatus to bypass the corresponding electrical block.