Subsea power switching device and methods of operating the same

1. A subsea power switching device comprising:

a first terminal for connection to a power source;

a second terminal for connection to a subsea consumer;

a semiconductor switching unit driveable into a blocking state electrically insulating the first terminal and the second terminal;

a decoupling unit comprising at least one contactor electrically coupled in series with the semiconductor switching unit for further electrically decoupling the second terminal from the first terminal when the semiconductor switching unit is in the blocking state to thereby provide a galvanically isolating state of the switching device;

an earth fault detection device for detecting an earth fault at a conductor and providing in response thereto an earth fault signal;

a load current sensor for providing a current signal indicative of a load current flowing through the switching device; and

a controller configured to:

(a) transition from an electrically conducting state of the switching device to the galvanically isolating state of the switching device by:

providing a first control signal to switch the semiconductor switching unit into the blocking state; and

providing a second control signal to drive the at least one contactor into the galvanically isolating state while the semiconductor switching unit remains in the blocking state; and

(b) transition from the galvanically isolating state of the switching device to the electrically conducting state of the switching device by:

providing a third control signal to drive the semiconductor switching unit into the blocking state;

providing a fourth control signal to drive the contactor into an electrically conducting state while the semiconductor switching unit remains in the blocking state; and

providing a fifth control signal to drive the semiconductor switching unit into an electrical conducting state.

2. Switching device according to claim 1 , wherein the semiconductor switching unit comprises two semiconductor switches electrically coupled anti-parallel with regard to each other.

3. Switching device according to claim 1 , further comprising a state unit for providing a state information signal indicative of whether the switching device is in the electrically isolating state or in the electrically conducting state.

4. Power supply comprising:

a switching device comprising:

first and second power source terminals for connection to a common power source;

a pair of first and second load terminals for connection to a common load;

a first conductor extending between only the first power source terminal and first load terminal, and a second conductor extending between only the second power source terminal and second load terminal;

a first semiconductor switching unit coupled to the first conductor and a second semiconductor switching unit coupled to the second conductor, the first semiconductor switching unit driveable into a blocking state electrically insulating the first power source terminal from the first load terminal and the second semiconductor switching unit driveable into the blocking state electrically insulating the second power source terminal from the second load terminal;

a decoupling unit comprising at least one contactor electrically coupled in series with the semiconductor switching units for further electrically decoupling the first and second power source terminals from the first and second load terminals when the first and second semiconductor switching units are in the blocking state to thereby provide a galvanically isolating state of the switching device;

an earth fault detection device for detecting an earth fault at a conductor and providing in response thereto an earth fault signal;

a load current sensor for providing a current signal indicative of a load current flowing through the switching device; and

a controller configured to:

(a) transition from an electrically conducting state of the switching device to the galvanically isolating state of the switching device by:

providing a first control signal to drive the first and second semiconductor switching units into the blocking state; and

providing a second control signal to drive the at least one contactor into the galvanically isolating state while the semiconductor switching unit remains in the blocking state; and

(b) transition from the galvanically isolating state of the switching device to the electrically conducting state of the switching device by:

providing a third control signal to drive the semiconductor switching unit into the blocking state;

providing a fourth control signal to drive the contactor into an electrically conducting state while the semiconductor switching unit remains in the blocking state; and

providing a fifth control signal to drive the semiconductor switching unit into an electrical conducting state.

5. Power supply according to claim 4 , wherein the power supply is a subsea power supply and the load is a subsea load.

6. Method of controlling a subsea power switching device having a first terminal and a second terminal, a semiconductor switching unit electrically coupled between the first terminal and the second terminal, and a switchable contactor electrically coupled in series with the semiconductor switching units and configured to selectively provide the galvanically isolating state of the switching device, the method comprising:

(a) transitioning from an electrically conducting state of the subsea power switching device to the galvanically isolating state of the switching device by:

providing a first signal, by a controller, to drive the semiconductor switching unit into a blocking state; and

providing a second control signal, by the controller, to drive the contactor into the galvanically isolating state while the semiconductor switching unit remains in the blocking state; and

(b) transitioning from the galvanically isolating state of the subsea power switching device to the electrically conducting state of the switching device by:

providing a third control signal, by the controller, to drive the semiconductor switching unit into the blocking state;

providing a fourth control signal, by the controller, to drive the contactor into an electrically conducting state while the semiconductor switching unit remains in the blocking state; and

providing a fifth control signal, by the controller, to drive the semiconductor switching unit into an electrical conducting state

monitoring an earth fault detection device for an earth fault at a conductor and providing in response thereto an earth fault signal; and

monitoring a load current sensor for a current signal indicative of a load current flowing through the switching device.

7. Method according to claim 6 , the switching device further having a contactor electrically coupled in series with the semiconductor switching unit, wherein further electrically decoupling the first terminal from the second terminal comprises:

after driving the semiconductor switching unit into a blocking state, subsequently driving the contactor into a galvanically isolating state while maintaining the semiconductor switching unit in the blocking state.