DC CONNECTIONS

Superconductors are very beneficial for DC power transmission because they can provide the following advances:

• Very low losses (no AC conductor loss and induced losses)

• Better utilisation of the superconducting tapes

• Simple superconducting tapes (no optimisation for AC needed)

• Simple cable design

Furthermore unique characteristics like extremely high current capability can be utilised for DC superconducting cables. DC connections are usually used for long distance transmission of bulk power, which will favour a superconducting solution.

AC transmission lines are the far most widespread type of connection in the electric utility system. But DC connections are steadily getting more common. One of the promising application of superconducting DC connections is to bring production from off-shore wind turbine farms to shore. By using a high current superconducting connection the following benefits can be achieved:

• Provide reduction of transmission losses by a factor of two or more.

• No high voltage transformers at sea.

• Provide a flexible and controllable power flow.

• Cost effective transmission concept for the future.

A DC connection needs power electronic in each end of the cable to convert the current between AC and DC. A future perspective is to use the cable cooling system for the power electronic. This will reduce the quite high converter losses. It is also possible to utilise the ability of both tire superconducting cable and the power electronic to transmit high currents.

DC connections are often used for long length transmission and sea crossing. Therefore long distance between cooling stations is required. If a superconducting cable is designed for large lengths, distance between cooling stations can be 40-60 km and still obtain the necessary cooling.

Design of a two-phase superconducting DC cable with conventional screen.

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	why superconducting cables?
	substation connections
	retrofit of existing cables
	high load connections
	DC cables
	long term visions