Generally overhead lines are used, but an important class of HVDC projects use submarine power cables.
A back-to-back station has no transmission line and joins two separate AC grids at a single point.
dc cable: Prysmian Common project of TenneT TSO and Transnet BW highlight: first 525kV fully underground DC cable project 2 As of 9 December 2015, LitPol Link started trial operations.
[185] 3 Caithness Moray HVDC serves a number of renewable energy sources in the north of Scotland - see map[186] 4 Contracts due to be placed in 2016.
6 Date is that quoted to support the Shetland Wind Farm that SSE is a part investor in.