NATIONAL Grid, a wholly-owned subsidiary of National Grid Transco, has three transmission crossings of the River Thames east of London, UK, in three different forms. One overhead transmission line, one cable tunnel build in the late 1960s and cables, installed in the 1960s, under the road deck of the west tunnel of the Dartford River Crossing. The 275 kV cables in the west tunnel of the Dartford River Crossing connect the Littlebrook Power Station to the Barking substation and need to be replaced. For a number of reasons, including the difficulties in the inspection and maintenance of the cables in the tunnel, a decision was taken to look at alternative ways of crossing the River Thames.
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