Benefits and experience of EHV cables in tunnels

The London network has a broad mix of primary system cables up to 132 kV. This includes gas filled, gas compression, fluid filled, XLPE and paper solid (up to 66 kV only). The total circuit route length is approximately 1565 km of which over 200 km are installed in tunnels at some point along their length. A network of 40 tunnels mainly in the central London area exists to accommodate these cables. Many of these tunnels were established in the early years of electricity expansion in the capital. They were generally built to connect the generating station to its main transmission switchboard, or to specifically overcome obstructions along the route such as the River Thames. Since the early 1990s some 70 km of 132 kV route length has been installed in 6 major tunnels. Unlike previous arrangements these new tunnels house the entire length of the circuit and are not used to just overcome obstructions along the route.