New onshore substation

The new onshore substation at Twineham is on a 7 hectare site located 13 kilometres north of the Sussex coast, adjacent to the National Grid’s 400kV substation at Bolney.

Here the electricity carried by the onshore cable is converted by supergrid transformers from 150kV to a higher voltage so it can feed in to the wider 400kV national grid transmission network.

The new substation at Twineham contains air insulated switchgear as well as 150kV gas insulated switchgear which, due to its compact design, has been located inside a purpose-built building. The switchgear incorporates surge arresters, circuit breakers, earth switches and disconnectors that control, protect and isolate equipment to clear electrical faults and allow maintenance activities.

National Grid imposes stringent requirements on generators in terms of power quality and network stability. Therefore the use of reactive compensation is key to controlling voltage levels and stability in electrical networks and substations. Shunt reactors, harmonic filters and STATCOM equipment have been installed at Twineham for this purpose. This prevents unwanted voltage fluctuations while also maintaining power quality to within tolerable levels.