On Tuesday 26th November 2019, members of the CIGRE UK NGN visited the St John’s Wood substation in London, one of most compact and complex substations operated by National Grid. This substation is the grid supply point (GSP) for both Westminster and Kensington & Chelsea boroughs. St John’s Wood substation hosts what is known as The London Connection, a 20km tunnel for a 400kV XLPE cable connection between Elstree and St John’s substation. This connection supports the supply for North West London and the City.
Before starting the visit around the substation, Julio Perez gave an overview of CIGRE UK and the activities organised by the NGN. Following this, James Watson from National Grid delivered a technical presentation on the importance of St John’s substation in the high-voltage supply for London, its configuration, as well as the type of equipment found at the substation.
After a safety briefing by James, the first stop was The London Connection underground tunnels, which houses the 400kV XLPE cables used for the connection to another major substation, Elstree. The London Connection is part of a series of underground tunnels designed to meet the increasing electricity demand from London whilst minimising road disruption.
Then we visited one of the buildings containing some of the gas-insulated switchgear, to reconfigure the supply points when required. James explained to us how the gas-insulated mechanism operated to interrupt an arc when opening circuit breakers and also what are the main procedures for managing faults. At the end of the visit, we had the chance to visit one of the main super-grid transformers which serve to step-down the voltage from the transmission level, from 400kV to 132kV.