London, 28 August, 2003
On the evening of 28 August 2003 London was hit by a localised power blackout concentrated in the south of the city. The blackout occured at 6.20pm and power was restored by 7pm. While the power blackout lasted only 40 minutes it served to demonstrate how much we rely on electricity and how the knock-on effects of an outage can be more serious than the outage itself. Thousands of commuters on London's underground and railway network were stranded and many underground stations were still closed several hours later.
The main cause of the power loss in London was found to be an incorrectly installed automatic protection relay which incorrectly read a change of power flow as a fault and automatically disconnected an area of south London from the rest of the transmission network. Full details of the event are available in the National Grid Report into the event.
Importantly, the blackout in London was contained to a single circuit and while the effect of losing that circuit was significant areas beyond that circuit did not lose power.
In the wake of the London blackout concerns have been expressed that the UK is on the verge of winter blackouts as spare capacity has dropped to a low of 15%, according the National Grid Transco(NGT). OFGEM has published a presentation on security of supply which addresses this situation, making the argument that the consequences of tight supply are now feeding through into the market and driving up prices to a point where mothballed capacity can be brought back online. NGT has advised OFGEM that it does not expect power cuts but has said, in a report published 14 October 2003, that it would like a larger cushion of reserve power to be available.