London August 2003 Power Blackout

Event Year: 2003 Reliability: Confirmed
Country: United Kingdom
Industry Type: Power and Utilities

The blackout was caused by a sequence of events. During this time period a scheduled maintenance shutdown was underway on one circuit of the line. Next, an alarm was received at the Electricity nation Control Centre, indicating that a transformer or its associated shunt reactor was in distress and could fail causing signigicant safety and environmental impacts. National Control contacted EDF Energy and asked them to disconnect the distribution system from the transformer, and switch.

After the switching process took place the automatic protection equipment on a circuit interpreted the switching as a fault. The automatic protection relay disconnected this circuit from the rest of the transmission system causing a loss of supply. (#1)


724MW of supplies were lost amounting to around 20% of total London supplies at that time. This affected about 410,000 of EDF Energy’s customers and supplies were lost to parts of London Underground and NetworkRail. (#1)

Action Description: Improvements are being reviewed in communications, security of electricity supplies, automatic protection equipment, managment of protection systems, as well as operating procedures. (#1)