refePURPOSE AND SCOPE

This Technical Report (TR) describes the over-voltage protection employed on the National Grid Transmission (Electricity) system and in particular, the use of metal oxide surge arresters. Surge arresters can provide essential protection of substation equipment from lightning or switching overvoltages, and also improve circuit availability and reduce operational complexity. This report justifies the move from co-ordinating gaps to surge arrester protection of key substation assets. This also supports the policy statement PS(T)021 ‘Surge arresters for Substations’ and Technical Guidance Note TGN(T) 27 on the application of surge arresters.