Load shedding and emergency load sequencing system at Sizewell B power station

Sizewell B nuclear power station has a main electrical system that connects together the main turbogenerators, generating at 23.5 kV, the 400 kV grid and the auxiliary equipment required to operate the station. A separate essential 3.3 kV electrical system fed from the main electrical system, supplies all the auxiliaries required to shut-down the nuclear reactor and maintain it in a safe shut-down condition. The function of the load shedding and emergency load sequencing (LSELS) system is to monitor the condition of the 3.3 kV incoming supply from the main electrical system to each essential 3.3 kV switchboard and initiate its replacement, with the supply from an associated diesel standby generator, if it is outside set parameters. Therefore the design of the system must be highly reliable and the purpose of this paper is to detail the design approach used to ensure that a high system reliability is achieved