This specification, in conjunction with related functional specifications, calls up the protection, control and measurement functions, and the associated interconnectivity, that are required within all bays (regardless of bay type) at National Grid owned substations only, on the 400 kV, 275 kV and 132 kV transmission system (including transformer low voltage connections, transformer tertiary connections and associated plant and apparatus). Functions that are specific to a particular bay(s) are called up in the appropriate Bay Level specifications. The specification goes on to identify the station-wide systems that need to be present at a substation on the 400 kV, 275 kV and 132 kV transmission system.