Protection of Large Steam Turbine-Generator Units on TVA System

This paper describes the relay protection applied by TVA to large steam turbine-generator units, including the main power transformer and its connections. The basic philosophy underlying relay applications is given, and the interrelations between generator protective relays and those on the station equipment and connecting transmission lines are included. The relation of protection to generator types is shown, and the performance record of the protective relay is presented for electrical faults that have occurred on the TVA system's 50 steam units, ranging in size from 125- to 700-MW capability. Practices relating to the electrical transmission system and those differing from conventional ones are emphasized. The mechanical protection afforded for the steam generator and steam turbine and their appurtenances required for unit operation is described.