Design of AC auxiliary power distribution systems for large TVA thermal power generating plants

This paper discusses TVA´s practices in the design of ac auxiliary power distribution systems of large thermal generating plants. Its scope is limited to the primary portions of the system, including the station service transformers which step down the main generator voltage or switchyard voltage, and the switchgear and buses which distribute power from the secondaries of these transformers. Single-line diagrams of one fossil and two nuclear plants are presented. The change from systems designed with common startup and emergency supplies to a system which provides startup power from the main transformer with independent alternate offsite power sources is discussed.