Performance assessment study of a 250 MVA air-cooled turbo-generator

Today, many customers require generators that combine high energy efficiency with user-friendly operation. The long term reliability of the unit is another of the most important customer considerations. To meet these expectations, Hitachi has designed a large air-cooled turbo-generator equipped with an Inter Cooler Ventilation System (ICVS), which achieves an efficiency of over 98.8% at 250 MVA. New findings based on studies of the 250 MVA generator are reported here. Due to the degree of circulating current losses, the temperature does not necessarily reach its highest point at the innermost position. After identifying the critical points, 1000 sensors were set in the test generator and it´s operational performance was evaluated. The temperature evaluations related to the stator windings and the measured flow in the air gap demonstrated a positive correlation with the measured values. The highest temperature in the generator had a wide margin relative to the class B temperature limitations. This performance-based assessment will assist in assuring the long-term reliability of the generator.