Vulnerability of Large Steam Turbine Generators to Torsional Interactions During Electrical Grid Disturbances

This paper presents a formalized and systematic approach for identifying the zone of vulnerability of a power plant to potentially damaging torsional stress. That is the region of the electrical network surrounding a plant where electrical disturbance may result in significant loss of life at critical rotor locations on the turbine generator. The approach is based on comparing the peak transient torques observed for various network faults and disturbances to the peak transient torque for a machine terminal fault. This is shown to be a useful methodology in the absence of detailed shaft fatigue data. The results of the study provide significant insight into the various factors that influence the level of torsional stress and how one would be able to assess when detailed torsional interaction studies are necessary. Finally, some key general conclusions are drawn with respect to system events that may result in turbine-generator shaft fatigue loss-of-life.