Shaft Torsional Stress Due to Asynchronous Faulty Synchronization

Oscillographic records of 345 kV breaker currents during an asynchronous faulty synchronization of a 955 MVA, 1800 r/min turbine-generator into a strong network are duplicated by a readily available digital program. The event is shown to have occurred with the machine running about 3% below synchronous speed and leading the grid by about 1200. Consequential shaft torsional oscillations are substantially greater in amplitude than those for a generator terminal fault. Furthermore, it is shown that for an asynchronous faulty synchronization, the character of the torsional oscillations will greatly increase the fatigue life expenditure. Rain flow cycle counts evaluated against manufacturer provided S/N curves show that the machine suffered moderately severe fatigue life expenditure. An argument for on-line analysis of system disturbance induced torsional stresses is provided.