Effect of clearing short circuits and automatic reclosing on torsional stress and life expenditure of turbine-generator shafts

Abstract

Recent concern over abnormal stresses imposed on the shafts of large turbine-generators, due to high speed switching of network faults, has led to intensive investigation of this phenomenon. Elaborate computer programs were developed for simulated model studies which revealed that hitherto unexpectedly high shaft stresses can occur merely by tripping a three-phase short circuit near the power station at an unfavorable instant. The effects of circuit breaker reclosing, both successful and unsuccessful, were also investigated together with those due to faulty synchronizing. Test data on a 780 MVA unit gained by telemetric means verified the calculated torques and established the damping coefficients in a running unit. The adverse influence of numerous repetitive instances of such over-stressing on life expenditure of rotor materials is being evaluated.