Limiting induction motor transient shaft torques following source discontinuities

When an induction motor experiences a momentary discontinuity in source power, the motor shaft is subjected to potentially damaging re-energization transients caused by transient electromagnetic torques from the motor, and by the dynamic mechanical shaft response. Source discontinuities may be the unavoidable result of supply dips and outages, or of planned motor bus transfers. Although it is possible to estimate the reconnection electromagnetic torque peak by general principles, without detailed simulation, there is currently no simple way to estimate the shaft reclosure torque peak in the worst case of a resonant shaft and load. In this paper, a general result on the magnitude of resonant shaft torque is given and the effect of reclosure delay and stator damping is shown.