Reduction Method of Transient Torques on Motors During Motor Bus Transfer

A large transient torque that occurs when the power is restarted and secured after a power failure is a major stress on the motor shaft in industrial power systems, so it is very important to reduce it. Induction motors may experience a large torque if there is a phase difference between the new power source and the residual voltage. For a more practical analysis of a MBT (Motor Bus Transfer) on the transient torque, an analysis is needed to consider the phase difference and to use the bus transfer speed after upper circuit breaker operation. Accordingly, the optimal phase difference is presented in this study and is used in the new MBT scheme, in which applied to change rate of between buses volts per hertz using Clarke's transformation. We analyzed a negative and positive peak torque and a transient torque after MBT using EMTP (Electromagnetic Transients Program) based on various conditions: phase difference, breaker speed, and inertia constant. The simulation results show that transient torque can be reduced by proposed the MBT scheme.