A novel simple method for elimination of DOL starting transient torque pulsations of three-phase induction motors

Abstract

This paper presents a novel method for elimination of transient torque pulsations of three phase induction motors which arises on direct-on-line (DOL) starting. When started DOL, during run-up period, induction motors produce large transient torque pulsations well in excess of full-load torque. These torque pulsations can be detrimental as it may cause shock-loading on the driven equipment and damage to the mechanical system components such as shaft, gear and couplings. Also, high inrush current is drawn by the motor and this, due to extra temperature rise, may cause winding insulation failure and extra stress on power utilities. With this method faster starting is achieved, which result in faster decaying of inrush currents, and hence reduced stress on both the winding insulation and supply utilities. The method is composed of inserting an optimized and series connected capacitor-resistor pair between the motor and the supply in order to eliminate the low frequency transient components available in the stator and rotor currents, which are the root cause of transient torque pulsations. The proposed method is simulated with full details on two different motors and the results obtained are very satisfactory and promising.