Methods to reduce the starting current of an induction motor.

Abstract

Power system loads that have high starting currents are a serious source of concern in smaller grids or remote locations on the main grid. This problem is envisaged to be exacerbated by the rollout of smart microgrids. When a high power induction motor is turned on in such a power system, its inrush current can be up to about ten times the full-load current. This transient current can cause problems when attached to weak grids. The increased current is due to the power required to start the load and the increased reactive power demand during the starting process. To protect the grid connection as well as the load, energy storage units can be used to compensate for the increased power requirement. A more pragmatic approach is to reduce the reactive power requirement using tuned compensation capacitors in order to reduce the inrush current. The aim of this research is to address the selection, calculation and switching of the capacitor bank for reactive power compensation. The capacitors are calculated and switched on to compensate the starting transient and disconnected when the machine has run up to speed using a point-on switching approach that reduces the switching transient.