Load equalization for high-power induction motors by speed control in limited range

Abstract

The paper presents a new method for load equalization of high power wound rotor induction motors driving the drums of belt conveyors. During exploitation, the diameters of the drums become unequal, due to the abrasion of rubber layer or sticking of dirt, leading to unequal load distribution between motors. The proposed solution of this problem implies the application of the ldquorotor resistor converterrdquo with the existing starting resistors. The rotor resistor converter consists of the group of three rotor resistors and the unit for their short-circuiting. For that purpose, the stator current of all motors is measured, and the instantaneous average value is used for the reference. This leads to the regime where one motor operates with the short-circuited rotor, with the semiconductor switch in the rotor resistor converter - always on. The currents of the remaining motors will be controlled by the PLC and the rotor resistor converters operating in the PWM regime, periodically short-circuiting the rotor terminals, i.e. the rotor resistors. In this way, the speed of the controlled motors will be reduced, to achieve equal load on all drives (load equalization). The results recorded on the laboratory model of the drive will be presented in the paper.