TRANSITIONAL PROCESSES INVESTIGATION OF INDUCTION MOTOR STARTING WITH LAUNCH RHEOSTATS IN THE PHASE ROTOR CIRCLE

Abstract

An induction motor electric drive (IM) is the most popular in industry and agriculture. This is result the ease of manufacture and operation, smaller than DC motors weight, dimensions, cost and reliability. Induction motors are divided into short-circuited (IMS) and with phase rotor (IMP). IMSs are characterized by high starting currents, torque and mainly operate in static mode. IMP has improved regulating properties, but they are characterized disadvantages as greater weight, dimensions and cost.
 In addition to the main static mode of operation, the IMS is often operated in transitional modes. Transitional modes occur when change shaft loading, power supply, circuit frequency, rotation direction when connected and disconnected from the network, when changing the parameters of the motor. The most difficult transitional modes are the processes of start-up, breaking, reverse and reconnection. There are current jumps in these modes and their duration depends on moment of inertia of all mechanism. Current jumps lead to the shocks of the drive, increased efforts in the windings of the stator and rotor. The electromagnetic torque in transitional modes has oscillation character with significant amplitudes, and the maximum rotor torque achieves five-time of nominal. Repeated and sometimes variable values of the electromagnetic torque IM in transitional modes cause accelerated wear of the mechanism, equipment and the motor.
 In mechanisms with repeated modes of operation (crane mechanisms etc.) IMP are widely used. In this case, additional start-up rheostats and contactors are required to limit current jumps and electromagnetic torque and as a result increase the smooth operation of the electric drive. Thus, the study of transitional processes in IMP in repeated modes is an actual task.