Comparative Analysis of Methods for Starting Squirrel-Cage Induction Motors

Abstract

Direct and soft starts of squirrel-cage induction motor are considered. Operation specificity due to nonsinusoidal supply voltage and equivalent circuit parameters changes due to variable voltage magnitude and frequency as well as magnetic circuit saturation and current displacement in rotor winding are studied. Consumed energy calculations show advantage of frequency converter start. Mathematical models are experimentally confirmed. Stator winding overheating during starts is analyzed. Analysis results of motor vibroacoustic indicators during start are given: vibrovelocity and –acceleration of magnetic origin, vibrovelocity of mechanical origin (radial and axial), ventilating and magnetic noises. Mechanical shaft stiffness indexes, shaft strength and dynamic bearing load are examined and compared at direct and soft starts. It was established that due to soft start at low intensities of the control parameters changes, dynamic bearing load surges can be excluded. Resulting shaft deflection at soft start reduces the stronger, the smaller is the control parameter change intensity