Transients during line-starting of squirrel-cage induction motors

This paper discusses the transients associated with line-starting of squirrel-cage induction motors and potential difficulties posed by these transients. These include transient torques significantly in excess of the rated motor torque, large inrush currents and corresponding large dips in voltage. Test results are presented which illustrate these problems. The paper then discusses various techniques to ameliorate the effects of the starting process, including reduced-voltage and soft starting. The benefits of these techniques are illustrated through simulation. The oscillatory transient torques discussed in this paper are not new, but have often been ignored.