Soft-start of an electric drive with induction motor

Abstract

During the work phases of my B.Elec.Eng. degree course, I am usually stationed at the Civil Abattoir at Marsa. In the new slaughtering room there exist several electric drives which stop and start abruptly. One of these, the lifter, starts and stops so abruptly that the butcher standing on top if it, holding a dangerous big saw in his hands particularly loses his balance as the lifter comments and ends its motion. Such conditions could result in serious accidents happening to the butcher with resultant physical injury. There was thus a need to find some method of controlling the speed of the induction motor of the lifter so that its starting and stopping became gradual while the rest of its motion remained unchanged. Now there are several methods of controlling the speed of an induction motor and these methods are described in detail in Appendix I of this thesis. However, the method chosen to control the speed in this case was the soft-start method because t t seemed most appropriate since the problem has to "soften" its acceleration and deceleration at the start and end of its motion respectively, leaving the speed during the rest of its motion unchanged. A control circuit was constructed!