Electrical Engineering ⇒ Topic : Repulsion-start induction motor

REPULSION-START INDUCTION MOTOR

As its name implies the repulsion-start induction motor starts as a repulsion motor with its brushes set to the maximum torque position. When the load has been accelerated to about 75 per cent of synchronous speed, a built in centrifugal device places a shorting ring in contact with the commutating bars, converting the armature to squirrel- cage rotor. The motor then runs as induction motor on its induction characteristic (Fig.a).Although at one time this type of motor was used almost exclusively where high starting torque was required, it has been replaced in nearly all cases by the capacitor motors because of the following reasons

                                            Fig.(a). Speed-torque characteristics of repulsion-start induction motor.