Question

Why the starting and mainwinding are spaced 90 degree electrical?

Answer 1

a single winding when powered with single phage supply cannot create the phase shify necessary for the production of rotating magnetic in the air gap for starting the motor,therefore a second winding which is of lower inductance and higher resistance in presence or absence ofcapacitor can create the necessary phase shift to create r.m.f is necessary to start the motor.As soon as induction motor reaches certain speed,the auxiliary winding may be cut off and the rotor continue to rotate as long as power is supplied with an electricity.