Answer / 1802.pranav

actually in stater of a vehicle there is one solenoid switch
which has one auxiliary and one main winding.so as soon as u
rotate the key of car,auxiliary winding comes into the
picture and 1st contact is made.in this situation motor runs
at low speed around 600rpm.But when 2nd switch comes into
contact due to main wdg then motor runs at max speed.and
when 2nd switch comes into contact it produces spark and
pushing action DUE TO WHICH HUMMING SOUND COMES.

Answer / s r mishra

humming noise is due to the pulsating torque in 1 phase induction motor.a 3 phase induction motor which has rotating torque does not make a humming noise.

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