Q) Why a single phase induction motor is not self starting?
A) When the stator winding of a single phase induction motor is connected to a single phase ac supply, a magnetic field is developed, which is only alternating not a rotating field and this alternating flux acting on rotor cannot produce rotation,as it can be done only by rotating magnetic field(RMF).
According to double revolving field theory,this alternating flux can be resolved in to two components namely forward and backward component and both have same magnitude but rotating in opposite directions. say forward component tries to rotate the rotor in one particular direction ,then backward component tries to rotate it in opposite direction, hence the net torque developed at the timing of starting is zero. However, if the rotor is given a push by hand or by other means in either direction, it will pick-up the speed and continue to rotate in the same direction developing operating torque.Thus a single induction phase induction motor is not inherently self starting requires some special means for starting.
A) When the stator winding of a single phase induction motor is connected to a single phase ac supply, a magnetic field is developed, which is only alternating not a rotating field and this alternating flux acting on rotor cannot produce rotation,as it can be done only by rotating magnetic field(RMF).
According to double revolving field theory,this alternating flux can be resolved in to two components namely forward and backward component and both have same magnitude but rotating in opposite directions. say forward component tries to rotate the rotor in one particular direction ,then backward component tries to rotate it in opposite direction, hence the net torque developed at the timing of starting is zero. However, if the rotor is given a push by hand or by other means in either direction, it will pick-up the speed and continue to rotate in the same direction developing operating torque.Thus a single induction phase induction motor is not inherently self starting requires some special means for starting.
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