Why Single Phase Induction Motor is Not-Self Starting?
When faradays electromagnetic induction law is applied to the rotor, electricity is induced and force is generated on the rotor bars. But according to Double Revolving Field theory, there are two magnetic fields with the same magnitude but revolving in the opposite direction. Thus, two force vectors are produced with equal magnitude but opposite in direction.
Thus, these force vectors, as they are of the same magnitude but opposite in direction, doesn’t cause the rotor to rotate. So, single-phase induction motors are not self-starting. The motor simply buzzes in this condition. To prevent this situation and rotate the rotor, the starting force has to be applied for a single-phase motor. As the force in one direction, becomes greater than the force the other direction, the rotor starts rotating. In single-phase induction motors, Auxiliary windings are used for this purpose.
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