Q5Electrical Machines II
Question
Explain the Split-phase starting methods.
Answer
Split-phase starting uses an auxiliary winding with a different R/X ratio to create a phase shift, simulating a two-phase rotating field.
A single-phase induction motor cannot start on its own. The Split-Phase Method solves this by temporarily simulating a two-phase electrical system.
The stator is equipped with two windings displaced in space: the Main Winding (highly inductive, low resistance) and the Auxiliary (Starting) Winding (highly resistive, low inductance).
When connected to the same single-phase supply, the difference in the R/X ratio of the two windings causes the current in the auxiliary winding to peak before the current in the main winding. This time-phase difference between the currents, combined with the spatial difference of the windings, creates a weak Rotating Magnetic Field that provides the initial starting torque. Once the motor reaches about 75% speed, a centrifugal switch often disconnects the auxiliary winding.