SOLUTION

In a split-phase motor, the starting winding is connected through a centrifugal switch.

Split-Phase Induction Motor

• The main components of the split-phase motor include main winding, auxiliary winding, and a centrifugal switch.
• This is the simplest way to establish a rotating magnetic field with two windings in the same stator core.
• The auxiliary or starting winding has a series of resistance that makes its impedance highly resistant.
• It is not the same winding as the main winding but has fewer turns of a much smaller diameter than the main winding.
• This will reduce the voltage lagging of the starting current.
• The main winding is inductive in nature to lag the voltage by a certain angle. This winding is designed to operate at synchronous speeds of 75% and above.

• These two windings are connected to the input AC supply in parallel.
• Because of the inductive nature, the supply voltage lags at a large angle, with the current induced by the starting winding almost being in phase with the voltage due to its resistive nature. Thus, there is a phase difference between these currents. The resulting current produces a rotating magnetic field and thus the starting torque.
• The centrifugal switch is connected to the starting winding in series.
• When the motor is 75-80% of the synchronous speed, the centrifugal switch is opened mechanically, thereby removing the auxiliary winding. The motor, therefore, only works with the main winding.