How is the required phase displacement between the current in the running and starting windings obtained?

The required phase displacement between the current in the running and starting windings of a single-phase motor is typically obtained through the use of a capacitor.

In single-phase motors, particularly in split-phase motors, two windings are used: a main or running winding and a starting (or auxiliary) winding. For the motor to start and run efficiently, these two windings must have currents that are out of phase with each other. This phase difference creates a rotating magnetic field, which is essential for the motor to start and continue running.

This phase displacement is most commonly achieved by connecting a capacitor in series with the starting winding. The capacitor introduces a phase shift of the current in the starting winding relative to the current in the running winding. Capacitors have a leading power factor, which means the current in the capacitor leads the voltage. When this is applied to the starting winding, the current in the starting winding leads the current in the running winding, typically by about 70 to 90 degrees.

Some single-phase motors may use other methods to achieve phase displacement, such as differing winding configurations or inductances, but the use of a capacitor (making it a capacitor-start motor) is one of the most effective and widely used methods. This is because the capacitor can be designed to provide a specific amount of phase shift, which optimizes the motor’s starting torque and reduces starting current. After the motor reaches a certain speed, the starting winding can be disconnected from the circuit by a centrifugal switch or