Question

What is the Ferrari's principle of single phase induction motor?

Answer 1

Ferrari's principle of a single-phase induction motor explains how the motor can start and operate, even though it uses a single-phase power supply.

In a single-phase induction motor, when the motor is powered by a single-phase AC supply, the current flowing through the stator winding creates a magnetic field that pulsates, but it does not rotate. This is because a single-phase supply produces a magnetic field that alternates back and forth, rather than continuously rotating like in a three-phase motor.

Ferrari's principle helps to understand how a single-phase induction motor can overcome this issue. It states that in order for the motor to start, a second rotating magnetic field must be created. This is achieved by using either:

1. Split-phase windings: In this method, two windings are placed on the stator – one is the main winding, and the other is a starting winding. The current in the starting winding is phase-shifted (using a capacitor or a phase-shifting device) to produce a rotating magnetic field. The interaction between the main winding’s magnetic field and the phase-shifted magnetic field of the start winding generates a rotating field that starts the rotor.
   

1. Use of a capacitor: In capacitor-start motors, a capacitor is added in series with the starting winding. This capacitor helps create a phase difference between the two windings, which generates a rotating magnetic field that helps the motor start.
   

So, the key idea behind Ferrari's principle is that a rotating magnetic field (essential for motor rotation) must be artificially created in a single-phase system, which is done by splitting the phase of the current to generate the required rotating field.

Once the motor starts, the starting winding is usually disconnected (in some motor designs), and the motor continues running using the main winding.