Exam Question

(a) A three-phase induction motor works by using three-phase alternating current (AC) to produce a rotating magnetic field, which causes the rotor to spin and generate mechanical energy. The stator, the stationary part of the motor, has three sets of windings spaced 120 degrees apart. When a three-phase AC supply is applied, it creates a rotating magnetic field around the stator. This rotating field moves at a certain speed, called synchronous speed.
The rotor, typically a squirrel cage design made of copper or aluminum bars, is placed inside this rotating field. As the magnetic field rotates, it induces an electric current in the rotor bars, which generates its own magnetic field.
The interaction between the stator’s rotating magnetic field and the rotor’s magnetic field creates a torque, causing the rotor to turn. The rotor always lags slightly behind the stator's rotating field, which is why it operates at a slightly lower speed than synchronous speed. This process allows the motor to efficiently convert electrical energy into mechanical motion without needing additional starting components.