Why an induction motor is also called a rotating transformer? The operating principle of an induction motor is similar to that of a transformer. The stator winding is equivalent to the primary winding and the rotor winding is equivalent to short circuited secondary winding of the transformer. In transformer, the secondary is stationary but in case of induction motor, it can rotate. Therefore, the induction motor is also called a rotating transformer.
The Correct Answer and Explanation is:
An induction motor is often referred to as a rotating transformer due to the similarity in the way both machines operate on the principle of electromagnetic induction. Although their applications differ—transformers transfer electrical energy between two stationary circuits, while induction motors convert electrical energy into mechanical motion—the underlying electromagnetic principles are closely related.
In a transformer, the primary winding receives alternating current (AC), producing a varying magnetic field that induces a voltage in the stationary secondary winding through mutual induction. Similarly, in an induction motor, when AC is applied to the stator winding (the stationary part of the motor), it produces a rotating magnetic field. This magnetic field links with the rotor winding (the rotating part), which acts like the short-circuited secondary of a transformer.
The relative motion between the stator’s rotating magnetic field and the stationary rotor conductors induces an electromotive force (EMF) in the rotor according to Faraday’s law of electromagnetic induction. Since the rotor is typically a closed circuit, this induced EMF causes current to flow in the rotor conductors. The interaction between the rotor current and the rotating magnetic field produces torque, which causes the rotor to turn—hence mechanical rotation.
Unlike a transformer, where the secondary is fixed, the rotor in an induction motor is free to move. This movement is a defining characteristic and is what gives the induction motor its mechanical output. Yet, since both machines involve energy transfer via magnetic induction between primary and secondary windings (or stator and rotor), the induction motor can be conceptualized as a transformer with a rotating secondary—thus the term “rotating transformer.”
This analogy helps in understanding induction motors better, particularly in terms of energy conversion, equivalent circuits, and performance analysis, drawing on well-established transformer principles.
