In an induction motor, the stator is also known as _________ and the rotor as __________

Question

Examoogle · Accepted Answer

field winding, armature winding

Explanation: In an induction motor, the stator carries the main supply windings creating the rotating magnetic field, commonly referred to as the field winding. The rotor carries the current induced by electromagnetic induction, acting as the armature winding where the electrical energy is converted into mechanical torque.

Working Principle: The stator winding is connected to an AC source to produce a rotating magnetic field ($RMF$). This $RMF$ cuts the rotor conductors, inducing an EMF according to Faraday's Law ($e = -N \frac{d\Phi}{dt}$). The resulting current interaction with the magnetic field creates Lorentz force, causing the rotor to rotate in the direction of the $RMF$.

Key Formulas: $N_s = \frac{120f}{P}$ — Synchronous speed of the rotating field; $s = \frac{N_s - N_r}{N_s}$ — Slip of the induction motor

Key Points: The stator provides the excitation required to set up the magnetic flux.; The rotor acts as the short-circuited winding (armature) where induced currents flow.; The interaction follows Lenz's Law, opposing the cause (relative motion) that produces it.

Advantages: Rugged and simple construction; Self-starting (for 3-phase machines); Low maintenance requirements

Disadvantages: Low starting torque compared to DC motors; Speed control is complex and expensive; Sensitive to voltage fluctuations

Applications: Industrial pumps and compressors; Conveyor belts and fans; Domestic appliances like washing machines

Additional Info: In DC machines, the terminology is reversed: the field is on the stator and the armature on the rotor, but in the context of Induction Motors, the stator provides the magnetic field and the rotor the load current.. Options B, C, and D are incorrect because they interchange the roles or incorrectly identify windings like compensators or interpoles, which are specific to DC machine commutation.

Answer: A is correct — The stator acts as the stationary excitation source (field), while the rotor serves as the conductor loop (armature) receiving induction.

Exam Tip: Remember that in induction motors, the stator-rotor relationship is functional: Stator sets the flux (Field), Rotor intercepts flux (Armature). Always visualize the energy flow from stationary stator to rotating rotor.

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