Three-Phase AC Supply Energizes the Stator
The stator (primary) is connected to a balanced three-phase AC supply. The three coils — Phase A, B, and C — are displaced 120° electrically from each other and carry sinusoidal currents that are 120° apart in time.
Travelling Magnetic Field is Produced
The combined effect of the three displaced currents creates a resultant magnetic field that moves linearly from one end of the stator to the other — the "travelling wave." Its speed is the synchronous speed: Vs = 2τf.
EMF & Eddy Currents Induced in Rotor
The moving magnetic field cuts through the aluminium rotor sheet, inducing an EMF by Faraday's Law. This drives eddy currents (shown in orange) circulating within the rotor plate in the plane perpendicular to the field.
Lenz's Law → Linear Thrust
By Lenz's Law, the induced eddy currents create their own magnetic field opposing the change. The interaction between the stator's travelling field and the rotor's induced field produces a linear thrust force, pushing the rotor in the direction of field travel.
Rotor Moves — Slip Always Exists
The rotor accelerates but can never reach synchronous speed (Vs). If it did, there would be no relative motion, no induced EMF, no current, and no thrust. The difference is called slip: s = (Vs − v) / Vs.
Speed & Torque Control
Speed is varied by changing frequency or switching between 2-pole and 4-pole configurations. Doubling the poles halves the synchronous speed, doubling the torque (τ = PAG / ωsync). Try the controls above!
Synchronous Speed
τ = pole pitch (m), f = frequency (Hz). Not dependent on number of poles — only pole pitch and frequency.
Slip
LIMs have higher slip than rotary motors due to end effects and larger air gaps, reducing efficiency.
Magnetic Field Speed
P = number of poles. Changing from 2-pole to 4-pole halves the magnetic field speed.
Induced Torque
PAG = air gap power. At constant PAG, halving ωsync (4-pole) doubles the thrust force.