Q4Electrical Machines II

The foundational principle behind modern industrial motors relies on placing three separate coil windings physically inside a stator core such that their magnetic axes are separated by exactly $120$ mechanical degrees (or electrical degrees for a 2-pole machine).

When these three windings are energized by a balanced three-phase AC power supply (where the currents reach their peaks $120$ time-degrees apart), the alternating magnetic fields produced by each individual winding mathematically superimpose. The resultant sum creates a single, strong magnetic field of constant magnitude ($1.5{\Phi }_{max}$) that continuously rotates around the stator at Synchronous Speed.

This concept is universally applied in the construction of the Three-Phase Induction Motor, which is the workhorse of global industry. The generated rotating magnetic field sweeps past the stationary rotor bars, inducing currents that create a magnetic field in the rotor. The rotor's field tries to align with the rotating stator field, producing continuous mechanical torque. Without this $120^{\circ }$ spatial shift concept, self-starting, highly efficient, commutator-less AC motors would not exist.