The stator produces a rotating magnetic field at synchronous speed $N_s$. The rotor is excited by DC, creating constant N-S poles. When the rotor approaches $N_s$, opposite poles attract and lock magnetically, causing the rotor to spin at exactly $N_s$.

For Synchronous Motor:

• Under-excited: Lagging PF (draws reactive power)
• Normal: Unity PF
• Over-excited: Leading PF (supplies reactive power)

An unloaded over-excited synchronous motor acts as a Synchronous Condenser to improve grid Power Factor.

Synchronous Motors are not self-starting because rotor inertia prevents it from instantly following the rapidly rotating stator field.

Damper Windings (Amortisseur)

Short-circuited copper bars embedded in rotor pole faces. The motor starts as an induction motor, accelerates near $N_s$, then DC excitation is applied to pull it into synchronism.