Electrical Machines – II

Rotating stator field induces current in rotor bars — rotor tries to catch the field but always runs slightly slower (slip). Workhorse motor in Indian industry.

A synchronous machine runs exactly at N_s = 120f/P and its real power output follows P = (E_fV/X_s)sinδ; changing field excitation controls reactive power, giving the characteristic V-curves.

A single-phase induction motor produces no starting torque on its own because its pulsating field splits into two equal counter-rotating fields; an auxiliary winding or capacitor creates the phase split needed to start it.

Special machines — stepper, BLDC, switched-reluctance, universal and servo motors — trade the simplicity of the induction motor for precise position/speed control, and are analysed through their distinctive step angle, commutation and torque relations.

Machine dynamics studies how rotor speed changes when driving and load torques differ: J dω/dt = T_e − T_L governs run-up and braking, while stored kinetic energy ½Jω² sets the inertia constant.