DC and AC machines: basics
Basic Electrical and Electronics Engineering · Engineering
Study notes
A 4-pole 50 Hz induction motor runs at 1440 RPM. Synchronous speed Ns = 120x50/4 = 1500 RPM. Slip s = (1500-1440)/1500 = 0.04 = 4 percent. The rotor must lag the field to induce rotor current; at zero slip there is no torque.