Question

A three phase induction motor is wound for 4 poles and is supplied from 50 Hz system. Calculate the rotor frequency when the rotor runs at 600 r.p.m. 

Answer 1

$N_s=\dfrac{120f}{p}=\dfrac{120\times{50}}{4}=1500\ rpm\\ N_r=N_s(1-s)\\ 600=1500(1-s)\\ s=1-\dfrac{6}{15}=0.6\\ Rotor\ frequency\ is\ =sf=0.6\times{50}=30\ Hertz$