Question

A 3-phase, 4 pair of poles, 400kW, 400V, 60Hz induction motor is 780 rpm full-load speed.

Determine the frequency of the rotor current under full load condition

Answer 1

f_r=sf

n_s=$\frac{120f}{p}=\frac{120*60}{8}=900rpm$

s=$\frac{n_s-n}{n_s}=\frac{900-780}{900}=0.1333$

f_r=sf

=0.1333*60

=7.998 Hz