Calculate the frequency of the rotor current when the synchronous speed is 1,500 rpm and rotor speed is 1,440 rpm and supply frequency is 50 Hz.

Correct option is A

Given

$$\textbf{Ans. (a) :} \text{ Given,} \\N_s = 1500 \, \text{rpm}, \quad N_r = 1440 \, \text{rpm} \\f = 50 \, \text{Hz} \\\\\text{Slip (S)} = \frac{N_s - N_r}{N_s} \\= \frac{1500 - 1440}{1500} = \frac{60}{1500} = 0.04 \\\\\text{Rotor current supply frequency } (f_r) = s \cdot f \quad \text{(Where, } f = \text{supply frequency)} \\f_r = 0.04 \times 50 \\\boxed{f_r = 2 \, \text{Hz}}$$​