Correct Answer - Option 3 : 5% and 150
Number of poles, P = 6
Frequency, f = 50 Hz
Rotor speed, Nr = 950 rpm at full load
Synchronous speed, \({N_s} = \frac{{120f}}{P} = \frac{{120\; \times \;50}}{6} = 1000\;rpm\)
Full load slip = \(\frac{{{N_s} - {N_{\rm{r}}}}}{{{N_s}}} = \;\frac{{1000 - 950}}{{1000}} = 0.05 = 5\% \)
Rotor frequency, fr = sf = 0.05 × 50 = 2.5 Hz
Rotor voltage speed \(= \frac{{120f}}{P} = \frac{{120\; \times \;2.5}}{P} = \frac{{300}}{P}\)
Since, P should be an integer hence,
P = 2 then speed of voltage \(= \frac{{300}}{2} = 150\;{\bf{rpm}}\)
P = 4 then speed of voltage \(= \frac{{300}}{4} = 75\;rpm\)