Correct Answer - Option 3 : 5% and 150

Number of poles, P = 6

Frequency, f = 50 Hz

Rotor speed, N_{r} = 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, f_{r} = 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 \(= \frac{{300}}{4} = 75\;rpm\)