Two slip ring induction motors having number of poles as P1 and P2 respectively are connected in cascade (cumulative). If the supply frequency is f, then the speed of the main motor will be ___________.
1
\(\frac{{60f}}{{{P_1} + {P_2}}}\)
2
\(\frac{{2f}}{{{P_1} + {P_2}}}\)
3
\(\frac{f}{{{P_1} + {P_2}}}\)
4
\(\frac{{120f}}{{{P_1} + {P_2}}}\)