A 4-pole, 3-phase slip ring induction motor is used as a frequency changer. Its stator is excited from 3-phase, 50 Hz supply. A load requiring 3-phase, 20 Hz supply is connected to the star-connected rotor through three slip-rings of SRIM. At what two speeds the prime mover should drive the rotor of this SRIM?
(a) 900 rpm
(b) 600 rpm
(c) 1500 rpm
(d) 0
I have been asked this question during an interview for a job.
The query is from Rotor Frequency topic in chapter Induction Machines of Electrical Machines