1.

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) 0I 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

Answer»

Right ANSWER is (a) 900 rpm

Explanation: NS = 1500 rpm. Speed of the rotor field with RESPECT to rotor structure = 120 * f2/P = 120*20/4 = 600 rpm

Nr = 1500-600

= 900 rpm.



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