A center ammeter connected to the rotor end circuit of a 6-pole,50 Hz, induction motor makes 45 complete oscillations in a minute. Then the rotor speed and the speed of stator field w.r.t. rotor is?(a) 985, 15(b) 970, 1000(c) 985, 985(d) 985, 970This question was posed to me at a job interview.I want to ask this question from Starting of Polyphase Induction Motors-II topic in section Starting of Induction Motors of Electrical Machines

A center ammeter connected to the rotor end circuit of a 6-pole,50 Hz,

1.	A center ammeter connected to the rotor end circuit of a 6-pole,50 Hz, induction motor makes 45 complete oscillations in a minute. Then the rotor speed and the speed of stator field w.r.t. rotor is?(a) 985, 15(b) 970, 1000(c) 985, 985(d) 985, 970This question was posed to me at a job interview.I want to ask this question from Starting of Polyphase Induction Motors-II topic in section Starting of Induction Motors of Electrical Machines
Answer» RIGHT option is (a) 985, 15 Explanation: Rotor FREQUENCY= s*F1 = 45/60 = 0.75 Hz. s = 0.75/50 = 0.015 rotor SPEED = 1000(1-0.015) = 985 rpm. Speed of stator field w.r.t. rotor = Ns-Nr = 1000-985=15 rpm.

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