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A 3-phase induction motor runs at almost 140 rpm at no load and 50 rpm at full load when supplied with power from a 50 Hz, 3-phase supply. What is the corresponding speed of the rotor field with respect to the rotor?

A 3-phase induction motor runs at almost 140 rpm at no load and 50 rpm at full load when supplied with power from a 50 Hz, 3-phase supply. What is the corresponding speed of the rotor field with respect to the rotor? Correct Answer 90 revolution per minute

Supply frequency=50 Hz. No-load speed of motor= 140 rpm. The full load speed of motor=50 rpm. Since the no-load speed of the motor is almost 140 rpm, hence synchronous speed near to 140 rpm. Speed of rotor field=140 rpm. Speed of rotor field with respect to rotor = 140-50 = 90 rpm.

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