A 3-phase, 12-polc induction motor is rated 500 hp, 220 V, 60 Hz. At no-load, wi

Question

A 3-phase, 12-polc induction motor is rated 500 hp, 220 V, 60 Hz. At no-load, with rated voltage and frequency, the line current is 20 A and the power is 14 kW. Assuming wyc-connccted windings, the stator resistance per phase is 0.4 ohm, rotor resistance per phase in stator terms is 0.2 ohm. stator and rotor reactance per phase are each 1 ohm (in stator terms). With rated voltage and frequency applied, the motor is loaded until its slip is 2%. For this condition, calculate (a) the rotor current in stator terms, (b) the stator current, (c) the torque developed, (d) the power output, (e) the efficiency, and (f) tlxr power factor. Use the approximate equivalent circuit (Fig. 5-10). (Notice that this is a repeat of Problem 5.41, but using a different circuit.) Ans. 120.0 A; 129.3 A; 6875 N midddot m; 409.4 kW (or 548 hp); 88.4%; 0.94 lagging

Explanation / Answer

efficiency is the ration of Power_Out/Power_In. So simply take the Power outRpm*Torque and divide by the Power in Volts * Amps Note: You need to younumbers found while the motor is running. Name Plate or Maximum values will notwork for this. Also the Efficiency will vary depending on the motor speed.

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