Question

 A 415-V, Y-connected, 4-pole, 50 Hz, three-phase induction motor has the following parameters on a per-phase basis, as referred to the stator:

 R1 = 0.25 ohms, X1 = 0.75 ohms, R2 = 0.55 ohms, X2 = 1.2 ohms, Xm = 50 ohms.

 The core loss is 200 W and rotational (mechanical) losses are 200 W. The machine is running at full load at a speed of 1450 r.p.m. Using the exact equivalent circuit, calculate-

•  The total input current,

•  The power factor,

•  The air-gap power developed,

•  The shaft power developed,

•  The overall efficiency.

 Add core loss to the total input power.

 Hint: Calculate air-gap power (and hence electromagnetic and output power) directly from input power and stator losses; you do not have to calculate rotor currents.

Answer 1