Question

Calculate the useful power developed by a motor using the given data: Pin= 1500 W, Ia= 6 A, Ra=.2 Ω. Assume frictional losses are 50 W and windage losses are 25 W.

(a) 1400 W

(b) 1660.5 W

(c) 1417.8 W

(d) 1416.7 W

The question was asked by my college professor while I was bunking the class.

This key question is from Energy Relations During Starting topic in division Starting of Electric Drives

Answer 1

The correct choice is (c) 1417.8 W

Easiest explanation: Useful power is basically the shaft power developed by the motor that can be calculated using the formula Psh = Pdev-(rotational losses). Pdev = Pin-Ia^2Ra = 1500-6^2(.2)=1492.8 W. The useful power developed by the motor is Psh = Pdev-(rotational losses) = 1492.8 –(50+25) = 1417.8 W.