Question

Calculate the useful power developed by a motor using the given data: Pin = 3000 W, Ia = 60 A, Ra = .4 Ω. Assume frictional losses are 200 W and windage losses are 400 W.

(a) 970 W

(b) 960 W

(c) 980 W

(d) 990 W

I have been asked this question by my college professor while I was bunking the class.

Question is from Dynamics in chapter Dynamics of Electrical Drives of Electric Drives

Answer 1

Right answer is (b) 960 W

For 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 = 3000-60^2(.4)=1560 W. The useful power developed by the motor is Psh = Pdev-(rotational losses)=1560 –(200+400)=960 W.