Question

Calculate the useful power developed by a motor using the given data: Pin = 10 W, Ia = .6 A, Ra=.2 Ω. Assume frictional losses are 2 W and windage losses are 3 W.

(a) 4.928 W

(b) 1.955 W

(c) 1.485 W

(d) 1.488 W

I had been asked this question in an online quiz.

My question comes from Induction Motors topic in section Speed Control of Direct Current Motors & Induction Motors of Electric Drives

Answer 1

Right choice is (a) 4.928 W

To elaborate: 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 = 10-.6^2(.2)=9.92 W. The useful power developed by the motor is Psh = Pdev-(rotational losses) = 9.92 –(5) = 4.928 W.