Question

A 2-pole lap wound generator with 44 armature conductors and a flux per pole of .07 Wb has an armature current of 80 A. The developed torque is _________

(a) 39.7 N-m

(b) 39.2 N-m

(c) 38.4 N-m

(d) 37.2 N-m

This question was addressed to me during an online exam.

I'd like to ask this question from Effect of Starting on Power Supply, Motor and Load topic in section Starting of Electric Drives

Answer 1

Right answer is (b) 39.2 N-m

Easy explanation: The developed torque in the motor is Km×I. The value of machine constant(Km) is Eb÷ωm = Φ×Z×P÷2×3.14×A = .07×44×2÷2×3.14×2 = .49 Vs/rad. The developed torque is .49×80 = 39.2 N-m.