Question

A 4-pole lap wound generator with 720 armature conductors and a flux per pole of .003 Wb has an armature current of 50 A. The developed torque is _________

(a) 17.25 N-m

(b) 17.19 N-m

(c) 16.54 N-m

(d) 16.89 N-m

The question was posed to me in a national level competition.

My question is based upon Dynamics topic in portion Dynamics of Electrical Drives of Electric Drives

Answer 1

Right option is (b) 17.19 N-m

For explanation I would say: 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 = .003×720×4÷2×3.14×4 = .3438 Vs/rad. The developed torque is .3438×50 = 17.19 N-m.