340 V, 45 A, 1400 rpm DC separately excited motor having a resistance of .7 ohm excited by an external dc voltage source of 90 V. Calculate the torque developed by the motor on full load.(a) 94.73 N-m(b) 94.52 N-m(c) 93.37 N-m(d) 94.42 N-mI had been asked this question at a job interview.This key question is from Modified Speed Torque Characteristics of DC Series Motors in portion Characteristics of DC & AC Motors of Electric Drives

340 V, 45 A, 1400 rpm DC separately excited motor having a resistance

1.	340 V, 45 A, 1400 rpm DC separately excited motor having a resistance of .7 ohm excited by an external dc voltage source of 90 V. Calculate the torque developed by the motor on full load.(a) 94.73 N-m(b) 94.52 N-m(c) 93.37 N-m(d) 94.42 N-mI had been asked this question at a job interview.This key question is from Modified Speed Torque Characteristics of DC Series Motors in portion Characteristics of DC & AC Motors of Electric Drives
Answer» The correct answer is (a) 94.73 N-m Easy explanation: BACK emf developed in the motor during the full LOAD can be calculated using equation Eb = Vt-I×Ra = 308.5 V and machine CONSTANT Km = Eb÷Wm which is equal to 2.1053. TORQUE can be calculated by using the relation T = Km × I = 2.1053×45 = 94.73 N-m.

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