Question

The full-load armature current of a 5 hp, 150 V shunt dc motor is 30 A. The field (shunt) resistance and the armature resistance of the motor are ????F = 125 ? and ???????? = 0.15, respectively. At a random speed of 1800 rpm magnetization curve of the motor has measured and is shown in the table below. ????0 (V) armature voltage 10 90 110 140 170 185 ???????? (A) field (shunt) current 0 0.82 1 1.2 1.7 2.88 Calculate the followings: (a) Calculate the field current at full-load. (b) Calculate the armature current at full-load. (c) Calculate the armature voltage ????0 at full-load. (d) Calculate the speed of the motor at full-load (hint: the field current remains unchanged at full-load and speed of 1800 rpm). (e) Calculate the output torque of the motor at full-load. (f) Calculate the copper and rotational losses of the motor at full-load. (g) Calculate the efficiency of the motor at full-load. (h) Calculate the no-load speed of the motor if terminal voltage remains the same. (hint: at no-load the armature current is zero). (i) Calculate the speed of the motor if at no-load condition field circuit opens. (assume the flux per pole drops to 1/10 times of the rated condition)

Answer 1