If the shaft load remains fixed but the field flux is

Question

A 15 kW, 250 V, 1200 rpm shunt motor has 4 poles, 4 parallel armature paths, and 900 armature conductors; R_a = 0.2 Ω. At rated speed and rated output the armature current is 75 A and If = 1.5 A. Calculate

(a) flux/pole,

(b) the torque developed,

(c) rotational losses,

(d) h,

(e) the shaft load, and

(f ) if the shaft load remains fixed, but the field flux is reduced to 70% of its value by field control, determine the new operating speed.