(Solved): Problem #25) A 30hp, 240V, shunt-excited DC motor running at 900 rpm draws a line current of 90A w ...

Problem #25) A 30hp, 240V, shunt-excited DC motor running at 900 rpm draws a line current of 90A when supplied at rated voltage and driving a constant-torque (not-rated) load. The respective field and armature resistances are 12012 and 0.25.2. Neglecting any mechanical losses in the machine: a) Determine the mechanical power produced by the machine in horsepower. b) If a resistor is placed in series with the field winding that decreases the pole flux by 25%, determine the new operating speed of the motor. a) Pmech 25.7 _hp b) Nnew = 1160 _rpm