A shunt-connected 240-V, 15-kW, 3000 r/min dc motor has the following parameters Field resistance: R _f = 132Ω, Armature resistance: R_a = 0.168Ω, Geometric constant: K_f = 0.422 V/ (A· rad/sec) When operating at rated voltage, no-load, the motor current is 1.56 A.

a. Calculate the no-load speed and rotational loss.

b. Assuming the rotational loss to be constant, use MATLAB to plot the motor output power as a function of speed. Limit your plot to a maximum power output of 15 kW.

c. Armature-voltage control is to be used to maintain constant motor speed as the motor is loaded. For this operating condition, the shunt field voltage will be held constant at 240-V. Plot the armature voltage as a function of power output required to maintain the motor at a constant speed of 2950 r/min.

d. Consider that the situation for armature-voltage control is applied to this motor while the field winding remains connected in shunt across the armature terminals. Repeat part (c) for this operating condition. Is such operation feasible? Why is the motor behavior significantly different from that in part (c)?