Consider a 3-hp, 220-V, 1800-r/min separately excited dcmotor controlled by a single-phase fully controlled rectifierwith an ac source voltage of 230Vat 60Hz.Assume that the full-load efficiency of the motor is 88%, and enough filter inductance is added to ensure continuous conduction for any torque greater than 25% of rated torque. The armature circuit resistance is 1.5 .

(a) Determine the value of the firing angle to obtain rated torque at 1200 r/min.

(b) Compute the firing angle for the rated braking torque at -1800 r/min.

(c) With an armature circuit inductance of 30 mH, calculate the motor torque for α = 60° and 500 r/min, assuming that the motor operates in the continuous conduction mode.

(d) Find the firing angle corresponding to a torque of 35 N·m and a speed of 480 r/min, assuming continuous conduction.