A dc machine is rated 5 hp with V_f = 240 V, V_a = 240 V, r_a = 0.63 ohms, and L_AF = 1.8 H. At rated condtions w_r = 127.7 rads/s and the total resistance of the field circuit is 240 ohms.
a) Calculate the rated armature current. The machine is to be operated in the constant-power mode beyond rated speed.
b) Calculate I_f at four times rated speed.
c) Calculate the boundary value of T_e for part b.