A 208-V Y-connected synchronous motor is drawing 50 A at unity power factor from a 208-V power system. The field current flowing under these conditions is 2.7 A. Its synchronous reactance is 0.8Ω. Assume a linear open-circuit characteristic.
(a) Find the torque angle δ.
(b) How much field current would be required to make the motor operate at 0.78 PF leading?
(c) What is the new torque angle in part (b)?