A 2300-V 2000-hp 0.8-PF leading 60-Hz two-pole Y-connected synchronous motor has a synchronous reactance of 1.5Ω and an armature resistance of 0.3Ω. At 60 Hz, its friction and windage losses are 50 kW, and its core losses are 40 kW. The field circuit has a dc voltage of 200 V, and the maximum IF is 10 A. The open-circuit characteristic of this motor is shown in Figure. Answer the following questions about the motor, assuming that it is being supplied by an infinite bus.
(a) How much field current would be required to make this machine operate at unity power factor when supplying full load?
(b) What is the motor's efficiency at full load and unity power factor?
(c) If the field current were increased by 5 percent, what would the new value of the armature current be? What would the new power factor be? How much reactive power is being consumed or supplied by the motor?
(d) What is the maximum torque this machine is theoretically capable of supplying at unity power factor? At 0.8 PF leading?
