A 3-phase, 5 MVA, 11 kV, 60 Hz synchronous machine has a synchronous reactance of 10 Ohms per phase and has negligible stator resistance. The machine is connected to the 11 kV, 60 Hz bus and is operated as a synchronous condenser (producing zero active power and being used for reactive power only). Neglect rotational losses.
(a) For normal excitation, find the stator current. Draw the phasor diagram.
(b) If the excitation (field current) is increased to 150 percent of the normal value at synchronization, find the stator current and power factor. Draw the phasor diagram.
(c) If the excitation is decreased to 50 percent of the normal value at synchronization, find the stator current and power factor. Draw the phasor diagram.