A 600 MV A generator having an internal reactance of 0.24 pu is connected to a large power system via a transformer of reactance 0.36 pu. The generator terminal voltage, and the power system voltage, are both maintained at 1.0 pu. All per-unit values relate to the generator rating.
(a) Draw a phasor diagram showing all voltages, reactive volt drops and the line current. If the generator exports 400 MW into the power system, find:
(b) The angle between the generator terminal voltage and the power system voltage.
(c) The magnitude of the generator internal emf.
(d) The angle between the internal emf of the generator and the power system voltage.
(e) A three-phase fault occurs at the generator terminals causing the angle of part (c) to increase. The fault is subsequently cleared. Find
the maximum value that this angle can reach during the fault (i.e. the critical clearing angle) so that the generator retains stability.