(Solved): b) A 275 MW, 16 kV 3-phase synchronous generator with a synchronous reactance of 1.67 Ohm per phase ...

b) A 275 MW, 16 kV 3-phase synchronous generator with a synchronous reactance of 1.67 Ohm per phase and negligible resistance is connected to an infinite busbar. The generator has a maximum continuous rating of 11.6 kA . The maximum line voltage that may be induced in the stator windings is 48 kV . A safety margin of 24.5 MW is allowed for the practical steady state stability limit. The generator is currently delivering 61.3 MW at a power factor of 0.447 lagging. i) Using a scale of 50 mm , plot the performance chart of the generator and clearly indicate the safe operating area. (10 marks) ii) The steam input is increased, at constant excitation, until unity power factor operation is achieved. Following this, the excitation is increased at constant steam input until the reactive power regains half of its original value. Determine, graphically or otherwise, the change in excitation between the original and the new operating points. (6 marks) iii) Indicate the trajectory of the synchronous generator operating point for the changes introduced in (ii) above on the performance chart. (3 marks)