Eo(LL) (V) 3000 2500 2000 1500 1000 500 0 0 No-load excitation curve @3600rpm |E0(LL) IF 2 IL 6 DC Excitation current (A

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Eo Ll V 3000 2500 2000 1500 1000 500 0 0 No Load Excitation Curve 3600rpm E0 Ll If 2 Il 6 Dc Excitation Current A 1 (154.8 KiB) Viewed 27 times

Eo(LL) (V) 3000 2500 2000 1500 1000 500 0 0 No-load excitation curve @3600rpm |E0(LL) IF 2 IL 6 DC Excitation current (A) The figure above shows the no-load excitation (LL) curve of a 3-ph, 2-pole, 60 Hz, 1000 kVA, 2.3 kV synchronous alternator at rated speed. The alternator has negligible resistance and Synchronous Reactance X, = 1.2 22/phase. Q3ph 4 If the alternator is synchronized to the Power Grid at 2.3 kV (Line to Line), calculate the following: a) The value of excitation current required for full load current at 0.7 pf lagging (over-excited). (2 marks) 8 10 b) The alternator current and reactive power when it is delivering 80% rated power (0.8 MW) and its DC excitation current is 4 A. (4 marks) Q3. (Total of 5 marks) Poperating (MW) Soperating (Ⓡ) PMAX (MW) A 200 MVA, three-phase, wye-connected, 60 Hz, 21 kV synchronous generator has negligible armature resistance and synchronous reactance of 2.5 02/phase. The field current is adjusted for a no-load excitation voltage of 20.5 KV LL and the generator is delivering 100 MW (a) Draw a neat and clearly labelled curve showing the relationship between the generator power output and the load angle. Calculate and show the maximum power and the operating power and load angle on your diagram. (2 marks)