Q3. (a) Two basic sets of characteristics for a synchronous generator are the open-circuit and the short-circuit charact

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Q3 A Two Basic Sets Of Characteristics For A Synchronous Generator Are The Open Circuit And The Short Circuit Charact 1 (129.87 KiB) Viewed 47 times

Q3. (a) Two basic sets of characteristics for a synchronous generator are the open-circuit and the short-circuit characteristics. Aiding with proper drawings of curves, explain: (1) The open-circuit characteristic in terms of armature voltages and field currents, and open-circuit no-load (core) loss as a function of armature voltages. (ii) The short-circuit characteristic in terms of armature currents and field currents, and the short-circuit load (copper) loss as a function of armature currents. (10 marks) (b) For a 300 kVA, 380 V, 3-phase, 50 Hz synchronous generator, the short-circuit test shows that a field current of 2 amperes (DC) at rated rotor speed is needed to produce the rating current (AC) on the armature windings. The open-circuit test shows that a filed current of 3 amperes at rated rotor speed leads a terminal voltage (line-to-line) of 400 volts. The DC test between two lines of the armature terminals gives a reading of 5 amperes (DC) on lines with a voltage of 3 volts (DC) between lines. Assume the AC resistance of the armature coil is 1.2 times that of the DC resistance. Estimate: (i) The per-phase synchronous impedance (resistance and reactance); (ii) The per-phase armature voltage drops (resistive and reactive) at rating current; (iii) The generated voltage (line-to-line) and the field current required when the generator is full-loaded at a power factor of 0.8 lagging. Assume the generator is linearly excited. (15 marks)