Q15. A three-phase, 2 MVA, 6.6 kV generator is driven at constant speed and has a synchronous reactance of 10 Ω/phase.
The generator supplies full-load current at 0.85 power factor lag and rated terminal voltage.
(a) Sketch a labelled phaser diagram to show the relationship between the e.m.f. generated, the terminal voltage and the load current. (4)
(b) Calculate the full-load voltage regulation. (6)
(c) Sketch the terminal voltage/load current characteristic for the generator to show the change in voltage, from rated terminal voltage at full-load, 0.85 lag, when the load is disconnected. Indicate full-load voltage and current and the generated e.m.f.
(d) Using the axes in Q7(c), sketch the characteristics for disconnection of full -load at rated terminal voltage for the following load power factors, indicating the generated e.m.f. in EACH case:
• unity
• 0.85 lead. (2)
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