The three-phase synchronous generator of Prob. 3.5 is operated on an infinite bus of voltage 15 kV and delivers 100 MVA at 0.8 power-factor lagging. (a) Determine the internal voltage E1, the power angle 8, and the line current of the machine. (b) If the field current of the machine is reduced by 10%, while the mechanical power input to the machine is maintained constant, determine the new value of S and the reactive power delivered to the system. (c) The prime mover power is next adjusted without changing the excitation so that the machine delivers zero reactive power to the system. Determine the new power angle δ and the real power being delivered to the system. (d) What is the maximum reactive power that the machine can deliver if the level of excitation is maintained as in parts (b) and (c)? Draw a phasor diagram fa the operation of the machine in parts (a), (b), and (c).
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