A 3-phase, 20 kVA, 208 V, 4-pole star-connected synchronous generator has a synchronous reactance of Xs = 1.5 ohm per phase. The resistance of the stator winding is negligible. The machine is connected to a 3-phase 208 V infinite bus. Neglect rotational losses. a) The field current and the mechanical input power are adjusted so that the synchronous machine delivers 10 kW at 0.8 lagging power factor. Determine the excitation voltage Ef and the power angle ?. b) The mechanical input power is kept constant but the field current is adjusted to make the power factor unity. Determine the percent change in the field current with respect to its value in part (a).