A synchronous generator is connected to the grid through a reactane of j0.65 pu. The grid voltage is 1 pu and the generator is feeding 0.7+j0.6 pu power to the grid. After some calculations, the generated emf is found to be 1.46 ∠18.12° pu. If the active power is increased such that new complex power is 0.8+j0.6 pu (reactive power unchanged), the generated emf comes out to be 1.48∠20.51°. I can understand the fact that the power angle δ increased so as to feed the extra real power. What I don't understand is why the generated emf increased. According to the equation E=Vt+ I*X, the value of E should increase since the current increased. But since the reactive component of the armature current is unchanged, why should the excitation be increased? If the armature current is lagging, its reactive component has a demagnetizing effect on the air gap and hence, terminal voltage drops. To bring the terminal voltage back to 1 pu, excitation is increased. In this problem, there is no change in the reactive component of armature current. So why is the excitation increased when the reactive power is constant? Thanks a lot in advance!