What happens to the Real and Reactive power when I increase the excitation current in a 3-Phase Synchronous Generator?
If you increase the excitation current under conditions where the armature terminal voltage increases but the load current and the real power do not change, the power factor must decrease because power = V X A X pf. That explains why it is possible. To explain why the power and current remained constant with increasing voltage, you must know more about the load or the distribution system that is acting as a load.