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Increasing excitation voltage to a Genset synchronized to a bus will decrease your Generator power factor and become lagging if you are synchronized in a large grid and cannot control your frequency. If you are in an island grid operation and your are controlling frequency it will increase your system voltage.
Over excitation will deliver additional inductive VAR to the grid and and will operate at lagging power factor and power factor will be reduced
Immediate Alternator current will increase
When the Excitation of an Alternator is increased,the induced emf(voltage) is increased.
Moreover Reactive power is adjusted by adjusting the excitation.
Sir, what you've said is correct. Lets put it this way.. For an alternator connected to an infinite bus, when the excitation is decreased, voltage and power factor of the system reduces, since Excitation current produces de magnetizing effect.Synchronous current lags altrenator terminal voltage by90 degree. This lagging current has de magnetizing effect, which reduces the terminal voltage. But for an infinite bus frequency and bus voltage remains constant so terminal voltage remains constant, hence power factor changes. When the load demand is more, we have to increase the input mechanical power, like hydro turbine, gas turbine etc.
So considering the Excitation Vs Armature current curve for an alternator, to decrease the power factor in the lagging direction, excitation has to be increased. To reduce the power factor in the leading direction, excitation has to be decreased.
Since pull in torque will be required for the said SM to reach synchronism, it will draw excitation required from the bus. This might cause a sudden voltage drop on the bus. Infinite bus might handle that kind of situation. Consider a bunch of SUVs (SM in this case) with a chain, if chain gets pulled a little, it can be handled, but if load is too might break. So if bus voltage is strong enough, reactive power is good, then it won't make much difference, but if voltage drop is high on the bus, it might cause others synchronous machines to come out of synchronism.
