If the excitation an alternator operating in Parallel with other alternator in changed then it will change the Power factor. ● Suppose the excitation of the alternator is decreased below normal excitation then Reactive Power will change and active Power output of alternator will Remain unchanges. ● The under excitation alternator delivers leading current to the infinite bus bar. ● It is because the leading current produces an adding mmf to increase the under excitation. ● Similarly, an over excited alternator operates at lagging Power factor and supplies lagging Reactive Power to an infinite Bus.