The synchronous machine can operate at lagging, leading, and unity power factors. In the synchronous machine, the total air gap flux is produced by the dc source. If dc excitation is decreased, lagging reactive power will be drawn from the ac source to aid magnetization and thus machine will operate at lagging power factor. If dc excitation is more, leading current drawn from ac source to compensate (oppose) the magnetization and the machine will operate a leading power factor.
Thus it can be concluded that an over-excited motor(Eb > V) draws a leading current (acts like a capacitive load) but an under-excited motor(Eb < V) draws a lagging current (acts as an inductive load).
EXAMIANS
