Explain Synchronous Generators?

They can be utilized to produce or absorb reactive power. An over-excited machine produces reactive power when an under-excited machine absorbs it. The generator is the major source of supply to the system of both of the positive and negative VArs. The ability to supply VArs is ascertained by the short-circuit ratio (1/ synchronous reactance).

For economic reasons, in current units this ratio is kept low and therefore the inherent ability to run at leading power factors is not large. For instance, a 200 MW, 0.85 p.f. machine with a 10% stability margin can just supply 45 MVAr at full power outputs.