Generator Reactive Power Capacity

Generator capability curve Leading and lagging areas of the curve

Generator Capability Curve

Generator Mvar and MW given by the following curve.

There are limits to how much reactive power a generating unit can supply or absorbing

mega Vars. A generating unit can safely operate while supplying or absorbing

mega VARs. When a generator is operating in the negative portion of the capability

curve (below the horizontal “mega watt line”), MVars are being absorbed from the system.

We can say that the generator is operating in a leading or under excited mode. During most loading conditions the generator will operate in the

lagging area or upper portion of the capability curve.

Generator Capability Curve

Consequence of exceeding capability curve. Over and under excitation limiters.

Operating a generator outside of its capability curve between points B and C will cause excessive current and over heating in the stator coils.

* lower current weakness magnetic field (cause instability).