i am working in a gas based power plant. want to know the condition of synchronous generator running at leading power factor comparing with lagging power factor condition.. and it's effects on power generation..

 

Every synchronous generator is provided with a chart or graph commonly referred to as a reactive capability curve, or generator capability curve. It's actually three curves that define the limits of operation of the generator.

For a quick look at a reactive capability curve see the following link:

http://www.jcmiras.net/jcm/item/80/

There are three limits: lagging power factor, leading power factor, and watts. In all three cases the primary concern for the generator is heat-related. Each limit represents the maximum amount of heat that can be safely tolerated in different regions of the generator, since each condition affects different regions of the generator.

Producing watts (kw, MW) results in current flows in the generator stator that cause heating in the generator stator. (Current flowing in a conductor generates heat, any conductor, even ones in generators.) The ability of the generator and it's cooling methods to remove that heat without damaging the insulation of the stator and phase windings represents the upper limit of the ability of the generator to produce watts (real power).

Lagging power factor operation requires increased excitation power for the rotating magnetic field of the generator. As with the stator, current flowing in a conductor generates hear (even the conductors of a synchronous generator's rotating magnetic field). The ability of the generator to remove the heat from the rotor before it damages the rotor and rotor windings represents the upper limit of the ability of the generator to operate in a lagging power factor condition.

Now, here's where we've had some disagreement in the past on control.com. Leading power factor operation results in increased heating in areas of the generator stator (leading power factor operation requires reduced excitation power to the generator rotor, so heating of the rotor because of current flowing in the rotor isn't so much of a problem). The areas of the stator that experience the increased heating when operating in a leading power factor are what has been the subject of some controversy in the past. But, there is no disagreement that heating does occur and it is a factor in determining the limit of operation of a synchronous generator.

Have a look at the reactive capability curve for the generator at your plant and you will see the relationships between real power and reactive "power" (there are some contributors to control.com that don't like that term, reactive "power" so we have to be careful here) that are allowable.