My generator power factor is 0.85 lagging and capacity 7.79 MW. we have 7 sets for same configuration. We need to run the plant with grid whose voltage is 132 kV and frequency changes from 48.5 to 51 Hz.

Now my question is if we run the plant below power factor 0.85 (lagging) and above 0.85 (lagging), then what's the effect on alternator? Why alternator designed power factor 0.8 always? Why not 0.7? please explain it clearly.

Thanks

 

Use your preferred Internet search engine and search for 'generator capability curve' and/or 'generator reactive capability curve'.

As for why it's "always" 0.8; it's not. It depends on how the purchaser orders the generator and how it's built. (Why are some bicycles more suited for mountain biking or stunt riding than others? Because they are generally built for one application or another. It's the same with most things, generators included.)

Find the generator capability curves for your machines and review them. They will tell you the limits of operation. You can operate your generator at a power factor of 0.8 (lagging or leading), or even lower, but you need to operate it within the limits defined by the curves provided by the generator manufacturer in order to prevent damage to the generator (usually caused by heat).

Contact the generator manufacturer with better details of operation than you have provided here and ask if the generators can be safely operated at the extremes you have indicated, and if so, for how long.

There have been many posts on control.com about generator capability and generator reactive capability. Use the 'Search' feature of control.com; it's at the far right of the banner at the top of every page. Use the Search Help to familiarize yourself with the context and format of search terms.

 

Further to the clarification issue, the generator rating is a "static" number, usually given at a typical operating temperature and usually given at a rating so that one generator can be compared to another, such as 0.85, or 0.8.

But that doesn't mean the generator can't be operated at other power factors; the generator reactive capability curve will tell you if you need to reduce the real power output (watts, kW, MW) in order to operate at a lower power factor.

It's all about where heat builds up in the generator when it's being operated at high real power outputs, or high reactive power factor(s), and the ability to cool the generator that defines the limits of operation.

Again, if you want to operate your generator at a power factor of 0.60 (lagging or leading) you probably can, but to do so for any extended period of time the reactive capability curve will probably tell you that will likely need to reduce the real power output (watts, kW, MW) in order to maintain that power factor.

Most reactive capability curves are provided for a specific air temperature (presuming the generator is air-cooled; it would a hydrogen gas temperature if the generator is hydrogen-cooled). Some use stator temperatures as the condition for each curve. But, in any case you will need to know something about either the ambient air temperature, or the temperature of the air entering the generator, or the temperature of the windings, or the temperature of cooling medium (such as hydrogen) and then you can refer to the proper reactive capability curve.

Find the reactive capability curves provided with the generators at your site; they are the applicable ones for the generators at your site. And, they define the limits of operation.

And, ask any questions of the generator manufacturer if you need more clarification about the curves they provided.