1lease explain me about the operation of generator when it is synchronised with grid.

2:-how frequency vary with change in turbine input and excitation.

3:-how stability of alternator gets affected by the change in frequency.
please clear my doubt briefly...........

 

We really can't address your doubts because we don't know what doubts you have. You have asked a couple of questions which have been covered many times before on control.com.

Use the 'Search' feature in the right corner of the Menu bar at the top of every control.com page to search for 'droop speed control' and 'isochronous speed control' and 'frequency excursion' and such. (You will find more terms as you search and read the results.)

It's also suggested you use the 'Search' Help function to understand how to type in search terms consisting of multiple words.

If you don't find the answers to your questions, and you still have doubts, then detail your doubts and we can try to address them here.

 

A book that explains generator operation very well (in my opinion) is "Operation and Maintenance of Large Turbo-Generators" by Klempner and Kerszenbaum.

http://www.amazon.com/Operation-Maintenance-Large-Turbo-Generators-Engineering/dp/0471614475

This is an extremely useful resource for anyone in the field.