would you please explain the purpose of excitation?

and during GT start up up to Field switch close and then how generator gets Dc?

the above is my question
note we have in our site the following

1- Pilot exciator <b>[moderator's note: exciter?]</b>
2- main exciator

the pilot exciator operate only during start up till the GT reaches 95% of speed then the field switch will close. after pilot exciator stop. what is the source of feeding DC to the generator?

i need details explanation regarding this matter i need it urgent.

 

Ayed,

Excitation is required to produce terminal voltage on a synchronous electrical machine (an alternator). The amount of terminal voltage is directly proportional to the amount of excitation.

Depending on the type of "main" or "primary" exciter used on alternators, sometimes it's necessary to have a method of establishing the generator terminal voltage during starting before the main or primary exciter can supply the excitation power necessary for synchronization and loaded operation.

We don't have access to the electrical drawings and manuals for the equipment at your site. So, we can't make comments on your specific application or problem without more details.

You should consult the manuals provided with the turbine and generator and exciter(s) at your site
to determine the operating philosophy and sequence.

If you need to know more about how synchronous generators develop generator terminal voltage, please use your preferred Internet search engine to find the basics of alternator operation. A really good site for basic information in a very useful format is candu.canteach.org.

Try this link for a good document:

http://canteach.candu.org/library/20030801.pdf