i have problem on my generator that gets shut down giving alarm of low voltage . what cause could it be ?

 

Since you haven't told us the type of generator it is or how it is being used we could only make wild guesses as to the problem and that's not productive. We need more info.

 

A wind powered generator (windmill) and the wind stopped blowing?

 

its diesel generator

 

When was the last time it was run?

Some need to be run periodically to keep the rotor magnetized.

Long shot, but is this an inverter type generator? (built in last 3 years or so)?

Diesel engine runs fine, generator does... what? (explain in detail, also post make and model number of genset)

 

its puma cummins . it has been in running condition since 5 years. run in parallel with other generators.

 

Has anything changed since the last time it worked?

You'll need to give us a bit more info, and may photos, but all our guesses will be shots in the dark without knowing more aobut it, how it quit, etc.

 

Please elaborate your problem.
Have you checked Its rpm? have you checked its maintenance hours? have you checked its voltage manually with a voltmeter on its output MCCB or breaker?
Please ease us by doing these tests.
If you have checked these problems, then look into you generator control relay how much voltage it shows on it display?