generator

-- please forgive me for my bad english --
i'm working on a brushless sincronous generator moved by a diesel engine.
i'd like to know what's the right procedure to start the load.
i need to start the motor at 800 rpm and only after a while the speed
reaches 1500 rpm. during the period when the engine is at 800 rpm i dont
want the generator to produce power...it would be at 20 Hz...Do i need to
use a contactor to connect the generator to the my local net?
does exist a control (working on excitation circuit) that make the generator
work only when it reaches the full speed?
And if i use a contactor...what can appen when i switch on the circuit? any
problem with over-voltage?
The total power is 250 kW
can i find a website where to find useful information about all this?
thanks
igor