RPM Problem

This sounds most likely like a governor problem, maybe something sticky in the mechanism.

I think-as lyn said- the problem is your Diesel Engine cannot produce Hp [rated at 1500 rpm ] at 1800 rpm. The fuel could be supplied, but the intake air will be less than required. The DG velocity is top and bottom limited.

Try to put the DG into operation without load .If the motor cannot reach 1800 rpm, steady, the governor may be the problem.

Your unit sounds as though it is shutting off on high RPM cut off. Check with the manufacture to see what it is designed to operate at. If it is 1500 RPM then you should be looking at reason for over speed. Such as malfunctioning Governor.

It seems to me you have a Diesel Generator of 200 hp 1500 rpm [4 poles] 50 Hz and you intend to supply a 60 Hz System with it. As the motor cannot raise the speed up to 1800 rpm but only up to 1660 rpm-and the governor is already at maximum speed- changing the governor could solve the problem. If the motor is not rated for 1800 rpm that means it will be an overspeed [20%].I am not a mechanical engineer but I think at least the intake air valve has to be suitable for this speed. Overspeed can result in reduced entire engine life.On the other hand the generator could be protected for off-frequency [1660 rpm=55.5 Hz], so it will shut-down the generator.