Supply Generator Power to PLN

What is the PLN? Is it your local electrical utility? Does it have more generating capacity than 3 MW?

Your generator should have a regulator to control its output (by varying the speed / phase of the turbine / generator). Assuming the PLN is your local electrical utility, you are essentially paralleling your generator to their generators.

One generator in the system should be the lead generator (probably on the PLN side), and all other generators should have a drooping regulator characteristic to (almost) match the speed / phase of your generator to that lead generator, thus controlling the power flow from your generator.

I would talk to the engineer's in charge of the PLN, tell them your problem, and ask them for advice.

You do not make clear whether your generator is 3MW or say 10MW with 3 MW available to export. Your words "supply 3MW" could mean generator output, your own load or the export to Grid. Also not clear if your generator is always 10 MW capacity (say steam turbine) or variable capacity with ambient temperature and air pressure (say gas turbine).

I would think about an automatic control loop measuring generator MW, with a set-point at the MW you wish your set to deliver and output contacts to lower/raise its governor setting automatically. If you have an obligation to support the grid when frequency gets very low, you could disable the loop below a set frequency. You may have to bias the MW setting with temperature and pressure inputs, if these affect your set rating. Maybe you need to regulate on the export MW to the Grid.

You say your "generator" trips, but is this alternator overload or prime-mover overload??