Parameter Setting for Generator Synchronizing While Varying Loads

Your variable speed motor, with regenerative power is generating harmonics. The harmonics are the cause of sync. failure. You will have to filter out the harmonics.

off coarse you should remove the causes rather than increasing the margin of synch conditions. it will lead you to even severe blow..........

Then you should consider synching up your generation machines before bringing your large variable speed drives on-line.

The difficulty sync-ing, makes it sound like you have a weak grid.

Depeding upon the size of the generator versus the grid, If you bring the generator up and slam the breaker in as it goes past sync speed and continue loading it will likely upset the drives, but this is done with some small -relative to the grid- hydro, including synchronous or induction, the problem is structural to the generator ad how tolerant your machines are to bumps.

I would bring the gen to just below grid - sync speed, set the window at +/- 10 degrees and it will take a while, as the governor bumps the speed up it should sync, as you open the sync acceptance window toward +/- 20 degrees you should find a happy time, it also depends on the governor time delays before poking the speed up/down to try to get closer to the grid frequency if it is stable.