I have noticed on several of our generators that when we are operating at full load and trying to stay near unity power factor there is a significant change in the amount of VARS we see from the generator. We might fluctuate from -8 MVAR to +8 MVAR. However if we try and regulate at 20 MVARs we won't se more that 1-2 MVAR variations. Has anyone else noticed this kind of performance or have a possible explanation?
Are the generators connected to the same bus? Does each generator have its own step-up transformer before the common bus?
When did the problem start? After some planned (or unplanned) outage? After a lightning strike?
Is the grid frequency stable when these problems are occurring?
Is the grid voltage stable when these problems are occurring?
There's really a lot of information we would need to be able to provide any meaningful suggestions or advice.