Generator Trip in Reverse Power

Just a guess, but when the 10600 KVA generator picks up the additional load from the the tripped 4500 KVA generator it slows and loses sync. with the grid. The current lag allows feedback that looks like, and actually is, reverse power. The best remedy would be seperate transmission lines for each Gen Set.

Are these two opposeing engines driving each genarator? Which generator carries the load feeder, which I assume is a local transformer.

alternator is separate for each engine, giving power in a common bus where load feeders and grid feeder are connected.

When grid VCB trips, there is excess power available in the generator system. This would boost the frequency of the generators prompting the engine governors to control the fuel input and in turn the generator output. In case the engine-5 governor response happens to be faster than the others, it is likely that the other generators drive power in to the engine-5 prompting it to trip on reverse power. A couple of questions:

• Why the engine reverse power setting is 3%, it can as well be 5% (for all the engines).

• Reverse power protection should always include a time delay like 2sec to prevent engine trip during momentary power swings. You didn't mention of this!
  

well, you are right, but my question is engine no. 4 is same rating as well as engine no. 5 then why engine no. 5 is tripped all time, engine no. 4 why not?