Diesel generator troubleshooting

[npower0073]

On site we make regular tests of a diesel generator set, 800kW 1500 rpm. What we experienced lately is that the generator suddenly decreased load (from 400kW to 117kW), increased frequency (from 50Hz to 60 Hz) adn tripped from overfrequency. Afterwards the opearation was OK. This is a stand by set to supply the auxiliary loads of the plant when it is isolated from the grid. It does not work continuously. At the time of the trip the genrator was synchronized to the 400V busbar, terminal voltage as 426V.
Can you advice on the troubleshooting? I suspect either the governor or temprary problem on diesel injection or filter dirt...

 

[TheBlacksmith]

Sounds like the load was dropped suddenly in the plant resulting in a generator overspeed. If the injection suddenly went too high, it would have increased speed and picked up load, if the injection went low or the filters plugged it would have decreased speed and dropped load. You should be looking at the loads, not the source (generator).

 

[npower0073]

TheBlacksmith , thank you very much. At that time the generator was supplying loads in parallel with the grid. The busbar where the generator is connected needed 440A and the gerneator produced 650A. SO if there was a filters plugging the load dropped but this was not a consumer load but an extra generating load.