Emergency Diesel Generator voltage hunting problem

[Shark96]

We have 2 emergency diesel generators (CAT 3512, 1250 kVA/1000 kW, 0.8, 400V, 50Hz) at our power plant. We are facing the subject issue at one of the generators, we have checked all electrical and mechanical parameters and found ok, hunting issue is on and off (intermittent). it has been observed on load as well as on no load condition. Occurrence of this event is not very common, we can say that hunting has been observed one time out of ten EDG running operation. Any suggestions would be helpful.

 

[ScottyUK]

Is the governor hunting too, or is the speed constant while the voltage moves?

 

[Shark96]

The governor is not hunting.

 

[catserveng]

What kind of voltage regulator is installed? Is it a CAT regulator or has it been retrofitted to something else?

What is biasing the voltage regulator? Since you have multiple units is there an automatic synchronizer installed? If so, what kind?

Is there a remote voltage adjust? If so what kind and how installed?

Typically, intermittent voltage fluctuations in generators with locally mounted voltage regulators is the result of wiring connections problems, such as loose connections, broken wires, chaffing, etc. This includes sensing, power, remote voltage adjust and remote auxiliary inputs, also a loose droop CT input can also cause a fluctuation but only when there is load. But since you say this happens with no load as well not likely.

Since you report this happens both loaded and unloaded I would likely start at the AVR power and sensing connections and make sure they are ok.

You don't mention how old these units are, but based on model and rating I'm assuming they are older units. If you have a remove voltage level adjustment potentiometer you may want to check it and it's associated wiring as well.

Hope that helps, MikeL