Cat Gen Set

It appears that the diesel was cycling due to fuel flow problems. Some reasons why you may not have seen a change in the voltage or speed (Hz) is related to the following...

The voltage output of the generator is usually controlled by a fast electronic controller, which would compensate for any potential voltage variation due to cycling speed leading to cycling currents.....

The Hz output or speed of the generator would only have to change slightly to create the current surges that you mention....ie. if the engines normal speed is 1800, a 5% speed drop or 90 RPM would be equivalent to a 3 hz change in frequency....Depending on the sampling rate and the meter algorithum (it may have an averaging function built in to smooth out noise) the meter output may not change at all.....You would probably have to put on scope on the output of the generator to detect the speed change....

First the engine would slow down due to restricted fuel flow, which would result in currents dropping on the two motors with Benshaw soft starts (it would not effect the VFD's as they are fed internally via a DC bus and supported by brown out ride through capacitors), then when sufficient fuel was availalbe the engine would return to it's set speed...(probably 1800 rpm) resulting in the currents for the two motors increasing as the motor speeds followed the speed of the engine.....After the two motors accellerated to match the engine speed (minus slip) the currents would return to their normal state.....

Hope this helps...

Tom C

Thanks Tom,I didn't think about the meters being ,what should I say "slow",neither my Fluke or meters on gen set showed any change at all,which led me away,also they had just serviced the Gen set a week before,but apparently picked up some crud in a fuel shipment.So next time I should bring along a scope, I learn everyday,realising just how much I don't know. LOL it seems so clear now.

Helped a lot

DG

The easy way to find this problem is via a fuel pressure gauge mounted on the filter base, you might also notice an audible change in engine sound. We always check the simple things first, fuel pressure, air filters, ect. Cat voltage regulators from 1990 on are solid state and do a very good job of maintaining voltage especially if they are permanent magnet style generators. signed "a CAT Service Manager"