Diesel Generator Paralleling

[Viceng]

Hi, I was hoping someone on the board may be able to shed some light on an issue that I am dealing with:

Setup: Two emergency diesel generators, 600V, paralleled together on a common bus. ATS, Governors, regulators all included. Both are in droop mode.

Situation: When a true utility failure occurs everything works fine, the generators feed the load as expected. However, During a test operation of the units, the lights in the facility flicker quite a bit as though both units are fighting eachother. It definitely sounds like the fuel racks are being moved quite a bit during this time.

Any ideas?

Thanks in advance.

 

[alehman]

You said they are both in droop mode. Are the generators isolated from the utility? If so, I think you should have one generator in isochronous mode to set the frequency.

 

[davidbeach]

If they are somehow in parallel with the utility, they won't run well in load following mode, which is where they have to be for standalone operation. More information is necessary.

 

[burnt2x]

Hi!
Make necessary adjustments for wattmeters to have equal readings so that the kilowatt load is divided in proportion to the generator ratings (if the generator ratings differ from each other). For systems operating in speed droop:
1. If the frequency is above normal, turn the governor control switches for the heavily loaded generators in
decrease speed direction.
2. If the frequency is below normal, turn the governor control switches for the lightly loaded generators in
the increase speed direction.
3. If the frequency is normal, make the adjustment in small steps. Turn the governor control switches for the
lightly loaded generators in the increase speed direction and for the heavily loaded generators in the
decrease speed direction.
Hope this helps:

 

[Viceng]

Thanks for the replies.

Alehman, I was thinking one should be in isochronous mode too but the system apparently works just fine under a real loss of utility scenario.

burnt2x, the gen's are identically sized. While I have seen the transfer everything has gone fine, frequency of both units was good...but apparently this is not always the case.

Davidbeach, the issue may lie like you say in the fact that under a test scenario there is a make before break on the transfer switch during which (for a small period of time) the units and their settings are not correct to be parralled to the utility. I will have to investigate.

Thanks for the input

 

[waross]

At no load you should be running at about 61.8 Hz.
Or, you may set the frequency at 60Hz. at maximum load.
What is different between a test and a normal power failure. If the load is lighter under test conditions you may have a governor problem.
Isochronous and droop do not work and play together very well. If you lose the load the drop machine may motor the isochronous machine. You will have interesting load transients with step changes in loading, either up or down.
Typically the drop machine runs at a set load. After the initial transients the isochronous machine takes up all new loads.
Stay in droop unless you have a generator control panel with load sharing capability.
respectfully