tunning experiences of "droop" of a AVR.

[cloonypan]

Hello,

There is a medium voltage M-G set and several loads at its downstream. I want to tunning the "droop" parameter and let the terminal voltage of generator keep in rating value when downstream loads are suddenly energized.

The said AVR is made by "AvK Cosimat N+" which is selling by Cummins.

How should I examine this funciton?

Thank you.

 

[Skogsgurra]

What is 'tunning'?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[FreddyNurk]

If you're expecting that tweaking the AVR will give you no voltage deviation when large step loads are applied then you're likely to be in for a surprise. Some voltage deviation is to be expected, but I can't comment on your specific situation as to how much you'd expect.

I don't know the AVK AVRs specifically, but the Stamford ones (also sold by Cummins) will actually roll the voltage off as the frequency lowers. Attempting to tweak this generally results in the opposite effect to the one you're after.

 

[waross]

ESL Gunnar. Should read tuning.
Hi cloonypan;
What exactly is the problem that you think that you have. I haven't worked on as many generators as some of the people here, maybe only about 50 or more. I have never had to adjust the "droop" of an AVR.
When a block load hits a set, the frequency drops until the governor can respond and get enough fuel into the cylinders to hold the extra load and come back up to speed. When the frequency drops, transformers and motors may go into magnetic saturation and the current will increase greatly. Even though the increased current is reactive and should not present a real load, there are I²R losses with any current. With the combined resistance of feeder conductors and motor and/or transformer windings, the load of the I²R losses associated with saturation may hinder or prevent the generator prime mover from returning to the set speed. The saturation currents may also fairly quickly burn out motors and transformers.
To address this issue almost all modern AVRs for smaller sets (less than about 2 MW as far as I know) have a feature called Under Frequency Roll Off or UFRO. The UFRO feature typically allows about a 3 Hz drop in frequency and for any further frequency drop will lower the voltage in proportion to the frequency. Thus if a load drops the frequency to 28.5 Hz ([60Hz-3Hz]/2=28.5Hz) you can expect the AVR to drop the voltage to 50% of the normal voltage.
It's doing its job.
You are probably seeing a UFRO effect. Trying to eliminate it by changing the droop setting will probably add instability to the AVR performance.

Bill
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"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

Thanks Bill. It is obvious now. What is ESL?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

English as a Second Language.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[nawao]

cloonypan,
The droop function is used only when genset is paralleled. In island mode, the generator working alone, this function should be canceled (droop potentiometer fully counterclockwise), in order not to affect stability.