Droop value of generating plants 1

[element230]

I've heard this few times before and I wanted to share w/ you this comment.

Is it necessary to set the droop value (R) in each machine of a control system to the same value? Most of the machines in my control area are set to 5%.... It seems to me this value is specific of each generator, rather than a system wide value.

 

[waross]

I prefer 3% but to your question:
Yes they should be the same unless you have a specific issue.
Consider two machines, one with 2.5% droop and one with 5% droop. On 60 Hz, the respective no load speeds will be 61.5 Hz and 63 Hz.
If you parallel the machines you will have to trim the no load speeds so that they are equal. As the load increases, the speed will drop. When the 2.5% droop machine is fully loaded, the 5% droop machine will be 50% loaded.
If you have a machine with full load issues such as an engine cooling problem or a generator over heating issue (possibly due to plugged cooling passages) or for whatever reason, you may use a non standard droop to limit that machines share of the load to less than full load rating.

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

 

[xnuke]

In simple terms, if all parallel generators have the same droop, they will share load in proportion to their ratings.

For example, if you have a 5 MW, a 10 MW, and a 15 MW generator group with all machines synchronized together and operating at 5% droop, when one machine is 10% loaded, all will be 10% loaded (that would be 3 MW total load - 0.5 MW, 1 MW, and 1.5 MW, respectively). If the load increases by 12 MW to 15 MW total load, all three machines will be 50% loaded - 2.5 MW, 5 MW, and 7.5 MW, respectively. No operator action will be required for this to occur. If they don't have the same droop, this even load sharing does not occur, and operator action will be needed to adjust the no-load speeds if even load sharing is desired.

xnuke
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