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to determine how many generators

to determine how many generators

to determine how many generators

(OP)
If a 7MW genset is needed, which is better, to choose three 3.5MW generators or four 2.5MW ones? If take into account gas or diesel generators, is the answer similar?

RE: to determine how many generators

The best answer depends on the exact demand profile.
E.g. is the demand always 7MW, or does it peak there but average 1MW etc.
You would also factor in the cost of blackouts, the possibility of bringing in rental units, stuff like that.

Diesels like to be loaded to a range of 65 to 100 pct of their capacity, so for a demand variable from 0 to 7MW, in one sense an ideal setup would include a row of Diesels of varying size from small to large that could be brought on line in various combinations to meet the demand. ... but the logistics of maintaining all those different engines would drive you crazy. The other extreme would be a huge array of tiny engines all the same size, probably not an efficient solution.

You also have to deal with the issue of providing power, or suffering brownouts, while Diesels are starting and accelerating but not ready to be synchronized. (For that reason, the nearby FAA air traffic control center has a row of big engines _and_ a large room full of batteries.)




Mike Halloran
Pembroke Pines, FL, USA

RE: to determine how many generators

(OP)
What is the load range of gas-fired generators like? I face a consumption curve which has three peeks.
So is it better group some gas generators and diesels and let them work at average load but increase the load for diesels during the
period of peaks? Or increase gas ones outputs? Or what?
Thank you.

RE: to determine how many generators

For critical standby, N+1.
For prime power, you may want to consider N+2 or N+3.
You will eventually have one unit down for a major overhaul.With N+3, you will be left with N+2. Now in the event of a failure which cannot be repaired immediately, You still have your N+1 protection.
Location may be important. Our little utility in the Caribbean had 5 diesel units installed, of two different sizes. More than once, I had one unit down for overhaul and a second unit down until the ship came in with a rewound generator end. e had the option of requesting our largest customer to disconnect and run on his standby set. That option was used fairly often when the peak AC season overlapped with the peak fishing season.

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

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