Standby Generator Specifications

[spark-e-eng]

I am sizing a standby power generator and need to know what power quality requirements would be adequate for my application without going overboard too much in generator size. More specifically, I am using the software supplied by a generator manufacturer for sizing and am not sure what I should select for maximum harmonic distortion, frequency dip and voltage dip. The loads that will be connected are mostly 3 phase motors with across the line starters, but there will be limited lighting, a PLC and a small UPS. Is there an industry standard that someone can point me to so that I don't overdesign?

 

[richwaskowitz]

Caution on Under-voltage Setting

Caution on Under-voltage Setting

This does not answer your question directly, but I wanted to warn you of a recent, very painful learning experience with a Generac 20 kW single phase unit we installed to back-up our information systems. It handled a few power outages just fine and then on Jan. 1st we experiences a prolonged brown-out where we ended up with only 180/60 volts (out of 240/120) for several hours. Since the Generac holds on down to 65% (168 volts) it never kicked in the transfer switch. We lost AC units, fridges, two UPSs and consequently two mail servers. I had a lot of explaining to do for management. Make sure the unit you select will ADEQUATELY protect against under-voltage. The Generac does not, and no, it is not adjustable. What kind of motorized equipment can you think of that will run on 168/84 volts? Apparently Generac thinks 65% is pretty good.

 

[dereckbc]

This is a really tough question to answer in which there are no right answers. After being in the telecom sector which is unique I have come up with a very simple rule to get started.

Try to determine your peak load and double it as a starting point. The right point will be 75% to 125% of peak demand if you have mostly non-linear loads. If you have significant motor and UPS loads lean to 100+.