KWH TO KW- generator sizing

jaggedben said:
We do when our backup generators are inverter based.
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An inverter output generator possibly shuts it's output off to protect itself much sooner than any overcurrent device will trip when the starting current exceeds a certain level. On conventional alternator output the impedance of the alternator is current limiting and essentially it acts like a soft starter when attempting to start a larger motor load. It will drag voltage of everything else that is running down as well during that starting operation.
 
kwired said:
An inverter output generator possibly shuts it's output off to protect itself much sooner than any overcurrent device will trip when the starting current exceeds a certain level. On conventional alternator output the impedance of the alternator is current limiting and essentially it acts like a soft starter when attempting to start a larger motor load. It will drag voltage of everything else that is running down as well during that starting operation.
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Obviously I know that or I wouldn't have made my comment.
 
jaggedben said:
(Ok, it's still weird when you quote and respond to my post like that without adding a phrase or two to explain that your doing so "Just to elaborate" or "For whoever is curious what this means...")
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My bad, I realize I tend to do that often. will try to do better and add things like "just to elaborate" in the future.
 
Jacob Gerstner said:
So if my utility company can’t provide peak KW then I need to size off either a load calc or a more general size based on loads ect. Thanks so much for this response and help.
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One possibility that some utilities will do is measure kWh over a 5 minute or 15 minute period, which you can then multiply by 12 or 4 (depending on if it is 5 or 15 minute kWh), and since the kWh is a relative short period, you can get closer to what the maximum demand is for the service when you choose the highest reading for the month / year, then apply that to your generator size.
 
Here is an example of what everyone has been saying about how you cannot use kWh to determine kW requirements;

kWh is kW divided by time, in hours. So 100kWh is 100kW continuously for 1 hour, in which case the PEAK REQUIREMENT from the source of that power is 100kW.

But if you used 1,000kW for only 6 minutes (0.1 hours) and nothing else, that is STILL only 100kWh on the meter, but the PEAK REQUIREMENT was 1,000kW. So if you had sized a generator based on that 100kW value and your load needed 1,000kW for only 10 minutes, your generator will fail.

So again, you need the “peak demand” values from the utility.
 
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