Man, I just love those Thumbnail Links!!!
I know that you explained how to create them before (in some old threads about ... who knows what we were all talking about then!), but could you E-mail me with a little info???
Anyhow, to the subject at hand.
Took a look at the plans - the Single Line Diagrams in Image "firesta1" aren't too bad (IMHO!).
Apparently the EE has figured no more than 75 KW will be needed in the event of Power Failure from the PoCo.
The Apparent Power rating of the Genny is 96 KVA, but that is only Apparent Power. The True Power (KW) is what the complete Gen Set can deliver within a given KVA / inside a given Power Factor.
Not sure as to how this figure of 75 KW was obtained, but most likely it would be the highest level of power needed to keep "Crucial" stuff running - such as egress lighting, F/L/S systems, certain machines which will cause some major problems if they are not stopped in a certain sequence, any servers which need to be powered down properly, and so on.
You might be able to find out what items are crucial loads by "Diving Into" the complete planset + Project's Specs Manual.
Simply, the Genny may be sized according to what loads are needed or desired when input power from the PoCo is lossed.
It could be sized Liberally - making it possible to run as much stuff anyone wanted during a power loss event (everyone runs around and turns all the lights on, or fire up all the machinery!).
Or it could be sized Conservatively - with intentions to drive the Necessary loads as figured to be crucially needed.
Even though the Genny is rated for 75 KW, the crucial loads might only total up to no more than 50 KW (or even 50 KVA). This would be a good planning idea for the Genny, as to not load it up to 100% Capacity for extended periods of time and allowing for some load diversity / variable load fluctuations.
I noticed there is a 150 Amp breaker between the Genny and the ATS. This is to protect the feeder between the Genny and the ATS in the event of a Ground Fault or an L-L / L-L-L Fault, not to limit the Genny's output.
To trip the 150 Amp breaker, the Genny would need to crank out >125 KW (or >125 KVA needs to pass through the breaker - which ever comes first).
The Prime Mover (in this case, the Diesel Motor) is rated for " × " horsepower, so once the demand of True Power (Wattage) starts to exceed the HP of the Prime Mover, the Prime Mover gets overloaded - resulting in a drammatic loss in speed.
This continues until one of three things happens:
1: Newly obtained speed results in reduced output True Power to connected equipment, which allows the Prime Mover to continue producing HP (resulting in horrible things on the "Electric Side"!!!),
2: The excessive loads are removed and Prime Mover returns to Full Governed Synchronous Speed,
3: The Prime Mover stalls - eliminating the conserns for #1 and #2 above
I hope this makes sense and explains why the Genny seems to be small.
Make sure the EE has the crucial load requirement figured correctly before accepting my reasoning as to why the 75 KW Gen Set should be sufficient!!!
Otherwise you must bomb me with
Seriously though, see if you can find out what equipment is considered to be crucial (or active 24/7 and uninterrupted), then you can determine how much back-up KW is needed as a minimum.