pump station

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cds9044

Member
Location
TN
Bidding on existing pump station project that requires changing out overhead service with new underground service and changing out existing switchboard. The loads are 3(Ea) 335 HP pumps(249.91KVA each), 2(Ea) panelboards(186.1KVA) for total of 935.83KVA or 749KW.
The problem is that there is an existing 650KVA(520KW) standby generator with ATS feeding entire load. Not sure that all pumps will ever run at same time or not. What is proper way to calculate load? I'm thinking NEC 08, 702.5(2)(a) will dictate resizing existing generator. Any thoughts?
 
RoberteFuhr

RoberteFuhr

Member
Location
Covington, WA.
Not only will you have to look at the load calculations, Generators have a limit for the size of motors that can be started. You'll also need to contact the generator manufacture and find out what the maximum motor load that the generator can supplies. The motor starting method will also have to be considered.
 
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lakee911

Senior Member
Location
Columbus, OH
Jraef said:
That's the first place to start. A typical solution is to use an input off of the ATS (assuming there is one) to disable all but the most critical loads.
Click to expand...

I think what he means is an output from the ATS to disable loads.

Better to interlock the loads with each other so that either can start independent of the other. Reason being is if you have lead / lag selection you may not want to disable your lead pump.
 
weressl

weressl

Esteemed Member
Location
Texas by the Gulf, geat crab, great shrimp
Jraef said:
That's the first place to start. A typical solution is to use an input off of the ATS (assuming there is one) to disable all but the most critical loads.
Click to expand...


Often times out mechanical brethren oversize the pumps.

It is pretty safe to say that you can start ONE pump at a time.

Panels also are seldom loaded to their nameplate. So I would establish the actual expected running load and then take appropriate measures and install control modifications, interlock, exclusionary and starting restrictions in a small PLC.

Look at EACH phase currents and power factor as well.

The more engineering effort you put in the more assurance will you have that the installation will be cost effective AND reliable on the long run.
 
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