Sizing of service (amperage) for 2000 HP....

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JacksonburgFarmer

JacksonburgFarmer

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Location
Butler County Ohio
Working on a quote for a design/build job, for a local grain handling elevator. They are planning a expansion, that will basically have two or three stages.

Currently they have a 1200A service, 120/230V Open delta. These loads will have to be re-fed through a buck transformer. The current addition will include about 572 HP. The third will include 922 HP. TOTAL of 2000 HP.

I figure about 2656 amps by table 430.250, or 2246 amps by the following equation 2000 HP X 746 / 480V X 1.73 X .80 PF = 1,492,000/664.32=2245.9

I am curious if I am calculating this right. Service needs to be sized for all motors to run/operate at full load at once, so I dont see how you might derrate this value.

SUPPOSEDLY....the other EC pricing this job says a 1200 A 277/480V service will work, however it may be slightley overloaded.:)
 
If you are figuring a 480v service, it obviously will depend on the various HPs, but you should be looking at a range of 2500-2700 amps (running).
I think I would be a bit more concerned about the max HP and if the motors will be ACL start or soft-start or drives. In rush could be important to say the least.

curious how do you plan to address the 120/230 thru "buck & boost".
I think a 480/240 transformer would be needed.
 
Augie
I think this should be moved to the Engineering Section. That's not to say you haven't given your usual insightful input.
 
bob said:
Augie
I think this should be moved to the Engineering Section. That's not to say you haven't given your usual insightful input.
Click to expand...

Your wish is my command :grin:
worth a try, but I wonder how may folks read just one or two sections.
 
augie47 said:
...

curious how do you plan to address the 120/230 thru "buck & boost".
I think a 480/240 transformer would be needed.
Click to expand...
Better yet, if the current loads are to remain, just add a 480 service and leave this one untouched... unless the POCO sees otherwise, of course. Then your suggestion of a 480>240 xfmr would be the best option.
 
Here is a list of the motors that are going to be on this new expansion.
(2)-125HP Fans, (2)-7.5HP Conveyors, (2)-75 HP Bucket Elevators, (2)-20HP Aug0 ers, (2)-25HP fans, (2)-15 HP augers, (1)-3HP auger, and (17)-2HP fans. My math adds to 572 HP. Most all of these motors would be running at one time, however a few may not, depending on the season(s). The largest motors (the 125HP and 75HP's, and possibly a couple of the 20HP's) will be on soft starts or VFD's.

I still cannot see how this other EC is thinking 1200 Amp service is going to work.....

And for the existing loads, yes I plan on installing a 480/240 transformer. At some point, they are wanting to convert that portion of the operation to 277/480 as well.

Leaving the existing service in place is not really a feasible soulution. Currently the poco dosent have true three phase to the facility. They only have two primarys, and are feeding two 167kVA single phase transformers sitting side by side. This setup worked for quite a while, but is now overloaded, and the motor current draws are really wacked up......that service needs to go the way of the dodo bird.....


Thanks for any and all help guys.....Mike
 
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