Site Power Sizing

[Spin_Dizzy]

I am a Trainee Engineer working I am on large site at the moment where a 200 man camp has just been built of porta kabin units. I have question regarding the design of the site power supply, just for my own education progress in future design applications. The system has been designed by an electrical engineer; one who is not keen on imparting his knowledge to others. The problem is a follows:

1 unit is is drawing 85amps 120/208V I obtained this using The NEC demand factors and the appliance ratings (the load centre for the individual unit has 100amp main breaker a tadge over the 125%).

The units consists of 2 18000Btu AC Circuits, 1 8.5KW Instant Water Heater, 2 Receptacle Circuits and Lighting at 294sqft.

Site is split to 3 3ph transformers 1 supplies 10 units, 1 supplies 37 units and another supplies 52 units 1 laundry and 1 kitchen.

Taking the 37 Units, which are split into 5 350A Sub DB's: 3 of which supply 7 units and 2 which supply 8 units.

The load per phase is:

1 phase @ 1105A
1 phase @ 1105A
1 phase @ 1020A

The 5 Sub DB's are fed by a 1600A Switchboard, The 1600A Switchboard is fed by 1no pad mount 3 phase 500KVA Delta Wye transformer (4150V Primary, 120/208 Secondary).

How do they go from these loads to the calculating the rating of the Transformer

The 52 units Kitchen and Laundry are pulling:

1 phase @ 1643A
1 phase @ 1477A
1 phase @ 1496A

This is also fed by a 1600A switchboard and another 500KVA 3ph Delta Wye transformer.

How do you get from those loads to the Transformer size, when complied these loads exceed the transformer rating, even without implying PF's and other system losses.

Any information that would shed light on the topic would be appreciated.

Thanks

 

[petersonra]

Based on your poor English I am guessing perhaps you are not a native English speaker, and that perhaps this installation is not in the US, thus while one might use NEC rules as guidelines they may well not be a requirement.

I think a lot more additional information would be required before one could make any judgements about this type of installation.

Its entirely possible the 4150V Primary, 120/208 Secondary xfmr is owned or under the control of the utility. If that is the case, the NEC pretty much gets tossed out the window for that piece of equipment.