Phase Current 1

[John2121]

It's been a while since I need to size feeders at the utility level..I have 3000 amp load at 480 volt and 3 phase Y connection..For the life of me I can't remember how to determine each phase current. I believe the formula is 1.73 x PF x amps but i'm not sure..I was planning on use 7- 750 mcm cables per phase & ground. Any input would be apreciated.

 

[weh3]

It sounds as though you already have the phase current, which, incidentally, is power/voltage/1.732. For a 2500kVA transformer, I = 2 500 000/480/1.732 = 3000 A.

Don't multiply by the power factor; that neglects the reactive current. Just use the full load current of the xf as a minimum for ampacity calcs.

I wish that sizing feeders were as simple as looking up a single value in a single table, but the size of cables you choose will ultimately depend on

1. Feeder ampacity, which depends on
Conductor size
Conductor material (Cu, Al)
Number of parallel conductors
Number of conductors per raceway
Insulation temperature rating
Insulation type
Ambient temperature
Delivery method (overhead, underground, cable tray)

2. Voltage drop, which depends on
Cable size
Distance
Conductor material
Raceway material
Load power factor

3. Conductor pulling tension, which depends on
Cable weight
Conductor size
Conductor material
Raceway material
Pulling distance
Number and degree of bends in raceway

I am sure I have left something out, but I hope this helps.

William