500 kVA Transformer, 3 Phase at 220 Volts, 60 hz. Sizing Cables, Paralleling Conductors

[mbrooke]

It is already common in downtown "network" areas.

Tell me more please

 

[kwired]

We know that the Full Load Secondary Current is 1312 Amps.

How do we choose for the right cable sizing. I mean we know that, we have a table that is base on NEC. We just choose cable that have ampacity above 1312.

My second questions is, how do we choose the cable size that is intended to be parallel with two conductors?
How does paralleling conductors work? Do we just look for the 1 conductors that have the ampacity above 656 A, So that, When we add the 2 conductor's ampacity is equal to 1312 A?

Line 1 - we use 2 conductors
Line 2 - we use 2 conductors
Line 3 - we use 2 conductors
Nuetral - we use 2 conductors

What would be the size of this cable in THWN, neglecting the voltage drop?

Depends on what you want to do to some extent, and what your limitations might be.

1312 is the rated capacity of your transformer. NEC likely allows 125% overcurrent protection on the secondary. NEC also will require conductor ampacity to be equal or greater than overcurrent proteciton for circuits over 800 amps - that could easily allow you to have 1600 amp overcurrent device but you also would need 1600 amp conductors.

If you want to have overcurrent protection that is no more than rating of the transformer you might opt for 1200 amp OCPD and would need 1200 amp conductors, unless you do need the remaining 312 amps capacity.

Knowing the load calculation of the supplied load factors into this. You later mentioned a diesel generator, is the diesel engine and/or generator capable of delivering the 500KVA or is there need or plans to ever have something that can? Answer here could justify smaller conductors and overcurrent protection.

 

[reyweesor]

Depends on what you want to do to some extent, and what your limitations might be.

1312 is the rated capacity of your transformer. NEC likely allows 125% overcurrent protection on the secondary. NEC also will require conductor ampacity to be equal or greater than overcurrent proteciton for circuits over 800 amps - that could easily allow you to have 1600 amp overcurrent device but you also would need 1600 amp conductors.

If you want to have overcurrent protection that is no more than rating of the transformer you might opt for 1200 amp OCPD and would need 1200 amp conductors, unless you do need the remaining 312 amps capacity.

Knowing the load calculation of the supplied load factors into this. You later mentioned a diesel generator, is the diesel engine and/or generator capable of delivering the 500KVA or is there need or plans to ever have something that can? Answer here could justify smaller conductors and overcurrent protection.

Thanks Mr. Kwired, I really appreciate this. About the generator, we are gonna use it to supply the whole loads which is about 1 MVA.

 

[kwired]

Thanks Mr. Kwired, I really appreciate this. About the generator, we are gonna use it to supply the whole loads which is about 1 MVA.

So I take it that means the generator is creating some other voltage, you do have some loads utilizing that voltage or at least distribution at a higher voltage because of distance or something like that, and then supplying said 500kVA transformer?

As I said before you wouldn't necessarily need conductors and overcurrent protection for the full capacity of the transformer if your calculated load is less than capacity of transformer, you do need conductors and other equipment that can handle the load they will carry though. If you instead choose to run conductors and overcurrent that can utilize full capacity (if more load were to be added) that is a design decision. Like I said in this instance, depending on actual load, you possibly may have choice of 1200 amp or 1600 amp conductors and gear.