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

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reyweesor

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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?
 
reyweesor said:
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.
Click to expand...
yes
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?
Click to expand...
yes
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?
Click to expand...
2000kcmil

I've never seen 2000kcmil wire, and I sure do not want to touch it. Will the lugs on your terminations accept that wire size?

I think you need to divide this to 4 sets of conductors.
 
reyweesor said:
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?
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In a nutshell yes. You need 1312 (maybe not more later) so you would divide the amperage by the number of sets and determine the individual conductor size. More importantly what size OCPD are you feeding with these conductors? The next standard size is 1600 amps so you would need 1600 amps worth of parallel conductors (4 sets of 600 kcmil copper @ 420 amps per conductor) or some type of adjustable OCPD if you wanted to get closer to 1312.
 
I have follow up questions.
Assume : All Wire is Copper
1336 kVA Diesel Generator
3 Phase, 220 Volts at 60 hz.
Full load Line Current = 1336 000 / ( 1.732 * 220 )
= 3506.1 A

The installed Wire from engine to its bus terminal is the following:

Line 1 = 3 - 125 sq. mm
Line 2 = 3 - 125 sq. mm
Line 3 = 3 - 125 sq. mm
Nuetral = 3 - 125 sq. mm

1 - 125 sq mm THWN have ampacity of 255 A

So, 3 sets of 125 sq mm wil have a total of 765 amps.
Thus, this mean that the Generator is only good for

kVA = 1.732 (220) (765)
= 291.495 kVA ?

or it can still operate to 1336 kVA?
if we install the wire like this

Generator to Bus - 12 - 125 sq mm
3 sets of 125 sq mm per conductor runs

Bus to Transformer - 20 - 500 sq mm
5 sets of 500 sq mm per conductor runs
Note : 1-500 sq mm have ampacity of 540 Amps;
5-500 sq mm have total ampacity of 2700 Amps

Transformer to Loads - .............
 
220 is kind of an unusual voltage for the usa. Is that what it says on the nameplate?

The standards found in the nec for conductor ampacity are different than for conductors within equipment.

We don't use mm^2 sized conductors here so it is not likely conductors sized that way would even be code legal.

Beyond those caveats, I generally agree with the other posts.

By the way, I think you are into what the code calls large equipment so probably some kind of ground fault for equipment protection is required. It can probably be programmed into the relaying that came with the genset.
 
yeap!
i am from philippines, and the generator are from china.
125 sq mm is equal to 250 kcmil.

petersonra said:
220 is kind of an unusual voltage for the usa. Is that what it says on the nameplate?

The standards found in the nec for conductor ampacity are different than for conductors within equipment.

We don't use mm^2 sized conductors here so it is not likely conductors sized that way would even be code legal.

Beyond those caveats, I generally agree with the other posts.

By the way, I think you are into what the code calls large equipment so probably some kind of ground fault for equipment protection is required. It can probably be programmed into the relaying that came with the genset.
Click to expand...
 
reyweesor said:
Broter, do you have pdf file of NEC, USA. May i have a copy of it?
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You might be able to poke around on the web and find a copy. I can't send you one. They are copyrighted and the copy I have had my bosses name on every page.

The thing is that the nec only allows certain types of conductor insulation to be used. I don't know if there are any insulated conductors made in metric sizes with nec legal insulation.
 
okay thanks, sir.
petersonra said:
You might be able to poke around on the web and find a copy. I can't send you one. They are copyrighted and the copy I have had my bosses name on every page.

The thing is that the nec only allows certain types of conductor insulation to be used. I don't know if there are any insulated conductors made in metric sizes with nec legal insulation.
Click to expand...
 
petersonra said:
220 is kind of an unusual voltage for the usa.
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Just wait its comming, now that incandescent lamps are almost gone my bet is the next revision of ANSI C84 you'll see a 5% notch up and 208Y120 will become 220Y127 like everyone else has. 208 will go the way of Philly Two phase.
 
reyweesor said:
It's should be, 230/120V ; 400/230V
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230 would be 230Y133 for three phase that would be a bit too high for the US. 400Y230 is used here but rarely, but since its mostly used at 50hz we prefer 480Y277 to get the same 8 volts/hz ratio.
 
tortuga said:
Just wait its comming, now that incandescent lamps are almost gone my bet is the next revision of ANSI C84 you'll see a 5% notch up and 208Y120 will become 220Y127 like everyone else has. 208 will go the way of Philly Two phase.
Click to expand...

Soon or latter its coming. Wouldn't be hard to pull off on Con Ed's networks.
 
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