Question on sizing transformer

[KWH]

I have a customer who is requesting a 200kva transformer for a new building that will be used mainly for some new machinery. I do not have much info but my question is with a 480volt primary and 208 volt secondary ( 200kva ) doing the math for a general service size on the secondary do you use the 1.73 multiplier or do you divide by 208 only. I was looking thru a Mike Holt guide and in the examples for figuring primary and secondary he was dividing by the voltage only. I am sorry if this seems basic just thinking to much.

 

[jumper]

If it is 3 phase, 1.732 is always a part of the equation.

 

[KWH]

Thanks Jumper

Thanks Jumper

N/A

 

[jumper]

Here is a link I keep book marked.

http://ecmweb.com/mag/electric_transformer_installation_made/

 

[charlie b]

If it is 3 phase, 1.732 is always a part of the equation.

And in this specific case, it appears as follows:
Rated current equals rated KVA times 1000, then divided by line-to-line volts (in this case, 208 volts), then divided again by 1.732.
I = (200 * 1000) / (208 * 1.732) = 555 amps.

 

[dkidd]

200 is not a standard size. 225 would be close.

 

[jumper]

And in this specific case, it appears as follows:
Rated current equals rated KVA times 1000, then divided by line-to-line volts (in this case, 208 volts), then divided again by 1.732.
I = (200 * 1000) / (208 * 1.732) = 555 amps.

Your math works either way, but your verbal/written explanation and equation do not seem to match. Your verbal/written equation would seem to be this:

I =(200*1000)/208/1.732=555 amps

 

[kingpb]

Now that is nit-picking :lol:

 

[jumper]

Now that is nit-picking :lol:

Yep. Gotta pick on a train driver(EE) when I can.