Specing 3 phase transformer

[kwired]

charlie b,

You are showing a Delta, but ideally the XFMR output, especially where it is 120/240 or 120/208 is a Y not Delta, so load can always be balanced.

Cheers!

TBNK

You can not get 120/240 out of a wye

If the wye is 208 line to line then all lines will be 120 to neutral.

If the wye were 240 line to line then all lines to neutral will be 138.5 volts.

240 volt delta with the midpoint of one phase grounded will have 120/240 across that phase, it will have 208 volts from midpoint to opposite corner of the delta.

You can't change those ratios unless you change the angles of corners of the triangle - and doing that will change lengths of sides and they will no longer all be equal leaving you with unequal line to line voltages if you designed a transformer that way. Similar result changing angles or lengths of the vectors forming the "wye".

 

[winnie]

charlie b,

You are showing a Delta, but ideally the XFMR output, especially where it is 120/240 or 120/208 is a Y not Delta, so load can always be balanced.

Cheers!

TBNK

Charlie showed a Delta secondary because you asked about 120/240 three phase. This strongly implies a high leg delta, which gives 120/240 on the 'base' and 240V line to line on all of 3 phases.

As others have said, you _can't_ get 120/240 out of a wye transformer. As others have said, with a standard high leg transformer you are limited to 5% 120V loading.

Further to your calculations, what sort of computers are you installing that require 1325W each? If this is some sort of server cluster then I can believe that number. But if this is a class room with computers at each seat I'd suggest looking more closely at the computer power requirements; in many cases the power supply has a peak consumption value that is rarely if ever actually used. You might want to get a couple of computers and log their power consumption.

If this is a server cluster then you should also double check your HVAC power requirements; all of the power going to the computers ends up as heat, and by your calculations you would need to get rid of some 400KW of heat, enough to boil some 170 gallons of water per hour.

-Jon