ECN Forum Forums Technical Discussion Electrical Theory and Applications 3 phase(240/120) delta bank

Does this configuration have one transformer larger or smaller than the other two (due to the high-leg not being utilized for 120 volt loads)?

Rojo-sy;

The 4 Wire Delta has a center Pot, which is sized according to the expected 120 VAC 1Ø 2 Wire (or combined 120/240 VAC 1Ø 3 Wire loads).

Larger center Transformers where more 1Ø 120 VAC needed, smaller where less is needed.

Scott35

Thanks, Scott.
I thought I'd seen larger ones, then recently, I saw a smaller one. This explains it.

(…under construction…)

Truth is, four-wire delta banks can have any size transformers, including one “zero-size” pot—that being only two transformers—a/k/a an “open delta” bank. See IEEE std C57.105-1978 §6/§8 or odds’n’sods from EPE overhead standards linked at http://6l6.net/bjarn/EPEdelta-loadg.DSO7.pdf (~1MB) for some sizing guidelines (that are not necessarily NEC-based.) A ‘shorthand’ sketch of delta and open-delta secondary interconnection…



 

[This message has been edited by Bjarney (edited 04-04-2005).]