On Tue, 29 Mar 2022 16:56:28 +0300, Dimitris Tzortzakakis
<
no...@nospam.com> wrote:
>???? 19/3/2022 6:34 ?.?., ?/?
gfre...@aol.com ??????:
Typically they want the ability to derive 120v single phase on a
general use service so you can end up with 240, center tapped delta
that will give you the full 240v across the line to line loads and on
one winding you get 120/240 center tapped like the normal single phase
service. In fact that is exactly what it is. They use a large single
phase transformer for the 120v loads and add a second one for the 3d
phase. It lets them provide 3p with two transformers but you usually
see that in a light industrial application where they need some 3
phase along with a normal 120/240 service. It is known as "Delta Vee"
or Red Leg Delta because that 3d phase is 208 above ground. You also
need to derate the current because of the missing leg and you should
not really use line to neutral loads on the 208v leg. It is for pure 3
phase loads like motors.
https://gfretwell.com/electrical/red%20leg%20transformers.jpg
The other common service is 3 phase wye with 208 between phases and
120v line to neutral on all three. That is better when you are using a
lot of 120v and willing to compromise on the 208 line to line. It does
require 3 transformers tho.
https://gfretwell.com/electrical/3%20p%20wye-wye.jpg