I find it really difficult to conceptualize how dimmers can work on a delta trnsformer, I would have thought that the chopped waveform would
play havoc with a "closed"
system like delta, can you elucidate?
(In the USA)
A floating Delta cannot be used for lighting. (Unless you are only splitting it up to run a bunch of movers that run on 240 volts!) Each hot-to-hot measures 240 volts, and there is no hard connection to (what would be) the
neutral. There are often bleeder resistors, or other drains (like MOVs) that may give you fictitious readings with reference to
neutral or
ground. No load can be placed there.
More common, or at least the one we would see used for lighting, is that one of the three windings is center-tapped. So, you have three windings connected end to end, giving you A, B, and C. We will say the winding between A and B is the center tapped one. As such, we are actually running a single
phase system. The "center tap" is your
neutral, and you therefore have 120-0-120 from your H-N-H. The third
phase leg is where the other two windings come together, and is often called the "wild
leg" as it is 208 to
neutral. For
practical purposes, this would not be used. (Or, at least, I would not want it mixed in with my feed!)
This type of Delta was common in buildings with mixed usage. All the heavy air conditioning would be run off the Delta 240-240-240, yet you would also have some 120 circuits for offices and such. Where I am in PA it has fallen out of favor. Almost everything is
Wye, where you have three legs of 120v and 208 between the hots to run AC and heavy equipment.
The heavy chopping (caused by dimmers) in this
circuit will occur across the tapped winding, but you are right in that the Delta is a balanced closed loop, so any sag caused by the chop is going to partially be felt on the other two windings. I am sure someone out there has done the math, but the loading to fill the sage would be fractional on the other two legs. On the bright side, since it is basically a single
phase (0 / 180)
circuit, there would be no
neutral over
current.
Picture credit: Random graphic found on internet