On Mon, 30 Jul 2018 13:06:50 -0700 (PDT), trader_4
wrote:

Abstract:
Distribution engineers have treated the standard "singlephase" distribution transformer connection as single phase because from the primary side of the transformer these connections are single phase and in the case of standard rural distribution single phase line to ground. However, with the advent of detailed circuit modeling we are beginning to see distribution modeling and analysis being accomplished past the transformer to the secondary. Which now brings into focus the reality that standard 120/240 secondary systems are not single phase line to ground systems, instead they are three wire systems with two phases and one ground wires. Further, the standard 120/240 secondary is different from the two phase primary system in that the secondary phases are separated by 180 degrees instead of three phases separated by 120 degrees. What all of this means is that analysis software and methods must now deal with an electrical system requiring a different set of algorithms than those used
to model and analyze the primary system. This paper will describe the modeling and analysis of the single-phase center tap transformer serving 120 Volt and 240 Volt single-phase loads from a three-wire secondary.

W. H. Kersting
Milsoft Utility Solutions, USA

When I read that I see him say he is talking about "modeling" not
reality.
My suggestion is maybe his software model needs to be adjusted to more
closely reflect reality.
Would you be happier if I found a half dozen articles by credentialed
people who explain why this is single phase?
I have certainly been in quite a few CEU seminars given by
professionals who explain it in very precise terms not software
models.
Perhaps this is just too complicated for homeowners to grasp. That is
why we say "hire an electrician".