In article ,
"Tzortzakakis Dimitrios" writes:

? "Andrew Gabriel" ?????? ??? ??????
...
In article WMGTj.5083$ch1.2983@trndny09,
"James Sweet" writes:

It's not 110V, it's 240V, we simply split it with a grounded center tap
which gives 120V between each side and neutral, or 240V between the
sides..

It's the regulation at 120V which people notice.
If you want to call it a 240V supply, then you
need to call EU supplies 400V or 415V. That's
equally misleading.

There's no transformer per house, except rural applications. Generally
5-10
houses are on each transformer, sometimes more. The problem with long
runs
is that the voltage fluctuates substantially with large loads such as
central air conditioning. Standard North American residential service is
200
Amps 240V, I gather this is quite a bit larger than typical European
domestic stuff, so stretching it over 1km distance would require
prohibitively large cables or suffer from wide voltage swings. Makes more
sense to run 7200V down the street and locate a smallish transformer near
every half dozen houses.

The transformers are small in comparison, which gives poor
regulation in comparison (and as I said before, it's the
regulation at 120V which is the primary concern -- regulation
of 240V across 2 hots doesn't matter much for typical US 240V
loads).
The regulation, at least in Europe, is done at 150/15 kV substations and at
the HV side of the transformers, thus at 150 kV. Typical current for 2 x 25
MVA transformers is 150 A, 150 kV and of course secondary at 15 kV, 1500 A.
The regulation is done automatically with tap changers, live. The local
transformers at your neighborhood are fixed tap, 15 kV (they intend to
change everything to 20 kV).

I'm referring to the transformer regulation (and also the LV
supply cable voltage drop) response to load changes. E.g. if
I switch on my 10kW shower, that's a 0.1% change against the
max load of my 1MVA substation transformer and therefore
makes no perceivable difference to the voltage in my house.
If I were to try that on a US 50kVA transformer, that load
is going to trigger a change of 20% of the transformer
regulation, which is much more significant and would
certainly be visible as a brightness change in light bulbs.

Having lived in both countries, I would say it's pretty much
expected in the US that lights dim even with quite moderate
loads coming on, whereas it's rare in the UK (generally only
in rural areas with long supply lines). There are many
contributory factors to this difference, but the 120V verses
240V (or if you must, 240V verses 415V) is ultimately the
underpinning reason.

Automatic tap changing in the HV network is completely
invisible to the residential consumer, as indeed it should
be.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]