On 11/25/2014 12:17 PM, Eric Smith wrote:
On the other hand, distributing three-phase to
residences, while great
for people with shop equipment or old computers, seems like expensive
overkill for normal homes.
And expensive. Copper isn't cheap and a 3-phase distribution
transformer costs considerably more than a single-phase one--and
provides very little advantage.
I'll submit that if your goal is phase-to-phase balancing, distributing
single-phase to individual residences and then shifting the residences
to one phase or the other is probably better in that respect. In
Germany, ordinary wall receptacles are single-phase, so depending on the
homeowner to phase-balance his load is probably not the best policy. On
the other hand, doing the same for multi-residence (i.e. apartment
blocks) does make sense.
The homes on my loop (each has its own single-phase stepdown
transformer, but the loop itself is fed by 3-phase HV) are, every few
years, rebalanced. Each residence has a large green distribution box
where the property line meets the street. All three HV lines come into
each box--re-balancing is just a matter of of swapping connections in
the box. Takes but a few minutes.
This may not be typical for the US, but my utility is a rural electric
co-op, so there's less emphasis on profits and more on member benefits.