David R Brooks wrote:

john wrote:


Jon Elson wrote:



F. George McDuffee wrote:

On Tue, 30 Oct 2007 09:01:36 -0500, Randy
wrote:


This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.


snip
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what a group! thread hijack [sort of]

Given the increased efficiency in terms of both size and power,
how would 3 phase residential power service (in new homes) affect
power distribution cost/efficiency and the life-cycle cost of
high reactive consumption units such as residential air
conditioners and possibly refrigerators if these were 220
3-phase?

The really big advantage of a 3-phase hermetic refrigeration compressor
is it needs no starting relay. Just apply power and the motor spins up.
I doubt there is a great increase in efficiency of small 3-phase
motors over single phase.

the efficiency comes with varying loads. A single phase motor is
designed to operate at a certain load, any load more or less the phase
shift to the second winding through the cap is not at optimum and will
generate more heat.

If you want REAL efficiency gains, permanent magnet
synchronous motors run by variable frequency drives do show large
gains in efficiency. All variable-speed air conditioners use some
sort of VFD, and permanent magnet motors are now replacing the
induction motor, as they ARE more efficient.

The liklihood of the US adopting 3-phase wall outlets for all
appliances is about as high as (your favorite never-will-happen
scenario here).
There would be REAL costs to extending 3-phase power to all
residences, and putting in 3-phase meters and 3-pole breakers in the
panels. With a basement full of machine tools, I'd love it, though.
I do NOT have 3-phase power on my pole, but it is "only" a block away.


I would look more to supplying houses with DC. With today's electronics
everything can easily run on DC with built in VFD's that run directly
from dc rather than first rectifying it inside the drive. The same goes
for any appliance. Using DC would make it much easier to eliminate
switching noise from vfd's and other similar devices by just adding a
couple of caps on only one circuit.

The problem with DC is that current interrupters (switches, fuses,
breakers) need to be much bigger. AC current drops to zero, 100 or 120
times per second, and this quenches any developing arc. To break a
significant current in a DC system can require quite special (read
costly) devices.

Once the air is ionized DC or AC will substain an arc. An inductive load
on a DC circuit will cause arcing but a resistive load will be a lot
less. Any high voltage device is costly... especially 3 Ø.

John