Jim Brown wrote:
> On Sun, 8 Aug 2010 10:17:39 +0200, Milan DlabaŠ wrote:
>
>> most of family houses in Europe (even in Czech
>> rep.) - probably more than 90% of family houses have 3 - phase power
> system
>> as normal way.Peak input power of my house is around 20 kW - including heat
>> pump, washer, dryier, el.stove, ham radio and etc. and still we have input
>> circuit breaker 3x32A.I thing, that this is normal modern way how to do
> it.I
>> can not imagine 200A input circuit breaker .
>
> Question. How much equipment actually RUNS on 3-phase power? Does your
> refigerator connect to a 3-phase outlet? Your washer, dryer, heat pump?
> Stove? Or do they connect to ONE PHASE of the 3-phase system that comes into
> your home? Same question for the guy from Anaheim. :)
Electric heat and hot water is often done with 3 phase elements (even
here in the US) because a 3 pole lower current switch is comparable in
cost to a 2 pole higher current one (more current means bigger contacts,
bigger springs, bigger electromagnet on the contactor, etc.)
>
> I'm asking this because I've never SEEN a 3-phase home appliance. Maybe they
> exist, and I live a sheltered existence. :) Remember, I said that except for
> running big motors, there was no good reason for 3-phase. Several suggested
> big DC power supplies are easier to filter, and that's certainly true, and I
> would do it for a broadcast transmitter, but not for ham power levels (at
> least not legal ones). Remember that what you might save in filter caps you
> might pay back with buying three smaller power transformers rather than one
> larger one. :) And, for that matter, there are switching power supplies,
> and they don't have to be noisy if they're done right.
I agree.. *today* it's probably a wash, because power semiconductors and
ASIC controllers make life easier. My washing machine has a 3 phase
inverter built into it (running off single phase feed, of course), but
I'm pretty sure it's a fairly high rate switcher.
>
> As to big air conditioners -- I can't even dream of owning or using one. I
> live in California, where my monthly bill for power averages $180, WITHOUT
> air conditioning, thanks to a billing rate of $0.42/kWh if our monthly draw
> exceeds a rather low limit.
Yow..
Our bills in SoCal run in that range, but we DO run A/C. Our peak rate
is 0.34/kWh (4th tier), bottom tier is 0.11/kWh.
If one lived in, a hot humid climate, say, Houston, a $300/month tab to
run the AC may seem cheap at the price (according to my aunt who lives
there anyway)..
Keeping this moderately ham radio related.. Solar Panels are still not
worth it economically.. Commercial power is just too cheap, unless you
manage to qualify for subsidies, etc. However, solar panels, if you
have battery storage, do provide a handy emergency backup, if sized
right. Most of the subsidies are for battery-less grid-tie systems these
days (which makes more sense in a bigger picture... reduces peak load on
the infrastructure, don't have waste/emissions issues from battery
manufacture, etc.)
That rate increases again if I add air
> conditioning. My major cost is pumping water from the well. And yes, three-
> phase motors would be more efficient -- IF they were available in sizes that
> matched the uses of a single family home. :)
More than a decade ago, we were looking for a 3 phase motor that was
less than 4" in diameter for a specific application, and that's very
similar to what well pumps need. Franklin Electric (a big maker of
smallish electric motors.. say <5HP) was developing a PWM inverter to
drive well pumps to eliminate the need for the accumulator. The idea was
that a variable speed drive would make for a smaller, more reliable pump
that would automatically adjust the speed to keep constant line pressure.
However, even there, I suspect that they were running off single phase.
>
>> Your system is older and I
>> understand, that rebuilding could be quite expansive.
>
> Yes, the infrastructure cost is the killer. As Jim Lux noted, it's far
> easier to do it right when you're forced by history to start from scratch,
> as was the case in much of EU after WWII (and in other countries much later
> in time). Heck, when I was a child, I learned that there was still a lot of
> DC wiring around NYC!
>
Not too many years ago, I was involved in a project to see if there is a
way to detect excessive leakage current in the wiring plant in NYC (e.g.
the stories of dogs being electrocuted when urinating on a metal cover
plate that happens to be live)..
Not only is the physical distribution plant mostly undocumented, a lot
of it dates from the days of Edison, and in some cases uses single wire
feeders with ground returns via the lead pipe conduit. Working for
ConEd is apparently an interesting job.
---
Keeping it more towerish... How big are the motors used on a telescoping
tower? Those might benefit from 3 phase, if only for the simpler
switching to reverse them. OTOH, in comparison to the $10k cost of a new
tower and installation, saving $100 in switches, etc, might not be worth it.
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