[Top] [All Lists]

Re: [TowerTalk] Power Distribution

To: Jim Brown <>
Subject: Re: [TowerTalk] Power Distribution
From: jimlux <>
Date: Sun, 08 Aug 2010 11:35:51 -0700
List-post: <">>
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. 

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.


TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>