why 3-phase power?

[WB2JKX]

<phil-news-nospam@ipal.net> wrote in message
news:bu2quj12cse@enews4.newsguy.com...

In sci.electronics.basics Louis Bybee <louistroutbybee@comcasttrout.net
wrote:

| Something close to what you describe is commonly available in many areas
of
| the US. 240 volt 3 phase in a delta configuration with one transformer
| center tapped for a grounded neutral to provide 120 volts for lighting,
and
| receptacle load, and three phase 240 volts for motor load or high
capacity
| heating loads. The transformers can consist of three individual units
with
| the center tapped one providing 120 volts being much larger than the
other
| two, or an "Open Delta" three phase configuration utilizing two
| transformers. It is very common in residential, office, and light
industrial
| areas. It can be superior where there is motor load, and 480 Y 277 isn't
| available. Unless motors are specifically rated for 208 volts there can
be
| significant power loss, and heating from the reduced operating voltage.

The problem with this configuration is that the 1 phase loads are limited
to about 5% of the total KVA capacity of the transformer. It's fine for
industrial users that have huge amounts of 3 phase need compared to the
lighting/office needs.

Interestingly enough, though, is that where I have commonly seen this is
mixed residential and
commercial areas where the primary need was for 120/240 single phase and
perhaps a single 3 phase user
such as a deli or gas station that used 3 phase motors for refrigeration or
air compressor. In these cases, the
configuration was typically open delta with a smaller transformer for the
additional 3 phase requirement

There are 277 volt lighting systems available, too, for those with
480Y/277.

But if your 1 phase load is a big part of your total, yet you still need 3
phase power for some big motors, my idea can achieve that and let you go
beyond the 5% limit on the 1 phase loads.

I am all too aware of the issue where equipment designed for 240 volts
just
can't do the job on 208 volts. In many cases things have to be derated,
such
as less HP in motors, and longer warm up times for ovens. In worse cases,
there can be failure (motor burnout due to overheating due to either
stalls
or excessive start current times). Getting 240 for what needs 240, under
the need also for 3 phase for other equipment, or because that's just how
the power is provided (utilities often don't provide 1 phase if your load
is more than 400 to 600 amps).

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[Don Kelly]

--
Don Kelly
dhky@peeshaw.ca
remove the urine to answer
"Smoke" <rsmokey@newsguy.com> wrote in message
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"Jonathan Barnes" <jbarnes@ATnetcomuk.co.uk> wrote in message
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"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> wrote in message

And in most places, "plain ole hot & neutral" comes in as 2
phase,
also
called "220".


Actually, this is normally called "split phase" rather than 2 phase
because
the the neutral 'splits' the single phase 240 volt drop.

Perhaps so, but "2 phase" is wrong.

In England a 230 V single phase is just that, one wire is nutral,
nominaly
earth but seperate from the true earth, and the other caries 230V ac.

I belive the American system is 2 x 110 V ac lines with respect to
earth,
but at 180 degree phase angle, to give 220 V ac potential between them.

I would say it's fair to call this 2 phase.



I am a sucker.

Direct and Alternating Currents by Oppenheimer and Borchers says " Any
circuit with a single source of a-c is simply referred to as single-phase
a-c"

If you look on the at the transformer on the pole and look at the primary
connection there would most likely be a single source of a-c feeding the
transformer.hence single-phase. Transformers fed by a single source of
a-c
do not create polyphase voltages.

Example 2: if one connects a train transformer to 110 a-c and the
transformer has many voltage taps you still have single phase voltages
because the transformer is fed by a single source of AC.

Rich.

To the people who use the 120/240 V centertapped system, -i.e. in North

America, it is a single phase 3 wire system or the Edison system (as he
developed it for DC) . However, to those outside this region (who don't use
the system) it is often called 2 phase.
There is some logic to this as 3 phase has 3 voltages, 120 degrees apart, 4
phase has 4 voltages (yeah I know it is "2 phase") 90 degrees apart. 6 phase
has 6 voltages 60 degrees apart so it follows that 2 phase should have 2
voltages 180 degrees apart.
Logic is not necessarily meaningful in life so that the single phase/ 3wire
nomenclature is happily used where this system is used (to the
confusion/annoyance of Brits and those from OZ) and 2 phase is often
reserved for two voltages 90 degrees apart as in some motors. This is on the
basis of "those who use it get to name it"

--
Don Kelly
dhky@peeshaw.ca
remove the urine to answer

 

[Stanley Hess]

You're right, Steve. This is getting brutal.

Stan


"Steve Nosko" <suteuve.nosukowicuz@moutouroula.com> writes:

What would you call it if you took 480 volt 3 phase delta config power,
and connected 3 transformers with 480 in, 120/240 center tapped out, with
all three neutrals tied together?

Time to read another thread...

Steve K;9;D:C:I

--
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[Stan de SD]

"Frank Bemelman" <fbemelx@euronet.invalid.nl> wrote in message
news:3ff1f974$0$16892$1b62eedf@news.wanadoo.nl...

"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> schreef in bericht
news:z9DJJLEr3e8$Ewhv@jmwa.demon.co.uk...
I read in sci.electronics.design that Frank Bemelman
fbemelx@euronet.invalid.nl> wrote (in <3ff1eb4a$0$166$3b62cedd@news.wan
adoo.nl&gt about 'why 3-phase power?', on Tue, 30 Dec 2003:
"Alan Horowitz" <alanh_27@yahoo.com> schreef in bericht
news:1e3670a7.0312300921.599776f8@posting.google.com...
what is the attraction of three-phase power? Why not 9 0r 317
phases? Why not plain ole hot & neutral?

9 phases.... 317 phases, have you ever wired a 317 prong plug?

318; you forgot the ground prong.

Yes, and even while being extremely careful, I swapped
phases 127 and 131, 177 and 178, 202 and 212, 214 and 215,
and 301 and 311.

I think a need phase tester too

Plus a color densitometer to differentiate between all the color-coded
wires. :Oo

 

[Stan de SD]

"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:lKt8k4ATto8$EwBr@jmwa.demon.co.uk...

I read in sci.engr.electrical.compliance that Matt Osborn
msosborn@spam_trap.?.net> wrote (in <clc4vvklhde4937050t1coj5isqs0p8t5i
@4ax.com&gt about 'why 3-phase power?', on Tue, 30 Dec 2003:
On Wed, 31 Dec 2003 08:11:59 +0900, "Brenda Ann"
brendad@shinbiro.com> wrote:


"Frank Bemelman" <fbemelx@euronet.invalid.nl> wrote in message
news:3ff1eb4a$0$166$3b62cedd@news.wanadoo.nl...
"Alan Horowitz" <alanh_27@yahoo.com> schreef in bericht
news:1e3670a7.0312300921.599776f8@posting.google.com...
what is the attraction of three-phase power? Why not 9 0r 317
phases? Why not plain ole hot & neutral?

9 phases.... 317 phases, have you ever wired a 317 prong plug?


In the US that would be a 319 prong plug.. 317 for the phases, one for
neutral, and one for ground.. LOL



But none for the little boy who cries in the lane?

The baa-baa black shield goes to the metal shell of the connector.

Have you any wool for all the insulation you will require?

(insert punch line here)