why 3-phase power?

"Smoke" <rsmokey@newsguy.com> wrote in message
news:btg3t301cqa@enews1.newsguy.com...
Hi Steve,

It may be nit picking, but how would you describe a
polyphase-3-wire-system,
one wire grounded, where voltages do not algebraically add?. (such as
supplied by two synchronous but out of phase generators sharing a common
neutral)
Click to expand...
I believe (but check with a real electrician, I was only an assistant) that
this would be an unbalanced Edison circuit. A balanced Edison circuit is a
three wire system (four, if you add a ground) where there is a common
neutral and two legs of equal voltage and opposite phase.
 
"Smoke" <rsmokey@newsguy.com> wrote in message
news:btg3t301cqa@enews1.newsguy.com...
This could be called nit picking, but if I have two which are 180
degrees
out of phase it does look like two phases, no? Any center tapped
transformer can do this and I think it is valid to call it two phase.
Connect across the two hots & you get twice the voltage, of course. Now
connect across two of the lines in a 3-phase system. You still get some
voltage ( don't know the numbers) , no? Why should 180 degrees not be
called two phases while 120 degrees is?
I agree that this can be called a "single phase system", but I still see
two phases for this special case. Symantics, perhaps as long as we all
know
what is really happening, no?



Hi Steve,

It may be nit picking, but how would you describe a polyphase-3-wire-system,
one wire grounded, where voltages do not algebraically add?. (such as
supplied by two synchronous but out of phase generators sharing a common
neutral)


Steve, K;9;D;C;I
Click to expand...

One place I worked had an odd feed into the transformer room.
100 V, 25 Hz., two phase.
Three wires, and the two phases were 90 degrees apart.
It was still live, but no longer connected to anything.

--

... Hank

Hank: http://horedson.home.att.net
W0RLI: http://w0rli.home.att.net
 
I believe (but check with a real electrician, I was only an assistant)
that
this would be an unbalanced Edison circuit. A balanced Edison circuit is
a
three wire system (four, if you add a ground) where there is a common
neutral and two legs of equal voltage and opposite phase.
Click to expand...
I heard that was called "Edison wiring". That is where they use 2 110v
branch circuits fed by 3 wires and there was 220v across the two hot wires.
I was told in the old days that kind of wiring was popular and most codes
required the neutral be soldered because if the neutral was opened there
was a good chance you would burn out every thing connected to one of the
branches (the one with the lighter load) .

Rich
 
Hi...er um... Smoke,

Well I wouldn't.
I only commented on the American system where two sources are availabe
(from a one phase system) that are 180 degrees out of phase and I can easily
call that two phases, but since you ask, I'll venture some speculation.

You say three things that seem to be self contradictory:
1- "voltages do not algebraically add"
2- "two synchronous but out of phase generators"
3- "sharing a common neutral"

#3 says that they WILL "algebraically add" as you say. Since they have one
common point to which they will reference. Therefore, you WILL measure the
difference of voltages wherever you measure between. What you read is
another matter depending on what #2 means.

By "synchronous ", you imply that they are the same frequency (zero phase
slip between them). If this is the case, there is still some phase
relationship between them and there will be some voltage difference between
any two randomly selected phases and therefore some voltage will be
measured.

If there is a phase slip (a small frequency difference), then the voltage
measured above will vary at the difference frequency.

If the phase randomly varies, then the measured voltage will do the same.

However, in all cases, you will measure the voltage difference of the two
phases you are measuring...Has to be... Unless you wait for another big
bang and hope the laws of physics are different...

'gards, Steve, K;9;d;c;i;;

I see that this will go to several groups and since I am ignorant of all
this kind of stuff, I am reading it on
rec.radio.amateur.equipment




"Smoke" <rsmokey@newsguy.com> wrote in message
news:btg3t301cqa@enews1.newsguy.com...
This could be called nit picking, but if I have two which are 180
degrees
out of phase it does look like two phases, no? ...[snip]



Hi Steve,

It may be nit picking, but how would you describe a
polyphase-3-wire-system,
one wire grounded, where voltages do not algebraically add?. (such as
supplied by two synchronous but out of phase generators sharing a common
neutral)


Steve, K;9;D;C;I
Click to expand...
 
In sci.electronics.basics Steve Nosko <suteuve.nosukowicuz@moutouroula.com> wrote:
| Hi...er um... Smoke,
|
| Well I wouldn't.
| I only commented on the American system where two sources are availabe
| (from a one phase system) that are 180 degrees out of phase and I can easily
| call that two phases, but since you ask, I'll venture some speculation.

In terms of the number of different vectors from neutral, then I, too, would
call that 2 phase. I think they do call that 2 pole.

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? Would you call that 6 phase? I'd call
it a lot of wires.

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
 
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?
Click to expand...
Time to read another thread...

Steve K;9;D:C:I
 
"
You say three things that seem to be self contradictory:
1- "voltages do not algebraically add"
Click to expand...
They will not add up using scalar quantities. You would have have to use
vector arithmetic or instantaneous values.

2- "two synchronous but out of phase generators"
Click to expand...
.. From MSBookshelf synchronous definition 3a. "Having identical periods".
I know by definition 3b means same frequency & phase. .

3- "sharing a common neutral"

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
Click to expand...
Feeding single phase loads or poly phase loads?

The 120/240 are commonly for single phase loads. Hence single phase supply.
The 120/240 volt tap could not feed a two phase load unless you tapped from
two transformers on seperate phases.(P.S. two phase loads are something one
would find in airplanes).

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? Would you call that 6 phase?
Click to expand...
Most 6 phase loads that I am familiar with would have the 6 phases but would
be internal connections and would only require 3 phase feeder (AFAIK).
 
I read in sci.engr.electrical.compliance that phil-news-nospam@ipal.net
wrote (in <btkj4e01rck@enews3.newsguy.com>) about 'why 3-phase power?',
on Thu, 8 Jan 2004:

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? Would you call that 6 phase? I'd call
it a lot of wires.
Click to expand...
If by 'neutrals' you mean the centre-taps, I'd call it 'nothing
surprising', because that's more or less how the US system works, AIUI,
except that the input is not 480 V but 4 kV or 12 kV.
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
Interested in professional sound reinforcement and distribution? Then go to
http://www.isce.org.uk
PLEASE do NOT copy news posts to me by E-MAIL!
 
"Smoke" <rsmokey@newsguy.com> wrote in message
news:btl4q901lhq@enews2.newsguy.com...
You say three things that seem to be self contradictory:
1- "voltages do not algebraically add"

They will not add up using scalar quantities. You would have have to use
vector arithmetic or instantaneous values.
Click to expand...
Hi Smoke

I think we're just getting tied up in words. I guess the terminology
"algebraically add" threw me. I was thinking, but not saying the following,
or did I...? I was describing using a _meter_. I thought the original
question was something like "What would you measure...". Since I (and it
appears you) understand adding or subtracting of AC signals must also
consider frequencies and phase, without realizing it, I was assuming we were
already on the same page in principle.
I think you must agree that A METER would actually read the difference
between the instantaneous voltages. I'm pretty sure you're saying this.

The intent of your next comment elludes me, however.

2- "two synchronous but out of phase generators"

. From MSBookshelf synchronous definition 3a. "Having identical periods".
I know by definition 3b means same frequency & phase. .
Click to expand...
Same periods = same frequency, therefore this implies some fixed phase
relationship. I believe my original comments then still hold. If you
triggered a scope on one phase of one system and did not move it, as you
move another probe around, you would see stationary sine waves of differing
phase shift on every phase line, right?
Steve K'9'D"C"I
 
ggober@alltel.net (Phideaux) wrote in message news:<fd732a29.0401050549.776e801f@posting.google.com>...
rpaisley4@cogeco.ca (Rob Paisley) wrote in message news:<bb39a577.0401040927.78fd8647@posting.google.com>...
ggober@alltel.net (Phideaux) wrote in message news:<fd732a29.0401030655.54992bda@posting.google.com>...
alanh_27@yahoo.com (Alan Horowitz) wrote in message 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?

Alan, from an industrial maintenance and engineering perspective, 3
phase motors can be reversed quite easily by switching any 2 of the 3
leads. This elliminates double stocking of single phase motors due to
them being directionally oriented in their rotation. Three phase
equipment is also less "noisy", electrically speaking, due to them not
having the zero voltage cross-over inherent in a single phase supply.

Happy New Year


Single phase motors can rotate in either directions simply by
reversing one of the windings at the connection terminals, usually the
starting winding. - No double stock is required.

Which direction it runs depends on which way the armature is kicked
when power is applied. When the motor reaches a certain speed the
starting winding cuts out.

Rob.

You are correct, of course. However, in a plant maintenance
environment, you do not wish to be out in bad weather, tearing down
connection heads and reversing winding leads. I'd much rather do that
in a climate controled motor control center where the starters are.
Starting 15,000 hp motors "in the shop" to check the initial rotation
would not be a practical matter, in my opinion. Vacuum contactors are
not cheep, and to have one, and the feed to it, just so this could be
done before installation just doesn't seem to be the right way to go.
I guess the old addage "Things are the way they are, for good reason"
seems to apply to the use of 3 phase motors in higher horsepower
applications.
Click to expand...
(Portion removed.)

No one would rotation test a 3 phase motor of any size "in the shop"
as the field connections are the ones that are important. If the
rotation was found to be wrong then yes it would be corrected at the
MCC.

As for testing single phase motors, as most are of small size and
field wiring orientation does not affect rotation, these could more
easily be checked in the shop before installation.

Single phase motors usually come with a stated rotation from the
manufacture so testing is not normally required.

Clock wise is the norm as this ensures that nuts on the ends of
shafts are being 'threaded on' when running.

Any millwrights and electricians I have worked with will rotation
test motors, single or polyphase, before coupling it to the load just
to be certain it is correct for the particular load.

Rob.
 
ggober@alltel.net (Phideaux) wrote in message news:<fd732a29.0401050549.776e801f@posting.google.com>...
rpaisley4@cogeco.ca (Rob Paisley) wrote in message news:<bb39a577.0401040927.78fd8647@posting.google.com>...
ggober@alltel.net (Phideaux) wrote in message news:<fd732a29.0401030655.54992bda@posting.google.com>...
alanh_27@yahoo.com (Alan Horowitz) wrote in message 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?

Alan, from an industrial maintenance and engineering perspective, 3
phase motors can be reversed quite easily by switching any 2 of the 3
leads. This elliminates double stocking of single phase motors due to
them being directionally oriented in their rotation. Three phase
equipment is also less "noisy", electrically speaking, due to them not
having the zero voltage cross-over inherent in a single phase supply.

Happy New Year


Single phase motors can rotate in either directions simply by
reversing one of the windings at the connection terminals, usually the
starting winding. - No double stock is required.

Which direction it runs depends on which way the armature is kicked
when power is applied. When the motor reaches a certain speed the
starting winding cuts out.

Rob.

You are correct, of course. However, in a plant maintenance
environment, you do not wish to be out in bad weather, tearing down
connection heads and reversing winding leads. I'd much rather do that
in a climate controled motor control center where the starters are.
Starting 15,000 hp motors "in the shop" to check the initial rotation
would not be a practical matter, in my opinion. Vacuum contactors are
not cheep, and to have one, and the feed to it, just so this could be
done before installation just doesn't seem to be the right way to go.
I guess the old addage "Things are the way they are, for good reason"
seems to apply to the use of 3 phase motors in higher horsepower
applications.
Click to expand...
(Portion removed.)

No one would rotation test a 3 phase motor of any size "in the shop"
as the field connections are the ones that are important. If the
rotation was found to be wrong then yes it would be corrected at the
MCC.

As for testing single phase motors, as most are of small size and
field wiring orientation does not affect rotation, these could more
easily be checked in the shop before installation.

Single phase motors usually come with a stated rotation from the
manufacture so testing is not normally required.

Clock wise is the norm as this ensures that nuts on the ends of
shafts are being 'threaded on' when running.

Any millwrights and electricians I have worked with will rotation
test motors, single or polyphase, before coupling it to the load just
to be certain it is correct for the particular load.

Rob.
 
In sci.electronics.basics John Woodgate <jmw@jmwa.demon.contraspam.yuk> wrote:
| I read in sci.engr.electrical.compliance that phil-news-nospam@ipal.net
| wrote (in <btkj4e01rck@enews3.newsguy.com>) about 'why 3-phase power?',
| on Thu, 8 Jan 2004:
|
|>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? Would you call that 6 phase? I'd call
|>it a lot of wires.
|
| If by 'neutrals' you mean the centre-taps, I'd call it 'nothing
| surprising', because that's more or less how the US system works, AIUI,
| except that the input is not 480 V but 4 kV or 12 kV.

Whatever the input, the point is having all 3 phases together at the same
place (not one phase on one street, another phase on another, and so on).
Graphically it would be a 6 pointed star. But I have never seen any dry
type 3-phase (3 coils on an E-core) transformer with this secondary wiring
configuration. I have seen them where they did 120/60 and tied all the
center tapped neutrals together. That gets you 120 volts, but that's not
any more useful than the more common 208Y/120, and in fact uses more wires
for the same benefit. What I was thinking was being able to get 3-phase
plus true 240 volt (instead of 208 volt), plus lots of 120 volt, where the
120/240 needs are well in excess of the occaisionally seen 240 delta with
a center tap to get 120/240 off one winding (which limits the load to a
small portion of the overall load ... which is fine to run some lights in
an industrial location that needs 240 volt 3-phase). But if the balance
is that some 3 phase is needed, but lots more 1 phase is needed, and some
true 240 is needed, this is a configuration that can do that and keep the
phases in fair balance.

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
 
In sci.electronics.basics Smoke <rsmokey@newsguy.com> wrote:
|
| "
|> You say three things that seem to be self contradictory:
|> 1- "voltages do not algebraically add"
|
| They will not add up using scalar quantities. You would have have to use
| vector arithmetic or instantaneous values.
|
|> 2- "two synchronous but out of phase generators"
|
| . From MSBookshelf synchronous definition 3a. "Having identical periods".
| I know by definition 3b means same frequency & phase. .
|
|> 3- "sharing a common neutral"
|
|> 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
|
| Feeding single phase loads or poly phase loads?
|
| The 120/240 are commonly for single phase loads. Hence single phase supply.
| The 120/240 volt tap could not feed a two phase load unless you tapped from
| two transformers on seperate phases.(P.S. two phase loads are something one
| would find in airplanes).
|
|> 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? Would you call that 6 phase?
|
| Most 6 phase loads that I am familiar with would have the 6 phases but would
| be internal connections and would only require 3 phase feeder (AFAIK).

But what I was thinking of was lots of 120/240 volt 1 phase loads spread
over 3 phases to keep them in balance, while still having true 3 phase
available for some loads that need that (you can still get 208Y/120 out
of this scheme).

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
 
<phil-news-nospam@ipal.net> wrote in message
news:bu1qsd12nem@enews2.newsguy.com...
In sci.electronics.basics Smoke <rsmokey@newsguy.com> wrote:
|
| "
|> You say three things that seem to be self contradictory:
|> 1- "voltages do not algebraically add"
|
| They will not add up using scalar quantities. You would have have to use
| vector arithmetic or instantaneous values.
|
|> 2- "two synchronous but out of phase generators"
|
| . From MSBookshelf synchronous definition 3a. "Having identical
periods".
| I know by definition 3b means same frequency & phase. .
|
|> 3- "sharing a common neutral"
|
|> 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
|
| Feeding single phase loads or poly phase loads?
|
| The 120/240 are commonly for single phase loads. Hence single phase
supply.
| The 120/240 volt tap could not feed a two phase load unless you tapped
from
| two transformers on seperate phases.(P.S. two phase loads are something
one
| would find in airplanes).
|
|> 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? Would you call that 6 phase?
|
| Most 6 phase loads that I am familiar with would have the 6 phases but
would
| be internal connections and would only require 3 phase feeder (AFAIK).

But what I was thinking of was lots of 120/240 volt 1 phase loads spread
over 3 phases to keep them in balance, while still having true 3 phase
available for some loads that need that (you can still get 208Y/120 out
of this scheme).

Something close to what you describe is commonly available in many areas of
Click to expand...
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.

Louis
 
I read in sci.engr.electrical.compliance that phil-news-nospam@ipal.net
wrote (in <bu1qnm02nem@enews2.newsguy.com>) about 'why 3-phase power?',
on Tue, 13 Jan 2004:
Whatever the input, the point is having all 3 phases together at the same
place (not one phase on one street, another phase on another, and so on).
Graphically it would be a 6 pointed star. But I have never seen any dry
type 3-phase (3 coils on an E-core) transformer with this secondary wiring
configuration.
Click to expand...
Well, of course I can't comment on whether that arrangement is used in
USA, but it seems to me that any site that has a LV 3-phase feed *needs*
such an arrangement for the reasons you cite - notably that it needs 120
V single-phase supplies as well as 240 V 3-phase. Or are all such
3-phase supplies provided at 277/480 V?
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
Interested in professional sound reinforcement and distribution? Then go to
http://www.isce.org.uk
PLEASE do NOT copy news posts to me by E-MAIL!
 
In sci.electronics.basics John Woodgate <jmw@jmwa.demon.contraspam.yuk> wrote:

| I read in sci.engr.electrical.compliance that phil-news-nospam@ipal.net
| wrote (in <bu1qnm02nem@enews2.newsguy.com>) about 'why 3-phase power?',
| on Tue, 13 Jan 2004:
|>Whatever the input, the point is having all 3 phases together at the same
|>place (not one phase on one street, another phase on another, and so on).
|>Graphically it would be a 6 pointed star. But I have never seen any dry
|>type 3-phase (3 coils on an E-core) transformer with this secondary wiring
|>configuration.
|
| Well, of course I can't comment on whether that arrangement is used in
| USA, but it seems to me that any site that has a LV 3-phase feed *needs*
| such an arrangement for the reasons you cite - notably that it needs 120
| V single-phase supplies as well as 240 V 3-phase. Or are all such
| 3-phase supplies provided at 277/480 V?

The typical low voltage drops in US and Canada are (with varying levels of
availability):

1 phase linear, 120 volts hot to neutral, 240 volts hot to hot
3 phase wye, 120 volts hot to neutral, 208 volts hot to hot
3 phase delta, 240 volts hot to hot, one winding center tapped for 120 volts
3 phase wye, 277 volts hot to neutral, 480 volts hot to hot
3 phase delta, 480 volts hot to hot
3 phase wye, 346 volts hot to neutral, 600 volts hot to hot
3 phase delta, 600 volts hot to hot

As you can see, 120 volts is available from the first three. In the case of
the center tapped delta, no more than about 5% of the load can come from the
single phase loads attached. You can't center tap the other windings to do
the same because you'll end up with unsafe neutral to neutral voltages (120).

Lots of things designed for 240 work on 208 volts, so the 2nd case is usable
in a lot of places. But those devices often work with less performance.
Motors, for example, would have less available horse power and may stall on
loads that would work at 240 volts. Thus I see a need to get a real 240
volts.

If the 1 phase load is less than 5% of the total capcity, the third case can
work. But if if your need for 1 phase power is large while you still need
3 phase power, there are a couple options. One is for the utility to provied
separate drops for 1 phase and 3 phase. I've never seen that done, and have
seen documentation that some utilities won't do that. The other option would
be to take regular 3 phase at whatever voltage you get it (208, 240, 480, 600,
2400, 4160, 7200, 12470, etc) and put 3 separate 1 phase transformers on each
phase (I've never seen a 1 phase transformer with a primary above 600 volts)
and just connect all the neutrals together. Then just make sure you divide up
the 1 phase load reasonably well balanced. You end up with 6 different hot
phase angles at 120 volts 60 degrees each, and 240 volts between the most
distant hots (3 sets). What I have not seen is doing this all on the same
E-core (like a regular 3 phase transformer does), but with the 6 hots and 1
neutral. But that is 7 wires total.

By the way, if you go with 6 single phase transformers/cores, 3 of which have
their primary connected to the hot to hot lines (208 or 480 or 600), and the
other 3 of which have their primary connected to the hot to neutral lines
(120 or 277 or 346), with all 6 secondaries center tapped for hot to neutral
at 120 volts, then what you have is 12 wires with 12 different hot phases at
30 degrees apart. You could do this (at whatever secondary voltage you need)
as part of a DC power supply to get a really low ripple level at a higher
frequency (720 Hz in US/Canada), doing better than a regular 3 phase DC power
supply would do (more ripple at 360 Hz).

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
 
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.

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).

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
 
On Wed, 14 Jan 2004 05:46:54 +0000, the renowned John Woodgate
<jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.engr.electrical.compliance that phil-news-nospam@ipal.net
wrote (in <bu1qnm02nem@enews2.newsguy.com>) about 'why 3-phase power?',
on Tue, 13 Jan 2004:
Whatever the input, the point is having all 3 phases together at the same
place (not one phase on one street, another phase on another, and so on).
Graphically it would be a 6 pointed star. But I have never seen any dry
type 3-phase (3 coils on an E-core) transformer with this secondary wiring
configuration.

Well, of course I can't comment on whether that arrangement is used in
USA, but it seems to me that any site that has a LV 3-phase feed *needs*
such an arrangement for the reasons you cite - notably that it needs 120
V single-phase supplies as well as 240 V 3-phase. Or are all such
3-phase supplies provided at 277/480 V?
Click to expand...
Commercial buildings in Canada and the US typically use 120/208
3-phase.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
In sci.electronics.basics Spehro Pefhany <speffSNIP@interlogdotyou.knowwhat> wrote:
| On Wed, 14 Jan 2004 05:46:54 +0000, the renowned John Woodgate
| <jmw@jmwa.demon.contraspam.yuk> wrote:
|
|>I read in sci.engr.electrical.compliance that phil-news-nospam@ipal.net
|>wrote (in <bu1qnm02nem@enews2.newsguy.com>) about 'why 3-phase power?',
|>on Tue, 13 Jan 2004:
|>>Whatever the input, the point is having all 3 phases together at the same
|>>place (not one phase on one street, another phase on another, and so on).
|>>Graphically it would be a 6 pointed star. But I have never seen any dry
|>>type 3-phase (3 coils on an E-core) transformer with this secondary wiring
|>>configuration.
|>
|>Well, of course I can't comment on whether that arrangement is used in
|>USA, but it seems to me that any site that has a LV 3-phase feed *needs*
|>such an arrangement for the reasons you cite - notably that it needs 120
|>V single-phase supplies as well as 240 V 3-phase. Or are all such
|>3-phase supplies provided at 277/480 V?
|
| Commercial buildings in Canada and the US typically use 120/208
| 3-phase.

But often the drop is a higher voltage. I've worked in places with 480Y/277
600 (not sure if it was 600D or 600Y/346), and 12470D. Then it gets lowered
to operating voltage by transformers inside. Heavy duty 3 phase motors can
be had for 208, 480, and 600 volts. Generators can be had for all kinds of
wiring configurations and voltages (certainly from Generac).

--
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| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
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