why 3-phase power?

[Tim Shoppa]

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?

In special-purpose applications, usually motor drives, more than three
phases are sometimes used.

For "regular" industrial motor drive, three phase is very nice because
it ensures that the motor runs in the right direction. That is, until
the electrician's rewire things so that they run backwards!

Tim.

 

[Brenda Ann]

"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

 

[Spehro Pefhany]

On Tue, 30 Dec 2003 23:18:49 +0100, the renowned "Frank Bemelman"
<fbemelx@euronet.invalid.nl> wrote:

"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> schreef in bericht
news:bam3vv8v5lr18ktiias5gi27lqr9mf0tr4@4ax.com...
On 30 Dec 2003 09:21:11 -0800, the renowned alanh_27@yahoo.com (Alan
Horowitz) wrote:

what is the attraction of three-phase power? Why not 9 0r 317
phases? Why not plain ole hot & neutral?

It better uses transformer iron and makes better/cheaper induction
motors. For making DC it requires less in the way of filtering. It
would be nice if we had something like 6 phase power, we could get rid
of the input filter caps in most equipment, the only part that we
can't make smaller by increasing efficiency and frequency of SM power
supplies.

With 3 phases you never run out of juice, even without a cap,
so why do you want 6 ?

Less ripple. You want to work out the difference?

If I did the calculations right, the ripple is from peak down to 50%
off of peak for 3-phase vs. only 3% down from peak for 6-phase.

The SMPS would have to work a lot harder to handle that range,
especially if you want the same supply to handle 50% * 85% * 100V for
"universal" input (Japan residential).

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

 

[Brenda Ann]

"Tim Shoppa" <shoppa@trailing-edge.com> wrote in message
news:bec993c8.0312301458.510cbed2@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?

In special-purpose applications, usually motor drives, more than three
phases are sometimes used.

For "regular" industrial motor drive, three phase is very nice because
it ensures that the motor runs in the right direction. That is, until
the electrician's rewire things so that they run backwards!

And 3 phase motors don't need those troublesome starter caps/windings..

I've worked with 3Ř 480 volt systems (for industrial clothes dryers).. until
I worked on those, I had never seen such strange things as a short in a
terminal block vaporizing wiring DOWNSTREAM from the short... : |

 

[Frank Bemelman]

"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> schreef in bericht
news:qn14vv0m4401g06cbs7dcc52c5dbre7tkj@4ax.com...

On Tue, 30 Dec 2003 23:18:49 +0100, the renowned "Frank Bemelman"
fbemelx@euronet.invalid.nl> wrote:

"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> schreef in bericht
news:bam3vv8v5lr18ktiias5gi27lqr9mf0tr4@4ax.com...
On 30 Dec 2003 09:21:11 -0800, the renowned alanh_27@yahoo.com (Alan
Horowitz) wrote:

what is the attraction of three-phase power? Why not 9 0r 317
phases? Why not plain ole hot & neutral?

It better uses transformer iron and makes better/cheaper induction
motors. For making DC it requires less in the way of filtering. It
would be nice if we had something like 6 phase power, we could get rid
of the input filter caps in most equipment, the only part that we
can't make smaller by increasing efficiency and frequency of SM power
supplies.

With 3 phases you never run out of juice, even without a cap,
so why do you want 6 ?

Less ripple. You want to work out the difference?

If I did the calculations right, the ripple is from peak down to 50%
off of peak for 3-phase vs. only 3% down from peak for 6-phase.

The SMPS would have to work a lot harder to handle that range,
especially if you want the same supply to handle 50% * 85% * 100V for
"universal" input (Japan residential).

That's a good point, the universal input. Is an inductor a better
storage for energy than a capacitor, I wonder, from a dimensions
point of view...

--
Thanks, Frank.
(remove 'x' and 'invalid' when replying by email)

 

[Ben Bradley]

In a crosspost involving:

rec.radio.amateur.equipment
sci.engr.electrical.compliance
sci.engr.manufacturing
sci.electronics.design
sci.electronics.basics,

alanh_27@yahoo.com (Alan Horowitz) asked:

what is the attraction of three-phase power? Why not 9 0r 317
phases? Why not plain ole hot & neutral?

Three-phase offers constant power transfer from instant to instant,
whereas in a single phase (into a resistive load) the power varies as
a 1+cosine (or sin squared) function, going from zero to a peak twice
per cycle. Constant power is essential for large generators and motors
so that they will have low vibration.
Look in any textbook with a name like "AC Circuits Analysis" for
more info and full mathmatical derivations.
-----
http://mindspring.com/~benbradley

 

In sci.electronics.basics Spehro Pefhany <speffSNIP@interlogdotyou.knowwhat> wrote:
| On 30 Dec 2003 09:21:11 -0800, the renowned alanh_27@yahoo.com (Alan
| Horowitz) wrote:
|
|>what is the attraction of three-phase power? Why not 9 0r 317
|>phases? Why not plain ole hot & neutral?
|
| It better uses transformer iron and makes better/cheaper induction
| motors. For making DC it requires less in the way of filtering. It
| would be nice if we had something like 6 phase power, we could get rid
| of the input filter caps in most equipment, the only part that we
| can't make smaller by increasing efficiency and frequency of SM power
| supplies.

Actually, you can get 6 and even 12 phases out of 3 phases fairly easily.
If you put a normal single primary to center tapped secondary (120/240 in
North America) on each of the three phases (tie all the neutrals together),
you really have 6 phases.

Y3 * * X2 X0 is in the center, and legs are X1, Y3, X2, Y1, X3, Y2
\ / X[123] to X0 gets 120 volts
\ / Y[123] to X0 gets 120 volts
X1 *----*----* Y1 Xn to Yn gets 240 volts
/ \ X1 to X2, or X2 to X3, or X3 to X1 gets 208 volts
/ \ Y1 to Y2, or Y2 to Y3, or Y3 to Y1 gets 208 volts
Y2 * * X3

I've never seen a 3 phase transformer with this configuration, probably
because there is virtually no need for it. If you really do want it,
you'd have to build it from 3 separate 1 phase transformers.

If you were building a large computer machine room with lots of switching
power supplies, and your power feed is three phase, this might actually be
useful to minimize the 180 Hz component on the neutral. If you used a
standard 208Y/120 feed and ran computers on everything, you could see as
much as 2-3 (depending on how wide your current pulse is) times the current
on the neutral because of the timing offsets of the switching power supply
currents. 1 phase power doesn't have this problem as long as the computers
have similar current waveforms (they cancel out on each side). With the
above 6 phase configuration, you'd get the advantage of 1 phase balancing
while keeping the load balanced on your 3 phase feed.

But the payoff might not be there since the above requires 7 wires, whereas
you can compensate for high neutral currents with larger neutral wires and
stick with 4 wires (one fat, or doubled or tripled). Also, you can get
UPSes that use 3 phase power, and that should take care of the problem.
You'd want to use UPSes, right?

Motors and transformer power supplies can work on 3 phase power as if they
were 6 or 12 phase. Normal power feeds have a wye secondary, so you get
either 208Y/120 or 480Y/277 or 600Y/346 depending on your service category
(the latter 2 use an additional transformer to get the 120v level). These
wires are labeled X0 for neutral, X1, X2, and X3 for the three hot legs.

Lets say you have a very high power motor that uses 480Y/277 (typical for
high power industrial motors) and does this with 12 windings. 6 of them
would be designed for 480 volts, and the other 6 for 277 volts. Then the
connections would be, in order:

12 o'clock X0-X1 277 volts, 0 degrees
1 o'clock X3-X1 480 volts, 30 degrees
2 o'clock X3-X0 277 volts, 60 degrees
3 o'clock X3-X2 480 volts, 90 degrees
4 o'clock X0-X2 277 volts, 120 degrees
5 o'clock X1-X2 480 volts, 150 degrees
6 o'clock X1-X0 277 volts, 180 degrees
7 o'clock X1-X3 480 volts, 210 degrees
8 o'clock X0-X3 277 volts, 240 degrees
9 o'clock X2-X3 480 volts, 270 degrees
10 o'clock X2-X0 277 volts, 300 degrees
11 o'clock X2-X1 480 volts, 330 degrees

An AC/DC power supply could use 6 transformers wired for each of the 6 phases
(but not the opposites), and feed full wave bridges to get nearly DC with a
very low 720 Hz ripple (the secondaries would have the 12 phases above). For
very large power supplies this can become practical since you don't need as
much of a capacitor bank to smooth it out (or you can get a much smoother DC
if that's your goal). 3 of the transformers would have one voltage for the
primary and the other 3 would have a different voltage (208 and 120 for the
most common three phase power in the US).

If you didn't want to go to that extreme, you could still do a 3 transformer
version that gets you a 360 Hz ripple. These would all have the same primary
voltage, and could be attached either between legs and neutral, or between
each hot leg, depending on voltage, or even work on a delta feed.

With more transformers strategically wired, you can get 24 phase, 96 phase,
and so on. At some point you might not need any filter caps

--
-----------------------------------------------------------------------------
| 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 Jonathan Barnes <jbarnes@atnetcomuk.co.uk> wrote:

| Well... the Europeans used 220V, the British used 240V, and we are all now
| harmonising on a nominal 230V.

Is that with one hot leg or two? If you get three phase power there, what
are the common voltages?

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

 

[Matt Osborn]

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?

 

[Spehro Pefhany]

On Tue, 30 Dec 2003 20:23:21 -0600, the renowned Matt Osborn
<msosborn@spam_trap@attglobal.net> wrote:

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?

We'd also accept "little boy who lives down the lane?"

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

 

[Phil Kane]

On Tue, 30 Dec 2003 22:16:27 +0100, Frank Bemelman wrote:

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

Pay them enough and Pyle-National will supply you with one.

--
73 de K2ASP - Phil Kane P.E.

 

[John Woodgate]

I read in sci.engr.electrical.compliance that Jonathan Barnes
<jbarnes@ATnetcomuk.co.uk> wrote (in <bsss8k$56l$1@taliesin2.netcom.net.
uk&gt about 'why 3-phase power?', on Tue, 30 Dec 2003:

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.

So do other people, but it's an inflammatory issue with some US experts.
--
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!

 

[John Woodgate]

I read in sci.engr.electrical.compliance that phil-news-nospam@ipal.net
wrote (in <bst9de11t6n@enews3.newsguy.com&gt about 'why 3-phase power?',
on Wed, 31 Dec 2003:

In sci.electronics.basics Jonathan Barnes <jbarnes@atnetcomuk.co.uk> wrote:

| Well... the Europeans used 220V, the British used 240V, and we are all now
| harmonising on a nominal 230V.

Is that with one hot leg or two? If you get three phase power there, what
are the common voltages?

230 V phase-neutral, so 230 x sqrt(3) = 400 V between phases.

--
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!

 

[John Woodgate]

I read in sci.engr.electrical.compliance that jimp@specsol-spam-sux.com
wrote (in <bssr1t$9im$1@mail.specsol.com&gt about 'why 3-phase power?',
on Tue, 30 Dec 2003:

In rec.radio.amateur.equipment John Woodgate <jmw@jmwa.demon.contraspam.yuk
wrote:
I read in sci.electronics.design that Brenda Ann <brendad@shinbiro.com
wrote (in <bssmvp$e07$1@news1.kornet.net&gt about 'why 3-phase power?',
on Wed, 31 Dec 2003:

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

The question of whether 120-0-120 is split-phase or two phase is not
just a fighting issue in the US, it's a TOTAL ANNIHILATION issue. (;-)

Wholly incredible to this poor Brit.
--
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!

How big would the sparks be if you crossed a British engineer with an
American electrician?

The sparks would be of chemical rather than electrical origin. Ask on
alt.rec.sexualchemistry?
--
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!

 

[John Woodgate]

I read in sci.engr.electrical.compliance that Frank Bemelman
<fbemelx@euronet.invalid.nl> wrote (in <3ff1f974$0$16892$1b62eedf@news.w
anadoo.nl&gt about 'why 3-phase power?', on Tue, 30 Dec 2003:

"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

And a cure for your colour-blindness. (;-)

--
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!

 

[John Woodgate]

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.
--
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!

 

[Tony Williams]

In article <1e3670a7.0312300921.599776f8@posting.google.com>,
Alan Horowitz <alanh_27@yahoo.com> wrote:

what is the attraction of three-phase power? Why not 9 0r 317
phases? Why not plain ole hot & neutral?

It comes from a standard sum that relates the power
capacity of electrical machinery to the number of
phases. Often shown in old elec eng textbooks.

In the example given in the textbook here he develops
sums for the relative power output for various phases,
for an ac motor of fixed frame size.

The baseline 1-phase motor is given a power output of P1.

A 2-phase motor in the same frame size would develop
a power output of P2= 1.414*P1.

A 3-phase motor would develop P3= 1.5*P1.

An m-phase motor (where m is an arbitrarily large number)
would develop Pm= 1.57*P1.

Pm is only 7% larger than P3, and so not worth the
complication. So P3 became the practical optimum number
of phases.

The same sum can be broadly applied to rotating machines,
transformers, and transmission gear.

--
Tony Williams.

 

[Mark Keith]

phil-news-nospam@ipal.net wrote in message news:<bst9de11t6n@enews3.newsguy.com>...

In sci.electronics.basics Jonathan Barnes <jbarnes@atnetcomuk.co.uk> wrote:

| Well... the Europeans used 220V, the British used 240V, and we are all now
| harmonising on a nominal 230V.

Is that with one hot leg or two? If you get three phase power there, what
are the common voltages?

Most the three phase I see runs 120v from two of the legs to ground.
The third leg is 240v to ground. Many residential A/C units used to
use three phase power here, if you had the power co. wire you up that
way. But they are getting much less common now as far as the smaller
residential units. You used to see a pretty decent advantage if you
ran three phase in the old days, but not much now. The newer single
phase units are more efficient than the older three phase with less
efficient coils, etc. I don't think the power co. will even hook you
up three phase anymore around this town for residential. Or if they
do, they will charge you three arms and a leg to do it. I think they
have to switch pole transformers. Many existing three phase units get
changed over to single phase when they die. Only the bigger units are
staying with three phase. IE: some 5 ton, 7.5 ton, etc...All you do to
switch three phase to single phase is tape off the 240 to ground line,
and use the other two as 240 single phase. You stay with three wires,
but the third becomes neutral instead of a hot 240v. BTW, the "240v"
here in Houston is pretty hot. I measure up to 248 volts at times at
this house. Needless to say, my henry amp usually has a happy plate
voltage..
I can't adjust the tap...The freakin 2k classic I have is about the
only henry console made that you can't adjust the line tap. Most have
multiple taps..But nooooooooo, not mine...:/ I run up to 3400v at
times. Bet my filament voltage is hot too... MK

 

[Tony Williams]

In article <bam3vv8v5lr18ktiias5gi27lqr9mf0tr4@4ax.com>,
Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> wrote:

It better uses transformer iron and makes better/cheaper
induction motors. For making DC it requires less in the way of
filtering. It would be nice if we had something like 6 phase
power, we could get rid of the input filter caps in most
equipment, the only part that we can't make smaller by increasing
efficiency and frequency of SM power supplies.

Industrial-strength rectifiers do use transformers
sets that supply 6 phases.

Severe thread drift here...... An interesting use of
filterless multi-phase rectification was in amplitude
stabilising of RC oscillators. No filter cap meant
a fast response to changes, without bounce. Made
obsolete when cheap analogue multipliers came along,
(rectification via sine-squared_plus_cos-squared).

--
Tony Williams.

 

[John Woodgate]

I read in sci.electronics.design that Mark Keith <nm5k@wt.net> wrote (in
<25eb70d7.0312310007.54c20af7@posting.google.com&gt about 'why 3-phase
power?', on Wed, 31 Dec 2003:

Most the three phase I see runs 120v from two of the legs to ground.
The third leg is 240v to ground.

This is a very special US technique, using a transformer with a delta-
connected secondary (like an equilateral triangle of windings), with one
winding centre-tapped and grounded.

In most countries, all three phase voltages are equal.
--
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!