why 3-phase power?

[Zak]

phil-news-nospam@ipal.net wrote:

But you can go straight to 12 phases from 3 phases. Your power feed needs
to have a wye configuration (most common) and you need to be able to deal
with some phases having a different voltage than others. For a DC power
supply you use 3 transformers to get 6 phases, but you can get 12 phases
out of 6 transformers all having primaries attached to various combinations
of the 4 wires coming from the wye secondary of the utility transformer
secondary. These still need to be mixed voltage (on the primary of the DC
power supply transformers). The voltages in the US would be 120/208 or
277/480 or 347/600 depending on what your utility can provide.

I think you could use a standard 3 phase core, and lots of secondary
windings. From 3 phase to 2 phase 90 degrees shift can be done (and the
reverse as well).

A winding on a certain phase in series with a few turns on the next
phase will have a resulting phase that is a bit in the direction of that
next phase.

As you make separate turns per output phase it is easy enough to ajust
voltages to be approximately equal.

http://optoelectronics.perkinelmer.com/Catalog/Product.aspx?ProductID=CIA
for a product that seems to do something like this.


Thomas

 

[Rob Paisley]

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?

---------

For larger horsepower motors, Three Phases means that they will
start with no external mechanical assistance.

For distribution many economies can be had with 3 Phases.

(Expensive) Alternators could be made with more phases and so could
the systems to deliver the power but the problems and costs would far
outweigh the benefits.

Rob.

 

In sci.electronics.basics Zak <spam@jutezak.invalid> wrote:
| phil-news-nospam@ipal.net wrote:
|>
|> But you can go straight to 12 phases from 3 phases. Your power feed needs
|> to have a wye configuration (most common) and you need to be able to deal
|> with some phases having a different voltage than others. For a DC power
|> supply you use 3 transformers to get 6 phases, but you can get 12 phases
|> out of 6 transformers all having primaries attached to various combinations
|> of the 4 wires coming from the wye secondary of the utility transformer
|> secondary. These still need to be mixed voltage (on the primary of the DC
|> power supply transformers). The voltages in the US would be 120/208 or
|> 277/480 or 347/600 depending on what your utility can provide.
|
| I think you could use a standard 3 phase core, and lots of secondary
| windings. From 3 phase to 2 phase 90 degrees shift can be done (and the
| reverse as well).
|
| A winding on a certain phase in series with a few turns on the next
| phase will have a resulting phase that is a bit in the direction of that
| next phase.
|
| As you make separate turns per output phase it is easy enough to ajust
| voltages to be approximately equal.

Having noted that utility distribution 3 phase transformers have a core
that is really one big core for all three (though spatially separated a
bit), I have been wondering what would happen in the magnetic field if
one were to take a toroid core, put the three phase primaries on it at
120 degree positions covering only 1/3 of the toroid each, and then have
a "rolling secondary" that slides around the toroid (mechanical support
for the mass would then be done with wheels holding up the 2/3 not being
used for the secondary).

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

 

[John Larkin]

On 1 Jan 2004 06:39:51 GMT, phil-news-nospam@ipal.net wrote:

I don't see much need for motors above 3 phases and certainly not above 12.
But DC power supplies might still get very good use of a lot of phases. One
thing I've wondered is if a big zener (bank) can "clip off" a small ripple
that a 12 phase power supply would have and virtually eliminate capacitors.

Motors are happy at three phases. Rectifier banks benefit from having
more, up to a point; for a rectifier, all phase voltages need to be
very nearly equal. Ripple is very small for a 12-phase or so rectifier
bank. With more phases, ripple amplitude decreases and frequency
increases, so a series inductor followed by a bit of capacitance
becomes an efficient way to filter ripple, if it matters. A zener bank
would waste a huge amount of power and would do nasty things if the
line voltage went up just a bit.

We did a 3-phase powered MRI gradient amplifier a while back. It puts
out +-100 amp pulses at up to 180 volts peak. The power transformer
weighs about 90 pounds, just about the same as Tammy, my smallest
production employee. We gave her an overhead electric winch so she
could load the transformers into the chassis. With fullwave
rectification, the ripple frequency is 360 Hz, so just a modest bunch
of capacitors filters things nicely.


John

 

[John Larkin]

On Thu, 01 Jan 2004 07:30:53 +0000 (GMT), Tony Williams
<tonyw@ledelec.demon.co.uk> wrote:

In article <j5o5vv8u2jk7uq0pcpsl2t0bdpkaa33a77@4ax.com>,
Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> wrote:

On Wed, 31 Dec 2003 08:42:58 +0000 (GMT), the renowned Tony
Williams <tonyw@ledelec.demon.co.uk> wrote:
Severe thread drift here...... An interesting use of
filterless multi-phase rectification was in amplitude
stabilising of RC oscillators.

Interesting. Did that use a transformer arrangement using
quadrature input (wide frequency range) or some kind of RC
kludge?

You have to start with a 2-phase oscillator for the
the basic Sin/Cos. Then lots of resistors and opamps
to get multiple arithmetic phase-shifted outputs. ISTR
that at about 8-phase rectification the harmonic
distortion effect of the residual ripple is sufficiently
attenuated by the oscillator itself.

Low distortion analog sinewave oscillators need a gain servo loop, and
that can have huge settling times at low frequencies. With a 2-phase
oscillator, you could feed back on sin^2 + cos^2 and have basicly zero
delay. Now all we need are good multipliers!

John

 

[John Larkin]

On 1 Jan 2004 16:57:29 GMT, phil-news-nospam@ipal.net wrote:

Having noted that utility distribution 3 phase transformers have a core
that is really one big core for all three (though spatially separated a
bit), I have been wondering what would happen in the magnetic field if
one were to take a toroid core, put the three phase primaries on it at
120 degree positions covering only 1/3 of the toroid each, and then have
a "rolling secondary" that slides around the toroid (mechanical support
for the mass would then be done with wheels holding up the 2/3 not being
used for the secondary).

It would blow up instantly.

John

 

[M Ewing]

Rich Grise wrote:

turn directly into the fuselage. I said to my cow-orker, "It's
4 feet from here, that way." pointing toward the centerline of the

I have never orked a cow, but it sounds unpleasant.

 

In rec.radio.amateur.equipment phil-news-nospam@ipal.net wrote:

In sci.electronics.basics John Larkin <jjlarkin@highsniplandthistechpleasenology.com> wrote:

<snip>

I don't see much need for motors above 3 phases and certainly not above 12.
But DC power supplies might still get very good use of a lot of phases. One
thing I've wondered is if a big zener (bank) can "clip off" a small ripple
that a 12 phase power supply would have and virtually eliminate capacitors.

To what purpose? Capacitors are a lot cheaper and smaller than transformers.

--
Jim Pennino

Remove -spam-sux to reply.

 

[Spehro Pefhany]

On Thu, 1 Jan 2004 17:22:21 +0000 (UTC), the renowned
jimp@specsol-spam-sux.com wrote:

In rec.radio.amateur.equipment phil-news-nospam@ipal.net wrote:
In sci.electronics.basics John Larkin <jjlarkin@highsniplandthistechpleasenology.com> wrote:

snip

I don't see much need for motors above 3 phases and certainly not above 12.
But DC power supplies might still get very good use of a lot of phases. One
thing I've wondered is if a big zener (bank) can "clip off" a small ripple
that a 12 phase power supply would have and virtually eliminate capacitors.

To what purpose? Capacitors are a lot cheaper and smaller than transformers.

I'm sure I could find cases where that is true. However, if you try to
make a 5 or 10HP inverter for motor control operate from single phase
power you will quickly find that the capacitors both represent a major
(probaby the largest single) portion of the materials cost and are the
determining factor in the life of the product.

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

 

[Owain]

"Frank Bemelman" wrote

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.

D'you work for The Wee Kirkcudbright Centipede Electrical Company Ltd
by any chance?

http://www.kirkcudbright.co.uk/club/centipede.htm

Owain

 

[Spehro Pefhany]

On Thu, 1 Jan 2004 20:03:33 +0000 (UTC), the renowned
jimp@specsol-spam-sux.com wrote:

Yeah, but the topic was 12 phase DC power supplies...

The first thing you do when you're making an inverter-style motor
control is turn the incoming AC to DC with a sufficiently low ripple.

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

 

[John Larkin]

On Thu, 1 Jan 2004 20:03:33 +0000 (UTC), jimp@specsol-spam-sux.com
wrote:

In rec.radio.amateur.equipment Spehro Pefhany <speffSNIP@interlogdotyou.knowwhat> wrote:
On Thu, 1 Jan 2004 17:22:21 +0000 (UTC), the renowned
jimp@specsol-spam-sux.com wrote:

In rec.radio.amateur.equipment phil-news-nospam@ipal.net wrote:
In sci.electronics.basics John Larkin <jjlarkin@highsniplandthistechpleasenology.com> wrote:

snip

I don't see much need for motors above 3 phases and certainly not above 12.
But DC power supplies might still get very good use of a lot of phases. One
thing I've wondered is if a big zener (bank) can "clip off" a small ripple
that a 12 phase power supply would have and virtually eliminate capacitors.

To what purpose? Capacitors are a lot cheaper and smaller than transformers.

I'm sure I could find cases where that is true. However, if you try to
make a 5 or 10HP inverter for motor control operate from single phase
power you will quickly find that the capacitors both represent a major
(probaby the largest single) portion of the materials cost and are the
determining factor in the life of the product.

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


Yeah, but the topic was 12 phase DC power supplies...

1. Don't be a lurker topic-droid.

2. A motor control inverter *needs* a good, polyphase-fed DC power
supply.

John

 

[Zak]

jimp@specsol-spam-sux.com wrote:

I don't see much need for motors above 3 phases and certainly not above 12.
But DC power supplies might still get very good use of a lot of phases. One
thing I've wondered is if a big zener (bank) can "clip off" a small ripple
that a 12 phase power supply would have and virtually eliminate capacitors.


To what purpose? Capacitors are a lot cheaper and smaller than transformers.

Capacitors cause peak currents. And if you need the transformer anyway
it doesn't cost a lot to add more output phases.


Thomas

 

In rec.radio.amateur.equipment Spehro Pefhany <speffSNIP@interlogdotyou.knowwhat> wrote:

On Thu, 1 Jan 2004 17:22:21 +0000 (UTC), the renowned
jimp@specsol-spam-sux.com wrote:

In rec.radio.amateur.equipment phil-news-nospam@ipal.net wrote:
In sci.electronics.basics John Larkin <jjlarkin@highsniplandthistechpleasenology.com> wrote:

snip

I don't see much need for motors above 3 phases and certainly not above 12.
But DC power supplies might still get very good use of a lot of phases. One
thing I've wondered is if a big zener (bank) can "clip off" a small ripple
that a 12 phase power supply would have and virtually eliminate capacitors.

To what purpose? Capacitors are a lot cheaper and smaller than transformers.

I'm sure I could find cases where that is true. However, if you try to
make a 5 or 10HP inverter for motor control operate from single phase
power you will quickly find that the capacitors both represent a major
(probaby the largest single) portion of the materials cost and are the
determining factor in the life of the product.

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

Yeah, but the topic was 12 phase DC power supplies...

--
Jim Pennino

Remove -spam-sux to reply.

 

[John Larkin]

On Thu, 01 Jan 2004 21:46:28 +0100, Zak <spam@jutezak.invalid> wrote:

jimp@specsol-spam-sux.com wrote:

I don't see much need for motors above 3 phases and certainly not above 12.
But DC power supplies might still get very good use of a lot of phases. One
thing I've wondered is if a big zener (bank) can "clip off" a small ripple
that a 12 phase power supply would have and virtually eliminate capacitors.


To what purpose? Capacitors are a lot cheaper and smaller than transformers.

Capacitors cause peak currents. And if you need the transformer anyway
it doesn't cost a lot to add more output phases.

In a beefy single-phase supply, the caps can often cost more that the
transformer. Polyphase, the transformer costs about the same as
single-phase, but you need far less capacitance.

John

 

In sci.electronics.basics John Larkin <jjlarkin@highlandsniptechthisnologyplease.com> wrote:
| On 1 Jan 2004 16:57:29 GMT, phil-news-nospam@ipal.net wrote:
|
|>Having noted that utility distribution 3 phase transformers have a core
|>that is really one big core for all three (though spatially separated a
|>bit), I have been wondering what would happen in the magnetic field if
|>one were to take a toroid core, put the three phase primaries on it at
|>120 degree positions covering only 1/3 of the toroid each, and then have
|>a "rolling secondary" that slides around the toroid (mechanical support
|>for the mass would then be done with wheels holding up the 2/3 not being
|>used for the secondary).
|
| It would blow up instantly.

OK, take the rolling secondary back off. Just have 3 primaries covering
1/6 of the toroid each, and 3 secondaries covering the remaining gaps
between those secondaries.

--
-----------------------------------------------------------------------------
| 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 Rob Paisley <rpaisley4@cogeco.ca> wrote:

| For larger horsepower motors, Three Phases means that they will
| start with no external mechanical assistance.

And, as I understand it, they can then "stand on one leg" although they
will be a bit "shaky".

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

 

[Spehro Pefhany]

On 2 Jan 2004 00:06:16 GMT, the renowned phil-news-nospam@ipal.net
wrote:

In sci.electronics.basics Rob Paisley <rpaisley4@cogeco.ca> wrote:

| For larger horsepower motors, Three Phases means that they will
| start with no external mechanical assistance.

And, as I understand it, they can then "stand on one leg" although they
will be a bit "shaky".

Correct.

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

 

[Rich Grise]

"Jonathan Barnes" <jbarnes@ATnetcomuk.co.uk> wrote in message
news:bsvmsh$gsl$1@taliesin2.netcom.net.uk...

Rich Grise wrote

Can you kids now see the difference between a 180 degree
phase shift and a simple inversion?

Not as long as SIN X = - SIN ( X + 180 )

There is no difference with a sine wave.

Can you give me details of any test you use to detect the difference ?

Yes. Use a phasor diagram.

See if you can find graph paper with polar and rectangular
coordinates, and draw directed segments [0,0][1,0] and [0,0]
[-1,0]. They're clearly inverses. Now, transform them both
to polar coordinates. Now it's vector 1.0 < 0deg and 1.0 <
180deg.

I think thinking of it as just going up and down is one way,
and thinking of it as going around circles is another.

And just another grain of sand - isn't there something about
reactance having to be involved?

Cheers!
Rich

--
Jonathan

Barnes's theorem; for every foolproof device
there is a fool greater than the proof.

To reply remove AT

 

[John Larkin]

On 1 Jan 2004 23:59:44 GMT, phil-news-nospam@ipal.net wrote:

In sci.electronics.basics John Larkin <jjlarkin@highlandsniptechthisnologyplease.com> wrote:
| On 1 Jan 2004 16:57:29 GMT, phil-news-nospam@ipal.net wrote:
|
|>Having noted that utility distribution 3 phase transformers have a core
|>that is really one big core for all three (though spatially separated a
|>bit), I have been wondering what would happen in the magnetic field if
|>one were to take a toroid core, put the three phase primaries on it at
|>120 degree positions covering only 1/3 of the toroid each, and then have
|>a "rolling secondary" that slides around the toroid (mechanical support
|>for the mass would then be done with wheels holding up the 2/3 not being
|>used for the secondary).
|
| It would blow up instantly.

OK, take the rolling secondary back off. Just have 3 primaries covering
1/6 of the toroid each, and 3 secondaries covering the remaining gaps
between those secondaries.

Still blows up. The primary phases are fighting each other. A
three-phase torroidal transformer needs three cores.

John