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'[OT] 240V in USA'
1998\07\21@051835 by Leo van Loon

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face
Dear friends,

In another mailinglist a member told about a two-phase 120V net with 180
degrees phase difference in parts of the US. I do not understand how high
power induction motors can be used with such an electricity supply. Three
phase rotary currant was invented for this type of motors.
Can anybody from the States tell me about the finesses of this type of
electricity supply?

Leo van Loon
SBB simpeltronics
Netherlands
tel +31 (0481) 450034
fax+31 (0481) 450051
mail spam_OUTsbb.simpeltronTakeThisOuTspamtip.nl
url http://www.sbb-simpeltronics.nl
SBB simpeltronics ontwikkelt technische projecten voor basisschool en
basisvorming.
SBB simpeltronics develops technical projects for children in primary and
secondary education.

1998\07\21@072359 by Dmitry Kiryashov

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face
Good day Leo van Loon.

> Dear friends,
> In another mailinglist a member told about a two-phase 120V net with 180
> degrees phase difference in parts of the US. I do not understand how high
> power induction motors can be used with such an electricity supply. Three
> phase rotary currant was invented for this type of motors.
> Can anybody from the States tell me about the finesses of this type of
> electricity supply?

Probably it was made for compatibility with european 220V industrial
machinery.

WBR Dmitry.

1998\07\21@085304 by Dennis O'Brien

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face
The 120/240 single phase power ( two lines and a neutral) basically goes into ev
ery home. The connection is simply a centre tapped transformer.

Low power appliances (TV, lights, ...) run on 120 V. Higher power loads (stove,
clothes dryer, electric furnace,...) run on the 240 V supply.

For light/medium industrial the power system typically uses  120/208 or 277/480
Volt, 3 phase power. In Canada we use 120/208 or 346/600 Volt 3 phase.

Hope this answers your question.


----Original Message-----
  >From:       Leo van Loon <.....sbb.simpeltronKILLspamspam@spam@TIP.NL>
  >To:         PICLISTspamKILLspamMITVMA.MIT.EDU
  >Subject:            [OT] 240V in USA
  >Reply-To:           pic microcontroller discussion list <.....PICLISTKILLspamspam.....MITVMA.MIT.
EDU>
  >Date:       Tuesday, July 21, 1998 05:15
  >
  >Dear friends,
  >
  >In another mailinglist a member told about a two-phase 120V net with 180
  >degrees phase difference in parts of the US. I do not understand how high
  >power induction motors can be used with such an electricity supply. Three
  >phase rotary currant was invented for this type of motors.
  >Can anybody from the States tell me about the finesses of this type of
  >electricity supply?
  >
  >Leo van Loon
  >SBB simpeltronics
  >Netherlands
  >tel +31 (0481) 450034
  >fax+31 (0481) 450051
  >mail EraseMEsbb.simpeltronspam_OUTspamTakeThisOuTtip.nl
  >url http://www.sbb-simpeltronics.nl
  >SBB simpeltronics ontwikkelt technische projecten voor basisschool en
  >basisvorming.
  >SBB simpeltronics develops technical projects for children in primary and
  >secondary education.
  >

1998\07\21@093926 by Leo van Loon

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Thanks,
This answers my question.
The system is quite complicated in comparison with the European only 230V
three phase. Has that a historical reason?

Leo van Loon

-----Oorspronkelijk bericht-----
Van: Dennis O'Brien <deobrienspamspam_OUTSYMPATICO.CA>
Aan: @spam@PICLISTKILLspamspamMITVMA.MIT.EDU <KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU>
Datum: dinsdag 21 juli 1998 14:58
Onderwerp: Re: [OT] 240V in USA


>The 120/240 single phase power ( two lines and a neutral) basically goes
into every home. The connection is simply a centre tapped transformer.
>
>Low power appliances (TV, lights, ...) run on 120 V. Higher power loads
(stove, clothes dryer, electric furnace,...) run on the 240 V supply.
>
>For light/medium industrial the power system typically uses  120/208 or
277/480 Volt, 3 phase power. In Canada we use 120/208 or 346/600 Volt 3
phase.
>
>Hope this answers your question.
>
>
>----Original Message-----
>   >From:       Leo van Loon <RemoveMEsbb.simpeltronTakeThisOuTspamTIP.NL>
>   >To:         spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU
>   >Subject:            [OT] 240V in USA
>   >Reply-To:           pic microcontroller discussion list
<TakeThisOuTPICLISTEraseMEspamspam_OUTMITVMA.MIT.EDU>
>   >Date:       Tuesday, July 21, 1998 05:15
>   >
>   >Dear friends,
>   >
>   >In another mailinglist a member told about a two-phase 120V net with
180
>   >degrees phase difference in parts of the US. I do not understand how
high
>   >power induction motors can be used with such an electricity supply.
Three
{Quote hidden}

and
>   >secondary education.
>   >
>
>

1998\07\21@094744 by lilel

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face
Leo wrote:

> Dear friends,
>
> In another mailinglist a member told about a two-phase 120V net with
> 180 degrees phase difference in parts of the US. I do not understand
> how high power induction motors can be used with such an electricity
> supply. Three phase rotary currant was invented for this type of
> motors. Can anybody from the States tell me about the finesses of
> this type of electricity supply?

Two phase was used in very old power systems, along with DC and other
obsolete voltages.  There are still areas of the US, mostly in
the cores of older cities, that have these obsolete systems still
operating on a few buildings.  Hey, if it ain't broke, don't fix it,
right?

I know for a fact that Downtown St. Louis, MO has a few blocks with
DC, and I think there is also a little two-phase.  Probably way less
than 1% of US buildings are wired this way.  No new buildings are
installed with these systems.

Why they picked two phase 120v I do not know.
-- Lawrence Lile

    "An Engineer is simply a machine for
     turning coffee into assembler code."

Download AutoCad blocks for electrical drafting at:
http://home1.gte.net/llile/index.htm

1998\07\21@103457 by er

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You can use 3 phase induction motors on single phase.  I have
three industrial quality machines in my shop that do very well.
Put the 240 V across two of the motor leads, and run the
third motor lead back to either of the 240 V supply through
a large (50 mfd or so) oil-filled AC capacitor rated to at least
380V.  The motor will begin turning in one direction or the
other depending on what side the cap is connected to.  Disconnect
the cap when the motor reaches about 75% speed, it is for
starting only.  You will get only about 65% of the torque that
the motor would give on 240V 3 Phase, but usually that is
plenty.  The 3 phase motor is almost indestructable, and
used industrial equipment is a much better bargain than new
single phase modern home shop equipment.

There is a company that markets a box that does the
automatic disconnect of the capacitor, called Phase-O-Matic,
but two switches and the capacitor does just fine.

John Shreffler.

{Original Message removed}

1998\07\21@104721 by Morgan Olsson

picon face
At 08:49 1998-07-21 -0400, you wrote:
>The 120/240 single phase power ( two lines and a neutral) basically goes
into every home. The connection is simply a centre tapped transformer.
>
>Low power appliances (TV, lights, ...) run on 120 V. Higher power loads
(stove, clothes dryer, electric furnace,...) run on the 240 V supply.

What kind of wall outlet connectors are used?

I worked some time in Taiwan, and there the same connector was used for 110
and 220V!  Crazy! Not even labelled.
(I first noticed when I burned up one appliance...)
/  Morgan Olsson, MORGANS REGLERTEKNIK, SE-277 35 KIVIK, Sweden \
\  mrtEraseMEspam.....iname.com, ph: +46 (0)414 70741; fax +46 (0)414 70331    /

1998\07\21@121523 by Mike Massen

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face
Interesting stuff this about 240V. Here in Australia we also
have 240V (used to be 250V) in Western Australia several years ago.

So - does anyone know of a commercial single phase to 3-phase
converter (other than a motor/alternator) - about 2KW max ?


Rgds ~`:o)

Mike
Perth, Western Australia
Products/Personal/Client web area at http://www.wantree.com.au/~erazmus
(Current feature - trip to Malaysia to install equipment in jungle power
site)

Some say there is no magic but, all things begin with thought then it becomes
academic, then some poor slob works out a practical way to implement all that
theory, this is called Engineering - for most people another form of magic.

1998\07\21@122601 by Harold Hallikainen

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Harold Hallikainen
EraseMEharoldspamhallikainen.com
Hallikainen & Friends, Inc.
See the FCC Rules at http://hallikainen.com/FccRules and comments filed
in LPFM proceeding at http://hallikainen.com/lpfm

On Tue, 21 Jul 1998 11:15:05 +0200 Leo van Loon <RemoveMEsbb.simpeltronEraseMEspamEraseMETIP.NL>
writes:
{Quote hidden}

       This is generally only used in residential electric supplies.  A
single phase of the three phase power on the pole is run thru a
transformer with a 240VAC center tapped secondary.  We then have two hots
and a grounded neutral.  240VAC single phase loads (like heating loads)
are run between the two hots.  Single phase loads are run hot to neutral.
       In industrial environments, we either have three phase delta or
wye.  The wye is used where there are a lot of 120VAC single phase loads,
since they can be connected between any hot and neutral.  You get 208VAC
between any two hots, which is acceptable for many 240VAC single phase
loads (though not all).  Other places have a three phase delta connection
where each transformer secondary is 240VAC.  One of the secondaries has
the center tap grounded and is used as a neutral.  Single phase 120VAC
and 240VAC loads use this secondary.  The third lead (the wild phase) is
208 volts above ground.
       Sometimes we get an "open delta" with only two transformers.
These are not favored much.
       Now, questions on European (and elsewhere) power.  I've read
about limitations on harmonic line current.  Though I have not read the
standards (IEC standars are expensive!), it appears these standards apply
to equipment that draws more than 16 amps.  We manufacture phase
controlled light dimmers, which draw more than 16 amps.  Is the 16 amp
limitation (if I've read correctly) a recognition that below this current
it is practical to use some sort of power factor correction and above it
phase control is indeed the most efficient way to control large loads?
       I'd be interested in hearing more on this (regulation of power
line harmonic current) anywhere in the world!

Thanks!


Harold


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1998\07\21@143141 by Peter L. Peres

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On Tue, 21 Jul 1998, Leo van Loon wrote:

> Dear friends,
>
> In another mailinglist a member told about a two-phase 120V net with 180
> degrees phase difference in parts of the US. I do not understand how high
> power induction motors can be used with such an electricity supply. Three
> phase rotary currant was invented for this type of motors.
> Can anybody from the States tell me about the finesses of this type of
> electricity supply?

 I'm not in North America, but from what wire gauge I see used on the
cables of equipment coming from there, I believe that they got the 240 V
thing so they can have dryers & ovens that are *lighter* than their *power
cables* ;).
 Most bigger household appliances for 110 Volts (toaster etc) have cables
so thick you could use them to tie a small boat with (1500 W toaster @ 110
V ~= 14 Amps, against only 7 here @ 220 V). So someone saw the light and
decided that people get to touch 'safe' 110 Volts, but large appliances
will be powered with a more sensible 220 Volts, so the Copper mines don't
get filthy rich on in-house wiring ;)

perhaps this helps,

       Peter

1998\07\21@143155 by Mike Keitz

picon face
On Tue, 21 Jul 1998 15:46:42 +0200 Morgan Olsson <RemoveMEmrtspam_OUTspamKILLspamINAME.COM> writes:
>At 08:49 1998-07-21 -0400, you wrote:
>>The 120/240 single phase power ( two lines and a neutral) basically
>goes
>into every home. The connection is simply a centre tapped transformer.
>>
>>Low power appliances (TV, lights, ...) run on 120 V. Higher power
>loads
>(stove, clothes dryer, electric furnace,...) run on the 240 V supply.
>
>What kind of wall outlet connectors are used?

Various connectors are used, keyed to the current capacity of the
circuit.  For stoves and clothes driers a rather large plug maybe 2"
across is used, rated 30 or 50A.  Large window-mounted air conditioners
use a plug about the same size as a 120V plug, only with the blades
aligned differently (horizontal instead of vertical) so it is impossible
to interchange.  These are rated for 20 or 25A.  Generally the 240-volt
outlets are installed in specific places where the appliance is expected
to stay, and have an individual circuit in the breaker box.  Furnaces,
water heaters, central air conditioners, etc. are wired in permanently.

Most of the plugs are 3-wire, having the two hot wires and safety ground.
Generally the appliances operate everything on 240V working between the
two hot wires.  In some cases the appliance derives a 120V circut between
one hot wire and ground, which is allowed by many codes.  There are also
4-wire plugs and sockets that seperate the ground and neutral circuits.

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1998\07\21@143200 by Mike Keitz

picon face
On Tue, 21 Jul 1998 10:22:11 -0400 John Shreffler
<RemoveMEJohn.ShrefflerTakeThisOuTspamspamavenuetech.com> writes:
>You can use 3 phase induction motors on single phase.  I have
>three industrial quality machines in my shop that do very well.
>Put the 240 V across two of the motor leads, and run the
>third motor lead back to either of the 240 V supply through
>a large (50 mfd or so) oil-filled AC capacitor rated to at least
>380V.  The motor will begin turning in one direction or the
>other depending on what side the cap is connected to.  Disconnect
>the cap when the motor reaches about 75% speed, it is for
>starting only.  You will get only about 65% of the torque that
>the motor would give on 240V 3 Phase, but usually that is
>plenty.

For light duty use (and most home uses of industrial machines are quite
light duty) this is fine.  In industry, motors are often burned out by
operating them (at full rating) without knowing that a phase has been
lost, so it is essential to keep such operation light and intermittent.

A more advanced technique uses another surplus 3-phase induction motor as
a converter.  The converter motor is started with a capacitor as
described and just allowed to idle with no mechanical load.  It will act
as a "rotating transformer" and generate a fairly good rendition of the
third phase.  The three wires of the converter motor, two of which are
the single phase power, form the 3-phase bus to the load.  The converter
motor should be considerably larger than the one in the machine tool.
The motor(s) in the machine tool can then be used at nearly full rating.
The standard controls can be used to start or reverse the load motors
just as if they had 3-phase utility power.



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1998\07\21@174007 by Sean Breheny

face picon face
Hi All,

Yeah, I know, its something that I should probably know already, but I
have never seen an explanation, so I'll ask anyway:

Does anyone have a quick explanation on why it is better (more
efficient?) to use 3 phases instead of two on industrial equipment?

Thanks,

Sean



On Tue, 21 Jul 1998, Mike Keitz wrote:

{Quote hidden}

1998\07\21@175834 by lilel

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Mike Kietz wrote:



> >I know for a fact that Downtown St. Louis, MO has a few blocks with
> >DC, and I think there is also a little two-phase.  Probably way less
> >than 1% of US buildings are wired this way.  No new buildings are
> >installed with these systems.
>
> How are these places energized?

Directly from the power plant.  It seems incredible that this system
would still even be in place.  I believe the utility is pressuring
these guys to upgrade, and the NEC code would require an upgrade any
time the building is renovated.


> What's in homes now shouldn't be called two phase since its just
> single phase available at two voltages.  Probably it was done to
> provide a choice of voltages, maybe it was thought that 240 V at
> every wall socket would be too dangerous.

There was a big argument 120V vs 240v, and DC versus AC in the elder
days.  The choice of 120V, 60Hz is unfortunate, because that is
exactly the most dangerous voltage and frequency range for the human
heart.  Lower frequencies  (like 50 HZ or DC) do not defribulate the
heart as severely.  Higher frequencies might be too fast for the
heart muscles to react.  Lower voltages (less than 50 volts) can't
generate enough current through human skin to cause burns and stop
your heart.  Higher voltages (like 240) tend to knock you off or tend
to make the muscles jerk so severely as to send the victim flying.

Solution:  Sue Edison and Tesla in court.

-- Lawrence Lile

    "An Engineer is simply a machine for
     turning coffee into assembler code."

Download AutoCad blocks for electrical drafting at:
http://home1.gte.net/llile/index.htm

1998\07\21@184204 by Ron Fial

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3-phase AC motors are much smaller and use less copper for the same torque than
1-phase AC motors, they also have less losses (are much more efficient) because
the AC line provides the phase rotation, rather than something (capacitor, imped
ance,etc.) in the motor providing phase rotation.

For a given amount of power transmitted across a distance, you can use much less
copper for the same losses with 3-phase (3-wire), and you can use lower voltage
s = smaller, lighter insulators) because the wire is being used at the peak curr
ent (peak of the sine wave, where most of the actual power is moved) three times
as often.

Finally with 3-phase, you can suffer the loss of one wire and still get apprecia
ble power to the destination.
 Regards,
   Ron Fial

=================================================
At 05:37 PM 7/21/98 -0400, you wrote:
{Quote hidden}

1998\07\22@004718 by Andy Kunz

flavicon
face
At 08:49 AM 7/21/98 -0400, you wrote:
>The 120/240 single phase power ( two lines and a neutral) basically goes
into every home. The connection is simply a centre tapped transformer.
>
>Low power appliances (TV, lights, ...) run on 120 V. Higher power loads
(stove, clothes dryer, electric furnace,...) run on the 240 V supply.
>
>For light/medium industrial the power system typically uses  120/208 or
277/480 Volt, 3 phase power. In Canada we use 120/208 or 346/600 Volt 3 phase.

Also, most homes are configured to use both sides of the phases as evenly
as possible.

Andy


==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\07\22@073823 by paulb

flavicon
face
Sean Breheny wrote:

> Does anyone have a quick explanation on why it is better (more
> efficient?) to use 3 phases instead of two on industrial equipment?

 Well, the American version of "two phase" being in fact one phase
since you use only the outer "ends" of the phase, 120V each side of
neutral, the question resolves to one-phase versus three phase.

 As such, the answer is: "Three phase is used as a means of providing
a supply with equal current in (rating of) each phase (thereby
minimising costs), with rotational sequence (to start/ run motors) at
the highest voltage between phases (again, to minimise current) whilst
minimising per-phase voltage to ground (for safety and insulation
economy).

--
 Cheers,
       Paul B.

1998\07\22@091952 by Andy Kunz

flavicon
face
> Does anyone have a quick explanation on why it is better (more
> efficient?) to use 3 phases instead of two on industrial equipment?

Can we all say "I-squared R" together now?!

Andy


==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\07\22@111908 by Peter L. Peres

picon face
On Tue, 21 Jul 1998, Sean Breheny wrote:

> Hi All,
>
> Yeah, I know, its something that I should probably know already, but I
> have never seen an explanation, so I'll ask anyway:
>
> Does anyone have a quick explanation on why it is better (more
> efficient?) to use 3 phases instead of two on industrial equipment?

A. Instant rotary torque in both directions for motors of any size.
B. Best DC by using rectifiers of any kind (extra picky large consumers,
as in Aluminium plant, use 6 phases).

Peter

1998\07\22@132949 by Sean Breheny

face picon face
Hi Andy, Paul, and others who responded,


Thanks for the explanation. I already understood that minimum current
causes minimum wire heating (i^2R), but I guess I still don't understand
why one couldn't just use a higher voltage instead of 3-phase. Using
multiple phases doesn't increase the voltage between phases much over the
single phase-to-ground voltage, does it?

THe only outstanding reason that clearly makes sense to me is that the
phases deliver the AC peaks in rotational order for motors.

Thanks,

Sean



On Wed, 22 Jul 1998, Andy Kunz wrote:

{Quote hidden}

1998\07\22@145542 by Mike Keitz

picon face
On Wed, 22 Jul 1998 13:28:12 -0400 Sean Breheny <RemoveMEshb7KILLspamspamCORNELL.EDU>
writes:
>Hi Andy, Paul, and others who responded,
>
>
>Thanks for the explanation. I already understood that minimum current
>causes minimum wire heating (i^2R), but I guess I still don't
>understand
>why one couldn't just use a higher voltage instead of 3-phase.

With three-phase, when peak current is flowing in one wire the returning
current is evenly distributed between the other two wires.  So the worst
case of I^2 is occuring in only one wire at a time.  In single phase,
peak current flows through both wires.   Increasing the voltage has
practical limits.  For a given voltage three phase can distribute more
power.

Using
>multiple phases doesn't increase the voltage between phases much over
>the
>single phase-to-ground voltage, does it?

It is increased by square root of 3, for example with 120V from each
phase to ground the voltage between phases is 208V.  Power transmission
networks use a "delta" referenced system where no current intentionally
flows through ground, it is all balanced between the phase wires.  Look
at a high-voltage power pole and note that the three live conductors are
larger than the neutral conductor, which really serves only as a safety
ground.  The insulators only have to withstand the phase to ground
voltage of course.

>THe only outstanding reason that clearly makes sense to me is that the
>phases deliver the AC peaks in rotational order for motors.

It's real easy to build a three-phase generator, in fact you'd almost
want to rather than a single phase machine because the windings can be
more evenly distributed around the stator.  I seem to remember that Tesla
built multiple-phase induction motors first then struggled with how to
make a single phase one work (I suppose to compete with DC, where "only
two wires" would be a big selling point).

Three phase techniques aren't limited to big industrial stuff.  The
alternator in a car is a three-phase generator with an internal diode
bridge.  Besides being easy to wind, the three phases provide better DC
output since the output current never goes to zero.  Losses in the diodes
are also diminished compared to a single-phase bridge.  Using 1.5 times
more diodes, the unit can deliver 3 times the current.  The larger
"Brushless DC motors" found in disk drives, VCRs, etc. are also
three-phase at heart.  Small ones such as in CPU fans are usually
two-phase.



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1998\07\22@171949 by Sean Breheny

face picon face
Hi Mike,

On Wed, 22 Jul 1998, Mike Keitz wrote:

> With three-phase, when peak current is flowing in one wire the returning
> current is evenly distributed between the other two wires.  So the worst
> case of I^2 is occuring in only one wire at a time.  In single phase,
> peak current flows through both wires.   Increasing the voltage has
> practical limits.  For a given voltage three phase can distribute more
> power.
>

Again, it is probably something obvious, but I can't figure out how this
is any more efficient than just using separate wires carrying the same
phase. In other words,in a single phase system:

2 wires, each with a 5 ohm resistance, for example, carrying 100 amps
(one in one direction, the other for return):

Power dissipated = 2 * 5 * 100^2 = 100,000 watts

For three phase, 1 wire at 100 amps, with 5 ohms resistance, two wires,
each at 50 amps, with 5 ohms resistance each:

Power dissipated = 5 * 100^2 + 2 * 5 * 50^2 = 75, 000 watts

For single (or dual) phase again, this time with one forward wire, and two
return:

power dissipated = 5 * 100^2 + 2 * 5 * 50^2 = 75,000 watts

no different from the 3 phase system.

Instead of using multiple wires, you could also just use thicker wire
with two phase, which you couldn't do with 3-phase ( you must have at
least three wires)

> It is increased by square root of 3, for example with 120V from each
> phase to ground the voltage between phases is 208V.  Power transmission
> networks use a "delta" referenced system where no current intentionally
> flows through ground, it is all balanced between the phase wires.  Look
> at a high-voltage power pole and note that the three live conductors are
> larger than the neutral conductor, which really serves only as a safety
> ground.  The insulators only have to withstand the phase to ground
> voltage of course.

Again, this doesn't quite make sense to me. If you stuck with two phase,
you could still avoid using ground for a return, and instead of a root 3
(1.73) factor by which the voltage to ground is decreased, you would get
a full factor of 2.

{Quote hidden}

These reasons (ease of motor/generator winding, better rectification)
make the most sense to me. It seems to me that these are probably the
REAL resons why 3-phase is used, because the other benefits which you and
others mentioned seem to be only side benefits, which could be achieved
using single or dual phase systems. Am I wrong?

Sorry if it seems that I am getting into a very argumentative tone <G>. I
really am just trying to get to the heart of why 3-phase is better than
two or one.


One last question, when voltage is stated in 3-phase systems, is it
referring to the peak voltage to ground, peak voltage between phases, or
an RMS voltage?

Thanks again guys,

Sean

1998\07\22@182545 by Leo van Loon

flavicon
face
Your calculation is a little bit wrong.

1 phase 100 A :Power dissipated = 2 * 5 * 100^2 = 100,000 watts

3 phase 100 A :Power dissipated = 3 * 5 * 33^2 = 16,666 watts

All other calculations are not correct cause the currants are not right for
AC. You may not simply add currants. There is no currant  in the neutral
lines in a symmetrical situation.
Normally a 2-phase situation has 90 degrees phase difference between the
phases. 2-phase with 180 degrees phase difference is essentially the same as
1-phase. To run an induction motor on 1-phase you have to create the second
phase (90 degrees phase difference) with a capacitor or a short-circuit
winding in the motor, or with some electronics

Leo van Loon

-----Oorspronkelijk bericht-----
Van: Sean Breheny <shb7STOPspamspamspam_OUTCORNELL.EDU>
Aan: spamBeGonePICLISTSTOPspamspamEraseMEMITVMA.MIT.EDU <KILLspamPICLISTspamBeGonespamMITVMA.MIT.EDU>
Datum: woensdag 22 juli 1998 23:23
Onderwerp: Re: [OT] 240V in USA


>snip<
>Thanks again guys,
>
>Sean
>
>

1998\07\22@183417 by paulb

flavicon
face
Sean Breheny wrote:

> Again, it is probably something obvious, but I can't figure out how
> this is any more efficient than just using separate wires carrying the
> same phase.

 You are *quite right*.  It isn't.  Using the American system and
comparing three phases at 120¡, each 120V to ground, with a split phase,
centred on ground, 120V each side, the efficiency is basically the same.
Each system requires the same insulation of each wire, and the total
power in a balanced state is 120V times the total of the currents in the
phase wires.

 Transformers and wires for either system are just as efficient.  The
advantage of using the third phase comes in the three areas previously
specified: Motors, Generators and Rectifiers.  Domestic consumers are
largely un-fussed, but industry is a *big* user of electricity.  Three-
phase motors are simpler than four-phase (i.e., two balanced pairs at
90¡) and are the minimum necessary to convey rotary impulse.

 Railways (trams, trolley-buses and trains) use DC, where six-phase
rectifiers make things so much easier (than rotary converters).  But the
most significant point is that the harmonic vibration content of the
generators is reduced by using three phases.  IOW, consider the forces
on the shaft of a single phase generator - it is being loaded when the
current peaks, unloaded when it nulls.  Sort of like a hammer drill.
Using a three-phase system, this effect is split among the three phases
so that the harmonic content is virtually cancelled.

--
 Cheers,
       Paul B.

1998\07\22@191358 by John Sanderson

flavicon
face
Hello PIC.ers,
..
Sure.
That's what a variable speed induction motor electronic inverter is.
They have a 3-phase output, generated by PWM switching a DC rail
rectified from the 1-phase supply.
..
Other features added, are for varying the frequency (thus RPM), and
boost at low freq., interlocks for safety, overload and the like.
..
This is not OT. A local manufacturer uses the 16c73, and other PIC
variants to run the smarts for this.
..
FWIW the last ASR33 teletype we used had a name given it.
`Chatanooga Choo Choo'

Best regards,   John

>Date:    Tue, 21 Jul 1998 12:15:23 -0400
>From:    Mike Massen <EraseMEerazmusspamEraseMEWANTREE.COM.AU>
>.Subject: Re: [OT] 240V in USA

>Interesting stuff this about 240V. Here in Australia we also
>have 240V (used to be 250V) in Western Australia several years ago.

>So - does anyone know of a commercial single phase to 3-phase
>converter (other than a motor/alternator) - about 2KW max ?
..
..
email from John Sanderson at
JS Controls, PO Box 1887, Boksburg 1460, Rep. South Africa
Manufacturer & purveyor of laboratory force testing apparatus
and related products and services.
Tel/fax: Johannesburg 893 4154    Cellphone 082 453 4815

1998\07\22@202324 by Harold Hallikainen

picon face
On Thu, 23 Jul 1998 08:30:24 +1000 "Paul B. Webster VK2BZC"
<@spam@paulb@spam@spamspam_OUTmidcoast.com.au> writes:

>  Railways (trams, trolley-buses and trains) use DC, where six-phase
>rectifiers make things so much easier (than rotary converters).

       Also, it's possible to combine delta connected transformers and
wye connected transformers into full wave rectifiers and get a ripple
frequency that is 12 times the line frequency.  This was used in an AM
broadcast transmitter made by Continental.  The FCC at one time required
AM stations to have hum and noise 45 dB below 100% modulation while FM
stations were required to be 60 dB down.  This AM had noise down about 65
dB.  The only AM I've ever seen where you could hear tape hiss on the
air.

Harold





Harold Hallikainen
spamBeGoneharoldspamKILLspamhallikainen.com
Hallikainen & Friends, Inc.
See the FCC Rules at http://hallikainen.com/FccRules and comments filed
in LPFM proceeding at http://hallikainen.com/lpfm

_____________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com
Or call Juno at (800) 654-JUNO [654-5866]

1998\07\23@045122 by paulb

flavicon
face
Rogerio Odriozola wrote:

(quoting Martin)
>> Sorry Mike, but there is never 240V across any two terminals in a
>> standard NA wall socket.

> Martin, Mike is right. He is talking about the large 20 amp., 50 amp.
> 3-wire plugs. They do have 2 live and 1 ground. You can get 240 volts
> out of the 2 live wires.  The connector you are talking about (1 live,
> 1 neutral, 1 ground) is for small 120 volt appliances, not large
> ovens, water heaters etc.

 Proves to me that the U S of A is such a polyglot place that even many
shall we hope, technically competent, people don't even know all the
variations in power reticulation.  I must go there sometime, even just
to see all the power points (local vernacular for power outlet, GPO
etc.)!

--
 Cheers,
       Paul B.

1998\07\23@050409 by jlepine

flavicon
face
In the USA we use 220v, 2 phase on many motors up to about 5 hp as often
found in air conditioner compressors.  We call it 220v single phase to
distinguish it from 3 phase,
but you are correct, it is really two 120v lines out of phase.

We do it this way just because 220 v single phase is all that is available in
most residential neighborhoods.  The single phase motor can be made almost as
high starting torque as the 3 phase by using capacitors.  The efficiency is
about equal.

A small 10 to 30 mfd is put across the start and run windings---mostly for
power factor.
A large, hundreds of mfd, is also across the same windings but is switched
out when the motor is up to about 80% of rated speed.  This is usually done
by a "potential" relay which reads the back EMF.

Hope this helps.                  73 de Joe, N6YMD


Leo van Loon wrote:

{Quote hidden}

1998\07\23@055716 by jlepine

flavicon
face
Actually, almost all, way more than 99%, of power delivered to modern
houses in the US by utility companies is 240 v single phase made with
two 120 v lines out of phase.

If you doubt it, just put your AC voltmeter across any 2 ADJACENT
breakers in your distribution box.  If you have only a single row of
breakers, that's adjacent vertically;
for 2 rows read adjacent horizontally.

1998\07\23@060722 by jlepine

flavicon
face
The "wild leg" of the center taped delta is actually 277 v above
ground.  It is used mostly for industrial lighting.

1998\07\23@064108 by jlepine

flavicon
face
Three phase is not inherently more efficient than single phase.  But it
does have higher starting torque and that is often important in
industrial applications where the motor must start under load.

1998\07\23@064727 by Caisson

flavicon
face
> Van: Sean Breheny <TakeThisOuTshb7.....spamTakeThisOuTCORNELL.EDU>
> Aan: TakeThisOuTPICLISTKILLspamspamspamMITVMA.MIT.EDU
> Onderwerp: Re: [OT] 240V in USA
> Datum: dinsdag 21 juli 1998 23:37
>
> Hi All,
>
> Yeah, I know, its something that I should probably know already, but I
> have never seen an explanation, so I'll ask anyway:
>
> Does anyone have a quick explanation on why it is better (more
> efficient?) to use 3 phases instead of two on industrial equipment?
>
> Thanks,
>
> Sean

A Two-phase system, provided it is a balanced shift, will have instances
where none of the phases supply current.  In a 3-phase system there will be
no instance where not at least two of the three will supply current.   This
means that for a three-phase system there will not be any 'dead' points.

Greetz,
 Rudy Wieser

1998\07\23@065347 by jlepine

flavicon
face
No, we can't all say I-squared R together.
I a single phase motor is wound with the same weight of copper as the
three phase motor,
given proper design, they will both have the same IR losses, same
efficiency, and same power at full speed.  But the three phase will have
higher starting torque and that is sometimes important.

1998\07\23@091254 by Bill Cornutt

flavicon
face
A story that I heard while sitting on my father's knee
was that DC got a bad reputation after it was used on
a 'electric chair'.  And the AC people said "That proves
DC kills!"

But then I heard a lot of stories while sitting on my
farher's knee.

Bill C.  .....billspamRemoveMEcornutt.com

1998\07\23@094012 by lilel

flavicon
face
Russell was rumored to say:

> WARNING - You can die if you try (but you may have to try hard).
>
> > Lower voltages (less than 50 volts) can't
> > generate enough current through human skin to cause burns and stop
> > your heart.  Higher voltages (like 240) tend to knock you off or tend
> > to make the muscles jerk so severely as to send the victim flying.

I correct myself - Voltages less than 50 volts are not intrinsically
safe, just less unsafe.

>
> While voltages under 50 volts are certainly safer and generally not
> known to cause fatal shocks it IS possible if the voltage is upplied
> correctly and under the right conditions.

In medical applications such as open heart surgery they worry about
MICROVOLTS.  Extra effort is made to ground everything in the room
back to a single point ground, and they have special ground monitors.


>
> Worst case I have heard of was an experiment long ago using convicts

Fortunately most of those experiments have been outlawed.  I keep
hearing about old experiments on convicts, minorities, etc.  that
surface.  Apparently it is very easy to convince oneself that an
underclass of people are less than human in the name of science.

> Yes, I've had hundreds if not thousands of shocks over the years and
> handle wiring up to about 30 volts without a second thought - so far
> I'm still alive. On a damp day 50 volts will prickle your hands if
> you touch live terminals (telephone exchange distribution frame
> during trainee engineering days.) Ringing voltage (70vac approx at
> 16 Hz) gives a very nice kick.
>

We used to charge capacitors to 100 volts or so and hand them to
another student.  "Here- hold this."   We'd also sneak up behind
someone that was gingerly using a high voltage probe on a TV picture
tube and goose them at the most inopportune moment.

-- Lawrence Lile

    "An Engineer is simply a machine for
     turning coffee into assembler code."

Download AutoCad blocks for electrical drafting at:
http://home1.gte.net/llile/index.htm

1998\07\23@120813 by Mike Ghormley

flavicon
face
Bill Cornutt wrote:
>
> A story that I heard while sitting on my father's knee
> was that DC got a bad reputation after it was used on
> a 'electric chair'.  And the AC people said "That proves
> DC kills!"

I sure could be wrong, but I believe that it was Edison (who was
promoting DC rather than Tesla's AC) who got the powers that be to use AC
in the electric chair to show that Tesla's idea was the dangerous one.  I
also think that he went around eletrocuting sheep with AC -- sadistic
spin doctor that he was.

As I said, I could be wrong.

Michael

*************************************************************************When th
e way of the Tao is forgotten, kindness and ethics must be taught.
Men must learn to pretend to be wise and good.  --  Lao Tzu
*************************************************************************

1998\07\23@123854 by Peter L. Peres

picon face
On Thu, 23 Jul 1998, Lawrence Lile wrote:

> In medical applications such as open heart surgery they worry about
> MICROVOLTS.  Extra effort is made to ground everything in the room
> back to a single point ground, and they have special ground monitors.

I was going to say that. Also, all electric/electronic equipment for
Hospital use that involves any kind of wire to the patient must pass a
test for leakage current several orders of magnitude below commercial
equipment.

> We used to charge capacitors to 100 volts or so and hand them to
> another student.  "Here- hold this."   We'd also sneak up behind

You are lucky with your 110 V ;) We had them charged to 310 V (220 pk). A
0.1 uF will pinch you badly and I guess 100 uF can make you hear angels
singing. I should know as it was done to me once. Keeps the charge quite a
while too.

Peter

1998\07\23@135556 by Andy Kunz

flavicon
face
I think Edison made the first electric chair (for NJ).  It used AC - he's
was trying to prove a point.

It didn't work very well.

They changed to DC.  Worked much better.

Andy


At 06:10 AM 7/23/98 -0700, you wrote:
{Quote hidden}

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\07\23@231421 by Ben Hamlett

flavicon
face
Mike Ghormley wrote:

> Bill Cornutt wrote:
> >
> > A story that I heard while sitting on my father's knee
> > was that DC got a bad reputation after it was used on
> > a 'electric chair'.  And the AC people said "That proves
> > DC kills!"
>
> I sure could be wrong, but I believe that it was Edison (who was
> promoting DC rather than Tesla's AC) who got the powers that be to use AC
> in the electric chair to show that Tesla's idea was the dangerous one.  I
> also think that he went around eletrocuting sheep with AC -- sadistic
> spin doctor that he was.
>
> As I said, I could be wrong.
>
> Michael
>
> *************************************************************************When
the way of the Tao is forgotten, kindness and ethics must be taught.
> Men must learn to pretend to be wise and good.  --  Lao Tzu
> *************************************************************************

 I read a book about Tesla and Edison was totally against AC and used it to kil
l animals in the street to show AC kills.
one more tid bit.... Tesla worked for Edison when he first arrived in America

1998\07\24@161858 by Pete Klammer

flavicon
face
1) A balanced 3-phase system delivers constant instantaneous power.
Even though each phase delivers power in sinusoidal surges,
the sum of the three is a constant level.
Thus, no motor vibration or hum, reduced mechanical deterioration, etc.

2) A balanced 3-phase system delivers the more power per conductor amp than
any other AC arrangement.
That means it's the most efficient way to provide electricity, in terms of
delivered watts per pound of copper.

Peter F. Klammer / spamBeGonePKlammer@spam@spamspam_OUTRacom.com
Racom Systems, Inc. / 6080 Greenwood Plaza Blvd / Englewood CO 80111
(303)773-7411 / FAX:(303)771-4708

> {Original Message removed}

1998\07\24@163533 by Gordon Couger

flavicon
face
It also draws a hell of a lot of current at start up. At Texas A&M they have
to give
the power plant 2 days notice and then start the wind tunnel at 3:00 am.

Gordon
Gordon Couger TakeThisOuTgcougerspamspamrfdata.net
624 Cheyenne
Stillwater, OK 74075
405 624-2855   GMT -6:00

{Quote hidden}

>> {Original Message removed}

1998\07\24@164743 by Timothy D. Gray

flavicon
face
Why dont they use 7200 volt motors for the wind tunnel? we use 350 and 600
horse electrics for our pumps at the water plant and we dont have to tell
them when we start 6 pumps at one time. or does the wind tunnel use alot
more horsepower?


On Fri, 24 Jul 1998, Gordon Couger wrote:

{Quote hidden}

> >> {Original Message removed}

1998\07\25@173657 by Alex Torres

picon face
>> Does anyone have a quick explanation on why it is better (more
>> efficient?) to use 3 phases instead of two on industrial equipment?
>
>Can we all say "I-squared R" together now?!


Of couse, its true. But I add something:

The most simple and cheapest electrical motors are async. motors with short
curcuit rotor (sorry, I don't know english tetminology).

==================================
Alex Torres, Kharkov, Ukraine (exUSSR)
E-Mail: EraseMEaltorspam@spam@geocities.com
2:461/28 FidoNet
Home Page: www.geocities.com/SiliconValley/Lab/6311
ICQ UIN  11083325

1998\07\25@173701 by Alex Torres

picon face
>Hi Andy, Paul, and others who responded,
>
>
>Thanks for the explanation. I already understood that minimum current
>causes minimum wire heating (i^2R), but I guess I still don't understand
>why one couldn't just use a higher voltage instead of 3-phase. Using
>multiple phases doesn't increase the voltage between phases much over the
>single phase-to-ground voltage, does it?

Becouse you increase a wires from 2 to 3 (*1.5) and increase the power in 3
times.
(At the same U and I). Power wires are not cheap.


>THe only outstanding reason that clearly makes sense to me is that the
>phases deliver the AC peaks in rotational order for motors.

Of couse. Async. morotors are very simple and cheap.

==================================
Alex Torres, Kharkov, Ukraine (exUSSR)
E-Mail: @spam@altorspam_OUTspam.....geocities.com
2:461/28 FidoNet
Home Page: www.geocities.com/SiliconValley/Lab/6311
ICQ UIN  11083325

1998\07\25@173704 by Alex Torres

picon face
>One last question, when voltage is stated in 3-phase systems, is it
>referring to the peak voltage to ground, peak voltage between phases, or
>an RMS voltage?

Usialy it is eff. voltage between the phases. In Europe we use 380v 3-ph
system. This system have 320v phase voltage and 220v LINE voltage (between
the phase and the ground). LINE voltage used at homes. Immagine the building
with 3 appatrment. Building powered from 3-phase 380v system and each
appartmend powered from the single line and the ground - 220v.
==================================
Alex Torres, Kharkov, Ukraine (exUSSR)
E-Mail: spamBeGonealtorEraseMEspamgeocities.com
2:461/28 FidoNet
Home Page: www.geocities.com/SiliconValley/Lab/6311
ICQ UIN  11083325

1998\07\28@070103 by Frank A. Vorstenbosch

flavicon
face
Pete Klammer wrote:
>
> 1) A balanced 3-phase system delivers constant instantaneous power.
> Even though each phase delivers power in sinusoidal surges,
> the sum of the three is a constant level.
> Thus, no motor vibration or hum, reduced mechanical deterioration, etc.
>
> 2) A balanced 3-phase system delivers the more power per conductor amp than
> any other AC arrangement.
> That means it's the most efficient way to provide electricity, in terms of
> delivered watts per pound of copper.

Unless you count 5-phase, or 7-phase or ...

Frank
------------------------------------------------------------------------
Frank A. Vorstenbosch     <SPAM_ACCEPT="NONE">    Phone: 0181 - 636 3000
Electronics and Software Engineer                 Mobile: 0976 - 430 569
Eidos Technologies Ltd., Wimbledon, London        Email: favspamBeGonespameidos.co.uk

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