Electrical Engineering - Why Is there 3-Phase?

Author

Why Is there 3-Phase?

ecarecar

2007-05-10, 5:25 pm

What are the top 10 (or 2 or 3) reasons for 3-phase power?

What advantages are there over single phase?

Pilgrim

2007-05-10, 5:25 pm

In article <p8Sdnfh16N46F97bnZ2dnUVZ_judnZ2d@centurytel.net>,
ecarecar <ecarecar@yahoo.com> wrote:

> What are the top 10 (or 2 or 3) reasons for 3-phase power?
>
> What advantages are there over single phase?

There is basically only one reason:

A more even load is placed on the prime mover and more even power
supplied to the load.

Chuck P.

The fact that 3 phase motors are simpler is just a side benefit.

Salmon Egg

2007-05-10, 5:25 pm

On 5/10/07 2:12 PM, in article
p8Sdnfh16N46F97bnZ2dnUVZ_judnZ2d@centurytel.net, "ecarecar"
<ecarecar@yahoo.com> wrote:

> What are the top 10 (or 2 or 3) reasons for 3-phase power?
>
> What advantages are there over single phase?

Economics.

You save money on generation and transmission because materials are used
more effectively. But there are other advantages as well. All these
advantages are achievable in other ways at higher cost.

The sheer amount of electrical power used overwhelms the advantages of other
sources. For example, high voltage dc would be of great advantage for x-ray
production but it is not economically feasible to drive x-ray tubes from a
suitable dc source.

Bill
-- Fermez le Bush--about two years to go.

ecarecar

2007-05-10, 8:25 pm

I'm not trying to pull an Edison. Specifically, what makes 3-phase more
efficient
than single phase?

Is it that you can kinda, sort of have a complete circuit with only one
wire?
Or, that you can have three complete circuits with only three wires
instead of six?

Remember, I am pre-admitting ignorance, so you don't have to tell me how
ignorant I am.

Salmon Egg wrote:

>On 5/10/07 2:12 PM, in article
>p8Sdnfh16N46F97bnZ2dnUVZ_judnZ2d@centurytel.net, "ecarecar"
><ecarecar@yahoo.com> wrote:
>
>
>
>
>Economics.
>
>You save money on generation and transmission because materials are used
>more effectively. But there are other advantages as well. All these
>advantages are achievable in other ways at higher cost.
>
>The sheer amount of electrical power used overwhelms the advantages of other
>sources. For example, high voltage dc would be of great advantage for x-ray
>production but it is not economically feasible to drive x-ray tubes from a
>suitable dc source.
>
>Bill
>-- Fermez le Bush--about two years to go.
>
>
>
>

The Great Attractor

2007-05-10, 8:25 pm

On Thu, 10 May 2007 22:18:33 GMT, Salmon Egg <salmonegg@sbcglobal.net>
wrote:

>
>The sheer amount of electrical power used overwhelms the advantages of other
>sources. For example, high voltage dc would be of great advantage for x-ray
>production but it is not economically feasible to drive x-ray tubes from a
>suitable dc source.

What? Nearly ALL X-ray tubes are driven by DC!

I have made several hundred supplies for such devices.

One was +90kV and -90kV for a 180kV DC electron beam splashing onto a
Palladium target in a $900 German made X-ray tube which was/is used at
every airport in the country!

The cleaner the DC E-beam, the cleaner the X-ray flux.The cleaner the
X-ray flux, the better the contrast ratio of the imagery.

Where did you ever get the idea that X-ray tubes were AC driven?

PURE DC.

Even the 50kV supply that we sent to LANL to look at nukes was ALL DC
ALL THE TIME.

Salmon Egg

2007-05-10, 8:25 pm

On 5/10/07 5:43 PM, in article fqe7439pc2ifdv49f6okhdis0nf5j5kbjf@4ax.com,
"The Great Attractor"
<SuperM@ssiveBlackHoleAtTheCenterOfTheMilkyWayGalaxy.org> wrote:

> On Thu, 10 May 2007 22:18:33 GMT, Salmon Egg <salmonegg@sbcglobal.net>
> wrote:
>
>
>
> What? Nearly ALL X-ray tubes are driven by DC!
>
> I have made several hundred supplies for such devices.
>
> One was +90kV and -90kV for a 180kV DC electron beam splashing onto a
> Palladium target in a $900 German made X-ray tube which was/is used at
> every airport in the country!
>
> The cleaner the DC E-beam, the cleaner the X-ray flux.The cleaner the
> X-ray flux, the better the contrast ratio of the imagery.
>
> Where did you ever get the idea that X-ray tubes were AC driven?
>
> PURE DC.
>
> Even the 50kV supply that we sent to LANL to look at nukes was ALL DC
> ALL THE TIME.

There are dc driven x-ray equipments for things like portable hand held
devices. I am willing to bet that most of the things you worked obtained
power over three-phase lines--even at airports. You just conditioned it to
be dc.

As a kid, I remember going to a dentist in the New York City region supplied
by dc. The dc was not used to power x-ray tubes directly. A motor generator
set was used to convert to ac which could be stepped up AND RECTIFIED to
produce dc for the tube.

As far as I know, that may have been the only time I had an x-ray taken
without a three-phase power being involved. In retrospect, I now believe
that three-phase power was sent into this area to be converted to
distributed dc.

Bill
-- Fermez le Bush--about two years to go.

The Streets

2007-05-10, 8:25 pm

"Salmon Egg" <salmonegg@sbcglobal.net> wrote in message
news:C268E849.76C14%salmonegg@sbcglobal.net...
> On 5/10/07 2:12 PM, in article
> p8Sdnfh16N46F97bnZ2dnUVZ_judnZ2d@centurytel.net, "ecarecar"
> <ecarecar@yahoo.com> wrote:
>
>
> Economics.
>
> You save money on generation and transmission because materials are used
> more effectively. But there are other advantages as well. All these
> advantages are achievable in other ways at higher cost.
>
> The sheer amount of electrical power used overwhelms the advantages of
> other
> sources. For example, high voltage dc would be of great advantage for
> x-ray
> production but it is not economically feasible to drive x-ray tubes from a
> suitable dc source.
>
> Bill
> -- Fermez le Bush--about two years to go.

My memory from working in manufacturing a long time ago is that 3 phase
motors were very easy to reverse -- just switch any two wires.

The Great Attractor

2007-05-10, 9:25 pm

On Thu, 10 May 2007 18:01:35 -0700, Salmon Egg <salmonegg@sbcglobal.net>
wrote:

>There are dc driven x-ray equipments for things like portable hand held
>devices. I am willing to bet that most of the things you worked obtained
>power over three-phase lines--even at airports. You just conditioned it to
>be dc.

Wrong. They were DC POWER SUPPLIES. It had nothing to do with the
source power. THEY WERE DC POWER SUPPLIES.

NOTHING to do with any "handheld device" either.

The Los Alamos unit was a 50kV DC supply.

DIRECT CURRENT.

ALL X-ray sources are DC fed. I do not know of any that are not.

The electron beam has to STRIKE the target, not emit from it.

The X-ray flux then emits from the STRUCK target media, typically
Palladium, but there are several other metals that are used as E-beam
targets for X-ray generation. ALL utilizing DC E-beam streams.

Even a TV electron gun is a DC device! Have that hit a polished
palladium ingot at a 45° angle of incidence, and you get an X-ray flux
emission from it.

The Great Attractor

2007-05-10, 9:25 pm

On Thu, 10 May 2007 18:01:35 -0700, Salmon Egg <salmonegg@sbcglobal.net>
wrote:

>
>As a kid, I remember going to a dentist in the New York City region supplied
>by dc. The dc was not used to power x-ray tubes directly. A motor generator
>set was used to convert to ac which could be stepped up AND RECTIFIED to
>produce dc for the tube.

What part of DC *IS* what results from rectified HV AC do you not
understand?

Salmon Egg

2007-05-11, 3:25 am

On 5/10/07 6:03 PM, in article %hP0i.41$j04.31@bignews2.bellsouth.net, "The
Streets" <streetsj.no.spam@sprintmail.com> wrote:

> My memory from working in manufacturing a long time ago is that 3 phase
> motors were very easy to reverse -- just switch any two wires.

That is also true for two phase if you switch the two hots. Two phase was
not as efficient in the use of materials.

Bill
-- Fermez le Bush--about two years to go.

Salmon Egg

2007-05-11, 3:25 am

On 5/10/07 6:32 PM, in article rhh743d51ohvnnejnqrivtmlde2t0lnoo6@4ax.com,
"The Great Attractor"
<SuperM@ssiveBlackHoleAtTheCenterOfTheMilkyWayGalaxy.org> wrote:

> Wrong. They were DC POWER SUPPLIES. It had nothing to do with the
> source power. THEY WERE DC POWER SUPPLIES.
>
> NOTHING to do with any "handheld device" either.
>
> The Los Alamos unit was a 50kV DC supply.
>
> DIRECT CURRENT.
>
> ALL X-ray sources are DC fed. I do not know of any that are not.
>
> The electron beam has to STRIKE the target, not emit from it.
>
> The X-ray flux then emits from the STRUCK target media, typically
> Palladium, but there are several other metals that are used as E-beam
> targets for X-ray generation. ALL utilizing DC E-beam streams.
>
> Even a TV electron gun is a DC device! Have that hit a polished
> palladium ingot at a 45° angle of incidence, and you get an X-ray flux
> emission from it.

These days, best practice is to drive x-ray TUBES with dc that is probably
filtered some. X-ray equipment is almost always run from ac lines.

Although I do not know the history, I would be very surprised if some x-ray
tubes were NOT run on ac. It is no trick to apply ac and have the tube be
its own rectifier. The hardness of outputduring the cycle.

It was common practice for some radio transmitters to be operated with
unrectified ac because of low cost. It was outlawed by treaty because of
interference. Also, good operators could not receive as well with the rough
tones.

Bill
-- Fermez le Bush--about two years to go.

Don Kelly

2007-05-11, 3:25 am

----------------------------
"The Great Attractor"
<SuperM@ssiveBlackHoleAtTheCenterOfTheMilkyWayGalaxy.org> wrote in message
news:rhh743d51ohvnnejnqrivtmlde2t0lnoo6@4ax.com...
> On Thu, 10 May 2007 18:01:35 -0700, Salmon Egg <salmonegg@sbcglobal.net>
> wrote:
>
>
>
> Wrong. They were DC POWER SUPPLIES. It had nothing to do with the
> source power. THEY WERE DC POWER SUPPLIES.
>
> NOTHING to do with any "handheld device" either.
>
> The Los Alamos unit was a 50kV DC supply.
>
> DIRECT CURRENT.
>
> ALL X-ray sources are DC fed. I do not know of any that are not.
>
> The electron beam has to STRIKE the target, not emit from it.
>
> The X-ray flux then emits from the STRUCK target media, typically
> Palladium, but there are several other metals that are used as E-beam
> targets for X-ray generation. ALL utilizing DC E-beam streams.
>
> Even a TV electron gun is a DC device! Have that hit a polished
> palladium ingot at a 45° angle of incidence, and you get an X-ray flux
> emission from it.

------------
Cool it.
Salmon Egg is considering the <source> for your DC power supplies. Do you
have a 50Kv circuit supplying wall sockets for airport X-ray machines?
These "supplies" take AC as input and convert to DC at the desired voltage
level. Even those that use batteries as supplies go through generation of
AC as a step in production of DC at the desired voltage level. These
"supplies" are an integral part of the unit- not something external and
independent of the unit.
No-one is trying to say that the X-ray unit itself is not DC driven but the
whole package X-ray and its included power supply (or more appropriately
power conditioner) , is driven from AC-just as my computer with 12 and 5 V
DC busses, depends on my household 120V AC supply.
You are thinking on a much smaller and specialized scale of things.

Don Kelly dhky@shawcross.ca
remove the X to answer

TimPerry

2007-05-11, 3:25 am

ecarecar wrote:
> I'm not trying to pull an Edison. Specifically, what makes 3-phase
> more efficient
> than single phase?
>
> Is it that you can kinda, sort of have a complete circuit with only
> one wire?
> Or, that you can have three complete circuits with only three wires
> instead of six?
>
> Remember, I am pre-admitting ignorance, so you don't have to tell me
> how ignorant I am.
>

as was explained to me in collage it's 3 times the transmitted power with
one third the copper... but then a lot of things they said in collage turned
out to be wrong.

for a much more elaborate explination see:
http://en.wikipedia.org/wiki/Three-phase_electric_power

Don Kelly

2007-05-11, 3:25 am

Economics as Salmon Egg indicates:
a) cheaper transmission-systems and lower losses per Kw delivered
b) better use of iron in generators, motors and transformers
c)Better operation of motors as well as being simpler than single phase
motors (single phase motors are less efficient than 3 phase motors and are
not inherently self starting).
d) Although not initially recognised, lower electric and magnetic fields
from transmission lines than would be the case with single phase.
e)The ability to supply single phase loads as well as 3 phase loads.
f)The ability to use 3 phase, 6 phase or 12 phase rectifiers to get smoother
DC without filtering where needed.

Shall I go on?

Sure the load on the prime mover etc. is more even but that is actually
an insignificant factor considering the mechanical time constants involved.

--

Don Kelly dhky@shawcross.ca
remove the X to answer
----------------------------
"Pilgrim" <pilgrim@noemail.net> wrote in message
news:pilgrim-24C7EF.14531910052007@news.west.earthlink.net...
> In article <p8Sdnfh16N46F97bnZ2dnUVZ_judnZ2d@centurytel.net>,
> ecarecar <ecarecar@yahoo.com> wrote:
>
>
> There is basically only one reason:
>
> A more even load is placed on the prime mover and more even power
> supplied to the load.
>
> Chuck P.
>
> The fact that 3 phase motors are simpler is just a side benefit.

The Great Attractor

2007-05-11, 3:25 am

On Thu, 10 May 2007 19:40:36 -0700, Salmon Egg <salmonegg@sbcglobal.net>
wrote:

>On 5/10/07 6:32 PM, in article rhh743d51ohvnnejnqrivtmlde2t0lnoo6@4ax.com,
>"The Great Attractor"
><SuperM@ssiveBlackHoleAtTheCenterOfTheMilkyWayGalaxy.org> wrote:
>
>
>These days, best practice is to drive x-ray TUBES with dc that is probably
>filtered some. X-ray equipment is almost always run from ac lines.

So fucking what? The SUPPLY that fires the X-ray source is DC. Your
precious AC line FEEDS a DC POWER SUPPLY in ALL CASES!
>
>Although I do not know the history, I would be very surprised if some x-ray
>tubes were NOT run on ac.

You*would* be surprised? Your the one that said they were. NONE OF
THEM ARE.

The entire principal relies on an E-beam striking a metal target!
Therefore, it relies on said E-beam traveling in only ONE direction!

> It is no trick to apply ac and have the tube be
>its own rectifier.

You're a dope. READ CAREFULLY... the better the DC source (NO RIPPLE
IDIOT), the better the generated X-ray flux, and the better the resultant
X-ray IMAGERY. It's all about contrast ratio, and that depends on how
clean the e-beam is!

> The hardness of outputduring the cycle.

The hardness of your head to realize how X-rays are generated, and ho
the purity of the flux determines the cleanliness of the resultant
images.

>It was common practice for some radio transmitters to be operated with
>unrectified ac because of low cost.

Whoopie fuckin' doo!

> It was outlawed by treaty because of
>interference.

No shit?!

> Also, good operators could not receive as well with the rough
>tones.

That must be what your brain is running on right now, because the noise
is staggering.

The Great Attractor

2007-05-11, 3:25 am

On Fri, 11 May 2007 03:03:04 GMT, "Don Kelly" <dhky@shaw.ca> wrote:

>Cool it.
>Salmon Egg is considering the <source> for your DC power supplies. Do you
>have a 50Kv circuit supplying wall sockets for airport X-ray machines?

BULLSHIT!

That's not what he said AT ALL.

The Great Attractor

2007-05-11, 3:25 am

On Fri, 11 May 2007 03:03:04 GMT, "Don Kelly" <dhky@shaw.ca> wrote:

>These "supplies" take AC as input and convert to DC at the desired voltage
>level.

No shit?

I would never have known without your special inside info.

Especially since I made the fucking things for years.

The Great Attractor

2007-05-11, 3:25 am

On Fri, 11 May 2007 03:03:04 GMT, "Don Kelly" <dhky@shaw.ca> wrote:

> Even those that use batteries as supplies go through generation of
>AC as a step in production of DC at the desired voltage level.

No shit?

I would never have known what the word RIPPLE referred to without your
special inside info.

The Great Attractor

2007-05-11, 3:25 am

On Fri, 11 May 2007 03:03:04 GMT, "Don Kelly" <dhky@shaw.ca> wrote:

>. These
>"supplies" are an integral part of the unit- not something external and
>independent of the unit.

They are external. They are specifically made for each type of tube
used. Some have 15 volt filaments, some have 6.3. Some have variable
filament voltages.

We were contracted to make a supply originally Mfgd by ECG for the
airport X-ray units. Both OURS as well as ECGs were SEPERATE units, NOT
integral... totally INTEGRATED third party devices!

Theirs had a lead lined steel box, and an oil overflow recovery vessel.

Ours had a BRASS tank and a recovery vessel. BOTH were separate
generation driver stages, and in the box was the final multipliers, and
transformers for the final DC outputs, all in oil bath, along with the
tube itself. The flux exited through a fiberglass wedge and got focused
by a huge Aluminum lens, which diffracts X-rays.

That was a nine inch long, 2.5 inch diameter tube that was $900 each.
It was made by a famous German doctor that now only makes X-ray tubes.
The target was Palladium, and ingot that was around 20 grams in weight.

The supply we made for LANL was ALSO a custom, built to order
replacement for an existing setup. They sent us the tube, and we made the
supply for it. It is currently being used to examine nuke warheads for
long term aging viability specs. That was 50kV.

We also made supplies for a gas pipe inspection device made in Boston,
IIRC. It was 4kV, and had a ripple of 0.00006% and was a DC to DC
converter.

The Great Attractor

2007-05-11, 3:25 am

On Fri, 11 May 2007 03:03:04 GMT, "Don Kelly" <dhky@shaw.ca> wrote:

>No-one is trying to say that the X-ray unit itself is not DC driven but the
>whole package X-ray

No. That is exactly what he said. He even said that "rectified AC could
be used to directly feed the tube".

The Great Attractor

2007-05-11, 3:25 am

On Fri, 11 May 2007 03:03:04 GMT, "Don Kelly" <dhky@shaw.ca> wrote:

>You are thinking on a much smaller and specialized scale of things.

Bullshit.

The airport unit was a box that measured over two feet by one and a half
feet by nine inches thick, and weighed over 90 Lbs. WITHOUT the oil.

The driver was external to that.

The 50kV unit for LANL was 50W, IIRC, and we even made one unit that
was a half rack at 50kV 250W.

The gas pipe unit was a little bigger than a pack of cigarettes.

So three out of four of those were bigger than any unit you or he ever
saw in any hospital or chip x-ray station.

The Great Attractor

2007-05-11, 3:25 am

On Thu, 10 May 2007 23:19:29 -0400, "TimPerry" <timperry@noaspama.net>
wrote:

>ecarecar wrote:
>
>as was explained to me in collage it's 3 times the transmitted power with
>one third the copper... but then a lot of things they said in collage turned
>out to be wrong.

Perhaps like the spelling of the word COLLEGE.

You are a collage of insanity! Bwuahahahah!

Don Kelly

2007-05-11, 3:25 am

"The Great Attractor"
<SuperM@ssiveBlackHoleAtTheCenterOfTheMilkyWayGalaxy.org> wrote in message
news:vuq743tei3lr1i313u9htrak6l90746hjp@4ax.com...
> On Fri, 11 May 2007 03:03:04 GMT, "Don Kelly" <dhky@shaw.ca> wrote:
>
>
> Bullshit.
>
> The airport unit was a box that measured over two feet by one and a half
> feet by nine inches thick, and weighed over 90 Lbs. WITHOUT the oil.
>
> The driver was external to that.
>
> The 50kV unit for LANL was 50W, IIRC, and we even made one unit that
> was a half rack at 50kV 250W.
>
> The gas pipe unit was a little bigger than a pack of cigarettes.
>
> So three out of four of those were bigger than any unit you or he ever
>
---------------------
Good heavens- a whole 250W at 50Kv!!!!! 5ma!!!
As I say, specialised and small stuff.

I am not saying that this is unimportant -it isn't, by any means-but it is
still a case of a small scale specialized load (which has far less useful
power output than a toaster).

How about 500-765KV and power levels of 4-7Gw ? This is not uncommon. DC
systems at +/-500Kv at 500A (5Gw) also exist.

However, none of these fit in a 2ft by 1.5 ft by 9 inch box. I grant you
that.
Nor could they be driven from a 15A 120V outlet. --

Don Kelly dhky@shawcross.ca
remove the X to answer
----------------------------
saw in any hospital or chip x-ray station.

Salmon Egg

2007-05-11, 1:25 pm

On 5/10/07 8:19 PM, in article 4643e0c0$0$1391$4c368faf@roadrunner.com,
"TimPerry" <timperry@noaspama.net> wrote:

> as was explained to me in collage it's 3 times the transmitted power with
> one third the copper... but then a lot of things they said in collage turned
> out to be wrong.

Just to nit pick, it is three times the power of a single pair for the 3/2
amount of copper for a single pair. Consider three single phase systems.
These deliver 3 times the power that can be delivered by a single pair. They
use 6 conductors. If these are combined into one three-phase line, the
common neutral can be eliminated for a balanced load. Thus, only three wires
are required and that is 3/2 the copper for a single pair. Thus, to deliver
a given amount of power, you can do with half the copper.

One can argue that you now need more insulation to insulate for the higher
line to line voltage compared to line to neutral. Even if that were a
problem, the insulation is much cheaper than the copper. Have you ever heard
of wire being stolen for the insulation?

Bill
-- Fermez le Bush--about two years to go.

Salmon Egg

2007-05-11, 1:25 pm

Are you sure that you are not the Great Repeller? You surely repel me.

Bill
-- Fermez le Bush--about two years to go.

Salmon Egg

2007-05-11, 1:25 pm

On 5/10/07 10:06 PM, in article rRS0i.175492$aG1.27529@pd7urf3no, "Don
Kelly" <dhky@shaw.ca> wrote:

> Good heavens- a whole 250W at 50Kv!!!!! 5ma!!!
> As I say, specialised and small stuff.

Ask about the efficiency of converting that 250W into x-ray power. That
number will make most electronic equipment look as if they were
thermodynamic marvels.

Bill
-- Fermez le Bush--about two years to go.

The Great Attractor

2007-05-11, 8:25 pm

On Fri, 11 May 2007 05:06:31 GMT, "Don Kelly" <dhky@shaw.ca> wrote:

>Good heavens- a whole 250W at 50Kv!!!!! 5ma!!!
>As I say, specialised and small stuff.

You're a dope. We aren't talking about power distribution systems
here, we are talking about X-ray machines.

The Great Attractor

2007-05-11, 8:25 pm

On Thu, 10 May 2007 21:53:19 GMT, Pilgrim <pilgrim@noemail.net> wrote:

>In article <p8Sdnfh16N46F97bnZ2dnUVZ_judnZ2d@centurytel.net>,
> ecarecar <ecarecar@yahoo.com> wrote:
>
>
>There is basically only one reason:
>
>A more even load is placed on the prime mover and more even power
>supplied to the load.
>
>Chuck P.
>
>The fact that 3 phase motors are simpler is just a side benefit.

Yes. Examining a full wave rectified single phase sine wave has a LOT of
time below the RMS value.

Looking at the three peaks a three phase probing yields show that there
is a lot of time when the sine value is up near of above the RMS value
for a single sine wave.

Far more efficient at the load end. It's like only needing 60 cycle
transformers but getting the value of a 180Hz wave.

I saw an explanation of the DC intertie once that stated that the feed
was no more than a rectified 3 phase AC set-up.

A series of "bumps"... all at a good voltage level, never going to
zero.

Benj

2007-05-12, 3:25 am

ecarecar wrote:
> I'm not trying to pull an Edison. Specifically, what makes 3-phase more
> efficient than single phase?

Um, it's FAR better at killing small animals especially dogs and cats
which is why it's always the current of choice for electric
chairs! :-)

Benj
(Oh, yeah, I lied about that, but everything is fair in love and
electric wars!)

Benj

2007-05-12, 3:25 am

Don Kelly wrote:
> Economics as Salmon Egg indicates:
> a) cheaper transmission-systems and lower losses per Kw delivered
> b) better use of iron in generators, motors and transformers
> c)Better operation of motors as well as being simpler than single phase
> motors (single phase motors are less efficient than 3 phase motors and are
> not inherently self starting).
> d) Although not initially recognised, lower electric and magnetic fields
> from transmission lines than would be the case with single phase.
> e)The ability to supply single phase loads as well as 3 phase loads.
> f)The ability to use 3 phase, 6 phase or 12 phase rectifiers to get smoother
> DC without filtering where needed.

I'll pick what is behind door number c.!

Back at the end of the 19th century when Tesla was inventing polyphase
electric systems, the main interest at the time was largely industrial
because of the scale of steam power plants required to generate
electricity as well as it's novelty which made it expensive. The
genius of Tesla who basically invented the 20th century, revolved
around several key patents.

One was the use of alternating current. The genius of this was that it
allowed transformers to adjust voltage levels along the distribution
network. The DC Edison system had no such easy methods and in spite of
a hard-fought political battle and Occam's Razor which says the
simplest system is always the "correct" one, Edison's failure to solve
this distribution problem led to demise of DC distribution until quite
modern times when DC-DC conversion advanced beyond the motor-generator
set level.

The second was Tesla's invention of the induction motor (which he
actually invented back in Europe before coming to the USA). And
induction motor is really sort of a variation on a transformer and
also requires alternating current for that reason. It eliminated all
the commutators, sparking and other deficiencies associated with DC
motors. The principle of the 3 phase induction motor is the rotating
magnetic field generated by sets of coils driven by AC phases 120
degrees apart. The genius here is that if you use 3 phases, you find
that the fields add in such a manner that the rotating field vector is
of constant amplitude! A 2 phase motor isn't that way and a greater
number of phases than 3 just adds complexity for no reason unless you
have a special application of some kind (say low ripple in a AC-DC
rectifier).

For you sitting here in the 21st century it's hard to understand the
huge advance the Tesla polyphase induction motor made on industry.
Your view of some "shop" is all these rows of machines sitting on the
factory floor with hoards of happy workers turning out parts. In the
19th century it wasn't like that. There were rows of machines alright,
but overhead in the factory were all these axles and pulleys running
down to other pulleys on each machine which was powered by a flat
leather belt. To "start" your machine you had to flip the flat belt
onto the ceiling pulley with a long pole. The whole room was a maze of
dangerous flapping flat belts. Outside the factory "stationary
engineers" fired and maintained the steam engine that ran all the
overhead axles, pulleys, and belts. The 20th century norm of a shop
where each machine was individual and self-powered by electricity came
from Tesla and his patents.

As Don pointed out, one huge advantage of a 3 phase induction motor
over a single phase motor is that the three phase motor is simple,
efficient and self-starting. Single phase motors take special efforts
to start. Also by replacing a local steam engine with a HUGE
generating plant steam engine you reap the economics of scale and the
cost of the stationary operating engineers is spread among many users.
Thus, industrially, the whole concept of electric-powered beltless
machine tools must have seemed like "Star Trek" to mechanics of the
19th century. It was such genius and so obviously "correct" that the
standard for whole next century was based upon these Tesla patents and
ideas!

And behind door e. we also have the bonus that the industrial
polyphase electric source also allowed single phase uses as well for
lighting and heating applications!

> Shall I go on?

Not necessary. You already said it!

I will note however, that in spite of agreements granting rights to
all this technology to Westinghouse, eventually the Westinghouse
investors reneged on the deal cheating Tesla out of most of the
revenue for his patents. There are vague rumors around that Tesla was
tapped by the government before or during WWII to work on some things
and that at the time he was waving around a check from Westinghouse
made out to him for one million dollars, but these rumors or his
participation in any WWII projects have never been confirmed. The
standard story is he died destitute in a NYC hotel in 1943.

Benj
(Those who do not study history are doomed to repeat it!)

Salmon Egg

2007-05-12, 9:25 am

On 5/11/07 10:41 PM, in article
1178948470.542402.265400@l77g2000hsb.googlegroups.com, "Benj"
<bjacoby@iwaynet.net> wrote:

> The second was Tesla's invention of the induction motor (which he
> actually invented back in Europe before coming to the USA). And
> induction motor is really sort of a variation on a transformer and
> also requires alternating current for that reason. It eliminated all
> the commutators, sparking and other deficiencies associated with DC
> motors. The principle of the 3 phase induction motor is the rotating
> magnetic field generated by sets of coils driven by AC phases 120
> degrees apart. The genius here is that if you use 3 phases, you find
> that the fields add in such a manner that the rotating field vector is
> of constant amplitude! A 2 phase motor isn't that way and a greater
> number of phases than 3 just adds complexity for no reason unless you
> have a special application of some kind (say low ripple in a AC-DC
> rectifier).

My nit picking comment is that two-phase rotating field is just as constant
amplitude and speed as three-phase. You still need three wires because
neutral current is not zero even with a balanced load. If you go four-phase,
the equivalent of center-tapping the two phases of two-phase you can avoid
using a neutral but then you need four conductors for the lines. You get no
advantage in terms of winding motors.

Bill
-- Fermez le Bush--about two years to go.

TimPerry

2007-05-12, 9:25 am

Salmon Egg wrote:
> On 5/10/07 8:19 PM, in article
> 4643e0c0$0$1391$4c368faf@roadrunner.com, "TimPerry"
> <timperry@noaspama.net> wrote:
>
>
> Just to nit pick, it is three times the power of a single pair for
> the 3/2 amount of copper for a single pair. Consider three single
> phase systems. These deliver 3 times the power that can be delivered
> by a single pair. They use 6 conductors. If these are combined into
> one three-phase line, the common neutral can be eliminated for a
> balanced load. Thus, only three wires are required and that is 3/2
> the copper for a single pair. Thus, to deliver a given amount of
> power, you can do with half the copper.
>
> One can argue that you now need more insulation to insulate for the
> higher line to line voltage compared to line to neutral. Even if that
> were a problem, the insulation is much cheaper than the copper. Have
> you ever heard of wire being stolen for the insulation?
>
> Bill
> -- Fermez le Bush--about two years to go.

TimPerry

2007-05-12, 1:25 pm

>
> Just to nit pick, it is three times the power of a single pair for
> the 3/2 amount of copper for a single pair. Consider three single
> phase systems. These deliver 3 times the power that can be delivered
> by a single pair. They use 6 conductors. If these are combined into
> one three-phase line, the common neutral can be eliminated for a
> balanced load. Thus, only three wires are required and that is 3/2
> the copper for a single pair. Thus, to deliver a given amount of
> power, you can do with half the copper.

that makes much more sense.
i probably misremembered the lecture.
speculation: with the cost of copper (and coopers) rising may we see more 3
phase appliances in residential?

>
> One can argue that you now need more insulation to insulate for the
> higher line to line voltage compared to line to neutral. Even if that
> were a problem, the insulation is much cheaper than the copper. Have
> you ever heard of wire being stolen for the insulation?
>
> Bill
> -- Fermez le Bush--about two years to go.

around here they will steal darned near anything.... but the insulation is
kinda hard to get off by itself

Michael Moroney

2007-05-13, 3:25 am

Benj <bjacoby@iwaynet.net> writes:

>The second was Tesla's invention of the induction motor (which he
>actually invented back in Europe before coming to the USA). And
>induction motor is really sort of a variation on a transformer and
>also requires alternating current for that reason. It eliminated all
>the commutators, sparking and other deficiencies associated with DC
>motors. The principle of the 3 phase induction motor is the rotating
>magnetic field generated by sets of coils driven by AC phases 120
>degrees apart. The genius here is that if you use 3 phases, you find
>that the fields add in such a manner that the rotating field vector is
>of constant amplitude! A 2 phase motor isn't that way

A 2 phase system is that way. Remember math where the sum of the
square of the sine and the square of the cosine is 1 everywhere?
Replace the cosine with the sine shifted 90 degrees, and you have
the phase relationship for a 2 phase system. Two phase systems were
fairly common in the early days of electricity. The problem with 2
phase systems is the 3 wire version has a heavy neutral current,
while a balanced 3+ phase system will have zero neutral current.
A 4 or 5 wire 2 phase system doesn't have this problem, but takes more
wires to transfer the power than 3 phase (4 hots vs. 3 hots)
In other words, 3 phase systems can transfer more power with the same
amount of copper than 2 phase could.

>For you sitting here in the 21st century it's hard to understand the
>huge advance the Tesla polyphase induction motor made on industry.
>Your view of some "shop" is all these rows of machines sitting on the
>factory floor with hoards of happy workers turning out parts. In the
>19th century it wasn't like that. There were rows of machines alright,
>but overhead in the factory were all these axles and pulleys running
>down to other pulleys on each machine which was powered by a flat
>leather belt. To "start" your machine you had to flip the flat belt
>onto the ceiling pulley with a long pole. The whole room was a maze of
>dangerous flapping flat belts. Outside the factory "stationary
>engineers" fired and maintained the steam engine that ran all the
>overhead axles, pulleys, and belts. The 20th century norm of a shop
>where each machine was individual and self-powered by electricity came
>from Tesla and his patents.

I once worked in a building complex that once had that system. 99.9% of
the pulley system was long gone, but there were occasional large pulleys
still up in the ceiling, or remains of slots in the ceilings for belts
etc.

phil-news-nospam@ipal.net

2007-05-13, 3:25 am

On Thu, 10 May 2007 19:43:49 -0400 ecarecar <ecarecar@yahoo.com> wrote:

| I'm not trying to pull an Edison. Specifically, what makes 3-phase more
| efficient
| than single phase?

We have to consider 2 reasons to use three phase power. One is because
there are demands/needs for three phase power, such as very large motors.
That may or may not be more efficient. But you can't serve those needs
unless you have the phases. You can get single phase out of three phase
easily, but not the other way around. The other is because of efficiency
even if the loads are all single phase (evenly balanced on three phases).

But let's consider a case of efficiency.

Comparing 3-phase power to a 2-pole single phase system (which looks like
it could be called "2-phase" but that isn't standard terminology): If
you have a need for 600 kW of power, you could get that by having 200 kW
on each of 3 line wires, or 300 kW on each of 2 line wires (pick your
own voltage to figure the amps). For the line wires alone, it works out
basically even, if cross sectional area of wires equates to cost, and in
large scale systems it does. However, unless all your loads are only
line-to-line loads, you need a neutral wire, too. Potentially it could
see the full current a line wire could see, in the most unbalanced case
(before assumping harmonics or differential power factors). So that
neutral will need to have the same size as the line wire, which will be
50% larger in the single phase case.

Consider another case.

For a given line-to-neutral/ground voltage, the line-to-line voltage will
be higher in single phase, and in certain circumstances require a higher
level of insulation. Or considered in reverse, for a given level of
insulation that handles line-to-line voltages, three phase lets you have
a 15.47% higher voltage (and thus get more power with the same amps) over
what you can do in single phase. This would apply even if the load does
not need a neutral and it is not carried over the wiring.

I don't know enough about motors, yet, to tell you how they might be more
efficient in three phase than in single phase. But I know that as the
motor power goes up, the probability a given installation uses three
phase over single phase also goes up. But this could be due to issues
that are similar to the cases for transmitting and distributing power.

| Is it that you can kinda, sort of have a complete circuit with only one
| wire?

No.

| Or, that you can have three complete circuits with only three wires
| instead of six?

You can have 3 "circuits" with 4 wires, vs. 2 "circuits" with 3 wires.

| Remember, I am pre-admitting ignorance, so you don't have to tell me how
| ignorant I am.

I'll refrain. We all started there at some point.

--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2007-05-12-2250@ipal.net |
|------------------------------------/-------------------------------------|

The Great Attractor

2007-05-13, 3:25 am

On 13 May 2007 04:19:04 GMT, phil-news-nospam@ipal.net wrote:

>On Thu, 10 May 2007 19:43:49 -0400 ecarecar <ecarecar@yahoo.com> wrote:
>
>| I'm not trying to pull an Edison. Specifically, what makes 3-phase more
>| efficient
>| than single phase?
>
>We have to consider 2 reasons to use three phase power. One is because
>there are demands/needs for three phase power, such as very large motors.
>That may or may not be more efficient. But you can't serve those needs
>unless you have the phases. You can get single phase out of three phase
>easily, but not the other way around. The other is because of efficiency
>even if the loads are all single phase (evenly balanced on three phases).
>
>But let's consider a case of efficiency.
>
>Comparing 3-phase power to a 2-pole single phase system (which looks like
>it could be called "2-phase" but that isn't standard terminology): If
>you have a need for 600 kW of power, you could get that by having 200 kW
>on each of 3 line wires, or 300 kW on each of 2 line wires (pick your
>own voltage to figure the amps). For the line wires alone, it works out
>basically even, if cross sectional area of wires equates to cost, and in
>large scale systems it does. However, unless all your loads are only
>line-to-line loads, you need a neutral wire, too. Potentially it could
>see the full current a line wire could see, in the most unbalanced case
>(before assumping harmonics or differential power factors). So that
>neutral will need to have the same size as the line wire, which will be
>50% larger in the single phase case.
>
>Consider another case.
>
>For a given line-to-neutral/ground voltage, the line-to-line voltage will
>be higher in single phase, and in certain circumstances require a higher
>level of insulation. Or considered in reverse, for a given level of
>insulation that handles line-to-line voltages, three phase lets you have
>a 15.47% higher voltage (and thus get more power with the same amps) over
>what you can do in single phase. This would apply even if the load does
>not need a neutral and it is not carried over the wiring.
>
>I don't know enough about motors, yet, to tell you how they might be more
>efficient in three phase than in single phase. But I know that as the
>motor power goes up, the probability a given installation uses three
>phase over single phase also goes up. But this could be due to issues
>that are similar to the cases for transmitting and distributing power.
>
>
>| Is it that you can kinda, sort of have a complete circuit with only one
>| wire?
>
>No.
>
>| Or, that you can have three complete circuits with only three wires
>| instead of six?
>
>You can have 3 "circuits" with 4 wires, vs. 2 "circuits" with 3 wires.
>
>
>| Remember, I am pre-admitting ignorance, so you don't have to tell me how
>| ignorant I am.
>
>I'll refrain. We all started there at some point.

Excellent reply, Phil.

Salmon Egg

2007-05-13, 9:25 am

On 5/12/07 8:44 PM, in article f261j6$ier$1@pcls6.std.com, "Michael Moroney"
<moroney@world.std.spaamtrap.com> wrote:

> I once worked in a building complex that once had that system. 99.9% of
> the pulley system was long gone, but there were occasional large pulleys
> still up in the ceiling, or remains of slots in the ceilings for belts
> etc.

As a kid, I remember shoe repair shops often had various machines powered
off of a main shaft by using pulleys, belts, and clutches. Circa 1943.

Bill
-- Fermez le Bush--about two years to go.

The Great Attractor

2007-05-13, 9:25 am

On Sun, 13 May 2007 01:29:31 -0700, Salmon Egg <salmonegg@sbcglobal.net>
wrote:

>On 5/12/07 8:44 PM, in article f261j6$ier$1@pcls6.std.com, "Michael Moroney"
><moroney@world.std.spaamtrap.com> wrote:
>
>
>As a kid, I remember shoe repair shops often had various machines powered
>off of a main shaft by using pulleys, belts, and clutches. Circa 1943.

There is a bar in downtown Denver that has ceiling fans that are all
operated by one motor and a leather belt that runs all around the bar to
each fan. It's over by the new ball park IIRC.

jak

2007-05-13, 5:25 pm

"ecarecar" <ecarecar@yahoo.com> wrote in message
news:p8Sdnfh16N46F97bnZ2dnUVZ_judnZ2d@centurytel.net...
> What are the top 10 (or 2 or 3) reasons for 3-phase power?
>
> What advantages are there over single phase?
>

Instantaneous 120 hertz power components cancel out - for large motors or
generators real power is a constant - that's why motors over a certain size
are almost always three phase.

Janet K.

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