On Oct 30, 4:01 pm, Randy wrote:
This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.

I realize this would have to be a 50 to 100 year task. Laws would
need to be passed and electronic devices would need to be sold that
would work on both frequencies. (many switching power supplies such as
in computers do not care what freq. power is input.)

I've read a bunch of articles about the newer inverter type welding
power sources that use 400 HZ and use small transformers and use much
less input power for the same output power.

I'm guessing it would take a panel of "experts" a few years to work
out the costs VS savings for this one. I've heard of some really
stupid things being studied by our government, maybe someone should
look into this.

I bought some old machinery from the Bethlehem Steel plant that was 25
cycle, WOW, talk about inefficient!! I had a 5hp motor that was built
on a 15 hp frame size.

Ideas, thoughts??

Biggest problem I think would be the generating end of things.

Thank You,
Randy

Remove 333 from email address to reply.

I think that you are mixing up size and efficency. The higher the
frequency the size for a certain power output decreases. But ! the
losses from eddy currents and the like increase. There is a crossover
point which was below 50 hz in the old days ....most of the old
generating stations were 25 hz and even 16 2/3 Hz.
Today with modern steels and thinner laminations the cross over point
is much higher. But that is not the only point to consider ! with high
voltage transmission lines the losses climb with frequency and
distance. The very big long ones even use DC !

Regards Bob

This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.

I realize this would have to be a 50 to 100 year task. Laws would
need to be passed and electronic devices would need to be sold that
would work on both frequencies. (many switching power supplies such as
in computers do not care what freq. power is input.)

I've read a bunch of articles about the newer inverter type welding
power sources that use 400 HZ and use small transformers and use much
less input power for the same output power.

I'm guessing it would take a panel of "experts" a few years to work
out the costs VS savings for this one. I've heard of some really
stupid things being studied by our government, maybe someone should
look into this.

I bought some old machinery from the Bethlehem Steel plant that was 25
cycle, WOW, talk about inefficient!! I had a 5hp motor that was built
on a 15 hp frame size.

Ideas, thoughts??

Biggest problem I think would be the generating end of things.

Thank You,
Randy

Remove 333 from email address to reply.

bob wrote:

On Oct 30, 4:01 pm, Randy wrote:

This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.

I realize this would have to be a 50 to 100 year task. Laws would
need to be passed and electronic devices would need to be sold that
would work on both frequencies. (many switching power supplies such as
in computers do not care what freq. power is input.)

I've read a bunch of articles about the newer inverter type welding
power sources that use 400 HZ and use small transformers and use much
less input power for the same output power.

I'm guessing it would take a panel of "experts" a few years to work
out the costs VS savings for this one. I've heard of some really
stupid things being studied by our government, maybe someone should
look into this.

I bought some old machinery from the Bethlehem Steel plant that was 25
cycle, WOW, talk about inefficient!! I had a 5hp motor that was built
on a 15 hp frame size.

Ideas, thoughts??

Biggest problem I think would be the generating end of things.

Thank You,
Randy

Remove 333 from email address to reply.


I think that you are mixing up size and efficency. The higher the
frequency the size for a certain power output decreases. But ! the
losses from eddy currents and the like increase. There is a crossover
point which was below 50 hz in the old days ....most of the old
generating stations were 25 hz and even 16 2/3 Hz.
Today with modern steels and thinner laminations the cross over point
is much higher. But that is not the only point to consider ! with high
voltage transmission lines the losses climb with frequency and
distance. The very big long ones even use DC !

Interesting you mention DC transmission lines. My neighbours were in
China last year and saw the new big dam, they were told the generating
station produced 500kV AC for local use and 500kV DC for long distance
transmission. Subsequently I have been told that some UK electricity is
supplied by France as DC. My question is what sort of gear is used to
convert the DC to AC. A big motor generator unit?.


Regards Bob

"bob" wrote in message
oups.com...
On Oct 30, 4:01 pm, Randy wrote:
This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.


snip



Thank You,
Randy


snip

But that is not the only point to consider ! with high
voltage transmission lines the losses climb with frequency and
distance. The very big long ones even use DC !

Regards Bob


Aircraft use 400 Hz stuff because it weighs a lot less. And
aircraft can get away with it because they are "small."

When a transmission line becomes a significant part (more
than a few percent) of a wavelength, interesting things start
to happen with the greatest "strangeness" occuring at a
quarter wavelength. You can easily make a transmitting
antenna that will radiate most of your power. And, if you
put a significant load (low impedence) a quarter wavelength
down the transmission line, it will reflect an open at the
other end of the line and you won't get any power to go down
it at all.

In free space, a quarter wavelength at 60 Hz is 775 miles
(somewhat less in a transmission line...). So, a line of up to,
maybe, 50 miles can be constructed with little or no attention
paid to the details. For longer lines, an engineer is going to
have to start paying attention to the design, which, of course, is
pretty much standard practice. But a wavelength at 400 Hz
is only 15 percent of that at 60 Hz, so the typical line lengths
found, say, running around an average city would have to
be carefully engineered...

(And, yes, some of the numbers I used are SWAGs. But I'm
a radio guy. A power guy might use a sharper pencil. YMMV,
but you get the idea...)

Jerry

Inductive reactance =2pifL, so, as frequency goes up, the reactance goes up
in direct proportion. Not what you want when you're sending power to a
load. Capacitive reactance = 1/2pifC, (that's 1 over 2pifC), so reactance
goes down as frequency goes up. This is leakage path between the
transmission lines and to ground. Also not what you want.

On Tue, 30 Oct 2007 08:51:25 -0500, Robert Swinney wrote:

"bob" sez:

"I think that you are mixing up size and efficency. The higher the
frequency the size for a certain power output decreases. But ! the
losses from eddy currents and the like increase. There is a crossover
point which was below 50 hz in the old days ...."

There is no specific coorelation re. size, frequency and efficiency. The efficiency of any
electrical device is a function of its design. i.e., efficiency is always a trade-off against cost,
performance, weight and a host of other things. Each device is designed to operate with a certain
efficiency (not always the maximimum efficiency) within certain boundaries, cost usu. being
foremost, among them.

Bob Swinney


A transformer's (or inductor's) core volume goes down as the reciprocal of
frequency for any given power level. Core materials can hold a nearly
constant amount of energy per unit volume, and the energy they must hold
is pretty close to power / frequency. This is why switching supplies (and
amplifiers) run as fast as the output transistors and catch diodes can go
-- they're trying to drive the transformer size down.

I believe that a motor's ability to transmit mechanical power follows a
similar trend, although the energy is stored in the gap between the
armature and coils -- I haven't done the math on this one yet.

So I certainly disagree as it pertains to transformers, and I think I do
for motors.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

Randy wrote:
...Laws would need to be passed ...

Do you like that? What we don't have enough of them already?
By the way, as others have implied, you can't really legislate physics...

cheers
T.Alan

On Tue, 30 Oct 2007 09:01:36 -0500, Randy
wrote:

This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.
snip
=========
what a group!

thread hijack [sort of]

Given the increased efficiency in terms of both size and power,
how would 3 phase residential power service (in new homes) affect
power distribution cost/efficiency and the life-cycle cost of
high reactive consumption units such as residential air
conditioners and possibly refrigerators if these were 220
3-phase?


Unka' George [George McDuffee]
============
Merchants have no country.
The mere spot they stand on
does not constitute so strong an attachment
as that from which they draw their gains.

Thomas Jefferson (1743-1826),
U.S. president. Letter, 17 March 1814.

On Oct 30, 7:33 am, David Billington
wrote:
bob wrote:
On Oct 30, 4:01 pm, Randy wrote:

This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.

I realize this would have to be a 50 to 100 year task. Laws would
need to be passed and electronic devices would need to be sold that
would work on both frequencies. (many switching power supplies such as
in computers do not care what freq. power is input.)

I've read a bunch of articles about the newer inverter type welding
power sources that use 400 HZ and use small transformers and use much
less input power for the same output power.

I'm guessing it would take a panel of "experts" a few years to work
out the costs VS savings for this one. I've heard of some really
stupid things being studied by our government, maybe someone should
look into this.

I bought some old machinery from the Bethlehem Steel plant that was 25
cycle, WOW, talk about inefficient!! I had a 5hp motor that was built
on a 15 hp frame size.

Ideas, thoughts??

Biggest problem I think would be the generating end of things.

Thank You,
Randy

Remove 333 from email address to reply.

I think that you are mixing up size and efficency. The higher the
frequency the size for a certain power output decreases. But ! the
losses from eddy currents and the like increase. There is a crossover
point which was below 50 hz in the old days ....most of the old
generating stations were 25 hz and even 16 2/3 Hz.
Today with modern steels and thinner laminations the cross over point
is much higher. But that is not the only point to consider ! with high
voltage transmission lines the losses climb with frequency and
distance. The very big long ones even use DC !

Interesting you mention DC transmission lines. My neighbours were in
China last year and saw the new big dam, they were told the generating
station produced 500kV AC for local use and 500kV DC for long distance
transmission. Subsequently I have been told that some UK electricity is
supplied by France as DC. My question is what sort of gear is used to
convert the DC to AC. A big motor generator unit?.



Regards Bob

Perhaps I can answer the question about the DC transmission of power.

The Dalles dam on the Columbia river transmits power to the LA area
using DC. In the late 1970's, I think, I was in the Portland Amature
Radio club. A member was an engineer for a local power company. He set
up tours for us to several interesting power generating facilities,
and one was the DC converter station at the Dalles dam. The station
takes 18 phase AC power, yes, 18 phase, at several thousand volts. The
power is then fed into several rows of mercury vapour controlled
rectifiers. They stand on ceramic insulators about 10 feet above the
floor. The output of the rectifiers feed power at 250,000 volts over a
pair of wires all the way to LA. The origional plan was to use both
lines at 500,000 volts and use the earth as a return. Law suits
stopped that because of the havoc caused by the ground currents.

An identical installation is on the LA side of the transmission lines.
There the controlled rectifiers convert the DC back to AC. The system
is symetrical in that when the river flow is low in the winter and the
people in LA are not using their air conditioners, the excess power is
sent back to the Northwest using the same AC to DC system.

The entire transmission system is controlled by computers. Even back
in the 1970's.

A very interesting and educational experience.

Paul

"Robert Swinney" wrote: Leo, And your point is ?
^^^^^^^^^^^^^^^^^
If it's not clear, then I may be wrong about something. The OP was
proposing to raise power line frequency from 50 hz or 60 hz to 400 hz. It
looks to me like that would raise the inductive reactance and lower the
capacitive reactance of the network, both of which would be wasteful. If
that's not correct, straighten me out, please.

"Leo Lichtman" wrote in message
...

"Robert Swinney" wrote: Leo, And your point is ?
^^^^^^^^^^^^^^^^^
If it's not clear, then I may be wrong about something. The OP was
proposing to raise power line frequency from 50 hz or 60 hz to 400 hz. It
looks to me like that would raise the inductive reactance and lower the
capacitive reactance of the network, both of which would be wasteful. If
that's not correct, straighten me out, please.



Regardless of the frequency, the laws of physics do not change. Power is
"consumed" (turned into heat, mostly) in a resistive load. And the IR
losses
will be the same (assuming the same voltage and current) regardless of the
frequency. There is no true loss due to reactance, only an opposition to
current flow. But, inductive and capacitive reactances are 180 degrees out
of phase with one another and, hence, if they are equal in magnitude,
cancel.
Thus, their contribution to the net impedence is zero; only the resistive
component has any effect on current flow and this effect is, of course,
minimized by using as high a voltage and low of current as practical. Now,
if the capacitive and inductive reactances are not equal, the dominant one
will twist the phase of the current with respect to the voltage and the
result
will be a loss of efficiency (a power factor of less than unity, to use the
buzz-
word...). So, the distributed inductance and capacitance of the
transmission
line become primary considerations of the engineer designing the line. And
the design will be different at different frequencies. But, in properly
designed
transmission lines, efficiency is independent of frequency.

This explanation is something of an over-simplification, of course. There
are
other things that come into play as the frequency goes up. But, at low
(power
line) frequencies, they can largely be neglected. (As one goes up into
radio
frequencies, things get complicated real fast...) And, of course, in the
trivial
case where the frequency is zero (DC), all of these concerns simply go away.

The bottom line is that, as the frequency goes up, the trickier the
transmission
line becomes.

Jerry

"Jerry Foster" wrote: (clip) Regardless of the frequency, the laws of
physics do not change. Power is
"consumed" (turned into heat, mostly) in a resistive load. And the IR
losses
will be the same (clip)
^^^^^^^^^^^^^^^^^^^^
I think you meant to say I^squared.
^^^^^^^^^^^^^^^^^^^^
There is no true loss due to reactance, only an opposition to
current flow. (clip)
^^^^^^^^^^^^^^^^^^^
If the current is out of phase, the quadrature* component will have
I^squared R loss associated with it.
*I'm amazed I remember this term from college--I graduated in 1952.
^^^^^^^^^^^^^^^^^^
(clip) the distributed inductance and capacitance of the transmission
line become primary considerations of the engineer designing the line.
And
the design will be different at different frequencies. But, in properly
designed
transmission lines, efficiency is independent of frequency.
^^^^^^^^^^^^^^^^^^
We must realize, of course, that this is not the same as saying that a
transmission line can be designed whose efficiency is independent of
frequency. Transmission lines have to be designed for the particular
frequency that they will carry. I think this is a point that needs to be
added to the list of obstacles to the idea proposed by the OP.

Thanks, Jerry and Robert for the clarification/expansion of my comments.

Randy wrote:
Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.

Thank You,
Randy

A big NEGATIVE on the transmission. The higher freq means more
rediated power. (lost)
Yes a LOT less iron in all the machinery and transformers.

The REAL long transmission lines are now very high DC for
this reason.
...lew...

On Tue, 30 Oct 2007 09:01:36 -0500, Randy wrote:

This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.

I realize this would have to be a 50 to 100 year task. Laws would
need to be passed and electronic devices would need to be sold that
would work on both frequencies. (many switching power supplies such as
in computers do not care what freq. power is input.)

I've read a bunch of articles about the newer inverter type welding
power sources that use 400 HZ and use small transformers and use much
less input power for the same output power.

I'm guessing it would take a panel of "experts" a few years to work
out the costs VS savings for this one. I've heard of some really
stupid things being studied by our government, maybe someone should
look into this.

I bought some old machinery from the Bethlehem Steel plant that was 25
cycle, WOW, talk about inefficient!! I had a 5hp motor that was built
on a 15 hp frame size.

Ideas, thoughts??

Biggest problem I think would be the generating end of things.

Thank You,
Randy

Remove 333 from email address to reply.

Higher frequency motors can be smaller for given power because they
run at higher speeds. A 4-pole 400 Hz induction motor would run at
about 11,500 RPM. System efficiency would probably be less because
speed reduction by gears etc would usually be required, but system
weight is what counts in aircraft.

As Bob Swinney points out, effiency is a matter of design, traded off
against other parameters like size, weight, cost, etc. In one sense,
lower frequency motors, though larger and more costly for given power,
could be more system-efficient where their lower speeds might reduce
or eliminate need for speed reduction kit which also has losses. Gear
trains are often considerably less efficient than ordinary AC
induction motors.

Power transmission over significant distance is generally more
efficient at lower frequency, with DC being most efficient. Further,
DC distribution would have the same advantage as 3-phase in that it
can deliver power continuously while single-phase AC delivers power
intermittently and thus requires energy storage in most useful
devices. In an ordinary motor this energy storage is in kinetic
energy and in the magnetic field. In electronic gear it's in
capacitors.

Developments in power electronics have made huge advances in the past
decade, and this will continue in terms of lower cost, higher
effiency and higher power levels. Power elex makes line frequency
about irrelevant because the power can be modified to suit the load --
as is already done in VFD's and brushless DC motors.

Power elex makes the notion of a "DC transformer" possible. The
actual xfmr is AC, usually at frequencies considerably higher than 400
Hz, but the functional block is DC in and DC out.

Inverter-type welders don't draw less power, but they do have much
better power factor than copper-iron machines so they draw less line
current, and thus result in lower losses in the distribution system.

Leo Lichtman wrote:
"Robert Swinney" wrote: Leo, And your point is ?
^^^^^^^^^^^^^^^^^
If it's not clear, then I may be wrong about something. The OP was
proposing to raise power line frequency from 50 hz or 60 hz to 400 hz. It
looks to me like that would raise the inductive reactance and lower the
capacitive reactance of the network, both of which would be wasteful. If
that's not correct, straighten me out, please.


A further point is the line length.
Speed of light = 300,000 km/sec
So, at 400Hz, 1 wavelength = 300,000/400 = 750km
And 1/4 wave is just less than 200km.

This is by no means an unheard-of length for a transmission line.
At 1/4 wave, all sorts of interesting transformer-like effects occur, as
any radio ham will tell you!

On Oct 30, 3:17 am, bob wrote:
On Oct 30, 4:01 pm, Randy wrote:





This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,


I seem to remember reading that Westinghouse-Tesla AC was chosen over
Edison DC because the AC could be transmitted with lower power loss
over distance. So was AC more efficent at the distances it was being
transmitted at the begining of the electrical revolution?
Thanks
Karl

On Oct 31, 6:36 am, " wrote:
On Oct 30, 3:17 am, bob wrote:

On Oct 30, 4:01 pm, Randy wrote:

This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,

I seem to remember reading that Westinghouse-Tesla AC was chosen over
Edison DC because the AC could be transmitted with lower power loss
over distance. So was AC more efficent at the distances it was being
transmitted at the begining of the electrical revolution?
Thanks
Karl

Yes, because unlike DC it could be transmitted at high voltage
(requires more cheap insulation or spacing) , low current (requires
less expensive copper) and easily transformed to low household voltage
at the end. The Edison system needed small, inefficient power plants
in every neighborhood. Also Edison wasn't as clever a businessman and
promoter as George Westinghouse, and I think the propaganda film of AC
killing a horse backfired on Edison.

On Wed, 31 Oct 2007 09:29:24 -0500, "Robert Swinney"
wrote:

An interesting side-bar comment may be in order he

One of the requirements of a transmission line is that it be able to transfer most of the power
applied to it. Transfer is attenuated by the inherent losses of the transmission line. The ideal
transmission line has only resistive loss (R=E / I) and that is, of course, a "DC" line - or simply
a piece of wire carrying only direct current.

Early on in the formative days of telephony it became apparent that a pair of wires, unto itself,
made a lousy transmission line for "voice currents". Oliver Heaviside, showed that a telephone wire
pair could be equalized for voice transmission over long distances. This was done via introduction
of "lumped constants" in series at strategic locations along the transmission path. Inductance was
inserted to offset the effects of capacitance, wire to wire, wire to pole, and wire to ground.
Later, this became known as "loading" and found its way into cable pairs carrying high frequiency,
multiple conversation, telephone carriers. A modern application is DSL.

Little known communications trivia: Transcontinental telephone service was available in the U.S.
long before the advent of electronic amplification. It was made possible by loading ("Heavifying")
ordinary open-wire telephone pairs. AFAIK, only the pair of wires separated by the telephone pole,
known as the "pole pair" were loaded. They were of heavier gage wire than ordinary and loaded with
series inductances.
Thus you could talk coast-to-coast over an unamplified open-wire telephone pair. The toll rate was
pricey.

Bob Swinney

The reason this worked is because it altered the characteristic
impedance (Zo) of the line to match the Z of the telephone transmitter
(carbon button mike) and receivers, which were about 600 ohms. Optimal
power transfer occurs when source, line and load are
impedance-matched. Zo of a line is sqrt(L/C) where the L and C are
per-unit-length as henries per meter and farads per meter. Adding
distributed series L's in the line raises the Zo of the line.

If you look inside an ordinary telephone of later vintage, one with a
dial on it (disc with 10 holes), you will find an inductor. Same
idea.

On Tue, 30 Oct 2007 17:20:30 -0600, Lew Hartswick
wrote:

Randy wrote:
Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.

Thank You,
Randy

A big NEGATIVE on the transmission. The higher freq means more
rediated power. (lost)
Yes a LOT less iron in all the machinery and transformers.

The REAL long transmission lines are now very high DC for
this reason.
...lew...

OK, we rule out 400HZ as too high, due to the 1/4 wave length problem,
would it be worth while to go to 90 or 120HZ?

Standard around here anyway is uninsulated high tension lines, would
insulation help?


I read a few articles in my welding mags where a shop bought all new
inverter type power sources and paid them off in less than a year in
power savings, so there has to be less power drawn by the supply,
correct?


Thank You,
Randy

Remove 333 from email address to reply.

On Wed, 31 Oct 2007 10:36:51 -0000, "
wrote:

On Oct 30, 3:17 am, bob wrote:
On Oct 30, 4:01 pm, Randy wrote:





This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,


I seem to remember reading that Westinghouse-Tesla AC was chosen over
Edison DC because the AC could be transmitted with lower power loss
over distance. So was AC more efficent at the distances it was being
transmitted at the begining of the electrical revolution?
Thanks
Karl

The difference wasn't AC vs DC per se, but voltage. Power can be
transmitted more efficiently at higher voltage and lower current. AC
enables use of high-voltage transmission because voltage of AC can be
efficiently changed up or down with transformers. Consider that the
feed for 200 amp 220-volt residential service is 2/0 copper, .365"
dia. This same size wire at 500,000 volts would serve 2273
residences. "Wire" to handle these 2273 residences at 220 volts would
be over 17" dia!

The DC equivalent to a transformer at the time would have been a large
motor-generator set which was expensive, inefficient, required
maintenance and would eventually wear out.

Randy wrote:
This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.

Others have addressed the true efficiency topic, so I won't. But, there
are a bunch of downsides to the use of 400 Hz power. First, ever heard
the whine of 400 Hz equipment in aircraft? If you think "hum" in your
Hi-Fi is annoying, just imagine what 800 Hz (full-wave rectified 400 Hz)
would sound like! And, for equipment powered by 3-phase, that would be
2400 Hz, totally piercing.

Another annoying point would be the speeds of motors. An ordinary
2-pole AC motor would run at 24,000 RPM! Now, of course, you can add a
bunch of poles in the winding, and get to more reasonable speeds, but
that all costs money, as do the much thinner motor laminations.
The power companies would be horrified, as they'd have to build those
transmission substation transformers with many feet of thin iron
laminations, and use Litz wire for the windings to control eddy
currents. Also, the radiation from the lines would be greatly
increased. That's a major reason why really long transmission lines
have gone to DC.

Jon

Tim Wescott wrote:

A transformer's (or inductor's) core volume goes down as the reciprocal of
frequency for any given power level. Core materials can hold a nearly
constant amount of energy per unit volume, and the energy they must hold
is pretty close to power / frequency.
But, the core losses per volume (or weight) goes up with frequency.
Hysteresis loss is directly proportional to frequency, you are forcing
the iron atoms to realign their spins at twice the frequency. Eddy
losses are not so simple, they have to do with Bmax and the lamination
thickness, mostly.

Jon

wrote:
On Oct 30, 3:17 am, bob wrote:

On Oct 30, 4:01 pm, Randy wrote:






This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,


I seem to remember reading that Westinghouse-Tesla AC was chosen over
Edison DC because the AC could be transmitted with lower power loss
over distance. So was AC more efficent at the distances it was being
transmitted at the begining of the electrical revolution?


Yes, because there WAS the AC transformer. You could use a DC-DC
motor-generator set, but there are practical limits to how much voltage
you can get out of a generator armature. It was pretty easy to see that
with no moving parts, you could get much better insulation in a
transformer, and thus transmit power at kilovolt levels with existing
technology in the late 1890's.

With Edison's DC system, you couldn't convert voltages without rotary
machines, and nobody was going to have a 1000 V line feeding a rotary
converter in their basement. And, nobody wanted 1000 V on their bulbs
and light switches. So, if the entire system ran on 120 V DC, then you
had large currents flowing all through the system, and got pretty big
voltage drops in just a couple city blocks. You could fight this with
big wire on the poles for a while, but it soon got out of hand.

The pole transformer outside my house runs on 7200 V, so it is a 30:1
winding (primary to the full 240 V secondary). So, if I am pulling the
full rated load for my house (200 A) the transformer is pulling 6.67 A
from the high voltage distribution mains. MUCH easier to send 6.67 A
down a wire than 200.

Jon

F. George McDuffee wrote:
On Tue, 30 Oct 2007 09:01:36 -0500, Randy
wrote:


This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.

snip
=========
what a group!

thread hijack [sort of]

Given the increased efficiency in terms of both size and power,
how would 3 phase residential power service (in new homes) affect
power distribution cost/efficiency and the life-cycle cost of
high reactive consumption units such as residential air
conditioners and possibly refrigerators if these were 220
3-phase?
The really big advantage of a 3-phase hermetic refrigeration compressor
is it needs no starting relay. Just apply power and the motor spins up.
I doubt there is a great increase in efficiency of small 3-phase motors
over single phase. If you want REAL efficiency gains, permanent-magnet
synchronous motors run by variable frequency drives do show large gains
in efficiency. All variable-speed air conditioners use some sort of
VFD, and permanent magnet motors are now replacing the induction motor,
as they ARE more efficient.

The liklihood of the US adopting 3-phase wall outlets for all appliances
is about as high as (your favorite never-will-happen scenario here).
There would be REAL costs to extending 3-phase power to all residences,
and putting in 3-phase meters and 3-pole breakers in the panels. With a
basement full of machine tools, I'd love it, though. I do NOT have
3-phase power on my pole, but it is "only" a block away.

I can just imagine having a 5-prong Harvey Hubbell twist lock plug on
those lamps with three bulbs and a 1-2-3 switch on them!

Jon

Randy wrote:
OK, we rule out 400HZ as too high, due to the 1/4 wave length problem,
would it be worth while to go to 90 or 120HZ?

One could argue the thing forever, as the losses are almost all
engineering tradeoffs when the various components are designed.

But, it is all moot. I have no way to calculate the cost, but if the
entire generating, transmission and distribution system had to be
replaced, plus most appliances more complicated than a toaster or light
bulb, the cost would certainly be in the trillions of $. Couldn't
possibly be any less than that. Maybe some power house alternators
could be re-wound for 4-poles to get the required frequency, and the
transmission lines could probably stay, but that's about it. Now, for
the transformers, the Bmax would go down at the higher freq, assuming
same voltage, and that would help the hysteresis loss, but I think some
of the other losses would go up.

But, this stuff gets REALLY complicated. For instance, the leakage
inductance of the transformers is carefully engineered to control fault
currents. At higher F, the fault currents would go down, but that means
voltage regulation would get worse, too.

Standard around here anyway is uninsulated high tension lines, would
insulation help?

Absolutely not at all. You could try shielding them, but that would be
insanely expensive. But insulation does not prevent the electric and
magnetic fields from radiating, so it would have no effect.



I read a few articles in my welding mags where a shop bought all new
inverter type power sources and paid them off in less than a year in
power savings, so there has to be less power drawn by the supply,
correct?
it could just be that they were getting blitzed by the power company for
having terrible power factor with the old welders. The way old welding
power supplies were made, they really were quite efficient, but the
transformers were intentionally made to have huge leakage inductance,
that's how they limited the welding current. Thus, the native power
factor was insanely bad. So, they had to add power factor correcting
caps, which drew a huge leading PF when not welding, and were a
compromise that only corrected the PF at one welding current.

Depending on the type of meter they had, they could get dinged REALLY
hard for the bad PF.

Jon

Don Foreman wrote:


As Bob Swinney points out, effiency is a matter of design, traded off
against other parameters like size, weight, cost, etc. In one sense,
lower frequency motors, though larger and more costly for given power,
could be more system-efficient where their lower speeds might reduce
or eliminate need for speed reduction kit which also has losses. Gear
trains are often considerably less efficient than ordinary AC
induction motors.

Why, yes, into the 1950's, Ingersoll Rand made direct-drive air
compressors with these HUGE 300 RPM synchronous motors. An interesting
feature of synchronous AC motors is that varying the rotor field allows
the motor to draw leading or lagging power factor, so a device was put
on the motor to read the plant's power factor and set the field to
correct the whole plant's PF. This saved them a BUNCH of money on the
electric bill.

Jon

Maybe in this context, this question is not too off topic. When people talk
about electric cars being non-polluting, they often fail to consider that
steam generation plants have smokestacks, and they DO put CO2 into the
atmosphere. Of course, they run MUCH cleaner than auto exhausts. so I'm
sure they pollute less. But, how much of the power they generate is lost
in transmission? You have to know this in order to estimate the
environmental benefit of electric cars. I would like to know: what is the
efficiency of the power grid? Just a ball-park figure, for purposes of
discussion will do.

"Jon Elson" wrote in message
...


F. George McDuffee wrote:
On Tue, 30 Oct 2007 09:01:36 -0500, Randy
wrote:


This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.

snip
=========
what a group! thread hijack [sort of]

Given the increased efficiency in terms of both size and power,
how would 3 phase residential power service (in new homes) affect
power distribution cost/efficiency and the life-cycle cost of
high reactive consumption units such as residential air
conditioners and possibly refrigerators if these were 220
3-phase?
The really big advantage of a 3-phase hermetic refrigeration
compressor
is it needs no starting relay. Just apply power and the motor spins
up.
I doubt there is a great increase in efficiency of small 3-phase
motors over single phase. If you want REAL efficiency gains,
permanent-magnet synchronous motors run by variable frequency drives
do show large gains in efficiency. All variable-speed air
conditioners use some sort of VFD, and permanent magnet motors are now
replacing the induction motor, as they ARE more efficient.

The liklihood of the US adopting 3-phase wall outlets for all
appliances is about as high as (your favorite never-will-happen
scenario here).
There would be REAL costs to extending 3-phase power to all
residences, and putting in 3-phase meters and 3-pole breakers in the
panels. With a basement full of machine tools, I'd love it, though.
I do NOT have 3-phase power on my pole, but it is "only" a block away.

I can just imagine having a 5-prong Harvey Hubbell twist lock plug on
those lamps with three bulbs and a 1-2-3 switch on them!

Jon
With 3 phase distribution you would not have 5-prong Harvey Hubbell
twist lock plug on your lamps.

In this country (Australia) 3 phase is available in most places but only
delivered to those homes that need it for Air con and such bigger loads.
Small things, lamps etc still run of one simple plug similar in size to
the US 120volt plug. The area served by a pole transformer or roadside
box seems to be larger than is common in the US but the single pase
homes are distributed across the three phases. Pole pig outside my house
was changed last week from 40KW to 60 KW (I think).

And Gloat!! I could have 3pahse in my workshop if I needed it but a
table saw is the biggest thing I have.

John G.

wrote:

I seem to remember reading that Westinghouse-Tesla AC was chosen over
Edison DC because the AC could be transmitted with lower power loss
over distance. So was AC more efficent at the distances it was being
transmitted at the begining of the electrical revolution?
Thanks
Karl

They didn't have the "marvolus" solid state and wonderful gas
switching devices back then so DC was at a SERIOUS disadvantage.
:-)
...lew...

Jon Elson wrote:



F. George McDuffee wrote:

On Tue, 30 Oct 2007 09:01:36 -0500, Randy
wrote:


This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.


snip
=========
what a group!
thread hijack [sort of]

Given the increased efficiency in terms of both size and power,
how would 3 phase residential power service (in new homes) affect
power distribution cost/efficiency and the life-cycle cost of
high reactive consumption units such as residential air
conditioners and possibly refrigerators if these were 220
3-phase?

The really big advantage of a 3-phase hermetic refrigeration compressor
is it needs no starting relay. Just apply power and the motor spins up.
I doubt there is a great increase in efficiency of small 3-phase motors
over single phase.

the efficiency comes with varying loads. A single phase motor is
designed to operate at a certain load, any load more or less the phase
shift to the second winding through the cap is not at optimum and will
generate more heat.

If you want REAL efficiency gains, permanent magnet
synchronous motors run by variable frequency drives do show large gains
in efficiency. All variable-speed air conditioners use some sort of
VFD, and permanent magnet motors are now replacing the induction motor,
as they ARE more efficient.

The liklihood of the US adopting 3-phase wall outlets for all appliances
is about as high as (your favorite never-will-happen scenario here).
There would be REAL costs to extending 3-phase power to all residences,
and putting in 3-phase meters and 3-pole breakers in the panels. With a
basement full of machine tools, I'd love it, though. I do NOT have
3-phase power on my pole, but it is "only" a block away.


I would look more to supplying houses with DC. With today's electronics
everything can easily run on DC with built in VFD's that run directly
from dc rather than first rectifying it inside the drive. The same goes
for any appliance. Using DC would make it much easier to eliminate
switching noise from vfd's and other similar devices by just adding a
couple of caps on only one circuit.



John

Leo Lichtman wrote:

Maybe in this context, this question is not too off topic. When people talk
about electric cars being non-polluting, they often fail to consider that
steam generation plants have smokestacks, and they DO put CO2 into the
atmosphere. Of course, they run MUCH cleaner than auto exhausts. so I'm
sure they pollute less. But, how much of the power they generate is lost
in transmission? You have to know this in order to estimate the
environmental benefit of electric cars. I would like to know: what is the
efficiency of the power grid? Just a ball-park figure, for purposes of
discussion will do.



There are many things to consider including idling at a stoplight with a
gas engine
while with a electric motor it is not using any electric. Also a motor
can be a braking device and put power back into the batteries. No oil
is needed for lubrication of the motor other than an ocasional shot of
grease. The down side is that the batteries have an finite lifespan and
they will be expensive to change. Another problem is heat in the winter
, unless there is a small aux engine generator.


John

Randy wrote:

This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.

I realize this would have to be a 50 to 100 year task. Laws would
need to be passed and electronic devices would need to be sold that
would work on both frequencies. (many switching power supplies such as
in computers do not care what freq. power is input.)

I've read a bunch of articles about the newer inverter type welding
power sources that use 400 HZ and use small transformers and use much
less input power for the same output power.

I'm guessing it would take a panel of "experts" a few years to work
out the costs VS savings for this one. I've heard of some really
stupid things being studied by our government, maybe someone should
look into this.

I bought some old machinery from the Bethlehem Steel plant that was 25
cycle, WOW, talk about inefficient!! I had a 5hp motor that was built
on a 15 hp frame size.

Ideas, thoughts??

Biggest problem I think would be the generating end of things.

Thank You,
Randy






The lower frequencies are more efficient but the motor size increases.
At 400 cps the size of a 1 hp 3Ø motor is one sixth of the size of the
same HP motor run at 60 cps. With the higher frequencies you need
less core material since the time of one cycle is proportionately less
and with the smaller core it will saturate in 1/400 of a second.
Proportionately 400 x a smaller flux is equivelent to 60 times
saturating a larger core for the same HP but the hysterysis and eddy
current loses go up with the higher frequency, but the core size goes
down. The weight savings on an aircraft are tremendous. The wiring on
many aircraft is 3Ø 115 volt Wye. All the lighting is fed at 115
vac.through transformers thus saving on wire size.


John

Jon Elson wrote:



F. George McDuffee wrote:

On Tue, 30 Oct 2007 09:01:36 -0500, Randy
wrote:


This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.


snip
=========
what a group!
thread hijack [sort of]

Given the increased efficiency in terms of both size and power,
how would 3 phase residential power service (in new homes) affect
power distribution cost/efficiency and the life-cycle cost of
high reactive consumption units such as residential air
conditioners and possibly refrigerators if these were 220
3-phase?

The really big advantage of a 3-phase hermetic refrigeration compressor
is it needs no starting relay. Just apply power and the motor spins up.
I doubt there is a great increase in efficiency of small 3-phase
motors over single phase. If you want REAL efficiency gains,
permanent-magnet synchronous motors run by variable frequency drives
do show large gains in efficiency. All variable-speed air
conditioners use some sort of VFD, and permanent magnet motors are now
replacing the induction motor, as they ARE more efficient.

The liklihood of the US adopting 3-phase wall outlets for all
appliances is about as high as (your favorite never-will-happen
scenario here).
There would be REAL costs to extending 3-phase power to all
residences, and putting in 3-phase meters and 3-pole breakers in the
panels. With a basement full of machine tools, I'd love it, though.
I do NOT have 3-phase power on my pole, but it is "only" a block away.

Interesting, a mate who used to work in Germany said that most houses
there had 3 phase and different floors were supplied with different
phases to balance the load. Here in the UK a house typically has 1 phase
and the phases are distributed around other houses to even the load. My
mothers house does have 3 phase wired to it though as the previous
owners built the house and said that having 3 phase wired at that time
was only a small additional cost, all the house need is a 3 phase meter
to use it as the meter is currently single phase, a small cost seeing as
the 3 phase is in place already.



I can just imagine having a 5-prong Harvey Hubbell twist lock plug on
those lamps with three bulbs and a 1-2-3 switch on them!

Jon

John G wrote:
I can just imagine having a 5-prong Harvey Hubbell twist lock plug on
those lamps with three bulbs and a 1-2-3 switch on them!

Jon

With 3 phase distribution you would not have 5-prong Harvey Hubbell
twist lock plug on your lamps.

No, it would be "abnormal", but I COULD do it if I had 3-phase
in the house! It would definitely WOW people, though.
In this country (Australia) 3 phase is available in most places but only
delivered to those homes that need it for Air con and such bigger loads.
Small things, lamps etc still run of one simple plug similar in size to
the US 120volt plug. The area served by a pole transformer or roadside
box seems to be larger than is common in the US but the single pase
homes are distributed across the three phases. Pole pig outside my house
was changed last week from 40KW to 60 KW (I think).

I just happen to be in a funny spot where it was inconvenient to
run the low voltage cable to other houses. Many of the houses
around here have a couple of them sharing a transformer. A
subdivision of really fancy ($500K - $1 million) houses have pad
mount trandformers in tasteful green camouflage for every 3
houses or so. We live on a full acre, most of the houses have
that much or more in this area.
And Gloat!! I could have 3pahse in my workshop if I needed it but a
table saw is the biggest thing I have.
OOOhhhh, pleas DON'T rub it in! Since the ready availability of
these VFDs, it is a lot less of a problem.

Jon

john wrote:


Jon Elson wrote:



F. George McDuffee wrote:

On Tue, 30 Oct 2007 09:01:36 -0500, Randy
wrote:


This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.


snip
=========
what a group! thread hijack [sort of]

Given the increased efficiency in terms of both size and power,
how would 3 phase residential power service (in new homes) affect
power distribution cost/efficiency and the life-cycle cost of
high reactive consumption units such as residential air
conditioners and possibly refrigerators if these were 220
3-phase?

The really big advantage of a 3-phase hermetic refrigeration compressor
is it needs no starting relay. Just apply power and the motor spins up.
I doubt there is a great increase in efficiency of small 3-phase
motors over single phase.

the efficiency comes with varying loads. A single phase motor is
designed to operate at a certain load, any load more or less the phase
shift to the second winding through the cap is not at optimum and will
generate more heat.

If you want REAL efficiency gains, permanent magnet
synchronous motors run by variable frequency drives do show large
gains in efficiency. All variable-speed air conditioners use some
sort of VFD, and permanent magnet motors are now replacing the
induction motor, as they ARE more efficient.

The liklihood of the US adopting 3-phase wall outlets for all
appliances is about as high as (your favorite never-will-happen
scenario here).
There would be REAL costs to extending 3-phase power to all
residences, and putting in 3-phase meters and 3-pole breakers in the
panels. With a basement full of machine tools, I'd love it, though.
I do NOT have 3-phase power on my pole, but it is "only" a block away.


I would look more to supplying houses with DC. With today's electronics
everything can easily run on DC with built in VFD's that run directly
from dc rather than first rectifying it inside the drive. The same goes
for any appliance. Using DC would make it much easier to eliminate
switching noise from vfd's and other similar devices by just adding a
couple of caps on only one circuit.

The problem with DC is that current interrupters (switches, fuses,
breakers) need to be much bigger. AC current drops to zero, 100 or 120
times per second, and this quenches any developing arc. To break a
significant current in a DC system can require quite special (read
costly) devices.

On Oct 31, 12:36 am, "
wrote:
On Oct 30, 3:17 am, bob wrote:

On Oct 30, 4:01 pm, Randy wrote:

This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,

I seem to remember reading that Westinghouse-Tesla AC was chosen over
Edison DC because the AC could be transmitted with lower power loss
over distance. So was AC more efficent at the distances it was being
transmitted at the begining of the electrical revolution?
Thanks
Karl

Thanks to everyone for clearing this up for me.
Thanks
Karl

"john" wrote: There are many things to consider including idling at a
stoplight with a gas engine while with a electric motor it is not using any
electric. Also a motor can be a braking device and put power back into the
batteries. No oil is needed for lubrication of the motor other than an
ocasional shot of grease. (clip)
^^^^^^^^^^^^^^^
John, I am well aware of the advantages of electric and hybrid cars. I am
trying to get a handle on HOW MUCH advantage they offer in terms opf air
pollution. An electric car is not totally non-polluting. The electricity
to run it comes from a power plant somewhere, connected the power grid. We
know how much CO2 is released when a pound of fuel is burned. The
comparison that needs to be made is, how much fuel does it take to run an
automotive engine, vs how much does it take in a power plant to drive it the
same distance? Some of the power fed into the grid is wasted as heat. How
much?

Leo Lichtman wrote:
"john" wrote: There are many things to consider including idling at a
stoplight with a gas engine while with a electric motor it is not using any
electric. Also a motor can be a braking device and put power back into the
batteries. No oil is needed for lubrication of the motor other than an
ocasional shot of grease. (clip)
^^^^^^^^^^^^^^^
John, I am well aware of the advantages of electric and hybrid cars. I am
trying to get a handle on HOW MUCH advantage they offer in terms opf air
pollution. An electric car is not totally non-polluting. The electricity
to run it comes from a power plant somewhere, connected the power grid. We
know how much CO2 is released when a pound of fuel is burned. The
comparison that needs to be made is, how much fuel does it take to run an
automotive engine, vs how much does it take in a power plant to drive it the
same distance? Some of the power fed into the grid is wasted as heat. How
much?

Roughly half.

According to Jon Elson :


Randy wrote:
OK, we rule out 400HZ as too high, due to the 1/4 wave length problem,
would it be worth while to go to 90 or 120HZ?

One could argue the thing forever, as the losses are almost all
engineering tradeoffs when the various components are designed.

But, it is all moot. I have no way to calculate the cost, but if the
entire generating, transmission and distribution system had to be
replaced, plus most appliances more complicated than a toaster or light
bulb, the cost would certainly be in the trillions of $.

Hmm ... the universal motors would probably still work
reasonable well -- mixers, hand-held electric drills, toolpost grinders
and the like. But most induction motors would have to be replaced, or
at least the start capacitance value changed (e.g. in single-phase
lathes and the like), or the run capacitance values (in things like my
air conditioning compressor and the associated fan, both of which use
phase-shift capacitors -- to run what I think are actually three phase
motors from single phase power.

For that matter (assuming that we are only talking about 120 Hz,
not 400 Hz) -- four-pole three-phase motors running lathes and milling
machines would probably handle the switch with only an increased speed
as a result, though two-pole ones might risk centrifugal disassembly of
the rotor. :-) For those which could handle the switch, we would
probably have to change pulleys to keep the speeds reasonable -- or to
hang a VFD between each motor and the new higher-frequency three phase,
which would at least isolate the motors from the frequency change.

I'm glad that you covered the question about insulation -- it
saves me the trouble, and makes me glad that I read the followups. :-)

As for the transmission lines, I notice that the high-tension
three phase lines every few towers appear to interchange two of the
three wires -- I guess making the equivalent of twisted pair wiring to
minimize radiation by canceling from the other phase. I suspect that
the interchanges would have to be redone to be closer together at a
higher frequency.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

David R Brooks wrote:

john wrote:


Jon Elson wrote:



F. George McDuffee wrote:

On Tue, 30 Oct 2007 09:01:36 -0500, Randy
wrote:


This group seems to have alot of electrical knowledge, sooo.....

The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.


snip
=========
what a group! thread hijack [sort of]

Given the increased efficiency in terms of both size and power,
how would 3 phase residential power service (in new homes) affect
power distribution cost/efficiency and the life-cycle cost of
high reactive consumption units such as residential air
conditioners and possibly refrigerators if these were 220
3-phase?

The really big advantage of a 3-phase hermetic refrigeration compressor
is it needs no starting relay. Just apply power and the motor spins up.
I doubt there is a great increase in efficiency of small 3-phase
motors over single phase.

the efficiency comes with varying loads. A single phase motor is
designed to operate at a certain load, any load more or less the phase
shift to the second winding through the cap is not at optimum and will
generate more heat.

If you want REAL efficiency gains, permanent magnet
synchronous motors run by variable frequency drives do show large
gains in efficiency. All variable-speed air conditioners use some
sort of VFD, and permanent magnet motors are now replacing the
induction motor, as they ARE more efficient.

The liklihood of the US adopting 3-phase wall outlets for all
appliances is about as high as (your favorite never-will-happen
scenario here).
There would be REAL costs to extending 3-phase power to all
residences, and putting in 3-phase meters and 3-pole breakers in the
panels. With a basement full of machine tools, I'd love it, though.
I do NOT have 3-phase power on my pole, but it is "only" a block away.


I would look more to supplying houses with DC. With today's electronics
everything can easily run on DC with built in VFD's that run directly
from dc rather than first rectifying it inside the drive. The same goes
for any appliance. Using DC would make it much easier to eliminate
switching noise from vfd's and other similar devices by just adding a
couple of caps on only one circuit.

The problem with DC is that current interrupters (switches, fuses,
breakers) need to be much bigger. AC current drops to zero, 100 or 120
times per second, and this quenches any developing arc. To break a
significant current in a DC system can require quite special (read
costly) devices.

Once the air is ionized DC or AC will substain an arc. An inductive load
on a DC circuit will cause arcing but a resistive load will be a lot
less. Any high voltage device is costly... especially 3 Ø.

John