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  #81   Report Post  
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Don Foreman
 
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Default Flywheel on a rotary phase convertor

On Sat, 07 Jan 2006 06:46:58 GMT, Ignoramus20351
wrote:

On Sat, 07 Jan 2006 00:21:44 -0600, Don Foreman wrote:

I must say I respect Iggy's rather consistent practice of
courteous and civil discourse.


Thank you Don. If I barge into some interesting discussion with
insults, am I really going to learn more?

i


That's up to you. I've learned some good stuff from some
insufferably arrogant assholes. Please don't read that as an implied
shot at Bob. Bob and I have corresponded for years. He ain't a bad
guy most days.

Hm, I wonder if there might be some others who have regarded me as an
insufferably arrogant asshole along the way. Oh well, **** 'em
if they can't take a joke. :)

It's not hard to ignore the skeeterbites if there are good fish to be
caught.

  #82   Report Post  
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Don Foreman
 
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Default Flywheel on a rotary phase convertor

On Fri, 6 Jan 2006 22:05:02 -0600, "Robert Swinney"
wrote:

This may be going out on a limb, and if so, I'm quite sure Don is ready with
a saw but here goes:

When I said: "Sorry, Don. The lead between the 3rd leg terminals does
not place them in
parallel with each other because it connects from one end of one winding
to
the *other* end of the other winding. "


This concept was immediatly poo-pooed by the "if its connected as a RPC,
then it is in parallel". Later, then a definition of parallel was given as:
"By this definition, if there are wires connecting each terminal of one
device to a corresponding terminal of another device, they are in
parallel -- regardless of what else might be connected to those
terminals."

Consider 2 wye motors connected as a RPC, seemingly in parallel. It appears
to me that 2 wye motors connected in parallel by the definition of
corresponding terminals, above, are not in parallel by that definition
unless the "star" or neutral points within each motor are connected by a
solid lead. Then, all corresponding points are connected.

RPC connected motors do not meet the criteria.

Kapeesh?


Poo-pooed? That connotes fluffy dismissal. I flat disagreed.

I do capish. Kapeesh indeed! Texas is obviously a long ways from
Brooklyn, Ol' Son. Roger thet, big ol' ten-four. Yer waltz ain't
quite in synch with mah foxtrot, but we ain't that fur apawrt.
See recent post. They're still topologically connected in parallel
per conventional definition, but I can see how one might regard them
as functionally in series, particuarly if neutral floats as it must
in an RPC.

In any case, my chainsaws are put away for the MN winter and I'm way
too lazy to pull a Swedesaw anymore.

Bob (getting tired of all this)Swinney


What, time for your nap? (ducking.....)
  #83   Report Post  
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Robert Swinney
 
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Default Flywheel on a rotary phase convertor

That is really doubtful, Iggy. You seem to barge into discussions just to
see your name in print. Maybe, I am wrong.

Bob Swinney
"Ignoramus20351" wrote in message
...
On Sat, 07 Jan 2006 00:21:44 -0600, Don Foreman
wrote:

I must say I respect Iggy's rather consistent practice of
courteous and civil discourse.


Thank you Don. If I barge into some interesting discussion with
insults, am I really going to learn more?

i



  #84   Report Post  
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Robert Swinney
 
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Default Flywheel on a rotary phase convertor

Don, now you are beginning to get the idea, my poor teaching technique not
withstanding. Take another look at your line below where you say, "but I
can see how one might regard them
as functionally in series, particuarly if neutral floats as it must
in an RPC." Yes, neutral *must* float in a RPC but it is still my
contention that the idler and load of a RPC are not truly connected in
parallel unless there is a solid connection between the 2 respective
neutral points. That satisfies the definiton of corresponding points being
connected, doesn't it?? Can we call your special definition of parallel
as applied to RPC's, maybe, huh, "quasi parallel"?


Bear with me for one more moment, please (courteously).

We have a 3-phase source and wish to connect n numbers of 3-phase loads
across it, in parallel. You'd have to agree there would be a "phase"
connected to each of the 3 input terminals (nodes ?) of the loads. In other
words, the connections looking into the loads would be in parallel, and
connected across the 3-phase source, would they not? OK, if you're with me
(I'm a poor teacher, I know), now disconnect the 3-phase source and look at
the loads, say, call one of them an idler and the rest of them loads. Now
the idler and load are not truly in parallel, by definition, because the
lead between star points (neutrals) is not there.

Now consider, a RPC (rotary phase converter) connected as in what I call
"quasi parallel" for want of a better description. You might agree, the
idler and load are not in true parallel because the solid lead between
neutrals is missing.
But they are connected as a RPC must be. Current from L1 to L2 "sees" the
RPC as a series load. Current flow via the 3rd leg and the 2 line legs into
the load, as connected in RPC fashion, results in circulating currents
throughout that appear to the load as 3 phases. (emulation?) As you've
said elsewhere, a RPC would not be possible if the neutrals were connected
as in what I deem to be a true parallel connection. Therefore, it seems
that in a RPC, the idler and load are not truly connected in parallel.

Bob Swinney


"Don Foreman" wrote in message
...
On Fri, 6 Jan 2006 22:05:02 -0600, "Robert Swinney"
wrote:

This may be going out on a limb, and if so, I'm quite sure Don is ready
with
a saw but here goes:

When I said: "Sorry, Don. The lead between the 3rd leg terminals does
not place them in
parallel with each other because it connects from one end of one winding
to
the *other* end of the other winding. "


This concept was immediatly poo-pooed by the "if its connected as a RPC,
then it is in parallel". Later, then a definition of parallel was given
as:
"By this definition, if there are wires connecting each terminal of one
device to a corresponding terminal of another device, they are in
parallel -- regardless of what else might be connected to those
terminals."

Consider 2 wye motors connected as a RPC, seemingly in parallel. It
appears
to me that 2 wye motors connected in parallel by the definition of
corresponding terminals, above, are not in parallel by that definition
unless the "star" or neutral points within each motor are connected by a
solid lead. Then, all corresponding points are connected.

RPC connected motors do not meet the criteria.

Kapeesh?


Poo-pooed? That connotes fluffy dismissal. I flat disagreed.

I do capish. Kapeesh indeed! Texas is obviously a long ways from
Brooklyn, Ol' Son. Roger thet, big ol' ten-four. Yer waltz ain't
quite in synch with mah foxtrot, but we ain't that fur apawrt.
See recent post. They're still topologically connected in parallel
per conventional definition,
In any case, my chainsaws are put away for the MN winter and I'm way
too lazy to pull a Swedesaw anymore.

Bob (getting tired of all this)Swinney


What, time for your nap? (ducking.....)



  #85   Report Post  
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Robert Swinney
 
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Default Flywheel on a rotary phase convertor

Don, in as much as you've railed against some of the definitions I used in
trying to explain my understanding of the RPC, I offer the following.

Generators and consumers: Motor windings, (elements of a RPC for example)
consume energy and give it up as torque. Those same windings also generate
energy in the form of counter EMF. In essense current is flowing in 2
directions through the winding. In electronic parlance, you might say there
is both a voltage rise and a voltage fall. I have sense and education
enough to know average current flow in an AC circuit is zero, but you have
tap danced all around the point, by even mentioning it. (Patronizingly,
perhaps)

Aggregate current: That which flows in a network as a result of everything
going on in the network.

Convoluted current: In a manner of speaking, that current which flows in
the load side of a RPC.

BTW much of the definition you question was duly addressed in the little
paper I sent you awhile back. At the time your comments were to the effect
the paper was well researched, well written, etc.

Bob Swinney




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Default Flywheel on a rotary phase convertor

On Wed, 04 Jan 2006 11:04:20 -0600, Don Foreman
wrote:

On Tue, 3 Jan 2006 23:14:07 -0600, "Don Young"
wrote:

Since the running idler and load motors are directly connected in parallel,
wouldn't plug reversing with identical motors and no mechanical load have an
equal chance of reversing either motor? When running free, it seems to me
that either motor could be considered to be the source or load for the third
phase leg. I tend to believe that the idler requires more mechanical inertia
than the load to maintain the best functioning.


Interesting! The relative impedances are also important here. The
larger motor with lower impedance (and probably higher inertia) will
govern. Look at the terminal voltage where the two third legs are
connected. If the motors were perfectly matched, their effects would
cancel and this terminal voltage would be zero. If they are not
matched, the voltage (phase) of that terminal will be determined by
the motor with the lower impedance, and the phase of this voltage
determines (or indicates) the direction in which both motors turn.

If an induction motor does not "generate", is induced counter EMF imaginary
and the use of common induction motors as generators impossible? There are
many ways to understand and describe how things work and I like to think of
the RPC as simply a running induction motor with the magnetized rotor
inducing EMF not only into the line energized windings (counter EMF) but
also into the unenergized and phase displaced windings.


Right, up to here.

Note that, when
disconnected and still turning, an induction motor still has voltage across
its windings and loading this voltage with "braking" resistors will
mechanically load the rotor.


Only if the rotor has some significant permanent magnetism -- not
usually the case.





A squirrel cage motor DOES generate a back EMF and will continue
to do so for several revolutions after all power has been removed
even if it has zero permanent magnetism.

In the case of a 2 pole motor, at the instant of disconection,
the induced circulating currents in the short circuited rotor
inductance provide a diametrical NS field which decays at at the
rotor L/R rate for several tenths of a second. The voltage
generated by this decaying field is is easily observed with an
oscilloscope - the initial voltage is close to full supply
voltage.

Jim


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Don Foreman
 
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Default Flywheel on a rotary phase convertor

On Sat, 7 Jan 2006 17:21:30 -0600, "Robert Swinney"
wrote:

Don, now you are beginning to get the idea, my poor teaching technique not
withstanding. Take another look at your line below where you say, "but I
can see how one might regard them
as functionally in series, particuarly if neutral floats as it must
in an RPC." Yes, neutral *must* float in a RPC but it is still my
contention that the idler and load of a RPC are not truly connected in
parallel unless there is a solid connection between the 2 respective
neutral points. That satisfies the definiton of corresponding points being
connected, doesn't it?? Can we call your special definition of parallel
as applied to RPC's, maybe, huh, "quasi parallel"?


Bear with me for one more moment, please (courteously).

We have a 3-phase source and wish to connect n numbers of 3-phase loads
across it, in parallel. You'd have to agree there would be a "phase"
connected to each of the 3 input terminals (nodes ?) of the loads. In other
words, the connections looking into the loads would be in parallel, and
connected across the 3-phase source, would they not? OK, if you're with me
(I'm a poor teacher, I know), now disconnect the 3-phase source and look at
the loads, say, call one of them an idler and the rest of them loads. Now
the idler and load are not truly in parallel, by definition, because the
lead between star points (neutrals) is not there.


It has finally occurred to me that the neutral is what's causing the
confusion.

Nearly all three phase machines are three-terminal devices. There
may be a physical neutral in a Y-connected machine, but it's rarely
used. We agree that the neutrals would not be connected with
Y-connected idlers and loads. If they were delta-connected, there'd
be no neutrals to connect.

Consider a delta-connected idler and load(s). There are wires
connecting each terminal of the idler to corresponding terminals on
each load. The machines are connected in parallel. Each winding of
the idler is in parallel with a corresponding winding in the load(s).
There are only three nodes in this circuit. Now connect mains
to two of the three terminals. We haven't broken any connections,
so the idler and load(s) are still connected in parallel, each
winding in the idler is still in parallel with a corresponding winding
in the load(s). There are still only three nodes in the circuit,
with power fed to two of them. The power line is connected across
one winding and one phase. We might not know what the potentials
across the other two phases might be, but it's clear that the
voltages across corresponding phases of the two machines are the
same. They're in parallel.

Now consider Y-connected idler and load(s). The winding not tied to
mains on the idler is in series with the corresponding winding on the
load. There are still 3 nodes, the two that mains are connected
to and the one between the two third windings.

Are these machines still in parallel? I assert that they are.
The confusion comes from looking at those windings that are connected
in series and referring to neutral.

In a Y-connected machine, a winding is not a phase. A phase is from
terminal to terminal whether the windings within are delta or Y
connected.

Each phase in a Y connected machine has two series-connected windings
from one terminal to the other. Each winding is a member of two
adjacent phases, and each phase has two windings in series. If you
draw a circle around each *phase* (not winding) of a Y-connected
machine, from terminal to terminal, you see that the idler phases are
indeed connected in parallel with the load phases, whether or not
there are any power lines connected. Let's leave the power off for a
moment. You see not just one, but three loops of four windings in
series -- two idler windings and two load windings. But each phase
in the idler is still in parallel with it's corresponding phase in
the load.

Now connect real threephase power to the terminals. I think you've
agreed that in this situation the idler and load are still in
parallel. Phase currents are currents into a terminal, and are the
same as line currents when the system is driven with threephase
power. Each winding has two phase currents flowing thru it, so the
net current in any winding is the vector sum of these two currents.

Now remove the threephase feed and connect a single phase power line
to two terminals, or one phase, and try to figure out what's going on
in the other two phases with the terminal between those two phases (on
both idler and load) connected to nothing else. We see two
windings in series between neutral of idler and neutral of load. But
the same situation is true with the other windings! You can go from
neutral to neutral via three routes, each thru one winding in the
idler and a corresponding winding in the load. If you drew circles
around the *phases* (pairs of windings) before, you'll see that each
phase in the idler is still connected in parallel with a corresponding
phase in the load.


It's tempting to think of a phase as line to neutral thru just one
winding, because that looks easier to understand. But it's
incorrect unless the neutrals are actually connected because the
voltages from the third node to the other two nodes, the other two
phase voltages, do not depend only on the windings connected to the
third node. Similarly, the current thru the wire connecting the third
nodes does not depend solely on the voltage from third nodes to their
respective neutrals unless those neutrals are tied together or
otherwise held at some known potential from one neutral to the other.








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Don Foreman
 
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Default Flywheel on a rotary phase convertor

On Sat, 7 Jan 2006 18:11:10 -0600, "Robert Swinney"
wrote:

Don, in as much as you've railed against some of the definitions I used in
trying to explain my understanding of the RPC, I offer the following.

Generators and consumers: Motor windings, (elements of a RPC for example)
consume energy and give it up as torque. Those same windings also generate
energy in the form of counter EMF. In essense current is flowing in 2
directions through the winding.


So my ammeter needs two needles?

In electronic parlance, you might say there
is both a voltage rise and a voltage fall.


Whoa! My voltmeter needs two needles too?

Just kidding, Bob. I know what you mean: sometimes its easier to
think of voltages and currents as vector sums of component voltages
and currents,

I have sense and education
enough to know average current flow in an AC circuit is zero, but you have
tap danced all around the point, by even mentioning it. (Patronizingly,
perhaps)


I know you do. In the following sentence I suggested that perhaps
you meant power flow which made sense in context.

Aggregate current: That which flows in a network as a result of everything
going on in the network.


Well, in that context the aggregate current in a balanced threephase
system is zero though the currents in various branches are certainly
non-zero.

Convoluted current: In a manner of speaking, that current which flows in
the load side of a RPC.

BTW much of the definition you question was duly addressed in the little
paper I sent you awhile back. At the time your comments were to the effect
the paper was well researched, well written, etc.


I didn't recall the definitions, but I do recall the comment and I
wouldn't have said it if I didn't mean it. That must have been two
computers ago because I can't find your writeup in this machine or
the last one.


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Don Foreman
 
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Default Flywheel on a rotary phase convertor

On Sat, 07 Jan 2006 22:39:02 -0600, Don Foreman
wrote:

Each winding has two phase currents flowing thru it, so the
net current in any winding is the vector sum of these two currents.


True for delta connection, not for Y. In a Y each phase voltage is
the vector sum of two winding voltages.


  #91   Report Post  
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Default Flywheel on a rotary phase convertor

Unfortunately when I learned about electric motors, I was taught that
an electric motor GENERATES a back emf because there is a magnetic
field which is cutting conductors.
So my view of say a motor is somewhat different from yours. If you
have an electric motor and you increase the load, the speed drops
slightly, the back emf drops, and the current drawn goes up. If you
decrease the load, the speed increases, the back emf goes up, and the
current drawn goes down. If you decrease the load until it is
negative, ( ie mechanical power is being applied to the motor ) , the
back emf goes up until it is more than the applied emf, and the current
drawn goes negative. That is current goes into the mains. That is an
induction generator. Works whether the motor is a single phase motor
or a three phase motor.

If you have three phase motor and get it running on single phase power,
things are a bit more complicated. But you still get a back emf
generated, and on the terminal that is unconnected to the power there
is a back emf, but there is no forward emf. So you can draw current
from that terminal.

Consider this. If you get a three phase motor running on single phase,
you can use it to produce mechanical power. So the way I think of a
RPC is as a three phase motor running on single phase, with some of the
mechanical power being used to drive an induction generator.

I am a bit confused by your statement about overdrive from the AC
mains. Mostly by the word "overdrive". As I see it a RPC is connected
to the AC mains, so I think it would be excited by overdrive from the
AC mains. However an induction generator does not have to be connected
to the AC mains in order to work. You can use a gasolene engine to
drive an induction motor and generate electric power with no connection
to the mains. It just is just sensitive to the amount of power you
draw and does not regulate the voltage at all well.

To further confuse you, you can build a very nice RPC by using a single
phase motor to drive a three phase motor via a belt drive adjusted so
mechanical power is going into the three phase motor. Now if you apply
single phase power to the three phase motor, it will act as a three
phase induction generator. If you do this use an adjustable pulley on
one of the motors and measure the current drawn by the single phase
motor. Adjust the pulleys so the current drawn by the single phase
motor is close to but below rated nameplate current when the RPC is
driving whatever load you are going to drive. As you might suspect
such a RPC produces voltages that are very closely balanced.

So I still analyse a RPC as an induction generator. Trying to analyse
it as some sort of transformer, I have a lot of problems figuring out
one ever gets anything that is not still in phase with the original
single phase mains. And how one calculates what the phase angle is
going to be.

I amy not be able to convince you that this is a valid way to analyse
RPC's, but it works for me.


Dan




Robert Swinney wrote:
Dan sez:
" In my opinion you need to realize that a RPC is an induction generator."

Dan, I know you have some experience with induction generators so I'll ask
you to respectfully consider that:

An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney

wrote in message
oups.com...

Robert Swinney wrote:
IMO, you need to lose the thinking of a RPC as being a form of generator.

Bob Swinney




As far as flywheels are concerned, a flywheel will keep the slip angle
from changing as quickly. So a RPC without a flywheel will draw power
from the mains more quickly when the load is increased. Score points
for that side. On the other hand, a RPC with a flywheel will draw
power from the flywheel when the load is increased as well as from the
mains. So score points for the other side.

In the real world, it does not make much difference as the change in
speed of the RPC should be slight, and therefore only a small amount of
power can be drawn from the flywheel. Having a flywheel would help
with an undersized RPC when the load motor is plugged.


Dan


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Default Flywheel on a rotary phase convertor

On Wed, 04 Jan 2006 21:59:47 -0600, Don Foreman
wrote:

On 4 Jan 2006 13:22:13 -0800, jim rozen
wrote:



When the converter is operating of course there is one special lead
that breaks the symmetry - it's missing the line connection. An
electrican would say that the absence of that line connection does
not change the fact the two sets of windings are in parallel. A
EE looks at the entire network as a system, including the incoming
power. He says parallel means all nodes have the same number of
connections.

Jim


He does? In circuit analysis, a set of two-terminal networks are
regarded as "in parallel" if they are each connected to the same pair
of nodes so the voltage across them is identically the same.
Similarly, a set of n-terminal networks are in parallel if they are
connected to the same set of n nodes so the various inter-terminal
voltages on each n-terminal network are identically the same for
corresponding pairs of terminals. This is regardless of whatever
else might be connected to, between or among those nodes and
regardless of any external symmetry or lack thereof. Some nodes may
well have more connections than other.

By this definition, if there are wires connecting each terminal of
one device to a corresponding terminal of another device, they
are in parallel -- regardless of what else might be connected to those
terminals.



Just to stir things up a bit further I register my support for
BOTH the parallel and non parallel camps - it just depends on how
you look at the circuit operation.

If we regard the idler plus load motors as two connected
passive three terminal networks the there can be no doubt that
this is a straightforward parallell connection. No playing with
words on the way any further conections are made (e.g single
phase power input) can alter this.

However,when the motors have rotating rotors, BOTH motors
accept input power on two of their terminals and BOTH try to
deliver output power to the third linked phantom phase
connection.

The direction of the power flow through the phantom phase
link then depends on the relative mechanical loading on the two
rotors. In the two limiting conditions of both motors idling or
both motors loaded to the same fraction of their rated HP, each
motor is self sufficient and little or no third phase power flows
through the link. In the normal case of one idling and one
loaded, the power flow is from idler to load motor.

It is equally valid to regard this current as a circulating
current within a parallel connected system or as the current
developed in the series connection of an idler generator to its
load motor


Jim

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jim rozen
 
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Default Flywheel on a rotary phase convertor

In article ,
says...

The direction of the power flow through the phantom phase
link then depends on the relative mechanical loading on the two
rotors. In the two limiting conditions of both motors idling or
both motors loaded to the same fraction of their rated HP, each
motor is self sufficient and little or no third phase power flows
through the link.


They don't really have to both be loaded to the same fraction,
it only has to be a very small loading in each case. Then you
see no current flowing on the third line, IF there are no
tuning capacitors, as in my system. Then a mechanical load
on the machine causes the current in that line to spike upwards.

The current in the third leg is *not* zero under all idling
conditions I believe if one installs tuning capacitors though.
Anyway that's my understanding as balancing those currents
seems to be one of the 'figures of merit' for tuining a
converter like that, aside from voltage balancing.

By current here I mean all currents of course, reactive and real.

The currents I see on my L1, L2 connections to my lathe
are mostly out-of-phase. They're not real, they don't represent
real work being done. The current flowing in the generated L3
connection only becomes noticeable when there's mechanical load
so I suspect it is mostly in-phase by its nature.

When I load the lathe, the L1, L2 currents shift in phase towards
real power, and the L3 one simply grows.

Jim


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Robert Swinney wrote:
Dan sez:
" In my opinion you need to realize that a RPC is an induction generator."

Dan, I know you have some experience with induction generators so I'll ask
you to respectfully consider that:

An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney



I am sorry but thinking of RPC's the way I do just seems to make sense.
When I learned about motors, I learned that they generate a back emf
because they have a rotating magnetic field and conductors that cut the
magnetic field. And if you increase the load on a motor, it slows
slightly and the back emf drops and the current rises. And if you
decrease the load the back emf increases and the current decreases.
Now consider decreasing the load even more, so that the load is
negative. ( putting mechanical power into the motor trying to make it
run faster than synchronous speed ) The back emf increases and the
current goes negative. That is current is being supplied by the motor
to the mains. So as I see it a motor can work from locked rotor to
being driven. ( Don't try locked rotor for very long unless you have a
AC servo motor ) Same physics for all cases.

Now this happens whether the motor is a single phase motor or a three
phase motor.

Now what happens when you have a three phase motor and run it on just
one phase?
After you get it started, it will run on single phase power. You still
have a rotating magnetic field, and windings for three phases. So the
rotating magnetic field generates a back emf in all the windings. So
you consume power from the single phase, but generate three phase
power.

Incidently you do not have to have an induction motor connected to the
mains in order for it to work as an induction generator. It just will
not work with a large variety of loads.

Another by the way. One of the better ways to make a RPC is to connect
a single phase motor to a three phase motor using an adjustable belt
drive. You monitor the current going into the single phase motor and
adjust the drive so the current is at or below name plate current when
driving the three phase load. Recommended ( by me ) for driving three
phase machines as surface grinders that are sensitive to unbalanced
three phase power.
In that case it is pretty obvious that you have a three phase induction
generator being driven by a single phase motor.

You may find this way of analysing a RPC as weird, but it works for me.
I have problems understanding RPC's as transfomers that produce a
voltage that is not in phase with the input voltage. And it lets me
think about how a flywheel would affect a RPC.


Dan



  #96   Report Post  
Posted to rec.crafts.metalworking
Christopher Tidy
 
Posts: n/a
Default Flywheel on a rotary phase convertor

To offer a little food for thought on the original topic, here's a
picture of the rotor from the motor which I'm proposing to use as an idler:

http://www.mythic-beasts.com/~cdt22/lse_rotor.jpg

I dismantled the motor to give it a good clean, repaint the rusty bits
and check the bearings. That's a 10" ratchet in the picture and the
rotor weighs 30 lbs, so it's pretty sizeable. Gunner and Jim may well be
right when they suggest that the rotor itself will be plenty adequate as
a flywheel.

By the way, the motor is rated at 2.5 hp at 940 rpm.

Best wishes,

Chris

  #97   Report Post  
Posted to rec.crafts.metalworking
 
Posts: n/a
Default Flywheel on a rotary phase convertor


Robert Swinney wrote:

An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney


In school I was taught that a motor generates a back emf because there
is a rotating magnetic field whose flux cuts the windings in the motor.
When a motor is running and you increase the load, the motor slows
slightly and the back emf drops so the net voltage increases causing
the current to increase. If you decrease the load the speed increases,
the back emf rises, net voltage drops and current drops. If you
decrease the load until it is negative, the back emf increases until it
is above the input emf, and the current goes negative. That is current
flows from the motor to the mains.

Now this works for both single phase and three phase motors from locked
rotor to being an induction generator. ( Don't try locked rotor for
very long unless you have an AC servo motor ) It even works for a
three phase motor running on just one phase. In that case the motor
consumes single phase power, but still generates back emf in all
windings. Which results in generating three phase power. Because the
back emf is less than the mains voltage, the voltage is not balanced.
But this can be improved by either adding capacitors.

So now you can at least see how I analyse RPC's. It isn't the only
way, but it works for me and maybe Don Young and Pentagrid. ( Speak up
if you disagree ).

As an aside issue, an induction generator will work without being
connected to the mains.
You can google and find some references to this as regards using an
induction motor driven by a small gas engine for operating ham field
stations. It is load sensitve.

And as another aside, you can build a fine RPC using a single phase
motor connected to a three phase motor via a adjustable belt drive. Two
terminals of the three phase motor are also connected to the mains. You
adjust the belt drive so the current drawn by the single phase motor is
at or below name plate rated current while the RPC is supplying three
phase power to whatever needs three phase power. I happen to think
this approach is good for things as surface grinders where good three
phase power is needed.


Dan

  #98   Report Post  
Posted to rec.crafts.metalworking
DoN. Nichols
 
Posts: n/a
Default Flywheel on a rotary phase convertor

According to Don Foreman :

[ ... ]

It has finally occurred to me that the neutral is what's causing the
confusion.

Nearly all three phase machines are three-terminal devices. There
may be a physical neutral in a Y-connected machine, but it's rarely
used. We agree that the neutrals would not be connected with
Y-connected idlers and loads. If they were delta-connected, there'd
be no neutrals to connect.


I've been wondering why nobody has considered the motors as
black-box devices, with only the three terminals leading to the outside
available for consideration.

Under those conditions, there is really no way to tell a Wye
from a Delta connected motor, if you allow that the windings could be
special to make them work from the same voltages.

And -- you could analyze the circuits from that basis (it is
commonly done when sufficient information about the internals is not
available, or when the details about the internals don't really *matter*
to the functionality.

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 ---
  #99   Report Post  
Posted to rec.crafts.metalworking
 
Posts: n/a
Default Flywheel on a rotary phase convertor

I hope this message actually gets posted. My last two attempts failed.
I am hoping the problem has something to do with cookies and posting
through Google.

When I learned about motors, I was taught that a motor generates a back
emf because there is a rotating magnetic field cutting the conductors
in the winding. When a motor is running the back emf is close the
applied voltage and the amount of current drawn is proportional to the
net emf / the inductance and resistance of the winding. Increase the
load on the motor and the speed decreases, back emf goes down, net
voltage goes up, and current goes up. Decrease the load and the speed
increases, net voltage goes down and current goes down. Decrease the
load some more until it is negative ( mechanical power going into the
motor ) speed increases, net voltage goes negative ( back emf is
larger that applied voltage ) and the current goes negative ( power
goes into the mains ).

This works from locked rotor to induction generator for single phase
and three phase motors. Just don't try the locked rotor for very long
unless you have an AC servo motor.

Now when you have a three phase motor running on single phase power, it
still works. A back emf is generated that keeps the net voltage across
the terminal connected to the mains from being very large. But you
also have a back emf generated in the windings that connect to the
terminal that is not connected to the mains. Not quite as large as the
emf from the mains, but nearly as large. So you have single phase
power being consumed and three phase power being generated.

This may not be the only way to analyse a RPC, but it works for me, and
I think it works for Don Young and Pentagrid. Speak up if you
disagree.

A couple of aside issues. An induction generator will work without
being connected to the mains. Google enough and you will find some web
sites that talk about using an induction motor and a lawn mower type
engine to power field ham radio stations. Such a generator is load
sensitive.

Also a rather nice RPC can be made using a single phase motor to drive
a three phase motor using an adjustable belt drive. Both motors are
connected to the mains and the belt drive adjusted so the current to
the single phase motor is at or below the nameplate current when
supplying three phase power to the load. I think this type of RPC will
supply three phase power that is more balanced and therefore suitable
to run things as surface grinders that are sensitive to harmonics in
the power.

Dan


Robert Swinney wrote:


An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney


  #100   Report Post  
Posted to rec.crafts.metalworking
 
Posts: n/a
Default Flywheel on a rotary phase convertor

I hope this message actually gets posted. My last two attempts failed.
I am hoping the problem has something to do with cookies and posting
through Google.

When I learned about motors, I was taught that a motor generates a back
emf because there is a rotating magnetic field cutting the conductors
in the winding. When a motor is running the back emf is close the
applied voltage and the amount of current drawn is proportional to the
net emf / the inductance and resistance of the winding. Increase the
load on the motor and the speed decreases, back emf goes down, net
voltage goes up, and current goes up. Decrease the load and the speed
increases, net voltage goes down and current goes down. Decrease the
load some more until it is negative ( mechanical power going into the
motor ) speed increases, net voltage goes negative ( back emf is
larger that applied voltage ) and the current goes negative ( power
goes into the mains ).

This works from locked rotor to induction generator for single phase
and three phase motors. Just don't try the locked rotor for very long
unless you have an AC servo motor.

Now when you have a three phase motor running on single phase power, it
still works. A back emf is generated that keeps the net voltage across
the terminal connected to the mains from being very large. But you
also have a back emf generated in the windings that connect to the
terminal that is not connected to the mains. Not quite as large as the
emf from the mains, but nearly as large. So you have single phase
power being consumed and three phase power being generated.

This may not be the only way to analyse a RPC, but it works for me, and
I think it works for Don Young and Pentagrid. Speak up if you
disagree.

A couple of aside issues. An induction generator will work without
being connected to the mains. Google enough and you will find some web
sites that talk about using an induction motor and a lawn mower type
engine to power field ham radio stations. Such a generator is load
sensitive.

Also a rather nice RPC can be made using a single phase motor to drive
a three phase motor using an adjustable belt drive. Both motors are
connected to the mains and the belt drive adjusted so the current to
the single phase motor is at or below the nameplate current when
supplying three phase power to the load. I think this type of RPC will
supply three phase power that is more balanced and therefore suitable
to run things as surface grinders that are sensitive to harmonics in
the power.

Dan


Robert Swinney wrote:


An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney




  #101   Report Post  
Posted to rec.crafts.metalworking
 
Posts: n/a
Default Flywheel on a rotary phase convertor

I hope this message actually gets posted. My last two attempts failed.
I am hoping the problem has something to do with cookies and posting
through Google.

When I learned about motors, I was taught that a motor generates a back
emf because there is a rotating magnetic field cutting the conductors
in the winding. When a motor is running the back emf is close the
applied voltage and the amount of current drawn is proportional to the
net emf / the inductance and resistance of the winding. Increase the
load on the motor and the speed decreases, back emf goes down, net
voltage goes up, and current goes up. Decrease the load and the speed
increases, net voltage goes down and current goes down. Decrease the
load some more until it is negative ( mechanical power going into the
motor ) speed increases, net voltage goes negative ( back emf is
larger that applied voltage ) and the current goes negative ( power
goes into the mains ).

This works from locked rotor to induction generator for single phase
and three phase motors. Just don't try the locked rotor for very long
unless you have an AC servo motor.

Now when you have a three phase motor running on single phase power, it
still works. A back emf is generated that keeps the net voltage across
the terminal connected to the mains from being very large. But you
also have a back emf generated in the windings that connect to the
terminal that is not connected to the mains. Not quite as large as the
emf from the mains, but nearly as large. So you have single phase
power being consumed and three phase power being generated.

This may not be the only way to analyse a RPC, but it works for me, and
I think it works for Don Young and Pentagrid. Speak up if you
disagree.

A couple of aside issues. An induction generator will work without
being connected to the mains. Google enough and you will find some web
sites that talk about using an induction motor and a lawn mower type
engine to power field ham radio stations. Such a generator is load
sensitive.

Also a rather nice RPC can be made using a single phase motor to drive
a three phase motor using an adjustable belt drive. Both motors are
connected to the mains and the belt drive adjusted so the current to
the single phase motor is at or below the nameplate current when
supplying three phase power to the load. I think this type of RPC will
supply three phase power that is more balanced and therefore suitable
to run things as surface grinders that are sensitive to harmonics in
the power.

Dan


Robert Swinney wrote:


An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney


  #102   Report Post  
Posted to rec.crafts.metalworking
 
Posts: n/a
Default Flywheel on a rotary phase convertor

I hope this message actually gets posted. My last two attempts failed.
I am hoping the problem has something to do with cookies and posting
through Google.

When I learned about motors, I was taught that a motor generates a back
emf because there is a rotating magnetic field cutting the conductors
in the winding. When a motor is running the back emf is close the
applied voltage and the amount of current drawn is proportional to the
net emf / the inductance and resistance of the winding. Increase the
load on the motor and the speed decreases, back emf goes down, net
voltage goes up, and current goes up. Decrease the load and the speed
increases, net voltage goes down and current goes down. Decrease the
load some more until it is negative ( mechanical power going into the
motor ) speed increases, net voltage goes negative ( back emf is
larger that applied voltage ) and the current goes negative ( power
goes into the mains ).

This works from locked rotor to induction generator for single phase
and three phase motors. Just don't try the locked rotor for very long
unless you have an AC servo motor.

Now when you have a three phase motor running on single phase power, it
still works. A back emf is generated that keeps the net voltage across
the terminal connected to the mains from being very large. But you
also have a back emf generated in the windings that connect to the
terminal that is not connected to the mains. Not quite as large as the
emf from the mains, but nearly as large. So you have single phase
power being consumed and three phase power being generated.

This may not be the only way to analyse a RPC, but it works for me, and
I think it works for Don Young and Pentagrid. Speak up if you
disagree.

A couple of aside issues. An induction generator will work without
being connected to the mains. Google enough and you will find some web
sites that talk about using an induction motor and a lawn mower type
engine to power field ham radio stations. Such a generator is load
sensitive.

Also a rather nice RPC can be made using a single phase motor to drive
a three phase motor using an adjustable belt drive. Both motors are
connected to the mains and the belt drive adjusted so the current to
the single phase motor is at or below the nameplate current when
supplying three phase power to the load. I think this type of RPC will
supply three phase power that is more balanced and therefore suitable
to run things as surface grinders that are sensitive to harmonics in
the power.

Dan


Robert Swinney wrote:


An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney


  #103   Report Post  
Posted to rec.crafts.metalworking
 
Posts: n/a
Default Flywheel on a rotary phase convertor

I hope this message actually gets posted. My last two attempts failed.
I am hoping the problem has something to do with cookies and posting
through Google.

When I learned about motors, I was taught that a motor generates a back
emf because there is a rotating magnetic field cutting the conductors
in the winding. When a motor is running the back emf is close the
applied voltage and the amount of current drawn is proportional to the
net emf / the inductance and resistance of the winding. Increase the
load on the motor and the speed decreases, back emf goes down, net
voltage goes up, and current goes up. Decrease the load and the speed
increases, net voltage goes down and current goes down. Decrease the
load some more until it is negative ( mechanical power going into the
motor ) speed increases, net voltage goes negative ( back emf is
larger that applied voltage ) and the current goes negative ( power
goes into the mains ).

This works from locked rotor to induction generator for single phase
and three phase motors. Just don't try the locked rotor for very long
unless you have an AC servo motor.

Now when you have a three phase motor running on single phase power, it
still works. A back emf is generated that keeps the net voltage across
the terminal connected to the mains from being very large. But you
also have a back emf generated in the windings that connect to the
terminal that is not connected to the mains. Not quite as large as the
emf from the mains, but nearly as large. So you have single phase
power being consumed and three phase power being generated.

This may not be the only way to analyse a RPC, but it works for me, and
I think it works for Don Young and Pentagrid. Speak up if you
disagree.

A couple of aside issues. An induction generator will work without
being connected to the mains. Google enough and you will find some web
sites that talk about using an induction motor and a lawn mower type
engine to power field ham radio stations. Such a generator is load
sensitive.

Also a rather nice RPC can be made using a single phase motor to drive
a three phase motor using an adjustable belt drive. Both motors are
connected to the mains and the belt drive adjusted so the current to
the single phase motor is at or below the nameplate current when
supplying three phase power to the load. I think this type of RPC will
supply three phase power that is more balanced and therefore suitable
to run things as surface grinders that are sensitive to harmonics in
the power.

Dan


Robert Swinney wrote:


An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney


  #104   Report Post  
Posted to rec.crafts.metalworking
 
Posts: n/a
Default Flywheel on a rotary phase convertor

I hope this message actually gets posted. My last two attempts failed.
I am hoping the problem has something to do with cookies and posting
through Google.

When I learned about motors, I was taught that a motor generates a back
emf because there is a rotating magnetic field cutting the conductors
in the winding. When a motor is running the back emf is close the
applied voltage and the amount of current drawn is proportional to the
net emf / the inductance and resistance of the winding. Increase the
load on the motor and the speed decreases, back emf goes down, net
voltage goes up, and current goes up. Decrease the load and the speed
increases, net voltage goes down and current goes down. Decrease the
load some more until it is negative ( mechanical power going into the
motor ) speed increases, net voltage goes negative ( back emf is
larger that applied voltage ) and the current goes negative ( power
goes into the mains ).

This works from locked rotor to induction generator for single phase
and three phase motors. Just don't try the locked rotor for very long
unless you have an AC servo motor.

Now when you have a three phase motor running on single phase power, it
still works. A back emf is generated that keeps the net voltage across
the terminal connected to the mains from being very large. But you
also have a back emf generated in the windings that connect to the
terminal that is not connected to the mains. Not quite as large as the
emf from the mains, but nearly as large. So you have single phase
power being consumed and three phase power being generated.

This may not be the only way to analyse a RPC, but it works for me, and
I think it works for Don Young and Pentagrid. Speak up if you
disagree.

A couple of aside issues. An induction generator will work without
being connected to the mains. Google enough and you will find some web
sites that talk about using an induction motor and a lawn mower type
engine to power field ham radio stations. Such a generator is load
sensitive.

Also a rather nice RPC can be made using a single phase motor to drive
a three phase motor using an adjustable belt drive. Both motors are
connected to the mains and the belt drive adjusted so the current to
the single phase motor is at or below the nameplate current when
supplying three phase power to the load. I think this type of RPC will
supply three phase power that is more balanced and therefore suitable
to run things as surface grinders that are sensitive to harmonics in
the power.

Dan


Robert Swinney wrote:


An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney


  #105   Report Post  
Posted to rec.crafts.metalworking
jim rozen
 
Posts: n/a
Default Flywheel on a rotary phase convertor

In article .com, DoN. Nichols
says...

I've been wondering why nobody has considered the motors as
black-box devices, with only the three terminals leading to the outside
available for consideration.


Basically everyone one does. The fun starts when you hook the
three black box wires up to something else!

Any efforts to explain rotary converters that invoke currents flowing
from the motor's 'neutral' are doomed to failure I would say.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================


  #107   Report Post  
Posted to rec.crafts.metalworking
Robert Swinney
 
Posts: n/a
Default Flywheel on a rotary phase convertor

Wow, Dan! Nine posts. I am flattered (Really !) you went to such trouble
to share your opinion with us. I am very sorry you apparently were
responding to my first reply to you, which was in error. Maybe your server
didn't deliver my second reply, the one in which I attempted to correct the
error in the first. I am sorry to have thrown such confusion into this
already overlong thread. Anyway FWIW, my 2nd reply in an attempt to correct
the
errorious one went like this:

{"Sorry, Dan - Make that overdrive via overspeed from the prime mover to
make
an induction generator. The induction generator (one made from a common
induction motor) will generate when excited by the mains and when its rotor
is driven by external means to a speed exceeding that of the motor's
synchronous speed. Slip is said to be negative under these conditions."}

Please note, the operative change made here was to insert "rotor driven by
external means to a speed exceeding that of the motor's synchronous speed"
in place of "overdrive from the AC mains". Again, I am very sorry for that
mistake and for you to have gone to the trouble of posting 9 times in order
to straighten me out on the matter.

As someone once said, "I'm afraid I've already told you more than I know".
Please understand, the following quote from McGraw-Hill EE Handbook, 10
Edition, Sec. 18-116 is the source of all my knowledge re. induction
generators; it goes:

"""Induction Generators. Any induction motor, if driven above its
synchronous speed when connected to an a-c source, will deliver power to the
external circuit. This generator action is easily visualized from the
motor-circle diagram. (Fig. 18-17)corresponding to the lower half of the
circle in which the current vector is directed below the OV line. [pls.
adivse and I can scan the figure to your direct e-mail addy, if you like] A
unique feature is that the power factor of the output is fixed in value by
the generator characteristics and is always leading, independent of the
external circuit. The explanation is that the generator draws all its
excitation from the system and so must receive a definite amount of lagging
kilovoltamperes for a given voltage and load current. For this reason,
induction generators alone cannot supply a power system but must always
operate in parallel with synchronous machines or with capacitors. They are
therefore, no more helpful in system stability than the addition of parallel
reactors with a rating equal to the generator magnetizing reactance.

An induction generator delivers an instantaneous 3-phase short-circuit
current equal to the terminal voltage divided by its standstill reactance,
but its rate of decay is much faster than that of a synchronous generator
of the same rating, and its sustained short-circuit current is zero.

Since an induction generator must have a laminated rotor, to provide for the
slip-frequency rotor magnetic field, its construction is not adapted to as
high speeds as synchronous machines employing solid steel rotors. For these
various reasons, induction generators have found few practical applications,
their chief use being perhaps, in variable-ratio frequency converter sets,
where the induction end of the set operates as a motor or a generator
depending on the direction of power flow through the set."""

Dan, I'm confused over the paragraph where you said:

"To further confuse you, you can build a very nice RPC by using a single
phase motor to drive a three phase motor via a belt drive adjusted so
mechanical power is going into the three phase motor. Now if you apply
single phase power to the three phase motor, it will act as a three phase
induction generator. If you do this use an adjustable pulley on one of the
motors and measure the current drawn by the single phase motor. Adjust the
pulleys so the current drawn by the single phase motor is close to but below
rated nameplate current when the RPC is driving whatever load you are going
to drive. As you might suspect such a RPC produces voltages that are very
closely balanced."

It seems to me you may be describing an idler driven by a pony motor,
similar to systems in which the pony is disconnected after the idler has
come up to speed. Could this be the case you're describing, except that the
pony motor is not disconnected after the starting interval?

Bob (easily confused) Swinney










  #108   Report Post  
Posted to rec.crafts.metalworking
Bruce L. Bergman
 
Posts: n/a
Default Flywheel on a rotary phase convertor

On 9 Jan 2006 05:35:43 -0800, jim rozen
wrote:

In article . com,
says...

I hope this message actually gets posted. My last two attempts failed.
I am hoping the problem has something to do with cookies and posting
through Google.


Coming through fine here Dan.

Jim


Yup - All six of 'em, and the other three you thought didn't, too...
Ain't Technology wonderful? ;-P

"There is nothing that can go wrong click can go wrong click..."

-- Bruce --
  #109   Report Post  
Posted to rec.crafts.metalworking
 
Posts: n/a
Default Flywheel on a rotary phase convertor


Robert Swinney wrote:
Wow, Dan! Nine posts.

I am very sorry for the multiple posts. I kept getting messages that
said " Server Error try again in 30 minutes " or it would seem to
accept the message but would not show up when I would read the thread.
Apparently the messages were buffered somewhere and all of them
eventually got posted.

Bob, the first reply was before your post that clarified what you meant
to say.


It seems to me you may be describing an idler driven by a pony motor,
similar to systems in which the pony is disconnected after the idler has
come up to speed. Could this be the case you're describing, except that the
pony motor is not disconnected after the starting interval?

Bob (easily confused) Swinney



I am more or less describing exactly what you said above. Except when
you use a pony motor you may have the pony motor only bring the three
phase motor to say 80 % of its rated speed. If you apply power to the
three phase motor while leaving power on the pony motor, the pony motor
will be driven faster than is synchronous speed until you disconnect
it. I think this is how Jim Rozens RPC is done, where his sytem throws
the belt when you apply power to the idler.

You might have the pony motor directly connected to the three phase
motor. In that case there would be little or no mechanical power
transferred between the two motor when power is applied to both.

So I am describing a subset of an idler driven by a pony motor, where
the drive is adjusted so that the pony motor turns the idler at a speed
which is faster than the idler would run by itself. The pony motor may
or may not be large enough to drive the idler above its synchronous
speed but mechanical power is still going to the idler ( actually not
an idler anymore, but a driven motor ).

Again I apologize for the multiple posts. None of my posts showed up
here until today.


Dan

  #110   Report Post  
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jim rozen
 
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Default Flywheel on a rotary phase convertor

In article , Robert Swinney says...

It seems to me you may be describing an idler driven by a pony motor,
similar to systems in which the pony is disconnected after the idler has
come up to speed. Could this be the case you're describing, except that the
pony motor is not disconnected after the starting interval?


Dan's comments there are about deliberatly driving the idler motor
at above slip speed. It will behave like an alternator at that point
and deliver the mechanical power that is entering the shaft to the
electrical load.

Jim


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Robert Swinney
 
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Default Flywheel on a rotary phase convertor

Jim and Dan . . . .

Hmmmmnnnn ... I never thought of it that way. If I may describe what I
think it was you said:

You have a pony motor driven RPC, connected as in other RPC's described in
this thread, where the single-phase pony and 2 terminals of the 3-phase
idler and 2 terminals of the 3-phase load are all connected across a
single-phase source. The pony, an induction motor, is belted such that it
mechanically drives the idler ( 3-phase motor) at a speed greater than
synchronous speed. If I "see" it correctly you'd have a RPC (includes load)
which runs at a speed somewhere beyond normal synchronous speed of the
3-phase load motor.

Jim's comment, "It will behave like an alternator at that point
and deliver the mechanical power that is entering the shaft to the
electrical load" seems to be spot on."


Well! Knock me over with a rubber dick, err, make that rubber duck. Seems
to me that ought to work. Id'd bet it is kind of tricky to get the right
belt, or gear, ratio between the pony and idler. I suppose, though, it
would just refuse to "generate" if everything was not properly sized. BTW -
how would you know if it was functioning as an induction generator ? If
the load motor was running at greater than its normal synchronous speed -
it'd be generating, right??

Bob (learns something new every day) Swinney

PS: Hey, why not use a 3-phase pony to get things started and then, and
then, then . . .connect the 3 terminals of the load back to the 3 terminals
of the pony. Vee-I-ola! Perpetual motion, Naw!



"jim rozen" wrote in message
...
In article , Robert Swinney says...

It seems to me you may be describing an idler driven by a pony motor,
similar to systems in which the pony is disconnected after the idler has
come up to speed. Could this be the case you're describing, except that
the
pony motor is not disconnected after the starting interval?


Dan's comments there are about deliberatly driving the idler motor
at above slip speed.
Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================



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jim rozen
 
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Default Flywheel on a rotary phase convertor

In article , Robert Swinney says...

Well! Knock me over with a rubber dick, err, make that rubber duck. Seems
to me that ought to work. Id'd bet it is kind of tricky to get the right
belt, or gear, ratio between the pony and idler.


That's why dan suggested a varispeed pulley setup in his post.

I suppose, though, it
would just refuse to "generate" if everything was not properly sized.


Yes, if it weren't line excited. But it is.

BTW -
how would you know if it was functioning as an induction generator ? If
the load motor was running at greater than its normal synchronous speed -
it'd be generating, right??


Generating on the third leg. I think the idea would be to make a
rotary converter that somehow would have better balance or lower
impedance by deliberatly driving the rotor above synchronous speed.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
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Default Flywheel on a rotary phase convertor


Robert Swinney wrote:

Well! Knock me over with a rubber dick, err, make that rubber duck. Seems
to me that ought to work. Id'd bet it is kind of tricky to get the right
belt, or gear, ratio between the pony and idler. I suppose, though, it
would just refuse to "generate" if everything was not properly sized. BTW -
how would you know if it was functioning as an induction generator ? If
the load motor was running at greater than its normal synchronous speed -
it'd be generating, right??





Actually it is dead easy to get it adjusted. Just monitor the current
going to the " pony " motor. Adjust the pulleys so the current is at
or slightly below the rated full load current on the nameplate. The
pony motor is then putting out its rated horsepower. Where is it going?
Got to be going into the three phase motor. With the three phase "
idler " connected to the mains, you won't notice much if any
difference in speed. Most four pole motors run at about 1750 rpm when
they are being used as a motor. 50 rpm slip. To drive at 1850 rpm,
-50 rpm slip, would take the same horsepower going in as the motor is
rated to put out. Actually a bit more to take care of windage and
other losses. So the drive ratio is very close to 1 : 1


Dan

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Don Foreman
 
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Default Flywheel on a rotary phase convertor

On 9 Jan 2006 18:28:27 -0800, jim rozen
wrote:

BTW -
how would you know if it was functioning as an induction generator ? If
the load motor was running at greater than its normal synchronous speed -
it'd be generating, right??


Generating on the third leg. I think the idea would be to make a
rotary converter that somehow would have better balance or lower
impedance by deliberatly driving the rotor above synchronous speed.

Jim


I think it'd be generating on all three phases; there would be a
component of current in the line-connected phase that flows against
the applied voltage, feeding power back into the mains. This
current component would be in quadrature with the magnetizing current
it draw from the mains.

I think it would have better balance because the sign or direction of
the IZ drop wrt the emf would be the same in all three phases. This
is not the case in a self-excited idler.



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