Hi all,

I'm trying to figure out if there is any benefit in adding a flywheel to
a rotary phase convertor. I've heard varying opinions on the subject.
Having thought about it myself, I've reached the following conclusions:

(i) The sag in voltage on the third line is caused by the fact that it
is not connected directly to the supply. The flywheel doesn't change
this. Nor will it change the steady speed at which the rotor turns, so
unless it has some averaging effect on a cycle-by-cycle basis which I
haven't considered, it won't affect the quality of the three phase
output when the convertor is running in a steady state.

(ii) It might be an advantage when trying to plug reverse the load
motor. As far as I can see (on the most simplistic level), the motor
with the most kinetic energy will win.

I can't seem to find any used flywheels to fit my motor, but I can get a
brand new flywheel for £40. I'm not sure if it is worth it in order to
satisfy my scientific curiousity. If I get a different motor, I can get
a flywheel for next to nothing, but that will involve lots of effort,
bartering and deals in order to get a motor which isn't quite so cool.

Any opinions and arguments? Thoughts would be appreciated...

Best wishes,

Chris

In article , Christopher Tidy says...

Hi all,

I'm trying to figure out if there is any benefit in adding a flywheel to
a rotary phase convertor.

There is no experimental data on this subject as far as I can see.

I have seen coherent, cogent arguments from respected folks
that support both views - one that it will help, the other that it
will hinder.

Those who suggest a flywheel is bad say that rotary converters
deliver transient power to the generated phase by allowing the rotor to
slip, and a flywheel prevents this.

Those who suggest a flywheel is good say that that flywheels store
rotational energy and will this is made available to transient loads.

Those two preceeding statements are pure paraphrase on my part, and
I of course apologize if I have mis-represented anyones comments.
But there's no empirical data out there as far as I can tell.

It wouldn't be that hard to instrument and measure.

Jim


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

Regarding plug reversing, I recently rewired an older BP head. I was surprised
to see considerable evidence of arcing near the contacts in the drum switch. I
figured that plug reversing it was the reason - a LOT of current flows, and
motors with all their inductance do NOT like current changes. So regardless of
what you do with your phase convertor, I strongly suggest that you not plug
reverse anything using a drum switch unless that switch is extremely heavily built.

I know of no value in adding rotary mass. The armature of an idler motor is
already quite a bit of rotary mass.

GWE

Christopher Tidy wrote:

Hi all,

I'm trying to figure out if there is any benefit in adding a flywheel to
a rotary phase convertor. I've heard varying opinions on the subject.
Having thought about it myself, I've reached the following conclusions:

(i) The sag in voltage on the third line is caused by the fact that it
is not connected directly to the supply. The flywheel doesn't change
this. Nor will it change the steady speed at which the rotor turns, so
unless it has some averaging effect on a cycle-by-cycle basis which I
haven't considered, it won't affect the quality of the three phase
output when the convertor is running in a steady state.

(ii) It might be an advantage when trying to plug reverse the load
motor. As far as I can see (on the most simplistic level), the motor
with the most kinetic energy will win.

I can't seem to find any used flywheels to fit my motor, but I can get a
brand new flywheel for £40. I'm not sure if it is worth it in order to
satisfy my scientific curiousity. If I get a different motor, I can get
a flywheel for next to nothing, but that will involve lots of effort,
bartering and deals in order to get a motor which isn't quite so cool.

Any opinions and arguments? Thoughts would be appreciated...

Best wishes,

Chris

Christopher Tidy wrote...

I'm trying to figure out if there is any benefit in adding a flywheel to
a rotary phase convertor.

A flywheel would reduce, not increase, the idler's ability to respond to
load changes. When the electrical load on the idler increases, the
idler's rate of rotation falls (I.e., the slip increases). This raises
the current draw from the single phase source. The higher winding current
increases the strength of the rotating magnetic field in the idler, which
pushes the generated third leg voltage up. The upshot of all this is that
the response rate of the third leg voltage to electrical load changes is
inversely related to the inertia of the idler's armature.

That's my understanding. Perhaps one of the old regulars can explain it
better. Is Fitch still around? I seem to remember his doing some tests on
this very thing a few years back.

Jim

jim rozen wrote:
In article , Christopher Tidy says...

Hi all,

I'm trying to figure out if there is any benefit in adding a flywheel to
a rotary phase convertor.


There is no experimental data on this subject as far as I can see.

I have seen coherent, cogent arguments from respected folks
that support both views - one that it will help, the other that it
will hinder.

Those who suggest a flywheel is bad say that rotary converters
deliver transient power to the generated phase by allowing the rotor to
slip, and a flywheel prevents this.

Those who suggest a flywheel is good say that that flywheels store
rotational energy and will this is made available to transient loads.

Then maybe one needs a "dual-mass" flywheel like they are putting on the
diesel pickups now.

Jim Wilson wrote:

Thanks for all the responses.

A flywheel would reduce, not increase, the idler's ability to respond to
load changes. When the electrical load on the idler increases, the
idler's rate of rotation falls (I.e., the slip increases). This raises
the current draw from the single phase source. The higher winding current
increases the strength of the rotating magnetic field in the idler, which
pushes the generated third leg voltage up. The upshot of all this is that
the response rate of the third leg voltage to electrical load changes is
inversely related to the inertia of the idler's armature.

I'm not sure about this. Yes, it will take longer for the rotor's speed
to fall, but surely the stored energy will be dissipated by driving
extra current through the load?

Best wishes,

Chris

IMO, you need to lose the thinking of a RPC as being a form of generator.
It isn't. Think more of the RPC as a network in which parts of it rotate in
order to supply current throughout. Part of the RPC is the load motor. The
idler generates nothing without the load as part of a network. IMO, a
flywheel on the idler cannot act as anything more than additional dynamic
load on the network. It would be aprox. the same to put the flywheel on the
load motor instead. Forget flywheels and spend the money on enhancing the
idler-load network with proper capacitance. Complex current flows in all
parts of the RPC. In simplistic terms, the idler-load current paths can be
viewed as series resonant circuits. Such circuits are "tuned" via
capacitance placed in series.

Bob Swinney
"Jim Wilson" wrote in message
.net...
Christopher Tidy wrote...

I'm trying to figure out if there is any benefit in adding a flywheel to
a rotary phase convertor.

A flywheel would reduce, not increase, the idler's ability to respond to
load changes. When the electrical load on the idler increases, the
idler's rate of rotation falls (I.e., the slip increases). This raises
the current draw from the single phase source. The higher winding current
increases the strength of the rotating magnetic field in the idler, which
pushes the generated third leg voltage up. The upshot of all this is that
the response rate of the third leg voltage to electrical load changes is
inversely related to the inertia of the idler's armature.

That's my understanding. Perhaps one of the old regulars can explain it
better. Is Fitch still around? I seem to remember his doing some tests on
this very thing a few years back.

Jim

On 3 Jan 2006 13:58:38 -0800, jim rozen
wrote:

In article , Christopher Tidy says...

Hi all,

I'm trying to figure out if there is any benefit in adding a flywheel to
a rotary phase convertor.

There is no experimental data on this subject as far as I can see.

I have seen coherent, cogent arguments from respected folks
that support both views - one that it will help, the other that it
will hinder.

Those who suggest a flywheel is bad say that rotary converters
deliver transient power to the generated phase by allowing the rotor to
slip, and a flywheel prevents this.

Those who suggest a flywheel is good say that that flywheels store
rotational energy and will this is made available to transient loads.

Those two preceeding statements are pure paraphrase on my part, and
I of course apologize if I have mis-represented anyones comments.
But there's no empirical data out there as far as I can tell.

It wouldn't be that hard to instrument and measure.

Jim

Some kinetic energy is necessary for the thing to work, but my bet is
that the rotor has more than enough and more would not help.

Kinetic energy is necessary for the idler to produce power in the
third leg during parts of the cycle when less or none is being drawn
from the mains. Energy is also stored in the magnetic field, but its
ebb and flow is in quadrature with third leg power. This is a
cycle-by-cycle event: it accelerates (accumulates energy) during
part of each cycle and decelerates (gives up energy) during other
parts of each cycle. The result is speed ripple, which would be
greater for rotors with small moments of inertia.

The power levels drawn and delivered are a function of slip speed
which governs both stator current and induced emf -- back emf in the
case of the driven windings and generated emf in the case of the third
leg. As the third leg produces more countertorque from higher
current flow thru it, the rotor will slow until slipspeed has
increased to the point where enough power is drawn from the mains to
regain equilibrium.

Observers (Jerry and Fitch) have said they didn't note much change in
idler slipspeed with varying loads. However, resolution of 1% or
better would be necessary to see speed variations because the slip
speed range from no load to full load in most induction motors is
only a few percent at most.

On Tue, 3 Jan 2006 22:53:42 +0000 (UTC), Christopher Tidy
wrote:

Jim Wilson wrote:

Thanks for all the responses.

A flywheel would reduce, not increase, the idler's ability to respond to
load changes. When the electrical load on the idler increases, the
idler's rate of rotation falls (I.e., the slip increases). This raises
the current draw from the single phase source. The higher winding current
increases the strength of the rotating magnetic field in the idler, which
pushes the generated third leg voltage up. The upshot of all this is that
the response rate of the third leg voltage to electrical load changes is
inversely related to the inertia of the idler's armature.

I'm not sure about this. Yes, it will take longer for the rotor's speed
to fall, but surely the stored energy will be dissipated by driving
extra current through the load?

Yes, but power is the rate of energy flow. The amount of power it
can produce for the third leg (energy delivered per cycle) is a
function of slip speed, and field strength hence stator current which
is also a function of slip speed.

In article , Robert Swinney says...

IMO, you need to lose the thinking of a RPC as being a form of generator.
It isn't. Think more of the RPC as a network in which parts of it rotate in
order to supply current throughout. Part of the RPC is the load motor. The
idler generates nothing without the load as part of a network. IMO, a
flywheel on the idler cannot act as anything more than additional dynamic
load on the network. It would be aprox. the same to put the flywheel on the
load motor instead. Forget flywheels and spend the money on enhancing the
idler-load network with proper capacitance. Complex current flows in all
parts of the RPC. In simplistic terms, the idler-load current paths can be
viewed as series resonant circuits. Such circuits are "tuned" via
capacitance placed in series.

Granted this kind of tuning is the very *first* thing one would do
before considering flywheels.

I specifically recall Gary Coffman claiming they would reduce transient
response, and yet there's a considerable group of well-informed
individuals on the practical machinist board who say they improve
matters.

I have to say I find *both* sides to be persuasive, at least at the
'hand-waving' level.

My suspicion is that flywheels probably help up to a point, if one
models the rotor as having zero mass to start with. And that the
optimum flywheel size will wind up being about one rotor unit in
size! This is what a former boss of mine calls 'the schwarz law
of the initial maximum.'

Ie, if it works the first time you set it up, anything you do to it
after that makes it work worse.

:^)

Jim


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

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

Hrm. Is this in response to my post, or Christopher's? I don't think I
view a RPC as a generator at all. Perhaps it's more like a rotating
transformer.

snip

It would be aprox. the same to put the flywheel on the
load motor instead.

Most of what you said seemed reasonable (I snipped all the
unobjectionable parts), but this statement can only be true under limited
conditions. There would be a large difference in performance between the
two systems for example when plug reversing is used.

Cheers,

Jim

"Jim Wilson" wrote in message
.net...
Robert Swinney wrote...
IMO, you need to lose the thinking of a RPC as being a form of generator.

Hrm. Is this in response to my post, or Christopher's? I don't think I
view a RPC as a generator at all. Perhaps it's more like a rotating
transformer.

snip

It would be aprox. the same to put the flywheel on the
load motor instead.

Most of what you said seemed reasonable (I snipped all the
unobjectionable parts), but this statement can only be true under limited
conditions. There would be a large difference in performance between the
two systems for example when plug reversing is used.

Cheers,

Jim

FWIW, you might view a plug reverse of the load motor as the worst case
flywheel effect.

Bob Swinney

The only reason I can see for a flywheel to be advantageous is if you
were spinning the rpc up by hand before cutting in the power to lessen
the duration of high current draw.

On 3 Jan 2006 16:04:40 -0800, jim rozen
wrote:

In article , Robert Swinney says...

IMO, you need to lose the thinking of a RPC as being a form of generator.
It isn't. Think more of the RPC as a network in which parts of it rotate in
order to supply current throughout. Part of the RPC is the load motor. The
idler generates nothing without the load as part of a network. IMO, a
flywheel on the idler cannot act as anything more than additional dynamic
load on the network. It would be aprox. the same to put the flywheel on the
load motor instead. Forget flywheels and spend the money on enhancing the
idler-load network with proper capacitance. Complex current flows in all
parts of the RPC. In simplistic terms, the idler-load current paths can be
viewed as series resonant circuits. Such circuits are "tuned" via
capacitance placed in series.

Granted this kind of tuning is the very *first* thing one would do
before considering flywheels.

I specifically recall Gary Coffman claiming they would reduce transient
response, and yet there's a considerable group of well-informed
individuals on the practical machinist board who say they improve
matters.

I have to say I find *both* sides to be persuasive, at least at the
'hand-waving' level.

My suspicion is that flywheels probably help up to a point, if one
models the rotor as having zero mass to start with. And that the
optimum flywheel size will wind up being about one rotor unit in
size! This is what a former boss of mine calls 'the schwarz law
of the initial maximum.'

Ie, if it works the first time you set it up, anything you do to it
after that makes it work worse.

:^)

We just call that syndrome "fix it 'til it's broke".

Snarl

On Tue, 3 Jan 2006 21:07:42 +0000 (UTC), Christopher Tidy
wrote:


I can't seem to find any used flywheels to fit my motor, but I can get a
brand new flywheel for £40. I'm not sure if it is worth it in order to
satisfy my scientific curiousity. If I get a different motor, I can get
a flywheel for next to nothing, but that will involve lots of effort,
bartering and deals in order to get a motor which isn't quite so cool.


I won't touch the theoretical discussions on this thread. However I
thought I might mention that if you wanted to experiment cheaply I'm
sure you can find a used cast iron pulley in large enough diameter to
serve as your flywheel. Preferably a multi-groove pulley.

Wayne Cook
Shamrock, TX
http://members.dslextreme.com/users/waynecook/index.htm

According to Ignoramus29795 :
On Tue, 3 Jan 2006 21:07:42 +0000 (UTC), Christopher Tidy wrote:

[ ... ]

(ii) It might be an advantage when trying to plug reverse the load
motor. As far as I can see (on the most simplistic level), the motor
with the most kinetic energy will win.

I am not sure why you think so. Would you clarify why you think that
plug reversing a load motor would somehow slow down the idler
motor. The idler, after all, spins with the frequency of the AC
mains.

I have read reports here of under-rated rotary converters
actually reversing, instead of the load motor, when plug reversing. I
think that the flywheel might indeed solve this problem.

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 ---

On Tue, 3 Jan 2006 17:20:12 -0600, "Robert Swinney"
wrote:

IMO, you need to lose the thinking of a RPC as being a form of generator.
It isn't. Think more of the RPC as a network in which parts of it rotate in
order to supply current throughout. Part of the RPC is the load motor. The
idler generates nothing without the load as part of a network.

Sure it does. With the idler spinning, a voltage is generated in
the third leg that is in quadrature to line voltage, even if there are
no capacitors anywhere. Transformer action can not produce a
quadrature voltage so it must be (and is) generated by the rotating
rotor field -- which always is in quadrature with the stator field.

IMO, a
flywheel on the idler cannot act as anything more than additional dynamic
load on the network. It would be aprox. the same to put the flywheel on the
load motor instead. Forget flywheels and spend the money on enhancing the
idler-load network with proper capacitance. Complex current flows in all
parts of the RPC. In simplistic terms, the idler-load current paths can be
viewed as series resonant circuits.

If there are capacitors. But idlers without any run caps still work.
In fact, they work quite well if they're large enough.

I agree, using large motors simplifies everything! You get the
advantage of great kinetic energy with very understressed component
parts. I favor a pony to "spin up" the first started (should be
largest by 1.5) motor.

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.

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. 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. I do not claim that this is the only way to
describe it or that any description can change the operating principles
involved.

Don Young
"Christopher Tidy" wrote in message
...
Hi all,

I'm trying to figure out if there is any benefit in adding a flywheel to a
rotary phase convertor. I've heard varying opinions on the subject. Having
thought about it myself, I've reached the following conclusions:

(i) The sag in voltage on the third line is caused by the fact that it is
not connected directly to the supply. The flywheel doesn't change this.
Nor will it change the steady speed at which the rotor turns, so unless it
has some averaging effect on a cycle-by-cycle basis which I haven't
considered, it won't affect the quality of the three phase output when the
convertor is running in a steady state.

(ii) It might be an advantage when trying to plug reverse the load motor.
As far as I can see (on the most simplistic level), the motor with the
most kinetic energy will win.

I can't seem to find any used flywheels to fit my motor, but I can get a
brand new flywheel for £40. I'm not sure if it is worth it in order to
satisfy my scientific curiousity. If I get a different motor, I can get a
flywheel for next to nothing, but that will involve lots of effort,
bartering and deals in order to get a motor which isn't quite so cool.

Any opinions and arguments? Thoughts would be appreciated...

Best wishes,

Chris

"Don Foreman" wrote in message
...
On Tue, 3 Jan 2006 17:20:12 -0600, "Robert Swinney"
wrote:

IMO, you need to lose the thinking of a RPC as being a form of generator.
It isn't. Think more of the RPC as a network in which parts of it rotate
in
order to supply current throughout. Part of the RPC is the load motor.
The
idler generates nothing without the load as part of a network.

Sure it does. With the idler spinning, a voltage is generated in
the third leg that is in quadrature to line voltage, even if there are
no capacitors anywhere. Transformer action can not produce a
quadrature voltage so it must be (and is) generated by the rotating
rotor field -- which always is in quadrature with the stator field.

No load, no generation, Don. An idler running with no load motor does not
constitute a RPC. The network and supported current flow through that
network makes a RPC. Remember the idler is running as a single-phase
machine and the 3rd leg is open, that is, until it is connected into a RPC.

IMO, a
flywheel on the idler cannot act as anything more than additional dynamic
load on the network. It would be aprox. the same to put the flywheel on
the
load motor instead. Forget flywheels and spend the money on enhancing the
idler-load network with proper capacitance. Complex current flows in all
parts of the RPC. In simplistic terms, the idler-load current paths can
be
viewed as series resonant circuits.

If there are capacitors. But idlers without any run caps still work.
In fact, they work quite well if they're large enough.

OK. So they aren't series resonant circuits when there are no run caps -
granted. But the interconnection of idler and load and their associated
current paths are the same, even without run caps.

Don Young sez:

"Since the running idler and load motors are directly connected in parallel
.. . ."

You are right about there being "many ways to understand and describe how
things work" but the concept of an idler and load motor's respective
windings being in parallel is not one of them.

Bob Swinney

"Don Young" wrote in message
...
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.

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.
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. I do not claim that this is
the only way to describe it or that any description can change the
operating principles involved.

Don Young
"Christopher Tidy" wrote in message
...
Hi all,

I'm trying to figure out if there is any benefit in adding a flywheel to
a rotary phase convertor. I've heard varying opinions on the subject.
Having thought about it myself, I've reached the following conclusions:

(i) The sag in voltage on the third line is caused by the fact that it is
not connected directly to the supply. The flywheel doesn't change this.
Nor will it change the steady speed at which the rotor turns, so unless
it has some averaging effect on a cycle-by-cycle basis which I haven't
considered, it won't affect the quality of the three phase output when
the convertor is running in a steady state.

(ii) It might be an advantage when trying to plug reverse the load motor.
As far as I can see (on the most simplistic level), the motor with the
most kinetic energy will win.

I can't seem to find any used flywheels to fit my motor, but I can get a
brand new flywheel for £40. I'm not sure if it is worth it in order to
satisfy my scientific curiousity. If I get a different motor, I can get a
flywheel for next to nothing, but that will involve lots of effort,
bartering and deals in order to get a motor which isn't quite so cool.

Any opinions and arguments? Thoughts would be appreciated...

Best wishes,

Chris

In article ,
Rex B wrote:

[...]

Then maybe one needs a "dual-mass" flywheel like they are putting on the
diesel pickups now.

That sounds like an interesting thingy. Got any details on it?

--
B.B. --I am not a goat! thegoat4 at airmail dot net

On 3 Jan 2006 13:58:38 -0800, jim rozen
wrote:

Those who suggest a flywheel is bad say that rotary converters
deliver transient power to the generated phase by allowing the rotor to
slip, and a flywheel prevents this.

Those who suggest a flywheel is good say that that flywheels store
rotational energy and will this is made available to transient loads.

Those two preceeding statements are pure paraphrase on my part, and
I of course apologize if I have mis-represented anyones comments.
But there's no empirical data out there as far as I can tell.

It wouldn't be that hard to instrument and measure.

Jim

Dont forget a nice heavy rotor IS a flywheel.

Gunner

The aim of untold millions is to be free to do exactly as they choose
and for someone else to pay when things go wrong.

In the past few decades, a peculiar and distinctive psychology
has emerged in England. Gone are the civility, sturdy independence,
and admirable stoicism that carried the English through the war years
.. It has been replaced by a constant whine of excuses, complaints,
and special pleading. The collapse of the British character has been
as swift and complete as the collapse of British power.

Theodore Dalrymple,

In article , Robert Swinney says...

No load, no generation, Don. An idler running with no load motor does not
constitute a RPC. The network and supported current flow through that
network makes a RPC. Remember the idler is running as a single-phase
machine and the 3rd leg is open, that is, until it is connected into a RPC.

No current flow, yes. But the third leg does come up in voltage, even
when open circuited. While it won't do any work, folks would be tempted
to say that the third leg is indeed "generated" even when it's open
circuited. Another one of those semantic mine fields....

Jim


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

Don, I think you have a great insight here. The two motors are clearly
in parallel; swap a lead on either motor and the "bigger" one wins. I
still am not sure if a flywheel has any significant effect on which one
is bigger (though it seems like it would).

Steve

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.

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. 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. I do not claim that this is the only way to
describe it or that any description can change the operating principles
involved.

Don Young
"Christopher Tidy" wrote in message
...


Hi all,

I'm trying to figure out if there is any benefit in adding a flywheel to a
rotary phase convertor. I've heard varying opinions on the subject. Having
thought about it myself, I've reached the following conclusions:

(i) The sag in voltage on the third line is caused by the fact that it is
not connected directly to the supply. The flywheel doesn't change this.
Nor will it change the steady speed at which the rotor turns, so unless it
has some averaging effect on a cycle-by-cycle basis which I haven't
considered, it won't affect the quality of the three phase output when the
convertor is running in a steady state.

(ii) It might be an advantage when trying to plug reverse the load motor.
As far as I can see (on the most simplistic level), the motor with the
most kinetic energy will win.

I can't seem to find any used flywheels to fit my motor, but I can get a
brand new flywheel for £40. I'm not sure if it is worth it in order to
satisfy my scientific curiousity. If I get a different motor, I can get a
flywheel for next to nothing, but that will involve lots of effort,
bartering and deals in order to get a motor which isn't quite so cool.

Any opinions and arguments? Thoughts would be appreciated...

Best wishes,

Chris

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

Bob Swinney

In my opinion you need to realize that a RPC is an induction generator.


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

Don sez:
" Sure it does. With the idler spinning, a voltage is generated in
the third leg that is in quadrature to line voltage, even if there are
no capacitors anywhere. Transformer action can not produce a
quadrature voltage so it must be (and is) generated by the rotating
rotor field -- which always is in quadrature with the stator field."

I'm not sure what you mean, Don. You said "Transformer action can not
produce a quadrature voltage so it must be (and is) generated by the
rotating rotor field -- which always is in quadrature with the stator
field".

Firstly, I don't understand why the issue must be complicated by bringing
the rotor field into the picture. It is well known the stator field and
rotor field are more or less locked into rotation at the same speed, but it
is incongruous to speculate the rotor field is solely responsible for the
stator field's third leg voltage. Remember we are essentially talking about
a single phase motor here with an open coil connected to the center point of
the line-fed main winding. I respectfully submit the third leg voltage is
not in quatrature with line voltage. The only way for that to be a true
statement would be in the special case of a precise amount of capacitance
connected from one line side to the end of the 3rd leg coil; an amount of
capacitance (start cap if you will) necessary to achieve an exact 90 degree
phase shift between line voltage and the 3rd. leg.

Bob Swinney

On Wed, 4 Jan 2006 00:12:38 -0600, "Robert Swinney"
wrote:

Don Young sez:

"Since the running idler and load motors are directly connected in parallel
. . ."

You are right about there being "many ways to understand and describe how
things work" but the concept of an idler and load motor's respective
windings being in parallel is not one of them.

Bob Swinney

Hey, Bob, what about delta-wound motors? Sure looks parallel to me!

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.

Hey, Don, it sounds like you are beginning to go off half cocked, sort of
"Iggy style".

Do this: Visualize 2 deltas connected in "parallel" if you will..
Obviously the current paths through the branches, where the lines are
connected, are in parallel. Now look at the common point where the other 2
legs of both deltas connect together. Those points are no more in parallel
than they would be if they were between two wyes.

It may be helpful to look at the configuration in its wye equivalent. Same
thing. All this speaks to the very complex current flow in an idler and
load connected as a RPC. Two 3-phase induction motors running on the same
3-phase line do not constitute a RPC. A RPC is two 3-phase induction motors
running on single-phase current. Capacitor augmentation assists in tuning
the network such that it appears to be operating from a 3-phase line.

Bob Swinney



"Don Foreman" wrote in message
...
On Wed, 4 Jan 2006 00:12:38 -0600, "Robert Swinney"
wrote:

Don Young sez:

"Since the running idler and load motors are directly connected in
parallel
. . ."

You are right about there being "many ways to understand and describe how
things work" but the concept of an idler and load motor's respective
windings being in parallel is not one of them.

Bob Swinney

Hey, Bob, what about delta-wound motors? Sure looks parallel to me!

Don,

See my previous post, where I tried to show 2 induction motors operating
from single phase current in a RPC configuration cannot be in parallel.

Bob Swinney
"Don Foreman" wrote in message
...
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.

On Wed, 4 Jan 2006 10:14:13 -0600, "Robert Swinney"
wrote:

Don sez:
" Sure it does. With the idler spinning, a voltage is generated in
the third leg that is in quadrature to line voltage, even if there are
no capacitors anywhere. Transformer action can not produce a
quadrature voltage so it must be (and is) generated by the rotating
rotor field -- which always is in quadrature with the stator field."

I'm not sure what you mean, Don. You said "Transformer action can not
produce a quadrature voltage so it must be (and is) generated by the
rotating rotor field -- which always is in quadrature with the stator
field".

Firstly, I don't understand why the issue must be complicated by bringing
the rotor field into the picture.

Because it's there, producing phase shifts and emf's that cannot be
produced by a network of similar topology having only R's and L's.

It is well known the stator field and
rotor field are more or less locked into rotation at the same speed, but it
is incongruous to speculate the rotor field is solely responsible for the
stator field's third leg voltage. Remember we are essentially talking about
a single phase motor here with an open coil connected to the center point of
the line-fed main winding. I respectfully submit the third leg voltage is
not in quatrature with line voltage. The only way for that to be a true
statement would be in the special case of a precise amount of capacitance
connected from one line side to the end of the 3rd leg coil; an amount of
capacitance (start cap if you will) necessary to achieve an exact 90 degree
phase shift between line voltage and the 3rd. leg.

The rotor field is always in space quadrature from the stator field.
This is well-established in about any textbook on the subject. That
being the case, the emf it induces in the third leg is necessarily
in quadrature with the emf impressed by the line (and countered by the
stator field) in the other two windings.

Now consider a Y-connected motor. Rotate the Y 30 degrees clockwise so
the right hand leg is horizontal, with line connected across the
lefthand legs. Note that the vertical components of the excited coil
windings add while the horizontal components cancel. Therefore,
there is no emf induced in the horizontal third winding by direct
transformer action. Emf induced in the third winding is therefore
solely due to the rotor field -- and since that field is in quadrature
with the stator field, the emf in the third winding must be in
quadrature with the excitation voltage. QED.

The terminal voltage on a loaded third winding will vary from exact
quadrature due to I Z drops, which have opposite sense in the excited
windings from those in a loaded third leg -- look at the directions of
current flow. . But if you connect a scope from third terminal to
neutral (center of the Y) in an unloaded idler, it would show an emf
in quadrature with line voltage.

Credit to Jerry Martes for showing me this aspect of induction idlers.

In article , Don Foreman says...

The rotor field is always in space quadrature from the stator field.
This is well-established in about any textbook on the subject. That
being the case, the emf it induces in the third leg is necessarily
in quadrature with the emf impressed by the line (and countered by the
stator field) in the other two windings.

I thought it was the rotor *current* that was in quadrature.

Basically the rotor currents cause a rotating B field to
exist inside the stator. How it does this doesn't matter
much, but suffice it to say that the phase of the rotating
B field agrees with the incoming excitation (which of course
supplies all the power to the gizmo) which means it will
cause the correct phase voltage to exist on the third lead.

Jim


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

On Wed, 4 Jan 2006 11:42:34 -0600, "Robert Swinney"
wrote:

Hey, Don, it sounds like you are beginning to go off half cocked, sort of
"Iggy style".


Look at
http://users.goldengate.net/~dforeman/delta_3D/

Colored lines are windings, white lines are connections.
'Splain to me how the windings of same colors are not in parallel...

Don "Half-cocked" Foreman

On Wed, 4 Jan 2006 11:45:55 -0600, "Robert Swinney"
wrote:

Don,

See my previous post, where I tried to show 2 induction motors operating
from single phase current in a RPC configuration cannot be in parallel.

I saw it. I just don't agree with it. See recent post showing things
in 3D.

Transform to Y using the usual Y-delta transforms if you like. See
any textbook on the subject.

In the Y case they don't look in parallel if there is no neutral
connection. However, since a delta depiction clearly shows that they
*ARE* in parallel, they are in freakin' parallel, BOB! Must I glue
up some popsicle sticks for you?

Can you explain the discrepancy? :)

Hint: if there is no potential between unconnected points (the
neutrals in a Y configuration) then they are effectively connected.

Don "half-cocked" Foreman
half cocked my arse....grumble mutter ....chuckle

Sorry, Don. We were discussing RPC's and I assumed (we know what that does)
you were thinking of RPC's as well. Two 3-phase induction motors connected
as a RPC are not, repeat are not in parallel. I'm afraid you have jumped to
the conclusion that two 3-phase induction motors connected in RPC fashion
are merely connected in parallel. That is not the case. See a later post
in which I tried to explain the defference.

Bob (if it sounds like Iggy, it might be Iggy, No! it can't be) Swinney

"Don Foreman" wrote in message
news
On Wed, 4 Jan 2006 11:42:34 -0600, "Robert Swinney"
wrote:

Hey, Don, it sounds like you are beginning to go off half cocked, sort of
"Iggy style".


Look at
http://users.goldengate.net/~dforeman/delta_3D/

Colored lines are windings, white lines are connections.
'Splain to me how the windings of same colors are not in parallel...

Don "Half-cocked" Foreman

Well, Don - you've missed the point again! What part of "2 induction
motors operating from single phase current in a RPC configuration cannot be
in parallel" did you fail to understand. Your well intentioned, and
colorful, drawings were not of a RPC configuration. Draw out a RPC and I
think you may understand. Oh! be sure to include some capacitors. They (in
electronic terms) might be considered as steering capacitors, for it is
their job to force the convoluted currents to flow in such a way as to
*emulate* true 3-phase. Note, I said *emulate* because current flow in a
RPC is not the same as current flow in parallel connected 3-phase motors, no
matter which transform is used.

Bob Swinney
"Don Foreman" wrote in message
...
On Wed, 4 Jan 2006 11:45:55 -0600, "Robert Swinney"
wrote:

Don,

See my previous post, where I tried to show 2 induction motors operating
from single phase current in a RPC configuration cannot be in parallel.

I saw it. I just don't agree with it. See recent post showing things
in 3D.

Transform to Y using the usual Y-delta transforms if you like. See
any textbook on the subject.

In the Y case they don't look in parallel if there is no neutral
connection. However, since a delta depiction clearly shows that they
*ARE* in parallel, they are in freakin' parallel, BOB! Must I glue
up some popsicle sticks for you?

Can you explain the discrepancy? :)

Hint: if there is no potential between unconnected points (the
neutrals in a Y configuration) then they are effectively connected.

Don "half-cocked" Foreman
half cocked my arse....grumble mutter ....chuckle

In article , Robert Swinney says...

Well, Don - you've missed the point again! What part of "2 induction
motors operating from single phase current in a RPC configuration cannot be
in parallel" did you fail to understand.

Probably the same one I can't see.

They look like they're in parallel to me. Unless I'm missing
something.

Granted the term "parallel" is a bit of a misnomer here but
each winding of my load motor is in fact in parallel with
a winding in the idler motor.

Jim (half cocked also?)


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

On Wed, 4 Jan 2006 13:00:58 -0600, "Robert Swinney"
wrote:

Sorry, Don. We were discussing RPC's and I assumed (we know what that does)
you were thinking of RPC's as well. Two 3-phase induction motors connected
as a RPC are not, repeat are not in parallel. I'm afraid you have jumped to
the conclusion that two 3-phase induction motors connected in RPC fashion
are merely connected in parallel. That is not the case.

Mine is! Works fine.

On Wed, 4 Jan 2006 13:00:58 -0600, "Robert Swinney"
wrote:

Sorry, Don. We were discussing RPC's and I assumed (we know what that does)
you were thinking of RPC's as well. Two 3-phase induction motors connected
as a RPC are not, repeat are not in parallel. I'm afraid you have jumped to
the conclusion that two 3-phase induction motors connected in RPC fashion
are merely connected in parallel. That is not the case.

Hanrahan seems to think it is the case. The presence of the
capacitors notwithstanding, his motors are connected in parallel.

http://www.metalwebnews.com/howto/ph-conv/fig1.html