On Wed, 4 Jan 2006 15:02:28 -0600, "Robert Swinney"
wrote:

The key point here is: "How my phase converter is wired when it runs a load
motor". The flawed logic is that a phase converter does not "run" a load
motor. Such a differentiation between phase converter and load motor is not
possible. An idler motor and load motor, taken together as a network, are
what constitutes a rotary phase converter. This all harks back to the
misunderstood "generator" concept as applied to an idler motor. The two
must work together to form a rotary phase converter. Remember a RPC (the
whole RPC) acts to manipulate current flow in a network so that the load
motor voltages, and currents, are the same as if the load motor was
operating from a 3-phase source. Remembering, all the while, the whole thing
is running on *single-phase* current.

Now as for parallel connectivity: The drawing is that of a classic RPC
(idler and load motor) operating from Hot 1 and Hot 2, both sides of a
single-phase source. Consider Hot 1. It connects to L1 of the idler motor
and also to L1 of the load motor. The same can be said for Hot 2 and the 2
respective L2's. By definition, the points designated as L1 and L2 in both
idler and load are operated in parallel across the line. That is to say the
2 main windings, L1 to L2 in your drawing of both idler and load are
connected in parallel across the line.

Now look at the way current flows in the L3 lead. The idler's L3 wire has 1
end connected to the 3rd. winding on the idler, call that a source point for
L3 current flow. The other end of wire L3 connects not to the analogous
same start point on the load motor but to a point on the other end of the
load motor's L3.

What "other end"? Nobody rewound the motor. It connects to the same
terminal that motor came with.


This is not, can not, be considered a parallel connection.
The only way the two 3-phase motors could be connected in parallel is if
they are both fed from a 3-phase source.

They are connected in parallel regardless of how they are fed. The
locus of confusion may be this: if you consider a Y connection, the
third legs are in series with each other, though the three-terminal
networks (idler and load motor) are connected in parallel. The
function of an RPC is to make the voltage on L3 resemble the voltage
of a third mains line in phase and magnitude if one were present.

In a manner of speaking, for a RPC (network) to do its thing, when taking in
*single-phase* current and delivering *3-phase current* to a load motor
(also part of the network) there has to be current flow in 2 directions the
3rd leg.

There's current flow in both directions everywhere in an AC system.
If you meant to say power flow, I disagree. Power flows from idler
third leg to load motor third leg. Net power over each cycle in
L3 is, by definition for RPC function, flowing into the load same
as it is on the other two lines just as would be the case if an actual
third mains line of different phase were feeding L3 and the load
motor. There will be some reactive component and power factor in
all three legs, but they won't be greatly different from each other
in an RPC that is working well.

I agree that the RPC must be treated as a system to get the voltage
on L3 to be right, because that voltage is determined by the idler,
the load motor and any capacitances that are present.

Another confusion factor is that the system is driven by "single"
phase. How d'ya get three phases with one more wire? The trick to
undestanding this is to regard the 220 mains as 110v and 110v180
(180 out of phase with the first line) either side of a neutral
which may or may not actually exist as it does in the US and Canada.

That can be viewed as being produced by two vectors of 127 volt
magnitude with phase difference of 120 degrees. Let's take a snapshot
in time where these vectors are at 120 and 240 degrees. The
resulting line-to-line voltage is 220, though the unconnected
neutral is now non-zero and in quadrature with the actual mains
voltages, a voltage vector at 0 degrees in our snapshot. The third
leg in the idler, referred to neutral in in a Y- connected motor,
produces additional quadrature voltage, at 0 degress in our snapshot,
as described in another post. If the magnitude and phase of the
idler's third-leg contribution is just right, the resulting voltages
on L1, L2 and L3 will look like balanced threephase mains.

The contribution of the third leg will never be "just right", hence
the addition of capacitors to adjust phase and magnitude as they
resonate with the various inductive reactances in the system.

Of course, aggregate current flow is such that current will flow
in the "right" direction in the load motor's 3rd leg.

What is aggregate current flow? Average current flow in any AC
circuit is zero.

Parts of the RPC act as both generators and consumers,

Which parts?

thus the heavier element will cause
current to flow, seemingly backwards, into the other element. And so it is
with the RPC - capacitor augmentation can enhance the convoluted current
flow

What does "convoluted current flow" mean? Convoluted compared to
what? Even if the earnest reader deduces that the context is
"intricate, complex, labyrinthine" rather than "rolled in a coil",
it doesn't add a bit to his understanding of how an RPC works.

Guys of our age, training and experience should be teaching what we
know, Bob. I'd like to see a higher standard of contribution from
you than I might expect from some others. I I think you know a
lot but I think you could do a lot better job of teaching. Being
tall enough to skip derision of readers who respectfully (or
otherwise) disagree or "don't yet get it" wouldn't hurt a bit.

in such a way as to make emulated 3-phase current flow in the load
motor.

Bob Swinney

I think you have the general ideas right, but I really doubt that
someone who didn't already have some understanding of how these things
work would be helped by your explanation. Further, it's not right
and not at all contributive to deride others who don't comprehend
what you meant rather than what you said.





"Ignoramus18299" wrote in message
. ..
Here's how my phase converter is wired when it runs a load motor:


idler Load

L3-------------------------L3
/ \ / \
L1 --- L2 L1---L2
| | | |
| +------------------------+
+-----------------------------+ Hot2
Hot1

L1 connected to L1, L2 connected to L2, L3 connected to L3. L1 and L2
are also connected to utility power Hot1 and Hot2.

How are these motors not running in parallel?

They are.

Leg numbering on the load motor is somewhat arbitrary, but however
these motors are connected, the poles are connected in parallel.

Maybe you have a different definition of "connected in parallel". My
definition is that potential between like points (L1 to L1, L2 to L2,
L3 to L3) is zero. Current does flow from L3 of one motor to L3 of
another.

i
(now I have more bells and whistles on my new phase converter, like
balancing and power factor correction caps, dual idlers, blah blah,
but they do not change the basic fact that these motors are indeed
parallel connected)


On Wed, 4 Jan 2006 13:20:04 -0600, Robert Swinney
wrote:
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






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