Flywheel on a rotary phase convertor

But, but, but.

No tune capacitors.

No pf correction.

No potential relay or starting capacitors.

No contactors, no control transformers.

It can't *possibly* work. These things have to be complicated.

Pardon me, I have to go make some chips...

Jim

Reply to
jim rozen
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Don sez:

"> A fella by the name of Swinney said elsewhere that idler and load

Yeah, But! That's not quite how I said it. I believe I said elements of a RPC function as both generators and consumers because of the way current flows in an entire RPC, not just in the idler motor.

Don, dig out the little paper I sent you a couple of years ago and in there you will see some diagrams describing current flow in a RPC - an entire RPC; You do still have that little paper, don't you? Naw! I suppose not or else you wouldn't have slipped into the Iggy school of RPC's.

Bob Swinney

Reply to
Robert Swinney

Jim, while I admire simplicity of your phase converter -- actually I decided to make my first RPC after I saw how easy it is to have a basic converter - I cannot see how you are addressing any of Don's points that he just made.

The third leg that is not connected to load, acts just as a power outlet with nothing plugged in. It makes voltage and is ready to produce power, but does not actually produce power.

i
Reply to
Ignoramus20351

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

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?

Bob (getting tired of all this)Swinney

Reply to
Robert Swinney

OK, but what does that mean? Currents in an entire anything flow thru the elements that comprise it, so current flow(s) in an entire RPC must flow thru its elements. The idler and the load motor are elements, are they not? Do you mean RPC to connote rotary phase converter? Do you assert that an RPC must have capacitors to be called an RPC? Is it the capacitors that function as both generators and loads?

Naw, I suppose not. I recall it, but I don't seem to have it on either computer. If it was paper, I certainly no longer have it.

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

Reply to
Don Foreman

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

i
Reply to
Ignoramus20351

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

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.

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 110v Of course, aggregate current flow is such that current will flow

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

Which parts?

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.

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.

Reply to
Don Foreman

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.

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

Reply to
Don Foreman

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

Reply to
Robert Swinney

I actually have my IGBT inverter working, pretty much, and am finishing up installation into the welder.

i

Reply to
Ignoramus6826

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

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

Reply to
Robert Swinney

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

Reply to
Robert Swinney

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

Reply to
pentagrid

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.

Reply to
Don Foreman

So my ammeter needs two needles?

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

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

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.

Reply to
Don Foreman

I stand corrected. It makes sense, now that you point it out. L/R ratio is pretty high because R is quite small.

Thanks, Jim!

Reply to
Don Foreman

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

Reply to
Don Foreman

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 Sw> Dan sez:

Reply to
dcaster

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

Reply to
pentagrid

See my later post that addresses this issue of series vs parallel. The situation is quite clear if idler and load are delta-connected: there is no neutral and phases are clearly in parallel however they may or may not be connected to singlephase or 3phase mains.

You know of and about Delta - Y transformations of three-terminal networks, particularly symmetrical threephase machines.

Everyone seems to agree that any neutrals that might exist in an RPC system are not connected. If neutrals are not connected or don't exist, then I say they can and should be ignored. Absent neutrals, the question of phase-to-phase and device-to-device parallelism seem quite clear to me.

Reply to
Don Foreman

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