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  • #31
    So Jerry, let me see if I hear you.
    Delta wound RPCs make 3 phase
    and Y wound RPCs make 2 phase? ? ? ? ?

    -D
    DZER

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    • #32
      Originally posted by Doozer View Post
      So Jerry, let me see if I hear you.
      Delta wound RPCs make 3 phase
      and Y wound RPCs make 2 phase? ? ? ? ?

      -D
      SIGH......

      Wye wound RPCs make the same 3 phase as anything else uses. Why, and how, would they do anything different? It's baked into the windings. But "wye" 3 phase has a "neutral" that is not the same as the incoming power neutral.

      You can look up the "Scott connection"..... That has one connection that is like the incoming power, with a center-tapped winding, the tap being in the same "location" as for the single phase neutral coming into an RPC.. and it has another winding from that center point to the 3rd wire (wound for a different voltage).

      Those two windings are phased at 90 degrees.

      The resulting 3 phase is indistinguishable from any other 3 phase, the conversion is perfect. This is because the result of that connection and phasing is completely equivalent to ordinary generated 3 phase.

      The whole thing comes out of the vector math.

      Now, if you WANTED 2 phase, you could get it, the connections are all there, you would just need one transformer with the right windings.
      Last edited by J Tiers; 02-19-2020, 04:04 PM.
      1601

      Keep eye on ball.
      Hashim Khan

      Comment


      • #33
        Ok, so just an observation....
        Y wound RPC motors Hummmm a lot.
        Delta wound RPC motors tend to run quiet.
        Is there something to that??

        -D
        DZER

        Comment


        • #34
          Originally posted by J Tiers View Post

          Yes that is correct. Emerson makes them, as do others. They are of course 3 phase, and made cheap,
          I was actually referring to the 1ph in 1ph out in order to run the typical 1ph motor with variable speed, but have heard so many story's of drop out of run at low speed and other issues etc.
          The reason that the majority now use the 1ph in and 3ph out with 3ph motor for DIY CNC etc.
          Max.

          Comment


          • #35
            Originally posted by MaxHeadRoom View Post

            I was actually referring to the 1ph in 1ph out in order to run the typical 1ph motor with variable speed, but have heard so many story's of drop out of run at low speed and other issues etc.
            The reason that the majority now use the 1ph in and 3ph out with 3ph motor for DIY CNC etc.
            Max.
            Well a "typical" 1 ph motor (capacitor or split phase) does not run well if at all with a VFD. Slighty less usual ones, PSC, or shaded pole, etc, run OK, but they still do nit necessarily slow down well under heavy load. Eventually the PSC run cap is too small to produce much torque, and the rotor is too light to "ride through" the zero torque times..

            I designed a couple of those inverters.... they have to start at or near full frequency and voltage, to get start torque. One had to start the PSC motor in an oil burner at -40C, running JP-8 as fuel (Mil stuff). It DID do it, but the VFD had to source over 12A at start, dropping to 3A or so when running. Well outside the usual VFD limits. Yes, the start was at 60Hz. Then it got slowed down to the proper run speed that the controller set. That one had a limited range because the fuel had to atomize correctly.

            another ran a set of cooling fans on an old radar set that apparently had many installs, and killed inverters on a regular basis if the fans jammed. That had a wider range and less power, fan loads work OK with a VFD. I believe those were also PSC motors. I do not think any of those failed, we put a protection circuit in them.
            Last edited by J Tiers; 02-19-2020, 04:42 PM.
            1601

            Keep eye on ball.
            Hashim Khan

            Comment


            • #36
              Jerry,

              If you are running a motor on 3 phase,
              and you loose connection in 1 wire,
              then is not the motor now running on 1 phase?

              If you tell me it is running on 2 phases with only 2
              wires, I have a hard time believing that.

              -D
              DZER

              Comment


              • #37
                You're getting 60 ohms between two wires. I'd say you have three coils, each 30 ohms. You probably have one connection not making it, either at the Y point, or at the junction where the open wire connects to a coil wire.

                It looks to me like three dark wires come together- just to the right of where the other wires come into the motor. That's probably your Y point. Opposite that you have 5 strings to cut to access the other wires- the green and the light blue are on top, and it looks like the red off to the right, just out of view. The red is the problem, so starting at about the 1 o-clock position go clockwise and cut seven strings binding the wiring. That should let you lift the red wire out a bit - that's the first point I would cut into to see whether you have a solid connection to one coil winding. If that looks good, then go to where the dark wires appear to go together and free that up. The yellow sleeves are what you have to cut into to get a look at the junction inside.
                Last edited by darryl; 02-19-2020, 07:01 PM.
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                Comment


                • #38
                  Originally posted by Doozer View Post
                  Jerry,

                  If you are running a motor on 3 phase,
                  and you loose connection in 1 wire,
                  then is not the motor now running on 1 phase?

                  If you tell me it is running on 2 phases with only 2
                  wires, I have a hard time believing that.

                  -D
                  If it was truly "wye", complete with neutral, it could. But if you lose one out of three, it is called "single phasing", because there is just one delta phase left. Three wires and no neutral ARE "delta". The MOTOR can be wired wye, and still works fine with a "delta" source. In fact, if you HAD a neutral, with a motor you would never use it.

                  However, to figure currents etc, it is often more convenient to consider it as if it were wye, that simplifies things in some cases. Don't let it get your undies in an uncomfortable wad, the two are compatible, and end up with the same important numbers.

                  Here's something to wrap your head around.... A transformer that gives delta-wye transformation, also creates a 30 degree phase shift. I leave it to you to figure out how that works!

                  1601

                  Keep eye on ball.
                  Hashim Khan

                  Comment


                  • #39
                    Originally posted by J Tiers View Post

                    If it was truly "wye", complete with neutral, it could. But if you lose one out of three, it is called "single phasing", because there is just one delta phase left. Three wires and no neutral ARE "delta". The MOTOR can be wired wye, and still works fine with a "delta" source. In fact, if you HAD a neutral, with a motor you would never use it.
                    ...
                    I have never seen a three phase motor in the Y configuration
                    powered by a Y transformer, hooked up with 3 legs and the
                    center of the Y leg as well. 4 wires?? Never seen it.
                    Phases are between the legs.
                    Don't know why you insist on this Y center tap and
                    neutral connection stuff, who wires shlt this way??
                    You are trying to prove your assertions with some
                    textbook vector analysis that never gets hooked up
                    that way ever. I understand vectors, phase shift
                    and the magnetic hysteresis of iron and the charge
                    cycle of a capacitor. I do not care about being right
                    or being wrong, I just want to learn, but you are not
                    providing me with anything cementitious here.

                    -D
                    DZER

                    Comment


                    • #40
                      Originally posted by Doozer View Post

                      I have never seen a three phase motor in the Y configuration
                      powered by a Y transformer, hooked up with 3 legs and the
                      center of the Y leg as well. 4 wires?? Never seen it.
                      Phases are between the legs.
                      Don't know why you insist on this Y center tap and
                      neutral connection stuff, who wires shlt this way??
                      You are trying to prove your assertions with some
                      textbook vector analysis that never gets hooked up
                      that way ever. I understand vectors, phase shift
                      and the magnetic hysteresis of iron and the charge
                      cycle of a capacitor. I do not care about being right
                      or being wrong, I just want to learn, but you are not
                      providing me with anything cementitious here.

                      -D
                      Doozie, baby........ NOBODY EVER connects a motor full wye with neutral. I said that. You are just makin stuff up here. If you DID do that, though, then dropping one wire would only lose ONE phase, not two.

                      Point being that "Phases" are often considered differently for delta and wye.. A wye "phase" can be a wire vs neutral OR between two wires. A delta phase is generally considered to be between two wires of the three, because it takes two wires to make a "circuit". But the individual wires may also be considered and labeled as "phases". If you do not know which a person means, it gets confusing.

                      The motor can be MADE with internal connections putting the coils in wye, and a lot of motors are made that way. Maybe most of them, I have not taken a survey to judge. But a wye or a delta motor act the same as far as the outside world, and either one works correctly on 3 wire standard 3 phase.

                      Now, you and your gibbering here, you askin a question or you just stirring the pot?

                      1601

                      Keep eye on ball.
                      Hashim Khan

                      Comment


                      • #41
                        Now everyones had a "Mines bigger than yours contest", how about a photo of the label the O/Ps mentioned? seems there COULD be a manufacturers logo on it. Seems to be a lot of information printed on it.

                        Regards Ian.
                        You might not like what I say,but that doesn't mean I'm wrong.

                        Comment


                        • #42
                          Originally posted by J Tiers View Post

                          ….Point being that "Phases" are often considered differently for delta and wye.. A wye "phase" can be a wire vs neutral OR between two wires....
                          No brother, not trying to be difficult.

                          I have just never heard of someone calling Y phase as the individual coil itself.

                          I have always heard of a phase in a Y connection
                          as the vectorial sum of the 2 Y legs,
                          as in through 1 coil,
                          and on through the center connection
                          through to the second coil.

                          Calling the COIL in a Y connection
                          "A Phase"
                          seems like confusing terminology
                          or a misnomer.

                          I was saying phases exist between legs.

                          You were telling me I was wrong.

                          Then you were telling me Y phases are the coils themselves.
                          And phases are often considered differently.
                          By who? Is my question? You?

                          I know one thousandth of an inch
                          is sometimes called a mill
                          and sometimes called a micron
                          depending of the different industries
                          that use the term.

                          Maybe this is such a case.

                          -Doozer


                          DZER

                          Comment


                          • #43
                            Originally posted by J Tiers View Post

                            I think you TOTALLY missed the distinction....

                            Now you mentioned "ROTARY" converters, "RPCs", so you are probably not talking about the same thing at all.

                            But, the "bank of capacitors" does NOT "make" the third phase. That third phase would exist in an RPC that had no capacitors in it at all. It is inherent in the motor itself, and many people have made and used RPCs that have not even a start capacitor. They use either a rope start, or a pony motor..
                            One: , PhasePerfect show in their block diagram and explanation that the 240v 1ph is passed directly through the convertor, unchanged, the 3rd phase is produced from these two.
                            Two: As per Fitch Wiliams design that I used when I first made a RPC.was that a Start capacitor was used via a suitable relay and P.B.
                            The rest of the Capacitor bank was then sized tuned to produce the suitable power factor.
                            Many other papers written on the subject of design recommended a self starting timer rather than the P.B. method that could cause the O/L to trip if held in too long.
                            My designs were based on this.

                            P.S. Apologies to the OP for the post wandering off in to the weeds !🙄
                            Max.
                            Last edited by MaxHeadRoom; 02-20-2020, 10:59 AM.

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                            • #44
                              Doozer: Not wrong that way..... only wrong to consider that as the only possible meaning..... Even the powerco labels the wires as the "A", "B", and "C" "phases" despite the power "existing between" the wires. Down at the end of the street the wires on the poles are labeled just that way on the 3 phase feeder.

                              Max... Not sure what you are saying there.

                              My point...

                              In an RPC (Rotary Phase Converter), a device based on a 3 phase motor, the 3rd phase is produced by induction in the motor coil(s) connected to the generated leg. There is a magnetic field in the rotor, produced by currents in the rotor conductors, and that field induces a voltage in the coils. The rotor current is produced by induction from currents in the two wires feeding the idler as in a normal induction motor. Essentially the "back EMF" of the motor is used to produce the output on the "generated leg".

                              Any "balance" capacitors are used to tune the voltage by interaction with the inductance of the motor and load. They are not required, but if using a normal unmodified motor, the generated leg voltage will be lower in voltage, because the back EMF must be lower than the applied voltage, and it will drop further under load, due to impedance, and also due to slowing of the rotor under load.. That is why "balance" capacitors are used. (A motor may be modified to produce a generated leg voltage equal to the input.)

                              In a "Static Phase Converter", there is no idler. That type is similar to just the start circuit in an RPC, applying a phase-shifted voltage to the 3rd wire of the load motor, using a capacitor for the phase shift. That capacitor is disconnected once the load motor is running, and the 3 phase motor continues running with single phase input on two of the three wires. In some, there may be a "run" capacitor to the third wire included to give some extra torque.

                              A static converter may be combined with a motor to make an RPC, and the Phase-A-Matic literature actually explained that.
                              Last edited by J Tiers; 02-20-2020, 11:18 AM.
                              1601

                              Keep eye on ball.
                              Hashim Khan

                              Comment


                              • #45
                                i decided to use the stator as a manitiser/demagnitiser. it woks well, the only thing is that it heats up too quickly for repetitive use. is there any way to reduce the heat up?

                                and then again the question comes to mind: if it works as a demagnitiser, why doent it run? there can be nothing wrong with the rotor, right?

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