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  • #16
    WHOOO! What 3 Phase source do you have??? I sounds from that last bit on the neutral that he may have the Delta source.
    In which case the "neutral" is not going to want to be used in the Star transformer. Explain it to him Paul .
    Note! ( his statement about the Neutral being for the 220 pair. )
    Paul can do much better job of explaining than me. :-)
    ...lew...

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    • #17
      Its a older french domestic supply. The utility company provide me with 4 wires 3 phase + neutral presented to the house that is a converted barn, I believe wired in wye/star upstream. I can get 380 between any phase and another, and 220 between any phase and neutral.

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      • #18
        "officially" its a 400v 3 phase supply I have to add, but if I put a meter on it, its 380v between phases. As I live in the middle of nowhere very rural, and the french standard used to be 3 x 380v + neutral done in wye, I would guess the local transformer infrastructure hasn't been changed out and theyre relying on 380v being in acceptable voltage tolerance to meet the new norm of 400v

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        • #19
          A few things.....

          1) The neutral is not "required" for a wye transformer setup, it is "nice", maybe "better", since it will tie things down against grounded neutral. Assuming the 3 phases take reasonably equal currents, the "neutral" point will not vary much from true neutral even if not tied to it.

          if you have it, use it. Since you DO have it, go ahead and connect it if you are sure of the wiring.

          2) What voltage do you really want?

          380 3 phase would be 380 from line to line (delta), and would be 220V from line to neutral (wye), as you see. Actual 220 line-to-line would be about 130 in wye, line to neutral.

          You will get more-or-less the expected result od 220V line-to-line using the 15 kVA transformer you have, which would be rated about 22A per phase regardless of voltage. In your setup, a 380V input wye autotransformer rated 15kVA would be about 8500 VA, based on the 22A current.

          If that's enough, you should be good.
          CNC machines only go through the motions.

          Ideas expressed may be mine, or from anyone else in the universe.
          Not responsible for clerical errors. Or those made by lay people either.
          Number formats and units may be chosen at random depending on what day it is.
          I reserve the right to use a number system with any integer base without prior notice.
          Generalizations are understood to be "often" true, but not true in every case.

          Comment


          • #20
            Well, in view of the subsequent posts, it sounds like he is in France, where I have zero experience, and has a Y or star connected service. So using a Y connected transformer would be appropriate.

            What I do not understand is exactly what is meant by "neutral" in this kind of connection. As far as I can see, the middle point of the Y, which I labeled common (neutral) in my drawing, is the only possible point that could be called a neutral. In my, US based thinking, that point should be grounded at the service pole and should be within a few Volts of ground potential at any other point in the wiring. I can understand having a safety ground, just as we have here, on separate conductors. SO, if that center of the Y is the neutral AND it is grounded at the service pole, then adding another grounded, "neutral" point somewhere else would result in a real problem.

            I would need to know all the details, from the pole transformers to the machine itself, to understand just what is going on here as far as neutrals are concerned. I would suggest that if our OP is not sure about the connections, he should not experiment with any added neutrals. Perhaps a local, qualified electrician is needed.


            Originally posted by Lew Hartswick View Post
            WHOOO! What 3 Phase source do you have??? I sounds from that last bit on the neutral that he may have the Delta source.
            In which case the "neutral" is not going to want to be used in the Star transformer. Explain it to him Paul .
            Note! ( his statement about the Neutral being for the 220 pair. )
            Paul can do much better job of explaining than me. :-)
            ...lew...
            Paul A.
            SE Texas

            And if you look REAL close at an analog signal,
            You will find that it has discrete steps.

            Comment


            • #21
              That's pretty much the point....

              He evidently has neutral, since he has 4 wire 380V with 220 line to neutral. That is pretty much standard all over the EU. it REQUIRES a neutral to be available, since the usual usage voltage is 220V (now "harmonized" at 230V nominal, using the minus tolerance to allow 220V) and is supplied line to neutral. With 3 phase, he has 3 separate 220V sources.

              He seems to *want* 220V line to line. At least if not, I have no idea WHAT he wants.

              That said, the wye point of the transformer, even if NO neutral is connected to it, would be *at* a virtual neutral, which would likely be within a few volts of true neutral as-supplied. Therefore he can connect it, and that is better, since it "ties down" all the outputs.

              So if it happened that he did NOT have a neutral conveniently available, the setup would work nearly as well for balanced loads, like a 3 phase motor. Since he *does* have it, there is no issue, ASSUMING that he is correct about the wiring of the transformer.

              If there is any question, he could check by powering the transformer with NO neutral, and checking the neutral-to-wye point voltage. It should be only a few volts at most.
              CNC machines only go through the motions.

              Ideas expressed may be mine, or from anyone else in the universe.
              Not responsible for clerical errors. Or those made by lay people either.
              Number formats and units may be chosen at random depending on what day it is.
              I reserve the right to use a number system with any integer base without prior notice.
              Generalizations are understood to be "often" true, but not true in every case.

              Comment


              • #22
                Yes, the machine requires 200-220v 3 phase line to line whereas its 380v out the board for the same measurement but it arrived with this seperate transformer that was used in previous install in a building with 440v line to line 3 phase supply (industrial standard 3 phase in the UK), and the jumpers are set on the transformer to the 440 setting. I have moved the links to the 380v setting to suit my French supply.
                I'm tiptoeing around it because I've been told by the seller the machine didn't run because the main transformer was declared bad by a electrician brought in to diagnose why the machine didn't run (I paid the did not run price, which is why I can justify having my own edm in a home shop). It could be one of the internal transformers to the machine and this is a red herring, or elsewhere and they just didn't want to get into the guts of the thing and diagnose further, but its why it had the focus of my attention rather than just plugging in and going initially, which triggered off the odd reading behaviour in my meter caused by the large inductance as mentioned by another poster. And I confess the operating principle of a autotransformer wasn't too clear, I was still thinking of it as a traditional isolated transformer and was stuck wondering why I could read continunity between input and out and it seemed to have a dead short wherever I measured it. Its been 25 years since I last sat in a classroom learning 3 phase theory!

                Also as I understand it, the neutral isnt at ground potential, as the supply wont be loaded evenly at all times as it has different 220v loadings on each leg in a normal domestic supply, so the neutral is used to return the phase difference current in these unbalanced loadings.
                I have to have a seperate ground install (not wired PME back to the supply transformer like the UK and other places), provided by me and certified at less than 50ohm, as tested with a ground impedance test meter as part of my supply commisioning test earlier this year.

                I could bring in a certified electrician locally, but I just rang one local and asked him if he knew if it was wired star or delta at the supply to confirm, and he just said he didn't know, but it wasn't important. Read into that what you may. I suspect if he walked into the barn and saw a EDM and a big transformer to power it, he'd just say "non", declare it didn't conform to french norms as it only has the uk ident plate on it and walk out again.

                One last point on the hidden contacter, it must be inside the actual transformer core itself if so, I can see the 3 seperate phase cores with the windings on them, and the wires from the switch go into the cores.

                Comment


                • #23
                  I strongly doubt any hidden contactor..... there will not be anything but transformer steel "inside the cores". Contractors are of a significant size, hard to "hide".

                  The supply WILL be wired "star"..... it is the ONLY way you can get 220V to neutral directly with a 380V line-to-line supply. ALL the traditional EU countries other than some legacy stuff in the Nordics have neutral grounded supplies, almost all the "TN-C-S" system with a grounded neutral and an earth bonded to it.

                  What we have here is a total failure to communicate.....

                  So, to prevent further "guessing" and so forth

                  GIVE US PICTURES.....

                  Include pics of the nameplates.
                  CNC machines only go through the motions.

                  Ideas expressed may be mine, or from anyone else in the universe.
                  Not responsible for clerical errors. Or those made by lay people either.
                  Number formats and units may be chosen at random depending on what day it is.
                  I reserve the right to use a number system with any integer base without prior notice.
                  Generalizations are understood to be "often" true, but not true in every case.

                  Comment


                  • #24
                    Here's what I would do. Referring to my diagram above, I would use my best Ohm meter to measure the continuity between each of the three Input or Line terminals and the center of the Y or the Neutral terminal with the transformer completely disconnected from any other circuitry. If the three readings are not the same, the transformer is probably bad.

                    But if those three readings are the same, that is only a low Voltage reading using DC, not AC. So more testing is needed.

                    While doing the following, be careful not to come in contact with both the transformer and a ground at the same time. There may be some kind of internal short. If possible, ground the outer case of the transformer.

                    I would then get three lamp sockets for incandescent bulbs of 100 Watts or more. Larger would be better for more current in this test. The more current, the better. Wire one lamp socket between each of the three output terminals and the center of the Y or Neutral point. Put the lamps in the sockets and then connect the input terminals of the Y to your power. Turn it on and then measure the Voltage from that center of the Y (Neutral) to each of the output terminals. If these three Voltages are the same, then there is a 99% chance that the transformer is good. If not, then it is certainly bad.

                    This tests the transformer with a real load on all three phases. This load will be somewhat lower than your EDM will be, but still somewhat substantial. And with the same bulbs in each socket, it will be a balanced load. Since you are stepping down from normal line Voltage, do not expect the lamps to come to full brightness. They may not light at all or perhaps only glow a dim red. Use the Voltage measurements to judge by.

                    Once you establish that the transformer is probably good, then carefully check for any potential between the outer case and ground (not Neutral). Anything over 5 or 10 Volts on a Voltmeter is cause for alarm as it probably indicates an internal short.

                    Be sure to have a good safety ground connection to both the transformer and the EDM outer cases/frames in your final wiring. I am sure local codes require this and it should not be ignored.
                    Paul A.
                    SE Texas

                    And if you look REAL close at an analog signal,
                    You will find that it has discrete steps.

                    Comment


                    • #25
                      Thanks Paul, I'll follow your proceedure as outlined and check for 200v, the bulbs will be bright enough at that voltage as normal household voltage is 220v here.
                      Just for the curious, this is the transformer. You cant see the coils from this angle so you will have to take my word there's no contactor hiding in there but we'll worry about what that switch does later on after it passes the test I think. No shot of the rating plate outside, but its stamped 15kva, the bakelite section on view here is about 30" wide to give a idea of scale.

                      Comment


                      • #26
                        That's a little different from what it seemed from the description.

                        1) Output is given as 200V, 10% low vs 220V.

                        2) Instead of a tapped OUTPUT, the INPUT is tapped, so the output kVA is not affected by voltage setting (output is always the same voltage) and the current rating is higher.

                        I see that what you actually said does in fact describe the unit, however it didn't seem like that from reading. A picture is worth a thousand words indeed.

                        There may be enough margin in the unit to allow setting the tap lower to get 220V out. No way to tell that from here. The tapping is at standard voltages, so no clues are given by the tap steps.

                        As for your switch... that does seem puzzling, since there is already a voltage selection system. I don't know what a switch would be doing. Are you certain it is a switch? and if so, has it any label?

                        The wire apparently going towards the front (and maybe the switch?) appears to be around 12 AWG, based on general size, and that would be about right... a 40A output would be 20A input at double the output voltage, and 12AWG or similar size wire would be suitable for that. So the switch could be in the high voltage side. An adjustment, maybe, depending on how big it is, how many contacts, etc.
                        CNC machines only go through the motions.

                        Ideas expressed may be mine, or from anyone else in the universe.
                        Not responsible for clerical errors. Or those made by lay people either.
                        Number formats and units may be chosen at random depending on what day it is.
                        I reserve the right to use a number system with any integer base without prior notice.
                        Generalizations are understood to be "often" true, but not true in every case.

                        Comment


                        • #27
                          I've opened the edm power cabinet up today and its labeled as 200vac inside, but 200-220 on a exterior plate so I think it'll be happy being fed 200v.

                          The switch has wafers and two positions but no label, in fact the knob is missing from it completely so it has to be turned by gripping the flat of the shaft, it is indeed at the right with the wires leading to it. I imagine the machine would have been isolated by a lockable supply switch upstream nowadays so its surplus to requirements so possibly someone removed the knob to facilitate this although it did seem to be left in what would be the "off" position so I will start testing with it the same. The other wires inside the transformer dwarf them for cross section.
                          Fingers crossed it could be as simple as someone fiddling just turned a forgotten about switch off one day and I have the gloat of the centuary as a result. I want to believe that, but know a plant electrician would spot it instantly but I can dream for a few hours while finishing building a test rig :-)

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                          • #28
                            To update, finally got around to wiring this in and testing it, and its fine. 200vac on all three phases with a small load on.
                            So I hooked up the machine it supplies and its got 200vac per phase as per design. The bad transformer turned out to be further into the machine amongst other parts which I'm currently working through fixing.

                            I still have no idea what the switch does as it doesn't turn output on or off.

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