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    Transformer Question

    No paper trail on this transformer but i was told that it is a spare for the current 1500kVA 4160/480V delta delta corner grounded secondary system that we have. Anybody know what do the switch positions on the picture #2 represent. Notice barely readable nameplate calling this 480Y/277 but CX1, BX2 and AX3 labeled blue white and red as the standard labeling we use for the current system.
    As always your time and input is very appreciated.
    Sincerely
    Amel

    #2
    Originally posted by AmeL View Post
    Anybody know what do the switch positions on the picture #2 represent.l
    My guess: primary taps for voltage adjustment, probably +/- 2.5 and 5% each way from nominal.
    Master Electrician
    Electrical Contractor
    Richmond, VA

    Comment


      #3
      Originally posted by AmeL View Post
      No paper trail on this transformer but i was told that it is a spare for the current 1500kVA 4160/480V delta delta corner grounded secondary system that we have. Anybody know what do the switch positions on the picture #2 represent. Notice barely readable nameplate calling this 480Y/277 but CX1, BX2 and AX3 labeled blue white and red as the standard labeling we use for the current system.
      As always your time and input is very appreciated.
      Sincerely
      Amel
      edit to add: I'm a slow poster. So as Larry said:
      Switch positions are likely a tap changer. The nameplate shows different primary voltages that likely correspond to the tap changer positions.

      It's a 480/277Y secondary. I suspect it has been hooked up ignoring the neutral and corner grounding one of the phases (BX2 probably)

      ice
      Without data you’re just another person with an opinion – Edwards Deming

      Comment


        #4
        Thanks very much. The numbers do represent what Larry said.
        Ice, how is that delta connection done (inside transformer I presume) and can it be rewired back to Y?
        Thanks

        Comment


          #5
          Originally posted by AmeL View Post
          ... how is that delta connection done (inside transformer I presume) and can it be rewired back to Y?
          Thanks
          The xfmr secondary is wye configured. There is nothing to rewire. If you connect to a 3-wire, corner-grounded system, you simply ignore the X0 terminal... and your output will be for the most part no different than a 480 delta-configured secondary.

          I believe the assumption was made that since one of your line colors is white, your current system is corner grounded, as it is a violation to use white for ungrounded conductors.
          [COLOR=RoyalBlue]I will have achieved my life's goal if I die with a smile on my face.[/COLOR]

          Comment


            #6
            Originally posted by AmeL View Post
            Thanks very much. The numbers do represent what Larry said.
            Ice, how is that delta connection done (inside transformer I presume) and can it be rewired back to Y?
            Thanks
            As S$ said the transformer looks like it was previously connected with b phase as the corner ground. But, I would not count on that being true.

            As you said, this xfm has been laying around long enough that no one knows the history. So naturally, before being pressed into service, you would test it to make sure it had not died from lack of use laying in the corner.

            Rarely, but occasionally, the XO terminal is internally connected to the transformer case. So naturally, one of the tests you would do is to make sure the secondary windings were not grounded (to the case). This will also tell you the XO is not internally bonded.

            And if I were going to connect the transformer as a wye secondary, then the Secondary winding resistance test - line to XO - tells you that some devious nut didn't go in and internally disconnect the XO. It's not likely, but since you don't know the history, I'd check.

            ice
            Without data you’re just another person with an opinion – Edwards Deming

            Comment


              #7
              Originally posted by iceworm View Post
              As S$ said the transformer looks like it was previously connected with b phase as the corner ground. But, I would not count on that being true.

              As you said, this xfm has been laying around long enough that no one knows the history. So naturally, before being pressed into service, you would test it to make sure it had not died from lack of use laying in the corner.

              Rarely, but occasionally, the XO terminal is internally connected to the transformer case. So naturally, one of the tests you would do is to make sure the secondary windings were not grounded (to the case). This will also tell you the XO is not internally bonded.

              And if I were going to connect the transformer as a wye secondary, then the Secondary winding resistance test - line to XO - tells you that some devious nut didn't go in and internally disconnect the XO. It's not likely, but since you don't know the history, I'd check.

              ice
              I think one of the problem you may encounter is that if you connect this to the existing system and it is a Service Entrance equipment, the corner grounding MAY also have been done there. So make SURE that
              [LIST][*]none of the downstream phases are grounded, and if so hunt them down and destroy them,[*]you establish the grounding of the Xo at the transformer,[*]have them make up their minds about the labeling as X1 should be labeled as A phase, and X3 as phase C,[*]make sure that the rotation is not reversed on the downstream equipment.[/LIST]

              Comment


                #8
                Just checked and the Xo is not internally disconnected and not connected to the case. But the transformer that is currently in use is the same type and has same markings. ( see attached pic) If nothing is done internally to change the configuration and no phases are grounded downstream and from what it looks like they just grounded center or B leg..... what is that system called? Is it a 3 phase or 2 phase? How does this change the rating of it?

                Also I wonder how the calculations work ... and where can I get references on how to calculate this ... What does a phasor diagram look like? Power quality analyzer would be nice now.
                Thanks again for all your inputs.

                Comment


                  #9
                  Originally posted by AmeL View Post
                  Anybody know what do the switch positions on the picture #2 represent.
                  It could also be a switch for a primary loop feed, if the transformer has two HV inputs.

                  Comment


                    #10
                    Originally posted by AmeL View Post
                    If nothing is done internally to change the configuration and no phases are grounded downstream and from what it looks like they just grounded center or B leg..... what is that system called? Is it a 3 phase or 2 phase? How does this change the rating of it?
                    Corner-grounded Delta.

                    3 phase. Line-to-line loads don't care which, if any line is grounded.

                    It doesn't.

                    Also I wonder how the calculations work ...
                    See second answer above.

                    Wait for the engineers among us for the rest.
                    Master Electrician
                    Electrical Contractor
                    Richmond, VA

                    Comment


                      #11
                      Originally posted by AmeL View Post
                      Just checked and the Xo is not internally disconnected and not connected to the case. But the transformer that is currently in use is the same type and has same markings. ( see attached pic) If nothing is done internally to change the configuration and no phases are grounded downstream and from what it looks like they just grounded center or B leg..... what is that system called? Is it a 3 phase or 2 phase? How does this change the rating of it?

                      Also I wonder how the calculations work ... and where can I get references on how to calculate this ... What does a phasor diagram look like? Power quality analyzer would be nice now.
                      Thanks again for all your inputs.
                      It sound like you have a common Delta/Wye transformer and the have chosen to isolate the Xo, instead of grounding it and grounded one of the Y legs. Never heard or see it done this way but from the theoretical standpoint it can be done. I would have an engineer review the system and convert it to a properly grounded Xo.

                      Comment


                        #12
                        Originally posted by LarryFine View Post
                        Corner-grounded Delta.

                        3 phase. Line-to-line loads don't care which, if any line is grounded.

                        It doesn't.

                        See second answer above.

                        Wait for the engineers among us for the rest.
                        I hear what people saying but the only evidence - the picture - tells me that it is a standard D/Y trafo. On the picture I don't see ANY extra wire on the center phase, each leg seems to have 3 wires landing on them and that would mean parallel feeders to me.

                        Comment


                          #13
                          Originally posted by weressl View Post
                          I hear what people saying but the only evidence - the picture - tells me that it is a standard D/Y trafo. On the picture I don't see ANY extra wire on the center phase, each leg seems to have 3 wires landing on them and that would mean parallel feeders to me.
                          Look more closely... there are four wires on the X2 terminal.

                          Even if there were only three, it could be grounded elsewhere.
                          [COLOR=RoyalBlue]I will have achieved my life's goal if I die with a smile on my face.[/COLOR]

                          Comment


                            #14
                            Yes there is a fourth bare copper wire tied to the X2 terminal.
                            It sound like you have a common Delta/Wye transformer and the have chosen to isolate the Xo, instead of grounding it and grounded one of the Y legs. Never heard or see it done this way but from the theoretical standpoint it can be done.
                            I think that this is the case but what benefits are there in doing this?


                            Larry just out of curiosity why would this be called a 3 phase delta?
                            Thanks
                            Last edited by AmeL; 12-22-10, 03:15 PM. Reason: PIc too large wouldn't upload

                            Comment


                              #15
                              Originally posted by AmeL View Post
                              Yes there is a fourth bare copper wire tied to the X2 terminal.
                              I think that this is the case but what benefits are there in doing this?
                              Larry just out of curiosity why would this be called a 3 phase delta?
                              [COLOR=RoyalBlue]I will have achieved my life's goal if I die with a smile on my face.[/COLOR]

                              Comment

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