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4160 Isolation Transformer

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    #16
    Originally posted by LMAO View Post
    I am a little confused; so there is a 13.8kV to 4160V transformer feeding a VFD and the output of VFD is connected to a phase-shift transformer powering a "motor"? Shouldn't the phase shift transformer be connected to the 12 pulse rectifier and not its inverter?

    The VFD has a bypass in it, with a kirk key interlock. So after finding the drawings, it all makes sense now. There is 13.8kv feeding a transformer to get it down to 4160, then into the bypass part of the VFD. Then that feeds the 4160/2300 phase shift transformer that then in turn feeds the VFD drive portion.

    I didn't design the system, we never used the bypass switch, and i am trying to remove the extra equipment out of my MCC rooms. My big question was the phase shift transformer and its purpose and to understand what was going on. I now understand the reason for it and why it's no longer needed.

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      #17
      I think some of the confusion stems from your having described the transformers as being between the drive and the motor, they are not. And although they are Delta-Wye transformers where the L-N potential on the secondary is 2400V, they are not used that way.

      So here's what I believe you have:
      1) One large single transformer that takes the entire load from 13.8kV to 4160V, that 4160V then feeds the VFD input, AND the input to a FVNR Bypass Starter.
      2) Within the VFD feed then, there are two phase shifting transformers that are 4160 in and out, but one is Wye the other is Delta, used in a 12 pulse harmonic mitigation scheme.
      3) The output of the VFD goes directly to the motor.

      If your new VFD is a PowerFlex 7000, it is probably an AFE drive and the phase shifting transformers would no longer be needed. But they COULD have quoted it as a 12 pulse diode front end, because you ALREADY own those transformers. It's something you should get clear. Either way, you will STILL need that 13.8kV to 4160V transformer, UNLESS because you no longer need the Bypass starter, they are quoting you a new AFE or 18 pulse drive with a NEW 13,8kV isolation transformer. That would be wasteful in my opinion, unless there is a problem with your transformer.
      __________________________________________________ ____________________________
      Many people are shocked when they discover I am not a good electrician...

      I'm in California, ergo I am still stuck on the 2014 NEC... We'll get around to the 2017 code in around 2021.

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        #18
        Originally posted by spikes2020 View Post
        I sure hope so . Rockwell is the one supplying it, they understand what is supplying the drive and what the drive is feeding. So they didnt seem to have any concerns.
        its up to you to tell them if you want AFE or passive. each has their own maintenance implications which need to be considered based on the skill levels of your maintenance staff.

        If possible, I would encourage you to consider mfr's other than Rockwell if footprint is a concern (trying to clear up space in MCC room). Their MV voltage source designs are massive compared to comparable Eaton, ABB, Yaskawa, Siemens ROBICON units.

        Be careful letting the mfr design anything other than what is inside the drive. I have had reputable mfr's suggest installing drives in a room where you couldn't get them all out after they were installed.

        disregard my post if this has already been considered.

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          #19
          Originally posted by Jraef View Post
          I think some of the confusion stems from your having described the transformers as being between the drive and the motor, they are not. And although they are Delta-Wye transformers where the L-N potential on the secondary is 2400V, they are not used that way.

          So here's what I believe you have:
          1) One large single transformer that takes the entire load from 13.8kV to 4160V, that 4160V then feeds the VFD input, AND the input to a FVNR Bypass Starter.
          2) Within the VFD feed then, there are two phase shifting transformers that are 4160 in and out, but one is Wye the other is Delta, used in a 12 pulse harmonic mitigation scheme.
          3) The output of the VFD goes directly to the motor.

          If your new VFD is a PowerFlex 7000, it is probably an AFE drive and the phase shifting transformers would no longer be needed. But they COULD have quoted it as a 12 pulse diode front end, because you ALREADY own those transformers. It's something you should get clear. Either way, you will STILL need that 13.8kV to 4160V transformer, UNLESS because you no longer need the Bypass starter, they are quoting you a new AFE or 18 pulse drive with a NEW 13,8kV isolation transformer. That would be wasteful in my opinion, unless there is a problem with your transformer.

          1) Yes, something like that. I believe it goes only to the "FVNR Bypass Starter" and then that feeds the VFD or the motor directly.

          2) The phase sift transformer is one unit sitting right next to the large 13.8/4160 transformer. It has 1 primary coil and 2 secondary coils as shown on the plate. Its all one unit and sitting outside taking up valuable space. 1 feed from the VFD/bypass feeds in, 2 feeds out back to the VFD.

          3) Yup.

          4) Rockwell knows what i am feeding them (3 phase 4160) from the 13.8/4160 transformer, and they know what they need to power the 4160 motor. So i wasn't afraid of an issue, but more curious of how the old system operated. They also had specification on harmonics and power factor that they must meet...


          Thanks for the insight though and this has been a learning experience.

          Comment


            #20
            Originally posted by drktmplr12 View Post
            its up to you to tell them if you want AFE or passive. each has their own maintenance implications which need to be considered based on the skill levels of your maintenance staff.

            If possible, I would encourage you to consider mfr's other than Rockwell if footprint is a concern (trying to clear up space in MCC room). Their MV voltage source designs are massive compared to comparable Eaton, ABB, Yaskawa, Siemens ROBICON units.

            Be careful letting the mfr design anything other than what is inside the drive. I have had reputable mfr's suggest installing drives in a room where you couldn't get them all out after they were installed.

            disregard my post if this has already been considered.

            No, thanks for your insight!

            I have specifications regarding harmonics and power factor injection onto our network. So they can supply what ever equipment they want, but if it contributes any additional harmonics or lowers our power factor they will be paying to fix it.

            I got a quotes from other manufactures and they were not significantly different in terms of cost or footprint. We also use Rockwell for most of our equipment and have a very good working relationship with them. Also i rather have one type of equipment for stocking spare parts and integrating systems.

            Comment


              #21
              Closure on this Topic

              I thought i'd post what the end results are.

              The drive is up and running perfectly with no issues. New feed of 13.8kv hits the tranformer and a new feed of 4160 from it to the drive and the motor.

              I have included some links to show the input and output waveform of the drive.

              The first image is for full load, the second image is at 50%

              The following lines show;
              1. Voltage input
              2. Current input
              3. Voltage output
              4. Current output

              https://i.imgur.com/DM1b9rE.jpg

              https://i.imgur.com/fL0knr2.jpg

              Results, there is almost no harmonic, just a bit of a 5th harmonic under 50% load.

              Anyway thanks again for everyone's help and i will defiantly use some of you'll advice!

              Comment


                #22
                Thanks for the follow up, we rarely get that.
                __________________________________________________ ____________________________
                Many people are shocked when they discover I am not a good electrician...

                I'm in California, ergo I am still stuck on the 2014 NEC... We'll get around to the 2017 code in around 2021.

                Comment

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