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Do you think this would damage a VFD?

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    Do you think this would damage a VFD?

    Had a major power blink and had faults on a VFD that required powering down the VFD to clear them. Found I couldn't power it down because a controls contractor had tied a foreign 24 VAC source into the drive's native 24 VAC control power for it's inputs/outputs. I.E. display never goes out on drive when you kill incoming power.

    Think it could cause any harm to drive's electronics? What tests would you want to run? Drive is 125 HP Altivar 61 with 480/3 phase input.


    #2
    Originally posted by Russs57 View Post
    Had a major power blink and had faults on a VFD that required powering down the VFD to clear them. Found I couldn't power it down because a controls contractor had tied a foreign 24 VAC source into the drive's native 24 VAC control power for it's inputs/outputs. I.E. display never goes out on drive when you kill incoming power.

    Think it could cause any harm to drive's electronics? What tests would you want to run? Drive is 125 HP Altivar 61 with 480/3 phase input.
    The manual shows there's a switch SW1 to select between the internal 24V supply or an external one. If the switch is in the Sink Ext position then it's set up to use external power and the behavior you mention might be expected. By the way, I think this is 24V DC not AC?

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      #3
      Most drives get their control power off the DC link so if it’s not running at the time it takes close to a minute or more to lose control power.

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        #4
        Power introduced by controls contractor is definitely 24 VAC. Can't say if drive's native power is AC or DC.

        Had 480 input power off for an hour. Verified no input AC voltage and no DC bus voltage. Display was still on and couldn't reset drive.

        Old energy management system used dry relay contacts so used drive's power supply. Seems that part wasn't noticed by new controls vendor. Strange part was when I broke the connection to their external power source at drive (and was able to reset drive) adjacent drive went down.

        Main question remains, could mixing these two different voltage sources damage my drive and what testing would you want to perform to satisfy yourself no damage has been done? I would say this external voltage source has been active for a couple of weeks without our knowledge but that is hard to say for sure.

        Seems a minor issue once root cause was discovered but it did end up in the cancellation of surgery in O.R's so it is a big deal (and even more so if it harmed my (3) drives).

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          #5
          These are indicating that external 24V power should be DC:

          https://www.youtube.com/watch?v=kjZi4PAjANU

          https://www.se.com/ww/en/product/VW3...r-speed-drive/

          https://www.se.com/sg/en/faqs/FA274659/

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            #6
            IDR any of the VFDs I've worked on as anything but DC. Admittedly limited,
            Tom
            TBLO

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              #7
              Originally posted by Russs57 View Post
              Had a major power blink and had faults on a VFD that required powering down the VFD to clear them. Found I couldn't power it down because a controls contractor had tied a foreign 24 VAC source into the drive's native 24 VAC control power for it's inputs/outputs. I.E. display never goes out on drive when you kill incoming power.

              Think it could cause any harm to drive's electronics? What tests would you want to run? Drive is 125 HP Altivar 61 with 480/3 phase input.

              Notwithstanding the effect this ghost voltage has on saving the VFD. . . your installation clearly violates all safety protocols in Engineering Design.

              When you kill the main source [incoming power] you should be able to kill power to the VFD. . . no ifs, no when.

              This applies whether you have foreign or alien voltage, or just plain induced (ghost) voltage coming in.

              Perhaps you want to rephrase your query in order to jibe with sensible engineering practices?









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                #8
                Hey, wasn't my engineering. Wasn't done with my knowledge. If it was going to be done, it should have been 24 VDC and SW1 should have been configured properly. Fact is, it was done and done with 24 VAC.

                I was able to get the 24 VAC removed today and the drives 24 VDC power seems to be okay. So all is well for the time being.

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                  #9
                  Sounds like if the external power option was really necessary for some valid engineering reason, the setup could be made compliant by running the external power through a relay which disconnects it when the main VFD AC input is removed?

                  But the AC kludge versus the sanctioned DC input rules out the way it was actually done.

                  Comment


                    #10
                    Originally posted by GoldDigger View Post
                    Sounds like if the external power option was really necessary for some valid engineering reason, the setup could be made compliant by running the external power through a relay which disconnects it when the main VFD AC input is removed?

                    But the AC kludge versus the sanctioned DC input rules out the way it was actually done.
                    It was common in the old controls design to have separately sourced power that enters a control cabinet.
                    A typical feature in a spread-out facility when several manufacturing processes are being undertaken.
                    I've serviced equipment in one facility where the complex was divided in two different areas. . .one area is the what they call the EDIBLE AREA and the other the INEDIBLE AREA.

                    No mingling of raw materials was high priority.

                    One section manufacture products like detergents, hygiene, cosmetics and bar soaps.
                    This is the inedible area.

                    The other was the edible area where they manufacture pancake syrup, margarine and cooking oil to mention a few.
                    In both of these areas-- on some control panels-- there were equipment that have common control stations that can be operated from either manufacturing areas like air vents, vehicle movement warning signage etc.

                    Needless to say, maintenance personnel have to open these MCCs and have to deal with voltages coming in from different sources that are not part of the MCC being worked on.

                    Although highly visible signs that remind technicians of the presence of foreign voltage (CAL OSHA) requirement, the local AHJ also required provisions like interlocks to disable all power. . .local or foreign.
                    These interlocks could be either mechanical or electrical. (relays or solenoids )

                    In today's modern facilities that cover a wide area like refineries, they are using wireless technology.
                    They still have to adhere to: "no ifs no when" compliance.

                    Comment


                      #11
                      Originally posted by myspark View Post


                      Notwithstanding the effect this ghost voltage has on saving the VFD. . . your installation clearly violates all safety protocols in Engineering Design.

                      When you kill the main source [incoming power] you should be able to kill power to the VFD. . . no ifs, no when.

                      This applies whether you have foreign or alien voltage, or just plain induced (ghost) voltage coming in.

                      Perhaps you want to rephrase your query in order to jibe with sensible engineering practices?








                      That 24 volt source is very possibly power limited and not considered a safety hazard to anyone working on the equipment if it is still energized.
                      I live for today, I'm just a day behind.

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