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VFD Ct test

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zepfan
zepfan Member Posts: 436
in A-C, Heat Pumps & Refrigeration

Does anyone know of a test to determine if a VFD has a defective CT? Other then swapping out the drive with another one? I am aware of the test to test the diodes .We have an ABB 550 that is only two years old, but since ABB no longer makes this model and it is out of warranty they (ABB) does not provide support.

The VFD about every 7 days goes off on overcurrent. We have disconnected, and megged the motor windings and they are all over 100 meg to ground. It is in a packaged ac unit so the length of the wires from the drive to re less the 6 feet. The only thing that I can think of is the component that measures the current in the drive (the CT) may be bad.

Any suggestions would be much appreciated. Thanks to all

Comments

  • 109A_5
    109A_5 Member Posts: 2,465

    There are different sizes of the ABB ACS550 Drives and the CTs are most likely different depending on drive size. They do go bad. I believe they are Hall Effect sensors since the AC waveform the motor sees is generated from switching a DC Buss. Were you able to get the actual fault code(s) ?

    For example; the Blue Doughnut like parts. For the effort to get in there to test them a shop may just change them if suspected bad. Small Electrolytic Capacitors go bad too, however not sure if that would give that error.

    image.png

    It is interesting they don't blame the drive.

    image.png image.png
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
    zepfan
  • ratio
    ratio Member Posts: 4,061

    Check the harness as well. I had an ERV that kept blowing fuses, it ended up being a weak spot in the insulation of the harness, when the humidity went up the 480V would break over & blow a fuse. It was a real bear to find, I even megged the harness right outta the gate, which is why I didn't find the fault until it got bad enough to start charring the insulation.

    I also had a bad motor once. It was a gear motor on a knockoff Big **** fan (HVLS). It passed every test, but still tripped the drive until I replaced the motor.

    zepfan
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 18,208

    Don't know if this will help as I saw it mentioned above but one thing that can solve drive issues is to increase the ramp times if the application allows it.

    Had a job with 100hp fan motors that was throwing expensive belts that the control guys had it ramping too fast.

    I have seen other motor's fault when shutting down you will usually get an error that says 'DC buss overvoltage" or something similar.

    A drive book I had said to ramp up and down as slow as possible less stress on the motor and the vfd.

    zepfan
  • zepfan
    zepfan Member Posts: 436

    thanks so much for the responses. Yes I have increased both the accel, and decel. Speed to 60 seconds. The strange part about it is that the max current for the motor is 81 amps. When checking the fault logger when the drive faults out the current shows at time of fault 34.4 amps

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 18,208

    Don't know your location but we used Flow Tech Inc in Connecticut.

    They do CT, Western, MA, Vermont and some NY counties

    860-291-8886

    maybe they can help

    They do ABB drives.

    zepfan
  • 109A_5
    109A_5 Member Posts: 2,465

    Is the Start-Up and / or Operational values correct ? Since the drive is only two years old I would not suspect failing Capacitors, but failing Capacitors can cause odd behavior.

    I am assuming it is the correct size drive for the motor. And this is a new problem. No strange overloads on the motor (from whatever equipment the motor is spinning).

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
    zepfan
  • zepfan
    zepfan Member Posts: 436

    Thanks for the responses. The drive was factory installed by Carrier in a RTU. This problem has just started. There are no external overloads on the motor. I have increased both the accel and decel times to 120 seconds and hope that does something.The unit is vav so the fan runs all the time. When it goes from un occupied to occupied it takes at least five minutes for the compressors to come on so this two minute ramp time should not effect anything

  • mattmia2
    mattmia2 Member Posts: 13,432

    there isn't much in a current transformer itself to go bad. are you sure it isn't short cycling and trying to start under too much head? doesn't the vfd have delay settings for that?

  • mattmia2
    mattmia2 Member Posts: 13,432

    i think it also calculates the current at a given condition but i'm not positive of that so if it thinks it is drawing too much current for the speed it might shut down.

  • ratio
    ratio Member Posts: 4,061

    Another thing to check is the DC bus voltage. I had a job where an Aaon kept tripping the blower drive. It turned out that the whole campus was running a little hot (490+ volts) & that caused the drive to over charge the DC bus which then caused it to trip if the voltage wiggled around any. IIRC the solution was to reduce the programmed motor voltage, I guess that allowed the drive to charge the DC bus to a lower voltage.

    HeatingHelp.comzepfan
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 18,208

    I would also get into the vFD and see what they set the motor current trip at it may have been set wrong. The trip current should be nameplate amps x 1.15 or 1.20 depending on the motor service factor. Most motors are not 1.0 anymore.

    About the only problem you can have with excessive ramp time it if you have to make an air switch to quickly make

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