Frequency drive question

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  1. #1
    vinnygalbo's Avatar
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    Default Frequency drive question

    I've got a question about a frequency drive.

    First, let me say I have little knowledge on this matter.

    Yesterday at work we were having trouble with a particular machine that has an OMRON frequency drive on it. It controls an AC motor that is mechanically "coupled" with a worm shaft. After opening up the control cabinet and watching a few machine cycles. A coworker had said to me that the display on the drive was showing that the motor was running at 80Hz. I said, "what's the matter with that?". His concern was that the motor that it was driving was only rated at 60Hz and the drive was programmed at 80Hz.

    I'm thinking with my little knowledge, that I know this is common because I've seen it done on many other applications. He was kind of confused on how the frequency could be bumped up higher than what the incoming supply voltage frequency was. I had him increase the frequency up to 90Hz and then back down to 60Hz. There was a considerable speed difference and told him, well obviously you can run a motor at higher frequency then the motor rating.

    Questions that I have:
    1. Is this a normal application?
    2. Will it hurt the motor? The motor does not run continuously.
    3. Will a higher frequency cause more noise. I'm only asking because I believe we have a noise problem with our PLC.

    Thank you in advance.



  2. #2
    Community Moderator Al_The_Man's Avatar
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    Default Re: Frequency drive question

    Most motors can be ran at a higher frequency using a VFD, this is one of the features.
    I tend to limit ordinary 4 pole motors to double the mains frequency, so if 4 pole 120Hz will take it up to what the 2 pole motor version would be, 3600rpm.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


  3. #3
    Member Jim Dawson's Avatar
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    Default Re: Frequency drive question

    Quote Originally Posted by vinnygalbo View Post
    He was kind of confused on how the frequency could be bumped up higher than what the incoming supply voltage frequency was.
    This is what inverters (called VFDs, frequency drives, or a few other names) are designed to do. The incoming AC (60 Hz in North America) is converted to DC, then is output as a variable frequency AC signal to run a motor, normally in the 0 to 400 Hz range. This is all done with ''electrical magic'' in the inverter.

    Questions that I have:
    1. Is this a normal application?
    An absolutely normal application, this is exactly what they are designed to do.

    2. Will it hurt the motor? The motor does not run continuously.
    In most cases, no. The motor is perfectly happy to run this way as long as you stay within the system design limits.

    3. Will a higher frequency cause more noise. I'm only asking because I believe we have a noise problem with our PLC.
    Inverters are electrically noisy, it's the nature of the beast. This can be mitigated with proper filtering and grounding. The inverter instruction manual normally has detailed instructions for filtering and grounding. In many applications just proper grounding is sufficient, in more critical applications filtering is required.

    Jim Dawson
    Sandy, Oregon, USA


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    lukebarber's Avatar
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    Default Re: Frequency drive question

    Quote Originally Posted by vinnygalbo View Post
    I've got a question about a frequency drive.

    First, let me say I have little knowledge on this matter.

    Yesterday at work we were having trouble with a particular machine that has an OMRON frequency drive on it. It controls an AC motor that is mechanically "coupled" with a worm shaft. After opening up the control cabinet and watching a few machine cycles. A coworker had said to me that the display on the drive was showing that the motor was running at 80Hz. I said, "what's the matter with that?". His concern was that the motor that it was driving was only rated at 60Hz and the drive was programmed at 80Hz.

    I'm thinking with my little knowledge, that I know this is common because I've seen it done on many other applications. He was kind of confused on how the frequency could be bumped up higher than what the incoming supply voltage frequency was. I had him increase the frequency up to 90Hz and then back down to 60Hz. There was a considerable speed difference and told him, well obviously you can run a motor at higher frequency then the motor rating.

    Questions that I have:
    1. Is this a normal application?
    2. Will it hurt the motor? The motor does not run continuously.
    3. Will a higher frequency cause more noise. I'm only asking because I believe we have a noise problem with our PLC.

    Thank you in advance.
    ( 1 ) Yes it is normal most AC 3Ph 4P motors can run up to 120Hz

    ( 2 ) Yes it can hurt the motor if the wiring is not don't correct, Shielded Cable is a must from the VFD Drive to the Motor and the Shield has to be correctly terminated at each end , an input Power Filter or line reactor will solve most of the problems related to motor protection

    ( 3 ) Yes you will get more noise, this can be controlled to a point by the Carrier Frequency Parameter a higher Carrier Frequency Setting can help with this but also can cause over heating so there is a limit as to how high you can go with this setting

    Mactec54


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    Community Moderator Al_The_Man's Avatar
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    Default Re: Frequency drive question

    Quote Originally Posted by vinnygalbo View Post
    3. Will a higher frequency cause more noise. I'm only asking because I believe we have a noise problem with our PLC.

    .
    One thing that can make the VFD output much 'quieter' is a 3 phase choke between VFD and motor, I have frequently used these where mounted in the same enclosure, or close by to the controller or PLC.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.


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Frequency drive question

Frequency drive question