Page 1 of 2 12 LastLast
Results 1 to 10 of 12

Thread: VFD and motor starter

  1. #1
    Join Date
    Dec 2013
    Location
    Hanover park, il
    Posts
    9

    VFD and motor starter

    I came across, a VFD connected to a motor starter, that is the first time I have seen this. I thought when you have a VFD you do not need a motor starter. The Line of side, is connected to the line side of the VFD, The load of the side of the VFD( T1-T2-T3) is connected to the line side of the motor starter, then the load side of the motor starter (T1-T2-T3) is connected to the motor. Can I remove the motor starter, and run the motor from the VFD?? Any Input will be very help. Thank You.

  2. #2
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    30,844
    There could be rare instances where you might do that, so more information about the equipment involved may help determine if there is good reason to do this.

    Otherwise as a general rule about all you put in between drive and a motor is line reactors and possibly overload sensing equipment.

    If you do have any switching device it should have aux contacts to open the run command of the drive whenever the switching device is opened. Many drives may not mind so much having the output circuit opened while running but won't like having the load suddenly closed into an active output.

  3. #3
    Join Date
    Sep 2008
    Location
    UK
    Posts
    9,093
    Quote Originally Posted by reyamkram View Post
    I came across, a VFD connected to a motor starter, that is the first time I have seen this. I thought when you have a VFD you do not need a motor starter. The Line of side, is connected to the line side of the VFD, The load of the side of the VFD( T1-T2-T3) is connected to the line side of the motor starter, then the load side of the motor starter (T1-T2-T3) is connected to the motor. Can I remove the motor starter, and run the motor from the VFD?? Any Input will be very help. Thank You.
    VFD?
    Si hoc legere scis nimium eruditionis habes.

  4. #4
    Join Date
    Sep 2008
    Location
    UK
    Posts
    9,093
    Quote Originally Posted by reyamkram View Post
    I came across, a VFD connected to a motor starter, that is the first time I have seen this. I thought when you have a VFD you do not need a motor starter. The Line of side, is connected to the line side of the VFD, The load of the side of the VFD( T1-T2-T3) is connected to the line side of the motor starter, then the load side of the motor starter (T1-T2-T3) is connected to the motor. Can I remove the motor starter, and run the motor from the VFD?? Any Input will be very help. Thank You.
    You can. If you keep, it you must ensure that there is an auxilliary contact of the contactor in the VFD enable circuit so that the VSD cannot be started with the contactor open.

    We supplied VFDs mainly into the petrochem and water industries. As far as I can recall, all had a contactor between the VFD and the motor. This was specified/mandatory for a hard-wired emergency stop with a physical disconnect of the motor.
    Si hoc legere scis nimium eruditionis habes.

  5. #5
    Join Date
    Jul 2006
    Location
    San Francisco, CA, USA
    Posts
    6,182
    Quote Originally Posted by kwired View Post
    There could be rare instances where you might do that, so more information about the equipment involved may help determine if there is good reason to do this.

    Otherwise as a general rule about all you put in between drive and a motor is line reactors and possibly overload sensing equipment.

    If you do have any switching device it should have aux contacts to open the run command of the drive whenever the switching device is opened. Many drives may not mind so much having the output circuit opened while running but won't like having the load suddenly closed into an active output.


    It generally boils down to one of three issues:
    1) There is a safety issue that requires a contactor downstream, in which case hopefully someone did it as kwired said with regard to an aux contact shutting down the VFDs Run command.

    2) Whomever did this was unfamiliar with how VFDs function and thought it was necessary.

    3) It's a really old VFD that does not provide motor running overload protection, and combined with #2, resulted in a complete starter, not just an OL relay.
    __________________________________________________ ____________________________
    Many people are shocked when they discover I am not a good electrician...

  6. #6
    Join Date
    Oct 2013
    Location
    newburgh,ny
    Posts
    378

    Line side of VFD

    You will see them on the line side of the VFD as a safety cutoff/e-stop. They are found on the line side incase something goes wrong inside of the VFD and it don't stop conducting.
    A cowboy may get thrown , but they always get up and walk forward.

  7. #7
    Join Date
    Dec 2012
    Location
    Southern Ca, USA
    Posts
    355
    I see plenty of machines and systems made with safety contactors that remove power from all drives and motor starters. So that's one way to do it.
    Safety applications would be the only reason to have a starter feeding a VFD.

  8. #8
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    30,844
    Quote Originally Posted by Aleman View Post
    I see plenty of machines and systems made with safety contactors that remove power from all drives and motor starters. So that's one way to do it.
    Safety applications would be the only reason to have a starter feeding a VFD.
    Makes sense, but OP's was on load side of drive.

  9. #9
    Join Date
    Jul 2006
    Location
    San Francisco, CA, USA
    Posts
    6,182
    Quote Originally Posted by kwired View Post
    Makes sense, but OP's was on load side of drive.
    Still the same issue though. In SIL 3 rated safety systems before the advent of STO options (and for some, even after), you need(ed) to have a contactor in series to need the safety redundancy standards, and in Europe its very common to put them on the load side of the VFD, between the drive and the motor. The reason is, putting a contactor on the line side adds stress to the pre-charge circuit of the VFD if they are used every time you shut down. On the load side, all you need do is ensure that the VFD output cannot be on when the contactor opens or closes.

    Name:  1637927.jpg
Views: 56
Size:  36.0 KB
    __________________________________________________ ____________________________
    Many people are shocked when they discover I am not a good electrician...

  10. #10
    Join Date
    Dec 2012
    Location
    Southern Ca, USA
    Posts
    355
    Quote Originally Posted by kwired View Post
    Makes sense, but OP's was on load side of drive.
    Looks like I need to read more carefully! But I have seen this on the load side too, done for safety reasons. Not a common practice but as
    long as the safety circuit shuts down the drive signal it 'might' make for a better safety, with the output completely isolated. Kind of like opening
    a local disconnect on a motor connected to a drive but automated.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •