Do 2-Pole and 4-Pole Motors Create Similar VFD Overvoltage at Same RPM?

Discussion in 'Power Electronics' started by Zero Potential, Sep 22, 2016.

  1. Zero Potential

    Thread Starter Member

    Mar 25, 2015
    64
    2
    Hope this is the right forum for this.

    I am trying to choose a motor for a belt grinder. I have a 3HP TECO VFD. I connected it to a 3HP 4-pole motor, and when I crank the RPM over 4000, I get a DC bus overvoltage, and the VFD quits on me.

    It's my understanding that the motor behaves like a generator, sending power back to the VFD, and the VFD doesn't like it. My wild guess is that this is related to the speed of the motor, since I would expect a generator to pump out more juice at high speeds, and because the problem only happens at high speeds.

    I turned off DC braking and deceleration; it didn't make a difference that I can detect.

    Is there any difference between 2-pole and 4-pole motors when it comes to creating overvoltages? If I get a 2-pole motor and run it at the same RPM, will I have the same problem? If so, I might as well get a bigger drive pulley and keep the existing motor. If not, maybe I can squeeze higher RPM out of a 2-pole motor.

    Thanks for any light you can shed.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,566
    2,379
    The usual rpm of a standard 1ph 4 pole motor on 60hz is something under 1800rpm, I would consider 4000rpm the absolute limit for a standard motor.
    A 2 pole motor, you may get something more, but if you want very high rpm motor, you may want to consider one of the specialized high frequency motors.
    What are you aiming for?
    Max.
     
  3. Zero Potential

    Thread Starter Member

    Mar 25, 2015
    64
    2
    I'm shooting for 5000 surface feet per minute. Right now I have a 4" drive pulley, and I can't do better than about 3600 RPM on the 3HP motor I have. I get an overvoltage error.

    I was wondering if a 2-pole motor would allow me to go faster without an overvoltage error.

    Right now I'm inclined to make a 6" pulley and keep my motor, but I am still curious about the overvoltage.
     
  4. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,041
    1,673
    It shouldn't be a problem on a 2 pole motor. I have a 2 HP 3450 RPM one on my Smithy lathe/mill unit set for 120 cycles top end which give it a ~6900 RPM top end. Never had issues with it at that speed even with DC braking turned on.

    As for your 4 pole motor creating a over voltage shutdown it sounds like you either have another setting wrong or a bad VFD or a bad motor being that an electric more cannot feed more energy back into the VFD than its being supplied with given a constant running speed and load. Physics won't allow it no matter how many YouTube videos try to convince you otherwise. :oops:
     
  5. Zero Potential

    Thread Starter Member

    Mar 25, 2015
    64
    2
    Thanks for the help, but please notice: I am using a 3HP motor, not 2HP.

    I have a 2HP motor, and it will run as fast as I want.
     
  6. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,041
    1,673
    And? o_O
     
  7. Zero Potential

    Thread Starter Member

    Mar 25, 2015
    64
    2
    And I can run the 2HP motor all day at whatever speed I like, but the 3HP motor stops the VFD, so your experience can't be extrapolated to mine.
     
  8. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,041
    1,673
    That makes no sense whatsoever.

    Either the VFD is set wrong or the motor has an issue you are not aware of.

    Who owns what and what size it is is irrelevant. Just because the 300 HP VFD and motor set at some place I worked at had an issue means nothing relating to any other VFD used anywhere else regardelss of location size or application.

    If yours won't work then obviously you have either a winding problem or a VFD related problem.

    Have you done any inductance testing or High Pot testing of the 3 HP motor to see if it is functioning correctly? Even tried another 3 hp motor of equal ratings to see if it does it with that one? o_O
     
  9. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    I'm afraid you're earning your name when you say things like that.:(
    TCM is the best motor guy on this site.
    I would do anything TCM says to do with a motor.
     
  10. Zero Potential

    Thread Starter Member

    Mar 25, 2015
    64
    2
    I wrote an explanation; please ignore it. I am editing it.

    Thanks for suggesting I look at the motor. I see an obvious problem, completely my fault, and I am now working to fix it.
     
    Last edited: Sep 23, 2016
  11. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,041
    1,673
    It's okay. Seems like everyones cranky and on edge lately. :(

    BTW, I still miss things all the time. Even on stuff I know better that I probably should . :p
     
  12. Zero Potential

    Thread Starter Member

    Mar 25, 2015
    64
    2
    This is unbelievable. I looked at the wiring briefly when the motor arrived, but I didn't do it carefully, because I just found out the motor was wired for 460 volts. Really embarrassing, but at least it's fixed.

    It runs like a nuclear sub now.

    Thanks for the suggestions.
     
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