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Thread: Defective Drive???

  1. #1
    Join Date
    Nov 2007
    Location
    Nevada, IA
    Posts
    102

    Defective Drive???

    At a grain elevator, I have a 480 volt 7.5 HP motor on a VFD. This motor is running a unload pit drag. Lately, it has been intermintently tripping out the drive overloads on start up (at times under load, other times no load). A week ago I showed up and opened up the drive to find it absolutely FULL of grain dust. We blew it out, cleaned it up and it started to run just fine. Now I'm being told it is doing the same thing. I'm on my way out the door to go troubleshoot it...this time I will disconect and meg the windings to check that out, I will also isolate the drive and check out the amperage. I'm wondering if the drive is shot? Any ideas and comments are much appreciated!

  2. #2
    Join Date
    Nov 2007
    Location
    Nevada, IA
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    102
    Megger readings at motor @ 1000vdc for 1 minute

    T1 327 Mega ohms
    T2 329 Mega ohms
    T3 327 Mega ohms

  3. #3
    Join Date
    Sep 2008
    Location
    UK
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    6,559
    Quote Originally Posted by jerjwillelec View Post
    Megger readings at motor @ 1000vdc for 1 minute

    T1 327 Mega ohms
    T2 329 Mega ohms
    T3 327 Mega ohms
    Have you also checked continuity of the windings and current balance?
    Assuming the VSD input is three phase, have you checked for current and voltage balance.

  4. #4
    Join Date
    Nov 2007
    Location
    Nevada, IA
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    102
    I bypassed the drive for flc readings...ran just fine

    T1 4.7 amps
    T2 4.9 amps
    T3 5.3 amps

  5. #5
    Join Date
    Nov 2007
    Location
    Nevada, IA
    Posts
    102
    Again bypassed the drive...

    P1-P2 493.9 vac
    P1-P3 496.6 vac
    P2-P3 499.1 vac

  6. #6
    Join Date
    Nov 2007
    Location
    Nevada, IA
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    Quote Originally Posted by Besoeker View Post
    Have you also checked continuity of the windings and current balance?
    Assuming the VSD input is three phase, have you checked for current and voltage balance.
    Sorry...VSD?

  7. #7
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    Nov 2007
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    Nevada, IA
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    102
    Continuity of the windings...

    P1-P2 2.04 ohms
    P1-P3 2.04 ohms
    P2-P3 2.04 ohms

  8. #8
    Join Date
    Oct 2004
    Location
    Rochester NY
    Posts
    122
    tripping out the drive overloads on start up
    Please describe what and where these overloads are. I normally don't put overloads on drives. I have a CB or fuses or a manual motor starter on the input side to protect/disconnect the branch circuit into the drive and the drive itself has settings for the motors FLA. Is that set correctly ?

    Or is the drive tripping ? If so what is the trip code and what does the manual say about it?

    Also, when you blew out and cleaned it up, did you actually clean the heat sink fins of all dust ? Even a small layer left over from blowing it out is a great thermal barrier.

    One last thought. It's hot here in Upstate NY, what's the ambient temp. of the drive and motor, etc? Direct sun on the drive ? Get where I'm coming from ?
    Free is not the man who works for a living.

  9. #9
    Join Date
    Nov 2007
    Location
    Nevada, IA
    Posts
    102
    Re connected to drive and ran with no product...

    L1 1.6 amp
    L2 2.0 amp
    L3 2.4 amp

    T1 4.5 amp
    T2 4.5 amp
    T3 4.5 amp

    Seems to run just fine for me with no product. Elevator manager says it is real inconsistent in it's failing...sometimes with no product, sometimes with product...sometimes after it's ran for a long period, sometimes on first start up

    The drive is a Magnetek GPD 503...approx 20 yrs old.

    I'm stumped!!!

  10. #10
    Join Date
    Feb 2003
    Location
    Wisconsin
    Posts
    8,808
    Many small drives are inherently rated for variable torque loads, which means they usually do not have much starting torque.

    Conveyors need to be started 'fully loaded' so they require a drive rated for constant torque loads, if not one that is oversized.
    Just because you can, doesn't mean you should.

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