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WHAT HAPPENED? VFD or Motor died?

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  • WHAT HAPPENED? VFD or Motor died?

    I was humming along nicely today, and suddenly my lathe stopped FAST! Dead in its tracks.
    The VFD went black.
    Everything turned off.
    I checked the breaker, and it was tripped.
    Reset it, turned on the VFD, It came to life, then shut off. Tripped the breaker again.
    So I disconnected the 3 wires going to the motor, and turned on the VFD.
    Everything looked normal.
    Turned it off, Re-connected the 3 motor wires, and now the VFD is giving me a "Ground Fault Alarm".
    The motor won't start-up.
    All wires are connected correctly, and have been for the past 3 years.
    I'm Electrically Ignorant, so what do I do now?
    Take the motor in for a checkup?
    Did something die?

  • #2
    Check your manual to see exactly what that error means. It could be you have a wire loose back in the breaker box.

    Comment


    • #3
      The Alarm says: Earth Fault. Drive has detected earth (ground) fault in motor or motor cable. Check motor Check motor cable.
      Well....
      I checked the motor cable, and everything looks fine. Nothing loose. It's been wired for 3 years without any problems.
      Did something happen internally in the motor?

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      • #4
        Have you got a spare slave motor you can connect to ?

        Failing that three mains light bulbs wired in delta Δ
        .

        Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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        • #5
          Two things you can try pretty easily. Kill the AC power prior to disconnecting or reconnecting any wires. Allow at least 3-4 minutes after the display dies before touching the wires.

          1) Disconnect all three motor leads and start the drive. If it still trips the drive is bad.
          2) Disconnect 2 of the motor leads and leave just one connected - Tape the disconnected leads separately. Now power up and start the drive. If that's OK, try each of the other motor leads, one at a time only, with the same test. If that faults the drive but test 1 above did not, it may be a motor winding grounded in the motor or even a wire grounded. I would not advise connecting two motor leads with one disconnected.

          BTW, unless your light bulbs are 230V, John's suggestion might get exciting. I would suggest a Y connection since you are in the US if you want to use light bulbs and that only if you are wired for a 230V motor.

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          • #6
            Most VFD's detect a ground fault on the load, you could check for a ground on the motor with a VOM, but it may only show with a Megger test unless it is a very low resistance fault.
            Max.

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            • #7
              Well CRAP!!
              I was fiddling with it, and reversed two wires as to reverse the motor, just out of curiosity.
              When I turned on the power, the VFD went KA-POW!!!, with a pretty Orange spark.
              Oh Hell.
              What have I done now?

              Comment


              • #8
                You have released the fabled "Magic Smoke". Your VFD's soul is now in digital heaven.

                Comment


                • #9
                  Originally posted by KiddZimaHater View Post
                  Well CRAP!!
                  I was fiddling with it,
                  What have I done now?
                  Well at least you now know the drive is bad. It's a shame you can't say yea or nay about the motor yet.

                  Go ahead and pull all three motor leads and power it up. If that is OK, start it. Wear safety glasses. If it doesn't fault, count your blessings, but I suspect it's dead now.

                  Comment


                  • #10
                    Instead of powering it up, may I suggest:

                    1) Ohmmeter check from wires to case......

                    2) power up, with case solidly grounded, and a suitable light bulb in series with each motor lead. a 40W is fine.... you can still buy those.

                    If a wire is grounded to case, the ohmmeter will show it, OR the light bulb will light.

                    240V is 138V to neutral (ground) so it;'s a little hard on the bulbs..... usually low wattage in the 40W area can take the most.


                    QUESTION:

                    What brand/type of VFD?

                    Most VFDs are protected against shorts and grounded wires, although some are not, being only protected against line-to-line shorts. Most of the ones that weren't ground protected before are changing over to being protected as new models come out.

                    It sounds like you have one motor lead grounded, and the VFD has only two sensors.... you can do that, the third wire should be mathematically known from the other two. Problem is, in a short to ground, the math isn't any good..... if the un-sensed wire is shorted to ground, the VFD doesn't "know" and does not shut down. Dollars to popped IGBTs that your problem is that.
                    Last edited by J Tiers; 04-01-2013, 09:21 PM.
                    1601

                    Keep eye on ball.
                    Hashim Khan

                    Comment


                    • #11
                      It's an ABB drive, Model acs150 purchased in 2010.
                      Why would the motor suddenly have one lead grounded, outta nowhere?
                      I hope I didn't kill that drive.

                      Comment


                      • #12
                        Originally posted by KiddZimaHater View Post
                        It's an ABB drive, Model acs150 purchased in 2010.
                        Why would the motor suddenly have one lead grounded, outta nowhere?
                        I hope I didn't kill that drive.
                        Drives and motors are ephemeral!
                        Take the motor to a a good rewind shop and have it completely tested.
                        Consider the drive a rental whose time has expired you did not kill it it died of natural causes

                        Comment


                        • #13
                          Originally posted by KiddZimaHater View Post
                          It's an ABB drive, Model acs150 purchased in 2010.
                          Why would the motor suddenly have one lead grounded, outta nowhere?
                          I hope I didn't kill that drive.
                          The ABB are fairly high quality, If it was an older motor, it would not be vector rated, it may have not taken kindly subjected to high frequency switching, I always make a practice of fitting a 3 phase inductor in the motor leads, this makes it easier on both motor and VFD.
                          Max.
                          Last edited by MaxHeadRoom; 04-01-2013, 11:23 PM.

                          Comment


                          • #14
                            I have had similar problems which puzzled me for a while. A mill with a 3hp motor which I was driving from a VFD. The motor was probably about 30-40 years old. Occasionally, on heavy cuts the VFD would fault and the motor stop. I just restarted and everything was fine for a while. Then it would fault and the RCD would drop out. At that point I started to become more concerned. The fact that the RCD dropped out gave me a clue that something was probably getting leaky to earth. I checked the motor windings resistance to earth with a multimeter and they looked reasonable, but not as high as I thought they should be, especially on one winding. It is hard to really test a motor with a multimeter and be sure, so I took the motor to a rewinder and got them to check it properly. The outcome was insulation beginning to break down, and the motor was not 'economically repairable'. New motor and all was well. Your VFD sounds like it may have suffered some damage, which is unfortunate, but check the motor before you try a new VFD.

                            Incidentally, the rewinder felt that a VFD might stress the insulation more than conventional 3 phase. I can see some logic behind this, but cannot say whether this was a contributing factor in the failure of my motor.
                            Bill

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                            • #15
                              Originally posted by willmac View Post

                              Incidentally, the rewinder felt that a VFD might stress the insulation more than conventional 3 phase. I can see some logic behind this, but cannot say whether this was a contributing factor in the failure of my motor.
                              The VFD DOES put a bit more stress on the first few turns of each coil. Motor companies have studied this and found that it really IS only the first few.

                              However, there is also significant stress on the between-phase coil-to-coil insulation, which is typically hand-placed spacers of insulating material, and also from the care taken to keep the different coil wires separated during assembly.

                              The "VFD rated" motors do have different insulation, largely due to more care taken in assembly (the wire coating is not an important issue, and the motor companies admit that, even as they tout it), and they also have improved cooling to allow running at much slower speeds without compromising the cooling too much. However, they are premium-priced, and are NOT representative of the standard motors you will find at Grainger, etc.

                              While VERY new "normal type" motors may have a slightly better insulation, the volts per turn are still low enough that wire-to-wire insulation (usually some form of "varnish" or other thin polymer coating) is not the biggest problem. UL treats wire insulation as if it were not there, for instance, they count the coating as having NO effect as far as insulation to ground. "Real" insulation is the paper and plastic placed between the coil and the metal core, and between adjacent coils of different phases, which is then typically filled with heat-cured varnish in a vacuum tank after winding is finished.

                              Older motors, more than 20 or 30 years old, tend to have been assembled with more care to properly place the insulation, and thus may actually have BETTER coil-to-coil, and coil-to-ground insulation than newer ones.

                              When a motor is assembled, the windings are actually beaten into place with a wooden hammer. If not done carefully, this can obviously do damage.... older motors were "built" by skilled people. Newer motors are made in ways intended to avoid having to use "skilled people", and are typically slammed-together as fast as possible, for the average commercial motor. In china, and other places, the above description may be too kind, the varnish tank may be replaced by a quick dip in varnish, or the varnish (which takes time and cost) may be eliminated, etc.....

                              So an older, carefully assembled motor may actually be better able to "take" the increased voltage stress from a VFD.

                              That said, time and heat will break down any organic-based insulation, whic h becomes leaky, and at some point the motor needs to be replaced, VFD or no VFD.
                              Last edited by J Tiers; 04-02-2013, 09:39 AM.
                              1601

                              Keep eye on ball.
                              Hashim Khan

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