Help in Diagnosing Problem - VFD, Motor, or Transformer???
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    Default Help in Diagnosing Problem - VFD, Motor, or Transformer???

    I have a 3 phase surface grinder (Boyar Schultz) running via a transformer that bumps power from 220V to 575V, then on to a VFD drive that converts that to 3 phase power.

    The setup was working flawlessly for years until about a year ago when I would get the odd OC Error (Output Current). After rest would work for a long while until another OC error. Now the error is much more frequent sometimes within seconds of starting the grinder.

    My question is in which component do you think the problem is - VFD, Motor, or transformer? Any tips on how to diagnose this?

    The VFD drive is a Fluxmaster FM500 made by Westinghouse.

    Thanks for any help you can provide. Would love for this to be an easy fix but.....

    Sean

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    Quote Originally Posted by smo10018 View Post
    The VFD drive is a Fluxmaster FM500 made by Westinghouse.
    "working .. for YEARS" hints that the VFD's capacitor bank is probably well-overdue for replacement. More critical components at your 575 VAC input than at 240 V, most especially when run off single-phase.

    The replacement interval should be in the manual. Usually BURIED, though. "Economy" units such as the Teco/Westinghouse, that info is probably in a separate document altogether.

    The mass-market having grown, competition as it is, parts no longer common? As you were probably fortunate to enjoy a working life already longer than the recommended replacement interval, a whole new VFD is usually both wiser and cheaper.

    RPC (and DC Drives..) endure. VFD (and Phase-Perfect) less-so. Nature of each beast,

    TANSTAAFL.

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    Check the amp draw or the motor running, then check the parameter in the vfd that has to do with full load amps. It should be slightly larer than the motors amp draw. Check the tag on the motor to be sure the running amps aren't higher than the tag. If they are, you may have a motor problem, if not, probably the vfd. AutomationDirect is a great place to get vfd's, great support and good prices. I'd get a GS2 series.

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    The VFD is lss reliable than the motor, because it has more parts and connections. So it is more likely to be a problem. That is a general observation, and does not really apply to any individual case.

    Overcurrent on startup i fairly typical as an issue and may be caused by a too fast acceleration (or even a too slow acceleration) especially with different grinding wheels put on and taken off. The larger or less worn wheels will be harder to get started, and more likely to cause an overcurrent.

    The VFD can be at fault, intermittent solder joints or the like can make for errors in measuring current, etc, etc. It is not really that easy to determine, but powering a different but similar load with the VFD would determine if the VFD still faults. if it does then it is more likely to be the issue.

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    Have experienced weird stuff happen when all it turns out to be is a loose screw clamp or interruption in a connection. Check your wiring.

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    Thanks very much for the replies, I appreciate the help. I did go through and check for loose wires with everything tight. Also took an air compressor and blew out the VFD drive as my shop creates a lot of dust.

    I did check the amp settings and things seem to be set correctly for the motor. Will try to check the motor running with a meter to double check.

    Was looking last night at VFD drives but not seeing one that matches my setup. Any VFD that I have seen that will take 550V in only says 3 Phase in and 3 Phase out. In my case the VFD will get 550V with 1 Phase In, then I want it to convert to 3 Phase out with 550V. I would think if it wants 3 phase in but is only getting 1 phase I will have a problem there???

    These are the specs on the motor on my grinder:
    Motor - 1hp, 550V, 3450rpm, 60Hz, 3 Phase, 1.15A, Cont. Duty, Rise 55

    What does Rise - 55 mean? Could this be how fast or slow the motor ramps?

    Again thanks for the help, obviously this is not my strong suit.

    Sean

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    I have found several drive manufacturers that don't list single phase input capability on their drives, but when tech support is called, they advise that single phase input is possible.

    Stuart

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    Quote Originally Posted by smo10018 View Post

    These are the specs on the motor on my grinder:
    Motor - 1hp, 550V, 3450rpm, 60Hz, 3 Phase, 1.15A, Cont. Duty, Rise 55

    What does Rise - 55 mean? Could this be how fast or slow the motor ramps?
    It means 55 degrees C temperature rise above ambient that the motor can be operated under.

    If ambient is 75 degrees then 75 + 131 (55 C) = 206 is your limit. A open frame motor can take less temperature rise than a closed frame motor, like 40 C.

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    Thanks again. I was looking at the wiring of my current VFD and one of the 3 phase input poles is jumpered so am guessing this is how it's done.

    Will start getting some quotes for a new VFD.

    Appreciate the help!

    Sean

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    Buy a replacement "bigger" than the minimum that you need. Bigger means more AMPS out.
    VFDs are easily programed to suit just about any motor rated less than maximum.

    The extra capacity will give you some "overhead" against over current situations. And other benefits.

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    Quote Originally Posted by smo10018 View Post
    Thanks again. I was looking at the wiring of my current VFD and one of the 3 phase input poles is jumpered so am guessing this is how it's done.

    Will start getting some quotes for a new VFD.

    Appreciate the help!

    Sean
    There is a chance that the VFD is fine. It's the motor instead. That would be worse.
    But if you have a doubt about which is not working 100%, choosing the VFD to replace would be the easiest thing to try.

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    You would need to up size (2 Hp 3 phase input) your VFD to handle single phase input, unlikely you will find a true single phase input VFD for this voltage. If you have been running a 3 phase input 1 Hp VFD, then most likely it may be failing. It is also possible that the motor insulation is breaking down. You might look at this VFD:
    https://dealerselectric.com/VACON0020-3L-0003-7-R02.asp

    If the motor can be easily replaced, you may ultimately be better off using a 230VAC motor and the VFD would also be less expensive.

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    My opinion, and you are not going to like it...


    VFDs don't "slowly get bad" in my experience. They work fine, until they don't work at all.

    MOTORS on the other had start to fail slowly. In this case I'd venture a guess that this motor was NOT built as "inverter duty" because you added the VFD to it after the fact. So it's entire more likely that you have created a turn-to-turn winding insulation fault inside of the motor due to the voltage stresses created by the VFD, a well known phenomenon called "reflected wave" or "standing wave" insulation damage. It's not very common in 240V motors, but it IS common in 460V and it VERY common in 575V motors that were not designed to be run from VFDs.

    The pulses in the PWM pattern that the VFD uses to create a 3 phase "pseudo AC" output cause the conductors to act like capacitors and create extra voltage pulses on the conductors that travel down the wires until there is an impedance change, i.e. the motor terminals. Some of them get reflected back the other way, where they combine with new pulses and then hit another impedance change, the drive terminals, and reflect back again. Even though these extra capacitive voltages are small, the constant reflection and addition back and forth (like a slinky wave) eventually become VERY HIGH voltage spikes that can exceed 3x the line voltage! So on a 230V motor, the insulation is the same as is used on a 460V or 575V motor; typically 1200V because it is 2x the normal voltage (575). With an inverter involved, 3x 230V is still below that value, but on a 460V motor that 1200V insulation is lower than the common spikes by 180V and on a 575V motor those spikes can easily be over 500V higher than the insulation value of the windings.

    So what happens is that where the insulation is thinnest, usually the "first turn" where the motor leads connect and go into the stator slots, the insulation fails between winding conductors on the same winding, effectively lowering the number of turns in that winding. That then causes the current to drop, reducing torque. But the motor will still TRY to do it's job, so slip increases, the motor draws more current, and that winding situation keeps getting worse and worse over time. The result is OFTEN a cascading increase int he number of Over Current trips in the VFD as the windings fail.

    Here is what that looks like inside of the motor:


    Bottom line, I think your motor is toast and buying a new VFD will not change a thing. A 1HP motor will cost more to fix than it will to replace. But when you replace it, use a motor that is DESIGNED to be operated by an inverter. What they do is use insulation that is rated for 1600V (or even higher in some cases). You could have ALSO used what's called a dv/dt filter on the output of the VFD, but it's too late for that now.

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    Quote Originally Posted by Jraef View Post
    My opinion, and you are not going to like it...

    ..
    Here is what that looks like inside of the motor:


    Bottom line, I think your motor is toast and buying a new VFD will not change a thing. A 1HP motor will cost more to fix than it will to replace. But when you replace it, use a motor that is DESIGNED to be operated by an inverter.
    Concur.

    And make it a 240 VAC "inverter duty" motor, rather than 575 VAC as well.

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    While there is a valid "theory" in JRAEF's post, it is fairly easily determined by checking the VFD with a different motor.

    You can also look inside the motor and see if you can spot damage. While it commonly will be on the "end turns" which are visible, that is not a guarantee.

    If your VFD then happily drives another motor, your odds of a bad motor go up. If you cannot visually see a defect, and you cannot find another motor to check, then you are reduced to "being a mechanic" and guessing which is bad, then replacing it.

    I HAVE seen intermittently bad VFDs.

    A VFD with a SERIOUS problem is generally either bad or good. But internal to the VFD, the circuits that measure current have lots of low voltage parts. All it takes is a vibration or temperature sensitive bad solder joint, and you have an intermittently bad VFD.

    Contrariwise, MOTORS, once they have been failing for a while, are usually bad or good. When the insulation starts to go, it goes qickly, and there will soon be a short, or a point that reliably breaks down. It is rare to find one that goes months of regular use after a serious voltage breakdown issue starts. Yes, it can happen. I've been in the electronic and electrical business too long to say there is much that cannot happen.

    We are all "guessing", good guesses, bad guesses, correct guesses, wrong ones...... So now you have to check to find out which is the correct one. Swap motors to check the VFD is a good plan, if you have another 575V motor around. Inspecting the motor is also a good plan. If you had another 575V VFD you would probably already have checked the motor with it.....

    Without those choices, it's not going to be easy or cheap. Taking the motor to a motor shop is your only other choice that is fairly easy to do if there is a shop within range of you.

    I like the idea of going to a 240V moor, but then you may have an issue with control voltages, See if there is a tapped transformer for controls before spending money on that route.

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    Quote Originally Posted by JST View Post
    I like the idea of going to a 240V moor, but then you may have an issue with control voltages, See if there is a tapped transformer for controls before spending money on that route.
    Good grief, J.

    That's akin to saying one dare not trade for a better motor vehicle as the new one may have a bird-splat on the windscreen as needs washed off!

    Trivial "issue" at worst. Non-existent more likely.

    No longer needing the POWER step-up transformer NOR as highly-stressed, harder on the motor, and costlier 575 VAC VFD are huge pluses vs "maybe" needing to source a dirt-common control transformer.

    As he has BEEN running 240 clear to the step-up transformer, there is isn't even any significant run of higher-Ampacity wire involved.

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    Quote Originally Posted by thermite View Post
    Good grief, J.

    That's akin to saying one dare not trade for a better motor vehicle as the new one may have a bird-splat on the windscreen as needs washed off!

    Trivial "issue" at worst. Non-existent more likely.

    No longer needing the POWER step-up transformer NOR as highly-stressed, harder on the motor, and costlier 575 VAC VFD are huge pluses vs "maybe" needing to source a dirt-common control transformer.

    As he has BEEN running 240 clear to the step-up transformer, there is isn't even any significant run of higher-Ampacity wire involved.

    He is free to do whatever.

    It is wise to point out things that "could" mess up our pet solution idea.

    He may not be using any of the controls, since he has a VFD, so it could be moot anyhow, so long as the existing wiring is OK at double the current..

    But look at the economics of it.......

    If he leaves the 575V VFD and the control transformer, and only needs a new motor, he can buy two things... the motor which he needs anyway if it is bad, and an inductor, which will take the spike stresses off the motor, and is generally much cheaper than the VFD and transformer.

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    Quote Originally Posted by JST View Post
    But look at the economics of it.......

    If he leaves the 575V VFD and the control transformer, and only needs a new motor, he can buy two things... the motor which he needs anyway if it is bad, and an inductor, which will take the spike stresses off the motor, and is generally much cheaper than the VFD and transformer.
    You left out the cost of at least a new set of capacitors for the cheap Teco that are "due" if not overdue.

    This is not a new install. He's been running it for some time already. That's also why jraef's point about possible motor damage is highly probable in the first place.

    A control transformer - if even NEEDED - is de minimus, all possible scenarios if we "look at the economics of it". Not hard to spend more on a pizza with extra cheese.

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    All excellent information, thanks very much. So not as easy a fix as I was hoping.

    The motor is not trivial to remove, if I did remove it I would want to replace it with a 220V and get rid of the transformer. The biggest problem is the motor mount is not an easy one to find - H56Y.

    I don't have a spare VFD or 575V motor. I live on an island so nothing close in terms of shops to help me out.

    Thanks again. The motor is as old as the surface grinder so may be a good idea to replace it either way, is a 1970's era grinder.

    Sean

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    If you can replace the motor with a 220/240V version, and NOT get into problems with the project expanding into a "full rewire", that makes sense, and as I said, I like it.

    But, it is going to be an expensive proposition. If you want to do it, and have been waiting for a reason, now's the chance. You will not need to determine where the problem is, you are replacing everything.

    Otherwise, you will need to troubleshoot. If that is not practical, then the total changeout may be a better proposition.

    To determine what the problem is, you would need, at the least, access to a clamp-on current meter with a "peak hold" capability, to see if there really IS an overcurrent. If the thing were to trip off and NO current spike is noted, you would suspect the VFD, If you DO see a current surge, the motor (or its wiring) would be the indicated issue.

    The meters are not perfect, a 'scope is better, but it's the minimum that could be of assistance. If you DO have such a meter available, then it is worth your time to check the system with it. You would check each of the motor wires , checking the meter after an "overload event" to see if a high current was measured.

    The concern here is that you COULD have something as silly as a motor wire that is wearing its insulation on a sharp edge somewhere. While replacing the motor etc may be a decent idea, you'd probably not want to do it unless there is a good reason. (yes, I know you checked the wiring.... been there done that, missed the one tiny spot, declined the t-shirt)


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