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Thread: Varible Frequency drives, Motor rotation

  1. #1
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    Varible Frequency drives, Motor rotation

    Just install Motor to VFD Systecon. Used a Phase meter to phase motors. Phased it in Manual/bypass mode and phasing is correct. When Switched to VFD mode. Motors run in reverse? Someone From Motor company Switch rotation in VFD. Motors Sound funny in this mode now. But sound perfect in Manual/bypass. Any clues?

    25 Hp. 460volt Wired @ 480v.

  2. #2
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    Quote Originally Posted by Fordean View Post
    Just install Motor to VFD Systecon. Used a Phase meter to phase motors. Phased it in Manual/bypass mode and phasing is correct. When Switched to VFD mode. Motors run in reverse? Someone From Motor company Switch rotation in VFD. Motors Sound funny in this mode now. But sound perfect in Manual/bypass. Any clues?

    25 Hp. 460volt Wired @ 480v.
    It is not unheard of for a VFD driven motor to sound different than one driven off real sine wave power. The VFD simulates a sine wave with digital pulses of pure DC voltage.

    There is sometimes a setting you can change called the carrier frequency that may or may not help with the noise issue.
    Bob

  3. #3
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    Quote Originally Posted by Fordean View Post
    Just install Motor to VFD Systecon. Used a Phase meter to phase motors. Phased it in Manual/bypass mode and phasing is correct. When Switched to VFD mode. Motors run in reverse? Someone From Motor company Switch rotation in VFD. Motors Sound funny in this mode now. But sound perfect in Manual/bypass. Any clues?

    25 Hp. 460volt Wired @ 480v.
    petersonra is correct.
    It's the carrier frequency you can hear. It's usually in the few kHz region so comfortably within the audible range particularly if there isn't too much background noise.Best I can describe it is that it sounds like a whistling/squealing noise.
    It's normal.

  4. #4
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    When you have a VFD with a manual bypass, you get the motor rotation correct as it comes out of the VFD, then swap leads on the load side of the bypass switch to make it match the VFD output.
    __________________________________________________ ____________________________
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  5. #5
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    Quote Originally Posted by Jraef View Post
    When you have a VFD with a manual bypass, you get the motor rotation correct as it comes out of the VFD, then swap leads on the load side of the bypass switch to make it match the VFD output.
    According to the OP it was correct in bypass but incorrect on the VSD.
    That can be, and evidently was, fixed in the VSD. No swapping leads required.

  6. #6
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    VFD does not care what phase sequence of input is. It converts input to DC then back to a somewhat simulated three phase output (for lack of better term to call it). Output will always be same rotation no matter what the input is. You can even only input two lines and it will still work (at a derated power level), but will also be same output rotation.

  7. #7
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    Most VFD's take an 3 ph input, convert to DC, and then convert back to AC by Modulating the Pulse Width of the Voltage Wave. The output voltage waveform looks like a series of high frequency voltage spikes. The carrier frequency of the output section firings is in most VFD's selectable by changing a parameter named something like 'carrier frequency' or 'motor noise'. there will be a distinctly different noise (pitch) at different carrier frequencies. The change in pitch is the result of the commutation frequency of the applied voltage. all the IGBT output section can achieve (in a normal VFD) is to switch the DC link voltage (700VDC or so) on and off in varying pulse widths necessary to emulate a sine wave.

    The current waveform is reasonably 'clean' since the inductance of the motor serves as a current choke.

    Most VFD output phase rotation is determined by the software alone, not the input phase rotation. Output phase rotation is almost always reversable in the software parameter settings.

    Many VFD's are capable of receiving 1 ph input (2 phases of a 3 ph system), and sucessfully operating at about 1/2 rated KVA, since the absence of one phase simply derates the rectifier section KVA Output, which is the input to the DC link. I have seen VFD's which care which line terminals the 1 ph input is connected to. There may be others which do not.

    Utility power is equivalent to a very low carrier frequency (no switching at all), and therefore the motor sounds 'normal'.

  8. #8
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    You can reverse the VFD by giving it a "reverse run" command either programmed or analog input.

    It still does not care what rotation of the input is when determining output rotation.

  9. #9
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    Quote Originally Posted by kwired View Post
    You can reverse the VFD by giving it a "reverse run" command either programmed or analog input.

    It still does not care what rotation of the input is when determining output rotation.
    Right, that's true.

    HOWEVER...

    If you tell the VFD rotation to match the bypass rotation, the VFD display may say "Reverse" when you look at motor direction, and although this is totally relative, it can confuse untrained people. That's the reason I always teach that you should correct the motor rotation to match the VFD output, THEN you adjust the bypass operation to match the VFD output. it avoids that confusion later. This is only relative to VFDs with a bypass system.
    __________________________________________________ ____________________________
    "Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
    — Kilgore Trout (via Kurt Vonnegut)

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