Connecting single phase to a VFD designed for 3-phase input
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    Default Connecting single phase to a VFD designed for 3-phase input

    I'm going to feed single phase 230V to a new to me TB Wood's 10HP VFD designed for 3-ph input.
    The manual, although quite good, doesn't have any schematic diagrams or suggestions on how to do it optimally.

    Based on simplified generic schematics below (and assuming that my VFD has the same rectifier type), I think that it may make sense to bridge the unused input leg to one of the used ones to help decreasing the current flowing through the diodes in this branch of the rectifier. Not that it will eliminate a need for de-rating, of course, but why not?

    The only reason not to do it, as far as I can see, may be the idea to have a spare rectifier in case of diode failure in one of the other two branches. And this is a very valid idea, IMHO.

    What are your thoughts? Do you think that the 3-ph rectifier in my VFD can be constructed entirely differently and this may affect the approach for a single phase input connection?

    Link to the manual: Dropbox - TB Woods WF2 VFD Manual.pdf - Simplify your life
    Attached Thumbnails Attached Thumbnails fig-3-5-800x451.jpg  
    Last edited by MichaelP; 10-12-2019 at 04:24 PM.

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    Posting a link to the manual for the VFD you intend to use would allow us to help you better.


    On the VFD's I have worked with there are 2 things to look for.

    1. A note on what 2 phases to use when powering with single phase.

    2. The parameter to set to ignore a phase loss alarm on incoming power.

    Bill

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    Quote Originally Posted by hitandmiss View Post
    Posting a link to the manual for the VFD you intend to use would allow us to help you better.
    Link added. My TB Wood's VFD Model# is WF2C2010-0B
    Thank you.

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    Try L1 to L2. If that does not work then L1 to L3. Basically you need to hit the legs that power up the controls (and display). If the display comes on you are good.

    But not all drives can be run on single phase. Some drives have phase loss protection so it won't run if you are missing the 3rd leg. Some actually measure the voltage of the 3rd phase so if it is missing you will get an immediate error.

    Others look at the ripple of the DC bus. This won't give you an error until the drive is under load. There are ways to get around this type of phase loss error, but it requires changing/additional hardware.

    Best thing to do is just to try it. And remember, derate the drive 50% f you use it as is. I have an older TB Woods 10 hp drive that has run very many years successfully on single phase.

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    Default Connecting single phase to a VFD designed for 3-phase input

    Quote Originally Posted by hitandmiss View Post
    Posting a link to the manual for the VFD you intend to use would allow us to help you better.


    On the VFD's I have worked with there are 2 things to look for.

    1. A note on what 2 phases to use when powering with single phase.

    2. The parameter to set to ignore a phase loss alarm on incoming power.

    Bill
    I would be surprised if it mattered which input legs you use since they are symmetrical. It’s all rectified to DC anyways

    #2 is a good point.

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    Yes, the drive was successfully fed by a single phase power by the previous owner. Naturally, it was de-rated from 10HP to 5HP. And he disabled phase loss alarm.

    Good point on the control circuitry, Mark. If they're fed from the AC, it'll be critical, of course. I wonder how often they are fed off the DC bus.
    Last edited by MichaelP; 10-13-2019 at 12:46 AM.

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    Quote Originally Posted by hitandmiss View Post
    Posting a link to the manual for the VFD you intend to use would allow us to help you better.


    On the VFD's I have worked with there are 2 things to look for.

    1. A note on what 2 phases to use when powering with single phase.

    2. The parameter to set to ignore a phase loss alarm on incoming power.

    Bill
    In my experience, not many of the drives I worked on gave you the ability to disable phase loss. But I'm getting dated now and not really keeping up with the latest bells and whistles of the new drives. Spending most of my time on motors nowadays. Its been a very long time since I was a drive field service engineer................

    This drive is fairly old - looks like its still a TB Woods design and not a Vacon design. In my experience they were pretty solid drives.

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    Quote Originally Posted by MichaelP View Post
    I wonder how often they are fed off the DC bus.
    480v VFDs with DC bus access were marketed heavily towards the passenger rail market... why? because 3rd rail power on subway and light rail was between 500 and 800v... so a 480v VFD's DC input was perfect...

    Now... I've worked on a few railcars that actually USED the VFD... but nobody manufactured NEW railcars that used VFDs as original elements- they build for-purpose auxiliary inverters, but the ones that got FITTED with VFDs, were older units that had been refitted by car rebuilders. A PCC car, for example, was never fitted with air conditioning... but a rebuilder could easily set one up by using a VFD to drive the compressor and blower systems... direct off the catenary feeder.

    That's where they'd go DC bus.

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    Most newer 3 phase input VFD's I have encountered allow derated single phase input. There is some variations as to if L1 and L2 are used or L1 and L3, and in some cases if a jumper from L3 to L2 is recommended if there is an input voltage detection. Each manufacturer typically specifies the terminals so like with Yaskawa it specifies connect the AC single-phase supply to VFD terminals L1(R) and L2 (S) to accommodate models that have cooling fans and soft charge circuits that utilize the AC line supply. The drive’s internal AC fan(s) and soft charge contactor are wired to terminals L1 (R) and L2 (S) from the factory. On the Hitachi WJ200 the single phase connections are L1 and L3(N), and they recommend a jumper from L2 to L3 if their is input phase loss detection.

    Both of these models indicate not turning off the phase loss detection, as these are based on THD and it voids the warranty. On the Fuji VFDs the input phase loss is turned off on their single phase models. Other than derating the VFD, I am not aware of any other software parameter changes required, but there may be some where input phase loss may need to be turned off so I would refer to the manual or check with the manufacturer. Newer VFD's/manuals tend to be more comprehensive on these issues. Almost all VFD manufactures recommend using a DC choke to decrease the THD and current surge to the DC capacitors. This also lowers the input fuse rating of the VFD and effects the buss currents.
    currents-flowing-across-inverter-terminals.jpg

    Three phase WJ200 input connections for single phase are L1 and L3(N), Yaskawa Fuji specify L1 and L2. So as stated by others there may be a terminal pair that provides AC power for other components before charging the buss.
    wj200-three-phase-single-phase-input..jpg

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