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Thread: VFD with Sine Wave Filter on LONG Leads

  1. #1
    Join Date
    Jan 2011
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    East Tennessee
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    VFD with Sine Wave Filter on LONG Leads

    I have an application where the location of about 20 of our well pumps (middle of aggie fields) will require us to run between 500' and 4100' from our VFD to our wells. The application really needs to be on a VFD, but reflected wave is a serious issue.

    I have been recommended by a vendor to use a sine wave filter. This vendor claims to turn the pulse square wave into a fairly clean (5% to 7% harmonics) sine wave. To me it basically looks like an L-R-C filter without matching impedences to the specific application, but I am likely missing a few details. With these filters, they say there is no reflected wave and runs of 15,000 feet are possible.

    Is anybody familiar with this technology? I have a few further questions, but mostly want to know if this is feasible.

    Thanks.

  2. #2
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    Texas by the Gulf, geat crab, great shrimp
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    Quote Originally Posted by Runnerzo View Post
    I have an application where the location of about 20 of our well pumps (middle of aggie fields) will require us to run between 500' and 4100' from our VFD to our wells. The application really needs to be on a VFD, but reflected wave is a serious issue.

    I have been recommended by a vendor to use a sine wave filter. This vendor claims to turn the pulse square wave into a fairly clean (5% to 7% harmonics) sine wave. To me it basically looks like an L-R-C filter without matching impedences to the specific application, but I am likely missing a few details. With these filters, they say there is no reflected wave and runs of 15,000 feet are possible.

    Is anybody familiar with this technology? I have a few further questions, but mostly want to know if this is feasible.

    Thanks.
    Hopefully that Vendor is the drive manufacturer, not an aftermarket supplier. ABB - for example - does build drives with optional outputs that allow you to have various lengths of leads, far longer than the ordinary drives. They DO work and you hook up the scope and some of them are hardly different from a pure sine-wave.

    There are also harmonic traps available that eliminates the standing wave problem, they are installed at the motor terminals. (EATON)

    Have you considered installing the drive closer to the motor? I know that we reflexively try to keep the drives in an MCC or Switchgear building, but they do offer drives with NEMA 12 enclosures and the work well. Another option is to put the drive in its own, purged and air-conditioned enclosure at the motor. Just have to calculate which of these are the most economical and reliable.

    (The 4100' almost sounds like calling for a MV drive or MV transmission anyway and the MV drives have much greater lengths allowance than LV.)

    Watch your carrier frequency! Greatly affects cable length....small print.
    Last edited by weressl; 01-05-11 at 05:15 PM.

  3. #3
    Join Date
    Jan 2011
    Location
    East Tennessee
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    Thanks for the response. I've discovered a few more things since I posted...

    I have been speaking with Allen-Bradley and with Yaskawa. As near as I can tell, A-B uses or recommends TCI and Yaskawa uses or recommends Schaffner for the sine wave filters that would work with their equipment. It seems "too good to be true", but in a sense you pay for it -- higher equipment costs, higher load on the system, and greater voltage drop past the VFD. Apparently I need to worry about common mode spikes when using these types of filters, but I think there is a filter product to take care of those as well. I wish I could find a white-paper or technical report describing how these things work a bit better. The advertising slicks and even the operations manals only tell you so much.

    As for location, we are in the middle of farm land and pasture and can not place a drive over the top of the wells. Harmonic traps do not work unless you can thrown them 100' down a well. MV would be serious overkill for 15HP to 40HP motors, but perhaps step-up and setup-down transformers might be possible (although I'd worry about changing frequency through a transformer). We are too far for load reactors to help. This leaves me with basically "sine wave filiters" like the TCI MotorGuard or Schaffner make.

    My basic questions are:

    Has anybody had experience with such product (either these two or others) and have witnessed the transformation from pulses to sine wave?

    Will a sine wave filter allow a VFD to work on a regular (high-efficiency) motor that has 1000V insulation?

    With a sine wave filter on a VFD, do I need to use armored, shielded cable (like Armor-X) or is regular XHHW insulation sufficient?


    Any help would be appreciated. I think I've worked out these answers to my satisfaction, but confirmation or challenges or application stories from similar installations would be most helpful.

    Thanks.

  4. #4
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    Jul 2011
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    Trussville, AL
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    Sine Wave Filters

    We use sine wave filters on all of our applications where the lead length is between 1000 and 15000' for submersible pumps. The TCI filters work quite well. That having been said, a 1000V insulation is a bit light for a 480V system with a VFD but it should work.
    Set the switching frequency to around 3kHz.
    As with any special VFD load, using the armored VFD cable will help.
    You'll see voltage drop across the filter of about 2%.
    Hope this helps

    Ted Wilke
    SPOC Automation

  5. #5
    Join Date
    Jul 2006
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    San Francisco, CA, USA
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    Both TCI and MTE make sine wave filters, or "long lead" filters as some people call them, specifically for this purpose and they have a very proven track record. Most of the external options that you see offered by VFD mfrs are brand-labeled from either TCI or MTE in this country, Schaffner tends to have the lion's share of the overseas business and brand-label their versions to people like ABB, Siemens, Schneider (Sq. D) etc. (looks like they got to Yaskawa now too, but that also may be a factor of your local distributor or rep, the local Yaskawa guys around here use TCI).

    Did you see this App Note from Yaskawa? It's one of the better ones out there and it's relatively generic. This one from Rockwell goes into some additional detail of how things work, but is decidedly specific to their product options.
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