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Thread: Old Inverter to new VFD

  1. #11
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    Quote Originally Posted by petersonra View Post
    I wonder what would have possessed someone so far back in time to have put a crazy expensive VFD on if they didn't really need one.
    I see it all the time. Some salesman told someone that they can save buckets of money by installing a VFD, with no clue (from either party) as to how that really works. In the early days, the utility might even have given them a rebate for it, basically paying for the VFD, even though their OWN people didn't really understand the benefits (or lack thereof). Utilities have learned their lesson now though and they will want to see proof.

    Every once in a while I do find a legitimate application where someone used a VFD as an expensive soft starter, because the utility restricts their starting current so severely that even a soft starter would not work. The benefit of a VFD in that case is that it can limit the current to 100% of FLA, even if that stretches out the acceleration time to 15 minutes, or 17.3 days... That's usually on really really big loads; I did one like that a few years ago for a 2,000HP gas compressor for a pipeline where the utility wanted to shut them down if they didn't quit making the lights flicker in the nearby town. The VFD did the trick, even though it takes almost 20 minutes to get it to full speed. They will never change the speed however, in fact they bypass the VFD when it's done ramping so as to not have the losses.
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  2. #12
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    Quote Originally Posted by Jraef View Post
    I see it all the time. Some salesman told someone that they can save buckets of money by installing a VFD, with no clue (from either party) as to how that really works. In the early days, the utility might even have given them a rebate for it, basically paying for the VFD, even though their OWN people didn't really understand the benefits (or lack thereof). Utilities have learned their lesson now though and they will want to see proof.

    Every once in a while I do find a legitimate application where someone used a VFD as an expensive soft starter, because the utility restricts their starting current so severely that even a soft starter would not work. The benefit of a VFD in that case is that it can limit the current to 100% of FLA, even if that stretches out the acceleration time to 15 minutes, or 17.3 days... That's usually on really really big loads; I did one like that a few years ago for a 2,000HP gas compressor for a pipeline where the utility wanted to shut them down if they didn't quit making the lights flicker in the nearby town. The VFD did the trick, even though it takes almost 20 minutes to get it to full speed. They will never change the speed however, in fact they bypass the VFD when it's done ramping so as to not have the losses.
    2000 hp VFD/2000 hp soft starter - something every supply house has a spare sitting there on a shelf.

    But the VFD probably still cost more.
    I live for today, I'm just a day behind.

  3. #13
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    Quote Originally Posted by kwired View Post
    2000 hp VFD/2000 hp soft starter - something every supply house has a spare sitting there on a shelf.

    But the VFD probably still cost more.
    5x more.
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  4. #14
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    Quote Originally Posted by kwired View Post
    2000 hp VFD/2000 hp soft starter - something every supply house has a spare sitting there on a shelf.

    But the VFD probably still cost more.
    Yes. Either way you replace modules, not the whole unit at that HP..

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