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Thread: Reactors

  1. #1
    Join Date
    May 2007
    Dry as a bone Tucson
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    Which impedance levels do you choose for input protection?
    What brand of reactors is your preferred choice?
    Do you always use a load reactor?
    Do you always use a line reactor?
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  2. #2
    Join Date
    Feb 2012
    New York City
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    Typically all of that stuff is provided packaged by the VFD vendor. The local rep may or may not understand this stuff, so call the rep and then if you don't get a clear or convincing answer escalate or have the rep escalate the issue to the factory guys.

    Line reactors, DC bus chokes, and multi pulse drives (i.e. > 6 pulse) deal with voltage and current distortion on the building power network. This is the bigger deal here. VFD vendors will help you out with this if you've got a big job. If you're doing a whole building, they'll do the entire analysis if they've got all or nearly all the VFDs in the facility. A lot of higher quality drives have a DC bus choke or line reactor as a standard feature. I typically put something like that in my specs.

    Load reactors are especially applicable if you're retrofitting a VFD on a non-inverter design motor (does not comply with NEMA MG-1 Part 31) or if you have long distance between the motor and the drive location. These are less important on new installations with inverter rated equipment. I would suggest considering budgeting for motor replacement on any 460V installation; 208V is less sensitive. The insulation in both motors is 600V rated. A 460V VFD will have a DC bus at close to 550/600 V. When you do V=L dI/dt (dI/dt is big because the VFD chops DC to PWM AC for the load), you see that it's really easy to exceed 600V in the motor coils as the VFD chops the load current. A 208V VFD will have a bus voltage closer to 300V, so it's less of an issue.

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