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Proper sizing Variable Frequency drive (VFD)


    Proper sizing Variable Frequency drive, selecting variable speed drive, VFD,


    It’s tempting to pick a variable frequency drive supported horsepower alone. After all, if you select a drive that has the same or more horsepower than your motor you are using, then you should be good too – right?

    Well … not necessarily. There are six other belongings you got to consider when specifying a drive: to form sure the drive can handle the motors current demands, just read the motors full load current requirement right off the name plate and find a drive that's rated for a minimum of that full load current.

    That is a great starting point, but you also need to make sure the drive can handle any overload conditions you may expect during startup or during periodic or intermittent extra loading. it seams that 150% for constant torque is applicable and 120% overload for VTA(variable torque application.

    So, confirm you recognize what your system overload conditions are. If you expect to exceed these overload specs, then up size the drive until you discover one which will handle. You will also got to know if your application is for variable Torque like fans and pumps or constant torque like conveyors and machine control.

    If you are not sure, assume constant torque. Knowing the appliance type is vital because all the spec tables are segregated by application type. As the altitude increases, the air becomes less dense, which reduces its ability to cool. Since there isn’t the maximum amount cooling available you'll got to oversize the drive to catch up on the decrease in cooling.


    AC Drives generate tons of warmth so if the drive is in an enclosure there's the likelihood that you simply will exceed the max temperature ratings of the drive if the enclosure doesn’t have additional cooling or ventilation.


    When specifying VFD size and power ratings, consider the operating profile of the load it'll drive. Will the loading be constant or variable?


    Consider both torque and peak current. Obtain the very best peak current under the worst operating conditions. Check the motor FLA, which is found on the motor’s nameplate. Note that if a motor has been rewound, its FLA could also be above what’s indicated on the nameplate.


    Don’t size the VFD according to horsepower ratings. But, VFD should be sized based on motor's maximum current. The VFD must satisfy the utmost demands placed on the motor.



    Consider the likelihood that VFD oversizing could also be necessary. Some applications experience temporary overload conditions due to impact loading or starting requirements. Motor performance is predicated on the quantity of current the VFD can produce.

    Many VFDs are designed to work at 150% overload for 60 seconds. An application that needs an overload greater than 150%, or for extended than 60 seconds, requires an oversized VFD.

    Due to air cooled, the altitude can influences the VFD sizing too. Most VFDs are designed to work at 100% capacity up to an altitude of 1,000 meters; beyond that, the drive must be derated or oversized







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