Sizing motor and VFD

[lionman999]

Hi everyone.

Am new to the forum.

need to ask a noob question.

Is there any correct procedures/steps to follow for sizing a motor using Variable frequency drive as a driver to prevent over/under sizing of VFD and motor.

what are the parameters i need to account for? i know we need to take into consideration the torque, Power capacity, Amperes drawn.

some examples / links will be appreciate!!

thanks guys

 

[weressl]

Hi everyone.

Am new to the forum.

need to ask a noob question.

Is there any correct procedures/steps to follow for sizing a motor using Variable frequency drive as a driver to prevent over/under sizing of VFD and motor.

what are the parameters i need to account for? i know we need to take into consideration the torque, Power capacity, Amperes drawn.

some examples / links will be appreciate!!

thanks guys

Motor sizing and selection is usually guided by the characteristics of the driven load. It is a mechanical engineering problem and solution. The selection of the ASD then will depend on the motor size AND the load characteristic, primarily if it is a constant or variable torque load.

 

[Jraef]

Size the motor to do the job, size the VFD to handle the motor. There really isn't much more to sizing issues than that.

That said, the type of load and budget issues may make a slight difference, depending on size. Under 10HP, no differences. Over 10HP and if budget money is tight, a "Variable Torque" rating on the VFD will save a little money IF the load is something like a centrifugal pump or fan. This is because VFDs are rated based upon their ability to handle overloads. A "Constant Torque" application, such as a conveyor or machine arbor, might need about 150% overload capability for 60 seconds and they are designed with that in mind. But a centrifugal load does less work at lower speeds, so the overload capability of the VFD can be lowered to take advantage of that; 110% overload for 30 seconds. That translates to smaller components inside the VFD, therefor less cost. But that does limit future use of the VT VFD; it cannot be used on CT loads without de-rating.

 

[skeshesh]

An additional application some of our mechanical engineering bring up is in buildings with air change and volume considerations are important such as hospitals, certain testing labs, etc. As the system air pressure changes due to wear in ducts, accumulation of dirt, etc. the drive allow maint. persons to adjust the air handler units to achieved required values.