Induction motors are at the heart of industrial processes and account for a majority of the energy consumed at most manufacturing facilities.  Facility operators who intend to reduce energy consumption must determine methods to deal with the energy requirements of their most central piece of equipment.  To provide the savings conscious manager or engineer with a way forward, here are three ways that a VFD can reduce operating costs.

Eliminate Inrush Current

Induction motors are subject to a phenomenon called inrush, where the amount of current drawn by a motor at startup is much greater than while running.  This sudden increase in current consumption translates to a sudden increase in electrical demand, and high demand leads to high demand charges. Variable frequency drives, however, eliminate the inrush phenomenon for induction motors that they control and, as a result, eliminate demand charges.  This can bring significant energy cost savings for motor operators.

Take Advantage of Affinity Laws

The activity of centrifugal fans and pumps are described by a set of relationships called affinity laws.  Of note is the relationship between the speed of these devices and the power input required:

As shown, the cube of the ratio of starting and ending speed is equal to the ratio of the starting and ending horsepower.  What this means in simple terms is that a 50% reduction in speed can create as much as an 80% reduction in power consumption.   A VFD in control of a pump or blower fan can, therefore, yield extensive savings across its operating life.

Economize Motor Control

Both the PowerFlex 525 and the PowerFlex 750 series can be configured for economize motor control.  Economize motor control is a variation of sensorless vector control (SVC).  While in economize mode, a VFD will operate in the same manner as SVC while decelerating or accelerating; however, once steady-state speed has been achieved by the motor the variable frequency drive will begin varying the voltage output levels to the motor to match actual load requirements maximizing the motor’s efficiency.

For more information about drives and drive systems, check out the Variable Frequency Drive Main Help Page