Starting an AC motor across the line requires starting current that can be more than eight times the full load amps (FLA) of the motor. Depending on motor size, this could place a significant drain on the power distribution system, and the resulting voltage dip could affect other equipment. Using a VFD can eliminate the voltage sag associated with motor starting, and cut motor starting current to reduce utility demand charges.
Controlling starting current can also extend motor life because across-the-line inrush current shortens life expectancy of ac motors. Shortened lifecycles are particularly prominent in applications that require frequent starting and stopping. VFDs substantially reduce starting current, which extends motor life, and minimizes the necessity of motor rewinds.
The ability to vary operating speed allows optimization of controlled processes. Many VFDs allow remote speed adjustment using a potentiometer, keypad, programmable logic controller (PLC), or a process loop controller. VFDs can also limit applied torque to protect machinery and the final product from damage.
Controlled stopping minimizes product breakage or loss, as well as equipment wear and tear. Because the output phases can be switched electronically, VFDs also eliminate the need for a reversing starter.
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