• Craig Drabyk

Variable Frequency Drives: Basics of VFDs


A variable frequency drive (VFD) is a type of motor controller that drives an AC motor and controls its speed and torque by varying the frequency and voltage supplied. The VFD can ramp up and ramp down motor speed to meet load requirements. They are most typically used to control fans, pumps and compressors.


There are a number of reasons to use a VFD, the most important of which is to save energy and improve system efficiency. Building systems are designed to meet peak loads, which account for less than three percent of annual operating hours. By matching speed and torque to load requirements, energy consumption is reduced and processes are more efficient. VFDs also provide soft-starts that protect motor windings from damage that can occur when motors are started and stopped frequently.


VFD requires careful selection to provide optimal performance for your specific application. It’s necessary to determine whether variable torque or constant torque is required, and choose an appropriate unit for the environment – indoor or outdoor, dry or wet, hot or cold, explosion-proof, etc. – in which it will be used. Ensure the VFD meets full load amperage, or FLA.


Observe installation requirements to avoid performance problems. Harmonic distortion can be prevented with the addition of output line reactors and other mitigation methods. Distance from the drive to the motor should not exceed 100 feet, and VFD-rated cable should be used. Also, do not mix other power or controls wiring with VFD wiring, which can cause induction issues.


For more information on variable frequency drive selection, contact Omni Instrumentation & Electrical Services at at (908) 412-7130 in New Jersey or (240) 341-7915 in Maryland.


About Omni

Omni Instrumentation & Electrical Services, Inc., located in New Jersey and Maryland, is a premier instrumentation and electrical contractor, providing superior total care solutions since 1986. Services include instrument installation, tubing installation, instrument calibration, control loop testing, startup and commissioning, power and lighting, process control wiring, BMS wiring, telecommunications and data wiring, fire alarm wiring, security wiring, process network wiring, and control panel fabrication. Omni Instrumentation & Electrical Services, Inc., is certified in Foundation Fieldbus, Profibus, DeviceNet and ASI-Bus installation.

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