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A variable frequency drive (VFD) controls the speed, torque and direction of an AC induction motor. It takes fixed voltage and frequency AC input and converts it to a variable voltage and frequency AC output. In small VFDs, a single power-pack unit may contain the converter and inverter. Control circuitry coordinates the switching of power devices, typically through a control board that dictates the firing of power components in the proper sequence. A microprocessor or digital signal processor (DSP) meets all the internal logic and decision requirements.
From this description, you can see a VFD is basically a computer and power supply. And the same safety and equipment precautions you would apply to these types of components apply here. VFD-maintenance requirements fall into three basic categories: keep it clean, keep it dry, and keep connections tight.
Keep it clean
Most VFDs fall into the NEMA 1 category (side vents for cooling airflow) or NEMA 12 category (sealed, dust-tight enclosure). NEMA 1 drives are susceptible to dust contamination, which can cause a lack of airflow, resulting in diminished performance from heat sinks and circulating fans.
Dust on an electronic device can cause malfunction or failure. Periodical spraying of air through the heatsink fan is a good PM measure. But while discharging compressed air into a VFD is viable in some environments, typical plant air contains oil and water. To use...