• VFDs: an Overview

Sample VFDby Guest Blogger Jeremy Ruppert

(photo courtesy of ABB/Google)

There are many ways to make a system more efficient, but this post will address ways a variable frequency drive can improve a customer’s pump performance, lower costs, and extend the life of the equipment.

Though initially not the cheapest option, a VFD can save the end-user thousands of dollars in a variety of ways. A VFD can be used in place of a programmable logic controller (PLC) since most VFDs have their own product-integral derivative loop, a control loop feedback mechanism that calculates error value as the difference between a measured process variable and a desired set point. The small number of parameters to set up a PID can be set directly in the VFD’s settings, which eliminates the need of a PLC program. In many cases, it eliminates the need for a PLC entirely, and the end-user enjoys the savings of a potentially smaller enclosure plus not having to purchase a PLC or pay someone to program it.

A VFD also provides pump and motor protection, and it accomplishes this through monitoring current, drive speed, frequency, and other critical values. The ability to monitor and adjust for these factors lowers energy costs and significantly reduces wear on the motor over a long period of time. VFDs can also receive analog or digital inputs to monitor level, flow, and other field equipment, and multiple pumps can be run in parallel for automatic lead/lag changeover and redundancy backup. The VFD can accomplish all of this while still communicating with a distributed control system or SCADA system. Some VFDs can even calculate your process efficiency by flow of product vs power consumption (in kW), which allows the user to see the best operating point for their pump.

In short, variable frequency drives make your plant much more efficient. They protect the pumps and motors, significantly reduce the plant’s operating costs, and provide feedback and the controls for field devices.

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