VFDs reduce costs through process optimization

Cover story: Variable frequency drives (VFDs), modern motor controllers, that communicate readily with process automation controllers can achieve much higher efficiency and process improvements by providing power consumption details. See VFD sizes, benefits, how to match a VFD to a process, and four questions to ask when specifying a drive.


Figure 1: Modern VFDs allow for control and monitoring online or wirelessly with a tablet or mobile device. Courtesy: Schneider ElectricBy incorporating communication between modern motor controllers, such as variable frequency drives (VFDs) and process automation controllers, it is now possible to achieve much higher efficiency along with process improvement by understanding in greater detail where and why power consumption varies. Companies are taking a greater look at process efficiency to protect the environment and enhance their bottom line. Resources are being stretched more than ever, and the demand for efficient use of those resources is being seen across industries. Evolving technologies that increase process efficiency and provide detailed information on energy use have helped, offering greater insight into the level of efficiency for their respective processes.

Equipment efficiency also has been a focus of federal regulators and industry organizations. The U.S. Department of Energy, for example, has convened a panel of experts to analyze the energy use, cost, and benefits associated with commercial and industrial pumps with the goal of developing energy conservation standards. They are also in the preliminary stages of examining commercial fans and blowers with a similar goal. The Air-Conditioning, Heating, and Refrigeration Institute (AHRI), an industry organization, recently developed the latest certification for VFDs—Standard 1210/1211—that is used in many of the applications with fans and pumps. 

VFDs drive efficiency

Many companies have looked to install modern VFDs—or update older drives—in their processes to improve efficiency. VFDs are designed to vary a motor's speed electronically to match demand within a given process.

These devices become critical to process improvement and often contribute to overall efficiency gains, without sacrificing system performance.

VFDs are available in different sizes and are paired based on the motors that they will support. 

VFD sizes, ratings, uses

Available sizes, ratings, and usage of VFDs follow:

  • Low voltage (600 V and less), fractional horsepower up to 2,000 hp
  • Medium voltage (2,400 V and higher) 500 hp up to 30,000 hp
  • General duty usually defined as 110% current overload capacity for up to 1 minute, support pumps, fans, and other variable torque loads
  • Heavy duty requiring 150% drive output current for the same 1-minute time period 
  • Support conveyors, compressors, and other constant torque loads.

Newer VFDs offer key enhancements to improve efficiency, including power conversion and power measurement. Power conversion circuits transfer the power from the distribution source to the motor with newer models accomplishing this more efficiently than ever. Insulated gate bipolar transistors, or IGBTs, and power capacitor technology have improved to reduce the overall heat generated in the drive (their largest contributor to energy loss), allowing for a drastic size reduction—often up to half that of older units—while still providing greater efficiency. Using the new power conversion semiconductors along with higher speed processors, coupled with low impedance conductors and improved capacitors, allows VFD design engineers to greatly improve their efficiency without compromising performance.

Power measurement has been greatly improved as well through enhanced sensors. This, when combined with network connectivity (Ethernet, embedded web server, and Wi-Fi), allows users to determine the exact power consumed by an individual motor running on their VFDs. By closely monitoring individual motor energy consumption, inefficiencies can be identified and action taken to improve it. Often in a process with multiple VFD/motor combinations, the one consuming the most energy can be addressed without impacting the others or the overall process throughput. 

Modern VFD benefits

Figure 2: Energy costs represent ~40% of the pump’s total cost of ownership. Courtesy: Schneider ElectricIn the past, when a drive indicated a trip condition, the user was left to largely guess at what had caused the condition. Did an interlock open? Was there a power spike? Did the motor get overloaded? Or was it something else? Modern VFDs are now capable of alerting users to not only the exact cause of a trip condition but can record conditions leading up to the trip that may indicate entirely different causes for that eventual trip.

For example, in the event of a motor overcurrent, the VFD would alert users to the increasing amp draw by the motor and provide data showing this long before an actual trip would occur, shutting down the process or showing a sharp instantaneous motor demand for current explaining the cause.

Another innovation for modern VFDs is the ability to produce dynamic QR codes to communicate critical information to users directly. Users with a cell phone or other mobile device can scan the code, and critical information on their drive is delivered literally to the palm of their hand. This can include diagnostics and suggested corrective actions, and they can even send a report directly to the manufacturer's customer service teams who can then analyze and suggest corrective customer actions.

Learn more about four tips on how to specify a VFD.

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