Facing Today's Installation Challenges of Adjustable-Speed Drives for Controlling Motors in Hazardous Location Areas

The benefits of electronic motor controllers are well understood. For example, adjustable-speed drives (ASDs) are used to vary the speed and torque of ac induction motors for improved process control, energy savings, and diagnostic capabilities. Their use, however, in hazardous area locations has presented unique challenges. One of the more significant reliability obstacles is the management of the heat generated by the ASD. This single attribute has precluded reliable ASD installations greater than a few kilowatts within National Electrical Manufacturers Association (NEMA) 7 flameproof enclosures, necessitating the need for either complex inert gas purging systems or the placement in nonhazardous control rooms. Installing the ASD outside of the hazardous area location and away from the motor often results in significant installation, maintenance, and labor cost challenges. Accordingly, there exists a need for electronic motor control solutions that are suitable for use in hazardous/classified environments. The medium-voltage challenge is developing an accepted NEMA rating comparable to the resin-encapsulated Ex-m requirements. We will review both low-voltage and medium-voltage ASD solutions suitable for hazardous area locations. The low-voltage ASD is installed in a NEMA 7 flameproof Ex-d enclosure and employs active cooling to keep the internal enclosure temperature within specification of the ASD. The NEMA 7 active cooling technology will be explained, and examples of installation savings will be illustrated by comparing the installation costs of the ASD in both the hazardous and nonhazardous areas.