Facing today´s installation challenges of Adjustable Speed Drives for controlling motors in hazardous location areas

The benefits of electronic motor controllers is well understood. For example, Adjustable Speed Drives 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 Adjustable Speed Drive. This single attribute has precluded reliable ASD installations greater than a few kilowatts within NEMA 7 flameproof enclosures, necessitating the need for either complex inert gas purging systems or the placement in non-hazardous control rooms. Installing the Adjustable Speed Drive 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 finding a solution to meet the Ex-m requirements of Figure 3, to include an equivalent NEMA rating. The authors will review both Low Voltage and Medium Voltage Adjustable Speed Drive 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 non-hazardous areas.