Allen Bradley Industry

Decide to install Allen‑Bradley® PowerFlex® 7000 variable frequency drives on the conveyor belts. Because variable frequency drives more accurately control motor speeds, they typically use less energy than hydraulic systems.

On conveyor belts, for example, variable frequency drives can reduce the current needed to start the motor from 650 percent of FLA typical of Direct On Line Starting, to 150 percent of FLA, typical of Current Limited VFD Starting – all without requiring a special rotor design. Meanwhile, the starting torque may be increased to approximately 150 percent of Full Load Torque. Using linear or S-ramp acceleration profiles, the belt can start without causing undue voltage sags, while the mechanical drive train, including gearboxes and the belt-tensioning systems, aren't exposed to the motor's breakdown torque. The speed control is infinitely variable and can be used to level load the belt. This helps mine operators ease motor startups or slow down the conveyor belt speed, for instance, when an issue in the pit disrupts coal delivery.

The drive installation process began at the beginning of the conveyor belt network. Since then, the drives have been added in stages to subsequent sections of the conveyor network, such as between the crusher and the prep-plant. Rockwell Automation also installed Allen‑Bradley PowerMonitor™ devices so managers could track the mine's energy use in real time.