VFDs for better efficiency
Like other companies in the cement industry, Ash Grove faces heightened competition, ever-fluctuating demand and intense pressure to efficiently increase productivity. The process of manually positioning equipment, called “spotting,” became difficult because technicians had no effective way to accurately apply torque to the medium voltage motor directly from the power system – the technique used to slowly rotate the mill. Consequently, Ash Grove decided to replace the antiquated generators that powered the mill spotting with preconfigured, 480-volt, 450-horsepower, AC variable frequency drives from Rockwell Automation. The Allen-Bradley AC drives power three existing 4,000-volt, 2,300-horsepower AC motors exclusively during the spotting process to efficiently rotate the ball mill and bring it to a controlled start and stop. As a result, Ash Grove had initial savings of $250,000 by selecting a low voltage AC drive, and it saves thousands of dollars annually in maintenance.
