When American Synthetic Fiber (ASF) planned the construction of a new 240,000-ft2 factory for non-woven fiber—mostly used as leak-proof lining for landfills—the company wanted to ensure the production of 14 million pounds of fiber annually. To prevent production downtime, ASF decided to combine PC control, multi-drive ac motor control, and a 700-volt dc bus power supply for all processes from the carding system to the fiber winder. It did the project with systems integrator Electric Systems Inc. (EIS), a subsidiary of N.S.C. Schlumberger (Chattanooga, TN).
The multi-drive, built by EIS, uses 43 ac motor drives from ABB Automation Inc. (New Berlin, WI), ranging from 3 to 200 hp, all connected to a common dc bus, which delivers the power supply to each drive. "ABB's multi-drive products were historically used in pulp paper and steel-making applications—applications that require high reliability," says Mike Mauny, director of business development for EIS. "Their multi-drives looked right for the ASF process, in which man-made fibers are locked together in a web and held together with barbed needles in a continuous sheet," he adds. "The ABB drivers are economical, as well."
When designing a system like this, Mauny says, EIS devises the amount of power needed for the line from the horsepower specified by the manufacturer of the processing equipment. The horsepower controls the amount of torque, so EIS chooses motors based on the equipment's needs and then works with the manufacturer to make sure a given motor fits the space available for it.
"In general, the motors are in continuous forward rotation, during which they need only about 60% of the power for which they're rated," Mauny says. The power requirement increases, however, during acceleration and deceleration. The multi-drives control those speeds and provide an added benefit. "As the power ramps up during those times, some areas of the production line use more power than others—and the drivers allow motors that don't need the extra power to share their 'surplus' with other motors down the line," says Mauny. The common DC bus makes it possible for all the drives in the multi-drive system to share energy within the system. This enables all the energy to be used, rather than excess energy being removed as heat from the system via resistors.
Each motor position may need different horsepower, so EIS converts the horsepower requirement to amperage and sizes the line for power allocation from the electric utility.
That calculation represents the maximum amount of power the plant will need. Yet because the multi-drives allow the motors to share power at acceleration and deceleration, the plant seldom reaches that maximum.
For more information about AC multi-drives from ABB Automation Inc.: Enter 534
Systems integration services from Electric Systems Inc.: Enter 535