Motors and Drives Grow Up and Graduate

Motors and Drives Have Been Moving Up to Variable-Speed Control for Better Accuracy, but Now They're Also Increasing Power Density and Efficiency and Even Coordinating More Closely With PLCs and Intelligent Systems

By Jim Montague

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Entirely new inventions may be dramatic, but they're rare. Reinventions or ongoing refinements of already familiar technologies aren't as exciting, but they're far more frequent,  so they likely result in greater total gains in performance and production. Likewise, while motors and drives may be everywhere in process applications and elsewhere, the fact that they're so long established shouldn't be an obstacle to improving them and their applications. They may be ubiquitous, but aided by variable-speed and variable-frequency drives (VSDs and VFDs) and other recent innovations, motors can instead be opportunities to achieve gains in many settings.

Speed Control Aids Quality

For instance, the PPC Jupiter plant of Pretoria Portland Cement Co., Ltd. recently improved the consistency and quality of its products by using VSDs and more accurate controls on the bucket elevators feeding and receiving new and recycled cement at its mills (Figure 1). PPC is the South Africa's leading cement supplier with eight plants and three mills in South Africa, Botswana and Zimbabwe.

The elevators use four Control Techniques' Unidrive SP AC drives, two at 37 kW and two at 55 kW, to start up with an acceleration and deceleration of 10-second and 100-Hz, and then run at a stable speed of 45-Hz until they reach their offload point. The drive runs at a preset speed control and can jog at 10-Hz minimum for maintenance purposes. PPC Jupiter reports that the four drives allow the buckets to achieve 0.1-Hz speed accuracy, deliver more precisely controlled loads of each key ingredient, and stop at preferred points with less tension and stress on their motors, gearboxes and other mechanical components, which reduces downtime and maintenance.

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Likewise, Mine Los Colorados iron ore mine in Chile recently added an ACS 1000 medium-voltage VSD from ABB to increase speed by 25%, and bring its conveyor up to nominal throughput without replacing its existing gearbox and 400-kW motor. The mine is operated by CAP Mineria-Compañia Minera del Pacifico S.A. (CMP) in Santiago, Chile.

The conveyor lifts material from the mine's stockpile to a train platform, but the existing gearbox and motor weren't running at the required speed above 50 Hz. The ACS 1000 enabled the motor and gearbox to soft start, ramp up smoothly, and run at 63 Hz. The drive's sinusoidal output voltage also allowed the motor to be used without derating, so the more than 100-meter cable length between the drive and motors was not a problem. Finally, the VSD meant the conveyor's hydraulic coupling was no longer needed, which simplified its layout and improved availability and efficiency.

Serving Specialized Settings

Perhaps the main benefit of advances in motor and drive technologies is that they can be deployed in settings where they haven't ventured before, or be more effective in applications where they've been hard to apply.

For example, Petrobras' Abreu e Lima refinery in Ipojuca, Pernambuco, Brazil, just installed 11 three-phase induction motors from WEG suitable for explosive atmospheres to drive the centrifugal pumps from KSB feeding water into the cooling towers associated with the refinery's main steam turbines (Figure 2). The pumps will provide water for circulation and cooling the plant's equipment, which is critically important in the refining process.

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