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A water treatment station has cut its energy bill by GBP12,000 a year after implementing AC drives from Parker Hannifin in place of a 40-year-old eddy-current clutch.

The city of Rock Hill, South Carolina, has replaced obsolete technology in its wastewater treatment plant with the latest variable-speed drives from Parker SSD.

The Wildcat Lift Station was constructed in the 1970s to accommodate rising population and includes three 150kW centrifugal pumps that lift 11 million gallons per day a total of 143ft (44m).

Until recently, pump flow was controlled by an eddy-current clutch from the original installation.

However, when maintenance supervisor Jon White had to deal with the failure of one of the pump’s drive systems, he realised that the repair cost and time were impractical.

Instead, he contacted Parker SSD to discuss a new variable-speed drive.

Parker estimated cost savings and a calculation on the return of investment (ROI) showing that in energy savings alone, without consideration for the cost of ongoing maintenance of the existing system, the return period would be less than 12 months.

Based on this, the decision was made to proceed with the upgrade.

The inefficient eddy-current clutch was removed and the existing 150kW, 460V, 447T frame motor was directly coupled to the pump shaft, requiring only a simple motor mount modification.

The 150kW high-power modular AC variable-speed drive was then connected through the existing control panel and pump sequencing logic.

The available bottom power-entry configuration on the drive allowed an installation with no visible external wiring.

The need for an expensive additional external harmonic filter was eliminated as the drive includes a three per cent line reactor built into its enclosure, as well as line fuses and a local power disconnect switch with door interlock and lockable handle.

Replacing the eddy-current clutch with a solid-state drive has provided several benefits to Rock Hill.

For example, eddy-current clutches rely on slip to adjust the speed of their load and dissipate energy through heat.

Their efficiency also drops off as speed increases.

By using a variable-speed drive to regulate the speed of the pump directly, there is no energy lost to slippage and the current draw of the motor declines with reduction of speed.

With a centrifugal pump, reducing the speed to 80 per cent will result in nearly a 50 per cent decrease in energy consumption.

In addition, the motor is now gently ramped up to speed with current limited by the drive.

The old direct-on-line starting system inflicted significant stresses on the motor, clutch and pump, resulting in increased wear and reduced service life.

The high peak starting current led to higher peak demands, which in turn resulted in additional surcharges from the utility company.

With Parker SSD drives, the possibility of component failure does exist, but their modular design means parts can be quickly and easily replaced.

Parker Hannifin — Parker Sales UK

With annual sales exceeding $10bn, Parker Hannifin is the world's leading manufacturer of motion and control technologies and systems, providing precision-engineered solutions for a wide variety of commercial, mobile, industrial and aerospace markets.

To meet its customers' needs in motion and control, Parker provides the broadest range of products available from any single supplier. This is supported by expertise in nine major technologies:

  • Hydraulics
  • Pneumatics
  • Electromechanical
  • Filtration
  • Process control
  • Fluid and gas handling
  • Sealing and shielding
  • Climate control
  • Aerospace

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