Pump drives cut power costs

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October 2007 Motion Control & Drives

Variable-speed drives for pump and fan applications are an effective antidote for rising power costs. The inverters of Mitsubishi Electric’s FR-F740 series can cut power consumption by up to 60%, as the operators of a sewage treatment plant in Lippstadt, Germany, discovered to their benefit.

The Westphalia Hospital in Lippstadt operates its own sewage treatment plant in the large hospital complex, which also includes the Westphalian Centre for Forensic Psychiatry. The plant processes the sewage generated by around 2300 patients and hospital staff and the 2300 residents of the nearby communities of Eickelborn and Lohe, and then runs the treated water into the Lippe river.

Four pumps, each with a capacity of 120 m³ per hour, pump the sewage up to the highest point in the plant, the drip filter tower. Individual pumps are activated and deactivated depending on the current sewage volume, which varies depending on the time of day and the season. As is common in building services and industry, the pumps were operated through DOL (direct on line) starters for many years, wasting a lot of electricity.

The hospital operators thus decided to perform a trial with power-saving Mitsubishi Electric frequency inverter drives designed specifically for the needs of pumps and fans.

The equipment was delivered and installed by Mitsubishi wholesale partner H. Gautzsch Grosshandel GmbH in Münster, Germany, who also provided consulting services.

Two FR-F740 inverters were installed with outputs of 7,5 and 15 kW respectively. The more powerful unit powers one of the motors at variable frequency and switches in a second pump motor automatically when required. The smaller inverter is used to power the third pump motor and the fourth motor is left connected directly to the mains and is only used as an emergency backup.

The operators of the hospital were impressed by the power savings achieved by the advanced control technology. After the two-month trial it was clear that the frequency inverters would pay for themselves within the space of a year, after which they will save the hospital nearly Euro 4000 in operating costs every year.

The inverters' simple monitoring and data management features have also been a bonus. Operating values like current, voltage and output can all be viewed quickly and easily and a user-friendly one-touch control provides quick access to all drive parameters. Configuration is just as simple: thanks to state-of-the-art circuitry and the integrated EMC filter the inverters are ready for operation as soon as they are connected.

For more information contact Sheldon Olivier, CBI-electric, +27 (0)11 928 2000, [email protected], www.cbi-electric.com

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Pump drives cut power costs

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