Drives reduce labour costs and cut irrigation energy use 40%

The cost of electricity means that for some South African farms, running their irrigation system is one of their largest operating expenses.  To reduce electricity consumption, one the farm owner began looking for alternatives to the old irrigation system of running the water pumps at constant speed, and using manual control of valves for flow control.

The old system was not energy efficient, took up to an hour to bring on line, and was start subject to up to three power outages a day, making the whole process very labour-intensive. To start one of the six pumping stations could take one person up to an hour and with sometimes as many as three power outages a day, start-ups became almost a full-time job.

The farm owner decided to test variable speed drives (VSD) on the water pumps at one of its six pumping stations. ABB drives were selected for five VSDs running irrigation pumps with 45 to 75 kW motors, and the sixth VSD used on the water transfer pump.

Labour and energy savings

The results were quite dramatic. With the new VSD units installed demands fell from 291 kW to 175 kW, or 40% for one pumping station. In financial terms, the irrigation pumps operate at 2,970 hours per year providing annual savings of around £15k in electricity costs. Reusing the existing motors gave a payback time of 7 months. The farm quickly made a repeat order and has installed similar drives on a second pumping station.

Additional benefits

In addition to the financial savings on the electricity bill, the farm also had further operational savings in both man-hours and trouble during the start-up process. Operators now only need to flick a switch to start, and in the event of power interruptions the system would start-up automatically at pre-set times.

The VSDs give a long ramp-up time that allows for a very smooth pipe filling process, so the previous mechanical stresses on the pump couplings during start-up were completely eliminated, together with fewer friction losses in the pipes. Additionally, water hammering following switching off disappeared and fewer losses on the impeller were seen due to these extended ramp-up and ramp-down times.

Cost efficient retrofit

–40 percent reduction in energy consumption gave rapid seven-month payback

–Reduced labour costs of manpower needed for start-up process is dramatically reduced

–Smoother operation and pipe filling, power drops handled more easily, and water hammer and system shocks eliminated

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