Cut electricity bills on irrigation systems
By F Steyn, ABB South Africa
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Electricity+Control, July 2013 (pages 8 – 9)
Understanding pump design is an important starting point when designing for the required head pressure. The safety factor is built into the irrigation design to ensure that the pump supplies sufficient pressure at the highest delivery point furthest away from the pump. Approximately 95% of the time the pump runs at full speed and the pressure is regulated with a mechanical device. This configuration wastes energy.
Most pumping systems are designed for the maximum flow rate requirement at a fixed maximum head position. This is also known as the constant speed pumping requirement. However, few irrigation systems operate at the designed constant speed pumping requirement because of the continuous change in static and friction head pressures in both block or centre pivot irrigation. This results in irrigation systems wasting energy.
The required power of a centrifugal pump varies in proportion to the cube of the speed. Therefore a small reduction in speed will result in a large energy reduction.
- A soft starter ramps up the speed of the machine whereas a VSD allows speed control.
- In pumping and irrigation applications, VSDs can play a significant role in optimising flow rates, and saving energy.
- In a typical irrigation application, VSDs can result in up to 40% energy savings.