Author
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Clark, Ray |
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SHITAO, LING - WEST TEXAS A&M UNIVERSITY |
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Submitted to: American Society of Mechanical Engineers
Publication Type: Proceedings Publication Acceptance Date: 1/29/1996 Publication Date: N/A Citation: N/A Interpretive Summary: Supplying water for livestock in remote pastures requires pumping systems that are reliable and capable of operating unattended. The mechanical windmill was used for years, but the grid-powered electric pump has gradually replaced the windmill as more rural electric lines have been installed. Now because of the high cost of long grid-lines, renewable energy fueled pumps are being used. Wind electric systems are being installed because the electric systems are more efficient, offer the flexibility to site the wind turbine some distance from the pump, and require little maintenance. Since the wind turbine operates over a wide range of wind speeds, a controller is needed to maintain stable conditions and improve the system efficiency. The USDA-Agricultural Research Service, Bushland, TX, has designed, built, and tested a smart controller using microchip technology. The new controller monitors the electrical frequency, voltage, and current, performs some calculations using these values, and then performs control functions. Cut-on and cut-off points are easily selected by the operator and the controller provides control for any abnormal conditions that might be encountered such as current overload, overheating of generator, and loss of one or more electrical phases. The controller disengages the motor and provides protection for both the generator and motor. This inexpensive controller can allow the pumping system to operate in all wind speed conditions with little risk to the pumping system. Technical Abstract: More and more wind electric water pumping systems are replacing the mechanical windmill for irrigation of crops and watering livestock because the electric systems are more efficient, offer the flexibility to site the turbine some distance from the pump, and require little routine maintenance. The motors and pumps used in most pumping systems were designed to operate at a constant rotational speed. However, the wind electric system operates at variable speed because the electricity generated by the wind turbine is variable frequency. Since the wind turbine operates over a wide range of wind speeds, a controller is needed to maintain stable conditions and improve the system efficiency. Experience of the past ten years with water pumping systems at USDA- Agricultural Research Service (ARS), Bushland, TX, has shown that the wind pumping system operates best when the nameplate voltage to frequency ratio (V/f) is maintained. Using this principle, a smart controller has been designed, built and tested for wind electrical pumping systems. Earlier controllers used only the frequency or the voltage to determine the cut-in and cut-out points when electricity from the turbine was connected to the load. This new controller also samples the voltage and calculates the ratio of voltage to frequency. Any abnormal conditions, such as current overload, overheating of generator and loss of one or more phase will drive the V/f ratio below a programmed set point and the controller will disconnect the load and protect the generator and motor from being damaged. This inexpensive controller can allow the pumping system to operate in high wind speed conditions with little risk of damaging the pump motor or wind turbine generator. |
