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ARS Home » Plains Area » Bushland, Texas » Conservation and Production Research Laboratory » Livestock Nutrient Management Research » Research » Publications at this Location » Publication #83208
Title: THE ROLE OF CAPACITANCE IN A WIND-ELECTRIC WATER PUMPING SYSTEM

Author
item LING, SHITO - WEST TEXAS A&M UNIVERSITY
item Clark, Ray

Submitted to: Windpower
Publication Type: Proceedings
Publication Acceptance Date: 6/17/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Wind-electric water pumping systems are composed of three main components: a wind turbine that generates electricity; a standard electric motor and pump; and a controller. The wind turbines used in wind-electric pumping systems are fairly standard, small electrical generating units that are produced by several manufacturers around the world. The electric motors and dpumps are sold by most well drillers and, in many areas, are available fro hardware stores. The controller is the unique component that is specially made only for water pumping applications. The USDA-Agricultural Research Service and the West Texas A&M University-Alternative Energy Institute have cooperatively developed and tested a new controller for wind-electric water pumping systems. An essential element of the controller is the amount and use of capacitance to regulate the voltage-frequency ratio. Regulation of the voltage-frequency ratio is necessary to insure the lifetime of the electric motor and to provide speed control for the pump. By adding additional capacitance when the wind speed exceeds 12 m/s, the pumping load can be maintained thus producing more water and greatly improving the system efficiency. This new controller has a two step system for adding capacitance. For the 850 W wind turbine tested and reported in the paper, 35 microfarads of capacitance was added at pump start-up, a wind speed of 4 m/s, and another 20 microfarads was added at 12 m/s.

Technical Abstract: The development of controllers for wind-electric water pumping systems to enable the use of variable voltage, variable frequency electricity to operate standard AC submersible pump motors has provided a more efficient and flexible water pumping system to replace mechanical windmills. A fixed capacitance added in parallel with the induction motor improves the power factor and starting ability of the pump motor at the lower cut-in frequency. The wind-electric water pumping system developed by USDA- Agricultural Research Service, Bushland, TX, operated well at moderate wind speeds (5-12 m/s), but tended to lose synchronization in winds above 12 m/s, especially if they were gusty. Furling generally did not occur until synchronization had been lost and the winds had to subside before synchronization could be reestablished. The frequency needed to reestablish synchronization was much lower (60-65 Hz) than the frequency where synchronization was lost (70-80 Hz). As a result, the load (motor and pump) stayed off an excessive amount of time thus causing less water to be pumped and producing a low system efficiency. The controller described in this paper dynamically connects additional capacitance of the proper amount at the appropriate time to keep the system synchronized (running at 55 to 60 Hz) and pumping water even when the wind speed exceeds 15 m/s. The system efficiency was improved by reducing the system off-line time and an additional benefit was reducing the noise caused by the high speed blade rotation when the load was off line in high winds.