DISTRIBUTED INSTRUMENTATION FOR OPTIMUM CONTROL OF VARIABLE SPEED ELECTRIC PUMPING PLANTS WITH CENTER PIVOTS

Pressure measurements at critical locations in the irrigation system (distributed pressure measurements) were used to optimize operation of an electric pumping plant equipped for variable speed operation. Operation of the pumping plant was optimized in terms of providing adequate irrigation coverage with minimum energy use. The pumping plant supplied water to a single center pivot on undulating topography. The center pivot was equipped with a supervisory control and data acquisition system for variable rate water application. Electrical demand of the irrigation system was evaluated under four variable speed pumping control schemes. Disregarding inefficiencies of the variable frequency motor controller, distributed pressure measurement resulted in 15.8 and 20.2% energy savings compared to constant speed pumping for uniform and variable rate irrigation, respectively. When the efficiency of the variable frequency motor controller is accounted for, distributed pressure measurement resulted in 7.5 and 12.4% energy savings compared to conventional constant speed pumping for uniform and variable rate irrigation, respectively. Use of distributed pressure measurements to control the variable speed pumping plant was highly effective in minimizing energy use while maintaining the pressure required throughout the irrigation system.