Distributed instrumentation for optimum control of variable speed electricpumping plants with center pivots

Pressure measurements at critical locations in the irrigation system (distr ibuted pressure measurements) were used to optimize operation of an electri c pumping plant equipped for variable speed operation. Operation of the pum ping plant was optimized in terms of providing adequate irrigation coverage with minimum energy use. The pumping plant supplied water to a single cent er pivot on undulating topography. The center pivot was equipped with a sup ervisory control and data acquisition system for variable rate water applic ation. 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 result ed 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 pres sure measurement resulted in 7.5 and 12.4% energy savings compared to conve ntional constant speed pumping for uniform and variable rate irrigation, re spectively Use of distributed pressure measurements to control the variable speed pumping plant was highly effective in minimizing energy use while ma intaining the pressure required throughout the irrigation system.