Brar, D. (2015). Conservation of Energy using Variable Frequency Drive for Center Pivot Irrigation Systems in Nebraska (Master's thesis), University of Nebraska-Lincoln.
The study introduces a novel approach to lower the operating pivot point pressure by varying the motor speed with the help of variable frequency drive (VFD) in contrast to the commonly used fixed speed approach. By varying the speed of motor, the required minimum pivot point pressure can be provided at any required flow rate. This was investigated through a GIS-assisted simulation on 100 randomly selected pivots located in 10 Nebraska counties using high resolution Digital Elevation Model (DEM) datasets. Center pivot irrigation systems are usually equipped with corner watering attachments like end guns and corner extensions to irrigate additional area at the corners of the field. Two different types of corner watering equipment i.e. end gun and corner extension were involved in this study. Four different scenarios were taken into consideration 1) standard systems with seven towers and no corner watering attachment, 2) end gun attached at the end of center pivot system, 3) corner extension attached at end of center pivot system, and 4) center pivot system equipped with corner extension and end gun. Two different approaches were used to operate the center pivot systems 1) at constant motor speed with fixed design pivot point pressure, 2) at varying motor speed according to the minimum required pivot point pressure. The varying topography as well as the shape of the pump performance curve at fixed motor speed were found to play a major role in energy conservation. The energy reductions obtained through varying speed approach, along with annual monetary savings were calculated for all the study counties under all the scenarios. The major factors contributing to maximum energy savings and annual returns were large topographical changes, shape of pump performance curve, long irrigation operating hours, and high electricity costs. Cedar County showed the maximum average energy reductions by using varying speed approach whereas Hamilton and Butler County expressed minimum energy reductions in all the scenarios. Economic analysis was conducted for the potential investment in VFDs along with the average payback periods for the cost of VFD in each county.
Overall, the suggested use of the Variable Frequency Drive has proven to provide savings in terms of energy conservation from the analysis performed in the study. However, there are emerging concerns about the cost-effectiveness of the approach. It is expected that the technology will receive high adoption, specifically in irrigation sector, from producers, research community and industry, if manufacturers are able to address economic concerns of the end user. This study provides a holistic approach in quantifying the energy savings over a large study area, which provides the producers, water resource managers, planners, and decision and policy makers, a clear picture of the widely variable anticipated benefits when aiming at adoption of a VFD.
Advisor William L. Kranz
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