Irrigation
Pacific Northwest – A small barley farmer was currently using a fixed speed pump to provide irrigation water to his acreage. The pump was started by using across the line voltage. During startup the pump motor drew up to 4 times it’s normal running current. The customer was charged based on this instantaneous start up current, not the running current, from the local utility company. Mitchell Lewis & Staver was brought in to assess the situation and provide a more economical and reliable mean of providing water.
Having numerous years of expertise in the irrigation industry, Mitchell Lewis & Staver Co recommended using a Variable Frequency Drive (VFD) instead of the standard On/Off positions of the pump and a water line pressure switch. A VFD will adjust the frequency of the power supply from 60Hz to something lower and back up to full speed as demand changes. During startup of the pump, the VFD slowly brought up the pump speed, never exceeding the current rating of the pump’s motor. As the line filled with water, the pressure switch signaled back to the VFD to adjust pump speed accordingly to maintain a predetermined set point. As more wheels were turned on, the pump was sped up, as wheels were shut down, the pump slowed down. The pressure switch/VFD combination could also turn the pump on and off as needed. As a additional benefit, the slow ramping of pump speed and line pressure, reduced wear on the pump, motor and mechanical line components (water hammer).
After several weeks in use, it was calculated that the VFD/pressure switch combination produced a annual savings of $12.00/acre. Typical sized farms can range from 4000-6000 acres in size, resulting in net savings of $48,000-$