Download Report Part 1

Variable Frequency Drive Corner Arm Pivot Case Study
Part 1: Instrumentation and data collection equipment
Prepared by: Gregg Dill, P.Eng.
December 2011
SUMMARY
A corner arm centre pivot operates about 20% of a circle at the maximum flow rate and 80% of the
circle at flow rates lower than the maximum flow rate. A typical flow rate range is 700 to 1200 gpm. A
corner arm centre pivot pumping unit is designed to deliver the maximum flow rate at the maximum
pressure and, therefore, operates at lower flow rates and higher pressures for most of the circle. The
variable frequency drive (VFD) adjusts the motor speed to allow the pump to deliver the required flow
rate at the required pressure which, effectively, reduces the kilowatts of power required for most of the
circle.
Instrumentation and data collection equipment required to test the power requirement for a corner
arm centre pivot without a VFD, with a VFD controlled by a pressure transducer at the pump discharge
and with a VFD controlled by a pressure transducer at the corner arm tower was assembled and tested.
Instrumentation will include an ultrasonic flow meter or a propeller flow meter, two wired pressure
transducers, three wireless pressure transducers, a power meter on the irrigation system service input, a
power meter on the input to the VFD, a wireless GPS receiver on the last tower of the centre pivot, a
wireless GPS receiver on the corner arm, and a speed monitor on the pump/motor.
The monitoring system was successfully assembled and tested.
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