Application of Variable Frequency Drives for Motor Energy Optimization in Water Pumping Stations in Oyo State

Water distribution pumping stations in Oyo State, South West Nigeria, represent a major component of urban water utility operational expenditure, with centrifugal pumping motors frequently operated at fixed speed regardless of actual demand variation. This study applies variable frequency drive technology to optimize motor energy consumption at four pumping stations operated by the Oyo State Water Corporation in Ibadan. Pre-installation energy audits quantified baseline electricity consumption and flow delivery performance at each station over a three-month period. VFDs rated for the motor capacities of 22, 37, and 55 kilowatts were installed and programmed with proportional-integral speed control loops responding to downstream pressure feedback signals. Post-installation monitoring over a subsequent three-month period measured electricity consumption, pump duty cycles, and water delivery volumes. Aggregate energy savings across the four stations were 34 percent compared to the fixed-speed baseline, translating to an estimated annual electricity cost reduction of 28.6 million Naira at current utility tariffs. Pump mechanical stress, measured through vibration monitoring, decreased in three of the four stations, with projected bearing life extension of 30 to 45 percent attributed to reduced starting current spikes and lower average operating speeds. Simple payback period for the VFD investment was calculated at 14 months. The study develops a business case template for VFD application at additional water pumping stations across Oyo State and presents a maintenance protocol for VFD systems in humid tropical environments. Keywords: variable frequency drive, pumping station, energy optimization, water utility, Oyo State