Outdated VFDs Driving You Crazy? Analyze This!

Replacement of medium voltage variable frequency drive (VFD) systems originally installed in the early 1990s was evaluated to determine if recent advancement in technology would benefit the owner/operator at two large raw wastewater pump stations at Boston's Deer Island wastewater treatment plant. Each of the two cases evaluated involved VFD systems controlling vertical synchronous brushless motors driving raw wastewater lift pumps. Case #1 involved eight 1250-hp synchronous motors with dual 1100 VAC windings, 2200 VAC, 400 rpm, 60 Hz. Case #2 involved ten 3500-hp synchronous motors with dual 2200 VAC windings, 2200 VAC, 400 rpm, 60 Hz. The Case #1 VFD system was successfully replaced with state-of-the-art voltage source pulse-width modulating (PWM) drive technology coupled with reconfiguring the two 1100 VAC windings of the existing motors to operate the motor and new VFD system at 2200 VAC. This VFD system replacement is providing increased reliability, efficiency, enhanced power factor, reduced power consumption, and reduced maintenance cost. The Case #2 VFD system replacement is currently in the design phase based on new synchronous motors and PWM drives.