Long Quarter Sewage Pumping Station – Pump Motor Replacement & Vibration Corrective Work

Key Accomplishments

Johnston Construction Company

• The replacement motors were approximately 450 HP, 900 RPM, 4,160-volt, three-phase units equipped with RTDs, anti-condensation heaters, vibration provisions, and associated accessories.
• JCC sequenced removal of the existing motors and coordinated rigging and installation of the replacement units while protecting existing equipment and station systems.
• Reconnected existing motor vibration accelerometers, RTDs, auxiliary winding heaters, and associated electrical devices required for operation and monitoring of the new motors.
• Reused and reconnected existing pump-motor power feeders where practical and coordinated required electrical modifications associated with the replacement work.
• JCC furnished and installed new motor support pads and coordinated the physical setting and alignment of the replacement motors.
• Performed required insulation-resistance testing, vibration testing, motor electrical testing, infrared thermography, and field performance verification.
• Coordinated startup and commissioning with Baltimore County, Flowserve, the motor manufacturer, and Rockwell Automation/Rexel.
• Successfully completed a phased acceptance process beginning with installation and operation of the first two replacement motors for a 30-day demonstration period before proceeding with the remaining motor replacements.
• Supported operation of one of Baltimore County's major sewage pumping facilities, whose existing dry-pit pump system included eight pumps arranged as four series pumping units, each pump designed for approximately 8,333 GPM at 162 feet TDH.
• Johnston Construction Company performed corrective motor replacement and vibration-resolution work at the Long Quarter Sewage Pumping Station for Baltimore County Department of Public Works. The work addressed noise and vibration issues affecting the motors associated with the station's large dry-pit sewage pumping system.
• The pumping station incorporated eight vertical dry-pit, non-clog sewage pumps arranged as four series pumping units. Each pump was designed for approximately 8,333 GPM at 162 feet TDH, with the paired series arrangement developing approximately 324 feet TDH. The pump specification allowed motors up to 500 HP and identified a 900 RPM operating speed.
• Following investigation of the motor noise and vibration concerns, the project team developed a corrective program involving replacement of all eight pump motors. The selected replacement motors were U.S. Motors / Nidec units rated at approximately 450 HP, 900 RPM, and 4,160 volts, incorporating platinum RTDs, anti-condensation heaters, non-reverse ratchets, and provisions for vibration monitoring.

B & R Electrical Contractors

• B & R Electrical Contractors, Inc. performed the electrical portion of the Long Quarter Sewage Pumping Station motor replacement program under Johnston Construction Company.
• Provided electrical isolation, disconnection, and reconnection for a staged replacement program involving eight pump motors arranged in four two-motor sets.
• BRE locked out the associated VFD cabinets and main breakers before removal of each motor set.
• Disconnected the existing 4,160-volt motor power connections at the motors and at the VFDs to support motor removal and electrical testing.
• Grounded the motors prior to removal and disconnected the associated space heaters, stator temperature detectors, and bearing temperature detectors.
• BRE returned after installation of the replacement motors to reconnect the 4,160-volt power circuits, VFD connections, motor space heaters, and temperature-monitoring devices.
• Modified existing flexible/sealtight raceway and shortened conductors where required to accommodate the replacement motor installations.
• Coordinated reuse of the existing 5 kV motor feeders and associated medium-voltage terminations where practical.
• Supported Baltimore County's motor-rotation verification and performed phase reversal when necessary to establish proper motor rotation.
• Completed multiple mobilizations for each motor set so the electrical systems could be safely disconnected before motor replacement and restored after installation.
• Coordinated the specialized electrical work with JCC's motor replacement, rigging, startup, and performance-testing activities.
• B & R Electrical Contractors, Inc. performed the electrical work associated with replacement of the pump motors at Baltimore County's Long Quarter Sewage Pumping Station in Towson, Maryland. BRE worked as a subcontractor to Johnston Construction Company as part of a larger corrective program addressing motor noise and vibration issues at the station.
• The motor replacement was performed in multiple stages, with the electrical work divided into four sets of two motors each. Each motor set required an initial mobilization to safely isolate and disconnect the existing electrical equipment before motor removal, followed by a second mobilization to restore the electrical systems after the replacement motors had been installed.
• Before removal of each motor set, BRE locked out the associated variable-frequency-drive cabinets and main breakers. The electrical crew disconnected the 4,160-volt power connections at the motors and also disconnected the corresponding VFD connections so insulation-resistance testing of the power wiring could be performed. The motors were then grounded before mechanical removal.