Whitestone Pump Station Variable Frequency Drive Design
Au Gres, MI
LAN contracted with Saginaw-Midland Municipal Water Supply Corporation (SMMWSC) to provide a feasibility study to investigate the operational cost savings for operating select pumps at variable speeds at the 285-mgd Whitestone Point Pumping Station. Currently, to provide water flows below 42-mgd, the pumps are operated against partially closed valves thereby increasing the total dynamic head on the pumps resulting in higher energy use. With the use of VFD’s on the motors, speed can be used to reduce the pump capacity/head curve resulting in energy savings.
The tasks performed by LAN included investigating available manufactured variable frequency drives, inverter rating of selected pump motors, and space needed to locate variable frequency drives; modifying the existing electrical systems, station and ventilation control systems; and identifying operational energy savings. Three options were presented to the client for review and selection. LAN recommended the third option as the most economically attractive at an implementation cost of $740,800, which will provide a payback in 6.5 years based on a projected savings of about $114,000 per year.
SMMWSC retained LAN to provide design and construction management services for two 1200-HP VFD units, medium voltage, secondary transformers and new 5KV switchgear. The selected medium voltage VFDs are 2400/4160 volt, dual rated and are manufactured by AB/Rockwell Automation. Equipment bids were received from multiple venders, with the lowest bid in the amount of $701,750. This equipment was installed by the client’s in-house forces. The first year power saving were approximately $122,000.
At a glance
Two 1200-HP active front-end variable frequency drive units
Converted two existing 2400 V motors to inverter duty rated motors
Project included new 5 KV switchgear
VFDs and switchgear were designed for 4160/2400 dual voltage
Increased ventilation by 17,000 cfm to remove excess heat generated by VFD isolation transformers during summer months
Use the 250,000 Btu excess heat from VFD isolation transformers to supplement building heat during cold weather
Achieved $122,000 saving in electrical energy during first year of operation.
Energy cost savings will achieve payback within 6 years
Identified power savings of approximately $114,000 per year
Coordinated system design with SCADA integrator
Developed installation sequence plan to minimize downtime
Construction Mgmt & Inspection
Planning & Modeling