Analysis recommends new units over upgrade
The Wastewater Collection Division’s Pumping Stations Branch operates and maintains the wastewater pump stations, flow meters, a largepressure sewer system and several facilities that add chemicals to control odor and corrosion. Unmanned and completely automated, each of the Fairfax County pump stations requires a standby power source that automatically comes online to keep the pumps running and wastewater flowing through the collection system when utility power is lost.
Recently, Cynergy Electric Company, Inc., an electrical contractor in Crofton, Maryland, completed a yearlong project for ALPHA Construction Company, Upper Marlboro, Maryland, to replace old backup power systems at three of the pumping stations. The original contract called only for upgrades and repairs of the existing standby generators at the three pumping stations. But after completing a costbenefit analysis, officials at ALPHA recommended replacing the existing generators instead of upgrading the old ones. The benefits of improved response time, reliability and reduced maintenance far outweighed the additional investment for the new units.
Compared to the generators they replaced, “The new equipment is more efficient and provides a higher degree of reliability,” said Dave Ashburn, president of Cynergy Electric.
Loads determine generator size
Cynergy Electric designed and installed new backup power systems, which included new generators, switchgear, batteries and battery chargers. For the generators, Cynergy Electric turned to Curtis Engine & Equipment Inc., a Baltimore-based distributor for mtu that supplies emergency standby power systems in the Mid-Atlantic region.
The loads and starting requirements of each pump motor determined the choice of generators: a 1,000 kW mtu unit to power up to four 250 hp motors; a 1,500 kW unit to power up to four 450 hp motors; and a 1,750 kW generator for up to four 600 hp motors. Each of the backup power systems has a 200-gallon day tank that pulls from a 5,000-gallon main fuel tank. Each generator set is EPA Tier-2 certified and meets and exceeds standards set by the Virginia Department of Environmental Quality, according to Ashburn.
New units pass early tests
Shortly after the new systems were installed, summer storms in Fairfax County caused several short power outages at the pumping stations. Ashburn said that in each case, the mtu generators sensed the outage, quickly started up and accepted the load. When power was restored, the units transferred the load back to normal utility power.
Based on the results of these early experiences, operations and maintenance personnel responsible for the three pumping stations can have confidence that the new backup power systems will perform as required. What’s more, county residents and businesses near the pumping stations can trust that mtu standby generators will keep wastewater flowing even when utility power is out.