Digital Beats Analog for 911 Back-up
Staff -- Consulting-Specifying Engineer, 3/1/2001
When Sacramento County, Calif., was about to built a vital new 130,000-square-foot facility, the electrical engineer wrote the specifications to include analog paralleling. However, after comparing the capabilities of analog versus digital, he chose the latter.
Reliability was the key for this structure, which houses the county's Office of Communications, Information and Technology (OCIT). The county's population-knowingly or not-ends up looking to this building in times of crisis. Housed in the structure are the sheriff's 911 system and a disaster-command center. All police and fire calls originate from the facility. In addition, the building hosts welfare, payroll, training and other functions.
Backing all of this up are three 1,500-kilowatt (kW) generator sets: two ready for duty and the third installed as back up. The standby power system includes two 750-kilovolt-ampere uninterruptible power-supply (UPS) units, designed to smooth power flow in case of disruptions. The 911 center has an additional dedicated 30-kW set and a connection to the facility for even more redundancy in case of emergency.
Load requirements for the building, as well as recommended redundancy factors for UPS and back-up power, came from IBM. Load-shedding and manual override controls of the digital system were a bonus of the selected electrical system.
In the design, the UPS system was integrated with the digital-control system through a building-automation system. The digital system offered the advantages of integration with both the automation system and the existing 911 facility.
"I like being able to pull up the alarm history and alarm annunciators," says Marvin Watts, Sacramento County's electrical supervisor. "I'm equally impressed by the smoothness of the paralleling and the ability to perform monthly load tests."
For more information on PowerCommand digital paralleling from Cummins Onan, circle 454 on the Reader Service Card.
From Pure Power, Spring 2001
