Gauging Reliability of Emergency Power
Arduous switching, testing and recording of generator test results are becoming distant memories for the operations staff at the Veteran Affairs Medical Center in Nashville, Tennessee. Using a new power monitoring system, the engineering staff can now accurately determine the reliability of the emergency-power and recently upgraded electrical system, according to Herschel Flannery, the facility...
Arduous switching, testing and recording of generator test results are becoming distant memories for the operations staff at the Veteran Affairs Medical Center in Nashville, Tennessee. Using a new power monitoring system, the engineering staff can now accurately determine the reliability of the emergency-power and recently upgraded electrical system, according to Herschel Flannery, the facility’s electrical engineer.
The power-monitoring system automates the generator testing sequence in order to document compliance with minimum loading criteria throughout the test cycle. The Joint Commission on Accreditation of Health Care Organizations (JCAHO) requires that hospitals regularly test emergency generator systems that protect a hospital during any electricity interruption. The system was installed as part of an electrical system improvement project.
Installed in the mid-60s, the original electrical system was a 480Y/277-volt electrical service from four network-connected 1,000-kVA transformers, which were owned and maintained by the utility—Nashville Electric Service (NES)—and fed from two NES 13.8-kV feeders. The transformer network provided reliable power for more than 30 years, but it was old, fully loaded and land-locked in an inaccessible vault. Concerns about future growth and the possibility of a transformer failure prompted the VA to replace transformers, service, service switchboards and other old and obsolete distribution equipment.
Nashville-based engineering firm Nash Lipsey Burch advised the hospital that replacing the “spot network” service with a conventional service—even a dual 480-volt double-end service—would be unsatisfactory. NES, however, no longer provided network transformers to its customers.
With the VA’s approval, Nash Lipsey Burch designed two new spot networks, each consisting of two 2,000-kVA transformers owned by the VA. Network protection for each spot network is provided by two 2,500-amp solid-state microprocessor trip circuit breakers equipped with directional current relays and a ground-fault scheme that totalizes zero-sequence currents flowing through the two mains. The two spot networks feed opposite ends of a double-ended 5,000-amp switchboard, providing additional redundancy.
The upgrade project provided the opportunity to include a computerized power-monitoring system for the entire facility. The monitoring and control system was installed on new electrical equipment and retro-fitted on older systems. The system was deployed in two phases: monitoring first, then control. The scope of work entailed installing meters and communicating breakers on the two mains and 17 branch breakers, as well as for several feeder circuits. The design also included 18 enclosure panels and provided wiring diagrams, PLC programming, interfacing with generator controls, system configuration, graphical one-line diagram development and commission and startup.
“The graphs and event logs that automatically document generator test runs show us when tests start, stop and if they are completed correctly,” says Flannery. “During the annual inspection, a generator paralleling service technician accidentally pushed an emergency stop button and the unit was left off-line for the remainder of the run. This type of inaccuracy may not have been caught without the power-monitoring system recording the results.”
From Pure Power, Fall 2002
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