Rex Hospital gets a power system upgrade
The upgrade increased the system’s emergency power generating capacity, boosted its fuel storage capacity, and added a SCADA system.
The recently upgraded power system at Rex Hospital in Raleigh, N.C., which came online in spring of 2013, was designed to ensure seamless delivery of normal and emergency power to the 660-bed facility. The hospital’s design team, led by Mike Raynor, director of facility and construction services, envisioned a fail-safe emergency power system that would serve the facility’s electrical power needs for the next 30 years.
Raynor and his team designed the modernized system to provide the hospital with an emergency power system with more capacity, reliability, redundancy, and flexibility than the system it replaced, which was installed in the mid-1980s. The design team chose Russelectric Inc., Hingham, Mass., to supply power control switchgear, transfer switches, the SCADA system, design assistance, and implementation support.
Rex Hospital’s emergency power system upgrade included replacing three 1.25 MW generators with two new 4,160-V, 1,800 rpm, 3.0 MW units (0.8 power factor). An existing 2.25 MW generator that matches the operating voltage of the new units was retained. The generators are capable of paralleling with each other as well as with the utility source.
The hospital’s previous backup power system was the closed-transition type. The upgraded system retained that configuration because no one wanted a service interruption when the feed switches from utility power to generator power (when both sources are available). The existing utility substation at the hospital was replaced, and new switches and switchgear were relocated from cramped quarters in the main hospital building to a newly constructed central energy plant. Another automatic transfer switch was added to protect the hospital’s data center. When the generators are up to speed, an outdoor switchgear arrangement fed by the utility’s outdoor transformers allows the hospital to disconnect from the utility either manually or automatically.
Whereas the previous system’s fuel capacity was 60,000 gal, the new system has two 40,000-gal underground fuel tanks. Also, the system maintains fuel in each generator’s emergency 150-gal day tank at all times. With all tanks full, the hospital could meet its peak demand of about 5,200 kW for almost six days. However, because that peak is reached only for short periods on warm summer days, and peak demand during winter doesn’t exceed 4,500 kW, the hospital could probably operate under its own power for more than nine days.
The hospital’s emergency power system employs a both-sides-hot strategy, which feeds utility power to both sides (normal and emergency) of every automatic transfer switch. If any downstream feed is lost, a breaker trips, immediately transferring power to the other side of the switch with minimal interruption and without starting the generators. This strategy also allows the power plant staff to test transfer switches with no interruption and without starting the generators.
Another feature of the hospital’s upgrade is a customized supervisory control and data acquisition (SCADA) system, which allows technicians to monitor and control the entire power system from interactive display screens in the control room at the central energy plant. The SCADA system provides real-time and historical trending; distributed networking; alarm management; and required reporting for testing, loads, exhaust temperature, and fuel consumption, and for the Joint Commission on Accreditation of Healthcare Organizations. In the event of an internal failure, the SCADA system can rapidly and automatically configure a path to bypass the failure and reenergize the system.
Presently, the hospital’s peak-demand load is about 5,200 kW. However, taking its anticipated growth into account, its power system now has enough emergency capacity (8.25 MW) for a seven-story heart center currently on the drawing board as well as a future cancer center addition. With this N+1 strategy, the facility could lose—or take out of service—any single generator and still have adequate capacity.
Regular equipment testing occurs with no interruptions or inconveniences. All tests run so far indicate that the power system is functioning perfectly. For example, the base load test connects 30% of the generation capacity to hospital load for 45 min biweekly (as required by and reported to authorities) without interrupting any hospital services or loads.
Edmund Malley is vice president of engineering and field service for Russelectric.