By Steve Blankinship, Associate Editor
Located 20 miles north of Atlanta, Ga., the not-for-profit WellStar Kennestone Hospital is one of the state’s largest and busiest medical facilities. The 633-bed, 1.2 million-square-foot facility has expanded in recent years to help meet the growing demand for its hospital’s specialty services.
With the addition of a new 200,000-square-foot cardiac care unit several years ago, the hospital began planning for a new energy facility. Today, three 2 MW/4160VAC diesel generator sets from Cummins Power Generation are housed in the new energy plant, which is located about 1,000 feet from the main facility to optimize patient comfort and power distribution.
The back-up emergency power requirements for the entire hospital campus total about 2,400 kW, with the system serving emergency loads in two bed towers, a center for women’s health and a cancer center. The three 2 MW generator sets offer redundancy to provide a premium level of reliability for the healthcare facility’s critical load requirements.
The distance between the plant and the hospital, plus provisions for anticipated future system growth, drove the electrical construction team, led by Inglett & Stubbs, to choose 4,160 volt supply lines to the hospital. The Cummins system includes a paralleling system to provide emergency/standby power from the new central energy plant. The new equipment was interfaced to existing transfer switch equipment from several different manufacturers.
“Cummins Power Generation is the first manufacturer of transfer switches proven to survive a fault condition and to continue to operate at full load without repair,” said Rich Scroggins, product manager for Cummins Power Generation. “This ability gives consulting engineers more design flexibility in addressing requirements and potentially to lower costs by using fewer transfer switches.”
Although not installed at WellStar Kennestone, Series OHPC and CHPC PowerCommand automatic transfer switches are among the first to achieve UL-listed 10 cycle and 30 cycle withstand and closing (short-time) ratings. The UL listing provides consulting and specifying engineers independent assurance that the OHPC and CHPC transfer switches offer high performance level, particularly for standby power systems requiring selective coordination. The OHPC open transition and CHPC closed transition switches showed short-time ratings of 25 kA at 10 cycles for 125 to 260-amp switches, 30 kA at 30 cycles for 300 to 600 amps and 42 kA at 30 cycles for 800-amp switches in UL tests. The switches continued to operate at full load, even after testing.
Selective coordination is mandatory for emergency and legally required electrical systems in buildings where life safety is paramount. That includes hospitals, health care facilities, emergency shelters and high-rise buildings with multiple elevators, as defined by the 2008 edition of the National Electrical Code (NEC). NEC 2008 also requires selective coordination for critical operation power systems in secure buildings such as banks, data centers, embassies and government offices.
The WellStar Kennestone Hospital design team selected the PowerCommand digital paralleling system for its integration with the generators and its ability to meet performance and interoperability requirements for existing equipment. The system features a genset-mounted PowerCommand paralleling controls and a system master control with separate touch-screen control panels for the generators and transfer system.
“While the system has yet to experience a utility outage, it has performed as specified and designed during the required acceptance tests,” according to Sam Jenkins, project engineer for WellStar Health Systems. Once the generators are operating and ready for loadwhich takes about 10 secondsthe system transfers power to the generators. Then the system senses when the utility comes back online and makes a coordinated switch back to utility power.
Alex Holbrook of Perry, Crabb & Associates had overall engineering responsibility for the project. Hal Barnes and Jason Hales of Perry, Crabb & Associates were the project’s prime consultants and Kenny Cole of Inglett & Stubbs was general contractor and electrical contractor. CDH Partners was the architect and Hardin Construction built the addition. Jenkins and Steve Fowler of Wellstar managed the project for Wellstar Health System.
In keeping with the facility’s master plan, the energy plant provides standby generators for the existing facility and its seven-story Blue Tower addition. Diesel generators were selected for their handling of block load, even while synchronizing. “This type of project made for some exciting engineering challenges,” said Holbrook. “It took teamwork to develop solutions for replacing obsolete switchgear, generators and busway while never shutting down the 24/7 hospital. The scope included an addition to enclose three 2 MW diesel generators with the infrastructure to add three more 2 MW units in the future.
Paralleling the three 4,160V, gensets provided the desired N+1 redundant system. A life cycle cost analysis was used to determine the appropriate voltage for the generators. Although the existing facility uses a 480V base for electrical distribution, the design and construction team analyzed installation cost of feeders for concurrent and soon-to-begin construction projects. Analysis revealed 4,160V as the more cost-effective solution.
This also allowed for emergency power to two 4,160V chillers. Although it’s not mandated, the facility chose to have the means for partial cooling of its hospital campus during a power outage. An added benefit is the ability to use the chillers to load the generators during testing, which assures exceeding the 30 percent load, thereby avoiding additional testing required by a hospital accreditation agency.
A Square D PowerLogic power monitoring system was designed to create hospital accreditation-compliant emergency power system test reports. The power monitors report back to a dedicated computer in the plant’s command room where a custom electrical one-line is used to view nearly any distribution point in the normal and emergency systems
Two pairs of Square D 4,160V:480V dry type transformers provide service from the 4,160V paralleling gear distribution to double ended 480V, 4,000A secondary unit-substations. One of these main-tie-main (M-T-M) switchboards serves the plant and the other 4,000A, M-T-M switchboard serves the Blue Tower’s main electrical room.
The Blue Tower’s new normal and emergency distribution switchboards enabled the team to design a complex system of feeders and duct banks that were arranged to feed each load in the obsolete “tunnel switchboard.” Replacement of the switchboard and its feeders was overdue in several ways. The switchboard had integral dry transformers with no physical means of replacement should they fail. Also the electrically operated circuit breakers were nearing the end of their lives and would frequently fail to reclose.
A complete blackout test was performed in keeping with NFPA 110 acceptance testing requirements. The four-hour test proved beneficial, revealing areas for improvement. As a result of the test, additional emergency lighting and power were added and the patient care staff used the opportunity to prepare for a real outage event.
Automatic transfer switches (ATS) furnished by ASCO Power Technologies were 480V, bypass isolation, open-transition type, ranging in size from 400A to 2,500A. The ATSs provide separation of critical, life safety and equipment EPSS loads. Although bypass isolation switches have a higher initial cost they were selected to allow contact maintenance on the switches without shutting down the essential loads served.
The utility services to the plant were reworked as well. Working with the local utility, design loop feeders controlled by S&C Co. loop switches were installed on the hospital campus to ensure reliable feeds to the central energy plant and the hospital.