May 24, 2004

S&C Vista^® UDS Minimizes Outage Time for a Switchgear Retrofit.

Compact S&C Vista Underground Distribution Switchgear was the key to a successful switchgear retrofit project at a southern U.S. hospital. A flashover in a bay of their existing metal-enclosed switchgear lineup forced the hospital to operate on emergency generators for almost two days. The event convinced the administration of the need to replace the 25-year-old gear, which was located in the basement of their central plant. Space limitations were a problem, though. The cramped area would necessitate removal of the old equipment before new gear could be installed. But the hospital could not afford to run on emergency generation for the time it would take to complete the project.

The hospital was very satisfied with the performance of previously installed S&C Source-Transfer Vista UDS located in a different building, and asked S&C to offer a similar solution to replacing the gear in the central plant. After reviewing the application, S&C determined that the central plant had enough room to accommodate new Vista UDS units. The new gear could be installed without disturbing the existing switchgear, so the retrofit could take place in a series of steps.

Other difficulties had to be overcome. If the Vista UDS were floor-mounted, there wouldn’t be enough space on the bushing side of the gear to connect the cables. Wall-mounted Vista UDS was a possibility. But space would be needed behind the gear for training the cables. And special support frames meeting Seismic Zone 3 requirements would have to be furnished to support the gear.

Working with the local contractor and the hospital’s consulting engineer, S&C developed a four-step plan for installing new wall-mounted Vista UDS units during scheduled weekend outages. See the one-line diagram below.

First, a new Model 330 Source-Transfer Vista UDS was installed, with the existing switchgear remaining energized.

Next, a 24-hour power outage was scheduled. The emergency generators provided power during this outage. A three-bay portion of the existing gear was removed at this time and a Model 514 Manual Vista UDS unit was installed in the vacated area. This unit was connected to the Source-Transfer Vista UDS and to the affected feeder circuits. The new Vista gear was then energized and power restored to the remaining bays of the existing switchgear.

Two more bays of the existing switchgear were removed during a second 24-hour power outage. A Model 413 Manual Vista UDS unit was then installed and temporarily powered by piggybacking the load-side elbow connectors on the Source-Transfer Vista UDS. With this step, the entire load was transferred to the new switchgear.

The final scheduled outage entailed removal of the incoming sections of the existing gear and installation of a new metering bay. All circuits were then rearranged in their permanent configuration as shown in the single-line diagram.

The Vista UDS units are secured in their special support frames upside down, so that the bushing cable connections are at the top and the switch operators at the bottom. The frames are adjustable, and can be positioned 12 to 24 inches from the wall to facilitate cable training and 24 to 48 inches from the floor to facilitate switching operations. Elbow connections on the top of the metering bay are at the same elevation as the bushings on the Vista UDS units for easy cable training with a minimum of bends. The frames are anchored to both wall and floor to meet Seismic Zone 3 requirements.

S&C Vista UDS demonstrated itself to be the best choice for this retrofit project, where downtime needed to be minimized and space restrictions hampered the installation of conventional metal-enclosed switchgear.