August 17, 2017
Industrial and commercial power systems everywhere are dependent on the reliable performance and durability of their electric power distribution transformers. Yet, while many high-quality transformers may operate flawlessly for years and even decades, all are susceptible to a variety of failures – particularly as they age.
The risk of outages, whether from mechanical, electrical or thermal stresses, is a critical concern for many facilities since transformer failures may cause catastrophic consequences by bringing production and other business operations to a halt.
Another issue for some is the nearing obsolescence of their present transformer design. This occurs particularly with the liquid-filled transformers, such as the Vaportran® product line, which was introduced in the 1970s. All liquid-filled transformers use a dielectric fluid in their cooling systems, ranging from mineral oil to refrigerants such as Freon and even dry cleaning fluids.
Because Freon and conventional cleaning fluids have been largely banned for environmental purposes (although some alternatives are still available), many power system facilities — particularly those indoors — have replaced their liquid-filled transformers with a dry-type model. These dry-type transformers offer design and operational advantages, including high efficiency, cost savings, and eliminating the need to deal with leaks that occur with liquid-filled units.
“Many users with indoor power systems are converting from liquid-filled transformers to dry-type units for a number of reasons, including the avoidance of having to deal with hazardous materials such as Freon and other chemicals,” says Alan Ober, vice president of Engineering and Manufacturing for Electric Service Company (ELSCO).
Founded in 1912 by former Westinghouse engineers, ELSCO specializes in providing quality new, repaired and rebuilt transformers ratings range from 500 through 3750 kVA in 2.5, 5 and 15kV primary voltages—including both liquid-filled and dry-type models—from their Cincinnati, OH manufacturing plant.
“Also, replacement of older or outdated transformers often requires a certain amount of customization to fit the space available, especially when replacing transformers that have a smaller footprint, such as Vaportran units,” Ober adds. “Tailoring the new transformer to fit the existing space not only facilitates successful installation, but also assures that the new transformer will integrate directly with existing switchgear.”
A healthy replacement in Boston
A good example of such a customization occurred in 2016 at the Union Hospital-North Shore Medical Center north of Boston, MA. When power systems management became convinced that the facility’s Vaportran transformer had reached the end of its service life, they contacted Thompson Consultants, Inc. (TCI) to have its engineering department analyze the situation and recommend a solution.
Headquartered in Marion MA, TCI is a 43-year-old mechanical, electrical, plumbing and fire protection (MEP/FP) consulting engineering firm that specializes in the design of healthcare, life sciences and central plant projects.
With over 30 years experience in power systems engineering, TCI’s David Martell, PE, was given responsibility for developing a plan for the replacement.
“The biggest obstacle we had to overcome when preparing to replace the transformer was being able to find a replacement transformer that would fit into the confines of the site while minimizing the outage of the primary power supply,” Martell explains. “It was also important that the new transformer would align precisely with the existing high- and low-voltage switchgear, which would allow us to reuse that equipment and save substantially on costs.”
To begin the project, Martell researched different transformer manufacturers, including those that made custom transformers. He then discussed project characteristics, limitations, and goals with supplier candidates, narrowing the choice of transformer manufacturers in the process.
“We realized that only one or two manufacturers could deal with the physical size requirements of the equipment,” Martell says. “The short turnaround time for design and fabrication was especially important because the existing transformer was no longer operating according to the original specifications of the equipment, and so there was concern that it could fail at any time.”
TCI selected ELSCO, who was able to deliver a replacement unit within a relatively tight time frame, and was highly involved in producing exacting dimensional and technical specifications for the new transformer.
“The replacement transformer is a dry, forced air model that was custom designed and fabricated to fit precisely within the old transformer’s space, Martell says. “ELSCO made modifications on the secondary side to marry up to the existing bussing, including a new enclosure to eliminate unwanted openings into the switchgear.”
The new, dry-type transformer is designed to meet and exceed all the NEMA, ANSI, and IEEE standards as well as the efficiency standards for Energy Star compliance, an ELSCO standard that the supplier says saves on installation and energy costs.
Martell’s team also included a contractor who was responsible for removing the old transformer (via subcontractors) as well as installing and testing the new equipment.
A successful transplant
Removal of the old Vaportran transformer and installation of the new unit involved some unique complexities and skills that could be difficult to manage. TCI selected Power Line Contractors, a Wilmington MA-based utility construction specialist to handle those tasks.
“The original equipment, the Vaportran transformer, was sandwiched between a 15-KV switch and the 480-Volt gear on the other side,” explains Brendan Regan, Power Line Contractors Vice President of Operations. “Because the conduits were already in the slab relocating the switchgear was not a realistic option. That meant we had to sever the old transformer, which could not be removed intact because of clearance problems.”
Regan explains that the contractors had to cut off the radiators on top of the unit, remove and dispose of the Freon, and get the equipment out of the power room quickly enough that the outage would last only a few hours.”
The ultimate challenge was would the ELSCO replacement transformer fit into the space vacated by the Vaportran unit so that all the connections align precisely.
“The new transformer had to meet UL, IEEE standards and have all of the required clearances,” Regan explains. “Accomplishing all of that correctly is a substantial challenge. But the new transformer’s custom buswork lined up exactly with the existing gear, so we were able to accomplish the entire replacement process overnight. That was quite a relief to the hospital’s power system managers.”
More recently TCI and Power Line Contractors installed dry-type ELSCO transformer at another hospital in the Greater Boston area. Not only did the installation process run smoothly, but because there were no complications in removing the old unit, the entire installation and energizing process was completed in just two-and-one-half hours.
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