Critical Xcel Energy Unit Installed and Energized in Downtown Minneapolis
December 12, 2011 – A number of examples exist in our business that clearly illustrate why we must meet our customers’ delivery dates. One such project involved a unique water-cooled transformer being built at the Wisconsin facility for Xcel Energy to replace a failed unit underneath Fifth Street in busy downtown Minneapolis. Due to the extremely tight time line Xcel Energy scheduled for its employees to install the unit in order to minimize the disruption to their customers’ daily routines, we had no room for delays in production, testing or delivery. As promised, the unit left the Wisconsin facility en route to its staging location at the downtown Elliot Park Substation on June 14th for a July 8, 9,10 installation, which also occurred as planned. Around 9:30 AM on September 14th, the project that began unexpectedly Halloween weekend of 2010, wrapped up when Xcel Energy personnel energized the Fifth Street transformer with 25kW of load. Now that you’ve heard the successful ending, it’s time to tell how the story began.
“I attended the Minnesota Power Systems Conference in Minneapolis the Monday after Halloween. We were hearing snippets from Xcel Energy personnel that they had a large failure over the weekend in a vault located under 5th Street downtown,” commented territory general manager, Preston Wietholter. “It turns out the vault held four water-cooled transformers. Three were built in 1965 and one in 1986, and the newest of the four was the one that failed.” The substation was designed to operate at N minus 2, meaning it could meet load demands with up to two transformers off-line at any one time. With one of the transformers already off-line for maintenance when the 1986 unit ceased to operate, Xcel Energy knew they needed to replace the failed transformer. Complicating access to the vault was a light rail line with a catenary (cable) system that ran parallel to the underground vault. This light rail line was installed years after the vault was opened for installation of the fourth transformer.
By late 2010, Xcel Energy was looking for a partner to work closely with them on this high profile project. At the same time, the utility company was engaged in discussions with city and state authorities to determine a project window in which they could extract the failed transformer and lower in a new one. The criticality of the light rail line for commuters and Minnesota Twins’ fans limited the ideal time frame to between a Friday night and an early Sunday morning when the baseball team was on the road. Sections of the light rail line and cable system would need to be removed, the transformer installed and then the light rail line placed back in service, all on a truncated time table: the last time Xcel Energy accessed the vault to install a transformer, they had two weeks; this time, they only had two days. Xcel Energy chose SPX Waukesha because of our willingness to work through the design with them and our proximity to the end destination—delivery to meet Xcel Energy’s project window was too critical to risk long distance freight.
From a technical standpoint, the core and coil assembly of this 84 MVA 119–13.8kV unit were standard. The cooling system, on the other hand, was something SPX Waukesha had not seen for quite some time. With this unit located in an underground vault,typical cooling—with radiators and fans—was not a viable option. Instead, the transformer was designed with two water coolers which allowed for a smaller footprint without compromising cooling capacity. Additionally, this unit prompted us to add permanent water piping to the south test floor so we could perform heat run tests using the water coolers on this transformer as well as test future transformers similarly designed.
Upon successfully passing the required tests in mid-June, a large truck pulled into the Wisconsin facility’s loading bay to pick up the unit which was delivered first to its staging location and then to the job site. After the successful weekend installation in July, Xcel Energy personnel worked diligently to get the unit operable. Getting the transformer assembled, tested and ready for energization and service was difficult due to limited space inside the vault. The process essentially became a serial operation — dress it, connect it, wire the control cabinet, test it, connect cooling water, reconnect fire deluge system, etc. all the way through until the transformer was ready to be energized.
VIDEO: View a time-lapse YouTube video of the transformer installation.
Overall, it took a team effort from many people at SPX Waukesha to help deliver this critical unit to Xcel Energy within their tight time frame. “I want to pass along the customer’s many thanks to everyone who pitched in to make this a success,” said Preston. “Xcel Energy was in Waukesha on September 13th for an Alliance meeting, and they expressed their gratitude and pleasure with the process and the transformer.”
Now, THAT’S a true Waukesha Experience!