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March 6, 2018

It's not just a facade: Huge angled walls screen new $208M Denny Substation

Journal Construction Editor

Photos by Gray Media Productions [enlarge]
This double-cantilever screen wall is what people see from the street. Crews will energize the station in April, and the facade should be finished in May.

From the street, the new $208 million Denny Substation is starting to not look like a substation.

That's a good thing. Seattle City Light wants to hide the electrical components from passersby within a “picture frame” of walls surrounding the equipment. The station is bounded by Denny Way, John Street and Minor Avenue North.

The angled facade — a double-cantilever screen wall — is being finished with a combination of metal and glass panels by The Walsh Group. Behind the facade are several buildings and three 62.5-ton transformers that were installed last year.

Walsh senior project manager Michael Sheeran said glazing is along the bottom of the south and west walls, and then inverts to the top on the north and east walls. Metal panels make up the rest of the walls.

Sheeran said the facade should be finished in May.

Metal panels are enameled so that graffiti is easier to remove. Glass panels have stainless steel trim.

The substation will also have several public amenities, such as an attached elevated walkway with decorative panels, off-leash dog park, public meeting spaces and art.

Sheeran said crews have pretested the electrical equipment and will energize the station on April 23. Then the station will go though a month or two of commissioning.

City Light anticipates the substation will be finished in the third quarter of this year. It will connect to the Denny Network, a new underground electrical distribution system, after that system is finished in October.

Related street and alley improvements will be finished in June.

Sheeran said one of the biggest challenges has been right of way coordination in the street because so much other construction is going on in the area.

The station will supply north downtown and the growing areas of South Lake Union, Cascade, Denny Triangle, Uptown, Belltown and First Hill, as well as the regional transmission grid. It is City Light's first new substation in 30 years.

Denny Network will serve South Lake Union and Denny Triangle, and will cost another $17 million. Shimmick Construction Co. is doing the civil work for the network and City Light crews are in charge of the electrical work.

An existing underground transmission line will power Denny Substation until a new transmission line connecting to an existing substation in the Sodo neighborhood goes into service.

Construction has been deferred until 2020-2021. Design for that work could restart in late 2019.

Behind the facade are several buildings and three 62.5-ton transformers.

Initial studies for the new transmission line showed three potential paths it could take to link the existing Massachusetts Substation in Sodo to Denny Substation. One path leaves Massachusetts Substation and travels east to Sixth Avenue South in an overhead or underground configuration. It would then travel underground along Fifth and Sixth avenues, and several blocks of Stewart Street before turning at Yale Avenue and connecting to Denny Substation.

A second path under consideration would put the line inside the bus tunnel, and exit near Ninth Avenue and then Stewart/Yale to Denny Substation. The third path is similar to the first proposal, but it would go east of Interstate 5 for most of the route.

City Light said it has not picked a preferred route.

Here's the rest of the substation team: NBBJ, architect; Power Engineers, electrical design; and KPFF Consulting Engineers, structural and civil engineer. Valley Electric, W.A. Chester and Transcon are key subcontractors. ABB and Mitsubishi are major electrical equipment suppliers and installers.

Benjamin Minnick can be reached by email or by phone at (206) 622-8272.

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