Seattle City Light Denny Substation

Seattle, WA

Seattle City Light




Key Sustainable Elements Include:
Site Contamination Cleanup
Increased Soil Depth at Plantings
Bioretention Planter
Drought-Tolerant Plants
High-Efficiency Sprinkler Nozzles
Weather Sensors
Solar Technology Panels
Heat Recovery System
Water Feature
Sunlight Access
Educational Graphics
Energy Metering

Services/Project Type
Structural Engineering
Civil Engineering

KPFF is providing civil and structural design for Seattle City Light’s first major substation construction in over 30 years. The substation need is driven by power demands of development within South Lake Union and the energization schedule is critical to support existing and proposed development. Similar to the University of Washington’s West Campus Utility Plant, the substation is located at the gateway to its neighborhood and requires significant attention to architectural character and integration. KPFF’s work involves both design of the substation as well as four miles of medium voltage distribution duct banks within areas of congested urban infrastructure.

The design includes over 44,000 square feet of open space, on-site solar power and other sustainability features. Other community benefits include places for gathering, an off-leash dog park, public open space along Minor Avenue N and John Street, an event zone, alley improvements, and a community space for events, meetings and lectures.

The substation will be served from an existing 115 kV pipe cable transmission line that crosses the site. This cable is oil-cooled, under pressure and operates with limited opportunities for outages. Connection and re-routing of this line requires freezing of the line to limit loss of oil and several large splice vaults. For these reasons each outage and connection is estimated to exceed $1,000,000 in cost. Initial substation layouts required multiple outages and relocations. To limit the costs of connections and relocations, KPFF and the design team re-envisioned the substation layout and associated infrastructure to allow the line to stay intact throughout construction of the new substation. This required the development of a temporary support and protection system to elevate the line 10 feet above substation construction activities. These design actions saved the project several millions of dollars of unnecessary pipe cable relocation costs as well as the schedule constraints of multiple outages.

Click here for a video project overview.