Client: Seattle City Light
Location: Washington State
This underground network distribution project involves significant upgrades to the electrical system in the north downtown Seattle area. The project is necessary to transfer existing load from the over-stressed Broad Street Substation as well as future loads from the Denny Triangle and South Lake Union areas to the new Denny Substation. The project’s related new network and distribution systems will ultimately help SCL serve high-load commercial and residential users alike including Amazon and Vulcan.
- Overall project management for 8 subconsultants
- Distribution network preliminary and detailed design
- Electrical design including vault diagrams, equipment tables, ampacity and pulling calculations
- Civil duct bank design
- Thermal analysis and ampacity studies
- Electrical specifications
- Cost estimates
- Overall project includes distribution network duct bank for 24 feeders, 4- 6 feeder subnets with over 3.5 miles of distribution
- Denny Network Phase 1: South Lake Union area, involves 13.8 kV network, 3 new duct banks, mainstem feeder cables, and 2 – 6 feeder subnet ultimate buildout
- Denny Network Phase 2: Denny Triangle area, involves 13.8 network, 2 new duct banks, mainstem feeder cables, and 2 – 6 feeder subnet ultimate buildout
- Denny Network Phase 3 (future): Denny Triangle area, involves 13.8 network and 2 duct banks, and mainstem feeder cables
Challenges and Highlights
- Highly urban environment. Both physical and electrical constraints exist within each of the three districts and physically separated phased areas. POWER’s design mitigated these tough logistics and chose optimal routes based on both the need for additional capacity and for existing utilities and roadway/traffic conditions.
- Feeder restrictions. POWER’s unique electrical design allowed each feeder subnet to handle loading exceeding N-1 conditions without exceeding normal cable and equipment load ratings.
- Engineering expertise. POWER and its associated subcontractors finished Phase 1 and 2 on time, on schedule, with zero issues.