Transmission and Distribution
City Light is currently conducting a SEPA evaluation of two alternative routes for the project's transmission line. The proposed transmission line will connect the proposed Denny Substation to the Massachusetts Substation located in the SODO area, approximately three miles to the southwest of the Denny Substation site. When installed, the transmission line will be operated at 115 kV with the capability to operate at 230 kV in the future as electrical demand increases.
The two alternatives currently under consideration through SEPA (both west of I-5) are:
- (Alternative TL1) - A route underground, primarily along the eastern edge of the downtown commercial core
- (Alternative TL2) - A route through the Downtown Seattle Transit Tunnel (sometimes referred to as the bus tunnel)
Both routes, as currently conceived, would transition from underground to overhead at their southern ends.
City Light continues to coordinate with King County and Sound Transit about placing the transmission line within the tunnel.
City Light will reach out to stakeholders along the Alternative TL1 route with meeting proposals to discuss potential construction impacts and issues of concern.
The transmission line is scheduled to be constructed between 2018 and late 2020. The existing Pine-Broad Street transmission line will be used to power the Denny Substation prior to completion of the new transmission line.
Seattle City Light has a policy of serving high load density areas using an underground network distribution system similar to Downtown, Belltown, the University District and portions of First Hill. The distribution work consists of installing up to 40 underground distribution feeders and associated underground duct bank systems, converting some existing customers to the new network service, and connecting new customers to the network. The distribution network will be installed within Denny Triangle and South Lake Union. The primary distribution areas to be built by this project are:
- Denny Triangle, in an area bound by Denny Way (to the north), I-5 (to the east), Olive Way (to the south), and Westlake Avenue (to the west).
- South Lake Union, an area bound by Republican Street (to the north), Pontius Avenue (to the east), Denny Way (to the south), and Terry Avenue (to the west).
The distribution network is scheduled to be constructed between 2014 and 2018. Additional lines will be constructed after 2018, as necessary.