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Puget Sound Energy substation project

Mount Si substation, switching station and transmission lines

Winter 2012-13 project completion
  • The substation site was annexed into the City of Snoqualmie in late 2010
  • Puget Sound Energy completed the permitting phase in summer 2011
  • Substation site and civil work, as well as electrical feeder work, was substantially completed in 2011
  • Substation electrical work and transmission line construction started in June 2012 and was completed in fall 2012 
  • The substation was completed and in service in winter 2012
Project overview

To meet current and future demand for power and maintain electrical system reliability, PSE built a new distribution substation in the Snoqualmie Ridge area. Previously, the distribution circuits serving Snoqualmie Ridge were nearing capacity during winter months, and future growth in the area was expected to increase significantly.

We constructed a new distribution substation, located near the intersection of Southeast Douglas Street and 356th Avenue Southeast in Snoqualmie, to add capacity and accommodate growth. The substation includes one 25 megavolt ampere transformer, with space to add a second 25 MVA transformer, allowing PSE to double the capacity in the future without changing the substation footprint.

The project also included the construction of transmission switching facilities, where three 115 kilovolt transmission lines will converge, providing redundancy for the new substation and greater operational flexibility and efficiency in delivering power to our customers. In the future, the plans for this utility site include additional transmission facilities to meet projected local and regional electric needs.

What is a substation?

Substations are critical links in the electricity distribution system, containing utility circuit protection, voltage regulation, and equipment that steps down higher voltage to lower voltage. Before reaching homes and businesses, power is routed through our transmission system to a substation where it is changed to a lower voltage that can be utilized by customers.

Download full-sized map

Project map (311 KB PDF)

What is a switching station?

A switching station is a transmission substation where the utility can switch or reroute power flow from one line or path to another to allow the power to be isolated to clear a fault (e.g., a fallen tree in the wires) or to take the power line out of service for maintenance. It also may act as a point of interconnection between two different transmission operators (e.g., Bonneville Power Administration and PSE). Unlike a substation with a transformer service neighborhood circuitry, switching stations do not step power up or down; they integrate power from one or more transmission sources on the regional and local grid to serve neighborhood substations.

What is a transmission line?

Transmission lines are key elements in the electrical distribution system. The lines safely transport high voltage electricity from power generation sources like dams and wind generating facilities to substations in local communities. Transmission normally takes place at voltages of 55 kV and higher.

Download the information

Construction notice, June 2012
News release, July 25, 2011
Construction notice, July 2011
Project map
Annexation presentation to Snoqualmie City Council, May 24, 2010 (1 MB PDF)
Annexation presentation to City of Snoqualmie Planning Commission, March 1, 2010 (2 MB PDF)