Rare view of Metaline Falls, on the Pend Oreille River., Photographed by Peter Clarke
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Denny Substation Project
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City Light is evaluating three alternative routes for a new transmission line to connect the proposed Denny Substation to the existing Massachusetts Substation located in the SODO area. The Denny Substation map shows all of these project components and locations.

When installed, the transmission line will be operated at 115 kilovolts(kV) with the capability to operate at 230 kV in the future as electrical demand increases and more areas of North Downtown Seattle are switched to a network distribution system.

The three transmission alternatives currently under consideration through the SEPA process are:
  • Alternative TL1 - A route 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)
  • Alternative TL3 - A route along the east side of Interstate-5 (I-5)
All three alternatives - as currently conceived - transition from underground to overhead structures at the southern end before entering the Massachusetts Substation.

Construction of the transmission line is scheduled to start in 2018 and be complete in late 2020. An existing transmission line (the Pine-Broad Substation transmission line) will be used to power the proposed new Denny Substation prior to completion of the new transmission line in 2020.

Distribution Network

A new underground 13kV network power distribution system will be built in the South Lake Union Urban Center and additional 13kV network power distribution capacity will be constructed in the Denny Triangle area of the Downtown Business District. These improvements will provide the higher level of reliability and electrical load density needed by our major medical centers, bio-tech research facilities, and high tech industries, and by current and future manufacturing and innovative entrepreneurial industries.

The map below indicates the proposed routes of the underground network distribution system installation. These routes are preliminary and may be revised based on further review. Network construction is anticipated to begin during the second quarter of 2015.

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