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Puget Sound Energy transmission line project

Central Pierce-Alderton 115 kV transmission reliability improvement project


Spring 2015 project updates

  • Phase 1 of construction is now complete. Work began in May 2014 and we energized the new transmission line on Oct. 9, 2014. Thank you for your patience during construction!
  • Phase 2 easement acquisition is now complete.
  • Engineering and permitting of Phase 2 is underway and construction is on target to begin in the second half of 2016, with several pre-construction activities happening between now and then.

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Project overview

PSE is working to improve electric service reliability for approximately 24,000 customers in the Bonney Lake, Orting and central Pierce County areas. Currently, the local electric system is prone to power outages due to limited capacity and redundancy. With 17 outages in the past five years, it is one of the top five least reliable electric systems in PSE’s service territory.

The existing 38-mile transmission line ties together three major substations in the area. If there is an outage on the line, the system does not have the redundancy to continue reliably serving customers, increasing the possibility of outages for many customers in the area.

To strengthen the current system and improve electric service reliability for our customers, we plan to construct three new 115 kilovolt transmission lines from points along the existing transmission system to the Alderton substation in Puyallup. The lines will be constructed in two phases:

  • Phase 1: Constructed one 115 kV transmission line along four miles of an existing water main corridor. The line runs from an interconnection point on an existing 115 kV line approximately 1,000 feet west of our existing Rhodes Lake substation in Bonney Lake to the Alderton substation.
  • Phase 2: Construct two 115 kV transmission lines along 3.2 miles of an existing regional utility corridor. The two parallel lines will run from the Alderton substation to an interconnection point on an existing 115 kV line at Myers Rd E near Highway 410. See the project map for reference. 

By constructing the new lines, we are segmenting the existing system into three smaller, more reliable systems that can back each other up in the event of an outage on one of the lines. This will add redundancy to the overall transmission system, limit the number of affected customers during an outage, and eliminate electric capacity constraints on the existing system – ultimately keeping the lights on for our customers. We estimate that this project will allow us to reduce outage risk for all 24,000 customers by at least 50 percent.

This project is related to our Pierce County 230 kV project , which will construct approximately eight miles of new 230 kV transmission line from the White River substation in Bonney Lake to the Alderton substation in Puyallup. These projects work together to strengthen the overall electric grid and increase electric reliability for our customers in Sumner, Bonney Lake, Orting and central Pierce County.

What is a transmission line?

Transmission lines are key elements in the electrical distribution system. These 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.

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.