Puget Sound Energy transmission line project

Central Pierce-Alderton 115 kV transmission reliability improvement project

Project overview

From 2011 to 2018, PSE worked to improve electric service reliability for approximately 24,000 customers in Sumner, Bonney Lake and Orting by installing 115kV transmission lines in central Pierce County.

An existing 38-mile transmission line had previously only tied together three substations in the area, lacking the redundancy needed to reliably serve customers and increasing the possibility of outages in the area.

To strengthen the system and improve electric service reliability for our customers, we constructed three new 115 kilovolt transmission lines from points along the existing transmission system to the Alderton substation in Puyallup. The lines will were 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: Constructed two 115 kV transmission lines along 3.2 miles of an existing regional utility corridor. The two parallel lines run from the Alderton substation to an interconnection point on an existing 115 kV line at Myers Rd E near Highway 410.

By constructing the new lines, we segmented the existing system into three smaller, more reliable systems that can back up each other in the event of an outage on one of the lines. This project added redundancy which limits the number of affected customers during an outage and eliminating electric capacity constraints on the existing system – ultimately keeping the lights on for our customers.

This work is related to our Pierce County 230 kV project, which constructed approximately eight miles of new 230 kV transmission line from the White River substation in Bonney Lake to the Alderton substation in Puyallup. The Pierce 230 kV project was completed in late 2017. 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.

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