The benefits of having a looped transmission system on Bainbridge Island

In late May and early June, Bainbridge Island experienced two substation-level outages: the first at Winslow Substation and the second at Murden Cove Substation. In both instances, vegetation had fallen into the transmission line that serves the substation, taking out power. Because these substations are only served by one transmission line each (called a “single radial transmission line”), if that line is affected, then the substation and all customers served by the substation lose power until crews are able to make repairs. 

In addition, the island’s electric grid is in an unusual configuration while our crews are completing upgrades at Port Madison Substation. The two supply lines that bring power to Bainbridge Island across Agate Pass bypass the Port Madison Substation and continue on, one to Winslow Substation and one to Murden Cove Substation. Without the usual connection into Port Madison Substation, these lines have increased exposure and, as a result, an increased risk of an outage. (Note, for this reason, we schedule construction for our substations for after the typical storm season, which is when chances of an outage are higher). 

PSE plans to help address this issue with the new Murden Cove – Winslow 115 kV transmission line (see graphic above). We know, if this new line were in place, these two outages, and their impacts on Bainbridge Island customers, would have been prevented. Additionally, if this new line were in place, we wouldn’t have needed to put the island’s grid in a more vulnerable position to perform the work at Port Madison Substation in the first place. 

This new line will connect the Winslow and Murden Cove substations, creating a transmission loop. Each substation will be connected by two transmission lines. If one of the transmission lines goes out, the other transmission line can still feed the substation and provide power to customers while crews make repairs.

By investing in transmission infrastructure like the new Murden Cove – Winslow 115 kV transmission line, PSE is adding redundancy to the island’s grid, improving its resilience and reducing the impact of any single outage. Currently, we continue field work, engineering, real estate planning and permitting on the Murden Cove – Winslow 115 kV transmission line project. We plan to build the project in 2027-2028. Learn more at pse.com/bainbridgemw.