What causes power outages on Bainbridge Island?

The most common cause of power outages in the Pacific Northwest, including Bainbridge Island, is tree-related damage. Outages can be caused by branches coming in contact with power lines as well trees falling through lines.  

Bainbridge Island is also especially vulnerable to outages since two of the three substations on the Island have only one source of power – one transmission line. It is best practice to feed a substation with two lines - or “loop” the substation. When substations are looped, they provide a redundant source of electricity for each other, therefore reducing the duration and frequency of outages. 

Transmission outages affect the largest number of customers.

In this example, one local 115 kV transmission line serves 4,000 customers.

If the transmission line serving the customers experiences a fault, the power does not reach the substation and all 4,000 customers served by the substation lose power.

Distribution outages affect fewer customers, but are more frequent.

In this next example, the local 115 kV transmission line connects to a substation, which delivers the power to four distribution circuits of 1,000 customers each.

If one of the distribution lines experiences a fault near the substation, all 1,000 customers served by the circuit lose power. The other three circuits do not lose power.

In this example, a distribution circuit serves 1,000 customers. Lateral lines from the circuit serve 50 customers each. 

If a lateral line experiences a fault, all customers downstream lose power. 

If the lateral line experiences a fault but can loop back with the circuit, PSE can close the looped lateral and reduce the outage time to all 50 customers. Power is restored to customers on the unlooped line once the fault is repaired.