In the aftermath of a wind storm that interrupted service on more than 40% of Puget Sound Energy’s transmission system, the regulator ordered an investigation to evaluate options for hardening the electric system. The initial phase of the study quantified the extent of tree exposure along the transmission system and examined the correlation between various field measurable variables and tree-caused outage frequency.

This phase of the work correlated 10 years of wind data with 10 years of outage data. Tree failure rates were calculated and used to model tree-caused outage expectations based on wind speed. Models were developed to assess the outage impact of interventions that reduce the transmission system exposure to trees.....(Read more...)