How to mitigate risk and ensure reliability

BY SARA SANKOWICH, Unitil

For most North American electric utilities, vegetation management (VM) is a critical part of system maintenance. Utilities strive to maintain normal conditions and ensure the system can withstand normal weather events. Even on a fair day, a broken limb or downed tree can cause an outage. By implementing a successful vegetation management program, utilities can help ensure reliability and mitigate risk.

One successful approach to vegetation management incorporates four key components that occur simultaneously: cycle pruning, hazard tree mitigation, a mid-cycle review, and a forestry reliability assessment. This four-component program is appropriate for most electric utilities and can be implemented with either internal or external vegetation management resources.

CYCLE PRUNING
For any utility creating or improving a VM program, cycle pruning should be the primary focus. Cycle pruning is, essentially, preventative maintenance, and technicians and arborists should utilize best management practices and techniques as described in the American National Standards Institute (ANSI) A300: “Standards for Tree Care Maintenance Operations” and its Best Management Practices companion publications.

Cycle pruning refers to the period of time in which a utility’s vegetation management team will prune the lines within its territory. For utilities designing a new program, the first step is to determine a cycle length. To do so, a company must balance multiple factors, including clearance created at time of pruning, growth rates of predominant species, climate, risk to system performance, aesthetics, public acceptance of pruning, and cost to implement.