The wisdom and inevitability of public safety power shutoffs – a utility vegetation management perspective

by Akan Ismaili

A new utility practice is routinely being utilized in California and it may soon become a wide-spread tool used by utilities in other fire prone states and provinces. The intentional pre-event de-energization of power, or Public Safety Power Shutoff (PSPS), has been successfully used to prevent catastrophic wildland fires involving utility infrastructure.

Let’s begin with a brief look at how utilities have customarily responded to extreme weather events. Utilities across North America have traditionally responded to imminent severe weather events by rallying and pre-staging resources in order to rebuild the electric system once it inevitably fails. When a hurricane, blizzard, tornado or derecho hits, there will be trees down, broken poles, dangling wires and inevitable power outages. The mechanics of these outages are quite simple to both visualize and understand. For example, when a tree is knocked into a powerline during driving winds and rain, there will likely be a bright flash followed by blown cut-outs and a loss of power to adjacent customers. Depending on the scope and size of the weather event, the utility can experience localized outages or large-scale impacts. In the latter case it can take days or weeks to re-energize every customer. In severe cases, such as Puerto Rico, power can be out for months or longer.

While no one likes the thought of being out of power for extended periods of time, there is a certain degree of acceptance given the palpable events that led up to the outage. “Just go outside and look at the tangle of trees and powerlines left in the aftermath of that hurricane.” Thankfully, most people generally understand a force majeure or act of God event when it happens. While generally explicable, extended outage have also resulted in calls for undergrounding, more tree clearing, and regulatory scrutiny of utility practices in maintenance and storm preparation.   

‘Red Flag’ events

As it turns out, the same mechanics of a force majeure weather event have been the cause of many of California’s most damaging wildland fires in recent years. These fires were also the result of anomalous weather conditions, namely “Red Flag” events. For those unfamiliar with the term, a Red Flag event is a weather episode characterized by high winds, high temperatures, and low humidity. Read that to simply mean a hot and windy day where all of the adjacent vegetation is bone dry and flammable.

With those particular weather conditions present, any flame or ignition source can easily lead to an uncontrollable wildfire.  The main difference between a Red Flag event and a hurricane or other typical weather event is, there is no rain or snow to extinguish the “flash” when a tree or object hits a powerline. Unlike wet or cold events, a spark from a downed powerline during Red Flag conditions typically results in a massive, rapidly moving conflagration.

In the aftermath of recent fires seasons in California, lawmakers, regulators and utilities have had to tackle the very difficult question of how to prevent utility related wildfires during Red Flag events.  Based on California Public Utility Commission (CPUC) analysis, trees or parts of trees falling into overhead facilities during Red Flag events represented the single largest cause of fires related to utility infrastructure. It is not growth “into” lines, but rather trees or portions of trees located outside of normal clearing limits that have failed during high winds and caused the initiating spark.

This problem is not easily addressed for numerous reasons. To begin, we do not have the tools or expertise to identify each and every tree that can break apart during a high wind event. Many of the trees that have been involved with these past fires had no pre-identifiable signs of imminent failure. In other words, you could have performed an ANSI A300 inspection just prior to the fire and not been able to identify the pending threat. Add to that the incalculable number of trees that could conceivably conflict with power lines. To get a sense of the enormity of that threat, take notice of how many trees near your own power lines are tall enough to hit the lines if they were to fall over during a high wind event.

Short of undergrounding all lines, or removing every tree tall enough to hit the facilities during a wind event, the most timely and reasonable approach to prevent any sparks is to “de-energize” the lines when a Red Flag event is expected. No energy flowing through the lines when hit by a tree, means no sparks and no subsequent massive fire. This has become a routine mitigating approach to fire prevention in California and all major utilities have used, or have plans to use, a PSPS event in the future.

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As should be expected, there is a huge difference between responding to weather related power outages “after” they occur, compared to “intentionally” shutting down power in anticipation of outages (and fires). A sampling of the related issues include having to address the questions of, how can you accurately predict exactly where the event is going to occur, and how can you limit the number of customers impacted? What about customers who have critical special needs, and how do you notify everyone of a pending power shut-off? What do you do about damage and claims related to a utility intentionally cutting off power?

These, and many more questions, have been the topics of numerous regulatory proceedings in the state and answers to all of the questions are still pending and the subject of debate. What we do know is this: it only takes one tree to hit an energized line and cause a devasting fire which can, and has, consumed both property and lives in the state. That fact has led to a societal zero tolerance for allowing the possibility of it happening again. The expectation in the state has been to do whatever is necessary to prevent another tragedy.

Utilities are the new “weather apps”

There are some related issues which are noteworthy for other utilities in fire prone areas. As it turns out, society’s existing weather prediction capabilities (state, federal and local) were found to be inadequate to predict Red Flag conditions at a granular enough level to help utilities identify and isolate potential damage and determine which areas should be de-energized. Rather than wait for the society to come up with better weather prediction capabilities, the utilities in California began to develop their own systems. As a result of the fires, utilities have invested hundreds of millions of dollars in weather stations and improved sensor and camera coverage of fire prone areas. These new data sources, coupled with improved A.I. and machine learning capabilities, have started to help utilities better manage the need for, and application of, PSPS events.

More stringent regulations

Another noteworthy impact can be seen in changes to UVM regulatory requirements, and oversight of these important activities. Interestingly, California has had the toughest mandatory “tree to power line” clearance requirements in North America for both transmission and distribution lines since the 1990’s. Contrary to most other states and provinces, it is almost impossible to find trees growing “into” high-voltage distribution lines in the state. Accordingly and as previously mentioned, this issue of fire is generally related to trees or portions of trees failing from “outside” of normal clearing limits. As a result of the recent fire seasons, regulators in the state have increased clearance requirements, developed active and full-time oversight programs, and made fire mitigation a principal objective of all utility companies in the state.

So how can PSPS events and changes to public and regulatory scrutiny of UVM activities impact other North American utilities? Consider the California model as a harbinger of things to come. If your utility is in a fire prone part of the continent and/or, if you have ever had a red flag warning in your service territory, you are likely going to learn about PSPS events in the very near future. Hopefully the lessons learned from California will not require, or be prefaced by, massive and costly conflagrations in your own service territories.   

About the Author:

Akan Ismaili is CEO of AERI, a Utility Vegetation Management service provider headquartered in California. A former telecommunications entrepreneur and executive in Europe, Akan has also served as the Republic of Kosovo’s Ambassador to both the United States and Canada.

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