Faulted Power Lines: Wildfire Risk Assessment & Prevention

Wildfires have burned millions of acres across the U.S. and around the world in recent years. As the global climate continues to change, wildfire season has lengthened, from early spring to late fall in some regions. In fact, just last week much of my home state of Oregon was under a red flag warning by the National Weather Service, one of the earliest such warnings on record.

Wildfires have many causes: lightning, human inattentiveness to campfires, and fireworks. However, wildfires caused by faulted power lines are particularly devastating because they could have been avoided with the proper risk assessment and mitigation techniques in place. Devastating wildfires like the  Beachie Creek Fire in Oregon or the  Camp Fire in California have been sparked by faulted power lines, and led to multiple lives lost, hundreds of thousands of acres burned, and billions of dollars in damages.

What can electric utilities do to minimize the risk of their lines sparking deadly wildfires? The first step is developing a good understanding how power lines can cause wildfires – energy release, ignition time, and dry vegetation considerations. Then, a wildfire risk assessment should be performed.

Prescient has created a unique wildfire risk assessment methodology to help inform utilities about their wildfire risk for specific lines. This proprietary risk matrix reliably predicts if vegetation is likely to ignite when a fault occurs. It also provides a specific risk score, which allows utilities to understand the relative risk of wildfires being initiated by faulted power lines, and to weigh prudent updates based on cost and time.

Let’s take a closer look at the factors that increase the probability of a faulted power line sparking a wildfire, as well as some more details about Prescient’s wildfire risk assessment service. You can also join us for a free webinar on May 27 to learn more.

Wildfire Ignition Factors

When a fault occurs on electric power lines, electrical energy is converted to thermal energy in the form of a spark. In areas with combustible material near power lines, the spark can easily ignite materials like dry leaves, tree branches, and other trimmings. Once ignited, these burning materials can quickly lead to a wildfire.

Not all faults cause wildfires, but they are much more likely when there is a confluence of a few factors, including:

• Energy released at a fault location: The energy released by the spark influences whether nearby vegetation ignites. When a fault occurs, electrical energy is converted to thermal energy. The result of this conversion can be either an enormous, instantaneous energy release in the form of an explosion, or a smaller, long duration energy release, much like a slow-burning fire. Typically, energy release is dependent on distance from the substation.
• Fault duration: The duration of a fault is a function of protective relaying schemes. Faults on extra high voltage transmission lines are cleared in less than 100 milliseconds. Faults on medium voltage, neighborhood distribution lines will be cleared in more than 2 seconds. Low current faults can persist for tens of seconds.
• Nearby vegetation: The energy needed to ignite nearby combustible materials is determined by the material type, its moisture content, and its thickness. Dry, thin materials, such as leaves and twigs, are easily ignited. Thick, damp materials, such as tree trunks, are resistant to ignition. Additionally, moisture content due to climate and seasonal weather patterns impacts ignition time.
• Distance between an arcing fault and nearby vegetation: The distance between an arcing fault and dry vegetation depends on the cause of the fault and vegetation management. This distance often determines whether the fault will ignite a wildfire.

Each of these factors influence whether a wildfire will be ignited. When these factors occur simultaneously, a wildfire is all but guaranteed.

Wildfire Spreads Rapidly

After the initial spark from a faulted line, a wildfire can spread to a several thousand-acre blaze in a dangerously short amount of time. Wildfires typically move at about 6 mph through forested areas, and up to 14 mph in grasslands. Some move even faster; for example, at the height of its speed, the Camp Fire burned the length of 80 football fields, which is about 4.5 miles, in one minute.

A wet winter and spring, which lead to rapid growth of shrubs, trees, grasses, and undergrowth, create ideal conditions for the rapid development of wildfires once the dry season arrives. Following the rainy season, sustained hot and dry conditions throughout the summer often lead to drought, which dries out the growth from spring, creating ample fuel for wildfires.

High winds feed oxygen to the flames, and help spread embers several hundred feet in the air. These embers can cause fires to start in areas not directly adjacent to the initial starting point of the wildfire. Wind-spread embers help wildfires jump to homes and developed areas, across cleared areas, and even across natural barriers like rivers.

Wildfire season, the time in which ideal conditions for the rapid spread of wildfire are most prominent, spans early spring to late autumn, depending on the region. Climate change and changing weather patterns are creating longer wildfire seasons throughout the U.S.

Prescient’s Wildfire Risk Assessment Methodology

Prescient’s wildfire risk assessment service provides a comprehensive review and analysis of overhead power lines to determine their risk of igniting wildfires. We assess power lines in fire-prone areas using our unique risk assessment matrix, which considers protective relaying schemes, distance from substation, right of way (ROW) conditions, and more. Our observations are entered into our proprietary algorithm, which gives us a specific risk score.

Wildfires caused by faulted power lines are predictable and can be prevented. Known conditions that lead to the rapid spread of wildfire, such as wind speed, relative humidity, and temperature, can easily be observed. The unknown factor is exactly when a fault will occur. Prescient’s wildfire risk algorithm accounts for these and other factors, including residual moisture and fault clearing time, which are more difficult to observe, but vital when predicting the likelihood of power lines sparking wildfire.

After completing an assessment, findings are compiled into easy to view graphs and a report is prepared outlining prudent changes to reduce wildfire risk along power lines. Recommendations may include enhancements to power line construction, maintenance, and operation, as well as protective relaying schemes and design practices. Specific modifications can be selected using a variety of criteria, including time to implement, cost of implementation, percentage of risk reduction, and more.  Prescient’s recommendations will help electric utility companies to modernize to the lowest possible wildfire risk.

Power Line Enhancements to Reduce Wildfire Risk

One enhancement that is already in use in vegetation management. However, most utilities approach vegetation management as an all or nothing strategy. Utilities frequently remove hazard and danger trees, while leaving other nearby vegetation, including brush piles.

Instead, a more strategic approach to vegetation management could provide specific risk reduction in targeted areas. Prescient’s assessment provides utilities with a detailed report outlining the ignition time of dry materials compared to the specific fault clearing time of each utility’s power line. This knowledge helps electric utility companies determine where increased vegetation management would be most beneficial.

Additionally, during high to extreme wildfire danger, detecting and isolating faults rapidly is the key to preventing a faulted power line from sparking a wildfire. To do this, protective relays should be equipped with sensors to detect a variety of weather-related factors, including relative humidity, ambient temperature, wind speed, and more. These parameters can be used to calculate vegetation moisture content and ignition probability, which will optimize protective relay actuation settings.

Algorithms using the inputs from these sensors will optimize settings within microprocessor-based relays. Settings can be automatically changed either to optimize sensitivity (i.e., trip at 1 amp) or to optimize coordination (i.e., trip at 100 amps). This will allow the relay to rapidly actuate for low fault currents during high wildfire risk conditions. When low energy faults are rapidly isolated, the possibility of wildfire ignition is minimized. 

For example, during wet conditions, setpoints can be increased so that tap fuses open for faults before protective relays actuate. During extreme wildfire risk conditions, however, protective relays should be allowed to actuate before tap fuses open for faults.

Learn More with Prescient’s Upcoming Webinar

To learn more about our wildfire risk assessment methodology and recommended mitigation techniques, join us for a free webinar entitled Power Lines: Wildfire Risk Assessment & Prevention on May 27 at 11:00 a.m. PST.  Sign up today to guarantee your spot! Check out our wildfire blog series to learn more about Prescient’s innovative concepts for wildfire risk reduction, and contact us with questions.