Updated: Apr 20, 2021
Wildfires have burned millions of acres across the U.S. and around the world in recent years. Though wildfires have many causes, including lightning, campfires and carelessness, to name a few, those caused by faulted power lines are particularly devastating because they could have been avoided with the proper risk assessment and mitigation techniques in place.
While it is difficult to quantify the risk of wildfires being sparked by faulted power lines, vegetation management and fault detection and isolation are key factors in mitigating wildfire risk. But how can electric utilities assess the most efficient way to handle vegetation management and fault detection and isolation?
Prescient has created an innovative wildfire risk assessment tool to calculate exactly that. In this post, we’ll describe our methodology and show how it could be implemented by any electric utility to help prevent future wildfires.
The Importance of Wildfire Risk Assessment and Analysis
The Camp Fire of 2018 is an infamous example of a wildfire sparked by faulted power lines. This fire raced through the town of Paradise, CA, in under 4 hours, forcing thousands to evacuate and killing 85 people.
At least 18,800 structures, including 14,000 residences, were destroyed in the Camp Fire. Over 5,000 firefighters from multiple states were dispatched to respond to the fire, and 153,335 total acres were burned. Insurance claims for losses totaled around $8.4 billion. Because PG&E power lines were identified as the cause of the Camp Fire, the utility company was on the hook for most of the cost of these damages.
More recently, the Beachie Creek Fire, which burned nearly 200,000 acres in Oregon during September 2020, was caused by sparks from faulted power lines. In addition, the Witch Creek and Rice Canyon Fires of 2007 caused almost $2 billion in damages, and were sparked by faulted power lines.
Had a more in-depth wildfire risk assessment methodology been used to properly assess wildfire risk, these fires could have potentially been prevented. Let’s take a look at Prescient’s advanced methodology.
How Prescient’s Wildfire Risk Analysis Works: The Toaster Analogy
When considering wildfire risk analysis, a helpful analogy is to think of a slice of fresh bread in a toaster. If the bread toasts for 3 minutes, it’s perfectly toasted and ready to eat. But if the bread toasts for 8 minutes, it will begin to burn. And if left in a few minutes longer, the toaster, which only delivers 10 watts of energy per square inch, will completely burn your piece of bread.
The toast burning is a predictable occurrence; similarly, Prescient’s experts have developed a unique method that will reliably predict if dry vegetation is likely to ignite when a fault occurs. Once the likelihood of a fault causing a wildfire can be consistently predicted, strategic steps can be taken to mitigate the risk.
A simplified comparison of energy released during power system faults and toasting bread is illustrated in Table 1. Especially noteworthy is that more than 10 times as much energy is released in 100 milliseconds during a power system fault as is released in a bread toaster in 10 minutes. This rapid release of energy in the form of heat is why wildfires can be sparked so quickly by a power line fault.
Prescient uses its innovative methodology to calculate energy release in watt-seconds as a function of circuit voltage. Additionally, Prescient has developed a unique method of calculating energy deposition in watt-seconds on surfaces of combustible materials, usually nearby, dry vegetation.
Accounting for Combustible Material
Combustible material ignition is a function of energy release, energy deposition, and time. The more energy that is deposited on the combustible material, and the longer that energy is deposited on the combustible material, the more likely it is that the material ignites.
When maximum fault current is calculated and protective relay settings and characteristics are available, Prescient can predict whether nearby vegetation – damp or dry, thick or thin – will ignite before a fault is cleared.
In order to convert theoretical concepts into useful data, Prescient’s team has developed a proprietary method to display fault clearing time and dry vegetation ignition time as a function of transmission or distribution line miles. When dry vegetation is predicted to ignite in less time than it takes to clear a fault, the probable result will be a fire.
Our model is illustrated in Figure 1, where the time scale is logarithmic and the mileage scale is numeric. Dry vegetation is a concern from Mile 2 through Mile 4 because the fault clearing line (shown in black) is above the dry vegetation ignition line (shown in red). This means that dry vegetation will ignite more rapidly than the fault is cleared.
For example, at mile 3.5, dry vegetation ignites in 4 seconds while the fault clears in 20 seconds. If a fault would occur at this point on the line, and no steps were taken to mitigate the risk, the result would be a fire.
Numbers That Anyone Can Understand
Of course, Prescient’s complex model includes many factors. We include arc length, right of way (ROW) conditions, distance to nearby vegetation, line construction, ambient temperature, and many other variables in all our calculations. While the calculations are complex, the results are presented in graphs that are easily understood by government agencies, news media, and other non-technical audiences.
After calculating the risk of a fault causing nearby vegetation to ignite, which would likely lead to a wildfire, Prescient will recommend strategic modifications and enhancements to protective relay schemes to improve fault clearing time. We will also recommend changes to vegetation management plans to decrease the risk of nearby vegetation catching fire.
By integrating Prescient’s recommended wildfire mitigation techniques, electric utilities can eliminate the risk of faulted power lines causing wildfires.
Let’s Prevent Wildfires Together
The most important reason for conducting wildfire risk analysis is to prevent catastrophic fires from starting. By understanding the risk of fire during each wildfire season, strategic modifications and enhancements can be made - modifications and enhancements that can be implemented by any power company. We will discuss Prescient’s recommended wildfire risk mitigation strategies in a future blog post.