With rising global temperatures and extended droughts, the duration of wildfire season continues to increase throughout the year, wreaking havoc across the western United States. A single spark around dry vegetation can lead to an inferno, destroying communities and the lives of those who live and work there.
Many utilities, particularly in western states, are taking precautionary measures to avoid sparking wildfires, performing preventive maintenance like vegetation management and updating old equipment to strategic operational practices such as Public Safety Power Shutoff (PSPS) de-energization programs. However, with worsening weather conditions, utilities are continually challenged to limit their role as the source of wildfires.
Enhanced System Protection
Enhanced system protection reduces the likelihood of ignition through technological advancements such as fast fault clearing schemes, downed conductor detection, and communications-assisted system automation.
Live, downed conductors create high-impedance faults (HIF), which generate very little fault current (typically less than 100 A). These high-impedance faults present a unique challenge for conventional distribution system protection, which consists primarily of overcurrent protection (e.g., relays, recloser controls, and fuses) to detect and clear faults. The application of specialized filtering and algorithms available in microprocessor-based relays and recloser controls can be used to detect the arcing signature associated with high-impedance faults. This HIF detection can be combined with data from advanced metering infrastructure (AMI), line sensors, and downstream intelligent electronic devices (IEDs) into an integrated downed conductor detection system that can quickly identify and locate downed conductors on power distribution systems.
To prevent momentary faults on overhead conductors, electric utilities typically use automatic reclosing to improve system reliability to avoid extended outages. However, in high-fire-risk areas, automatic reclosing can increase the risk of ignition from repeated arcing. Due to weather conditions, utilities frequently disable reclosing on feeders during wildfire season. Selecting a recloser that provides this type of flexibility allows utilities to easily adapt protection and reclosing schemes to meet the dynamic challenges associated with preventing wildfires.
Due to the dynamic nature of weather, environmental, and other factors that impact the risk of wildfires, protection schemes must also adjust in real time. Integrating a recloser into a supervisory control and data acquisition (SCADA) system allows system operators to quickly disable reclosing, sectionalize the high-risk fire areas, and adjust other settings manually or automatically based on changing conditions.
Utilities have several ways to collect data for fire risk models to provide system operators with the information they need to make decisions to disable reclosing or even shut off power during extreme conditions. Adjustments to reclosing and protection schemes can be differentiated by circuit and location to adjust to existing and forecasted conditions — for example, remotely disabling reclosing or remotely opening the recloser to sectionalize the perimeter of a high-fire-risk zone when an existing or anticipated fire risk is elevated.
In cases where part of a power line passes through a high-fire-risk area, the reliability of the entire feeder can be affected. By installing fault transmitters and receiver systems at laterals or the boundaries, utilities can automatically disable reclosers in high-fire-risk areas, allowing them to focus on public safety while maintaining system reliability in areas not at risk.
System hardening strategies help create a more robust, fire-resistant grid by upgrading aging infrastructure to mitigate and eliminate ignitions caused by sparks.
The exposed energized conductors prevalent throughout the overhead grid can produce sparks or flashovers that can ignite wildfires. From system faults to wildlife violating electrical clearances, many different ignition sources need to be taken into consideration.
Reclosers can provide flexibility with independent pole designs in which each phase has its own fault interrupting mechanism. This enables customizable, extended phase spacing in frame designs that can mitigate phase-to-phase external flashovers. Traditional designs use a 15-inch phase-to-phase spacing, while newer designs extend this to 24, 30, or more inches. This extended spacing helps prevent flashover ignitions caused by vegetation, overvoltage, and wildlife contact.
In an overvoltage event that results in a system-induced flashover, a module with a dead-tank design can conduct the fault to the ground potential of the module. This reduces the probability of the flashover propagating from phase to phase and resulting in a larger flashover. This also reduces the need for external sensors, which in turn reduces exposed live energy sources. A dead-tank design can also mitigate wildlife-induced flashovers by reducing live energy sources.
Creepage distance is the shortest allowable distance between conductive potentials, considering the path along the sheds of the insulator. Strike distance, or flashover distance, is the shortest straight-line path between potentials. Adding more safety margin to strike and creepage distances reduces the probability of flashovers that can ignite wildfires. Reclosers that meet IEEE 386 standard are designed for separable insulated connector systems, making the insulators removable and field upgradable.
In addition to silicone insulators, industry standard rubber elbow connectors designed with IEEE 386 interfaces can also be connected to applicable recloser interfaces. These elbow connectors can combine with dead tank reclosers to significantly reduce the number of exposed live connections on the overhead line that can be a flashover source. Elbow-connected reclosers have been applied to protect transformers and riser pole overhead-to-underground transitions, and to mitigate wildlife-induced flashovers.
To protect electrical equipment from wildlife, it is extremely important to have proper safeguards in place to minimize exposure to energy potentials and prevent flashovers caused by animal contact. Flame-retardant wildlife guard materials prevent flashover events from igniting the guards, thus preventing flaming material from dripping on the ground below. For an added layer of protection, wildlife guards can be custom-fitted with certain recloser insulators that comply with IEEE 1656-2010 and UL 94 V-0 flammability ratings.
Working with the Best to Achieve Fire Mitigation
As mentioned before, there are several strategies for utilities to achieve wildfire mitigation, including partnering with electrical distribution experts who can help determine the best fire mitigation strategies that can be rapidly implemented across your electrical infrastructure, providing flexible solutions to meet your unique needs in eliminating wildfire risk, addressing public safety concerns, and satisfying regulatory mandates.
Fire mitigation strategies based on enhancing system protection and system hardening are critical in laying the foundation for a fire-resistant grid. With changing environmental conditions causing increased threats to public safety and infrastructure, advanced technology can be leveraged to mitigate grid-induced ignitions. The distribution protection strategies and solutions mentioned present technologies available today for achieving quick progress toward the fire-resistant grid of tomorrow. UP
The Authors: Nick Nakamura is product manager for sensors at G&W Electric Co. He is involved in several professional organizations including the IEEE Switchgear Committee and is an IEEE PES member.
Anthony Rahiminejad is lead product sales manager at Schweitzer Engineering Laboratories Inc. (SEL) in the distribution controls and sensors group. He is a registered professional engineer in the state of North Carolina.