DOWNLOAD PDF SCE needed a wildfire hardening solution for poles to support its heavier covered conductor. By Clinton Char and Brian O’Keefe, Southern California Edison, and Galen Fecht, RS Technologies Inc. A recent study by the journal Nature predicts an increase in the length of the California fire season from 36 days per year up to 58 days or 71 days, depending on moderate and high emission scenarios, respectively. An extended fire season means the threat of fire will start earlier in the spring, when historically there has been enough moisture to reduce fire threats, and extend later into the fall, which is particularly challenging considering the problematic combination of strengthening regional Santa Ana winds, which are associated with the lowest relative humidity of the year in Southern California, and already dry vegetation. High fire threat areas (in red and orange) in SCE service territory Confirming this ominous trend, in the last five years, California endured 13 of the 20 most destructive fires in the state’s history. With larger and more devastating fires now becoming the new normal, the term gigafire has emerged to label fires with over 1 million acres (404,686 hectares) burned. With 5 million customers in a 50,000-sq mile (129,500-sq km) service territory consisting of 4300 distribution circuits over 91,000 miles (146,450 km) of lines, Southern California Edison (SCE) has clearly mapped out high fire risk areas and understands the need for an effective fire-threat mitigation strategy. Prevention is one component of SCE’s strategy, manifested by the replacement of bare conductor with an insulated, covered conductor. However, with 1.4 million poles in its grid – most of which are wood – SCE also needed a proven wildfire hardening solution for poles to support the new, heavier covered conductor. Resilient Material Although it is the most prevalent material for distribution poles, wood is combustible. Steel poles are conductive and, in studies conducted by SCE, have the low potential to initiate wildfires under certain conditions. Concrete poles are too heavy to install in the remote areas of SCE’s service territory. Because they do not support combustion and they are the most wood like (that is, they can be drilled in the field), composite poles quickly emerged as a front runner for consideration in SCE’s wildfire-threat mitigation strategy. Two general polymer categories exist: thermoplastics and thermosets. Thermoplastics, also known generally as plastics, are items like a water bottle or the molded bumper cover on a vehicle. They are formed from pellets or powder using heat. Thermoplastics are not structural materials, so they melt when exposed to heat. Thermoset materials are entirely different than thermoplastics. Thermosets are composed of two components – a resin and hardener – that are mixed to create an exothermic reaction resulting in an irreversibly cured solid. When combined with a reinforcing fiber like nonconductive electrical glass, or E-glass, a structural element known as fiber-reinforced polymer (FRP) composite is created. Because thermosets do not melt when exposed to fire, they maintain their form. The non-combustible performance characteristics of composite materials are widely understood. However, extreme fire exposure can be the ultimate test for any material type. Full-Scale Test Method Flame temperatures recorded during the 3-min RS-Ackerman fire test. Although composite materials do not support combustion, their surface can char with sufficient heat flux exposure. Historically, flammability tests for polymer materials relied solely on laboratory-based tests initially designed for the home appliance market. While effective for their intended purpose, these coupon-scale tests did not realistically simulate the intensity of a wildfire, which has been described by wildfire survivors as a huge wall of fire. Going back to 2011, composite pole manufacturer RS Technologies set out to design a full-scale test that would represent a severe wildfire moving through a utility line right-of-way. Partnering with a fire expert from the University of Alberta, Mark Ackerman, a test method was developed. The test parameters were established based on known wildfire characteristics: Peak heat flux (energy) of 22 Btu/sq ft (250 kW/sq m) Maximum temperature of 1472°F to 2192°F (800°C to 1200°C), with most fires below 1832°F (1000°C) Exposure durations ranging from less than 30 sec for grass-fueled fires up to 90 sec for heavy coniferous forest fires, with most wildfire residence times in the 45-sec to 60-sec range. The total heat flux, or total amount of energy, of the fire depends on many factors, including fuel type, quantity, moisture content and fire duration. The RS-Ackerman full-scale fire test method starts with a full pole embedded in the ground, with an embedment depth consistent with an installed pole. Next, a 10-ft (3-m) tall steel shroud is installed around the base of the pole. The shroud has three holes spaced at 120 degrees around the base, which allows for three propane-fed burners to deliver the flame exposure. Typically, the test is run for either a 2-min burn or 3-min burn. This establishes the performance on both severe and extreme fire scenarios, respectively. The peak temperature of the test is 2332°F (1278°C) with a total heat flux of 16,540 kW-s/sq m, which is applicable for the 3-min exposure version of the test on the RS Fire Shield, a composite shell made from the same materials used on any round cross-section pole, including composite poles, to provide extreme fire protection. After the exposure duration has been achieved, the fuel source is turned off and the steel shroud removed. RS-Ackerman fire test method setup. The RS-Ackerman test duplicates both radiative (the transfer of heat without any physical contact) and convective (the transfer of heat from one place to another by the movement of air) heat flux exposure. Utility pole heat flux exposure depends on whether the energy transfer is purely radiative, where the surface is not contacted by flames, or a combination of radiative and convective. Perhaps the most important element in the RS-Ackerman fire test is the post-fire exposure strength test. After the steel shroud is removed, the complete pole is extracted from the ground and loaded into a test fixture to complete a vertical full-scale bend test to failure,