According to Troutman, an additional factor that makes this transmission arm unique is the custom fiber architecture designed by engineers from Transmission Innovations and Creative Pultrusions. “It incorporates a lot of stitched fabrics, roving and continuous filament mat, but the big difference is it’s made out of a polyurethane matrix,” he explains.
Polyurethane resins are well suited for applications with extraordinary requirements for robustness, impact strength and longevity. Those characteristics are needed for a transmission line that must resist high wind and ice loads and the possibility of critical stress should a component break. “The polyurethane is a very forgiving resin in terms of its ability to help distribute stresses,” Troutman explains. “It drastically increases the interlaminar shear strength, which increases the bond strength between the layers of mat and roving – and it’s very, very tough.”
The polyurethane profile is reinforced with E-glass and features a polyester surfacing veil to give it added protection from the fiber blooming that can result from long-term UV exposure. Creative Pultrusions used high-pressure injection molding technology to push the polyurethane through a series of custom dies.
Troutman expects the crossarms to last 75-plus years, unlike their wooden counterparts. “In areas that are swampy or have high moisture, wood degrades relatively fast,” he says. “Wood has a tendency to rot, so utility poles and crossarms in those types of environments may only last 20 years.”
The performance of the composite poles will be put to the test as up to 1,000 GFRP crossarms will be installed on existing poles in one of the world’s largest temperate rainforests, the Great Bear Rainforest between Vancouver and southeast Alaska. Installation in such a remote area requires helicopters to bring products on site – another reason composites were a good choice. Because the GFRP crossarms are lighter than wooden or steel ones, the installers are able to use a smaller helicopter. In addition, the helicopters could fly in the top section supporting the crossarms of each transmission tower with one lift rather than five, which is typical for heavier products. “Because the helicopter has to climb fewer times than traditionally necessary, the chopper overhead time for the linemen is greatly reduced, improving not only fuel costs but also worker safety,” says Lockhart.
Years of testing the composite crossarms are finally paying off for Transmission Innovations and Creative Pultrusions as work continues on the large installation project in northwestern Canada. And it’s not a one-time success story: More and more utilities are expressing interest in composite solutions.