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Pultruded fiber reinforced polyester/PU poles offer advantages for underground utility cables |
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In the sixties, fiber-reinforced polymer (FRP) or composite poles were first installed in Hawaii as a solution to wood pole degradation and steel pole corrosion caused by the moist salt air. Since then, significant advances have been made in composite pole technology as they find increasing usage in power distribution, power transmission and lighting applications. With their high strength-to-weight ratio, environmental friendliness, non-conductivity and resulting enhanced safety, and longest lifespan on the market, composite utility poles for monopole and H-frame configurations are steadily gaining in popularity with electric utilities.
Traditional distribution poles made from wood are the least expensive option but throw up a number of challenges. No two wooden poles are alike and quality can suffer from natural defects like knots, twists, cracks/splits, necessitating costly manual inspection to ANSI standards to ensure worker safety. Special pretreatment is required to prevent rot, deter insect and bird damage, improve flame retardancy and extend service life.
At an approximate weight of 220 kg, steel poles are significantly lighter and more uniform than wood, but are highly conductive, require use of special insulating platforms and equipment, and necessitate that lines be de-energized (and service disrupted) when linemen are working nearby along with periodic maintenance to reduce corrosion.
Pre stressed concrete is resistant to wind and vehicular impact, weigh 1350 kg, making it impractical or impossible to install in rugged or remote locations.
Polymer composites have also been used for distribution poles. First-generation products were commonly filament-wound glass and unsaturated polyester or urethane. Lighter than any previous technology, these poles had high stiffness and strength, were inherent electrical insulators, self-extinguishing and fire resistant, rot and corrosion resistant, low maintenance, and impervious to bird and insect pests. However, filament winding is a slow and costly open-mold technology and is prone to voids, which can lead to strength issues. To compensate, extra material is used, leading to poles that are both over-engineered and heavier than necessary, and far-more costly than wood. Powertrusion International, Inc. USA has found a faster, more cost-effective method for producing composite distribution poles. The company uses the pultrusion process to produce hollow, glass-reinforced unsaturated polyester or urethane poles. Since pultrusion is a closed-mold process where polymer and reinforcement are pulled through a die under high pressure, voids are avoided, yielding poles that have higher strength and are more reliable, yet also lighter and less costly. The UV-stabilized poles can be colored to look like wood, and using an octagonal rather than round cross-section with flat sides makes them easier and safer to stack. The pultruded poles are 3 times more electrically insulating, eliminating the need to de-energize lines to ensure worker safety and reduce disruptions to customers. The strength/weight ratio of the pultruded poles is also 3 times higher than wood, so they are able to tolerate strong winds without snapping and are more ductile in the event of vehicular crashes. Despite this, they are one-third the weight of wood (168 kg for a 40-ft/Class 3 pole), and their center of gravity is roughly in the middle of the pole, so typically only 4 linemen are needed to carry and install a pole instead of the typical 10-12 (and the greater number of trucks required to carry workers and poles). They are impervious to rot and corrosion, are self-extinguishing, fire-resistant, and immune to pest damage. Since no harmful chemicals are used to extend service life, and the cured composite is considered to be inert, the environment is better protected and there are no disposal issues at end of life. Because they are produced in a highly repeatable industrial process, transportation, inspection, and stocking costs are greatly reduced (50-75%) vs. wood, and the non-tapered shape significantly reduces the need to stock multiple sizes of hardware to accommodate different diameters. With up to an 80-year life expectancy, the new composite poles provide twice the service of wood with far fewer problems.
The pole's design and an innovative structure enable it to continuously distribute stress evenly over its entire structure providing greater strength, consistency and safety compared to wood distribution poles. These composite utility poles have been designed to be interchangeable with similarly-sized wooden poles so there are virtually no hardware issues involved in "change-outs." The poles are non painted, pigmentable, with better weathering and water absorption properties. Powertrusion's automated manufacturing process allows each pole to be serialized with tracking numbers. This allows the company and its customers to track each pole to a particular batch and date of production. |
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