Structures are more than the sum of parts.
Who could have guessed how much the basic concept of a utility pole would change since its origin? It used to be that trees were converted to telegraph poles. Then there came a time cross-arms were added, creating power poles that supported electric lines. Driving down a street today, it is apparent how much poles and towers have morphed from that simple concept.
Poles have changed and changed big time. In many cases, the structures do not even resemble utility poles. They have been transformed into what are referred to as joint-use structures. It is fun to try to identify these shapes with common items — sort of like Rorschach testing (a test subject's perception of inkblots) on the fly. Some structures are reminiscent of tennis racquets, fly swatters, paper clips and pyramids. One structure design has a bent top and is shaped radically enough that it is a hybrid, both pole and arm. Picasso would be proud.
Crossarms, bracing and trusses are literally supporting this scope change. Utilities are making the best use of space by suspending distribution equipment from the poles. They include everything from pole-top transformers to disconnect switches and cutouts, to all manner of smart grid paraphernalia. It does not end there; local entities are dangling traffic signals, streetlights, police call boxes, community Internet facilities and cell phone facilities from the structures. Some poles have so many crossarms they look more like ladders than power poles.
Transmission structures are not immune from this type of dual role, either. They have been used by cell phone companies to host repeater stations and all their required antennas. This has been going on for many years. After all, what better way to camouflage their unsightly facilities than with the T&D industry's attractive structures?
Another example is optical ground wire. It was a great addition to improve communications and generate revenue, but it also required access points along the right-of-way for fiber customers. Then there are all the devices the utility adds to make the system more reliable, such as instrumentation, isolation switches with motor operators, solar panels to provide power for those motor operators, and other gear.
It all adds up. The towers and poles have a more demanding function in today's world, and that is why many of the pieces and parts have become so sophisticated.
Simple Approaches Improve the Bottom Line
True, pressure-treated wood is still the most widely used material for poles, crossarms and bracing. Even with the latest innovations in preservative protection, wood requires regular inspection and remedial preservation treatments, which add to the bottom line.
Utilities are looking for materials that extend the useful life of the structure and decrease maintenance costs. Operations and maintenance (O&M) budgets have been taking a pounding as utilities try to cut costs. Besides the actual upright structural members and pole, the parts that make up the structure — crossarms, bracing, coatings and other hardware — play an important role, as well.
Crossarms and bracing technologies have been attracting a lot of attention within the industry, because they do not have the service life of the poles supporting them. Typically, these components have to be replaced several times during the life of their poles.
The replacement of a crossarm assembly can cost a utility US$1,000 or more, depending on the location of the structure, the equipment needed to perform the replacement and the cost of the outage required for the replacement. If some technical improvements can result in a crossarm that does not need to be replaced over the life of a pole, it will generate attention.
Wood is Good, But…
Sure, utilities are committed to wood, but they would like to stop the annual O&M inspection and replacement programs required to keep the towers and poles intact. There are some simple methods for prolonging a wooden crossarm assembly's service life.
Take split ends, for example. Although this is a relatively simple problem, it takes a terrific toll on crossarms. It happens when the end of the crossarm starts splitting. Moisture gets into the wood along with insects and other undesirables, which can lead to failures such as rotting or insulator pins pulling out. The utility has to replace the crossarm.
One simple preventive approach is Dis-Tran Wood Products' Dura-Arm, a steel endplate that is pressed into each end of the crossarm. The endplate locks itself into the crossarm, which prevents the ends from splitting and keeps water out of the wood.
Manufacturers like Brooks Manufacturing Co., Hughes Brothers Inc. and Dist-Tran Wood Products LLC use an incising process to improve preservative penetrate. The wooden crossarm is passed through a machine that makes incisions (puncture holes) in the surface. Because of the incising, preservatives can penetrate deeper into the wood, improving the protection.
Woodpeckers are another problem. They cause millions of dollars in damage around the world to utility poles, cross-arms and bracing. Maybe some woodpecker species are endangered, but the poles they have infested are in danger, too. The birds excavate nests and drill holes in search of insects in wood members, which can cause failure due to structural breakdown.
The U.S. Department of Agriculture and Colorado State University tested Brooks' Extenda-Life coated crossarm in their research to fight woodpecker damage to crossarms. Brooks uses a polyurea elastomer coating similar to the coatings used in truck bed liners but with a higher tensile strength and more tear resistance. In the test, 18 pileated woodpeckers were presented with the Extenda-Life crossarms and some uncoated crossarms in a controlled situation. After 10 days, the Extenda-Life crossarms were undamaged while the uncoated crossarms were damaged.
TimberSIL Products has developed a process that fuses glass with wood to create a glass-wood product. This process has been used in the flooring industry, giving floor coverings a rock-like finish. The TimberSIL process is a polymerization of sodium silicate (sand) into amorphous glass. This fuses the glass within the wood, creating a crossarm that is fire-retardant, has improved water repellency, resists dry rot and mold, and is non-toxic.
Of course, coatings are not limited to wood. They are being applied to other types of structural materials. The first coatings that come to mind for steel structures are painting and galvanizing. Computer control technology has boosted the paint and galvanizing processes by applying the steels' coating in thicker, more uniform layers.
Technology advancements allow utilities to select different galvanizing finishings, too. They can choose from the traditional galvanizing (bright) finish or several dark galvanizing finishes. American Electric Power has been successful with customizing dark finishes for its 765-kV projects, which make structures appear to disappear from the landscape.
Another method used for steel finishing is the COR-TEN process developed by United States Steel Corp. many years ago. The process was so successful that the name has become generic and is now referred to as corten, much like the term Kleenex has become a general term for paper tissue. Corten is a weathering process that darkens the steel and produces a finish that is corrosion-resistant and aesthetically pleasing to the general public.
Polyurethane coatings also are being used on steel successfully. Tucson Electric Power started using polyurethane on the butts of its steel poles for corrosion protection but found the coating protects the steel during shipment. The utility now specifies polyurethane for the entire pole to reduce chipping damage during shipping.
Composite crossarms are generating a great deal of interest from utilities. Manufacturers such as Amistad Fiberglass, Chance, Hubbell Power Systems, Hughes Brothers, MacLean Power Systems, Fiberglass Crossarms and RS Technologies report that their crossarms are being used for dead ends, tangents and beams to support equipment installations such as switches, voltage regulators and metering. They also have found their way into substations for trusses and equipment support.
Part of the reason for such wide acceptance is the fact composite crossarms are stronger and lighter weight than wood crossarms. For example, a quick look in a wood catalog shows that an 8-ft (2.4-m) crossarm used for a dead end has a weight of about 129 lb (59 kg) and a strength rating of 6,500 lb (2,948 kg). A composite catalog lists a crossarm for the same application with the same dimensions at roughly 56 lb (25 kg) and rated at 10,000 lb (4,536 kg).
This may seem like a small thing, but the lighter the crossarm, the less time it takes to install. Being lighter also means the equipment needed for installation can be smaller, which saves money, too. Add up the savings in installation time of a lighter crossarm, then multiply that by the thousands of crossarms the typical utility buys each year, and the savings can be substantial. Utilities with an eye on the balance sheet are not missing this fact.
Riley George, area vice president of sales-north for PUPI Fiberglass Crossarms, said, “The increased strength has allowed engineers to replace two or three wood crossarms with one composite crossarm in many applications. In addition, composites have about twice the service life of wood, are also impervious to woodpeckers, insects, rot and mildew, and have improved electrical insulation levels.”
Companies like Laminated Wood Systems Inc., Hughes Brothers and Dis-Tran Wood Products offer a variety of laminated crossarms and bracing with several advantages over standard lumber. Laminating products reduce waste by taking trees and limbs that are unsuitable for standard poles or structural members and making them into acceptable structures. By cutting the undesirable wood into strips, the strips can be glued together to form usable poles, crossarms and bracing components. The shapes can be hollow, thus lighter. Also, the geometry of gluing the strips together can make the members stronger than solid wood.
There is even one group advocating to make laminated crossarms from decommissioned chromated copper arsenate (CCA)-treated utility poles. The group recycles old poles that would have been consigned to landfills. It also conserves trees for other uses — again, less waste. Initial testing has proven quite positive.
These technological advancements have inspired creative thinkers to come up with intriguing solutions. One composite manufacturer is developing a one-piece crossarm assembly that includes the pin insulators and the bracing. This reduces components, hardware and assembly time. The installation crew unpacks the crossarm assembly, bolts it to the pole, secures the conductor to the insulator and is finished.
Another interesting concept is the snap-joint composite structure developed by W. Brandt Goldsworthy & Associates Inc. The company has taken pultruded structural members and shaped the ends so they snap into each other. Several years ago, a demonstration project began that uses this joint method on three transmission structures near Los Angeles, California, U.S. The structures resembled a lattice structure. Testing was performed, and the snap structure met all the requirements that had been set for it.
Out-of-the-box thinking does not have to be complex, either. Thomas & Betts has introduced a time-saving innovation called QuickPin for connecting a steel crossarm to its structure.
“It is the fastest arm connection system in the world,” said Jim Palmer, director of marketing, Thomas & Betts steel structures division. “Typical installation time has been reduced from approximately 30 minutes per arm to about 5 minutes. Instead of torquing nuts and bolts, the lineman inserts structural pins and secures them with cotter key-type assembly.”
Thomas & Betts has been working with several utilities to develop this system, which is expected to undergo field testing this year.
Hughes Brothers got into the composite strain insulator business several years ago and branched out into fiber-reinforced polymer rebar. The fiber rebar was designed for applications where corrosive conditions cause concrete to fail, but it also has found a home in electrical substations. Substations can be a very high electromagnetic environment. Devices such as air-core reactors produce high magnetic fields that cause excessive heating in steel rebar cages used in their foundations. Before the availability of fiber rebar, engineers were forced to use sections of rubber hose cut to fit over the steel rebar at all crossings and hoped the contractor installed it correctly.
It seems that nothing is safe from the relentless forces of technology. Even something as simple as rebar has been improved by composite technology. Crossarms, trusses and bracing are another simple facet of towers and poles that are being improved. Coatings are giving new life to wooden crossarms and the list grows daily. Traditionalist may be uncomfortable, but they have to remember the industry is changing every day, and the change is for the better.
Environmentally Responsible Transmission
How about this for a radical green approach? By building above the forest canopy, no vegetation management is required. It might surprise some, but this concept has been around for many years.
The Korea Electric Power Corp. built a double-circuit 765-kV transmission line through heavily forested mountainous portions of their country using this type of approach (T&D World, February 1998).
Powerlink Queensland used this same approach to address concerns brought about by building lattice towers that cleared the canopy of the underlying fragile ecosystems with their unique helicopter landing pads for routine maintenance (T&D World, April 1999).