Utilities are adding facilities to increase the transmission capacity of the grid like never before. Photo by Gene Wolf.

Supporting Today’s Power Delivery System

Oct. 28, 2014
Innovation defines today’s tower and pole technology.

There is an old French proverb that loosely translated says, “The more things change, the more they stay the same.”

When the electrification process started more than 100 years ago, one of the biggest areas of concern was transmission. Early utilities saw their customer base expand over larger and larger service territories. They also recognized the benefits of having large centrally located generation facilities and being connected with neighboring utilities. This thinking resulted in the network now called the grid. Like all good ideas, the transmission system grew and kept on growing, leading to this expression being coined: There is no substitute for wire in the air.

That adage still holds true today, and transmission remains a hot issue for utilities and regulators. The grid is congested. It’s aging, it needs modernizing and renewable generation is demanding access. Like those pioneering utilities, today’s utilities are faced with building more transmission. An enormous effort is taking place, but many feel it is not happening fast enough. To get perspective and an order of magnitude of the task, just look at some recent research.

Transmission lines are constructed faster and with less environmental disturbance using techniques such as helicopter placement. Courtesy of Black

Structure Spending

In its 2014 Transmission Projects at a Glance publication, the Edison Electric Institute reported its members’ transmission investment was US$14.8 billion in 2013 and estimated total expenditures in 2014 would be approximately $17.5 billion. It is estimated the cost of structures typically runs about 40% of the transmission project cost.

Interestingly, GlobalData published a report specifically on the amount of money being spent on the global transmission tower market. According to GlobalData’s study, nearly $9.6 billion was spent on transmission towers during the period from 2006 to 2013, and it projects this amount will climb to about $11.2 billion between 2014 and 2020. GlobalData pointed out a great deal of this increased spending will be focused on replacing old transmission and distribution infrastructure. And research group MarketsandMarkets says the transmission market in the Asia-Pacific area would be the
No. 1 growth area, followed by the Middle East and Africa in the No. 2 position, and the Americas in the No. 3 spot.

The GlobalData numbers are big, but what makes them astounding is the fact they represent the money that will be spent on transmission structures worldwide, and they represent structures only.

Increased Circuit Miles

The GlobalData report supports the upswing in transmission circuit miles being built globally. Europe estimates there are more than 187,800 miles (302,240 km) of transmission operating at voltages from 220 kV to 750 kV. Estimates for North America say there are more than 300,000 miles (482,803 km) of transmission lines with voltages ranging from 115 kV to 765 kV. China reports there are more than 408,000 miles (655,000 km) of transmission operating at voltages from 110 kV to 1000 kV. Worldwide, the transmission circuits represent well over 1 million miles (1.6 million km).

Add in the distribution feeders and the numbers become mind boggling, so it should not come as a surprise structures have attracted the attention of technological wizards. They have modified and altered transmission structures until they are nothing like those of the good old days. Even though they may still resemble the poles and towers of yesteryear, they have really morphed into something truly amazing.

Structural technology has been transformed by the smart grid like everything else in the electric power industry. Powerful computers, sophisticated software and cutting-edge material science are driving the shape of the structure world. The big three — wood, steel and concrete — are still the major players, but fabricators have invested heavily in research and development (R&D). R&D has not only led to the improvement of those three, but also to the creation of several other materials being added to the transmission engineer’s toolbox.

Utilities are looking for ways to maximize their infrastructure, and double-circuit 345-kV steel-concrete hybrid single-pole structures provide improved designs to help that effort. Courtesy of Valmont.

Materials and Computer Science

Some remarkable state-of-the-art structural advancements have been made by steel fabricators through R&D by combining carbon technology and other super alloys in the steel manufacturing process. Steel fabricators also have improved structure life by adding enhanced coatings such as inorganic zinc silicates, advanced paint systems and metalizing processes. The results are lightweight, extremely tough, highly corrosion-resistant structures with very long service lives, but that is only part of the story.

Many fabricators such as DIS-TRAN Steel, Trinity Meyer Utility Structures, SAE, Sabre Industries, TransAmerican Power Products and others have invested in the development of powerful and sophisticated software programs. They enable manufacturers to take advantage of the improved physical characteristics and optimize designs, in the end achieving stronger structures that use less steel and take less time to fabricate. These cutting-edge software programs allow engineers to analyze new designs completely and quickly.

What previously took weeks to verify can be done in a matter of hours, which allows innovation like never before. In many cases, these new designs are so much stronger that fewer structures are needed for the transmission line. This is a huge advantage when utilities are under pressure to be more efficient and to keep down costs.

Steel suppliers are mixing shapes to match the job requirements such as this combination of a multi-sided and round-shaped single pole being constructed for a new double-circuit transmission project. Courtesy of Valmont.

As impressive as these developments are, the application of 3-D software really has been getting attention, both in the engineering department and on the factory floor. For years, computers have been controlling an army of robots, laser and plasma cutters, and computer numerically controlled (CNC) machine tools, but a process known as 3-D rapid prototyping has made it a new ball game. This process allows the engineer to model each tower element on the computer. When the structure is acceptable, the software generates a detailed digital file of each part. These digital files are read directly by the control software of the factory’s automated fabrication equipment. The process reduces setup and fabrication time, and practically eliminates fabrication errors.

An entire composite structure can be loaded by a couple of linemen and transported to the construction site in the back of a pickup truck without heavy construction equipment, saving time and money. Courtesy of Utility Composite Solutions.
Composite poles can be modified in the field with simple hand tools and little expense. Courtesy of Duratel.

This design flexibility has led to improvements in something as simple as better slip joints, to things more complex such as moving tubular steel structures into voltage levels once thought of as the realm of lattice structures only. Another innovation for steel structures comes from Meyer in the form of its QuickPin system to connect steel crossarms to its structures. The system replaces the old-school nut-and-bolt process with an unthreaded tapered pin connection that takes about one-third of the time to assemble.

Modern laminated wood structures support line taps and the isolation disconnect switches necessary for this type of application. Courtesy of Laminated Wood Systems.

High-Tech Wood

Wood was the structural material of choice at the beginning of the electric industry and still is the most popular material for the transmission and distribution grid today. Amazingly, wood has remained a mainstay for more than 170 years. It is estimated there are more than 150 million wood poles in North America alone. This is pretty good evidence of the basic soundness of using wood for towers and poles, but wood structures have not been immune to the pressure of technology.

When suitable trees were getting scarce, scientists turned to genetic engineering to produce fast-growing, arrow-straight trees for a sustainable renewable resource. R&D also has led to wood products with coatings that make wood structures more resistant to oxidation, corrosion, rot and insects. In addition, wood is a sustainable resource, which is hugely important because of today’s green initiatives.

Composite wood structures also have been subject to technological enhancements. The variety of these engineered wood products, such as laminated crossarms and bracing, has been increasing. Laminated structures for transmission and distribution structures are available for every function needed in line design (that is, tangent structures, deadend structures, angle structures, unguyed structures and more). Companies such as Hughes Brothers, DIS-TRAN Wood Products, Laminated Wood Systems Inc., McFarland Cascade and others have been developing these laminated transmission and distribution poles and towers for every application imaginable.

These fabricators have found the second growth material, which means less-than-desirable trees and limbs, can be made into very desirable laminated poles and towers. In addition to that type of raw material, reclaimed poles are being used as a source of wood. This process keeps old poles out of the landfill and conserves trees. They cut up all of this wood and shape it, glue it, treat it with resins and form it into the desired product. Technology has been refining the process, finding new methods to improve the product and speeding up the entire process while reducing costs.

At one time, laminated poles were offered only in round, square and rectangular shapes, but R&D is exploring a variety of new shapes. One area of interest has been the hollow polygonal-shaped poles that promise to be lighter and stronger. This type of composite wood pole technology is opening new venues for wood applications.

Today’s complex structures require extensive testing to verify new materials and designs. Courtesy of Trinity Meyer Utility Structures.

Computerized Concrete

Like wood and steel, concrete has been used for utility structures since the beginning, and like those other materials, technology has had an impact on concrete. Gone are the days of mixing a load of sand with several bags of cement, throwing in some aggregate, adding water and calling it good. Making concrete has become an exacting science everywhere in the industry, but more so when it comes to poles. Every phase of the process is controlled by computers using high-tech analytical software. Through R&D efforts, the best mixtures are being tailored to specific applications, leading to reduced costs, improved strength and increased durability.

High-strength concrete with low shrinkage properties works best, but these concrete structures require more than that. The concrete mixtures are carefully crafted using admixtures and new components. Fly ash mixtures are being used to reduce cement content in concrete, which reduces the price, in turn, and uses a material readily available because of its abundance. There also has been a lot of admixture development to enhance concrete characteristics. Suppliers are adding chemicals to reduce the amount of water used in the pole or to increase the viscosity, making the concrete more flowable, which improves the overall process. There also is a high-strength self-consolidating mix that does not require vibration to eliminate air voids.

Shapes also have been subject to scrutiny. At one time, round and square shapes were the only ones available; today, rectangular shapes have been added and experiments are being done on polygonal offerings such as hexagonal poles. The designer is only limited by imagination. In addition to shapes, fabricators are mixing materials. They have filled tubular steel poles with concrete to improve the structure’s strength. They also have made poles that are part steel and part concrete.

Utilities have the ability to combine composite poles with wood crossarms and bracing as needed. Courtesy of Utility Composite Solutions.

Chemicals and Computers

What do polyester, Kevlar, epoxy and resins have in common? They all are used to make transmission and distribution structures. About 50 years ago, the first distribution pole came out of the test tube. It was a fiber-reinforced polymer composite pole developed to address the pole-killing characteristics of the warm, moist, salt-laden air found in the coastal areas of Hawaii. Being a child of technology, composite poles have been in a constant state of R&D since those early days. Fabricators such as Duratel, Powertrusions International Inc., PUPI, RS Technology, Shakespeare Composite Structures, Utility Composite Solutions and Strongwell are taking advantage of this plethora of materials to customize their products and provide designer poles for almost every utility application.

A good example is their ability to create a composite pole that is strong in a specific direction. With metal or wood poles, strength can only be achieved by increasing the structure’s thickness, which increases the weight of the structure. This feature is referred to as the strength-to-weight ratio. Because of new manufacturing processes and materials, composite poles have the highest strength-to-weight ratios in the industry today. Fabricators can craft a pole to resist corrosion, withstand chemicals, survive severe weather, and be nonconductive and nonmagnetic. The poles can be made to absorb impacts, be fire resistant and withstand the onslaught of a variety of pole-damaging animal life without harming the animals.

Manufacturers also are taking advantage of the latest CNC technology. These machines control all aspects of the composite pole fabrication process, resulting in lighter, stronger and more cost-effective poles in greatly reduced time periods. It is estimated advances in the CNC technology have reduced the production time for utility poles from days to hours, which reduces production costs. All of these advancements are bringing the purchase price of composites more in line with their competition.

This design flexibility has enabled utilities to become creative with the applications, too. In areas prone to severe weather such as wind and ice storms, utilities mix super-strong composite structures with existing wood, steel and concrete structures to prevent the structural domino effect. Hollow, nonmetallic transmission poles are being used to hide wireless, cellular, satellite and radio antennas. This keeps them out of the public’s site, but still allows the electronic signal access to and from the equipment. Another innovation is the modular pole section. Various-strength sections can be stockpiled by utilities. When a failure happens, the utility can mix and match the sections to create a pole of virtually any length or strength needed for the replacement.

Composite crossarms allow utilities to reduce insulation without reducing reliability. Courtesy of PUPI.

Old Dog, New Tricks

Structural technology is maturing and providing the industry with applications about which past generations of designers could only dream. Aluminum, wrought iron and various plastic combinations have been added to the list of materials used in towers and poles. There are researchers experimenting with nano-material for future applications, but the combination of advanced materials with powerful computers has really impacted the structural world. The computer has taken over control of the fabricator’s factory, and now engineers are tinkering with 3-D design programs, which are linked directly to the factory’s production equipment, reducing fabrication time and eliminating measurement errors.

All of this effort has had many positive changes on the structures. They are stronger, they are cheaper, they have longer lives and their production time has been reduced. It may seem nothing is safe from technology, but is that bad?

The traditional engineer may be very uncomfortable with these unorthodox approaches, but as Thomas Edison said, “The value of an idea lies in the using of it.” The industry needs these advantages.

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