The grid is a complex network of transmission paths and distribution circuits. The majority of these electrical pathways are overhead construction comprised of a myriad of poles, towers and structures made of every imaginable material. Wood and steel make up the bulk of these structures, but there is much more to the story.
The designs and components for the first electric power lines were scavenged from another industry. Back in the 1840s, the first telegraph companies originally had tried to place their telegraph cables underground. It was a good idea, but the insulation materials of the period were not mature enough for the task. After several critical failures, the telegraphic systems went overhead using wood poles to support the wires. Some of the first schemes attached the wire directly to the pole, but it was discovered wet weather (rain) shorted out the signal. That led to adding insulators between the wood and wire, which required crossarms to hold up the insulators and wires. With these components, only hardware was needed to attach everything.
Several years later, all the kinks had been worked out and all the necessary paraphernalia was in place. Luckily, all of this equipment was readily adaptable to the transmission of electricity; after all, the main concept was the same (that is, an energized wire insulated from its supporting structure).
Granted, there were a lot of issues to be resolved before electricity would flow cross country, but the idea was taking shape. It proved the old adage that when the time is right, the right idea has the power to overcome an overwhelming challenge. Fortunately, this was one of those points in history when the stars were aligned. The stage was set and major changes were coming.
By the mid-1870s, the application of electrical power was mostly an odd assortment of small isolated direct-current (dc) electric systems scattered around the world. It is important to remember that electricity was in competition with several established mechanical systems such as the one displayed at the Philadelphia Centennial Exhibition of 1876. These early exhibitions and expos were the trade shows of the day, taking place in all the major cities. The Philadelphia exhibition featured modern-for-the-time power applications from vendors. What made this expo interesting was the massive 1400-hp Corliss engine and the transmission system it powered.
This engine drove a large shaft said to have been more than a mile (1.6 km) in length. The enormous shaft powered every contraption and gizmo in the exhibition through a system of belts, bands and tackles. It is hard to imagine city life if these behemoths were commonplace. Opportunely, early electrical entrepreneurs also took part in these trade shows to focus public awareness on electricity. The 1878 Paris Exposition featured an exhibit that could be called an early electric transmission line. This system powered an arc lighting system that attracted a great deal of attention. It covered nearly a half mile (0.8 km) along the Avenue de l’Opéra and lit up the Place de l’Opéra.
Exhibits like those paid off handsomely for the electrical entrepreneurs. The arc lighting was much brighter than the gas lamp systems available and the public saw the benefits. The electric arc lamp was the proverbial foot in the door for the electrical industry. These small arc lighting ventures were critical to the industry’s development.
In 1879, the industry took a huge step when the first electric utility was formed in California. The California Electric Co. (now Pacific Gas & Electric Co.) built a dc distribution line in San Francisco and began selling electricity for lighting. Electricity was generated from sundown until midnight every day of the week, and, for a fee, electric arc lighting was available to anyone along the power line who wanted it.
Almost simultaneously, similar utilities sprung up around the world with copper wires strung on wood poles and electricity to sell. The early utilities used wood telegraph poles and insulators to build their power lines. Transmission of electricity was a reality at long last, though the distances were not great. For the dc low-voltage levels of the era, the short distances challenged the technological capabilities of these schemes.
The Game Changer
The game changer came in 1882 when Thomas Edison perfected the incandescent lightbulb. His Edison Electric Illuminating Co. built an electric system in New York City consisting of a central power station with distribution lines and lightbulbs. The fledging utility started out with approximately 85 customers, 400 bulbs and a distribution system that covered about 1 sq mile (2.6 sq km) of lower Manhattan. Within a short time, there were more than 200 such power utilities in North America, which really added to the wire in the air.
While Edison and his cronies were fixated on dc, another kind of electricity came on the scene. Known as alternating current (ac), it was soon locked in competition for dominance in the power business. The culmination was the 1891 International Electro-Technical Exhibit. The expo was held in Frankfurt, Germany, and ac proved to be a showstopper.
Behind the scenes, German engineers had constructed the world’s first three-phase ac transmission line to bring electricity to the exhibit. It was a real transmission line in every sense. Rated 25 kV, the line ran from Lauffen to Frankfurt, a distance of nearly 109 miles (175 km), and used wood poles, copper wire and porcelain pin-and-sleeve insulators installed on wood crossarms.
This 25-kV transmission line was an important step toward the transmission grid technology necessary for electrification. The trade shows had established ac power in the public’s mind, which paid off handsomely for the pioneering electrical businessmen. Of course, a lot of work still had to be done before there would be anything closely resembling the transmission and distribution networks, but it was moving forward.
Many of these early businessmen understood the commercial applications of their work as well as the technology. The companies they founded — ASEA (now ABB), English Electric (now Alstom), General Electric Co., McGraw-Edison (now Cooper Industries), Siemens, Westinghouse and many others — produced a wide range of devices for both controlling electricity and commercially using electricity, which helped to define the industry. Electric-powered lights may have started as a fad, but that was the base for the industry. At the start of the 20th century, demand for electricity increased.
The increased demand corresponded to the need for higher voltage levels to meet the demand. Unfortunately, as the industry pushed the electrical ratings on the modified telegraph technology, everything from the support structures to the conductors needed to be improved. A perfect example is the simple insulator used to connect the wire to the crossarm. The insulators being used were still the insulators scavenged from the telegraph industry, designed to be able to insulate only for voltages below 30 kV. As a result, a group of engineers working for the newly formed General Electric Co. developed the first practical disc insulator that was able to be stacked.
Transmission engineers could link the discs into long strings of insulators for higher-voltage transmission lines. This success led to more research from other manufacturers, and that research opened the door to new insulating materials such as glass, ceramics and polymers. Many of today’s insulator manufacturers — NGK Locke, Sediver, Salisbury, Lapp, Hubbell and Okonite — can trace their state-of-the-art products back to this work and their steady progress of the research.
The Domino Effect
The technology continued to advance at a solid pace, but each new solution seemed to bring about another challenge. The disc insulator allowed longer insulator strings, which, in turn, required stronger crossarms and new attachment hardware, which precipitated the need for taller structures to keep the conductor above minimum clearance levels. Taller poles required loftier trees, which impacted the available supply. This did not make wood structures out of date — in fact, this technology is still a major player in today’s marketplace — but it did push the envelope in the industry once more.
Research from suppliers such as Guelph Utility Pole Co., Hughes Brothers, KW Reese, McFarland Cascade, Stella-Jones, Trans Canada Utility Pole Co. and many others have kept wood technology suitable for all distribution and transmission line applications. But utility engineers have always wanted more choices and selections. They need to modify, change and improve things like they need to breathe. It’s about pushing the design envelope and getting more watts out of the system.
Steel and Concrete
The first wood structures were adapted from the telegraph industry, but early power systems also used steel and concrete structures to support the conductors. The steel lattice structure design was very popular and known for its extreme strength in a relatively small space, but steel lattice structures were (and still are) labor intensive to assemble.
About 50 years ago, labor-reducing steel tubular shapes became available to transmission line designers. These structures quickly became popular and could be found on just about every system. The hollow steel poles were fabricated either as one piece or several sections, and fitted together to form the structure. Light-duty tubular steel poles became popular for distribution designs. They proved to be lighter than wood poles, which was important in congested areas.
Like the wood suppliers, steel fabricators such as Comemsa, Dis-Tran Steel, FWT, Sabre Industries, SAE, TransAmerican Power Products, Trinity Meyer Utility Structures, Valmont and others provided custom designs blending old and new materials to solve structural problems as they developed. When the apparatus technology was ready to move to 500 kV, 765 kV and 1100 kV, the towers were ready for the transmission lines.
Concrete has also been used since the beginning, which may be surprising but true. Concrete poles have been used in European telegraph systems since the 1850s. The first ones were solid castings that came in round and square shapes reinforced with heartwood, which was later switched to mild steel.
Improvements came in the form of spun-cast concrete poles in 1907. The spinning process formed a void in the center, which made the pole less expensive and lighter in weight. Several years later, the idea of pre-stressing solid-cast concrete poles came along. It made poles more elastic and enabled them to withstand higher loads without cracking. But there was a price for this strength — they were heavy.
It made sense to combine the best characteristics of the spun-cast process with the pre-stressed procedure to produce a pre-stressed spun-concrete pole, lessening the unwanted features. Over the past 50 years, manufacturers such as Europoles, StressCrete, Titan Concrete Poles, Utility Structures and Valmont have conducted a lot of research to optimize concrete mixes, reinforcement, design procedures and durability, which allows concrete poles to be engineered to provide the exact characteristics needed by the utility.
Wood and steel structures are still the most common overhead line structures in use worldwide. These structures can be simple or complex, but, by understanding the past, the industry can keep these trusted materials relevant in today’s marketplace.
Trinity Meyer Utility Structures, for example, has developed a hybrid structure that joins a lattice base section with a tubular top section. While the structure has the strength characteristics of lattice, the tubular portion reduces assembly labor and uses a smaller right-of-way footprint.
Keeping with the hybrid design, Valmont has combined steel poles with concrete poles to make a steel-concrete hybrid pole. It has a concrete base in the ground and a steel section in the air. It gives the structure the strength of steel in the air and the impermeability of concrete in the ground. Wood structures also are subject to hybridization.
Fabricators such as Laminated Wood Systems have developed a laminating process that takes strips of wood and bonds them together with synthetic resins. The process allows the company to use low-grade trees, crooked logs, recycled poles and other less-than-acceptable wood sources and turn them into structures with long design lives and increased strength.
Fabricators also began using unique chemical materials such as fiberglass, carbon fibers and others to develop a variety of poles, towers and structures many years ago. These test-tube structures were designed to mimic wood, steel and concrete, as well as to improve on their weaknesses.
The first attempt at a plastic pole took place in the 1960s. Fabricators used a fiber-reinforced polymer design to combat the environmental problems (warm, moist salt air) found on the island of Maui, Hawaii. The fiberglass proved to be very strong — not subject to the degradation from which wood and steel suffered — but it lacked the ability to resist ultraviolet radiation. Designers added some new coatings, and the problem was solved.
These structures have been classified as composite structures and considered very modern. Fabricators continued to improve their products with thermosetting resins for their raw material, but the biggest breakthrough was the development of specialized polyurethane resins. These super-strong composites allowed manufacturers to develop modular pole systems for utilities to mix and match sizes, lengths and diameters, giving them the ability to make up the exact type of pole system needed for a project. As the technology developed, the choices became almost unlimited.
Today’s designer can select products from manufacturers such as PUPI, RS Technology, Shakespeare Composite Structures, Utility Composite Solutions, Strongwell, Powertrusions International and Duratel to meet the needs of their projects.
The early days of the electric industry was shaped by imagination, vision and a lot of hard work. Edison said, “Genius is 1% inspiration, 99% perspiration.”
That spirit drove every step of the way as the industry moved from small isolated operations to networks and grids interconnected. All along the way, the focus stayed on bettering what there was and developing the technology that allowed transmission lines to go from a shaky idea on a telegraph pole to the 1100-kV behemoth structures stretching across China, carrying gigawatts to load centers thousands of miles from the generation source.