The first electrical distribution system was installed in the US in 1882 at Thomas Edison’s Pearl Street plant, serving New York City’s Financial District. 1889 saw the first transmission line, bringing power 24 miles from Willamette Falls in Oregon City to downtown Portland. Today, there are over 5.5 million miles of distribution lines and 240,000 miles of high voltage power lines in the U.S. History has demonstrated that humanity’s health and prosperity are inseparably tied to the availability of electric power.
Forecasters expect 1-2% increases in peak U.S. demand to continue until around 2030, due to natural load growth, high power consumption sites like data centers used for cryptocurrency and Artificial Intelligence, and new industrial sites for manufacturing and distribution. Predictions taper to 1% load growth from 2030 to 2050, based on renewable energy sources substituting heavily for fossil fuels, energy efficiencies coming into play, battery storage reducing fossil fuel-based generation during peak hours, and increased use of renewables such as solar panels on commercial buildings and homes.
All of this points to the need for more power lines, but how much construction should we anticipate, and how can we do it in a reliable and sustainable manner? A 27% increase in demand by 2050 implies a minimum 27% increase in grid infrastructure. However, the American Society of Civil Engineers reports that approximately 70% of T&D lines are already well into the second half of their useful service lives, having been built in the 1950s and 1960s with a life expectancy of 50 years. It is abundantly clear that our aging legacy infrastructure will have to be significantly augmented, if not almost entirely replaced, by 2050.
Standard options for distribution voltage lines have been bare wire, with underground (UG) lines being used in urban centers as well as residential developments, and covered conductor lines, both Spacer Cable and Tree Wire. While UG transmission is an attractive option for engineering as well as aesthetic reasons, its cost structure makes it prohibitive for more than short runs.
A key barrier to building more power lines is obtaining regulatory approval. Moving forward, focus will be on minimizing Right-Of-Way (ROW) requirements, protecting flora and fauna, and minimizing the carbon footprint of any proposed line.
The goal to reduce ROW requirements has driven research into compact construction. Compact construction is more expensive than standard bare wire construction since components used are more specialized. One example of compact construction is High Voltage Direct Current (HVDC) lines, which were introduced in the U.S. in 1970 for the Pacific Intertie to deliver hydro power from the Pacific Northwest to Southern California. The benefits of HVDC are reduced ROW, a reduction in line losses, and visual impact reduction. While there is no interconnected HVDC grid in the U.S. and relatively few lines existing today, the Plains and Eastern Clean Line project proposed 720 miles of 600 kV HVDC from Oklahoma to Tennessee, bringing clean energy wind power from out west to the eastern U.S. After eight years, the project was terminated due to the inability to procure the needed ROW. When ROW crosses state or county boundaries, the required coordination between multiple jurisdictions inevitably ratchets up the complexity, costs, and negative appetites of investors.
In the state of Maine, The New England Clean Energy Connect project aimed to construct a 145- mile transmission line to bring clean Canadian hydro to the New England power grid. The project was rejected by voters who claimed that “The benefits were overstated, and the project would harm woodlands along the route.” Similarly, the Eversource Northern Pass Project, a 182-mile line to bring hydro from Quebec to New Hampshire was cancelled due to local concern over disturbing environmentally sensitive areas. The irony in both cases is that lines intended to replace fossil fuel plants with clean energy sources were rejected essentially on environmental grounds.
Another option to achieve compact construction is the use of composite conductors, which are strong, lightweight and use composite cores in lieu of steel. This results in lower sag, allowing longer spans to be built and for reconductoring long spans with larger current carrying conductors. This is a means of increasing the MW capacity of a given transmission corridor without requesting expanded ROW width, changing poles, or requiring taller poles. Still another option for compact line construction is the use of Spacer Cable systems. The fundamentals behind using these systems, which have a non-shielded multi-layer insulation system, is that the polyethylene replaces most of the air between the conductors, allowing them to be positioned very close to one another. Among other benefits, this vastly reduces the ROW required to build a power line.
As an example, the horizontal space savings for Spacer Cable compared to bare wire construction at 115 kV is a full 18 feet. This is illustrated below.
This ROW reduction offers significant environmental benefits. For every mile of a 100-ft. ROW through a forested area, approximately 12 acres of trees are lost. In the Midwest, the average number of trees per acre is 200, yielding a loss of about 120,000 trees for a new 50-mile transmission line. Spacer cable construction on that same route would save approximately 240 acres and 48,000 trees, which in turn counteracts a significant amount of carbon pollution. Consequently, the environmental stewardship attributed to compact construction is viewed favorably by regulators when utilities seek new ROWs.
The first aerial covered conductor line was installed in 1951 in Massachusetts. Seventy plus years later there are aerial covered conductor lines in all fifty states and U.S. territories, on all even continents, and in over 75 countries. Covered Conductor systems are available from 15 kV through 46 kV, and 69 kV Spacer Cable was introduced in 1995 (see photo below)
Spacer Cable lines are compact enough to allow a ROW to accommodate multiple power lines without expansion. Note that adding lines to an existing ROW (rather than requiring a new one) can streamline the permitting process and project timeline from 7-13 years down to 2-3 years. The photo below shows a new 115 kV Spacer Cable line built on an existing ROW, with a 25 kV Spacer Cable line underbuild.
What does the future hold for critically needed new power line construction? Can the regulatory approval process be streamlined to allow faster ROW approvals? Should we continue to rely solely on bare wire lines? Can we expand the HVDC network? Can we utilize compact construction techniques of composite core conductors, as well as reliable, environmentally friendly covered conductor systems? Will composite core conductors be used in covered conductor systems to synergistically combine the advantages of each? These are questions utilities and regulators will have to answer as we plan the future of powerline construction.
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