This is the second in a series of articles on the coming wave of transmission-related innovations and its implications for the electricity sector.
NEMA President & CEO Kevin J. Cosgriff
Possibly the biggest advancement in transmission technology is the resurgence of direct current for high-voltage transmission. So-called HVDC transmission projects are gaining traction globally—not just as a way to transmit electricity between the various asynchronous interconnections, but also to move power efficiently over long distances, from wind-rich parts of the country to the cities and towns where the electricity is needed.
According to one analysis, a 1200-mile HVDC line would be about 95% efficient, whereas a similar-length alternating current (AC) line would lose about 10% of transmitted power. It took 120 years, but it seems like Thomas Edison is ready to refight “the war of the currents” against Nikola Tesla.
HVDC transmission lines can move power efficiently, over land or under water, without some of the limitations of a long-distance alternating current line (e.g., capacitance and reactive power challenges with AC). They can also move power between different synchronized interconnections (e.g., between the Eastern, Western, Texas, and Quebec interconnections). These lines can be an economically break-even proposition around 350 miles because of their increased efficiency.
The other innovation in transmission lines is what is referred to as high-temperature, low-sag lines. Basically, these are reinforced transmission cables—called “conductors” in industry parlance—that can sometimes double the amount of electricity carried over a single transmission line. They can do this because the reinforcement—whether it is from steel or some composite material—allows the lines to sag less under high heat, which is normally the limiting factor in how much electricity a given line can safely carry.
By increasing the amount of electricity that a single transmission line can carry, high-temperature, low-sag lines can reduce the need for additional transmission lines and the associated land-use impacts (whether environmental or eminent domain) new transmission lines bring.
But when antiquated siting and permitting processes slow the time it takes to build a transmission line to ten years or more, we risk postponing or even foregoing many of the benefits provided by modern technologies. I will write more about the policy challenges facing the transmission sector in a future post—stay tuned.