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| Fig. 1: U.S. Transmission and Distribution Losses as a Percentage of Total Electricity Use. [2] (Image Source: J. Martinez-Navarro). |
Electrical power transmission systems form the backbone of modern energy infrastructure, delivering electricity from power plants to homes, businesses, and industries. However, as power travels through transmission lines, some energy is inevitably lost through the following mechanisms:
Resistive Losses: As electricity flows through transmission lines, the inherent resistance of the conductor material causes energy to dissipate as heat. Aluminum is the primary conductor for power transmission due to its low cost and lightweight properties, despite having higher resistivity than materials like copper, silver, or gold. While using lower resistivity materials could theoretically reduce losses, aluminum's favorable cost-to-performance ratio makes it the practical choice for large-scale power transmission.
Corona Losses: Corona losses occur when the electric field around a high-voltage transmission line ionizes the surrounding air, allowing current to flow through the ionized air instead of the conductor, resulting in energy loss. This effect becomes more significant at higher voltages and under conditions like fog or rain, where the air's conductivity increases. The ionization leads to the formation of charged particles, dissipating energy as heat, sound, and light. To reduce corona losses, utilities often use conductors with larger diameters or bundled configurations to lower the electric field intensity and minimize current leakage into the air.
Capacitive Losses: Transmission lines create an electric field between themselves and the ground, acting as a capacitor. Alternating current (AC) constantly charges and discharges this parasitic capacitance, leading to energy losses. This effect is more pronounced in high-voltage lines, but it is minimized by elevating lines far above the ground and carefully spacing conductors to reduce their interaction with the Earth.
Inductive Losses: The alternating current flowing through transmission lines generates a magnetic field that interacts with nearby conductive materials, such as other lines or structures. This interaction induces unwanted currents or energy transfer, leading to losses. Proper line configuration, such as maintaining adequate spacing and optimizing conductor arrangements, reduces these magnetic interactions.
In 2022, California experienced transmission and distribution losses of 1.36x1010 kWh, accounting for 4.9% of the states total electricity consumption. [1] With a retail electricity price in 2022 of $0.2233/kWh, these losses equated to an economic impact of $3.0 billion. While this is substantial, transmission losses have significantly decreased over the years. As shown in Fig. 1, U.S. transmission and distribution losses as a percentage of total electricity consumed have steadily declined from 15% to 5% over a 70-year span. [2] The North American power grid has become increasingly efficient over time due to a series of technological and regulatory advancements. One key improvement was the increase in transmission line voltages, which reduced resistive losses by enabling long-distance power transport with lower current. In the 1950s and 1960s, the first development and implementation of computer systems allowed utilities to better monitor electricity supply, match demand, and minimize losses. Legislative efforts to prevent monopolies and foster competition in the electricity sector further incentivized utilities to adopt more efficient practices. More recently, the implementation of SMART grid technologies has enabled real-time monitoring and management of electricity flows, improving load distribution and reducing inefficiencies. Together, these advancements have enhanced grid stability, reduced energy losses, and ensured electricity is delivered more reliably and economically.
The U.S. power grid has achieved remarkable efficiency, with transmission and distribution losses falling below 5% in 2022. While further reductions in resistive losses could be achieved by using lower-resistivity materials like silver or copper, the costs would be prohibitively high, highlighting the trade-off between efficiency and feasibility. Engineering solutions such as line elevation, optimized spacing, and the use of high-voltage power lines already effectively mitigate inductive, capacitive, and resistive losses, with corona discharge being an unavoidable consequence of operating at such voltages. Without a revolutionary breakthrough in conductor materials, the efficiency of modern transmission systems is likely approaching an asymptote in the range of 4-5%.
© Joshua Martinez-Navarro. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "State Energy Consumption Estimates, 1960 Through 2022," U.S. Energy Information Administration, June 2024.
[2] "Monthly Energy Review, November 2024," U.S. Energy Information Administration, DOE/EIA-0035(2024/11), November 2024, Table 7.1.