What voltage defines the primary function of high-voltage transmission lines?

High-voltage transmission lines are primarily defined by their ability to efficiently transport electricity over long distances, minimizing energy losses due to resistance. This efficiency is achieved at higher voltage levels, which is why the threshold for what qualifies as high voltage is established at greater than 138,000 volts.

At this elevated voltage, transmission lines can carry large amounts of power with reduced line losses and allow for the interconnection of widely spaced generating plants, which is crucial for balancing supply and demand across large regions. Operating above this voltage level is vital for the stability and reliability of the electric grid, making it the standard benchmark for high-voltage transmission lines.