From coast to coast, electricity travels via high-voltage transmission lines in order to supply power to our homes. The need for a high transmission voltage occurs when a large amount of power has to be transmitted over a long distance. In some parts of the U.S. grid, electricity is transmitted at up to 500,000 volts (500kV) or even 765,000 volts (765kV), which are considered “EHV,” or “extra-high-voltage.”

Why High Voltage

The primary reason electric utilities choose to transmit power at high voltages is to increase efficiency. As electricity is transmitted over long distances, there are inherent energy losses along the way.

High-voltage transmission minimizes the amount of power lost as electricity flows from one location to the next. How? The higher the voltage, the lower the current. The lower the current, the lower the resistance losses in the conductors. And when resistance losses are low, energy losses are also low. Electrical engineers consider factors such as the power being transmitted and the distance required for transmission when determining the optimal transmission voltage.

There is also an economic benefit associated with high-voltage transmission. A higher transmission voltage allows more power to be transferred for the same amount of current. This means power is transferred with less losses, yielding greater efficiency. Also, a higher-voltage transmission line could replace multiple transmission lines operated at a lower voltage. As a result, higher voltages lower construction and maintenance costs. These considerations make high-voltage transmission over long distances an economical solution.

High-Voltage Market Growth

The rapidly growing renewable and data center markets have played a large role in the increase in high-voltage substation and transmission line builds in recent years. Across the United States, the replacement and upgrade of the existing transmission infrastructures, as well as new capacity additions of generation and transmission, are key drivers for the high-voltage market.

Difference Between High-Voltage and Extra-High-Voltage (EHV)

“High-voltage” means equipment with nominal system voltages greater than or equal to 100kV and less than or equal to 230kV. Two common voltages in the electric utility space that would be considered “high-voltage,” then, would be 138kV and 230kV transmission lines and stations. In contrast, “extra-high-voltage" ranges from nominal system voltages greater than 230kV but less than 1,000kV. Common examples of EHV would thus be 345kV, 500kV, and 765kV transmission and substation systems.

According to the American National Standards Institute (ANSI), low- to ultra-high-voltage voltage ranges are defined as follows: ‍

• ‍Low Voltage (LV): ≤1,000 volts  

• Medium Voltage (MV): >1,000 volts and <100 kV

• High Voltage (HV): ≥100 kV and ≤230 kV

• Extra-High Voltage (EHV): >230 kV but <1,000 kV.

• Ultra-High Voltage (UHV):  ≥1,000 kV

Increased Growth of 765kV Transmission Projects

765kV is the highest voltage used in the U.S. grid. While not new (the first 765kV system came online in 1969), the U.S. began experiencing unprecedented growth in planned 765kV EHV projects since 2025, primarily in Texas (ERCOT), across the Southwest (SPP), and in the Midwest (MISO). Electric utilities and independent system operators are planning these 765kV projects to build a stronger backbone across their regions, opening up new pathways for power, increasing system reliability, and supporting new power interconnects and load growth.

According to electric utility American Electric Power (AEP), transmitting power at 765kV offers benefits beyond more typical EHV transmission systems, such as 345kV. Because one 765kV circuit can carry six times more power than a 345kV line, utilities can deliver more power with fewer lines, reducing right-of-way footprints, construction costs, and, ultimately, the impact on communities and the environment. 765kV transmission lines also experience half the transmission losses seen at lower voltage levels, capitalizing on the efficiencies of high-voltage transmission explained above.

About Beta Engineering

Beta Engineering is a substation EPC company headquartered in Pineville, LA., with an office in San Diego. Since 1975, we’ve helped utilities, renewable developers, and other power delivery companies across the U.S. complete high-voltage substation and transmission line projects. Contact our team to tap into 50+ years of problem-solving experience—and a proven commitment to safety. View our extensive portfolio of substation, switchyard, GIS, FACTS, and extra-high-voltage projects.