EhV

Extremely high voltage (EHV) refers to a class of electric power transmission voltages that exceed conventional high-voltage levels used for distribution. In practice, EHV covers transmission voltages starting around 230 kV and extending into hundreds of kilovolts for long-distance service. In some contexts the term extra high voltage is used interchangeably, with ultra high voltage (UHV) reserved for voltages at or above about 1000 kV.

Systems at EHV are designed to move large amounts of electrical power over long distances with lower line losses and increased capacity, enabling interconnections between regional grids and the integration of distant generation. EHV networks may include 345 kV, 400 kV, 500 kV, and 765 kV lines, with 800 kV and higher still used in some regions; actual standards vary by country.

Key equipment comprises high-voltage transformers, circuit breakers, switchgear (including gas-insulated switchgear in some installations), conductors, insulators, and transmission towers. Insulation coordination, corona control, and thermal management are critical at EHV, and substations require robust protection, monitoring, and reliability practices. Transmission planning often involves reactive power management and voltage control.

Because of their operating voltages and power levels, EHV systems may employ HVDC links for grid convergence, improved controllability, or asynchronous interconnection. Maintaining transmission reliability at EHV levels also entails strict clearances, right-of-way considerations, and environmental protection.