UHV
UHV turns up in 2 fields: electrotechnology, vacuum. Here is what it means to the people in each one.
UHV in electrotechnology
Ultra-high voltage, referring to transmission systems operating above 800 kilovolts.
UHV stands for ultra-high voltage. It classifies AC transmission lines operating at 800 kV or higher, and DC lines at plus or minus 800 kV or above. These extreme voltages are engineered to push massive amounts of bulk power over thousands of kilometers with minimal resistive losses. The equipment requires massive clearances and specialized insulation to prevent flashovers.
"We're reviewing the clearance requirements for the new UHV interconnector tower design."
UHV in vacuum
Ultra-high vacuum: pressures below about 10⁻⁷ mbar, reached only with baked, metal-sealed systems.
Ultra-high vacuum, taken as below 10⁻⁷ mbar, and in surface science usually below 10⁻⁹ mbar. At these pressures a freshly cleaned surface stays clean for hours instead of seconds, so UHV is the working range for surface analysis, particle accelerators and molecular beam epitaxy. Getting there demands CF metal seals, a bake-out at 150 to 250 °C, low-outgassing materials and capture pumps such as ion pumps and NEGs, and the residual gas ends up mostly hydrogen from the steel walls.
"System's been UHV for a month, low 10 to the minus eleven on the B-A, so nobody touch that gate valve."