Transmission voltages are defined as any line with voltage greater than 39,000 volts or 39 kV. The metric abbreviation kV for kilovolts is commonly used when talking about transmission line voltages. Commonly used transmission voltages are 69 kV and 138 kV. There are also 44 kV, 115 kV, 161 kV, 169 kV, and 230 kV systems.
On large utility systems, there are bulk transmission and inter-connection circuits at 345 kV, 500 kV and more recently 765 kV. The use of UHV (ultra high voltage) lines is now being explored for equipment and lines rated for 1100 kV.