High voltage power transmission lines transmit electric power over greater distances with as little distribution loss as possible. The live wires are not additionally isolated, but fixed to the pylons with isolators. Both three-phase alternating current and direct current (HVDC) can be used for transmission.
According to the voltage levels in the German power supply grid, power lines can be assigned to three different levels:
1) middle voltage level: 10 kV - 72.5 kV
2) high voltage level: 72.5 - 125 kV
3) extremely high voltage level: from 125 kV
However, this division is not unambiguous as all power lines from 1 kV are called high voltage power transmission lines with reference to the DIN EN 50110-1 norm. The term high voltage therefore comprises both the middle and the extremely high voltage level.