A hybrid pylon is a pylon which carries electric circuits for different types of current. In principle, hybrid pylons supply parallel guidance to the following types of electrical lines:
However, only the first pair listed above is relevant. To date, no parallel guidance of traction current lines and HVDC lines or three-phase alternating current lines and HVDC lines have been realized on the same pylon.
A hybrid pylon carries two electric circuits for traction current and two for three-phase alternating current. The lowest cross bars are for the traction current circuits, which are arranged in one level. The highest crossbars are used for the three-phase circuits and can be arranged in one, two, or three levels. To prevent excessive pylon height and width, an arrangement of three-phase circuits in two levels is usually used.
In Switzerland, hybrid pylons with three crossbars are used. One mast carries half of a three-phase system; the other two masts have traction current circuits. If the traction current line shares the pylon with a three-phase alternating current line operated by more than 220kV, the isolation of the traction current line must be designed for 220kV. Otherwise, over-voltages—which overtax an insulation for 110kV—can occur in some failure cases of the 380kV line along the traction current line.