Hybrid pylon

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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:

• Three-phase alternating current and traction current
• HVDC and three-phase alternating current
• HVDC line and traction current

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.^{[citation needed]}

[edit] Construction

A hybrid pylon carries two electric circuits for traction current and two for three-phase alternating current.^{[citation needed]} 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.^{[citation needed]} 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.^{[citation needed]}