Pylons of Messina - Conductors

Conductors

Until 1971, the crossing consisted of a single 150 kV three-phase AC system. Four conductors, of which one was used as backup, were installed on the crossbar. In 1971 the voltage was increased to 220 kV and two additional conductors were installed at the bottom site of the V-shaped pinnacles. This gave the crossing a total transmission capacity of 300 MW.

As conductors for both systems single conductors consisting of steel and aluminium with a diameter of 27.8 mm were used. They had an aluminium cross section of 45 mm2 and a steel cross section of 305 mm2. The minimum height of the conductors over the Messina Strait was 70 metres, to allow large ships to pass safely below. This, together with the span of 3.646 kilometres (2.266 mi), required a tension force of 608 N/mm2 in the conductor cables. Antivibration ropes were used to damp oscillations.

By the early 1980s, the transmission capacity was no longer sufficient. It could not be increased by using bundle conductors or more conductive cables, as bundle conductors tend to have much greater wind-induced oscillations than single conductors, which can result in short circuits in the long span. Normal overhead lines use conducting cables with a larger aluminium portion but these do not have the tensile strength needed for the span. In 1985 a 380 kV three-phase AC submarine cable with a maximum transmission capacity of 1000 MW was laid across the Messina Strait.

The crossing was decommissioned in 1993 and the conductors were removed a year later.