"I" as in Ice sleeves

Ice sleeves are tubes of ice created due to wet snow - snowflakes with high water content. This type of snow can be found in various geographic areas, from northern Europe to the United States to Japan, at temperatures near freezing and with low wind speed.

When the wind blows, wet snow may stick to the conductor, the wire through which electricity passes, causing it to rotate. As the snow solidifies, it creates the ice sleeve. This mechanism can lead to the formation of a coating of frozen snow up to 10 times the diameter of the conductor. The weight borne by the span, the electrical wire which connects two pylons, can be significantly increased by even thousands of kilos, in extreme cases leading to damage to the conductors, shield wires and supports.

Power lines are built after taking into account numerous factors and loads which will act upon the support, including wind, snow and temperature effects. When an ice sleeve is formed, conductors may be lowered which reduces the insulation distance separating them from surrounding land and vegetation to below the minimum clearance. In these cases, Terna technicians must carry out on-site inspections of the line to determine whether conditions are safe for people and infrastructure before it begins operating again. If needed, they work to remove the ice sleeves from the conductors or shield wires.

Conductors vary in diameter and type based on the current transmitted. In 132 and 150 kilovolt high-voltage networks conductors have diameters which range from 13 to 31.5 millimetres. If overloaded by the ice sleeves, a conductor may break, requiring technicians to physically visit the line to repair it. Shield wires can also be damaged by ice sleeves. A shield wire is found at the top of the supports and does not transmit energy but protects conductor wires from lightning.

In extreme cases, the ice sleeves can be so heavy that they damage the support, even breaking major parts such as the brackets, the highest part of the pylon. When this occurs, Terna technicians must travel to the pylon and rebuild it.