"That time we repaired a power line at 8,000 feet in the snowy Dolomites"

Winter, when it comes to electrical infrastructure, is one of the most critical times. The bad weather and cold temperatures put a real strain on all the elements that guarantee the normal operation of the electricity network, despite the precautions and measures taken. Power lines are built taking into account the many factors and loads that will act on the structures in certain locations and weather conditions, but excluding all risks is impossible.

For conductors, shield wires and supports, the biggest threat is: snow. In mountain areas, snow, in addition to being a constant winter condition, can become a major problem when it comes to pylons and electricity. Snowfall is the source of "sleeves", cylinders of ice caused by wet snow (i.e. with a high content of liquid water in the flake) that can reach dimensions of up to ten times the diameter of the conductor. They form when snowfalls are at temperatures close to zero and the wind is low. As a result of the latter, wet snow is able to adhere the conductor - the wire which electricity flows along- causing it to rotate as it gradually solidifies, this is how the sleeve effect is created.

This casing of frozen snow can become so heavy (even thousands of pounds) that it weighs down the span, i.e., the electrical wire that joins two pylons together. Overload results in damage to conductors, shield wires and supports, up to and including the rupture of entire parts of the pylon. In addition, when the sleeve is formed, the conductors can sag, reducing the insulation distance which separates them from the ground and surrounding vegetation. In all these cases, Terna's technicians must inspect the line on site and repair the damaged parts, also ascertaining the safety conditions for people and infrastructures in the field, before the line returns to service.

A procedure to be carried out even in impervious areas, such as under the Three Peaks of Lavaredo. It is precisely there that on 11 December 2020, a team of six technical power line operators flew in by helicopter for a special maintenance operation on the Dobbiaco-Somprade power line. 8,000 feet above sea level, a temperature of minus 15 degrees celsius and a height of 82 feet: these are the conditions in which Terna's technicians had to repair the bracket of a pylon bent by the accumulated weight of the ice sleeves.

It was the 8 December when the control room in Scorzè (Venice) received a report on the Dobbiaco-Somprade power line. In the previous days several snowstorms had affected the area of Trentino-Alto Adige as far as Friuli-Venezia Giulia, as well as the province of Belluno and the Alpine area. Given the forecasts of bad weather, the Vittorio Veneto Plant Unit had already been pre-alerted to ensure maximum operativity; Terna's helicopters were ready to lend a hand in the inspections. Specifically, the report indicated a problem on the power line. In spite of the protections - which basically try to restore power automatically - it did not come back into operation: a "power failure"was therefore declared.

From the type of information received from the control centre, it can be seen what the type of fault is. In this case, a phase-to-ground contact may give rise to various scenarios: a conductor-support contact, the conductor falling to the ground or a tree falling on the high voltage wires. However, operators, by studying the distances indicated, can make a more educated guess and discard some faults a priori. Since the area is that of the Three Peaks of Lavaredo, where there are not many trees, the most likely hypothesis was that a bracket had bent or that the conductor had fallen.

Normally, the procedure involves a site inspection to see the extent of the problem, either on foot or by helicopter. But the weather conditions made this prohibitive, in both cases: the ongoing snowstorms were such that the safety of the operators could not be guaranteed. With the bad weather it was in fact almost impossible to fly with the helicopter; on the ground, instead, there were about three meters of snow to prevent the power line from reached on foot.

Two days passed before the snow let up enough to inspect the site. On 10 December, thanks to the helicopter, the operators managed to get out and verified that on post 39, near the Peaks, there was indeed a problem: one of the brackets was deformed and by bending no longer guaranteed the safety distance between the various conductors. The protectors had acted promptly and no one was in the dark, but the line needed to be repaired as soon as possible. Having identified the point and type of failure, at this point it was possible to plan the operation putting safety first and analysing every risk, detail and problem.

As expected, it was impossible to reach the site. The only way to get to the peaks was to transport the technicians and material by helicopter, but the problem of fresh snow remained. For this reason, two local experts also came to the aid of Terna's technicians: a mountain guide and a mountain rescue worker. They would be flown in by helicopter along with the team in order to prepare the landing pad and route to the power line. Moreover, while waiting for works to be completed, the two experts would open a path to reach the Auronzo refuge, not far from the pylon. In the case of fog, at least, it would be possible for the operators to follow their tracks and get their bearings.

Another major issue was in fact timing. The period of good weather in which to carry out the operation was unfortunately very limited; the weather forecasts spoke of a few hours, from 9am to 2pm. The risk was that the men would be stuck there, with no chance of being rescued by the helicopter, if the fog came in or the weather worsened. Plan B was therefore to provide sleeping bags and food for the operators, so that they could stay at the Auronzo refuge for a couple of days (until the weather cleared up): a necessary solution to safely tackle the night. The instructions were, in any case, to return to base immediately, by air, in the event that the conditions were not safe to operate; people always come first.

This time there were six Terna employees and, despite the difficulties, they managed to complete the "mission" without any hiccups,in just one and a half hours. In practice, the operation consisted of locking the bracket to the main body of the post. To do so, the operators had to climb the post (82 feet high) in snowy and icy conditions using double belts. Actually, 82 feet is not that high for these experts: however, with nine feet of fresh snow below and the post completely enveloped in ice, neither climbing or tightening a screw or bolt is as easy it sounds, at minus 15 degrees celsius.

Three men climbed up the pylon and three remained on the ground, to help with the parts and coordinate operations. The aim was to make as few moves as possible, to reduce the risk of slipping; fewer people would take longer, but there wasn't enough time. Speed was of the essence, for operation of the grid, but also as regards safety. In fact, if bad weather came on, it would not have been easy to get down. The bracket was pushed out and secured to the pylon, to ensure that the system would operate until late winter, before final replacement. Operations at heights are rarely standard, ad hoc solutions are needed. The operating instructions are well thought out, but in the event of a failure one often has to "improvise" and evaluate on the spot, always in absolute safety.

Terna, from this point of view, ensures quite lengthy training at its training camps: operators train on all fronts, from how to put on the belts, to climbing up and down the post, and the operations to be carried out on the supports, once up the post. Over the years there are refresher sessions, because protective devices and procedures change. Each operation is in fact a chance to improve, to see if the available means are suitable and increase operators’ confidence and safety. Again, as always, people come first.