Project: San Pellegrino Pass
Location: Italian Alps
Company: TERNA
Cable type: 132 KV
TERNA, a large Italian operator in electricity transmission grids, invited Tratos to install a high load carrying, low sag conductor in the San Pellegrino Pass in the Alps, on the 132 KV Moena-Cencenighe overhead line. The installation process proved to be comparable with those of a traditional conductor of a similar size.
A report prepared by the OEM after of the installation said: “The installation of the line at high altitude (2,000 meters above sea level) is a severe test for the conductor: in fact, at low temperatures the mechanical load is transferred from the carbon core to aluminum alloy coats, determining a state of high stress for the latter.”
Very low ambient temperatures are detrimental to overhead lines because cable reduces in length increasing mechanical tension applied to the pylons (in really severe cases pylons can be damaged or even collapse). Expansion and contraction in the aluminium tension applied to this relatively fragile material (instead of high strength carbon), can lead to excessive permanent elongation or even wire breakage and, at low temperatures, ice can grow on the conductor, causing a considerable weight gain, dramatically raising tension within the conductor.
The solution was to increase the current carrying capacity – with a newly developed, non-traditional conductor whose mass is not very different from a traditional ACSR (Aluminium Conductor Steel Reinforced) type.
Innovative new materials were used, in particular an alloy with high conductivity, a maximum tensile strength comparable to pure aluminium and, more importantly, a maximum strength that remains unchanged at high temperatures. With this new alloy it is possible to build a replacement conductor with high thermal limits, working at temperatures not attainable with traditional counterparts.
New heat resistant materials combined with detailed attention to overall design resulted in the greatest increase in the conductors‘ current carrying capacity. These new conductors simply replace existing conventional steel reinforced counterparts in transmission lines using existing pylons and towers, with the added benefit of a reduction in sag.
The conductor operated successfully without problems for several years before it was carefully removed, examined and re-evaluated by TERNA. The results of this work showed no deterioration in the Tratos OHC-HV.