The report deals with the characterisation of high temperature low sag (HTLS) conductors with cores in carbon (ACCM) and aramid yarns (ACFR) in relation to creeping and high mechanical loads (such as those associated with snow and ice overloads to which overhead lines are increasingly subjected).

The topic is addressed starting from the results of the mechanical/thermal characterisations of the above-mentioned conductors and continues that which was dealt with in the previous System Research period in connection with the European Best Paths Project.

In particular, the above-mentioned characterisations were carried out according to the test protocol developed with Terna in the framework of System Research, which allows for estimating the extent of the elongations that the conductor will undergo over its life, both with reference to the mechanical loads in EDS (Every Day Stress), or creeping, and with reference to very high mechanical loads (50% of the maximum load, applied before/pre-stress, or after creeping, post-stress), which can occur in particularly adverse environmental conditions.

Creep tests were also carried out both at room temperature and at average operating temperature.

The results were also correlated with similar results obtained in previous System research activities on traditional conductors (ACSR, AAAC) and HTLS (TACIR), which, however, were completely made of metal.

For the above-mentioned conductors, the test process revealed an invariance of the elongation in relation to the phases when high loads were applied: the overall elongation was the same for the pre-stressed and post-stressed samples.

The overall elongation values of the carbon core conductor were practically the same for the two samples (even at operating temperatures), which demonstrates the applicability of the adopted measurement procedure to this type of conductor. Furthermore, the overall elongation values are completely comparable with those of traditional conductors.

For the aramid yarn core conductor, the invariance of the elongation with respect to the load application phases was less evident and above all, the overall elongation (in particular with reference to the test at operating temperature) was particularly high.

The report also details the international regulatory framework (IEC TC7 and IEC TC11) on high-temperature conductors and, in particular, composite core conductors; in this activity, RSE, TERNA and the main Italian manufacturers of conductors and terminal blocks are at the forefront.

Finally, the report addresses the issue of monitoring snow and ice overloads on overhead lines using sensors that can be interfaced with IoT networks by detecting the angle of inclination and torsion of the conductor in the presence of ice sleeves on the span.