Ricerc@Sapienza

Temperature plays an important role on the failure rate of electrical cables and their joints as well as of any electrical components. In fact, Arrhenius Law (1889) states that temperature accelerates any chemical reaction and, therefore, it is evident that aging or a fast degradation of any insulating materials increases with temperatures. For this reason, the maximum operating temperature that can be accepted for the insulation of the extruded underground cables must be limited by controlling the transmitted current by proper relays (integrated in the switchgear). Anyway, the temperature of the insulation of the underground cables is the function of both the ambient temperature and the thermal resistivity of the ground, which must be carefully evaluated, case by case, at the time of the original installation. Anyway, during the hottest months of the year, both these parameters (ambient temperature and thermal resistivity of the ground) present their highest values and consequently it is possible that the cable insulation may reach higher temperatures than those received, with a faster degradation of the insulating Materials and, hence, an increase of failure rate. For this reason, the thermal current capacity of the cables installed in the distribution grids of modern Smart Grid can be optimized with on-line information on both ambient temperatures and load currents. Also, a more accurate control of the same parameters may lead to a reduction in the number of failures registered on these distribution cables. The purpose of this research project is to report a preliminary study which classifies failures of medium voltage underground cables and their joints in function of the estimated or measured ambient temperatures and other parameters. Also, some observations on the relationship between the failures of cables, ambient and cable temperatures and thermal resistivity of the ground will also be considered also by carrying out as an experimental campaign of measures.