Analysis of hourly interruption distribution: the case of the Milan’s medium and low voltage grid

Comparative analyses between medium voltage (MV) and low voltage (LV) networks are rarely found in the literature, and it remains unclear whether these networks share common features or diverge entirely. This paper focuses on the MV and LV grids of Milan, operated by the distribution system operator (DSO) Unareti, from which the analyzed data are sourced. The interruptions analyzed in this study come from interruption logs that have been appropriately filtered; every DSO in Italy is required to record these logs according to the regulations imposed by ARERA, the national authority. The study compares the hourly distribution of interruptions in 2013 and 2023, first considering the entire year and then dividing results into summer and off-summer periods. The comparative analysis reveals that the LV network maintains a stable daily interruption pattern, closely linked to user consumption habits and unaffected by seasonal changes, while the MV network exhibits evolving interruption profiles, with increased events during early mornings and evenings, especially in summer, indicating latent insulation degradation rather than load-driven faults. These findings suggest the need for differentiated asset management and predictive maintenance approaches for the two networks. The work provides new insights for improving urban grid resilience and guides future measurement campaigns to further characterize network behavior.