Assessing the vulnerability of overhead line wires to flashovers due to reduced insulation distances for power system resilience studies

An accurate assessment of the vulnerability of power system components is a key pillar for long term resilience assessment studies and it helps prioritize the grid reinforcement interventions on the grid assets. Historical failure records indicate that neglecting the flashovers due to reduced insulation distances under specific conditions (wind-induced oscillations and increased sags) may affect the accuracy in the assessment of the overhead line vulnerability to threats, especially in presence of augmented sags due to vertical loads (wet snow). The paper proposes an analytical model to quantify the vulnerability of Overhead Lines (OHL) to flashover induced by reduced insulation distances, due to the combination of wire swinging conditions and moderate vertical loads. The model evaluates the conditional probability of OHL span flashover when subject to a specific vertical load, accounting for both geometric aspects (XYZ positions of the attachment points of the OHL wires) and electrical aspects (dependence of the dielectric distance on weather and orographic conditions). Tests on a set of lines in an area of the Italian transmission grid with frequent fault records due to such phenomena demonstrate the ability of the model to identify the most exposed lines and its good robustness to cope with uncertainties in the positions of the attachment points.