The report presents an analytical model of interphase spacers (IS), a passive measure to reduce the vulnerability of overhead line spans to wet snow and galloping, simulating the beneficial effects on phase conductors. Simulations show a significant increase of span failure return periods, especially adopting a combination of IS with anti-torsional devices.

Two optimal reconfiguration strategies are proposed to enhance distribution network resilience to N-k contingencies: they respectively solve a MILP problem to minimize load curtailment and a modified OPF including switches model. The former is less time consuming, but its accuracy depends on the effect of voltage limits and reactive power flows, while the latter is more accurate, incorporating all classical OPF constraints.

Moreover, the methodology for the identification of the optimal mix of measures for resilience enhancement is extended: it is customized for a new threat (indirect effects of strong wind) by adopting suitable vulnerability models for grid assets and by modeling new passive measures (maintenance of trees also outside the line right-of-way and the conversion of overhead lines into cables). Simulations on an IEEE test system confirm that the tree maintenance measure is suggested as it is more cost effective than the line conversion into cables, potentially competitive only considering jointly the two threats (wet snow and wind) and it is applied to the branches which assure the optimal cost-benefit tradeoff.

The efficiency of the method is improved by applying “memoization” to the simulation (avoiding repetition of already simulated code). The speedup factor on a simple system ranges from 11.4 to 41.7 times with respect to the version without memoization (with greater speedups for the cases with higher computation burdens). Also, the application of the Variable Neighborhood Descent (VND) technique further reduces the computation time with respect to the “memoize in simulation” approach and slightly improves the objective function values.

Finally, the optimal mix method is extended to consider the construction of new lines (resilience-oriented transmission grid expansion). Given the combinatorial complexity of this problem, a submodule selects the candidates of new lines as branches connecting substations with the lowest and highest values of a specific indicator (e.g. Expected Energy Not Served). The solutions of a test application still rely on anti-torsional devices and on tree maintenance practices, which are cheaper than building new (greenfield) lines.