# Quantification of the Benefits for Power System of Resilience Boosting Measures
## 5 Case Studies
### Grids Under Study and Simulation Cases  
The power grids where the methodology has been applied are:  
* GRID 1: A model of the Italian High Voltage (HV, 132/150 kV) and Extra-High Voltage (EHV, 230/400 kV) grid which includes 5500 electric nodes, 8000 lines, 800 generators [20]. * GRID 2: a combined T&D system consisting in two MV feeders connected to a portion of the surrounding HV/EHV transmission grid in Aosta Valley, specifically around HV/MV primary substation at Villeneuve, particularly critical in terms of operation and maintenance as it provides energy to a very large area (about 770 km\({}^{2}\)) [37; 38]. The model includes 92 MV electrical nodes, of which 60 nodes are MV/LV substations, 29 transit nodes in correspondence of line poles, and 3 MV nodes at Villeneuve HV/MV substation. The model includes three counterfeeds, 10 HV (132 kV) nodes, 8 EHV (220 kV) nodes, 20 OHLs, 6 generators and 3 EHV/HV transformers. The goals of the simulations are: 1. To validate the methodology in operational planning mode (OP) by proving its effectiveness in anticipating the set of most risky contingencies. 2. To carry out a sensitivity analysis in engineering mode (EM) accounting for various threat intensities and measures, with the goal of quantifying the benefits to resilience. 3. To calculate the return times of component outages in long term planning mode (PL), for specific characteristics of component vulnerability. The model to forecast the combined ice and wind loads accounts for four main exogenous variables i.e., the wind speed intensity and direction, the ambient temperature and the precipitation rate. The probabilistic vulnerability model of the OHLs in case of wet snow includes the vulnerability of phase conductors, shielding wires and tower equipment (e.g., bracings). The simulation scenarios focus on two threats: Wet snow events, and tree falls due to combined wind and snow loads. As far as wet snow events are concerned, the simulated scenarios are aimed to quantify the benefits of the following measures:  
* Active measures: Forecasting of contingencies under critical conditions, Generation redispatching in transmission system to assure minimum anti-icing current requirements; OPF based measure acting on generators setpoints and OLTC in distribution networks to assure minimum anti-icing current requirements; optimal reconfiguration of counterfeeds to restore full load at the best post-contingency operational conditions. * Passive measures: Anti-torsional devices; super-hydrophobic coatings, branch reconductoring, construction of new branches. All of the use modes of the resilience assessment tool are adopted in the case study. In particular:
* A real wet snow event affecting the North of Italy in February 2015 is analyzed in the operational planning mode. To this purpose, the tool is fed by the 72 h ahead forecast of weather variables, thus forecasting the riskiest contingencies affecting the area. * Wet snow events with different intensities are applied to the Central part of Italy in the engineering mode, considering different active and passive measures, characterized by different parameters. * The extreme value distributions provided by Std EN 50341-2-13 [39] for area 1 (North of Italy) are used in long term planning mode, with the aim of calculating the return periods (RPs) of OHL outages due to combined wind and wet snow loads in the portion of HV and EHV transmission grid in the GRID 2 model. Table 2 summarizes the simulation cases described in the study. In order to demonstrate the flexibility of the methodology to deal with different threats, some simulation cases in Table 2 refer to threats different from wet snow events, i.e., simulation cases EM5- * referring to tree fall due to wind and ice loadings, and case PL2 referring to pollution on component insulators.