# Quantification of the Benefits for Power System of Resilience Boosting Measures
## 3 Classification of Resilience Boosting Measures  
The key actionable measures mentioned in Section 2 and described in [12] characterize any power system: In fact, the adoption of defense plans to absorb the contingency impact, the upgrades of operating and maintenance procedures on the basis of past events, the scheduling of maintenance teams are only few examples of current practices of grid operators to face severe disruptive events. However, a resilient system should be capable to exploit these measures to achieve acceptable targets for the energy supply in case of extreme events. The corresponding capabilities of the system to deploy the previous key measures, i.e., the anticipative, absorptive, adaptive, and restorative capabilities, must be quantitatively assessed by means of suitable metrics, so that it becomes possible to set objectives, to establish suitable strategies and measure the improvements, thus providing a valuable support to the decision making process. A classification of the resilience boosting measures has been provided in [20] distinguishing:  
* Passive approaches, with the goal of enhancing the capability of the infrastructure to resist in case of threats, by limiting their impact via redundancies, component hardening and protective mechanisms or barriers. The first solution decreases the infrastructural vulnerability by introducing redundancies, e.g., by increasing the number of branches, thus improving the grid meshing. The other two measures decrease component vulnerability, avoiding that threats can damage the grid infrastructure: Some examples are the hardening of the lines, the maintenance of the rights of way (ROW) of the lines, the application of anti-torsional devices, the conversion of overhead lines into cables. * Active approaches, with the goal of minimizing disruptions, enhancing system absorption capacity and speeding up the restoration process. Smart solutions for active approaches are:
* The assessment, forecasting and mitigation of threats. * The scheduling of control actions which reduce component and system vulnerability. * The defense plans, aimed to limit degradation process (hence, load disconnections). The restoration procedures, which must be adapted to the specific situation of disruption and the subsequent restoration process. Passive approaches mainly refer to the design and the planning of components and of the grid; active ones refer to the design of smart protection and defense systems and of the actions which are to be taken during the operational planning and real time operation, which must be as \"tuned\" as much as possible on the actual situation in terms of threats and system condition. In this context, methodologies based on the risk concept like the one presented in Section 2.3 assume a fundamental role: they allow to quantify the occurrence of extreme events and their impact on the system, and to identify effective planning and operation solutions also in case of significant threats. It should be noted that in many cases the adoption of passive approaches, such as expanding the grid with new power lines, can be subject to considerable delays due to the timing of authorization processes. From this point of view, whenever possible, the adoption of approaches or solutions based on the strengthening of existing infrastructures or plants may be preferable. Moreover, low-cost \"operational\" active measures for resilience enhancement deserve attention, especially if compared to large investments for grid hardening. It is worth remarking the tight connection between CIGRE list of key actionable measures and the aforementioned classification of the resilience boosting measures. To this regard Table 1 reports some examples of mitigation measures in relation with the key actionable measures indicated in the CIGRE definition and the bow tie model. The same measures can be classified according to other criteria:  
1. The time horizon when the measures are applied. 2. The activation depending on the actual occurrence of the disturbance.