The report presents the further research activities performed in the context of resilience assessment and enhancement, performed in the last year of the three-year research plan 2015-2017.

The increasing frequency of extreme events due to climate changes suggests the need for tools aimed to quantify the power system performance in the case of these disruptive events. Introducing the concept of “resilience” may help better quantify system behavior in case of multiple contingencies due to extreme weather events, with respect to conventional “security” criteria, like the N-1 criterion.

After recalling the main aspects of the RSE methodology for power system risk-based resilience assessment, this report focuses on a specific threat, the wet snow events, and it describes the integration of the abovementioned methodology with a short term weather forecasting system which provides the forecasts – over a time horizon of 72 hours – for the weather variables (wind magnitude and direction, temperature, precipitation rate) which most affect the wet snow events. This makes the relevant integrated tool extremely useful at an operational planning stage because it potentially allows the control center operators to identify the most critical components and the most risky (also multiple) contingencies, by exploiting the available weather forecasts. The case study, concerning a real wet snow event occurred in the North of Italy in recent years, demonstrates the applicability and the potential benefit of the proposed integrated tool for hazard analysis and risk-based resilience assessment and enhancement not only in anticipating the criticalities in the system but also in quantifying the benefit of specific grid upgrading measures (e.g. the ice-phobic coatings) in resilience enhancement.

Another important topic tackled in the present report is the improvement of resilience: the stakeholders, like TSO’s or DSO’s, are very interested in enhancing the resilience of their systems. To this purpose different measures can be deployed: the two main categories include “passive” measures of grid hardening or upgrading (e.g. conversion of overhead lines into cables, installation of anti-torsional devices on conductors) and “active” measures in operation or recovery phases to reduce the impact of a disturbance and/or to speed up the recovery process.

Given the huge variety of possible actions, the report proposes some classifications of these measures and it gives some examples of possible measures with reference to the “wet snow” threat. In particular, the report discusses different “active” and “passive” measures to counteract the effects of the “wet snow” threat and it focuses on one specific “active” measure, i.e. the preventive redispatching of conventional generation to assure a minimum current on the conductors, thus also a minimum temperature on the conductor surface in order to avoid the formation of wet snow sleeves.

The report proposes an advanced formulation for a security constrained redispatch (SC-R) problem with additional minimum current constraints on the critical branches exposed to a risk of “ice sleeves formation”. The SC-R is formulated as a Successive Mixed Integer Linear Programming (SMILP) problem: this technique solves a sequence of first-order approximations (i.e. linearizations) of the model, which consist in mixed integer linear programming problems, solved efficiently.

The relevant case study on an Italian Extra-High Voltage grid model demonstrates the effectiveness and identifies the potential limitations of this active measure.