# Quantification of the Benefits for Power System of Resilience Boosting Measures
## 5 Case Studies
### Quantifying the Benefits of Passive and Active Measures in Engineering Mode
#### 5.5.4 Effect of Generation Redispatching (EM1-A, EM2-A Cases)  
Generation redispatching may represent an interesting active measure to enhance the power system resilience to wet snow by assuring a minimum anti-icing current on 230/400 kV lines. However, it may be less effective on 132 kV lines because 132 kV grids are usually operated with few generators and the sensitivity on HV line power flows of generators belonging to the EHV grid is largely limited by the impedance of EHV/HV transformers. Table 5 has showed that all the most critical lines are 132 kV lines in cases EM1 and EM2. However, some 220 and 400 kV lines have a not negligible failure probability due to wet snow sleeve formation. In this case, the minimum current constraints refer only to the 230/400 kV lines which show failure probabilities higher than 5% in base cases EM1 and EM2: Even if their failure probabilities are relatively low, the loss of these lines generally determine very larger variations of power flows with respect to 132 kV lines.  
For 132 kV lines, other measures like coatings can effectively reduce the risk of outage, as reported in the previous subsections; accordingly, an effective increase of power system resilience can be obtained by combining two or more measures.  
In case EM1-A (severe storm and redispatching), if one assumes a penalization factor for grid losses [29] equal to 10, simulations indicate a redispatched power equal to 8675 MW and an overall redispatching cost equal to \(9.10\times 10^{5}\) arbitrary monetary units (a.m.u.). This large cost is in a few hours is explained by the large social, economic impact that these events would have. Table 7 reports the initial, final currents and the anti-icing requirements on the critical lines for cases EM1-A and EM2-A. The current of line MONR-VLR reaches 467 A, superior to the alarm level set at the TSO control center, i.e., 70% of the minimum anti-icing current (70% \(\times\) 582 A = 407.4 A). If one considers line PRVR-SGIR connecting PRVR power plant to the rest of 220 kV grid, the maximum active power generation of the unit (50 MW) is not sufficient to attain the minimum anti-icing requirement in cases EM1-A and EM2-A. This represents an intrinsic limit of the measure: It is often ineffective in case of branches which connect single power plants (or load centers) to the rest of the grid.  
In presence of moderate wet snow events (case EM2-A) the two affected 220 kV lines are near PRVR power plant and the minimum anti-icing current for both is 300.1 A, higher than the initial currents in the base case, but smaller than the anti-icing requirements for severe events.  
These results are obtained with a total redispatched generation equal to 1837.2 MW and a total cost of \(1.92\times 10^{5}\) a.m.u.: The measure effectively prevents wet snow sleeves from accreting on line PR2R - SGIR in moderate events (EM2-A).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{2}{c}{**Severe Storm—EM1-A**} \\ \hline Branch ID & Initial Current, A & Final Current, A & Anti-Icing Current Requirement, A \\ \hline VLVR-TERR & 345 & 920.7 & 1990 \\ MONR-VLR & 89 & 467.9 & 582 \\ PRVR-SGIR & 54 & 144.5 & 663 \\ \hline \multicolumn{4}{c}{**Moderate Storm—EM2-A**} \\ \hline Branch ID & Initial Current, A & Final Current, A & Anti-Icing Current Requirement, A \\ \hline PR2R-SGIR & 38 & 301.1 & 300.1 \\ PRVR-SGIR & 54 & 132.0 & 300.1 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Initial, final, anti-icing currents for the critical branches—EM1-A and EM2-A cases.