# 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
#### 5.5.7 Effect of Passive Measures (EM3-P1 and EM4-P2) for Wet Snow Scenarios  
Case EM4-P2 considers the reconductoring of some small section conductors. The OHLs with a 35 mm\({}^{2}\) section found to be critical in base case EM4 are upgraded: Their section areas pass from 35 mm\({}^{2}\) to 70 mm\({}^{2}\). This noticeably limits the failure probability of critical components (the highest failure probability is \(7.15\times 10^{-1}\)). The total LOL risk over 10 min passes from 1.33 expected lost MW in the base case to 0.72 expected lost MW in the present case. The construction of the new counterfeed in case EM3-P1 only slightly decreases the total LOL risk over the whole set of contingencies but significantly reduces the impact for a set of about 20 contingencies. Figure 12 shows the LOL impact of these contingencies before and after the application of this measure. The highest reduction of LOL is identified for the busbar contingencies affecting nodes 64 thru 90 along the feeder in Valsavarenche valley which also includes the terminals of the counterfeed i.e., nodes 48 and 91. On the contrary, high order N-k contingencies cause very large disruptions that the activation of a single counterfeed cannot reduce the LOL due to the contingency [37]. 5.8 Tree Fall Scenarios for T&D Grid: Base Case (EM5) and Application of Passive Measures (EM5-P1 and EM5-P2)  
In base case EM5, RELIEF identifies 7 critical lines, i.e., the lines more prone to fail due to tree contact. CORINE database [41] has been used to derive the data about tree coverage in the area. All of these critical lines are MV lines which are more affected than HV lines by tree contacts due to their smaller size. These MV lines all belong to the \"Val Savarenche\" feeder: The risk of tree fall in this zone is also reported in the resilience plan of DEVAL, the local DSO, [38] which proposes the construction of an underground cable to increase the resilience of the area. This good matching obtained using only standard design criteria for the lines and public data demonstrates the relatively low sensitivity of the model to the specific choice of parameters, provided that reasonable ranges of parameter values are considered. The set of most risky contingencies involving the critical lines includes N-1 branch outages, N-k common mode branch outages, and N-k busbar dependent contingencies which lead to a total LOL risk indicator of 0.508. Figure 13 reports the absolute contribution to the risk of load disruption for each contingency category. The largest contributions to the overall LOL risk are due from multiple common mode branch contingencies, also characterized by the largest median impact indicator (around 0.6 lost MW). Relatively low-order contingencies (e.g., N-2) can have high median LOL impacts due to the absence of a counterfeed which can take over the end section of the Val Savarenche feeder. This confirms the need for the underground cable explained in [38]. Case EM5-P1 simulates an enlargement of the ROW width by 30% with respect to standard TSO practices. This measure decreases the number of critical lines from 7 to 6; however, the failure probabilities of the critical lines decrease only by a relatively low amount, because the trees of the dominant species (i.e., larches) have a height up to 30 m and generally the ROW assigned to MV lines is relatively small (around 15-20 m). From Figure 13 it can be noticed that the total LOL risk passes from 0.508 to 0.358 expected lost MW's (30% reduction), of which the largest contributions are due to N-k common mode branch outages. In this case, a 30% enlargement is not sufficient if the trees outside the ROW are not properly trimmed [28]. To demonstrate the effect of trimming, case EM5-P2 assumes that the trimming policy changes in the utility: The ROW is kept the same as in the base case but a more frequent trimming is applied so that the expected height for trees just outside the ROW is kept at 10 m. This measure leads to the absence of critical lines.