## 2 Method  
The proposed approach is partly similar to contingency ranking methods based on the performance index. Using the Power Flow Performance index, the system state is determined by the total load of all lines after a fault. The state with a higher index is likely to be more severe. Our method uses data from the normal (pre-emergency) mode, which is the main advantage of our proposed method over existing approaches, i.e., it is sufficient to perform one simulation and then the elements (in our case transmission lines) can be ranked according to the proposed criteria afterwards. The highest ranked lines (higher than a predetermined threshold (%)) of three lists created based on three criteria are included in the combined list. The size of the combined list can vary depending on the predetermined threshold (%) and the number of appearances of identical lines on at least two different lists. The construction of an efficient and accurate list allows us to reduce the number of contingency simulations. This is important for the N-2 scenario, as the total number of N-k contingencies increases exponentially. Generators and transformers are not included in this ranking. The N-1 and/or N-2 contingency methods are usually used to check whether the electrical system (power or bulk system) can withstand unexpected/unplanned equipment disconnections/failures and maintain the electricity supply to consumers. We use N-1 or N-2 contingency criteria to check the pre-contingency list provided by the proposed method. Electric network operators themselves determine what load level is considered safe in the network or in individual power lines. In reference [29], the following load levels were considered acceptable: N-0 (50%) and N-1 (100%). Power transmission lines will be ranked according to three criteria. These criteria are as follows: transmission line capacity Sn, line flow, MVA, and the ratio between line flow and line capacity. Sn--design capacity of the power line, MVA. Though Sn partially determines whether the line is important for the electrical system, the design capacity of transmission lines and its importance do not always correlate/coincide. Some of the transmission lines may be spare or duplicate. There are also cases, such as those in Eastern Europe, where the capacity of the electricity network was designed with a large reserve and an expectation of significantly growing industry and consumption in the future. LF (line flow)--power flow in an electric transmission line, MVA. The main indicator that determines the importance of a line for the power system. The more flow through the transmission line, the more electricity flow will be redistributed when it is lost. The Ratio of LF/Sn. This ratio may seem to be a redundant criterion, but it also performs a function. The cumulative ratio level of power lines of the system determines the load level of the system. Also, by examining the electrical network, it was found that capacities of lines connected to the same busbar are usually the same; therefore, knowing the ratios of the lines, we can estimate future overloads on adjacent (neighboring) lines. Checking all possible failure/contingency combinations is a tedious process, so such calculations are mostly used to check the system capacity in long-term planning. If the real or explored system is not large (<100 elements), then both N-1 and N-2 can be tested by performing a full check even in daily or hourly modes. However, larger systems typically use expert knowledge to verify at least some of the N-2 instances. Table 2 shows the variation of the number of possible combinations when a brute-force search (checking all possible combinations) is used (for the N-2 case) and when 10%, 20%, and 30% of the system elements are taken into consideration, respectively. When only 10% of the lines are taken into consideration for the N-2 case, the calculation time (combination number) is reduced by about 100 times, when 20%--about 25 times, and when 30%--about 11 times.