## 5 Calculations for Different Test Networks  
The first test network, which shows the effect of different line lengths, different line ages, and transformers on the reliability index, is the modified IEEE 118 test network. This network was modified to adapt it to the operating parameters of the European network. Therefore, the voltage levels were adjusted to 400 kV, 220 kV, and 110 kV. The cross sections and load capacities of the conductors were also adjusted. Additionally, the total load value in the network was adjusted to the value occurring in the Polish power system. The authors performed an analysis of the reliability results for a set of data for a period of 5 to 9 years. There are 158 110 kV lines in the IEEE 118 network. Based on the data obtained by the authors, as well as literature data and reports from the Polish Power Transmission and Distribution Society, the average number of failures was assumed to be at level 5. The average time of the month was also assumed to be 30 days. The average line lengths were taken from the test network. Then, the average annual failure rate was 1.41 failures per 100 km (9-year data) and 2.54 failures per 100 km (5-year data) using the relationship (5). The test network is also made up of 8 220 kV lines. For this voltage level, the average annual reliability rate was 0.92 failures per 100 km (9-year data). For the 5-year data, the failure rate was 1.32 per 100 km of line using the relationship (5). For the 400 kV lines, of which there are 11 in the test network, data from the literature [125] were used to determine the average number of failures, and the average number of failures was taken at level 3. Average line lengths were taken from the IEEE test network. Then the average annual failure rate was 0.54 failures per 100 km of line (9-year data). For the 5-year data, the reliability factor was 0.96 failures per 100 km of line using the relationship (5). For calculating the reliability factor of transmission lines, the relationship (6) can also be used, which can be used to calculate the reliability factor for transmission lines with the same voltage level. Using this relationship, the annual reliability factor for 110 kV lines is 1.1 failures per 100 km of line (9-year data), 1.94 failures per 100 km of line (5-year data), with an assumed average number of failures of 2. For 220 kV lines, the reliability factor is 0.74 failures per 100 km of line (9-year data). For the 5-year data, this factor is 1.32 failures per 100 km. At the 400 kV voltage level, the failure rate amounts to 0.26 failures per 100 km of line according to data accumulated over a nine-year period, and to 0.46 failures per 100 km of line based on data collected over a five-year period. The IEEE 118 test network examined also consists of 29 system transformers, which are made up of 9 220/110 kV transformers, 4 400/220 kV transformers, and 16 400/110 kV transformers. To determine their reliability coefficient, the authors used the obtained data, as well as the items in the literature [125], where the authors had precise data on the Polish power system. On this basis, the authors assumed an average number of failures of 0.12 failures per 100 units in the case of 400/110 kV transformers, 0.12 failures per 100 units in the case of 220/110 kV transformers, 0.1 failures per 100 kV transformers, and 100 damages in the case of 400/220 kV transformers. Since the damage indicators are small, in networks containing several hundred transformer units, the number of damages will be less than 1 or close to one; therefore, the calculations for one damage during the year are presented below as an example. According to the relationship (22), the reliability indicator for system transformers is 3.3 failures per 100 transformers during the year.