# Method for Calculating of Lightning Impact Level on Overhead Transmission Line
## 4 Discussion  
Let us try to estimate a possible range of the buffer area of the selected power lines according to the models of estimate flash incidence to a line overground ([PERSON] [17], [PERSON] and [PERSON] [18], [PERSON] [19], [PERSON] [20]). Now, all models of the estimated flash incidence to a power line are based on Ground Flash Density \(N_{g}\). Only some coefficients in structurally similar equations are different:  
\[N_{l}=\frac{N_{g}}{10}.(b+D\cdot h^{x})\cdot\frac{L}{100} \tag{10}\]  
where \(N_{l}\) is the number of strokes to a line; \(N_{g}\) is ground flash density, 1 km\({}^{-2}\) year\({}^{-1}\); \(b\) is the overhead ground wire separation distance, m; \(D\) and \(x\) are empirical parameters given in Table 3; \(h\) is the height of the power line tower or average conductor height for various cases, m; \(L\) is the line length, km. If you use \"The Electrical Installation Rules\" to estimate, then \(N_{g}\) depends on the number of thunderstorm hours, which for \"North\" power lines has a vague value of \"less than 10\" and for \"South\" power lines a little more specific \"10 to 20\". However, a map of lightning density in the Murmansk region for the last 5 years has already been drawn (Figure 3), so it would be logical to use it. Using a map based on cells with a defined area, you need to divide the overhead line into sections lying in each of these cells. Then for each site, you need to calculate and summarize the results. The results of the estimated flash incidence to a power line according to the aforementioned models are shown in Table 4.  
On average, over the last 5 years, the actual number of strikes to the \"North\" overhead line obtained with these models corresponds to a buffer area range of 350 to 400 m. For the \"South\" overhead line under the same conditions, the buffer area range is 200 to 310 m. Therefore, the predictive model should be used with caution, as it is assumed that in an ideal model, the widths of the overhead line corridors should be approximately equal. Each of the mentioned models is based on the average annual lightning density per one km\({}^{2}\), which is almost impossible to predict, and only statistical historical data are used. In this context, the problem of the northern regions, including the Murmansk region, is the rarity of thunderstorms. For example, a single thunderstorm of 3-4 h duration can leave a strong trace on the annual average lightning density map for several years, while in areas with high thunderstorm intensity, such phenomena are smoothed out or completely absent. One such case can be seen in the 5-years map in Figure 3, where a thunderstorm that occurred on 7 June 2019 from 20:00 to 23:59 UTC was permanently stored in cells \(n\in\) (80, 100) and E \(\in\) (280, 360). In addition, it would be interesting to apply the method to overhead lines located in southern latitudes with high thunderstorm intensity. However, it was only possible \begin{table}
\begin{tabular}{c c c} \hline \hline
**Model** & **North Power Line** & **South Power Line** \\ \hline [PERSON] [17] & 0.821 & 3.706 \\ [PERSON] [19] & 1.170 & 4.594 \\ [PERSON] [20] & 1.345 & 5.456 \\ [PERSON] and [PERSON] [18] & 0.946 & 3.613 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The estimated flash incidence to a power line according to different models. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Model** & **\(D\)** & \(x\) \\ \hline [PERSON] [17] & 4 & 1.09 \\ [PERSON] [19] & 38 & 0.45 \\ [PERSON] [20] & 28 & 0.6 \\ [PERSON] and [PERSON] [18] & 45.2 & 0.32 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: \(D\) and \(x\) parameters from Equation (10) for different models. to obtain a set of OHTL data for the Murmansk region. In general, the openness and availability of data to engineers and scientists around the world can spur the qualitative development of electrical systems.