3.3.3.3 Lightning strikes to supply lines

For direct lightning strikes to an incoming line we have (Equation 3.3.3.3.1):

[equation](3.3.3.3.1)

Where N_L is the annual number of surges on the line section with a maximum value of at least 1 kV.

C_I is the installation factor of the supply line (Table 3.3.3.3.1) which takes into account whether an overhead line or a buried cable is concerned. If there is a high-voltage transmission line rather than a low-voltage transmission line within the area A_L, the transformer required in this case reduces the level of overvoltage at the point of entry into the structure. In such cases, this is taken into account by the line type factor C_T (Table 3.3.3.3.2). Finally, C_E is the environmental factor (Table 3.3.3.3.3) which defines the building density near the supply line and thus the probability of a lightning strike.

The collection area A_L for direct lightning strikes to the supply line (Figure 3) is calculated as per equation 3.3.3.3.2: