The standard recommends calculating earth resistance, potential rise (GPR), and voltage gradients using accepted methods (e.g., IEEE 80‑style substation earthing analysis).
For example, at 245 kV rated voltage, the minimum phase-to-earth clearance in air for a lightning impulse withstand of 1050 kV is typically 2.1 m (under standard conditions). iec 61936-1:2021