Shielding failure flashover rate under conditions of complex landscapes in mountainous areas

Based on the field investigation, a new Monte-Carlo method, combined with the improved Electro-geometric model (EGM), which can properly reflect the characteristic of random processes with good precision is developed to calculate the lightning flashover rate of transmission lines. Using this calculation system, this paper studied the influences of different landscapes in mountainous area, such as mountain peak, hollow, slope, ditch, etc., on the shielding failure flashover rates (SFFOR) of transmission lines. The decrease of the shielding effects of ground is the main reason of the SFFOR increase. As the increase of the ditch depth and the tower height, the SFFOR increases significantly. The same phenomenon appears when the slope gradient is larger than 20°. Ditch under lines often is ignored in the previous design. But according to the research result, it will apparently influence the ground shielding effect, and therefore lead to shielding failure flashover. This research is helpful for the design, reconstruction and operation of transmission lines.