Preliminary studies on flashovers of high-voltage transmission lines induced by wildfires by field survey and experimental tests

By the field survey of typical burned area and original forest area, geographical information of fire region, brief status of wildfire and flashover accidents were analyzed, the types and evolution process of potential wildfires, and the flashover mechanism of transmission lines were explored; by using single, double and three wood cribs and simulative single-core, double bundle and four bundle conductors, the discharge properties of high voltage transmission lines and their relationship with fire filed parameters under fire conditions on medium scale were experimentally explored. Results show wildfires easy to induce flashover are ground frres and crowning fires converted from ground fires with medium and high intensities and upswept propagation direction at a medium and high spread rate since ambient conditions prone to induce flashover are easier to establish with high flame height, high thermal output, high temperature and high concentration (smoke particles and electric mass points). Primary wildfire fuels are unspecified trees, weeds, pines and cedars. In experiments, conductors are easier to discharge in flames than in pure air (the average breakdown intensity in flames decreases by 64.9% of that in air); fire intensity shows determinative effect on average breakdown intensity, while fire duration, flame height and fire load density shows decreasing effect (when wood fire source changes from two cribs to three cribs the amplification of average breakdown intensity to fire intensity, fire load density, fire duration and flame height takes 2.11, 0.482, 1.70 and 0.582 respectively); corresponding three possible flashover mechanisms (or modes) are presented.