Influence of forest fire particles on the breakdown characteristics of air gap

The frequent forest fires become a serious threat to the performance of transmission lines' external insulation. Gap breakdown in forest fire relates to many factors, such as flame temperature, conductivity and particles. Large quantities of smoke (carbon black) and flying ash are produced during the combustion of vegetation, causing the dielectric strength of gap to decrease drastically. In order to analyze the influence of forest fire particles on the breakdown characteristics of air gap, the experimental setup consisting of a conductor-plane was built to simulate the effect of forest fire particles. At the same time, a theoretical model was developed to analyze the influence mechanism of multiple particles on the discharge characteristics of gap. Experimental results show that, a chain of carbon particles has been formed between flame and conductor by the action of electric field. The gap's insulation strength decreases significantly, which is about 40% of that in the pure air under AC voltage. The particles movement and the breakdown characteristics of air gap have an evident effect of polarity characteristic under DC voltage and the breakdown voltage is reduced to about 29% of that in the air gap under negative DC voltage. The simulation results show that, the electric field distribution between conductor and plane become uneven, and the distortion degree of the elongated particle to the background electric field is not related to the distance between particles with high-voltage electrode. According to the electric field diagram, it is obvious that the particles make the background electric field distortion, and the maximum field strength increased by about 100%. More close to the conductor, the greater electric field strength is at the both ends of particles.