Study on the dielectric characteristics of simulation transmission line gap under fire conditions

Abstract

The frequent forest fires become a serious threat to the performance of transmission lines' external insulation. Hence, the AC/DC breakdown characteristics study of the simulation transmission line gap in the flame conditions has an important meanning for the transmission lines' construction and safety operation. Gap breakdown in forest fire relates to many factors, such as flame temperature, conductivity and particles. Different vegetation's combustion characteristics determine that the discharge characteristics of the gap under the fire conditions are different. In order to research the breakdown characteristics of transmission lines gap under the vegetation flames (fir, straw and reed), the AC and DC breakdown characteristics tests were performed in a simulation test platform. Experimental results show that, the gap's insulation strength in the flames decreases significantly. As the gap is full bridged by the flame, the order of gap breakdown voltage under different vegetation is: fir branch<straw<reed<fir trunk. Under the fir branch fire, the AC breakdown voltage of gap is reduced to about 10% of that in the air gap, and which is reduced to about 20% under the fir trunk. Gap breakdown has an evident effect of polarity characteristic under DC voltage, and the breakdown voltage of positive polarity is smaller than that of negative polarity. When the conductor-plate gap is enveloped by the flame, the breakdown voltage has a linear changed trend with the gap distance under the vegetation flames. The AC breakdown voltage is slight lower than that of DC positive polarity voltage under the same test conditions.