Study on DC voltage breakdown characteristics of gap under fire conditions

Hill fire is a serious threat to the reliability of UHV DC transmission lines and security of power grids. So, it is very important to study the DC voltage breakdown characteristics and discharge mechanism of gap under fire conditions. However, there has been few researches on the DC gap voltage discharge characteristics under fire conditions at home or abroad. Gap breakdown in forest fire is related with flame temperature, conductivity and ashes and different vegetation's combustion characteristic result in the different influence degree of the three factors on triggering discharge, thus breakdown voltage has great diversity. This paper studied the flame characteristics of typical vegetation, DC voltage breakdown characteristics of wire-plate gap under different affecting factors using simulated forest fire, and then analyzed the gap breakdown mechanism in the forest fire conditions. Experimental results show that the gap's insulation strength in the flames is down to about 20% of pure air, and the gap breakdown in DC voltage has obvious polarity effect. © 2014 Chin. Soc. for Elec. Eng.