Abstract: In recent years, the risk of fire in forest grassland caused by power transmission and distribution lines in China is increasing. In order to explore the characteristics and mechanism of low-voltage overhead bare wire fire, a 380/220 V low-voltage line simulation experiment platform was built. Branches short-circuiting lines and two phase contact short circuit tests were carried out. The phenomenon of short-circuited melted marks often occurred in the close place between low voltage bare wire crossing forest area and trees was analyzed by the experiments and simulation. The results indicate that there were no spark discharges when normal twig and rain-soaked twig overlapped line. The temperature of the splash beads generated by the contact short-circuit discharge between two phase lines falling to the ground is low, which can not ignite the combustible material on the ground. Combined with the investigation results of low-voltage line fire causes in recent years, the line overcurrent protection plays a significant role in preventing low-voltage line fire. In strong wind and heavy rain, the twigs and leaves short-circuit two phase line, which may lead to short-circuit discharge and obvious melted marks on the wire. The research can provide technical reference for low-voltage line fire cause investigation and prevention.

Key words: low-voltage overhead power lines, forest fire, bare wire, fire investigation, transmission and distribution line fire