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Breaking out of fire in the power line protection area will endanger the electric transmission line, so fire prevention is one of the important contents in the daily maintenance of the transmission line. This paper put forward a method to assess the risk of line caused by fire. The method evaluates the fire hazards by a mathematical model, which providing the reference to eliminate the hidden danger. Through the concise data, the investigation scope will be reduced and the quality of special patrol will be improved. Introduction The energy distribution in China is unbalanced, so it demands to develop EHV and UHV transmission line, which can transmit the power to the load center from remote places with less energy loss. Because the transmission line corridor is insufficient, many lines go over the lush mountains. It is possible to cause a fire disaster when the weather is dry, which may make a trip and bring great difficulties to us. There are a lot of assessment methods for natural disasters at present, but the assessment method of fire risk to the transmission line is still need to be improved. Through the risk assessment, we can not only distinguish the hidden danger clearly, but also reduce the scope of the investigation and improve the quality of inspection. Influence of Fire on Transmission Line There is a large scale of transmission line currently, whose DC voltage level is as high as ±800kV while AC voltage level is 1000kV. The impact of line trip on the grid is increasing while the voltage level gets higher. When the fire disaster occurs in the line protection area, the external insulation strength of the transmission line is reduced, and the breakdown voltage becomes lower. The reduced insulation strength will have serious risks to the grid. Domestic scholars have made high voltage test and found that when the fire occurred below the line, the phase voltage and the line voltage will not change, while the nature of the surrounding air, such as density, temperature, humidity, charged particles, will change[1,2]. Firstly, the fire causes the temperature of the surrounding gas to rise, which will reduce the density of the air; secondly, the upper smoke will bring a lot of charged particles around the lines and distort the electric field[3]. The factors above will reduce the insulation strength and breakdown voltage. What’s more, the interphase short circuit or short circle to earth caused by the fire disaster will last long time and the closure can hardly reclose, leading to serious consequences. The Common Hidden Danger Dry weather, fuel and source of ignition are three necessary conditions for the occurrence of fire disaster. There are some climate conditions apt to fire such as drought, high temperature, and strong wind. The long term drought and high temperature weather will promote evaporation, so that the dry branches and fallen leaves on the ground will loss water and become easy to ignite. The wind can accelerate the evaporation of water and promote the spread of the fire.

An Idea of Fire Risk Assessment for Electric Transmission Lines