Simulative Experimental And Numerical Study Of Wildfire Induced Breakdown Of Transmission Lines

The high voltage transmission lines are the lifelines of the power grid and connect closely with the national economy and people’s livelihood. In recent years, more and more transmission line breakdown events caused by wildfires have appeared in our country, which lead to great losses. In order to control and prevent this kind of hazards effectively, it is required the in-depth understanding of wildfire induced breakdown process of transmission lines and the factors which affecting this process.Because of the complexity of vegetation combustion process, the mechanism involved in wildfire induced breakdown process of transmission lines is very complicated. At present, there are many different, even conflicting, viewpoints on this mechanism. Summarily, there are three models to explain the breakdown mechanism in the literature, that is, the reduced air density model, particle-initiated flashover model and flame conductivity model. This paper tries to study the breakdown process by theoretical analysis, simulative experiments and numerical simulation. The main contents are as follows:1. Theoretical mechanism analysis of wildfire induced breakdown of transmission lines;2、Simulative experimental study on fire caused breakdown of transmission lines;3、Numerical simulation of transmission line breakdown.This paper has investigated the influential mechanism of high temperature and charged particles produced by flame on the electric field distribution of discharge channel which eventually initiates the breakdown of high voltage transmission lines. Firstly, it was explained theoretically that the effect of flame temperature on relative air density and the relative dielectric constant in discharge process, the effect of charged particles on electric field distribution of the channel and the effect of increasing conductivity to promote the development of the discharge process. Secondly, N-heptane and wood cribs were used as experimental fire sources. A series of DC high voltage breakdown experiments were carried out by testing the breakdown voltages of the electrodes arranged in different regions of flames with different spacing distances. The experimental results verified the high temperature flame and a large number of charged particles reduce the breakdown voltage remarkably. By using the numerical simulation method, the electric field intensity along the discharge channel in the presence of the charged particles were calculated. The influence of space charge density on the electrode surficial electric field was analyzed. The results showed that the space charged particle density affected the space electric field strength and its variation.Through the above theoretical analysis, experimental and simulation study, this paper describes the micro mechanism of the discharge process of wildfire induced breakdown in a certain extent. The effects of high temperature and charged particles on breakdown voltage and electric field intensity on the occurrence of the breakdown discharge phenomenon are examined. The research is of certain significance for the recognition of induced breakdown phenomenon and the prevention from this kind of hazards.