Analysis And Measurement Of The Safety Distance On Unmanned Aerial Vehicle Inspection

Against the Background of the Increasing Scale of Power Grid,the unmanned aerial vehicle(UAV)Electric Power Patrol has incomparable advantages in many aspects,such as large scope of single patrol,low operation cost and high degree of autonomy.It will gradually replace the traditional electric power patrol mode in the future and become the preferred means of operation and maintenance of the national power grid.Among them,the safety and stability of UAV Patrol has always been the the links that people attach most importance to.On the one hand,UAV's stable flight in the process of power inspection is affected by the obstacles of power facilities,such as intricate transmission lines,insulators and shock hammers distributed between transmission lines and towers,which cause potential safety hazards for UAV's inter-phase flight and close-range photography;On the other hand,the electric and magnetic fields distributed around the high-voltage transmission facilitiescause electromagnetic interference to the remote control and signal transmission of UAV,adsorption on UAV airframe has great influence on UAV's stable flight.In order to ensure the safety of UAV patrol,a new method of visual ranging based on line feature matching is proposed in this paper.Firstly,the paper constructed a 500 kV and a 750 kV AC transmission line model and analyzed the attenuation of electric field intensity and magnetic field intensity at different distances in three directions,i.e.inner measurement,outer measurement and lower measurement of transmission lines under two voltage levels;designed a simple UAV model with wing frame and scaffold and analyzed the influence of UAV on the distribution of electric field and magnetic field around transmission lines.At last,combined with the UAV flight speed,signal transmission delay characteristics,wind speed and other factors to obtain the approximate safe flight distance of UAV in the environment of high voltage AC transmission line.In the image captured by UAV,the transmission line generally presents a linear feature with one or two pixel widths across the whole picture.Under the changeable natural background and illumination conditions,this feature will be masked by noise and complex background color caused by channel blockage,strong light and other factors,and cannot be effectively recognized,which makes visual ranging difficult.Through image preprocessing,edge detection,line detection and other steps,this paper roughly accurately locates the power line in the image.In this paper,we try to use gray histogram stretching to improve the contrast of transmission line features,and at the same time,we use bilateral filtering to remove a lot of noise and preserve the complete transmission line edge.In the edge detection link,we use ROA ratio edge detection algorithm,Ratio operator generally chooses the horizontal direction to calculate and compare the average gray level of the pixels,while the horizontal distribution of the transmission line across the whole image makes the algorithm have certain advantages in this application scenario..Based on the principle of binocular ranging,a method of image matching based on line feature continuity is proposed in the process of image matching,which avoids the cumbersome calculation of traversing the whole picture by traditional matching algorithm.According to the polar geometry constraint,the matching points of binocular image are quickly found,disparity is calculated and distance is obtained.Finally,around the core argument of unmanned aerial vehicle patrol flight distance,design experiments: we used the Phantom 4 Four-rotor unmanned aerial vehicle to collect relevant images on a section of the transmission line of Binhe East Road in Taiyuan City;and then carried outthe distance measurement through the proposed ranging process,and compared with the actual mileage measured in advance.The experimental results show that the proposed ranging method can be more accurate and accurate.The distance measurement method proposed in this paper can accurately determine the distance between UAV and transmission line,and provide certain guarantee for UAV Power Patrol flight safety.