Research On Multi-field Coupled Dynamic Modeling Of Secondary Arcs With Half-wavelength Transmission Lines And Three-dimensional Image Reconstruction

The half-wavelength transmission line features high voltage level, long distance transmission, large power, thus it has the outstanding problem in terms of the secondary arc. An arc chain model was adopted to integrate the electromagnetic force, the thermal buoyancy, the wind load force and the air resistance as to establish the stress equations as well as dynamic model of the secondary arcs with half-wavelength transmission lines to aim to solve this problem. With extensive analysis of the arc formation and movement mechanisms, an arc root model was also given and a criterion for optimal length selection of the current element in simulation was proposed. The simulation results were compared with the experimental ones to verify the validity of the proposed models. The acting mechanism of the electromagnetic force, the thermal buoyancy and the wind load force on the secondary arcs was elucidated in terms of the arc trajectory and self-extinction time under different secondary current, wind speed and wind direction, which indicated that the proposed arc models can effectively count in the wind load effect on the arc motion and self-extinction characteristics. The secondary arc trajectory and self-extinction time regarding different initial arcing position were obtained based on simulation studies, which showed that initial arcing at the end of the electrodes presented long duration time and was difficult to be extinguished. The simulations also reproduced the jumping phenomenon of the upper root during arc moving to the end of the electrodes, which can reasonably justify the experimentally found case that the upper arc root position was relatively close to the arc column but behind the lower arc root.The specific location of the secondary arc as it appears cannot be determined in the process of the primary arc changed to the secondary arc due to the diameter of the primary arc is much greater than that of the secondary arc, and so the initial position of the secondary arc was random. A simulation model was established for the first time in order to solve this problem in this paper. Its principle was that the initial position of the secondary arc was related to the space electrical conductivity, the greater the conductivity was, the more easily to break down and form the secondary arc. The relationship between conductivity and temperature was calculated based on this understanding, and then the radial distribution of conductivity along the arc was also obtained under different primary current. On this basis, the initial arc length of randomness was calculated under different primary current. What’s more, the stochastic model of the initial position of the secondary arc was applied to the arc chain model and the decentralized arcing time was acquired for the first time, and then the simulation results were compared with the experimental ones. The results showed that, with increase of the primary current, the average length of the initial secondary arc and the arc length dispersion increased accordingly, also, the overall trend of the calculated arcing time coincided well with the experimental results with small relative errors, which verified effectiveness and reliability of the proposed model.The secondary arc motion was complex and diverse in the space, two-dimensional image was difficult to fully express all information of arc movement. The binocular stereo vision method was adopted to reconstruct arc images, and then more exact motion process and information could be acquired than 2D pictures, which would lay a good foundation for the later research work.