| As the voltage level of transmission lines rises in our country, the selection of energy-saving wires、the electromagnetic environment of bundled conductor and the design of lightning protection are attached more and more importance to engineering designers. However, when the mechanical characteristic of wire is drawn by SLCAD with the existing wire selection method, mechanical strength of tower is taken into account, but windage yaw is ignored in the factor of wind pressure asymmetrical coefficient. The traditional method of selecting the bundle spacing and calculating electric field intensity on conductor surface according to regulation relies on the empirical formula, so its precision is bad. Lightning withstand level of transmission lines is classically computed by the standard method which bases on simplified formula and considers sufficient margin, making the results obviously conservative. Considering above problems, the following work is done in this paper:1) In the wire selection stage, considering the wind pressure asymmetrical coefficients corresponding to mechanical strength and windage yaw are different, so the mechanical characteristic of wires was revised accordingly. The technical indexes of ordinary aluminum cable steel reinforced and three kinds of energy-saving wires were compared amply in mechanical properties and electrical character. The advantages are found in electrical character of energy-saving wires, but they do not have the advantage in mechanical properties except high conductivity aluminum conductor steel reinforced. Finally, combined with the factors of universal tower design, high conductivity aluminum conductor steel reinforced was recommended.2) A simplified physical model of a 220 kV transmission lines was built by the finite element analysis software COMSOL. The simulation results of maximum electric field intensity on conductor surface were compared with that of Markt-Megele method. It turns out the maximum electric field intensity on surface of mid-phase conductor is higher than that of side-phase conductor. The error of the results by two methods is in the range of 5%. In the location of median line, a distribution map of maximum electric field intensity at different height from the ground was drawn. The results at the height of 2 meter from the ground are lower than the standard 5000V/m. The effects of some parameters(the bundle spacing、sub-conductor radius、ground wire、icing and attached raindrops)on maximum electric field intensity around conductor surface were discussed an analyzed, the results show that bundled conductors with different sectional area have different optimal bundle spacing, which minimizes the maximum electric field intensity on conductor surface. After removing the ground wires, the maximum electric field intensity decreases by 1 percent, which can be negligible. Considering icing and attached raindrops, the maximum electric field intensity around conductor surface rises severally to 2.83 and 2.36 times.3) A detailed simulation model of a 220 kV transmission lines was built by ATP-EMTP and then the simulation results were compared with the regulation method. The influences on back-flashover lightning withstand level of different insulator string models and lightning strike points at the top of transmission tower are analyzed. The results show that,the ATP-EMTP method is reasonable and beneficial to save lightning protection costs. When the OPGW side is struck by lightning at the top of transmission tower, it has a higher back-flashover lightning withstand level than the aluminum clad steel side. The calculation of back-flashover lightning withstand level with IEEE insulator string model is lower than that of Wuhan High Voltage Research Institute. |
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