Study On Treatment For Windage Yaw Of Extra High Voltage (EHV) Transmission Line

With the increase of the power load and the requirement of the reliability of the power supply, the infrastructure of power grid and the construction of the extra high voltage transmission line are constantly developed. Due to the high voltage level and the long transmission distance, extra-high voltage (EHV) transmission lines are easily affected by weather, environment, external forces, insulation aging, and other factors. In recent years, short time dangerous wind and other extreme weather have made the frequency of windage yaw of EHV transmission line stay on a high level. The windage yaw becomes a great hidden danger threatening the safety of power grid. The prevention and control of windage yaw turn into an important section to improve the ability against wind and to ensure the safety of power grid.Taking the treatment for windage yaw of the EHV transmission line 500kV Liaochang II transmission line in Shandong Power Grid as the clue, this paper gives an explanation of treatment for windage yaw of the EHV transmission line and discusses characteristics, causes, treatment methods and schemes, program of test and practice etc.(1) This thesis discusses the characteristics of windage yaw of transmission line, including severe weather conditions, low success rate of reclosing and clear, obvious discharge paths. According to the difference of discharge paths, windage yaw is divided into three categories, i.e., discharge between wire and components of tower, discharge between wire and earth wire and discharge between wire and surroundings. Based on the above analysis, the causes of windage yaw are intensively discussed from two aspects:bad weather (typhoon, squall line wind, tornado and local wind) and design flaws (imperfect calculation models, lack of attention to the surroundings, underestimated harsh weather and half-baked line modification). Finally, the analysis on fault locations, weather, surroundings and investigation results of typical windage yaws of the EHV transmission line 500kV Line Liaochang I, II in Shandong Power Grid from 2004 to 2015 provides effective support for rationality and correctness of the analysis of causes of windage yaw.(2) This thesis presents a method to identify transmission lines with high-risk of windage yaw, consisting of investigation of line with risk, investigation of section with risk and localization of tower with potential fault, combining theoretical knowledge and practical operating experience. Seven kinds of treatment methods for windage yaw of transmission line, i.e., Mid-phase Traction+Side-phase Barrier and Support, Mid-phase Traction+Side-phase Support at Interior Angle, Mid-phase Traction+Side-phase Oblique-pull at Exterior Angle, Wire Wraping, Tower Wraping, Composite Insulator and Cross arm, and Jumper Support at Interior Angle are described in details. Various methods are compared and analyzed on applicable scope, principle, advantages and disadvantages, which provides reference for the practical selection and application of treatment methods for windage yaw. Finally, by combing and checking all towers of Liaochang II transmission line with high risk of windage yaw, the management of windage yaw of the whole line is determined. A treatment scheme for tangent tower is put forward with "Side-phase Barrier+Mid-phase Traction" flexible device against flashover caused by windage yaw as the core, Weight and String Modification method as the auxiliary measures, "insulation, buffer, adjustment, installation, insurance" as important elements.(3) This thesis discusses the test of treatment for windage yaw of Liaochang II transmission line, including assembly test of device, suspension test of device, impact test of device and analysis of test result. Flaws of basic design and quality problem of components discovered in the test effectively reflect the function of discovery, control and identification of test. Aiming at solving the problems and eliminating risks discovered in the test, improvement measures are taken, which makes the experimental data consistent with the theoretical analysis and validates the correctness and effectiveness of device against windage yaw. The test of treatment for windage yaw lays an important foundation for comprehensive promotion of treatment of Liaochang II transmission line, speed-up of construction progress, and assurance of construction quality. Finally, the transformation of towers of 500kV Liaochang II transmission line against windage yaw is completed by integrated using Weight, String Modification, Side-phase Barrier+Mid-phase Traction (flexible device) and Jump String Increment, which completely solves the trip of windage yaw. In the summer of 2016,500kV Liaochang ? transmission line survived from times of strong winds, heavy rain and other inclement weather in Northwest Shandong and suffered no windage yaw, which verified the good effectiveness of treatment method for windage yaw of 500kV Liaochang ? transmission line.