| The UHV DC transmission which has unique advantage in long-distance,large-capacity power transmission,has become the main development direction of electric power construction in our country.UHV DC wall bushing is the core equipment in UHV DC transmission system,which has the function of current-carrying,insulation and support.UHV DC wall bushing plays a very important role in the economic transfer,flexible allocation and safe operation of HVDC transmission system.However,the UHV DC wall bushing is a double-edged sword.The electrical insulation structure of UHV DC wall bushing electrical insulation structure is unique,and its electric field distribution is also very complex.In case of insulation fault happens to UHV DC wall bushing,not only it loses the protection function of transmission system,but also can cause other electrical equipment damaged,even pose a great loss to power system.In addition,the production of UHV DC wall bushing unable to achieve localization all time,which brings great inconvenience to the daily maintenance.There have been dozens of UHV DC wall bushing failure events in Yunguang HVDC project,which seriously affect the safe and reliable operation of the UHV DC transmission system.Therefore,it is necessary to take researches deeply for the external insulation performance and structure optimization of UHV DC wall bushing.Based on this background,and combined with the project of China southern power grid EHV power transmission company "UHV DC wall bushing failure diagnosis technology and structure improvement research",this paper has carried out UHV DC wall outside casing insulation research and structure optimization design.This paper mainly carried out research in four aspects:the structure of the UHV DC bushing analysis,calculation method of electric field of UHV DC bushing,Yunguang HVDC project±800kV wall bushing external insulation performance study,and Yunguang HVDC project ±800kV wall bushing structure optimization design.In this paper,the main research contents and research results are as follows,Firstly,in allusion to the structural feature of UHV DC bushing and design requirements,the current common DC bushing structure and electric field characteristics are studied,comparative analysis is mainly focused on advantages and disadvantages of two kinds of UHV DC wall bushing used in State Grid and South Grid,and some technical requirements in the design and problems needed to be focused on of UHV DC wall bushing are cleared,which provides the theoretical basis to carry out the concrete structure optimization design.Secondly,in order to solve electric field numerical simulation calculation of UHV DC bushing,based on the principle of equivalent circuit,the electric field distribution of sleeve type structure is studied.Based on the finite element simulation principle and simulation environment of Infolytica,radial electric field and capacitor core plate edge method for calculating the maximum field strength are studied.Thirdly,for external insulation flashover failure problems of Suidong converter station±800kV UHV DC wall bushing,the finite element electric field simulation calculation is carried on.The set of tube end of equalizing ring lateral electric field distribution is the weakest,leading to insufficient casing external insulation margin,which is the fundamental cause of external insulation flashover.The insulation optimization measures of increasing casing dry arc distance,and adding equalizing ring at the flange outer are put forward,which significantly improve the external insulation of bushing through the validation of simulation.Finally,for many major defects of the faults founded in parameter test missile detection of Chuxiong converter station ±800kV UHV DC wall bushing.On the basis of analysis of fault casing collapse and failure mechanism of defects,we find the bushing produced by HSP exists familial structure defects.The bushing internal docking structure optimization scheme of increasing equipotential lines,increasing sealing ring,and silver plating are put forward.Through the comparative analysis of electric field distribution simulation before and after improvement of bushing,it is found that the improved scheme obviously effect.According to the scheme of bushing structure modification,HSP produces improved bushing and passed the test.In this paper,the finite element simulation research of 800 kV UHV DC wall bushing is carried on,the proposals to improve the performance of external insulation and structure optimization scheme of familial defect are put forward,which have important theoretical significance and engineering application value for the manufacture of UHV DC bushing and the development of UHV DC transmission technology. |
