| In order to improve the dynamic large capacity reactive power support capacity of ultra-high voltage direct current（UHVDC）power grid,a batch of 300 Mvar condenser are installed in UHV converter station.300 Mvar condenser can quickly provide large capacity dynamic reactive power to the system because of its larger capacity,higher reliability and strong dynamic voltage maintenance ability.However,due to the complex structure of the end of the condenser for UHV transmission and the more stringent requirements of operation specifications and assessment indicators than conventional motors,it is of certain theoretical significance and engineering value to carry out the analysis of the electromagnetic field and fluid temperature field in the end of the condenser for UHV transmission in view of the magnetic leakage,heating and cooling problems under the complex structure of the end of the condenser for UHV transmission.Taking a 300 Mvar large synchronous condenser as the research object,this thesis establishes the two-dimensional and three-dimensional transient nonlinear electromagnetic field physical model in the end of the condenser.Based on the electromagnetic field theory,by solving the end electromagnetic field,the magnetic flux leakage distribution law in the lower end of the condenser under rated working conditions and the eddy current loss of structural parts such as new double-step copper shield,convex clamping plate and pressure finger in the end are obtained.The effects of different conductivity of the convex clamping plate in the end of the condenser on the magnetic flux leakage in the end and the eddy current loss of each structural part in the end are further explored.At the same time,the effects of different structures and material characteristics in the end,i.e.original structure（with copper shielding and steel clamping plate）,scheme I（without copper shielding but steel clamping plate）and scheme II（without copper shielding but aluminum clamping plate）on the magnetic flux leakage distribution in the end and the eddy current loss of each structural part in the end are compared and studied.In addition,combined with the actual structure of the end of the condenser,based on the basic theories of heat transfer and hydrodynamics,a complex three-dimensional fluid structure coupling heat transfer model in the end of condenser is established,and the basic assumptions and boundary conditions are given.The eddy current loss of each structural member obtained from the solution of the three-dimensional electromagnetic field is used as the heat source of the heating structure in the end of condenser,The velocity distribution law of cooling medium in the end of condenser under rated working conditions and the temperature distribution characteristics of each structural member are obtained.The influence of the conductivity of the convex clamping plate in the end of the condenser on the flow thermal coupling field distribution in the end of the condenser is studied.Furthermore,the effects of different end structures,different material properties and different cooling media（air and hydrogen）on the velocity distribution of end fluid and the temperature distribution of structural parts are explored.Furthermore,the calculated results of copper shield temperature are compared with the experimental results,and the two results are basically consistent,which verifies the accuracy of the end model of the condenser and the reliability of the multi physical field calculation method.It has certain reference significance for improving the end structure of the condenser,improving the heat dissipation efficiency of the ventilation and cooling system of the condenser,developing the condenser cooling system with larger capacity for UHV transmission,and selecting the optimal cooling medium. |
