Research On Transient Characteristics And End Structure Magneto-Thermal Problem For Large Synchronous Condenser

Large synchronous condenser has strong dynamic reactive power compensation capability and short-time overload capability,and has become an important reactive power compensation device in Ultra-high voltage direct current(UHVDC)transmission system.In the process of voltage drop fault in the UHVDC transmission system,large synchronous condenser sends out a large amount of reactive power to the power grid instantaneously.The strong impact current leads to large eddy current loss induced in the end structure of the synchronous condenser and causes heating,which seriously threatens the safe operation of the synchronous condenser and power system.Therefore,the analysis of the magnetic field,loss and temperature rise of the end structure is one of the key technologies for the design and operation of large synchronous condenser,which is characterized by short-term and strong transient operation.This dissertation takes a 300 MVar synchronous condenser as the research object,and studies the transient characteristics,end magnetic field,end structure’s eddy current loss and temperature rise during the fault process of the UHVDC transmission system.The unit-network coupling transient model of large synchronous condenser is established,and the transient characteristics of large synchronous condenser during the short time and continuous fault of the AC voltage at the sending end of the UHVDC transmission system are analyzed.The regulation capability of large synchronous condenser to the AC voltage at the sending end of UHVDC transmission system under different fault levels is studied,and the transient reactive power characteristics and its influencing factors of large synchronous condenser under different faults of transmission system are revealed.By comparing with the measured results,the accuracy of the unit-network coupling transient model of large synchronous condenser is verified.A three-dimensional analytical method is proposed to calculate the magnetic field in the end region and the eddy current loss in the clamping ring of large synchronous condenser.The virtual equivalent current in space is established,taking into account the influence of the stator back core and the rotating shaft on the magnetic field in the end region.Combined with the finite element method,the calculation of the magnetic field in the end region of synchronous condenser and the eddy current loss in the clamping ring is realized,and the influence of the material properties and structural parameters of the clamping ring on the eddy current loss is analyzed.The problems of difficult mesh generation,long calculation time and high requirement of computer configuration in solving the end magnetic field and structure’s eddy current loss of large electrical machines in the early stage of engineering research are effectively solved.The accuracy and efficiency of the proposed method are verified by comparing the calculation results and calculation time with the three-dimensional finite element method.A novel shielding topology and a clamping finger topology are proposed,which can effectively reduce the eddy current loss in the end structure.Three dimensional nonlinear transient electromagnetic field calculation models under traditional structure and new structure are established respectively to calculate the distribution law of magnetic field in the end region and eddy current loss in the end structure under steady and transient operating conditions of large synchronous condenser.The effectiveness of the proposed structure topology is verified by comparing the maximum regions of magnetic flux density and eddy current density in the end structure.A three-dimensional flow-heat coupling calculation model for the end region of large synchronous condenser is established.Combined with the distribution law of eddy current loss in end structure,the sub region grids of end structure are constructed.With the eddy current loss of the sub region as the heat source,and the given fan inlet velocity and outlet pressure as its boundary conditions,the flow-heat coupling field of large synchronous condenser under rated operating conditions is calculated.Analyze the fluid velocity and temperature distribution rule in the end region of the condenser,reveal the relationship between the loss,cooling conditions and temperature rise distribution of the end structure,explore the influence of the proposed end shielding and clamping finger topology on the temperature rise of the end fluid and end structure,and verify with the measured results.