Transient Circulating Current Calculation And Optimization Of Stator Transposition Windings In Large Synchronous Compensator

Large capacity synchronous condenser is an important reactive power compensation equipment in ultra high voltage direct current.Different from conventional synchronous condenser,it has large capacity and strong overload capacity,and works in transient conditions such as strong over-excitation and strong under-excitation for reactive power adjustment when the grid fails,which leads the surge of circulating current of the stator transposition windings,and the insulation will be burnt out in case of serious damage.Therefore,predicting the circulating current of the stator transposition windings accurately is a key for the research and development of a large-capacity synchronous condenser,and it is also a prerequisite for the design of the stator windings.Due to special operating conditions of large capacity synchronous condenser,the main field,saturation nonlinearity,transient variation and complex braiding transposition structure should be considered in circulating current calculation.But the existing methods based on steady-state operating condition cannot be implemented.Therefore,the calculation method and optimization method of circulating current of stator transposition windings are studied in this thesis.when the main magnetic field,saturation nonlinearity and transient are considered.A fast calculation method which is called three-dimensional transient electromagnetic coupling network method based on the equivalence of local magnetic field for transient circulating current of the stator transposition windings is presented.The method of equivalence of local magnetic field,the modeling method and parameter calculation method of three-dimensional transient magnetic network and three-dimensional transient electric network,and the direct solution method of electromagnetic coupling network are given.In this method,the complex three-dimensional global nonlinear transient electromagnetic problem is equivalent to two-dimensional nonlinear transient electromagnetic field and three-dimensional local linear transient electromagnetic field,It can not only consider the influence of main magnetic field,saturation nonlinearity and transient state,but also apply to different operating conditions and different transposition structures.A 300 Mvar synchronous condenser is taken as an example,the transient circulating current of the stator transposition windings is calculated and analyzed by three-dimensional transient electromagnetic coupling network method.And the three-dimensional transient electromagnetic coupling network method is verified by finite element method combined with experiment.The results show that this method can significantly improve the computing speed under the premise of guaranteeing the computing accuracy.On this basis,the influence of the main magnetic field and saturation nonlinearity on the transient circulating current of the stator transposition windings of different transposition modes and different operating conditions is studied.Fast non-dominated sorting genetic algorithm with an elite strategy（NSGA-II）is combined with the three-dimensional transient electromagnetic coupling network method.Transposition angle and The length and position of empty transposition are taken as optimization variables,the optimal transposition angle and the optimal length and position of empty transposition are concluded.