Research On The Simulation Modeling Of Internal Faults Of Magnetically Controlled Shunt Reactor

The magnetically controlled shunt reactor(MCSR)is a very important reactive power compensation equipment for UHV power grid,which has the function of smooth regulating capacity,eliminating the overvoltage of operation and submersible current.At the same time,the stable operation of MCSR is related to the stability of the voltage and power flow of the whole power grid.So it is particularly important to model accurately and study it in depth.The structure of MCSR is complex,and it works in the saturation state of AC and DC mixing.Its precise mathematical model construction and internal fault analysis are more complex,and there are few references at home and abroad.This thesis takes MCSR as the core of research,and focuses on the following 4 core problems:its basic working principles and modeling methods,Ansoft finite element modeling and steady state analysis,simulation and analysis of new structure and internal fault of control winding,and closing transient problem.In this thesis,the basic principle of UHV MCSR is introduced in detail.Based on the structure of line winding series,"two strings and three" connection of control winding,compensation winding triangular connection,MCSR mathematical model is constructed by magnetic path decomposition.However,because of neglecting the yoke of the iron core and using the equivalent replacement of the transformer,the accuracy is low and the internal fault of MCSR can not be studied accurately.Therefore,a new idea of the finite element analysis method and the Ansoft Maxwell software to build the MCSR structure model is proposed.Based on a 500V MCSR low voltage physical model,this thesis uses Ansoft Maxwell software to build two dimensional finite element model of MCSR,and the external circuit editor as the excitation source of the finite element model.Then the simulation results show the operating characteristics of MCSR under AC and DC independent action and three operating capacity.The result is that in the normal steady state operation of MCSR,when the rated capacity is reached,the working point of the iron core reaches a half cycle in the saturated zone,with a good adjustment effect.Based on the problem of MCSR failure or closing can not accurately reflect the overvoltage of the DC bus of existing control winding structure,this thesis presents a new type of control winding structure for the thyristor rectifier installed with parallel resistors,diodes and switches.On the basis of this structure,the winding separation method is put forward.According to the MCSR internal network occurring turn-to-turn and turn-to-ground fault of line and control winding,the finite element and external circuit model are modified respectively.The simulation shows that under four internal faults,the total control current(the sum of the three-phase current of the control winding)and the DC bus are obviously increased because of the superposition of the AC components,which is beneficial to the protection of the configuration.The two core flux is not symmetric,which does not affect the overall performance of MCSR,but has serious impact on safety and stability of MCSR.Therefore,Ansoft finite element analysis can be used to study the internal fault of MCSR,and to solve the defects of other modeling methods that can not be accurately modeled and analyzed.In the end,this thesis analyzes and compares the current and DC bus AC overvoltage problems of MCSR direct closing and preexcitation switching.Based on the theoretical deduction,the external circuit model of closing problem is corrected by using Ansoft.The simulation shows that MCSR with pre excitation closing can help to reduce the switching inrush and DC bus overvoltage.It is also distinguished from the internal fault of the structure,and verified by dynamic model test.The result also shows the accuracy and applicability of Ansoft Maxwell finite element analysis.