Research On Magnetically Controlled Shunt Reactor Excitation System Fault Influence And Control Winding Ground Protection

The ultra-high voltage magnetically controlled shunt reactor(MCSR)is an important member of the flexible AC transmission equipment.The special structure of MCSR makes its fault characteristics extremely complicated,and MCSR requires high requirements for protection reliability.This paper centers on MCSR control winding protection and focuses on four issues,including MCSR working principle and its simulation model,excitation system fault influence and solution strategy,control winding fault analysis and new protection scheme,and physical model internal fault experiment.Firstly,this paper introduces the structure,working principle and steady-state operating characteristics of the MCSR and its excitation system,and summarizes the two MCSR modeling methods based on finite element analysis method and magnetic circuit decomposition method.According to the actual parameters of the 750kV MCSR which put into service in the Yuka substation,a 750kV three-phase MCSR five-segment magnetic circuit simulation model is established in MATLAB/Simulink based on magnetic circuit decomposition approach.Based on the parameters of the 500V MCSR physical model designed and customized by the research group,a two-dimensional MCSR finite element simulation model is established in ANSYS software.Secondly,in the case of excitation system fault,the fundamental frequency component is generated in DC bus current,which cause the control winding interturn protection to malfunction.Two different generating mechanisms of fundamental frequency component of DC bus current are summarized,futher explains the cause of the malfunction of the interturn protection based on fundamental frequency compenent.The difference characteristics of the second harmonic between the turn-to-turn fault and the excitation system fault are analyzed,and the turn-to-turn protection anti-malfuncion strategy based on the decaying rate of secondary harmonic is proposed,which effectively identifies the excitation system fault and solve the problem of turn-to-turn protection malfunctionTo solve the problem that the DC bus does not exhibit AC overvoltage characteristic which causes the protection to fail to identify the fault,this paper proposes a novel control winding grounding protection scheme based on the unbalanced voltage of the DC bus.The ground fault of control winding is identified based on the characteristic that the unbalance voltage of the DC bus rises obvious when the control winding has a ground fault.The principle of the scheme is simple and easy to implement,which overcomes the problem that the conventional protection cannot identify the control winding end part ground fault.Finally,in order to verify the accuracy of two different simulation models for the simulation of internal fault characteristics,the research group uses vacuum circuit breakers with high time accuracy programmable PLC controller,the research group built an internal fault experiment platform for MCSR physical model,which accurately grasp the fault period and automatically control the fault process.Simulation and experimental results verifies the accuracy of the two modeling methods.