Research On Modeling Method And Inner-Turn Protection For Shunt Reactor With Auxiliary Windings

The Shunt Reactor with Auxiliary Windings(SRAW)is a new type of shunt reactor that can provide reactive power compensation for long-distance power transmission lines and provide power for the low-voltage equipments in reactor stations.The multiple air gaps arranged on the iron core enable SRAW to obtain good linear volt-ampere characteristics,while also causing weak magnetic coupling between the power windings and the auxiliary windings.Due to the unique structure of SRAW,no simulation model has been integrated into various simulation platforms,which hinders relevant theoretical research.At the same time,its unique coupling form makes the inner-turn fault characteristics of SRAW different from those of common fixed shunt reactors,which increases the difficulty of inner-turn protection design.This paper focuses on the construction of the equivalent model of SRAW,the fault characteristics of SRAW under innerfault,and the configuration of inner-turn protection for SRAW.The main research and innovation points are as follows.(1)Based on the structure and wiring of SRAW,the magnetic circuit expression for SRAW was formulated and its weak magnetic coupling characteristics were analyzed.Utilizing the magnetic circuit decomposition modeling method,the electrical characteristics of SRAW were equivalently represented by the combination of three double-winding saturated transformers,thereby presenting the Three-segment Magnetic Circuit Equivalent Model(TMCEM).This approach effectively overcomes the simulation challenges caused by the lack of integrated SRAW models in simulation platforms.To validate the effectiveness of the proposed model,TMCEM was constructed on the MATLAB/Simulink platform and compared with a low-voltage physical model.The results demonstrate that the proposed model accurately simulates the electrical characteristics of SRAW,including no-load operation and load operation.(2)Based on the fault records of the low-voltage physical prototype,the simulation capabilities of TMCEM under various fault conditions were verified.The results indicate that TMCEM can accurately simulate the fault characteristics of SRAW under external and inner-turn fault conditions.Subsequently,based on TMCEM,the fault characteristic analysis was carried out,and the zero-sequence equivalent circuit of SRAW based on TMCEM was derived.The phase and amplitude differences of the winding zero-sequence current were analyzed under different faults.Finally,the validity of various fault characteristic theoretical analyses was demonstrated by fault records of the SRAW physical prototype.(3)The limitations of existing zero-sequence power directional protection and zero-sequence differential protection for inner-turn faults in auxiliary windings have been identified,including low sensitivity and the inability to detect small inner-turn faults.Therefore,based on analysis of the zero-sequence equivalent circuit based on TMCEM under various fault scenarios,a novel protection scheme based on the amplitude and phase of the zero-sequence current against the inner-turn fault of auxiliary windings is proposed.This scheme can identify small inner-turn faults in both the power and auxiliary windings,and does not necessitate voltage measurement,manual calculation,or adjustment.Subsequently,based on fault test data from SRAW physical prototype,the performance of the proposed protection method was compared with the existing zero-sequence differential protection method,and the results showed that the proposed method has higher reliability and sensitivity.