Topology And Parameter Optimization Of High Coupled Split Reactance Type Fault Current Limiter

With the continuous development of national economy,increasing demand for electricity in the whole society and expansion of the power grid,the connection between the grids is getting closer while the voltage level of the power grids under construction continues to increase.However,it is getting more and more serious that the fault current level of the power grids excesses the regulation standard.Apparently,it is necessary to take measures to effectively control the short-circuit current level of the power grid.In recent years,Fault Current Limiters,namely FCLs,has gradually become a research hotspot of experts and scholars at home and abroad.Nevertheless,the high-capacity fault current limiters that have been developed so far have some problems such as slow response speed,long recovery time,complicated structure and poor economy,which makes it difficult to apply to high-capacity occasions,like high-voltage power grid,ultra-high-voltage power grid.Thereinto,high coupled split reactance type fault current limiter,namely HCSR-FCL,is expected to be applied to high-voltage and large-capacity applications due to its advantages such as automatic current sharing,simple structure and reliable performance.In order to realize the engineering application of HCSR-FCL in high-voltage and ultra-high-voltage power grids,a series of exploratory studies have been carried out on the key issues.In addition to the necessary research on its own topology and current-limiting characteristics,it also studied the influence and optimization of HCSR-FCL related parameters.Firstly,a new topology structure of 220kV HCSR-FCL combining HCSR and fast vacuum switch was proposed.Furthermore,the current limiting principle and working logic of HCSR-FCL were studied.HCSR has the functions of automatic current sharing and current limiting,which can double the breaking level of the fast vacuum switch;The fast vacuum switch adopts artificial zero-crossing arc quenching technology,which can limit the fault current in the first half-wave of the short-circuit fault,thus solving the problem of excessively slow response speed commonly existing in current FCLs.Then,the HCSR-FCL field-circuit coupling model was established based on the finite element software,and the detailed data of the entire current limiting process were obtained by simulation.The current limiting characteristics of the HCSR-FCL were analyzed in detail according to these data.The relevant current limit indicators of HCSR-FCL were calculated,where the expected short-circuit current was 60kA,the steady-state operating loss was 0.005%,and the fault response time was less than 5ms,all of which meet the actual project requirements;The time-varying trend of HCSR magnetic field was studied:the HCSR magnetic flux density increases rapidly from zero to the first peak value of 5.76T about 7ms after FCL operation;The spatial distribution law of HCSR magnetic field was obtained:the internal magnetic field of HCSR is large,while the external magnetic field decays rapidly.The magnetic flux density values in the radial and axial directions 4R2 away from the center point of HCSR was less than 0.11t and 0.05t,respectively;The amplitude of the HCSR steep-wave overvoltage was calculated to be about 179kV,and the wavefront rise time of the steep-wave overvoltage was about 1.24 × 10-7s.Finally,the effects of the HCSR-FCL fault response time,single-arm current-limiting inductance,and coupling coefficient on the HCSR-FCL current-limiting characteristics were studied based on the HCSR-FCL field-circuit coupling model,and the HCSR-FCL parameter optimization scheme was obtained much further.The longer the fault response time,the smaller the first peak value of the system fault current after the HCSR-FCL operation,but the greater the fault current pressure the system bears before the operation;The current limiting effect of the HCSR-FCL can be effectively improved by increasing the HCSR single-arm inductor.However,it will increase the steady-state active loss of HCSR-FCL and space magnetic field value;Reducing the HCSR coupling coefficient can slightly improve the current limiting effect of HCSR-FCL;Nevertheless,the HCSR coupling coefficient cannot be too small,otherwise the ideal low impedance,low voltage drop and low-loss state of HCSR-FCL cannot be maintained.Based on the above parameter impact analysis,the HCSR-FCL parameter optimization scheme was finally obtained,which is to calculate the maximum value of HCSR-FCL fault response time,the maximum value of HCSR single-arm inductance and the minimum value of HCSR coupling coefficient,under the constraints of the maximum value of system fault current before fault current limiting,loss of HCSR-FCL,magnetic flux density at the center of HCSR,the voltage drop of HCSR-FCL and the limitation of actual production process.The research content of this paper focuses on the key issues of HCSR-FCL engineering practicality.The research results will further promote the high-voltage and high-capacity of PMFCL and its application in large-scale power grids,which has important theoretical reference value and practical guiding significance.