Research On Saturated Iron-Core Fault Current Limiter Of Tightly Coupled Structure

In recent years,with the expansion of power system's scale,the increase of energy interconnection and the access of large power stations,the short-circuit current level of power system has gradually approached the upper limit of the current circuit breaker's interrupted capacity,which has seriously restricted the operation and development of our power grid.The development of economical current limiters based on conventional electrical equipment or components with high current-limiting impedance and low steady-state impedance is undoubtedly the first choice to solve the current limiting problem,in which the performance of the saturated iron-core fault current limiter(SICFCL)is the best.In view of the defects of traditional SICFCL in the engineering application,the SICFCL with tight coupling structure is taken as the research target to provide effective countermeasures for solving the problem of high short-circuit current and lay the foundation of theory and engineering for the in-depth study of high voltage level's SICFCL.Firstly,a tightly coupled SICFCL is proposed by analyzing the causes of the loosely coupled SICFCL's defects.On the basis of satisfying the basic principle and structure of SICFCL,the SICFCL's current-limiting performance is improved by altering the coupling structure between AC and DC windings,redesigning the connection structure between AC windings and adopting the more efficient control method.The device overcomes the inherent defects of the loosely coupled SICFCL,making it more practical in engineering.Secondly,the mathematical model is established base on the method of equivalent magnetic circuit,and the impedance calculation formula is derived by this mathematical model.Furthermore,based on the steady-state impedance characteristics,a preliminary parameter design method is analyzed by taking a tightly coupled SICFCL applied to a 10 kV power system.In addition,the control strategy selection,structural design and mathematical modeling of the excitation and monitoring protection system are carried out.Thirdly,a novel de-excitation circuit is proposed,and the mathematical model is established.By reasonably designing the transformation ratio of the isolation transformer and utilizing the series circuit's characteristics of inductor and capacitor,the rapid demagnetization of the DC winding is realized.Through the energy storage characteristics of capacitor and the single-conductivity of diode,the function of energy storage and reuse that the conventional de-excitation circuit doesn't have is realized.Finally,the simulation model is built and the experimental prototype is made according to the design parameters.The performance of the tightly coupled SICFCL is verified by simulations and experiments.The feasibility and effectiveness of the proposed tightly coupled SICFCL is demonstrated.