The Research On Superconducting Fault Current Limiter

With the rapid expansion of Power Systems, the capacity of Power Systems gradually increases and the level of short-circuit current increases rapidly. Due to the problems of technological, the capacity of traditional circuit breaker gradually can not meet the demand for rapidly developed electric power system, while the conventional current-limiting devices, such as air-core reactors, thermal resistance and so on, will give a negative impact on normal operation of the system. With the development of superconducting materials, Superconducting Fault Current Limiter (SFCL) bring a new dawn for current limited. Superconducting material is an ideal current-limiting material, in the superconducting state, its resistance is zero, When it is transformed into a normal state, shows high impedance. Limiting short-current with superconducting current-limiter have no effect on power system when the system normally operate. Once the short-circuit fault occurs, the superconducting current limiting impedance increases rapidly to limit short-circuit current.In this paper, first, described the two properties of Superconductor, namely, zero-resistance characteristics and Meissner effect. Described the structure and working principle of a variety of superconducting current-limiter in detail and established their mathematical model in theory. Calculated its impedance when the system is working normally or at short-circuit condition. Analyze the advantages and disadvantages of superconducting current-limiter.Second, study the bridge-type Superconducting Fault Current Limiter. Describe the resistance switching type, mixed type, active-type bridge superconducting current limiter working principle, analyze the process of limited current in detail. Established their mathematical model in power system and study their limiting effect through simulating, On this basis, analyze advantages and disadvantages of this three kinds of bridge superconducting current limiter.Third, According to analysis of advantages and disadvantages in the front, Propose a new type of bridge Superconducting Fault Current Limiter, analyze its working principle and limiting process. Calculate the current changes of each component during the system working normally or short. Design current-limiting transformer, superconducting bobbin, DC source and control circuit. Study the limiting effect of applying DC power supply to the superconducting current limiter. Last, this thesis introduces the tools of PSCAD/EMTDC. Combined with 35kV transmission line system to build the transmission system short-circuit models and calculate the relevant parameters, Study of a new type of superconducting current limiter limiting effect by simulation, Compare current suppression ratio to validate the advantage of new superconducting current limiter.