행렬방식을 이용한 저항형 초전도 한류기의 전기적 특성

Abstract

Due to a continuous increase in power demand and an extension of electric facilities, a capacity of the electric power system is increased and an equivalent impedance of the system is decreased. Accordingly, a fault current by a ground fault and short-circuit fault is bigger, and the fault current frequently exceeds a breaking capacity of a circuit breaker so that we are required to prepare effective measures. Many measures against the fault current have been proposed such as the use of high-impedance devices, bus separation, increase in a breaking capacity of circuit breakers, series reactor, etc. Of those measures, the bus separation, increase in a breaking capacity of circuit breakers and the use of series reactors are used as efficient methods. The bus separation is the method that a complex network system of the electric power system divide into a several section to prevent a breaking from spreading, and that is used mainly although the method has some problems such as a decline of power quality and reliability problem of power supply. In order to solve the problems, a study on superconducting fault current limiter (SFCL), which can reduce a fault current by using a superconductor, is progressed energetically in the domestic and international market. The SFCL is a powered appliance using a zero-impedance behavior of a superconductor, and the superconducting unit has to satisfy three conditions of the critical behaviors, which are a critical current, critical magnetic field and critical temperature, for the state of zero-impedance. The SFCL can be applied as a lossless appliance in the normal state of the electric power system. When a current of the electric power system is increased rapidly due to a ground fault and short-circuit fault, in other words, if an excess current in a critical current of the superconducting unit is generated then the superconducting unit is quenched and reduce a fault current within 4 msec, the reduced fault current is cut off by circuit breaker. Thus, the powered appliance and electric lines can be protected by the SFCL. A proposed SFCL in this paper is one of the resistive-type SFCLs and is directly connected to electric power system. The SFCL consists of the trigger part to apply magnetic field and the current-limiting part to limit a fault current. The resistive type SFCL limits a fault current by using a critical current and critical magnetic field of three conditions of the critical behaviors. Existing SFCLs have only differences in operating mechanism, in the type and component of the superconductor, but they are not the SFCL to improve a behavior of the superconductor. Because critical behaviors of the superconducting units are different when those are produced, The SFCL which can improve an unbalanced quenching behavior by controling the critical magnetic field is proposed. But we are required to miniaturize the SFCL. The SFCL should be produced as three-phase SFCL to apply to the electric power system. Many faults such as single line-to-ground fault, double line-to-ground fault or short-circuit fault, etc, frequently occurs in the three phase system. Accordingly, the SFCL has to limit the fault current due to many faults, in addition, the SFCL need a stable operation because it can not predict that any accident occurs. In order to increase a capacity of the SFCL, several superconducting units are connected in series or in parallel, but the structure has a problem of individual damages from a mechanical impact or an electrical impact. In this circumstance, the SFCL should be operated stably. in other words, it is important to study on reliability of the SFCL. However, the study is not enough so far. The results of this study are as follows.

○ We manufactured the SFCL's limiting module with 1×3 matrixes on the basis of analytical results of critical characteristics in the superconducting units, and analyzed characteristics according to variation of turn number of the reactor.

○ The fault current limiting and quenching characteristics of the SFCL were analyzed according to the number of turns of the reactor and fault conditions of three phase SFCL with 1×3 matrixes.

○ The fault current limiting, quenching and recovery characteristics were analyzed according to fault conditions of three phase SFCL with 2×3 matrixes for increment of power capacity.

○ We evaluated the reliability and stability on three phase SFCL according to disconnection fault of superconducting units.