초전도 한류기의 전력부담 저감 방안 연구

Abstract

With an increase in the amount of electricity demand, additional electricity generation, transformation, transmission and distribution facilities are being built. Accordingly, for efficient power supply and demand, economic operation and stable power supply are being made through power system interconnection. However, the reduction of system impedance can cause the increase of current in case of an accident. As the system impedance is reduced, the fault current exceeds the limitation capacity of the existing protection facilities, which can then cause malfunction of protection device, leading to the damage of power equipment and more accidents. To solve this issue, various plans have been proposed, but these plans often degrade the reliability of power supply. Therefore, research is being conducted, which uses superconductivity. Impedance of superconductiong element almost goes down to zero below the threshold value, resulting in no loss when they are applied to the system. Also in case of an accident, the increase of current causes the threshold value of the superconducting element to exceed its limitation. At this point, the impedance of the superconducting element increases, restricting the fault current. In the existing resistive-type superconducting fault current limiter, the superconducting element takes all fault current during the fault. This may break superconductivity of the superconductor due to the deterioration. To reduce electric burden, it is necessary to increase the capacity of the superconducting element. While one could use the series or parallel connection of the superconducting element, but this requires to solve the problem of irregular quench of the superconducting element. Also the superconducting element should maintain the state of superconductivity under extreme low temperature. Therefore, a cooling facility is required, which results in economic burden due to its repair and maintenance. This thesis proposed a high-speed fault current limiter through high-speed switching as a plan to reduce fault current due to the power system interconnection. In case of any fault in the system, the superconducting element rapidly limits only the initial fault, and at the same time, reduces power burden of the superconducting element by limiting the fault current with the normal conductor through high-speed switching. At the same time, the proposed model reduces power load of the superconductor as well as the economic cost of the cooling facility and increases the capacity of the superconducting element. Accordingly, to improve the weaknesses of the existing resistive-type fault current limiter, We used the high-speed fault current limiter and compared the analyzed the results through an experiment. The experiment simulated faults based on voltage increases and different types of faults and compared and analyzed the operational characteristics of the high-speed fault current limiter and those of the resistive-type fault current limiter.