DC전력망 전력부담 저감을 위한 초전도 차단시스템에 관한 연구

Abstract

Distributed power system is increasing as power consumption increases. This is the trend of connecting these distributed power grids to form a large power grid. Frequency synchronization and long distance power transmission technologies are required for the large power grids. If a distributed power is connected using an existing AC transmission, the grid-connecting will fail because of different frequencies in distributed power system. So, a frequency converter is needed to connect it. Due to frequency component in AC, the long distance AC transmission can’t flow the steady state current until the allowable current. Additionally, line inductance occurs and it leads to induced interference in other lines and inductive disturbance. This AC transmission problem can be solved by adopting a DC transmission. The reason is that DC transmission does not have a frequency component, it dose not necessary to consider frequency synchronization when connecting different systems. Moreover, In DC transmission, the steady state current can flow up to the allowable current. It makes the high efficiency transmission. To commercialize the DC transmission, however, it is necessary to secure fault current interrupting technology. Recent developments in power semiconductors have led to the development of a static state circuit breaker, a hybrid DC circuit breaker. However, the DC interruption technology is still insufficient to isolate the fault current generated in the HVDC system. This is because it is difficult to solve the problem of arc furnaces and semiconductor element heating problems. In this thesis, it proposed a superconducting DC interruption system to cut-off the fault current in fast and stable. superconducting DC interruption system is a combination of superconductivity and mechanical DC circuit breaking technologies. When a fault occurs, a superconductor limits the fault current. Subsequently, a limited fault current is blocked using a mechanical DC circuit breaker. By limitation the current in first, it ensures that the mechanical DC circuit breaker can isolate fault currents quickly and reliably. Superconducting DC interruption system was designed with the PSCAD/EMTDC. In addition, to analyze in various conditions, it established a theory and increased reliability in superconducting DC interruption system. In the simulations, the operation of the superconducting DC interruption system works quickly and reliably. It also confirmed that a stable interruption has occurred in various fault conditions. At this time, the average fault current limitation rate was 52 % and the average interruption time was approximately 20 ms.