DC 전력계통의 과도전류 저감을위한 초전도 DC 차단기 특성 연구

Abstract

DC 시스템은 저탄소 및 신재생에너지 정책과 더불어 재생에너지 확대 보급에 따라 주목받고 있다. 그 중 HVDC (High Voltage Direct Current) 시스템은 초고압 직류 송전으로 기존의 HVAC(High Voltage Alternating Current) 시스템과 비교하여 높은 송전 효율, 장거리 송전 손실 및 절연비용 저감, 계통 연계가 쉬운 이점을 갖는다. HVDC 시스템에는 약 0~3 ms이내의 매우 짧은 커패시터 방전단계가 포함되어있어 방전전류로 인해 시스템의 손상과 장치가 파괴될 가능성이 존재한다. 따라서 과도 상태에서 발생되는 고장전류를 저감하기 위해 초전도체를 활용한 한류기가 제안되고 있다. 본 논문에서는 HVDC 시스템에서 발생하는 과전류를 저감하고, 차단하기 위한 기술로 초전도 한류 모듈과 DC 차단기로 구성된 초전도 DC 차단기를 제안하였다. PSCAD/EMTDC 프로그램을 통해 실 계통 파라미터를 적용한 HVDC 시스템을 모델링하고, 초전도 DC 차단기 유무에 따른 동작 특성 데이터를 확보하고자 하였다. Scale-down DC Test-bed 규모에 맞는 초전도 DC 차단기의 설계 및 실험을 통해 동작 특성 데이터를 분석하고, 시뮬레이션을 통해 동작 특성을 구현하였다.HVDC 시스템의 적용을 위한 초전도 DC 차단기의 동작 특성은 회로 해석을 통해 설계된 HVDC 시스템에 적용하였고, 초전도 DC 차단기의 유무에 따른 시스템의 동작 특성 데이터를 확보하였다.결과적으로, 초전도 DC 차단기의 적용을 통해 DC 1선 지락 고장의 경우 과전류를 최대 75.8 % 감소하였고, DC 시스템의 차단 시간은 최대 4.1 ms 단축되었다. DC 2선 단락의 경우 사고 전류는 최대 약 57.74 % 감소하였으며, 차단 시간은 최대 약 440.6 ms 단축되는 결과를 확인하였다. | The DC system is attracting attention due to the expansion and distribution of renewable energy along with low-carbon and renewable energy policies. Among them, the HVDC (High Voltage Direct Current) system is an ultra-high voltage direct current transmission, and compared to the existing HVAC (High Voltage Alternating Current) system, it has advantages of high transmission efficiency, long-distance transmission loss and insulation cost reduction, and easy grid connection. However, since there is no frequency in DC, there is no zero point in current and voltage, making it difficult to interrupt the system in the transient state. There is a possibility of system damage and device destruction due to the discharge current since the HVDC system includes a very short capacitor discharge stage within about 0 to 3 ms. Therefore, the current limiter using the superconductor has been proposed to reduce the fault current generated in the transient state. In addition, research on hybrid methods that combine superconducting technology and DC interrupting technology to limit and quickly interrupt the overcurrent of the DC system is also active. In this paper, the superconducting DC circuit breaker composed of a superconducting current-limiting module and a DC interruption module was proposed as a technology to reduce and interrupt the overcurrent generated in HVDC system. It was intended to model the HVDC system with real system parameters through the PSCAD/EMTDC and to secure operating characteristics according to the existence of the superconducting DC circuit breaker. The operating characteristics were analyzed through the design and experiment of the superconducting DC breaker suitable for the scale-down DC test-bed, and the operating properties were implemented through simulation. The superconducting DC circuit breaker for application to the HVDC system were applied to the HVDC system designed through circuit analysis, and the operating data of the system according to the existence of the superconducting DC circuit breaker were obtained. As a result, through the application of the superconducting DC circuit breaker, the overcurrent was reduced by up to 75.8% in case of the DC 1-line ground fault, and the interruption time of the DC system was shortened by up to 4.1 ms. In case of the DC short circuit, it was confirmed that the fault current was reduced by up to about 57.74% and the interruption time was reduced by up to about 440.6 ms.