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시간영역에서 순시 유효/무효전력을 이용한 마이크로그리드의 단독운전 판단
이영귀(Young-Gui Lee),김연희(Yeon-Hee Kim),정태영(Tai-Ying Zheng),김태현(Tae-Hyun Kim),강용철(Yong-Cheol Kang) 대한전기학회 2012 전기학회논문지 Vol.61 No.1
Correct and fast detection of a micro-grid (MG) islanding is essential to the MG since operation, control and protection of the MG depend on an operating mode i.e., an interconnected mode or an islanding mode. When islanding occurs, the frequency of the point of common coupling (PCC) is not the nominal frequency during the transient state owing to the frequency rise or drop of generators in the MG. Thus, the active and reactive power calculated by the frequency domain based method such as Fourier Transform might contain some errors. This paper proposes an islanding detection algorithm for the MG based on the instantaneous active and reactive powers delivered to the dedicated line in the time domain. During the islanding mode, the instantaneous active and reactive powers delivered to the dedicated line are constants, which depend on the voltage of the PCC and the impedance of the dedicated line. In this paper, the instantaneous active and reactive powers are calculated in the time domain and used to detect i slanding. The performance of the proposed algorithm is verified under various scenarios including islanding conditions, fault conditions and load variation using the PSCAD/EMTDC simulator. The results indicate that the algorithm successfully detects islanding for the MG.
마이크로그리드에 한류기 투입에 따른 적응형 과전류 계전 방식
강용철(Yong-Cheol Kang),김연희(Yeon-Hee Kim),국경수(Kyung-Soo Kook),이영귀(Young-Gui Lee),정태영(Tai-Ying Zheng),이혜원(Heye-Won Lee) 대한전기학회 2010 대한전기학회 학술대회 논문집 Vol.2010 No.7
This paper proposes an adaptive over-current relay (OCR) considering the effect of fault current limiters (FCLs) in a micro-grid (MG). The protection schemes of a MG are much more complicated and difficult than those in a distributed generation (DG) system, due to the more flexible operation schemes and some additional equipments i.e. FCLs. In this paper, all possible operational conditions are analyzed, and the appropriate setting values of an OCR corresponding to each operational condition are obtained and used in the proposed adaptive OCR. The effect of FCLs is also considered, and the setting value of the proposed adaptive OCR will be varied when FCLs operate. The performance of the proposed adaptive OCR is verified with the PSCAD/EMTDC generated data. The results indicates that the proposed adaptive OCR can satisfactorily detect the fault even though the magnitude of the fault current is low due to the disconnection between the MG and the grid, and/or the operations of fault current limiters.
Fault ride-through 요구를 고려한 풍력발전단지 연계선 보호 거리계전 알고리즘
강용철(Yong-Cheol Kang),강해권(Hae-Gweon Kang),정태영(Tai-Ying Zheng),김연희(Yeon-Hee Kim),이영귀(Young-Gui Lee) 대한전기학회 2010 전기학회논문지 Vol.59 No.6
A large modern wind farm should satisfy the requirements for a grid and accomplish the optimization of the wind farm system. The wind farm intertie protection system should consider a Fault Ride-Through (FRT) requirement for more reliable protection. The wind farm should keep connected to the grid in the case of a grid fault whilst it should be isolated for an intertie fault. This paper proposes a distance relaying algorithm suitable for wind farm intertie protection considering the FRT requirement. The proposed algorithm estimates the impedance based on a differential equation method because the frequency of the voltage and current deviates the nominal frequency. The algorithm extends the reach of Zone 1 up to 100 % of the length of the intertie to implement the FRT requirement. To discriminate an intertie fault from a grid fault, the algorithm uses a voltage blocking scheme because the magnitude of the voltage at the relaying point for an intertie fault becomes less than that for a grid fault. The performance of the algorithm is verified using a PSCAD/EMTDC simulator under various fault conditions. The algorithm can discriminate successfully the intertie fault from grid fault and thus helps to implement the FRT requirement of a wind farm.