• Journal of Electrical Engineering and Technology
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• 제6권4호
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• pp.466-473
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• 2011

This paper proposes a protection algorithm for a wind turbine generator (WTG) in a large wind farm. To minimize the outage section, a protection relay for a WTG should operate instantaneously for an internal fault or a connected feeder fault, whereas the relay should not operate for an internal fault of another WTG connected to the same feeder or an adjacent feeder fault. In addition, the relay should operate with a delay for an inter-tie fault or a grid fault. An internal fault of another WTG connected to the same feeder or an adjacent feeder fault, where the relay should not operate, is determined based on the magnitude of the positive sequence current. To differentiate an internal fault or a connected feeder fault from an inter-tie fault or a grid fault, the phase angle of the negative sequence current is used to distinguish a fault type. The magnitude of the positive sequence current is then used to decide either instantaneous operation or delayed operation. The performance of the proposed algorithm is verified under various fault conditions with EMTP-RV generated data. The results indicate that the algorithm can successfully distinguish instantaneous operation, delayed operation, or non-operation depending on fault positions and types.

• 조명전기설비학회논문지
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• 제29권2호
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• pp.97-103
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• 2015

This paper introduces two on-going projects for DC high temperature superconducting (HTS) cable systems in South Korea. This study proposes the application of DC HTS cable systems to enhance power transfer limits of a grid-connected offshore wind farm. In order to develop the superconducting DC transmission system model based on HTS power cables, the maximum transfer limits from offshore wind farm are estimated and the system marginal price (SMP) calculated through a Two-Step Power Transfer (TSPT) model based on PV analysis and DC-optimal power flow. The proposed TSPT model will be applied to 2022 KEPCO systems with offshore wind farms.

• 전기학회논문지
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• 제59권6호
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• pp.1053-1058
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• 2010

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.

• Journal of Power Electronics
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• 제12권3호
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• pp.495-502
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• 2012

This paper presents an improved grid voltage control strategy for wind farms with doubly-fed induction generators (DFIGs) connected to distribution networks based on an analysis of the operation limits of DFIG systems. A modified reactive power limit calculation method in different operation states is proposed and a reactive power control strategy during grid voltage dips/rises is further discussed. A control strategy for compensating unbalanced grid voltage, based on DFIG systems, by injecting negative sequence current into the grid through the grid side converter (GSC) is proposed. In addition, the negative current limit of the GSC is discussed. The distribution principle of the negative sequence current among the different DFIG systems in a wind farm is also introduced. The validity of the proposed voltage control strategy is demonstrated by Matlab/Simulink simulations. It is shown that the stability of a wind farm and the power grid can be improved with the proposed strategy.

• Journal of Electrical Engineering and Technology
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• 제11권2호
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• pp.320-328
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• 2016

The introduction of renewable energy sources into the AC grid can change and weaken the strength of the grid, which will in turn affect the stability and robustness of the doubly-fed induction generator (DFIG) wind farm. When integrated with weak grids, the DFIG wind turbine with vector power control often suffers from poor performance and robustness, while the DFIG wind turbine with synchronized control provides better stability. This paper investigates the critical short circuit ratios of DFIG wind turbine with vector power control and synchronized control, to analyze the stability boundary of the DFIG wind turbine. Frequency domain methods based on sensitivity and complementary sensitivity of transfer matrix are used to investigate the stability boundary conditions. The critical capacity of DFIG wind farm with conventional vector power control at a certain point of common coupling (PCC) is obtained and is further increased by employing synchronized control properly. The stability boundary is validated by electromagnetic transient simulation of an offshore wind farm connected to a real regional grid.

• 한국태양에너지학회 논문집
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• 제33권4호
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• pp.39-45
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• 2013

This paper presents the estimation of minimum BESS capacity for regulating the output of wind farms considering power grid operating condition in Jeju Island. To analyze the characteristics of wind farm outputs with a BESS, the real data of wind farms, Sung-San, Sam-dal and Hang-Won wind farm, located in the eastern part of Jeju island is considered. The wind farms are connected to Sung-san substation to transfer the electric power to Jeju power grid. Consequently, at PCC (Point of Common Coupling), it can see a huge wind farm connected to the substation and thus it can be expected that the smoothing effect is affected by not only the different wind speeds for each area but also the different mechanical inertia of wind turbines. In this paper, two kinds of simulation have been carried out. One is to analyze the real data of wind farm outputs during a winter season, and the other is to connect a virtual BESS to eliminate the unintended generating power changes by the uncontrolled wind farm outputs as shown in the former data. In the conclusion, two kinds of simulation results show that BESS installed in the substation is more efficient than each wind farms with BESS, respectively.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.702-703
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• 2011

Large offshore wind farms using high voltage direct current transmission system (HVDC) have been considered and exploited in many countries in the world. The maintenance of the stable operation of wind farm and interconnected system is an important issue, especially in the case of fault. To ensure the stable operation after fault clearance, the PCC voltage must be restored as soon as possible and meet the grid code requirement. This paper will evaluate the PCC voltage recovery ability of a large offshore wind farm as it is connected to a weak grid via a VSC-HVDC.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 A
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• pp.236-238
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• 2004

In recent years wind turbine technology has undergone the rapid development in response to the demands for increased use of renewable sources of energy. Using wind turbines for production of electrical energy requires reliable operation. The increased share of wind power in electrical system makes it necessary to have grid-friendly interfaces between the wind turbines and the grid in order to maintain power quality. Increasingly wind turbines are being connected into electricity distribution system. The grid-connected wind power stations have many impacts on power systems such as voltage variations, harmonics. The paper investigates the influences of grid-connected wind power generation system on substation bus voltage.

• 조명전기설비학회논문지
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• 제20권10호
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• pp.41-46
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• 2006

상업용으로 계통에 연계되어 운전되는 대부분의 풍력발전기는 유도발전기가 주로 사용되고 있으며 동기발전기와 다른 양상을 보이고 있어 계통에서의 사고발생 후 정상상태로 복귀할 수 있는 최대의 시간(임계 제거시간)을 이용하여 과도상태를 해석하고 있다. 본 연구에서는 풍력 발전시스템이 연계된 계통에 대해 임계 제거시간에 미치는 요인을 분석하였으며 계통해석 프로그램인 Digsilent Power Factory를 이용하였다. 임계 제거시간에 미치는 요인으로는 연계되는 계통의 단락용량(단락전류). 풍력발전 용량, 풍력발전기 역률, 풍력 발전시스템과 연계되는 계통사이의 전용선 길이, 부하 용량이나 역률 등이 있으며 이들의 변화에 대한 임계 제거시간의 영향을 분석하였다.

• 대한전기학회논문지:전력기술부문A
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• 제52권3호
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• pp.151-157
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• 2003

Wind farm interconnected with grid can supply the power into a power network not only the normal conditions, but also the fault conditions of distribution network. If the fault happened in the distribution power line with wind fm, the fault current level measured in a relaying point might be lower than that of distribution network without wind turbine generator due to the contribution of wind farm. Consequently, it may be difficult to detect the fault happened in the distribution network connected with wind generator This paper describes the effect of the interconnected wind turbine generators on protective relaying of distribution power lines and detection of the fault occurred in a power line network. Simulation results shows that the current level of fault happened in the power line with wind farm depends on the fault impedance, the fault location. the output of wind farm. and the load condition of distribution network.