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CT와 CCVT의 오차를 고려한 거리 계전기의 응동 분석
강용철(Yong-Cheol Kang),정태영(Tai-Ying Zheng),최재선(Jae-Sun Choi),강해권(Hae-Gweon Kang),김광무(Kwang-Moo Kim),장성일(Sung-Il Jang),김용균(Yong-Gyun Kim) 대한전기학회 2008 대한전기학회 학술대회 논문집 Vol.2008 No.11
A distance relay has been widely used for transmission line protection. The distance relay detects a fault based on the calculated impedance i.e. the ratio of the voltage to the current measured from a current transformer (CT) and a coupling capacitor voltage transformer (CCVT), respectively. When a fault occurs and a C saturates due to the magnitude of fault current, dc component, primary time constant, and the remanent flux of the iron core, the secondary current of a CT is distorted. On the other hand, non-fundamental components generated during a fault can increase the error of a CCVT, particularly when a fault distance is short. The distortion of the current and voltage can cause mal-operation or the operating time delay of a distance relay. This paper describes the response of a distance relay considering the errors of a CT and a CCVT. The results indicate that the severe distortion of a CT and a CCVT have noticeable effect to a distance relay.
강용철(Yong-Cheol Kang),정태영(Tai-Ying Zheng),국경수(Kyung-Soo Kook),강해권(Hae-Gweon Kang),이병은(Byung-Eun Lee),김연희(Yeon-Hee Kim) 대한전기학회 2010 대한전기학회 학술대회 논문집 Vol.2010 No.7
This paper proposes a wind turbine protection method using the negative sequence current flowing through the wind turbine. The feasibility of the proposed method is proved by applying the symmetrical analysis to the power system integrated with a large scale wind farm. The performance of the proposed method is verified based on the EMTP-RV simulation. The results show that the negative sequence currents flowing through the wind turbines connected to the faulted feeder, where a single-phase-to-ground fault occurs, is much larger than those flowing through the wind turbines connected to the healthy feeder, and thus the magnitude of the negative sequence current can be used to easily detect whether there is a single-phase-to-ground fault occurring in the connected feeder.
자속-자화 전류 곡선과 전압-철손 전류 곡선을 이용한 측정용 철심 변류기의 보상 알고리즘 개발
강용철(Yong-Cheol kang),정태영(Tai-Ying Zheng),강해권(Hae-Gweon Kang),이병은(Byung-Eun Lee),김용균(Yong-Gyun Kim) 대한전기학회 2009 전기학회논문지 Vol.58 No.10
This paper describes the design, evaluation and implementation of a compensating algorithm for an iron-cored measurement current transformer (CT) that removes the effects of the hysteresis characteristics of the iron-core. The exciting current resulting from the hysteresis characteristics of the core causes an error of the CT. The proposed algorithm decomposes the exciting current into the core loss current and the magnetizing current and each of them is estimated. The core loss current is calculated from the secondary voltage and the voltage-core loss current curve. The core flux linkage is calculated and then inserted into the flux-magnetizing current curve to estimate the magnetizing current. The exciting current at every sampling interval is obtained by summing the core loss and magnetizing currents and then added to the measured current to obtain the correct secondary current. The voltage-core loss current curve and flux-magnetizing current curves, which are different from the conventional curves, are derived in this paper. The performance of the proposed algorithm is validated under various conditions using EMTP generated data. The experimental test results of an iron-core type electronic CT, which consists of the iron-core and the compensation board, are also included. The results indicate that the proposed algorithm can improve the accuracy of the measurement CT significantly, and thus reduce the size and the cost of the CT.
김연희(Yeon-Hee Kim),정태영(Tai-Ying Zheng),이진식(Jin-Shik Lee),강용철(Yong-Cheol Kang) 대한전기학회 2011 대한전기학회 학술대회 논문집 Vol.2011 No.10
This paper assumes that a wind mast (WM) is installed several kilometers from a wind power plant (WPP) to collect the direction and the speed of wind. The distance between the WM and the WPP is determined based on the expected storm speed to meet the ramp rate requirement of a grid code. This paper proposes a supervised shutdown algorithm of a large off-shore WPP in a heavy storm situation. Based on the information on the direction and the speed of wind measured at a WM, a sequence of wind generator group is generated. Each group is shut down with the required maximum ramp-down rate in the order of wind arriving time. The shutdown start/end times of each group may be re-scheduled to avoid superposition between adjacent two groups. If the wind speed exceeds the expected speed, the ramp rate is unable to meet the required grid code. In this case, the minimum number of the wind generator groups rate is decided, which are shut down with the twice the required ramp rate. The performance of the proposed supervised shutdown algorithm is verified considering various heavy storm scenarios. The results show that the proposed algorithm can protect the large WPP from various heavy storm situations, generating energy as much as possible with the minimal adverse effects on the power system stability.
강풍 시 전력망 연계기준을 만족하는 해상풍력발전단지 강제종료 방법
유약(Yue You),김연희(Yeon-Hee Kim),정태영(Tai-Ying Zheng),강용철(Yong-Cheol Kang) 대한전기학회 2011 전기학회논문지 Vol.60 No.7
A wind turbine (WT) should be shut down as fast as possible to minimize its own damage in a storm-driven situation. Shutdown of a large wind farm requires a power grid to have a ramp-up capability large enough to balance between generation and consumption of electrical energy. This paper proposes a supervised shutdown algorithm of a wind farm to meet a required ramp-down rate in a grid code in the case of a storm-driven situation. The information on the speed and the direction of wind is measured at a wind mast (WM) installed around a wind farm. If the wind speed exceeds a cut-out speed, the number of WTs to be shut down simultaneously is decided to meet a required ramp-down rate of a grid-code. Arrival times to each WT from the WM are calculated and sorted in the order of time. Then a sequence of groups is generated. The shutdown start/end times of each group are decided to avoid superposition between adjacent two groups. The performance of the proposed shutdown algorithm is verified under various storm scenarios. Results indicate that the proposed algorithm can not only protect the wind farm in the case of a storm-driven situation but also meet the required ramp-down rate. In addition, the algorithm can produce more energy than that of a conventional shutdown algorithm.
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.
강용철(Yong-Cheol Kang),최재선(Jae-Sun Choi),정태영(Tai-Ying Zheng),강해권(Hae-Gweon Kang),장성일(Sung-Il Jang),김용균(Yong-Gyun Kim),유영식(Young-Sik Ryu) 대한전기학회 2008 대한전기학회 학술대회 논문집 Vol.2008 No.11
A protection current transformer (CT) has been widely used for protection devices. When a fault occurs, a CT should provide the faithful reproduction of the primary fault current However, a CT may saturates due to the magnitude of fault current, dc component, primary time constant, and the remanent flux of the iron core, and the secondary current of a CT is distorted. The distorted current can cause mal-operation or the operating time delay of a protection relay. This paper provides a modeling of CT saturation using EMTP-RV. The performance of the proposed CT saturation modeling was investigated under various fault conditions varying the fault distance, fault inception angle, and remanent flux of the iron core. The results indicate that the proposed EMTP-RV modeling can operate correctly, and the reasons for CT saturation are verified by EMTP-RV simulations.
이혜원(Hye-Won Lee),김연희(Yeon-Hee Kim),정태영(Tai-Ying Zheng),이상철(Sang-Cheol Lee),강용철(Yong-Cheol Kang) 대한전기학회 2011 전기학회논문지 Vol.60 No.6
In a wind farm, a large number of small wind turbine generators (WTGs) operate whilst a small number of a large generator do in a conventional power plant. To maintain high quality and reliability of electrical energy, a wind farm should have equal performance to a thermal power plant in the transient state as well as in the steady state. The wind farm shows similar performance to the conventional power plant in the steady state due to the advanced control technologies. However, it shows quite different characteristics during fault conditions in a grid, which gives significant effects on the operation of a wind farm and the power system stability. This paper presents an analysis of response of a wind farm during grid fault conditions. During fault conditions, each WTG might produce different frequency components in the voltage. The different frequency components result in the non-fundamental frequencies in the voltage and the current of a wind farm, which is called by “beats”. This phenomenon requires considerable changes of control technologies of a WTG to improve the characteristics in the transient state such as a fault ride-through requirement of a wind farm. Moreover, it may cause difficulties in protection relays of a wind farm. This paper analyzes the response of a wind farm for various fault conditions using a PSCAD/EMTDC simulator.
강용철(Yong-Cheol Kang),이병은(Byung-Eun Lee),정태영(Tai-Ying Zheng),장성일(Sung-Il Jang),김용균(Yong-Gyun Kim) 대한전기학회 2009 대한전기학회 학술대회 논문집 Vol.2009 No.7
Ferroresonance is a resonance condition between a nonlinear iron core of a potential transformer (PT) and a capacitance. It can lead to PT voltages several times the normal equipment ratings, and cause the isolation broken and damage to equipments near the PT. This paper proposes a analysis method of PT ferroresonance in the time domain. Based on the simplified equivalent circuit, a differential equation was found and the flux was calculated when ferroresonance generates. The forced response and natural response were also analyzed. The performance of proposed analysis method was verified with the EMTP-RV generated data. The method can help analysis chaotic ferroresonance and periodic ferroresonance.