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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.
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.
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),이병은(Byung-Eun Lee),정태영(Tai-Ying Zheng),김연희(Yeon-Hee Kim) 대한전기학회 2010 전기학회논문지 Vol.59 No.5
When a circuit breaker is opened, a large capacitance around the buses, the circuit breaker and the potential transformer (PT) might cause PT ferroresonance. During PT ferroresonance, the iron core repeats saturation and unsaturation even though the supplied voltage is a rated voltage. This paper describes an analytical analysis of PT ferroresonance in the transient-state. To analyze ferroresonance analytically, the iron core is modelled by a simplified two-segment core model in this paper. Thus, a nonlinear ordinary differential equation (ODE) for the flux linkage is changed into a linear ODE with constant coefficients, which enables an analytical analysis. In this simplified model, each state, which is either saturated or unsaturated state, corresponds to one of the three modes, i.e. overdamping, critical damping and underdamping. The flux linkage and the voltage in each state are obtained analytically by solving the linear ODE with constant coefficients. The proposed transient analysis is effective in the more understanding of ferroresonance and thus can be used to design a ferroresonance prevention or suppression circuit of a PT.
풍력단지의 Fault Ride-Through 기능을 위한 연계선 보호용 거리계전기의 성능향상 기법
강용철(Yong-Cheol Kang),강해권(Hae-Gweon Kang),정태영(Tai-Ying Zheng),이병은(Byung-Eun Lee),장성일(Sung-Il Jang),김용균(Yong-Gyun Kim) 대한전기학회 2009 대한전기학회 학술대회 논문집 Vol.2009 No.7
A large wind farm should satisfy the requirements for a grid and accomplish the optimization of the wind farm system. In that point of view, the wind farm intertie protection system, which must consider the Fault Ride-Through (FRT) requirement for more reliable protection, should be improved. This paper proposes a modified distance relay suitable for protection of a wind farm intertie considering a FRT requirement. The frequency change is used to discriminate the intertie fault from a outside zone fault. The performance of the proposed algorithm is verified using a PSCAD/EMTDC simulator.
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.
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.
강용철(Yong-Cheol Kang),이혜원(Hye-Won Lee),정태영(Tai-Ying Zheng),강해권(Hae-Gweon Kang) 대한전기학회 2009 대한전기학회 학술대회 논문집 Vol.2009 No.7
Power output of a wind farm fluctuates throughout a day. This affect a distance relay for wind farm intertie protection because a voltage of a relaying point varies due to fluctuating output of a wind farm. This paper describes the analysis of the response of a distance relay for intertie protection when the power output of a wind farm increases. A series of single phase to ground faults were also simulated and analyzed with PSCAD/EMTDC generated data.
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.
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.