• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 추계학술대회 논문집 전기설비전문위원
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• pp.83-88
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• 2004

As the electric system is getting larger to meet the increasing demand for electric power, the rating of power apparatus is becoming inevitably higher in its working voltage and larger in its capacity. According to KEPCO reports, power transformers in the KEPCO system have undergone troubles such as winding short insulation breakdowns every year since 1981. the cause of this troubles were high one line grounding fault currents in KEPCO systems that had direct grounding systems. KEPCO has installed the NGR(neutral grounding reactor) to lower this fault current and reduced winding short insulation breakdowns in power transformers. But when a circuit breaker opened a no load bus, some trips of circuit breakers for protecting transformer have occurred by mal-operation of 59GT(overvoltage ground relay) that detect disconnection of NGR. Therefore, in this paper, we analyzed the cause and examined the effect of time delav circuit to prevent wrong operation of 59GT.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 C
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• pp.946-948
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• 1998

The distance relay is very important for transmission line protection. A quadrilateral zone shape is used mainly for a modern digital distance relay. The shape of quadrilateral is vendor specific. At the stage of design, the shape is determined considering all possible types of faults and diverse configurations of system. Also this type relay must be designed to avoid the operation by a sound phase at single-Phase-to-ground fault, by a sound phase at two-phase-to-ground fault. The effect of a source impedance and a load impedance is another important factor to design. In this paper, a reliable zone shape which is appropriate for the KEPCO's transmission system is provided.

• 대한전기학회논문지:전력기술부문A
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• 제55권12호
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• pp.555-560
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• 2006

As it has been reported that more than 60% of transmission line faults occurs due to lightning strokes, lighting is one of concerned issues in electric power utility company. Most of transmission line is double circuit in Korea. Double circuit outages account for 33.7 percent of total lightning faults from 1996 to 2004. Even though transmission fault might be cleared shortly by protective system, it could deteriorate the power quality accompanied with sag or flicker. Moreover, double circuit fault may lead to more aggravated situation, for instance, blackout. To Protect transmission lines from lightning stroke, reduction of tower footing resistance, multiple ground wires and unbalanced insulation in double circuit lines have been adopted. In this paper, we would like to introduce insulation design standards for lightning protection of Korea Electric Power Corporation.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.566-570
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• 2001

Generally, grounding systems are responsible for the safe operation of a power system. Their performance guarantees equipment protection and personnel safety under condition of the limited ground potential rise and touch voltages as well as step voltages under ground fault conditions. Therefore, it is necessary to measure the ground resistance frequently for checking the performance of grounding system, In this paper the ground resistance measuring system using digital signal processor and high-performance L-C resonant band pass filter is presented. The signal current magnitude for measuring ground resistance in this system is $10^{-1}[A]\;to\;5\times10^{-2}[A]$ and the current frequency is 30[Hz].

• 조명전기설비학회논문지
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• 제22권1호
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• pp.141-148
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• 2008

본 논문에는 22.9 kV-Y 배전계통의 1선 지락고장이 인체의 안전 및 저압설비의 보호에 대한 실험적 결과를 기술하였다. 새로이 제정된 KS C IEC 60364 규격군에 따른 고압 충전도체가 대지에 접촉되는 지락고장에 의한 위험전압과 저압기기의 스트레스전압을 평가하기 위해서 22.9[kV] 중성점 다중접지계통에 대한 실증실험을 수행하였다. 실험결과로부터 KS C IEC 60364 규격군을 기존의 국내배전계통에 적용할 때 부합되지 않는 중대한 문제점을 도출하였으며, 22.9 kV-Y 다중접지와 수용가설비접지를 공용하는 공통접지계통에서 발생하는 지락고장에 의한 일시적 과전압에 대한 효과적인 보호대책을 제시하였다. 결국 22.9 kV-Y계통과 저압설비를 공통접지로 하는 경우 인체와 저압설비의 안전을 위한 효과적인 보호대책의 구현에는 등전위본딩이 중요한 필수적 요건임이 밝혀졌다.

• 조명전기설비학회논문지
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• 제22권2호
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• pp.71-79
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• 2008

철도 고압배전선로의 경우 궤도를 따라 양방향으로 선로연변에 통신 및 신호설비와 병행하여 가공 또는 지중선로로 설치되어 있다. 가공선로의 경우에는 대기중에 노출되어 있어 뇌격, 폭풍우, 염해 등 자연현상으로 인한 고장발생이 다수 발생하고 있으며, 이에 따른 보호장치의 오 부동작이 빈번하게 발생하고 있다. 철도 고압배전선로에서 발생하는 사고 중 가장 많은 것은 1선 지락이지만 이밖에 선간 단락, 심할 경우에는 3선 지락(단락)으로까지 진전되는 사고가 있을 뿐만 아니라 단선 사고까지 발생하는 경우도 있다. 따라서 사고를 방지하기 위해서는 보다 상세한 점검보수가 필요하며, 고장발생시 조기발견과 신속한 고장처리는 철도안전수송에 중요하다. 본 논문에서는 철도 고압배전계통의 주류를 이루게 될 22.9[kV] 직접접지 계통을 대상으로 고장 발생시 고장 위치를 신속하게 표정할 수 있는 고장점 표정 알고리즘 개발을 위해 22.9[kV] 고압배전계통을 모델링 하여 특성해석과 고장해석을 수행하였고, 정확한 고장점 표정이 가능한 반복계산법을 이용한 알고리즘을 제시하였으며, 사례연구를 통해 성능을 입증하였다.

• 조명전기설비학회논문지
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• 제26권7호
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• pp.70-76
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• 2012

In general, the unidirectional power flow is normal in distribution feeders before activation of distributed power source such as PV. However, the interactive power flow is likely to occur in case of the power system under distributed generation. This interactive power flow can cause an unexpected effect on convectional protection coordination systems designed based only on the unidirectional power flow system. When the power line system encounters a problem, the interactive power flow can be a contributed current source and this makes the fault current bigger or smaller compared to the unidirectional case. The effect of interactive power flow is varied depending on the location of the point to ground fault, relative location of the PV, and connection method. Therefore it is important to analyse characteristics of fault current and interactive flow for various transformer connection and location of the PV. This paper proposes a method of improved protection coordination which can be adopted in the protective device for customers in distribution feeders interconnected with the PV. The proposed method is simulated and analysed using PSCAD/EMTDC under various conditions.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2005년도 추계학술대회 논문집
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• pp.699-704
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• 2005

In the station of the railway and the subway various illumination equipment and a general power equipment for a passenger convenience, the signal equipment and the communication equipment which is necessary to the train operation provided. At the all of like this equipment from the electric room which is established in each station by changing from high voltage to low voltage and it supplies from the illumination transformer, the power transformer and the signal transformer. If it supplies to the equipment from the high voltage to the low voltage, it must be established to contact protection device in between the high voltage coil and the low voltage coil. Also it must do the grounding faulting device at the low voltage lines, the earthing devices at apparatus for the protection of an electric shock and an electric fire by the electric relation law. Compared the related regulations between the facilities which require protective functions such as grounding fault or earthing in public utilities like subway stations, and the facilities which do not require line earthing or protective functions such as electricity supplied for signalling the train. Also, will describe a countermeasure for the accident from a grounding fault.

• Smart Structures and Systems
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• 제24권1호
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• pp.53-65
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• 2019

Misaligned wind-wave and seismic loading render offshore wind turbines suffering from excessive bi-directional vibration. However, most of existing research in this field focused on unidirectional vibration mitigation, which is insufficient for research and real application. Based on the authors' previous work (Sun and Jahangiri 2018), the present study uses a three dimensional pendulum tuned mass damper (3d-PTMD) to mitigate the nacelle structural response in the fore-aft and side-side directions under wind, wave and near-fault ground motions. An analytical model of the offshore wind turbine coupled with the 3d-PTMD is established wherein the interaction between the blades and the tower is modelled. Aerodynamic loading is computed using the Blade Element Momentum (BEM) method where the Prandtl's tip loss factor and the Glauert correction are considered. Wave loading is computed using Morison equation in collaboration with the strip theory. Performance of the 3d-PTMD is examined on a National Renewable Energy Lab (NREL) monopile 5 MW baseline wind turbine under misaligned wind-wave and near-fault ground motions. The robustness of the mitigation performance of the 3d-PTMD under system variations is studied. Dual linear TMDs are used for comparison. Research results show that the 3d-PTMD responds more rapidly and provides better mitigation of the bi-directional response caused by misaligned wind, wave and near-fault ground motions. Under system variations, the 3d-PTMD is found to be more robust than the dual linear TMDs to overcome the detuning effect. Moreover, the 3d-PTMD with a mass ratio of 2% can mitigate the short-term fatigue damage of the offshore wind turbine tower by up to 90%.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 추계학술대회 논문집 전력기술부문
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• pp.283-285
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• 2005

This paper presents a new two-terminal numerical algorithm for fault location estimation and for faults recognition using the synchronized phasor in time-domain. The proposed algorithm is also based on the synchronized voltage and current phasor measured from the PMUs(Phasor Measurement Units) installed at both ends of the transmission lines. Also the arc voltage wave shape is modeled numerically on the basis of a great number of arc voltage records obtained by transient recorder. From the calculated arc voltage amplitude it can make a decision whether the fault is permanent or transient. In this paper the algorithm is given and estimated using DFT(Discrete Fourier Transform) and the LES(Least Error Squares Method). The algorithm uses a very short data window and enables fast fault detection and classification for real-time transmission line protection. To test the validity of the proposed algorithm, the Electro-Magnetic Transient Program(EMTP/ATP) and MATLAB is used.