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현승호(Seung Ho Hyun),이성오(Sung O Lee) 대한전기학회 2009 대한전기학회 학술대회 논문집 Vol.2009 No.7
It is expected, in the near future, that the use of distributed generation systems should be increased considerably. In this case, distance relay algorithm should be developed in the manner that it can reduce the error due to the in-feed effect. This paper presents a method to consider the fault current rushed from the remote end of a line. In the steady-state, the relays in both ends exchange the voltages of upper nodes. If a fault is perceived, the relay calculates fault location taking the fault current from the remote end by using voltage data of the remote ends obtained just before the fault. Even though this method has inevitable error, it can show more precise fault allocation. The suggested method is applied to a typical transmission system with two power sources in both ends to verify its effectiveness.
CH₄/Air 예혼합화염의 하류영역에서 NOx 생성특성에 관한 수치해석
현승호(Seung-Ho Hyun),황철홍(Cheol-Hong Hwang),탁영조(Young-Jo Tak),이창언(Chang-Eon Lee) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11
In this study, the NOx formation characteristics of one-dimensional CH₄/Air premixed flame using detailed-kinetic chemistry are examined numerically. The combustor length and the amount of heat loss are varied to investigate the effect of residence time and heat loss on the NOx formation in a post-flame region. In the flame region, NO is mainly produced by the Prompt NO mechanism including N₂O-intermediate NO mechanism over all equivalence ratio. However, thermal NO mechanism is more important than Prompt NO mechanism in the post-flame region . In the case of adiabatic condition, the increase of combustor length causes the remarkable increase of NO em ission at the exit due to the increas e of residence time. On the other hand, NO reaches the equilibrium state in the vicinity of flame region, considering radiation and conduction heat transfer. Furthermore the NO, in the case of φ=1.2, is gradually reduced in the downstream region as the heat loss increase. From these results, it can be concluded that the control of heat loss and heat transfer near combustor wall should be recognized as an important NOx reduction technology.
CH₄/Air 예혼합화염의 고효율 연소조건에서 열손실에 따른 NOx 및 CO 배출특성
현승호(Seung-Ho Hyun),황철홍(Cheol-Hong Hwang),이창언(Chang-Eon Lee),김세원(Se-Won Kim),장기현(Gi-Hyun Jang) 한국연소학회 2008 한국연소학회지 Vol.13 No.1
Emission characteristics of NOx and CO with heat loss under high efficiency combustion conditions of CH₄/Air prmixed flame were examined numerically using detailed-kinetic chemistry. The one-dimensional combustor length was fixed 5cm, and the equivalence ratio was varied from 0.75 to 0.95. To consider the effects of heat loss on NOx and CO formation, the radiative heat loss rate and combined heat loss rate of conductive and convective heat transfer are included. The following conclusions were drawn. In order to reduce the NOx and CO emission level simultaneously, the temperature of product gases must be reduced under 1,800K as soon as possible but kept over 1,300K during the residence time which is needed to converge CO to CO₂.
현승호(Seung ho Hyun),이성오(Sung O Lee) 대한전기학회 2009 대한전기학회 학술대회 논문집 Vol.2009 No.11
In this paper, a fault allocation method is suggested for distribution systems with fault currents at both ends. Tn a smart grid with various distributed generation systems in operation, the power flow may not be one directional. Therefore, the over-current relaying protection, most common in distribution system protection is not proper anymore. The proposed method uses the power balance condition in a section for both fault detection and allocation. The suggested method cannot consider the effect of the power loss at grounding. However, in spite of this weakness, the fault allocation error was not more than 5.2% even in the case with fault currents at both ends. Furthermore, there is no recursion process which can be the cause of time consuming. It is expected, if the grounding condition is considered adequately, the suggested method can be a candidate of protection method for complicated distribution systems like smart grids.
분산전원이 연결된 배전계통에서의 모델 기반 지락고장 위치 검출 방법
현승호(Seung Ho Hyun),강석준(Seok Jun Kang) 대한전기학회 2021 전기학회논문지 Vol.70 No.8
In a distribution system with distributed energy resources, power flow is not fixed in a single direction. Therefore, from the protection coordination’s point of view, existing over-current protection scheme is not adequate any more. On the other hand, in future’s distribution systems, it is expected that various kinds of information is available with more accuracy, which is one of the advantageous points in protection. This paper suggests a novel fault location method with these factors considered. In the proposed scheme, an existing protective device like a recloser of fuse is replaced by a smart relay with simple calculation and communication ability. A distribution system is divided into several segments and the fault location is calculated through successive circuit analysis at each segment using concentrated parameters of the lines. In this, synchronized power data are assumed to be available at each loading point before a fault occurs and it is also assumed that each load is not changed abruptly. The suggested method is applied to several distribution system models, through computer simulations, and is verified to be useful with accurate fault location.
玄升鎬(Seung Ho Hyun),陳保建(Bu Gun Jin),李承宰(Seung Jae Lee) 대한전기학회 2007 전기학회논문지 Vol.56 No.11
This paper presents a distance relaying algorithm for phase-to-ground faults in transmission lines under Multi- Agent protection environment. In normal condition, a distance relay agent stores the latest states, e.g., voltage of source side, voltage of the opposite side and the loading conditions, etc., through communication between the agents. Once a fault occurs, the relay calculates the fault location using the knowledge about the states just before the fault happens. This stand-alone operation is to improve reliability under the fault condition at which the accuracy or time required for communication may not be guaranteed. The mathematical expression of fault location is derived through loop analysis, before hand, in the manner that both fault current from the opposite end and fault resistance are included implicitly so that their effects are minimized. The suggested algorithm is applied to a typical transmission system with two power sources on both ends to show its effectiveness.
계통 부하량과 풍력발전량의 확률적 관계를 고려한 발전량 적정성 평가 연구
김광원(Gwang-Won Kim),현승호(Seung-Ho Hyun) 한국조명·전기설비학회 2007 조명·전기설비학회논문지 Vol.21 No.10
본 논문에서는 발전량 적정성 평가를 위한 풍력발전 모형의 제안하였다. 풍력 발전량과 계통 부하량은 일 년을 주기로 하는 주기함수 형태이므로, 둘 중 하나의 물리량이 주어지면 다른 물리량의 발생 확률을 계산할수 있다. 본 논문에서는 가상의 데이터를 바탕으로 두 물리량을 k-means 클러스터링 알고리즘으로 단계화하였고, 각 단계간의 확률적인 관계를 계산하였다. 제안하는 풍력발전 모형은 상태샘플링(state sampling)에 기반을 둔 몬테카를로 모의로써 발전량 적정성을 평가하는데 적합하다. This paper presents the wind-power model for generation adequacy assessment. Both wind-power and system load depend on time of a year and show their periodic nature with similar periods. Therefore, the two quantities have some probabilistic relations, and if one of them is given, the other can be decided with some probability. In this paper, the two quantities are quantized by k-means clustering algorithm and related probabilities among the cluster centers are calculated using sequential wind-power and system load data. The proposed model is highly expected to be applied for generation adequacy assessment by Monte-Carlo simulation with state sampling method.
이창언(Chang-Eon Lee),현승호(Seung-Ho Hyun),황철홍(Cheol-Hong Hwang),이성민(Sung-Min Lee),하영철(Young-Cheol Ha),이강진(Kang-Jin Lee) 한국연소학회 2007 한국연소학회지 Vol.12 No.1
The diversification of import districts of natural gas is trying to prepare an increase in the demand and price. The interchangeability of natural gases should be examined prior to supply to gas appliances, although compositional differences among natural gases are not large. The object of this study is to investigate numerically the thermodynamic and transport properties as well as information on combustion of 6 natural gases. Comparing the properties of BOG1 with those of standard gas, the maximum differences of heating value, Wobbe index, air-fuel ratio, and specific heat are 10%, 4%, 10% and 5.54%, respectively. That is, the BOG1 is required careful application. However, all gases except for BOG1 show the similar properties with standard gas. Finally, the combustion information such as flame temperature and burning velocity are examined. These results will provide the useful information related to the interchangeability of various natural gases in practical combustion appliances.
김광원(Gwang Won Kim),현승호(Seung-Ho Hyun) 한국조명·전기설비학회 2013 조명·전기설비학회논문지 Vol.27 No.7
This paper presents an effective pedagogical method for nodal analysis in linear circuit. In the proposed method, basic equations are built only for passive elements and independent current sources. And then, the basic equations are modified by considering other sources such as voltage sources and dependent current sources. In the proposed method, the equations are presented in form of a matrix and a vector of which elements are built systematically by considering every element in a circuit one by one. This make the proposed method easy to apply to intricately composed circuit and easy to solve the final simultaneous equations and easy to realize as computer program for nodal analysis and easy to memorize compared to the conventional method.