• 한국소음진동공학회논문집
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• 제19권12호
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• pp.1252-1259
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• 2009

Due to the international competition and global pressure, the roll speed is increased. However, higher speeds increase the power density in the process as well as the plant's potential to react with vibrations. Under certain operating conditions, vibrations may occur, which again cause chattermarks, strip rupture or coil break fault. The appropriate condition monitoring is needed to improve product quality and availability. The aim of condition monitoring is to reduce maintenance costs, increase productivity and improve product quality. This paper proposes a condition monitoring tool designed for the classification of coil break fault. This method is used to cold rolling mill for faults monitoring based on vibration and motor current signals. The results show that the performance of classification has high accuracy based on experimental work.

• International Journal of Aeronautical and Space Sciences
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• 제4권1호
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• pp.1-8
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• 2003

In this paper, a reconfigurable flight control system is designed by applying the sliding mode control scheme. The sliding mode control method is a nonlinear control method which has been widely used because of its merits such as robustness and flexibility. In the sliding mode controller design, the signum function is usually included, but it causes the undesirable chattering problem. The chattering phenomenon can be avoided by using the saturation function instead of signum function. However, the boundary layer of the sliding surface should be carefully treated because of the use of the saturation function. In contrast to the conventional approaches, the thickness of the boundary layer of our approach does not need to be small. The reachability to the boundary layer is guaranteed by the sliding mode controller. The fault detection and isolation process is operated based on a sliding mode observer. To evaluate the reconfiguration performance, a numerical simulation using six degree-of-freedom aircraft dynamics is performed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 A
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• pp.476-478
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• 2001

Coordination under short-circuit conditions is a systematic application of protective devices in the electrical power system, which, in response to a fault, will remove only a minimum amount of equipment from service. The objective is not only to minimize the equipment damage and process outage costs, but also to protect personnel from the effects of these failures. The coordination study of an electric power system consists of an organizes time-current study of all devices in series from the utilization device to the source. This study is a comparison of the time it takes the individual devices to operate when certain levels of normal or abnormal current pass through the protective devices. The objective of a coordination study is to determine the characteristics, ratings, and settings of overcurrent protective devices that will ensure that the minimum unfaulted load is interrupted when the protective devices isolate a fault or overload anywhere in the system. At the same time, the devices and settings selected should provide satisfactory protection against overloads on the equipment and interrupt short-circuit as rapidly as possible.

• 한국콘텐츠학회논문지
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• 제7권3호
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• pp.25-33
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• 2007

전력계통의 갑작스런 고장은 막대한 경제적 손실을 초래함으로 이를 방지하기 위한 전력계통의 상태를 진단하는 모니터링은 무엇보다도 중요하다. 본 논문에서는 FCM과 SOM을 이용하여 다양한 전력설비 중에서 가장 중요한 역할을 담당하는 전력용 변압기의 고장진단 알고리즘을 개발한다. 즉, FCM은 효과적인 특징점을 선택과 학습시간을 줄이기 위해 수행하고, SOM에 의해 변압기의 고장진단이 이루어진다. 제안된 방법은 변압기의 고장진단 뿐만 아니라 열화진행추이 특성까지 분석한다. 제안된 방법은 다양한 사례 연구를 통해 우수성을 입증하였다.

• 조명전기설비학회논문지
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• 제12권2호
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• pp.38-44
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• 1998

본 논문에서는 변전설비 운용의 자동화를 실현하기 위하여 변전설비에서 발생하는 다양한 사고를 판정할 수 있고, 변전설비 사고가 송전설비로 확산되는 경우에 대비하기 위하여 송전설비의 진단기능을 부가시킨 지역급전분소의 운전자 지원을 위한 지능적 통합 고장진단 시스템을 개발하였다. 본 논문에서 제안한 전문가 시스템은 변전설비와 송전설비에서 발생하는 다양한 사고를 진단할 수 있으며, 데이터 이중화 장치를 통하여 감시제어 시스템의 데이터 베이스를 공유하게 함으로서 최소한의 부담으로 기존의 감시제어 시스템에 설치할 수 있도록 하였다. 또한 지식에 포함된 불확실성을 처리하기 위하여 퍼지추론을 수행하였고, 모듈라 프로그래밍 기법과 메타-인퍼런스 기법을 사용하고 있으며, 저가의 개인용 컴퓨터로 구현하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2003년도 가을 학술발표회 논문집
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• pp.103-114
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• 2003

This paper aims to propose a method that helps maintenance engineers to evaluate the damage states of bridge structure systems by using a Fuzzy Fault Tree Analysis. It may be stated that Fuzzy Fault Tree Analysis may be very useful for the systematic and rational fuzzy reliability assessment for real bridge structure systems problems because the approach is able to effectively deal with all the related bridge structural element damages in terms of the linguistic variables that incorporate systematically experts experiences and subjective judgement. This paper considers these uncertainties by providing a fuzzy reliability-based framework and shows that the identification of the optimum maintenance scenario is a straightforward process. This is achieved by using a computer program for LIFETIME. This program can consider the effects of various types of actions on the fuzzy reliability index profile of a deteriorating structures. Only the effect of maintenance interventions is considered in this study. However. any environmental or mechanical action affecting the fuzzy reliability index profile can be considered in LIFETIME. Numerical examples of deteriorating bridges are presented to illustrate the capability of the proposed approach. Further development and implementation of this approach are recommended for future research.

• Smart Structures and Systems
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• 제21권2호
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• pp.249-255
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• 2018

Many studies in risk management have been focused on management process, contract relation, and risk analysis in the past decade, but very few studies have addressed project risks from the perspective of risk efficiency. This study started with using Fault Tree Analysis to develop a framework for the decision-making support system of risk management from the perspective of risk efficiency, in order for the support system to find risk strategies of optimal combination for the project manager by the trade-off between project risk and cost of project strategies. Comprehensive and realistic risk strategies must strive for optimal decisions that minimize project risks and risk strategies cost while addressing important data such as risk causes, risk probability, risk impact and risk strategies cost. The risk management in the construction phase of building projects in Taiwan upon important data has been analyzed, that provided the data for support system to include 247 risk causes. Then, 17 risk causes were extracted to demonstrates the decision-making support system of risk management from the perspective of risk efficiency in building project of Taiwan which could reach better combination type of risk strategies for the project manager by the trade-off between risk cost and project risk.

• 한국철도학회논문집
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• 제12권2호
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• pp.190-198
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• 2009

본 연구에서는 승객, 공중 및 직원의 철도 사상사고를 대상으로 위험도 평가모델을 개발하였다. 이를 위해 철도 사상사고의 위험요인을 분석하여 관련 위험사건을 정의하였고, 위험사건의 발생을 초래하는 위험요인들의 논리적 연계성을 사건발생 시나리오로 구성하여 사건발생빈도 평가모델을 고장수목(Fault Tree)을 이용하여 개발하였다. 또한 사건수목(Event Tree)을 이용하여 인명피해를 초래하는 영향인자를 사건진전 시나리오로 구성하고, 위험사건별 사고 심각도를 등가사망지수로 환산하여 계산하는 위험도 평가모델을 개발하였다. 본 연구의 결과는 비용효과 분석, 안전대책의 민감도 분석 등에 다양하게 활용될 수 있다.

• Journal of Electrical Engineering and Technology
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• 제13권1호
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• pp.1-10
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• 2018

Wide-area monitoring of tree-related high impedance fault (THIF) efficiently contributes to increase reliability of large-scaled network, since the failure to early location of them may results in critical lines tripping and consequently large blackouts. In the first place, this wide-area monitoring of THIF requires managing the placement of sensors across large power grid network according to THIF detection objective. For this purpose, current paper presents a framework in which sensors are distributed according to a predetermined risk map. The proposed risk map determines the possibility of THIF occurrence on every branch in a power network, based on electrical conductivity of trees and their positions to power lines which extracted from spectral data. The obtained possibility value can be considered as a weight coefficient assigned to each branch in sensor placement problem. The next step after sensors deployment is to on-line monitor based on moving data window. In this on-line process, the received data window is evaluated for obtaining a correlation between low frequency and high frequency components of signal. If obtained correlation follows a specified pattern, received signal is considered as a THIF. Thereafter, if several faulted section candidates are found by deployed sensors, the most likely location is chosen from the list of candidates based on predetermined THIF risk map.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.102-103
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• 2007

In order to apply resistive superconducting fault current limiters into electric power systems, the urgent issues to be settled are as follows, such as initial installation price of SFCL, operation and maintenance cost due to ac loss of superconductor and the life of cryostat, and high voltage and high current problems. The ac loss and high cost of superconductor and cryostat system are main bottlenecks for real application. Furthermore in order to increase voltage and current ratings of SFCL, a lot of superconductor components should be connected in series and parallel which resulted in extreme high cost. Thus, in order to make practical SFCL, we designed novel hybrid SFCL which combines superconductor and conventional electric equipment including vacuum interrupter, power fuse and current limiting reactor. The main purpose of hybrid SFCL is to drastically reduce total usage of superconductor by adopting current commutation method by use of superconductor and high fast switch. Consequently, it was possible to get the satisfactory test results using this method, and further works for practical applications are in the process.