• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.409-412
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• 1997

The phenomenon of water tree degradation of underground distribution power cables is taking place in polymeric insulation materials under the existence of water and application of electric stress, but water tree is not easy to observe, o water tree features in power cables are shown after cutting and dying with methyleneblue. In previous method, it is impossible to acquire continuous treeing data, and when the insulation material has been cut, the micro crack(water tree) has been damaged. In this paper, to overcome these deflects, the etching method is made use of making needle electrode about 170[${\mu}{\textrm}{m}$] diameter, and AgNO$_3$(silver nitrate) solution is used as liquid electrode to accelerate the growth of water trees. As a result of this study, water tree is observed in real-time with microscope. Electrical tree owing to water treeing is initiated at low electric field and grown with discontinuous. Namely, water tree is shown up a different characteristics of tree growth.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.04a
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• pp.346-349
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• 1997

It is well known that water treeing is one of the main cause of breakdown in underground power cables, but water tree is not easy to observe. This aging phenomenon was resulted in effect of water and electric field and so on. In this paper, Distilled water was used as water electrode to observe the water treeing in XLPE(cross-linked polyethylene). To observe easily, sample was made of pallet types so water tree was able to show by microscope. As a result, electrical tree appears at niddle electrode tip which was concentrated electric field, but water tree was shown up different types that were appealed in total area of water electrode as well as water electrode tip.

• Journal of Electrical Engineering and Technology
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• v.13 no.2
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• pp.637-647
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• 2018

In this paper, we propose a method to search candidates of network reconfiguration to restore distribution system with distributed energy resources using a level-based tree search algorithm. First, we introduce a method of expressing distribution network with distributed energy resources for fault restoration, and to represent the distribution network into a simplified graph. Second, we explain the tree search algorithm, and introduce a method of performing the tree search on the basis of search levels, which we call a level-based tree search in this paper. Then, we propose a candidate search method for fault restoration, and explain it using an example. Finally, we verify the proposed method using computer simulations.

• Journal of Institute of Control, Robotics and Systems
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• v.4 no.1
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• pp.123-133
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• 1998

In this paper, an algorithm of fault detection and diagnosis during operation of induction motors under the condition of various loads and rates is investigated. For this purpose, the spectrum pattern of input currents is used in monitoring the state of induction motors, and by clustering the spectrum pattern of input currents, the newly occurrence of spectrum patterns caused by faults are detected. For the diagnosis of the fault detected, a fuzzy fault tree is designed, and the fuzzy relation equation representing the relation between an induction motor fault and each fault type, is solved. The solution of the fuzzy relation equation shows the possibility of occurence of each fault. The results obtained are summarized as follows : (1) Using clustering algorithm by unsupervised learning, an on-line fault detection method unaffected by the characteristics of loads and rates is implemented, and the degree of dependency for experts during fault detection is reduced. (2) With the fuzzy fault tree, the fault diagnosis process become systematic and expandable to the whole system, and the diagnosis for sub-systems can be made as an object-oriented module.

• Proceedings of the KIEE Conference
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• summer
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• pp.135-137
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• 2004

This paper describes new land use estimation method for long term load forecast using $R\startree$ algorithm. Where $R\startree$ algorithms is a proposed method for efficient spatial search. An estimation result showed that execute time of the proposed method is prior to execute time of conventional method.

• Fire Science and Engineering
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• v.14 no.1
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• pp.1-7
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• 2000

Internal insulators give rise to partial discharge(PD), which cause local breakdown and even entire insulation breakdown. Treeing due to PD is one of the main causes of breakdown of the insulating materials and reduction of the insulation life. Therefore the necessity for establishing a method to diagnose the aging of insulation materials and to predict the breakdown of insulation has become important. From this viewpoint, we have studied on Electric Field dependence of tree shape in Low Density Polyethylene about treeing phenomena occurring on the high electrical field. As the result, under the reasoning that the growing of tree supposing when the inner part of tree is either dielectrec or conductor has the intermediate characteristics between dielectrec and conductor, theoretically investicated results well according with the experimental results.

• Bulletin of the Korean Mathematical Society
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• v.57 no.1
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• pp.245-250
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• 2020

Let γt(G) and τ(G) denote the total domination number and vertex cover number of graph G, respectively. In this paper, we study the total domination number of the central tree C(T) for a tree T. First, a relationship between the total domination number of C(T) and the vertex cover number of tree T is discussed. We characterize the central trees with equal total domination number and independence number. Applying the first result, we improve the upper bound on the total domination number of C(T) and solve one open problem posed by Kazemnejad et al..

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.1
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• pp.9-15
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• 2010

As catenary supply electric power directly to the railway system, it is very important to prevent an accident of a catenary for appropriate train operation. This paper proposed the assessment the outage data for "British Catenary Safety Analysis Report" and Korean data to compare the reliability of the railway system. The analyzed data were applied to Event Tree and Fault Tree algorithm to calculate the reliability indices of railway system. Event tree is created and gate results of fault tree analysis are used as the source of event tree probabilities. Fault tree represents the interaction of failures and basic events within a system. Event Tree and Fault Tree analysis result is helpful to assess the reliability to interpreted. The reliability indices can be used to determine the equipment to be replaced for the entire system reliability improvement.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.270-273
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• 2001

Electrical tree is studied widely by manufacture state of insulating material fare and blazing fire diagnosis system of use in phenomenon of part discharge that happen for main cause of dielectric breakdown of equipment for electric power. Use process that draw tree pattern here measuring above zero to study special quality of this electricity tree, real-time processing by image processing is proposed because reproduction of tree blazing fire process drops and pattern of tree is difficult correct quantification of tree growth by existent visual observation by involution. This research presents general process that need in image processing of tree blazing fire, and that remove various noises that happen in above zero by measuring electrical tree dividing background and complete view in measured above zero taking advantage of specially proposed complete view object abstraction techniques effectively and quantification of tree becomes easy naturally, can apply to dielectric breakdown estimate because can chase growth process of tree.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.5
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• pp.960-967
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• 2009

Power supply system of electric railway has a diversity of safety problems since it should supply high electric power to the trains moving high speed with a lot of passengers on board. This paper provides a risk assessment approach to safety management of the electric railway facilities. Construction of database from field accident information, risk assessment and management of the risk are carried out systematically to ensure the safety. The risk assessment includes hazard identification, cause analysis by FTA(Fault Tree Analysis), consequence analysis by EVA(Event Tree Analysis), and loss analysis. In terms of the severity and the probability of the accidents deduced by these analyses, the risk of the accidents is assessed by using a risk matrix designed for electric railway facilities. Based on the risk assessment, possible risk mitigation options are identified and evaluated by analyzing their impact on the risk reduction and their cost benefit ratio. The long-term safety of the electric railway facilities can be ensured by renewal of the risk assessment and the risk mitigation option analysis with continuous accident database update. The proposed approach is applied to the electric railway facilities of Korean railway based on the accident data from 2002 to 2008.