• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.9
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• pp.31-39
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• 2009

This paper shows prioritization process for equipment investment plans considering reliability indices and economical efficiency. To decide prioritization of distribution investment projects, we made a distribution system model using system configuration, it's component and load information and designed several investment alternatives to improve reliability of present system. Lastly, we proposed a evaluation model of economical efficiency assessment on distribution investment alternative projects. To analyze influence by reliability and economical efficiency, we produced economical effects with applying time-varying failure rate of KEPCO's main equipments of distribution system and interruption cost of electric power affected by investment. Finally, in order to insure the validity of this proposed methodology, we compared investment prioritization by economical evaluation with that of real investment alternatives of KEPCO's branch office. In conclusion, this paper shows what and how to interpret the reliability effects of distribution system investments into financial indicators beneficial for power utilities's managers to make decision on the perspective of corporate value.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.60 no.3
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• pp.114-119
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• 2011

Large Power transformer is a complex and critical component of power plant and consists of cellulosic paper, insulation oil, core, coil etc. Insulation materials of transformer and related equipment break down to liberate dissolved gas due to corona, partial discharge, pyrolysis or thermal decomposition. The dissolved gas kinds can be related to the type of electrical faults, and the rate of gas generation can indicate the severity of the fault. The identities of gases being generated are using very useful to decide the condition of transformation status. Therefore dissolved gas analysis is one of the best condition monitoring methods for power transformer. Also, on-line multi-gas analyzer has been developed and installed to monitor the condition of critical transformers. Rogers method, IEC method, key gas method and Duval Triangle method are used to failure diagnosis typically, and those methods are using the ratio or kinds of dissolved gas to evaluate the condition of transformer. This paper analyzes the reliability of transformer diagnostic methods considering actual dissolved gas concentration. Fault diagnosis is performed based on the dissolved gas of five transformers which experienced various fault respectively in the field, and the diagnosis result is compared with the actual off-line fault analysis. In this comparison result, Diagnostic methods using dissolved gas ratio like Rogers method, IEC method are sometimes fall outside the ratio code and no diagnosis but Duval triangle method and Key gas method is correct comparatively.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.7
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• pp.2389-2413
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• 2015

High data rates in long-term evolution (LTE) networks can affect the mobility of networks and their performance. The speed and motion of user equipment (UE) can compromise seamless connectivity. However, a proper handover (HO) decision can maintain quality of service (QoS) and increase system throughput. While this may lead to an increase in complexity and operational costs, self-optimization can enhance network performance by improving resource utilization and user experience and by reducing operational and capital expenditure. In this study, we propose the self-optimization of HO parameters based on fuzzy logic control (FLC) and multiple preparation (MP), which we name FuzAMP. Fuzzy logic control can be used to control self-optimized HO parameters, such as the HO margin and time-to-trigger (TTT) based on multiple criteria, viz HO ping pong (HOPP), HO failure (HOF) and UE speeds. A MP approach is adopted to overcome the hard HO (HHO) drawbacks, such as the large delay and unreliable procedures caused by the break-before-make process. The results of this study show that the proposed method significantly reduces HOF, HOPP, and packet loss ratio (PLR) at various UE speeds compared to the HHO and the enhanced weighted performance HO parameter optimization (EWPHPO) algorithms.

• Journal of the Korea Safety Management & Science
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• v.17 no.4
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• pp.161-169
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• 2015

A fire sprinkler system is very important to extinguish fire in the building. The sprinkler system initiates sprinkler discharge if the detection system identifies a developing fire and opens the pre-action valve. However, pre-action fire sprinkler systems mainly installed in the underground parking lot at the apartment complex do not properly operate at fire if the connection type of fire sprinkler systems does not properly installed and operated. This study identified the relationship between fire dispersion & damage and the connection type of water supply in the sprinkler system from many fire cases at the apartment complex in South Korea. In addition, this study also identified the water supply differences and characteristics between South Korea and foreign countries. The main purpose of this study is also to improve the water connection types in the sprinkler system that can reduce the potential failures of pre-action valve operation through electrical signal system. The study also suggests the improvement plan for water connection types in pre-action fire sprinkler system that can minimize potential failure of pre-action fire sprinkler system. The suggestions for revising the fire safe standard in South Korea includes letting the water supply pipe of sprinkler system water inlet connect to the second side of pre-action valve and the water flow device that can minimize potential failure of sprinkler system.

• Journal of Ocean Engineering and Technology
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• v.30 no.6
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• pp.526-534
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• 2016

This study had the goal of designing onboard structures for a pre-pilot mining test (PPMT), which is required for the commercialization of the deep-sea mining industry. This PPMT is planned to validate the performance of a hydraulic lifting system and verify the concept of operating through a moon-pool in the east sea, Korea. All of the onboard equipment and facility were designed by KRISO. Because the test was performed at the first development, it is difficult to determine what risk will occur in the facility. Therefore, risk-based design is required in the facility for the PPMT, which includes the facility layout, failure mode and effect analysis (FMEA), and risk reduction plan. All of the expected performances of the lifting system itself and the onboard facilities were qualitatively validated using the risk-based design.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.6
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• pp.69-78
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• 2007

In this study, for the evaluation of seismic safety of the isolated Emergency Diesel Generator (EDG) System more quantitatively, the seismic fragility analysis method were proposed. Using the proposed method, seismic fragility analysis performed and a seismic risk of EDG system was present. The fragility analysis performed not for an existing EDG system but also for an isolated EDG system which increases the seismic capacity. At first, numerical models for existing and isolated EDG system were constructed and seismic response analysis performed according to input seismic waves and peak ground accelerations. An uncertainty factors and failure modes of both fixed and isolated EDG system were assumed for fragility analysis. The HCLPF values were evaluated for the compare the improvement effect using the isolation system. As a result, the isolation system can make better the seismic fragility of EDG system, but the failure of isolation system was govern the behavior of whole system.

• Journal of the Korean Institute of Gas
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• v.6 no.1 s.17
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• pp.86-91
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• 2002

This study introduces a method that selects equipments, so as to reach the reliability level, carrying out an optimization analysis which considers the reliability data and cost of the equipments. A more practical optimization problem has been formed using the object function based on the discrete function and the constraints. The jacked reactor being the subject, an optimization analysis was performed on equipments that have different failure rates depending on costs in order to reach the target reliability level required by the system. The mixed-integer programming (MIP) was used for this optimization analysis. When the jacked reactors target level of reliability was $1.65{\times}10^{-4}$, the result of the analysis showed the equipments with high cost and low failure rate were selected. However when the target level of reliability was low, the result showed that by choosing the equipments with lower cost and reliability over the more expensive one, the desired target level could be reached.

• Journal of Advanced Navigation Technology
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• v.23 no.5
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• pp.460-465
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• 2019

In this study, we aim to derive a solution from the structural analysis for electrical failure of single board computers for computing navigation information. By analyzing the characteristic factor, we identify that crack occur on the central processing unit board due to a certain structural problem, and that the physical effect by the crack make communication function be impossible to perform, which it causes booting error. In order to find the location of excessive stress causing the crack, structural analysis for the single board computer is done. From the structural analysis, the areas where stress concentration occurs are identified, and improvement methods changing the structures are developed. As a result, we shows that stresses are reduced entirely on the stress distribution for the improved structure. In addition, heat analysis shows that changing the structure to reduce stresses is not affect to the heat radiation, and the thermal resistance of the actual equipment is verified by measuring the temperature of the heat sink applied with the improved structure.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.2
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• pp.329-335
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• 2019

Reliability growth analysis was conducted for a guided weapons system. In the development phase, reliability management activities were continuously carried out by identifying failure modes and causes and analyzing faults found during the testing. The missile system consists of an all-up-round missile and a launcher, and the analysis was carried out according to the test results of each system. The test results for the all-up-round missile were obtained with discrete data, which were success and failure as a one-shot-device. The test results for the launcher were obtained with continuous data by operating the equipment continuously in the test. For each test result, the reliability growth model was applied to the Standard Gompertz model and the Crow-Extended model. The models were used to identify the growth analysis results of the test so far. It was also possible to predict the reliability growth results by assuming the future test results. The study results could be useful in achieving the desired reliability goal and in determining the number of tests. Then, the planned test will be confirmed and the growth analysis of the missile system will continuously be conducted.

• Journal of Korean Biological Nursing Science
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• v.23 no.4
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• pp.339-346
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• 2021

Purpose: To determine the extent of environmental contamination and the effect of disinfection around patients with carbapenem-resistant Enterobacteriaceae (CRE) using adenosine triphosphate (ATP) measurements and microbial culture tests. Methods: The subjects of this study were 10 patients hospitalized in a single room due to CRE from April 13 to 21, 2021. One hundred and sixty samples were collected using cotton swabs from the patients' environment including the surface and drain of sinks and toilet seats before and after disinfection of the room after discharge. Twenty-one samples were collected from the nurses' personal digital assistants (PDAs), keyboards, and computer mice before disinfection. The relative light units (RLUs) and CRE colony-forming units (CFU) of 181 samples were measured using ATP test equipment and chrome agar plates, respectively. Results: The highest RLUs were measured at the sink drains before and after disinfection. Four CRE samples from the sink drains (2), sink surface (1), and toilet bowl (1) before disinfection were cultured. Based on the failure criteria (≥ 250 RLU/cm² and ≥ 1 CFU/100 cm²), 90 % and 50 % of the samples from the drain exceeded the failure criteria before and after disinfection, respectively. In the culture tests, CRE was not detected after disinfection. Conclusion: According to the RLU and CFU measurements of drain samples, disinfection was not effective. Thus, improvements in the disinfection methods of drains, as well as more efficient and systematic environmental decontamination and disinfection evaluation tools, are needed to accurately evaluate the effectiveness of disinfection in various places.