• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.4
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• pp.291-296
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• 2022

Capacitor is one of the reliability-critical components in power converters. The lifetime of the capacitor decreases as the operating temperature increases, and power losses caused by capacitor current are the main cause of the capacitor temperature increase. Therefore, various studies are being conducted to improve the lifetime of the capacitor by reducing the current of DC-link capacitors. In this study, pulse width modulation methods proposed for improving the lifetime of DC-link capacitors of the three-level NPC inverter are comparatively analyzed. The lifetime evaluation of the DC-link capacitor under different modulation methods is performed at component level first and then system level by considering all capacitors by applying Monte Carlo simulation. Furthermore, their effects on the efficiency and THD of the output current are also considered.

• Journal of Institute of Control, Robotics and Systems
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• v.17 no.11
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• pp.1090-1094
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• 2011

The major goal of nuclear power industries during past 10 years has been increasing reliability and utility capacity factor. But as capacity factors crept upward, it became harder and harder to attain next percentage of improvement. Therefore, other innovative technologies and method are required. The monitoring, diagnostic and prognostic technologies have been applied to the fossil power plants and contributed a lot on improving their reliability and performance. However nuclear industries are still reluctant to apply the technology by several reasons. In this paper, current preventive maintenance status of nuclear power plants and industrial practice of monitoring, diagnostic and prognostic technologies are investigated. In addition, the restriction in the implementation of the technologies to the nuclear power plants are defined. Finally, we suggest appropriate methods of implementing the technology to nuclear industries for improving current reliability and performance.

• Journal of Korean Society for Quality Management
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• v.46 no.3
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• pp.641-650
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• 2018

Purpose: This article provides a cause of breakage and a method for improving reliability of the headlight system installed in the main battle tank K2. Method: The natural frequency of the headlight system is estimated by using the finite element method. In addition, the allowable stress level under the severe conditions is provided through vibration test of a single item and a system level. Results: Based on the finite element analysis and the vibration test in the frequency domain, the lamp of the left headlight system fails by the resonance effect. Conclusion: For improving the reliability of the headlight system, the thickness of protector frame is increased to avoid the resonance effect.

• Korean Journal of Health Education and Promotion
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• v.23 no.2
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• pp.47-61
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• 2006

Object: This research has been conducted in order to conduct obesity prevention education providing feedback which is currently taught to the second grade students of middle school, understanding how this method of education affects the knowledge and of behavior towards obesity prevention, and that could be actually applied to classrooms. Method: A questionnaire was supplemented questionnaire whose content validity and reliability was verified in the preliminary research was used. The reliability of the research tool was Cronbach' ${\alpha}=0.70$ for obesity knowledge tool, and Cronbach' ${\alpha}=0.84$ for obesity prevention behavior tool. Result: 1) It turned out that feedback was significantly effective in improving the knowledge. 2) It turned out that the education method providing feedback was effective in improving the behavior. Conclusion: From the results of this research, it can be said that the obesity prevention education providing feedback was the most effective method in improving the obesity knowledge and prevention behavior of middle school students. Therefore, it is advisable that the obesity prevention education methods providing feedback should be developed and applied continuously.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.1
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• pp.15-23
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• 2005

For reliability assessment for machine tools, failure mode analyses by two viewpoints were studied in this paper. First, this study developed the reliability data analysis program, which searches f3r optimal failure distribution like failure rate or MTBF(Mean Time Between Failure) using failure data and reliability test data of mechanical parts in the web. Moreover, this data analysis program saves both failure data or reliability data and their failure rate or MTBF for database establishment. Second, this paper conducted failure mode analysis through such performance tests as circular movement test and vibration testing for machine tools when reliability data is not available. A developed web-based analysis program shows correlations between failure mode and performance test result and also accumulates all the data. These kinds of data analysis programs and stored data furnish valuable information for improving the reliability of mechanical system.

• Journal of the Microelectronics and Packaging Society
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• v.27 no.1
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• pp.55-65
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• 2020

The use of underfill materials in semiconductor packages is not only important for stress relieving of the package, but also for improving the reliability of the package during shock and vibration. However, in recent years, as the size of the package becomes larger and very thin, the use of the underfill shows adverse effects and rather deteriorates the reliability of the package. To resolve these issues, we developed the package using a solid epoxy material to improve the reliability of the package as a substitute for underfill material. The developed solid epoxy was applied to the package of the application processor in smart phone, and the reliability of the package was evaluated using thermal cycling reliability tests and numerical analysis. In order to find the optimal solid epoxy material and process conditions for improving the reliability, the effects of various factors on the reliability, such as the application number of solid epoxy, type of PCB pad, and different solid epoxy materials, were investigated. The reliability test results indicated that the package with solid epoxy exhibited higher reliability than that without solid epoxy. The application of solid epoxy at six locations showed higher reliability than that of solid epoxy at four locations indicating that the solid epoxy plays a role in relieving stress of the package, thereby improving the reliability of the package. For the different types of PCB pad, NSMD (non-solder mask defined) pad showed higher reliability than the SMD (solder mask defined) pad. This is because the application of the NSMD pad is more advantageous in terms of thermomechanical stress reliability because the solderpad bond area is larger. In addition, for the different solid epoxy materials with different thermal expansion coefficients, the reliability was more improved when solid epoxy having lower thermal expansion coefficient was used.

• 한국ITS학회:학술대회논문집
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• 2004.11a
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• pp.36-41
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• 2004

• Proceedings of the KOR-KST Conference
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• 2007.02a
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• pp.236-245
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• 2007

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.64 no.4
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• pp.297-302
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• 2015

Replacing a manual switch installed in a feeder for a distribution system with an automatic one increases the reliability of the electric power system. This is because the automatic switch can shorten the duration of a fault the customer experiences by splitting the faulty section faster than the manual one does. However, improving the reliability of the distribution system may increase investment costs. Here, the investment costs include automatic switch cost, replacement work cost and labor cost. For this reason, importance should be attached to the proper balance between the increase of the investment costs and the improvement of the reliability of the distribution system. This article analyzed reliability index and economics when manual switches installed in a feeder (RBTS Bus2 model) was replaced by automatic ones. In addition, it attempted to draw the optimum rate of automation of manual switches by automatic ones using the GRG optimization method, considering the current economic requirements.

• Journal of Applied Reliability
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• v.16 no.3
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• pp.208-215
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• 2016

Purpose: ASRP for the domestic development guided missiles requires not only for the reliability evaluation of the products in storage but also for the life cycle management of the products including development prototypes and initial production items. Methods: For this purpose, it should be performed to build a performance database before and after the accelerated aging test with shelf life items including development prototypes and initial production items, based on which the lifetime prediction should also be carried out. In addition, HILS must be applied for the acceptance test with the initial and follow-up production items, and also for ASRP for the long-term storage products in order to secure systematic quality assurance. Results: The results for the life cycle reliability Improving of domestic development of guided missiles are DB building of prescription Item performance, active application of HILS, Management associated with guided missiles life cycle and to Secure technology data about the introduction of foreign guided missiles. Conclusion: Furthermore, it is demanded that DTaQ, the managing agency of ASRP, actively take part in the process to maintain reliability engagement consistency over the life cycle of guided missiles.