• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.372-378
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• 2018

Life management technology is required as the failure risk of aged power transformers increases. Asset management technology is developed to evaluate the remaining life, establish the replacement strategies, and decide the optimal investment based on the reliability and economy of power transformers. The remaining life assessment uses data such as installation, operation, maintenance, refurbishment, and failure of power transformers. The optimal investment also uses data such as maintenance, outage, and social costs. To develop the asset management system for power transformers, determining the degradation parameters related to the aging of power transformers and evaluating the condition of power transformers using these parameters are important. In this study, since 1983, 110,000 Dissolved Gas Analysis (DGA) data have been analyzed to determine the degradation parameters related to the aging of power transformers. The alarm rates of combustible gases ($H_2$, $C_2H_2$, $C_2H_4$, $CH_4$, and $C_2H_6$), TCG, CO, and $CO_2$ were analyzed. The end of life and failure rate (bathtub curve) of power transformers were also calculated based on the failure data from 1981 to 2014. The DGA gases related to discharge, overheating, and insulation degradation were determined based on alarm and failure rates. $C_2H_2$, $C_2H_6$, and $CO_2$ were discharge, oxidation, and insulation degradation parameters related to the aging of power transformers.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.11
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• pp.7773-7780
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• 2015

Analysis of existing kettle and its heating system has been the topic for localization technology development. Test pieces are made, polished and etched for existing kettle analysis. Surface of test pieces is observed using SEM, the kettle is verified to be made by deep drawing process from Ferrite-Perlite material. The kettle is also identified to be plated $16{\sim}49{\mu}m$ of thickness with Nickel(16%). Also heat transfer characteristics based on hot wire arrangement is investigated and optimal hot wire system is developed. Developed control system detects overheating and stops the whole system on the long operating time. Developed kettle takes the performance evaluation test for volume expansion and satisfied for standard 'KS G3602'.

• Transactions of the Korean Society of Automotive Engineers
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• v.23 no.1
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• pp.122-129
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• 2015

Excessive overheating to a manual transmission clutch system under operating conditions can be considered the main reason of its performance degradation. The clutch system has to be ensured with its service life by showing that it passes the extreme tests called anti-fade test and hill start test in a certain design step. In general, design feedbacks from these kinds of the experiments are adapted to the system to enhance its performance. However, it usually takes much time and costs a lot due to the repetition of the tests. In this research, a process to calculate temperature of the clutch system was developed to determine whether the design can be passed the anti-fade test and hill start test in the design phase. The process incorporates many CAE techniques such as heat transfer analysis using 1D dynamic simulation method, system dynamics, CFD and parametric optimization. CFD is utilized to analyze 3-dimensional heat transfer of the clutch system and fluid dynamics of air in the clutch housing. The process was applied for the clutch systems in several vehicle models. The results was compared with those of the experiment. The applicability of the developed process was verified by comparing the predicted results with experimental results.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.2
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• pp.425-431
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• 2011

The harmonic distortion level may be significant in electric propulsion systems, as the main loads usually are variable speed propulsion/thruster drives. Distortion of currents and supply voltage waveforms may lead to: Increased power dissipation(losses) in equipment connected to the network, such as generators, motors, transformers, cables, etc., from the harmonic currents, may cause overheating and deterioration of the insulation, and reduced life time of the equipment. In this paper introduced the canceling method of harmonic currents by a multipulse drive with phase shifting transformer. The simulation results indicated a good speed response to the middle speed range of electric propulsion motor. And also, THD(total harmonic distortion) and torque ripple could be reduced in comparing the 12-pulse drive with 6-pulse drive.

• Journal of Welding and Joining
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• v.23 no.6
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• pp.49-54
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• 2005

Inner Structured and Bonded(ISB) panel, a kind of metallic sandwich panel, consists of two thin skin plates bonded to a micro-patterned inner structure. Its overall thickness is $1\~3mm$and it has attractive properties such as ultra-lightweight, high efficiency in stiffness-to-weight and strength-to-weight ratio. In many previous studies, resistance welding, brazing and adhesive bonding are studied for joining the panel. However these methods did not consider productivity, but focused on structural characteristics of joined panels, so that the joining process is very complicated and expensive. In this paper, a new joining process with resistance welding is developed. Curved surface electrodes are used to consider the productivity and the stopper is used between electrodes during welding time to maintain the shape of inner structure. Welding time, gap of electrodes and distance between welding points are selected as the process parameters. By measuring the tensile load with respect to the variation of welding time and gap of electrodes, proper welding conditions are studied. Welding time is proper between 1.5-2.5cycle. If welding time is too long, then inner structures are damaged by overheating. Gap of electrode should be shorter than threshold value fur joint strength, when total thickness of inner structure and skin plate is 3.3mm, the threshold distance is 3.0mm.

• Journal of Korean Society for Quality Management
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• v.47 no.3
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• pp.437-451
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• 2019

Purpose: The purpose of this study is to improve the quality of the PGM system by improving the structure and production process of slip-ring rotary joint for radar. Methods: The improvement measures for each cause are established through failure analysis of broken items. Specifically, changing in the housing to improve the heating system. Changing the transportation method to prevent damage to equipment during transport. Changing work process of the attenuator ring to prevent damage. etc. Results: The results of this study are as follows; improving the heating system reduces heat generated by the attenuator by about 7 degrees and obtain additional temperature margins. Reduction of defect rate because of adding X-band rotary joint run-out measurement test, ESS of slip-ring rotary joint and Transportation improvement(reinforced flight boxes, tube protection, etc). Getting stable VSWR values by improving work process of attenuator overheating due to a bad bonding process. Conclusion: Through this study, improvements were made to slip-ring rotary joint that failed repeatedly for various reasons. As a result of the application of the improvements, the same fault does not occur until now, so we can see that the quality of PGM has improved.

• Journal of the Korean School Mathematics Society
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• v.24 no.3
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• pp.243-259
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• 2021

This study examines trends by school level, region, subject, and type centered on elementary schools when private education is perceived as a social problem due to the overheating of private education and its over-dependence. This study aims to provide a direction to ease the school mathematics education and meet the expectations of school mathematics education. As a result of this study, in mathematics subjects, the graph of private education expenses for mathematics subjects was not affected by the period and showed a somewhat consistent linear trend. In other words, we found that the private education cost of the mathematics subject was solid compared to other factors, and was not significantly affected by external variables, and was consistent. It is meaningful to examine the trends of private education costs in mathematics subjects with a comparison between the past and present and to grasp what factors and how they have changed and developed.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.10a
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• pp.807-808
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• 2016

With the recent rise in nuclear families and single-member families, there is a need for the kind of home management unaffected by neither space nor time. Moreover, electronic devices in and around the home need to be managed efficiently and prevented from overheating, and there is an increasing risk of fire, theft, and leak of personal data with these devices, which is leading to an increase in the economic costs. Accordingly, there is a growing need for an efficient and secure smart home management system. This paper proposes a home management system that uses smart devices. This system has addressed the shortcomings of a conventional Internet-based home network. Furthermore, it communicates with IoT-enabled devices and features intelligent information home appliances that are isolated from personally identifiable information and which are secure against advanced persistent threats, a type of cyber-attack.

• Journal of IKEEE
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• v.23 no.1
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• pp.107-111
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• 2019

In FPD WET equipment, heaters are used a lot. There are many electric accidents caused by short circuit and overheating due to the use of heater, so it is necessary to have a safe electric system and interlock. Therefore, in this paper, we propose an electrical schematic and interlock for FPD WET equipment. In this paper, a hardware interlock such as a level sensor, an overheat protector, and an SSR heater sink is inserted, and the electric system is composed of ELB - MC - SSR - EOCR - heater. When the interlock occurs, the magnetic contactor (MC) is turned off and the power of the heater is cut off.EOCR, an electric overcurrent protection device, has an interlock to shut down the MC when there is an abnormality in the heater while checking the overcurrent, undercurrent and disconnection. These circuit configurations and interlocks are likely to be useful not only for WET equipment but also for any equipment in which the heater is placed.

• Journal of the Korean Society of Clothing and Textiles
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• v.44 no.6
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• pp.1154-1162
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• 2020

In this study, the soft textile actuator is produced for a smart wearable with the shape memory effects from linear shape memory alloys of Nickel and Titanium using the driving force through the fabrication process. The measurement model was designed to measure dynamic characteristics. The heating method, and memory shape of the linear shape memory alloy were set to measure the operating temperature. A shape memory alloy at 40.13℃, was used to heat the alloy with a power supply for the selective operation and rapid reaction speed. The required amount of current was obtained by calculating the amount of heat and (considering the prevention of overheating) set to 1.3 A. The fabrication process produced a soft textile actuator using a stitching technique for linear shape memory alloys at 0.5 mm intervals in the general fabric. The dynamic characteristics of linear shape memory alloys and actuators were measured and compared. For manufactured soft textile actuators, up to 0.8 N, twice the force of the single linear shape memory alloy, 0.38 N, and the response time was measured at 50 s.