• Journal of the Microelectronics and Packaging Society
• /
• v.26 no.3
• /
• pp.75-80
• /
• 2019

Silicon solar cells have been widely used as a most promising renewable energy source due to eco-friendliness and high efficiency. As modules of silicon solar cells are connected in series for a practical electricity generation, a large voltage of 500-1,500 V is applied to the modules inevitably. Potential-induced degradation (PID), a deterioration of the efficiency and maximum power output by the continuously applied high voltage between the module frames and solar cells, has been regarded as the major cause that reduces the lifetime of silicon solar cells. In particular, the migration of the $Na^+$ ions from the front glass into Si through the anti-reflection coating and the accumulation of $Na^+$ ions at stacking faults inside Si have been reported as the reason of PID. In this research, the thickness effect of $SiO_x$ layer that can block the migration of $Na^+$ ions on the reduction of PID is investigated as it is incorporated between anti-reflection coating and p-n junction in p-type PERC solar cells. From the measurement of shunt resistance, efficiency, and maximum power output after the continuous application of 1,000 V for 96 hours, it is revealed that the thickness of $SiO_x$ layer should be larger than 7-8 nm to reduce PID effectively.

• Journal of the Korean Electrochemical Society
• /
• v.17 no.1
• /
• pp.7-12
• /
• 2014

There is increasing demand on the reducing the weight and the volume of the major components in lithium secondary battery to improve energy density. Separator not only provides pathway for lithium ion movement but also prevents direct contact between anode and cathode. Herein we fabricated polyethylene separator by varying biaxial stretching ratio to obtain membrane thickness of 16, 12, and $9{\mu}m$. Mechanical and thermal properties of the separator with different thickness were investigated. Also rate capability and charge-discharge cycle property up to 500 cycles were studied using coin type full-cell with $LiCoO_2$ and graphite as a cathode and an anode, respectively. All the cells using separator with different thickness demonstrated excellent capacity retention after 500cycles (around 80%). Considering the rate capability, cell using separator with thickness of $9{\mu}m$ showed best performance. Interestingly, separator thickness of $9{\mu}m$ was more resistant to heat contraction compared to that of $16{\mu}m$ separator.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.6
• /
• pp.700-707
• /
• 2016

Recently, ammunition malfunctions of the 40mm grenade were reported during live fire training. When 72 40mm grenades were fired by the army, 11 duds were encountered. The dud ammunition rate was approximately 15%. Because ammunition is used a long time after its manufacture, it is necessary to ensure its performance after long-term storage. In this study, we attempted to decrease the dud ammunition rate of 40mm grenade (K200) fuzes through quality improvement. First, it was determined by the detonator performance test that abnormal explosions occurred due to the degradation of the detonator as a result of its aging characteristics. Second, we improved the fuze quality of the 40mm grenade. Third, we tested its shelf life to estimate its life expectancy. The shelf life of the 40mm grenade fuze obtained using the Arrhenius equation was 6.5 years for the existing grenade fuze and 45.5 years for the improved grenade fuze. This showed that the shelf life of the improved grenade was increased approximately 7 times. Therefore, the improved 40mm grenade fuze contributes to the quality improvement of the 40mm grenade by decreasing the dud ammunition rate during long term storage.

• Proceedings of the Korean Society for Agricultural Machinery Conference
• /
• 2017.04a
• /
• pp.150-150
• /
• 2017

조립라인에서 볼트의 수량을 정확하게 검출하는 장치는 작업속도의 향상 및 불량발생을 줄이기 위해 필요한 것이다. 현재 조립에 필요한 수량을 작업자의 시각에 의해 파악하고 있기 때문에 작업시간이 증가되고 있으며 특히 조립 과정 중 작업자의 실수로 볼트가 제품의 내부에 침투하여 제품의 소음, 성능저하 및 수명단축을 초래하고 있다. 본 연구에서는 작업자의 편의성 및 조립속도 향상을 위해 볼트를 감지하여 자동으로 수량을 검출하는 장치를 개발하였다. 볼트의 특성에 따라 볼트 선별부의 치수를 수정하면 되도록 하였다. 조립라인의 생산성을 향상시키기 위한 설계는 Auto CAD를 이용하였다. 조립라인의 공간 효율 증가를 위하여 볼트 수량 검출기의 가로${\times}$세로의 크기를 최소로 하여 $220{\times}360{\times}1170mm$로 설계하였다. 받침대는 $60{\times}60$ 프로파일을 이용하였고 다른 구성 부품은 SUS304 재질을 가공하여 조립하였다. 실험은 실험구 마다 100회 측정하여 평균값을 나타냈으며, 소수점은 시스템에 영향이 없기 때문에 절사하였다. Test 19-27 구간이 배출부가 가장 적게 구동하는 것으로 나타났다. 정렬부의 각도가 10, $15^{\circ}$의 경우는 볼트와 배출부의 마찰력이 증가하여 구동횟수가 증가한 것으로 판단된다. $20^{\circ}$이상의 각도에서는 볼트가 배출부에 안착하기 전에 하강하기 때문에 반복횟수가 증가한 것으로 판단된다. 따라서 최적의 정렬부 각도는 $20^{\circ}$로 나타났다. 볼트의 지름이 3, 5, $7{\phi}$ 일 때 정렬부의 각도에 따른 정렬부의 반복횟수에 대한 결과 값을 한 결과 $20^{\circ}$에서 정렬부의 구동횟수가 가장 적은 것 으로 나타났다. 정렬부의 각도가 큰 경우 구동에 의한 볼트와의 운동에너지의 증가로 반복횟수가 증가한 것으로 판단된다.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.21 no.6
• /
• pp.618-629
• /
• 2001

This paper presents a result of failure analysis and reliability evaluation for high voltage ceramic capacitors. The failure modes and failure mechanisms were studied in two ways in order to estimate component life and failure rate. The causes of failure mechanisms for zero resistance phenomena under withstanding voltage test in high voltage ceramic capacitors molded by epoxy resin were studied by establishing an effective root cause failure analysis. Particular emphasis was placed on breakdown phenomena at the ceramic-epoxy interface. The validity of the results in this study was confirmed by the results of accelerated testing. Thermal cycling test for high voltage ceramic capacitor mounted on a magnetron were implemented. Delamination between ceramic and epoxy, which might cause electrical short in underlying circuitry, can occur during curing or thermal cycle. The results can be conveniently used to quickly identify defective lots, determine $B_{10}$ life estimation each lot at the level of inspection, and detect major changes in the vendors processes. Also, the condition for dielectric breakdown was investigated for the estimation of failure rate with load-strength interference model.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.21 no.7
• /
• pp.406-418
• /
• 2020

When developing weapons systems, it is important to implement the functions and performance of equipment suitable for development purposes, but it is very important to ensure that the equipment is capable of operating without any vacuum with reliability after development. Therefore, various activities are carried out to enhance reliability of equipment. Reliability is enhanced by using high-specification parts in development, reliability verification through analysis, and testing using development prototypes to reinforce and improve the parts that are lacking in equipment. However, recently, development schedules are shortened due to rapidly changing external conditions and technologies, and there are cases where sufficient reliability growth activities were not carried out due to problems such as cost. Examples are projects that perform reliability activities only in analytical methods (reliability, FMECA). In this paper, analyzing and testing methods for analysis and testing were carried out on the same equipment through FMECA and super-accelerated life test, the contents of reliability growth activity were derived, the results of design change/review were accordingly compared, the differences between the two methods were analyzed, and measures were proposed to strengthen reliable growth activities. It was concluded that reliable growth activities through analysis from the beginning of development and reliable growth activities through testing should be carried out at the completion of initial prototype production.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.3
• /
• pp.209-214
• /
• 2017

Most of the present potential transformers of train vehicles are of the oil-type filled with insulating oil and are susceptible to problems such as explosion due to the increase in the internal pressure during train operation and poor reliability near the end of their life cycle. As a solution to this problem, it is necessary to develop a molded dry-type potential transformer with excellent pressure-resistance performance using insulating resin. In order to localize the product, the Korea Railroad Research Institute has been developing a molded dry-type potential transformer. As part of this research, it is necessary to analyze the vibration characteristics of the developed product and to check the transformer performance in a vibration environment. In this study, a resonance test and simulated long-term life test of the developed product were conducted according to the KS R 9144 and IEC 61373 standards, respectively, which are vibration test methods for railway vehicle parts. Their natural frequencies were analyzed by comparing the results of the numerical modal analysis and resonance test, in order to confirm their adherence to the standards. Also, the performance test after the simulated long-term life test confirmed that the operation of the developed transformer was not problematic even in a long-time vibration environment.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.16 no.2
• /
• pp.128-139
• /
• 2017

Railway is one of the public transportation systems along with shipping and aviation. With the recent introduction of high speed train, its proportion is increasing rapidly, which results in the higher risk of catastrophic failures. The wheel bearing to support the train is one of the important components requiring higher reliability and safety in this aspect. Recently, many studies have been made under the name of prognostics and health management (PHM), for the purpose of fault diagnosis and failure prognosis of the bearing under operation. Among them, the most important step is to extract a feature that represents the fault status properly and is useful for accurate remaining life prediction. However, the conventional features have shown some limitations that make them less useful since they fluctuate over time even after the signal de-noising or do not show a distinct pattern of degradation which lack the monotonic trend over the cycles. In this study, a new method for feature extraction is proposed based on the observation of relative frequency energy shifting over the cycles, which is then converted into the feature using the information entropy. In order to demonstrate the method, traditional and new features are generated and compared using the bearing data named FEMTO which was provided by the FEMTO-ST institute for IEEE 2012 PHM Data Challenge competition.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.5
• /
• pp.468-476
• /
• 2019

This paper presents the means of improving the strength of LTV's FRP structure for resolve and prevent quality problems. LTV secures enough kerb weight by applying FRP materials at hood and rear van assembly. However, because of FRP's inherent limitations, many initial quality problems such as crack at connections have occurred. Moreover, hood assy' is concerned about fall of endurance, because hood assy' have operated in abnormal condition. Therefore, this study executes lamination structure optimizations of FRP structure for improving bending strength. As a results, hood and rear van's bending strength at connections is improved 8.1 times and 1.5 times, respectively. Also hood assy's plate secures endurance life and improve 1.7 times of critical load about abnormal operating conditions through 1.4 times improvement of bending strength.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.45 no.10
• /
• pp.10-16
• /
• 2008

Generally, the satellite circling round in a low orbit goes through Van Allen belt connecting with the magnetic fold, in which electronic components are easily damaged and shortened by charged particles moving in a cycle between the South Pole and the North Pole. In particular, Single Event Upset(SEU) by radiation could cause electronic device on satellite to malfunction. Based on the idea mentioned above, this study considersabout SEU effect on the On-board Computer(OBC) of STSAT-1 in the space environment radiation, and shows algorithm to cope with SEUs. In this experiment, it also is shown that the repetitive memory read/write operation called memory wash is needed to prevent the accumulation of SEUs and the choice for the period of memory wash is examined. In conclusion, it is expected that this research not only contributes to understand low capacity of On-board Computer(OBC) on Low Earth Orbit satellite(LEOS) and SaTReC Technology satellite(STSAT) series, but also makes good use of each module development of Korea Multi-Purpose Satellite(COMPSAT) series.