• Journal of Electrical Engineering and Technology
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• v.6 no.4
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• pp.474-483
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• 2011

Solid-state fault current limiters (SSFCL) in power systems are alternative devices to limit prospective short circuit currents from reaching lower levels. Fault current limiters (FCL) can be classified into two categories: R-type (resistive) FCLs and L-type (inductive) FCLs. L-type FCL uses an inductor to limit fault level and is more efficient in suppressing voltage drop during a fault. In contrast, R-type FCL is constructed with a resistance and is more effective in consuming the acceleration energy of generators during a fault. Both functions enhance the transient stability of the power system. In the present paper, a novel SSFCL is proposed to enhance power system transient stability and power quality. The proposed SSFCL uses both functions of an L-type and R-type FCL. SSFCL consists of four diodes, one self-turn-off IGCT, a current-limiting by-pass inductor (L), and a variable resistance parallel with an inductor for improvement of power system stability and prevention of over-voltage across SSFCL. The main advantages of the proposed SSFCL are the simplicity of its structure and control, low steady-state impedance, fast response, and the existence of R-type and Ltype impedances during the fault, all of which improve power system stability and power quality. Simulations are accomplished in PSCAD/EMTDC.

• Proceedings of the KAIS Fall Conference
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• 2010.11a
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• pp.76-79
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• 2010

본 논문에서는 고 효율 및 고 출력 특성을 가지는 질화갈륨(GaN) 소자를 이용하여 WiMAX 및 LTE System에 사용될 수 있는 DPD용 Pallet Amplifier를 제작하였다. 제작된 Pallet Amplifier는 Pre-drive로써 저 전류의 MMIC를 채택하고, Drive 단과 Main 단에 15W 급과 30W 급의 질화갈륨 소자를 사용 하였으며, 추가적인 효율 개선을 위해 PCB상에 Doherty Structure를 적용함으로써 보다 높은 효율을 구현하였다. 제작된 Pallet Amplifier는 음 전원 Bias 제어 회로, 온도에 따른 Gain 보상회로, Sequence 회로 및 Main 전원 Drop에 따른 보호 회로를 구현하였다. WiMAX Signal을 이용한 Modulation Power 10Watt Test에서 약 36.8~38.3%의 Pallet 효율과 DPD Solution인 TI GC5325SEK DPD Board 사용 시 ACLR은 약 46dBc 이상을 가지는 것으로 측정되었다. 본 논문에서 제작된 Pallet Amplifier는 Upper Band와 Lower Band로 나누어 제작되었던 기존 Pallet Amplifier와 달리 하나의 Pallet Amplifier로 2496~2690MHz에서 모두 사용하면서 종전에 사용되고 있는 Pallet Amplifier에 비해 Size가 최소 10% 이상 축소되어 효율 및 크기 면에서 종전 Pallet Amplifier보다 큰 이점을 갖는다.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.10
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• pp.805-811
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• 2016

Prior to installation in a navy ship, shipboard equipment should be qualified by shock test requirements. The multi-function console mounted on the elastic platform of the ship should also withstand given shock loads. In this study, both real shock test methods, as well as numerical computer simulations using the finite element method were used to verify structural durability under shock load conditions. First, we used domestic test facilities to perform possible shock tests, including an impact hammer test, a drop table test and a shaker shock test. Full model tests satisfying the shock response spectrum level were performed. Thereafter, an analytical model of the complex console structure was built by the finite element method. Finally, numerical results were verified by modal test results of the real product and an FEA analysis was also performed with a full model transient response analysis.

• Journal of the Korean Institute of Gas
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• v.4 no.1 s.9
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• pp.49-54
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• 2000

The DCPD(Direct Current Potential Drop) method has been adopted for the crack measurement of a structure. The objective of this paper is to develop a multi-channel DCPD system not only for detecting crack depth, but also for determining the accurate shape of the surface crack. For this purpose, an exclusive software was also developed. In order to verify the developed DCPD system it was initially tested on a CT specimen, and subsequently was applied to a wide plate specimen. The developed multi-channel DCPD system was proven to provide an efficient and accurate measurement of a surface crack during the crack growth.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.9
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• pp.1297-1305
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• 2004

Reliability of MEMS devices is receiving more attention as they are heading towards commercial production. In particular are the reliability and long-term stability of wafer level vacuum packaged MEMS gyroscope sensors subjected to cyclic mechanical stresses at high frequencies. In this study, we carried out several reliability tests such as environmental storage, fatigue, shock, and vibration, and we investigated the failure mechanisms of the anodically bonded vacuum gyroscope sensors. It was found that successful vacuum packaging could be achieved through reducing outgassing inside the cavity by deposition of titanium as well as by pre-taking process. The current gyroscope structure is found to be safe from fatigue failure for 1000 hours of operation test. The gyroscope sensor survives the drop and vibration tests without any damage, indicating robustness of the sensor. The reliability test results presented in this study demonstrate that MEMS gyroscope sensor is very close to commercialization.

• Journal of the Korean Society of Clothing and Textiles
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• v.24 no.8
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• pp.1115-1124
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• 2000

The purpose of this study was 1) to determine physical properties, and subjective evaluation of sensation of sports socks with various type of fiber content and fabric structure, and 2) to develop regression equations for predicting each sensation from physical properties of socks. Thirty healthy male students participated in the wear test with ten replications. The ANOVA, Duncans multiple test, and multiple regression, and paired-t test were used in the statistical analysis, using an SAS package. The results of this study are as follows: 1. 100% cotton socks had higher absorbency and wickability among five different socks. Comfort sensation, tactile sensation and fit sensation of socks were significantly influenced by types of fiber content. People felt that polypropylene socks were less comfortable & slightly tighter, and cotton socks were drier than the other socks. Terry socks were warmer than single jersey socks. 2. The results of the regression analysis showed that tactile sensation of socks after exercise can be predicted from the cube of moisture permeability($R^2$=0.99), and fit sensation can be predicted from drop absorbency, moisture permeability, wickability in wale and weight($R^2$=-0.98).

• Journal of the Korean Society for Aviation and Aeronautics
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• v.19 no.4
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• pp.51-57
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• 2011

The spin-up and the spring-back are most severe load cases in the aircraft landing gear design. These load cases are caused by reciprocal action of complex physical phenomenon such as the friction between a tire and ground, inertia of the rotation of a tire and the flexibility of a landing gear structure. Generally, the empirical formula or the theoretical formula is used to calculate the spin-up and spring-back load in the early stage of the development program of the aircraft landing gear. After the materialization of the design of a landing gear, spin-up and spring-back load are acquired by the free drop test. In this study, the spin-up and the spring-back load of the rubber shock absorber type KC-100 nose landing gear are calculated by the explicit finite element analysis. Through this analysis, more accurate and realistic spin-up and spring back loads could be applied to the early phase of the development of the aircraft landing gear.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.2
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• pp.485-490
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• 2010

We propose the equivalent circuit model including all parasitic components in input gate of sense amplifier of DDI DRAM with butting contact structure. We analysed the effect of parasitic schottky diode by using the proposed model in the operation of sense amplifier. The cause of single side fail and the temperature dependence of fail rate in DDI DRAM are due to creation of the parasitic schottky diode in input gate of sense amplifier. The parasitic schottky diode cause the voltage drop in input gate, and result in decreasing noise margin of sense amplifier. therefore single side fail rate increase.

• Journal of Biomedical Engineering Research
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• v.27 no.6
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• pp.343-350
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• 2006

Medical magnetic stimulator generates strong magnetic field pulses. Clinical applications of the magnetic pulse are the stimulation of nervous system and the contraction of muscle. The unique source of the strong magnetic pulse is a capacitor-inductor resonator and this inductor generates a strong sinusoidal magnetic pulse by discharging the capacitor with high initial voltage. Continuous muscle contraction needs sequential generation of the magnetic pulses. However, to keep the magnitude of sequential pulses identical, an expensive high-voltage power supply have to support voltage drop of the capacitor between the pulses. A protection circuit between the supply and the resonator is necessary to protect the supply from reverse current caused by capacitor voltage reversal. In this paper, a new circuit structure of the magnetic stimulator adopting a low-frequency fly-back switching is proposed. The new circuit supports sequential pulse generation and allows the reverse current without damage. Performance of the new circuit is examined and a low-cost magnetic stimulator for urinary incontinence therapy is being developed using the presented method.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.1
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• pp.27-30
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• 2004

In this paper, a new small size Lateral Trench Electrode Power MOSFET is proposed. This new structure, called "LTEMOSFET"(Lateral Trench Electrode Power MOSFET), is based on the conventional MOSFET. The entire electrode of LTEMOSFET is placed in trench oxide. The forward blocking voltage of the proposed LTEMOSFET is improved by 1.6 times with that of the conventional MOSFET. The forward blocking voltage of LTEMOSFET is 250V. At the same size, a increase of the forward blocking voltage of about 1.6 times relative to the conventional MOSFET is observed by using TMA-MEDICI which is used for analyzing device characteristics. Because the electrodes of the proposed device are formed in trench oxide, the electric field in the device are crowded to trench oxide. We observed that the characteristics of the proposed device was improved by using TMA-MEDICI and that the fabrication of the proposed device is possible by using TMA-TSUPREM4.