• Corrosion Science and Technology
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• 제15권3호
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• pp.135-140
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• 2016

Piping and equipment are degraded by flow-accelerated corrosion (FAC) in nuclear power plants. FAC causes numerous problems and nuclear utilities maintain programs to control FAC. The key parameters influencing FAC are hydrodynamic conditions, water chemistry, and effect of materials. Recently, a nuclear utility has planned slight power uprates in Korea. Operating conditions need to be changed in the secondary system according to power uprates. This study analyzed the effect of wall-thinning caused by power uprates. The change of operation data in the secondary cycle is reviewed, and wall-thinning rates are analyzed in the main lines. As a result, two phase (mixture of water and steam) lines have a greater impact than a water line under power uprate conditions. Also, the quality of steam is the most important factor for FAC in two phase lines.

• 전력전자학회논문지
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• 제4권5호
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• pp.413-422
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• 1999

Auto-connected multipulse(12/24pulse) rectifier schemes are cost effective methods for reducing line current hamonics in PWM drive systems. Employing these schemes to enhance utility power quality requires careful attention to several design considerations In particular, excursion of dc-link voltage at no load, effect of pre-existing voltage distortion, impedance mismatches, unequal diode drops on rectifier current sharing and performance, are fully analyzed, Several corrective measures to improve the performance of 12/24­pulse rectifier systems are also discussed. Finally, experimental results on a 460V, 60Hz 400kVA commercial ASD, retrofitted with 12/24pulse rectifier systems are discussed in detail.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2003년도 춘계전력전자학술대회 논문집(1)
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• pp.213-215
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• 2003

This paper presents an instantaneous space vector modulated voltage source type three-phase soft-switching PFC rectifier using a single auxiliary resonant DC Link snubber for alternative energy utilizations. in the first place, the operating principle of an active auxiliary resonant DC link snubber circuit is described including its unique features. In the next place, the simulation analysis of three-phase soft-switching PWM rectifier is implemented, and the operating performances or the three-phase voltage-fed PWM rectifier treated here, which can operate under the conditions of sinewave line current shaping and utility power factor are evaluated and discussed on tile basis of this simulation results.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 춘계학술대회
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• pp.51-54
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• 2005

Generator efficiency optimization is important for economic saving and environmental pollution reduction. In general, the machine loss can be reduced by the decreasing the flux level, resulting in the significant reduction of the core loss. This paper proposesan model-based controller is used to decrement the excitation current component on the basis of measured stator current and machine parameters and the q-axis current component controls the generator torque, by which the speed of the induction generator iscontrolled according to the variation of the wind speed in order to produce the maximum output power. The generator reference speed is adjusted according to the optimum tip-speed ratio. The generated power flows into the utility grid through the back-to-back PWM converter. The grid-side converter controls the dc link voltage and the line-side power factor by the q-axis and the d-axis current control, respectively. Experimental results are shown to verify the validity of the proposed scheme.

• 터널과지하공간
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• 제7권4호
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• pp.299-309
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• 1997

Soil and rock improvement and reinforcement techniques are applied to achieve safe tunnel excavation in difficult geological conditions. The Umbrella Arch Method(UAM), one of the auxiliary techniques, is used to reduce ground permeability and improve stabtility of the tunnel by inserting a series of steel pipes into ground around the crown inclined to the longitudinal axis of the tunnel. Additionally, multi-step grouting is added through the steel pipes. UAM combines the advantages of a modern forepoling system with the grouting injection method. This technique has been applied in subway, road and utility tunneling sites for the last few years in Korea. This paper presents the results of analysis of the case studies on ground movements associated with UAM used in the Seoul Subway line 5 constructon site. Improvement of tunnel stability and decrease of ground settlement expected with pipe insertion are also discussed. Finally, the method to minimize ground settlements caused by NATM tunnelling are suggested.

• 한국가구학회지
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• 제19권3호
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• pp.203-210
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• 2008

This study intended to develop wellbeing flowerpots on desk which could create a healthy atmosphere in an office and raise people to joy. The pots developed by Blooming company emphasized a design as touching people's emotion through the organic design of the streamline which is different from the geometric line of the flowerpots manufactured by the company as focusing the design on the utility before. As a result, the pots derived from the organic design concepts could provide happiness or joy to the people, and would be a necessity on the narrow desk along with books or writing materials while working. Therefore, the beautifully streamlined pots are expected to compete with European market as the foreign buyers had a great interest in them at the Fair held in Hong-kong at the end of April, 2008.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1992년도 하계학술대회 논문집 B
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• pp.1035-1037
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• 1992

Generally, fuel cell has characteristics of low voltage, large current and voltage variation under load change. Therefore, DC output voltage of fuel cell is too low to convert into AC with high efficiency and good performance. For this reason, fuel cell generating system is composed of DC-DC converter and inverter in cascade. This paper used 2-phase boost DC-DC converter to obtain low distortion waveform and reduce input-output current ripple, and discussed inverter which can be operated in independent drive mode and utility line interface drive mode. Then, the change of modes can be achived smoothly.

• 한국학교수학회논문집
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• 제1권1호
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• pp.185-196
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• 1998

This study is undertaken to clarify the evolution of the mathematics regarding the $\pi$ ratio, square root, trigonometric ration which are dealing by approximate value according to the curriculum of Korean Middle School and its subsequent growth of methods for attaining the approximate value. Furthermore a brief survey has been thought for assessing the significance of the core of approximate value and its utility which will be given a guide line to many young learners. I'd better teach these historical background to the students and it makes clear the approximate value and the content about the approximate value. This research should help to improve the student's ability of solving a problem by making them think it mathematically through the life and the effort of the mathematician.

• Journal of Microbiology and Biotechnology
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• 제19권10호
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• pp.1135-1138
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• 2009

The bioassay-guided fractionation of MeOH extract from Naematoloma fasciculare afforded a petroleum ether fraction (NFPF) and four known compounds, which showed good antitumor activities to inhibit MCF-7 cell line proliferation in vitro and tumor growth in $H_{22}$ implanted mice in vivo. In addition, a number of unsaturated aliphatic acids were identified in NFPF by GC analysis. These results showed that NFPF inhibits tumor growth through the activity of unsaturated aliphatic acids together with two active compounds, ergosterol peroxide (1: 62.17 mg/g in NFPF) and ergosterol (2: 3.13 mg/g in NFPF), and indicate the potential utility of NFPF as an antitumor drug.

• 전기학회논문지
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• 제56권5호
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• pp.854-859
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• 2007

A wind farm consists of many wind generator(WG)s therefore, it is generally a complex power system. A wind farm as a distributed generation(DG) affects utility power system. If a conventional protection schemes are applied, it is difficult to detect faults correctly and the schemes can't provide proper coordination in some cases. This paper presents a protection algorithm for a wind farm which consists of a looped collection circuit. Because the proposed algorithm can distinguish between an internal fault and an external fault in a wind farm, The proposed algorithm can disconnect the faulted section in a wind farm. This algorithm is based on an overcurrent protection technique with the change of the ratio of the output current of a generator to the current of the looped line connected to each generator to collect the each generator's power. In addition, operating time of the algorithm is shortened by using the voltage drop at a generator collection point. The performance of the proposed algorithm was verified under various fault conditions using PSCAD/EMTDC simulations.