• 제목/요약/키워드: Tip-off

검색결과 141건 처리시간 0.034초

고압전동기 Off-Line 절연진단시험 효율개선을 위한 데이터자동취득 및 원격진단시스템 구축 (Development of Automatic Data Acquisition & Remote Diagnostic System for Improving Efficiency of High-Voltage Motors Off-Line Insulation Diagnostic Test)

  • 강상무;강대정;한현석;김원경
    • 대한전기학회:학술대회논문집
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    • 대한전기학회 2015년도 제46회 하계학술대회
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    • pp.707-708
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    • 2015
  • This paper proposes a method for improving efficiency of high-voltage motors off-line insulation diagnostic test. The conventional manual test method has measurement errors and excessive processing time. We developed the KITAS system and solved these problems by using the instrument remote control and communication technology. The result of proficiency testing by interlaboratory comparisons using Power Factor Tip-Up test was '${\mid}E_n{\mid}$ < 1'. It was possible to confirm the validity of acquired data from the KITAS and establish a remote diagnostic system for easy access without physical limitations.

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대형발전기 고정자권선 절연재료의 열 사이클에 의한 열화에 관한 연구 (A study on the heat cycle aging of insulation materials in large generator stator windings)

  • 김희곤;박영관
    • 대한전기학회논문지
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    • 제45권4호
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    • pp.553-557
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    • 1996
  • Heat cycle aging of insulating materials in large generator stator winding has been investigated using both on-line and off-line test methods. On this study, principally, off-line test against actual generator in service was carried out to acquire information about polarization index(PI) and dissipation factor, dissipation factor tip-up, maximum partial discharge for the purpose of remnant breakdown voltage and life assessment. It was found from the tests that both dissipation factor and maximum partial discharge decreased with the increase of operating hours and starting numbers. It was found from off-line tests that the remnant breakdown voltage had a strong relationship with both dissipation factor and maximum partial discharge the remnant breakdown voltage as a results of both operating hours and starting number and the nondestructive tests were proposed as parameters which can predict the remnant lifetime of insulating materials in large generator stator windings. (author). 8 refs., 8 figs., 2 tabs.

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Experimental Study of the Multi-Row Disk Inlet

  • Maru, Yusuke;Kobayashi, Hiroaki;Kojima, Takoyuki;Sato, Tetsuya;Tanatsugu, Nobuhiro
    • 한국추진공학회:학술대회논문집
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    • 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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    • pp.634-643
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    • 2004
  • In this paper are presented a concept of a new supersonic air inlet, which is designated a Multi-Row Disk (MRD) inlet, aiming at performance improvement under off-design conditions, and results of wind tunnel tests examined performance characteristics of the MRD inlet. The MRD inlet is frequently called ‘a skeleton inlet’ because of its appearance. The performance of a conventional axisymmetric inlet with a solid center body (spike) deteriorates under off-design Mach number conditions. It is due to the fact that total pressure recovery (TPR) governed by the throat area of inlet and mass capture ratio (MCR) governed by an incidence position of an oblique shock from the spike tip into the cowl can not be controlled independently in such air inlet. The MRD inlet has the spike that is composed of a tip cone and several disks arranged downstream of it, based on the experimental fact that several deep cavities on a conical surface have little negative effect on the boundary layer growth. The overall spike length of the MRD inlet is adjustable to the given flight speed by changing space between disks so that a spillage flow can be controlled independently from controlling the throat area. It could be made clear from the result of wind tunnel tests that the MRD inlet improves TPR by 10% compared with a conventional inlet with a solid spike under off-design conditions.

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소금쟁이의 尖體形成 (Acrosome Morphogenesis in Gerris paludum (Heteroptera))

  • Lee, Young-Hwan;Lee, Chang-Eon
    • 한국동물학회지
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    • 제24권2호
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    • pp.65-75
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    • 1981
  • Gerris paludum의 精子形成 동안의 尖體形成에 대한 연구를 요약하면 다음과 같다. 1. Golgi體는 精母細胞의 초기단계에서 細胞質에 산재되어 있다가 서로 융합하여 囊 胚形을 하며 이들이 모여서 감수분열 전기에는 몇 개의 큰 Golgi體群을 형성하는데, 이들은 결국 精細胞에 균등히 분포된다. 2. 精子完成에서 acroblast는 처음에 하나의 큰 胞로 나타나다가, 그 내부에서 尖體顆粒이 分化된 후, acroblast는 顆粒에서 分離되어 결국 tail filament를 따라 사라진다. 3. 尖體는 mitochondrial derivatives의 반대편인 核 전면부로 이동한 후, two zones 즉 core와 sheath로 分化된다. 4. Basal bodies와 tip은 모두 sheath에서 由來한다. Basal bodies는 sheath의 基部에서 발생해서 尖體가 伸長되고 좁아짐에 따라 점차로 尖體의 基部를 싸기 시작하여 결국 완전히 둘러싸게 되며, 分化된 tip은 core의 前端部에 인접해서 나타나지만 sheath와 뚜렷이 연결되어 있다. 5. 分化된 tip은 basal bodies보다 앞서서 伸長한다. Basal bodies는 精細胞 후기에 하나의 顆粒으로 융합하지 않고 서로 연결된 wtin-tubes로 나타나며, sperm bundle에서는 basal bodies group을 형성한다.

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A Study of a Novel Wind Turbine Concept with Power Split Gearbox

  • Liu, Qian;Appunn, Rudiger;Hameyer, Kay
    • Journal of international Conference on Electrical Machines and Systems
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    • 제2권4호
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    • pp.478-485
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    • 2013
  • This paper focuses on the design and control of a new concept for wind turbines with a planetary gearbox to realize a power split. This concept, where the generated wind power is split into two parts, is to increase the utilization of the wind power and may be particularly suitable for large scale off-shore wind turbines. In order to reduce the cost of the power electronic devices, a synchronous generator, which is driven by the planetary gear, is directly connected to the power grid without electronic converter. A servo drive, which functions as the control actuator, is connected to the power grid by a power electronic converter. With small scale power electronic device, the current harmonics can also be reduced. The speed of the main shaft is controlled to track the optimal tip speed ratio. Meanwhile the speed of the synchronous generator is controlled to stay at the synchronous speed. The minimum rated power of the servo motor and the converter, is studied and discussed in this paper. Different variants of the wind turbine with a planetary gear are also compared. The controller for optimal tip speed ratio and synchronous speed tracking is given.

스톨 근처에서 원심압축기 임펠러의 내부 유동현상에 관한 연구 (Analysis of Flow Phenomena in a Centrifugal Compressor Impeller Operating near Stall)

  • 음학진;강신형
    • 대한기계학회논문집B
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    • 제28권3호
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    • pp.330-337
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    • 2004
  • Analysis of flow phenomena in a centrifugal compressor impeller has been carried out with numerical simulation to understand the physics of flow near stall. Near stall point, tip leakage flow spills ahead of the leading edge of adjacent blade and other leakage flow passes over the clearance of the adjacent blade instead of rolling up into vortex within the passage. The tip leakage flow at the mid chord of impeller blade impinges against the pressure surface of the adjacent blade and then rolls up into vortex within the passage, which blocks the flow passage and generates viscous loss. The spillage of leakage flow ahead of the adjacent blade generates the recirculation of flow entering the impeller, which causes the power transferred into the flow by the impeller to decrease and blocks the flow passage. Near diffuser hub wall, flow recirculation occurs. As operating point goes to stall point, the core of recirculation approaches the impeller exit The length rises to peak point and then drops with mass flow reduction, while the height steadily rises.

Prediction of Ultra-High ON/OFF Ratio Nanoelectromechanical Switching from Covalently Bound $C_{60}$ Chains

  • Kim, Han Seul;Kim, Yong-Hoon
    • 한국진공학회:학술대회논문집
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    • 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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    • pp.645-645
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    • 2013
  • Applying a first-principles computational approach combining density-functional theory and matrix Green's function calculations, we have studied the effects [2+2] cycloaddition olligormerization of fullerene $C_{60}$ chains on their junction charge transport properties. Analyzing first the microscopic mechanism of the switching realized in recent scanning tunneling microscope (STM) experiments, we found that, in agreement with experimental conclusions, the device characteristics are not significantly affected by the changes in electronic structure of $C_{60}$ chains. It is further predicted that the switching characteristics will sensitively depend on the STM tip metal species and the associated energy level bending direction in the $C_{60}-STM$ tip vacuum gap. Considering infinite $C_{60}$ chains, however, we confirm that unbound $C_{60}$ chains with strong orbital hybridizations and band formation should in principle induce a much higher conductance state. We demonstrate that a nanoelectromechanical approach in which the $C_{60}-STM$ tip distance is maintained at short distances can achieve a metal-independent and drastically improved switching performance based on the intrinsically better electronic connectivity in the bound $C_{60}$ chains.

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Fabrication of Sputtered Gated Silicon Field Emitter Arrays with Low Gate Leakage Currents by Using Si Dry Etch

  • Cho, Eou Sik;Kwon, Sang Jik
    • Transactions on Electrical and Electronic Materials
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    • 제14권1호
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    • pp.28-31
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    • 2013
  • A volcano shaped gated Si-FEA (silicon field emitter array) was simply fabricated using sputtering as a gate electrode deposition and lift-off for the removal of the oxide mask, respectively. Due to the limited step coverage of well-controlled sputtering and the high aspect ratio in Si dry etch caused by high RF power, it was possible to obtain Si FEAs with a stable volcano shaped gate structure and to realize the restriction of gate leakage current in field emission characteristics. For 100 tip arrays and 625 tip arrays, gate leakage currents were restricted to less than 1% of the anode current in spite of the volcano-shaped gate structure. It was also possible to keep the emitters stable without any failure between the Si cathode and gate electrode in field emission for a long time.

원자간력 현미경 탄소 나노튜브 팁을 이용한 플러렌 나노 구조물 제작에 관한 분자동역학 시뮬레이션 (Molecular Dynamics Simulations of Fullerene Nanostructure Fabrications by Atomic Force Microscope Carbon Nanotube tip)

  • 이준하;이홍주
    • 한국전기전자재료학회논문지
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    • 제17권8호
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    • pp.812-822
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    • 2004
  • This paper shows that carbon nanotubes can be applied to a nanopipette. Nano space in atomic force microscope multi-wall carbon nanotube tips is filled with molecules and atoms with charges and then, the tips can be applied to nanopipette when the encapsulated media flow off under applying electrostatic forces. Since the nano space inside the tips can be refilled, the tips can be permanently used in ideal conditions of no chemical reaction and no mechanical deformation. Molecular dynamics simulations for nanopipette applications demonstrated the possibility of nano-lithography or single-metallofullerene-transistor array fabrication.

케이싱 그루브가 장착된 천음속 축류압축기의 작동 안정성 향상을 위한 수치최적화 (Numerical Optimization of a Transonic Axial Compressor with Casing Grooves for Improvement of Operating Stability)

  • 김진혁;최광진;김광용
    • 한국유체기계학회 논문집
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    • 제14권5호
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    • pp.31-38
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    • 2011
  • Optimization using a hybrid multi-objective evolutionary algorithm coupled with response surface approximation has been performed to improve the performance of a transonic axial compressor with circumferential casing grooves. In order to optimize the operating stability and peak adiabatic efficiency of the compressor with circumferential casing grooves, tip clearance, angle distribution at blade tip and the depth of the circumferential casing grooves are selected as design variables. Three-dimensional Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model are discretized by finite volume approximations. The trade-off between two objectives with the interaction of blade and casing treatment is determined and discussed with respect to the representative clusters in the Pareto-optimal solutions compared to the axial compressor without the casing treatment.