• Title/Summary/Keyword: Symmetric currents

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SYMMERIC CURRENTS OF A TWO-LAYER FLUID WITH FREE SURFACE OVER AN ELLIPTIC OBSTRUCTION

  • Park, J.W.
    • Journal of the Korean Mathematical Society
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    • v.34 no.1
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    • pp.119-133
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    • 1997
  • This paper concerns the symmetric wave solutions between two immiscible, inviscid, and incompressible fluids of different but constant densities in the presence of small elliptic obstruction of compact support at the rigid bottom when the effect of gravity is considered (Fig. 1).

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Axi-symmetric eddy currents analysis by FEM (유도가열 시스템에서 축대칭도전체의 와전류 유한요소 해석)

  • Choi, K.H.;Ahn, C.H.;Kim, D.H.
    • Proceedings of the KIEE Conference
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    • 1994.07a
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    • pp.119-121
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    • 1994
  • In solving axisymmetric field problem by FEM, absorbing boundary condition is introduced to approximate the normal derivatives on artificial boundary to truncate the finite analysis legion. To verify this scheme eddy currents of an conducting sphere in an uniform magnetic field are calculated, and it shows better results than one with Neumann boundary condition. Also eddy currents of conducting cylinder surrounded by coils are calculated, which is typical model in induction heating system.

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Algorithm for Fault Location Estimation on Transmission Lines using Second-order Difference of a Positive Sequence Current Phasor

  • Yeo, Sang-Min;Jang, Won-Hyeok;Kim, Chul-Hwan
    • Journal of Electrical Engineering and Technology
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    • v.8 no.3
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    • pp.499-506
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    • 2013
  • The accurate estimation of a fault location is desired in distance protection schemes for transmission lines in order to selectively deactivate a faulted line. However, a typical method to estimate a fault location by calculating impedances with voltages and currents at relaying points may have errors due to various factors such as the mutual impedances of lines, fault impedances, or effects of parallel circuits. The proposed algorithm in this paper begins by extracting the fundamental phasor of the positive sequence currents from the three phase currents. The second-order difference of the phasor is then calculated based on the fundamental phasor of positive sequence currents. The traveling times of the waves generated by a fault are derived from the second-order difference of the phasor. Finally, the distance from the relaying point to the fault is estimated using the traveling times. To analyze the performance of the algorithm, a power system with EHV(Extra High Voltage) untransposed double-circuit transmission lines is modeled and simulated under various fault conditions, such as several fault types, fault locations, and fault inception angles. The results of the simulations show that the proposed algorithm has the capability to estimate the fault locations with high speed and accuracy.

Study on Phase Balancing by Thyristor-Controlled Shunt Compensators (다이리스터제어 병렬보상기를 이용한 상평형에 관한 연구)

  • 차귀수;정태경;최성종;한송엽
    • The Transactions of the Korean Institute of Electrical Engineers
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    • v.31 no.11
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    • pp.133-140
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    • 1982
  • In recent years, a number of thyristor-controlled shunt compensators have been used in industrial and utility systems for phase balancing, power-factor correction and flicker reduction. This paper describes a simple and basic control scheme and circuits for shunt compensator with a fixed capacitor and thyristor-controlled reactor. Feedforward-control scheme is applied, and compensating currents are computed from the symmetrical components of the disturbed system. A 8 bit microprocessor is used for the computation of the compensating currents as well as for the measurements of the symmetric components. A 3-phase 1 KVA compensator is developed and a good reduction of the unbalance factor of the power source is achieved using it.

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Possible pinning of grain-boundary vortices by neighboring Abrikosov vortices in the nearby grains (Abrikosov 볼텍스에 의한 결정입계 볼텍스의 속박 현상)

  • Kim, Dong-Ho
    • 한국초전도학회:학술대회논문집
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    • v.9
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    • pp.1-5
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    • 1999
  • The critical currents I$_c$ of the YBCO grain boundaries of 90-degree [100] symmetric tilt showed a hysteretic behavior depending on how the external magnetic fields were applied. Near 77K for fields less than ${\sim}$1 T, the field-cooled I$_c$ of grain boundaries was larger than the zero-field-cooled I$_c$. This result is consistent with the model in which the grain-boundary vortices can be pinned by neighboring Abrikosov vortices in the nearby grains.

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Finite Element Method employing Localized Functional for analyzing The Axi-symmetric Induction Heating System (축대칭 유도가열기의 해석을 위한 국부범함수를 이용한 유한요소법)

  • Baek, Seung-Kook;Cheon, Chang-Yul;Jung, Hyun-Kyo
    • Proceedings of the KIEE Conference
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    • 1994.07a
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    • pp.18-20
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    • 1994
  • The axisymmetric variational approach employing localized functional is applied to calculate the leakage magnetic field from an induction heating system consisting of an exciting coil and a conducting circular plate. The open boundary is treated by introducing the exterior functional which is representated using the spherical fundamental solutions. For the application to the voltags source problems, the currents on the exciting coil is treated as unknowns. Our results are compared with the previous results, which showed good agreements.

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Study on Generation of Harmonic Voltage using Synchronous Machine with d-axis and q-axis Harmonic Field Windings

  • Mukai, Eiichi;Kakinoki, Toshio;Yamaguchi, Hitoshi;Kimura, Yoshimasa;Fukai, Sumio
    • Journal of international Conference on Electrical Machines and Systems
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    • v.2 no.3
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    • pp.254-259
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    • 2013
  • We examined the generation of harmonic voltage by a synchronous machine adding d-axis and q-axis harmonic field windings in order to reduce the harmonics in a power line. We derived the expressions of the armature voltage in the case of supplying the currents with the frequency nf to the d-axis and q-axis harmonic field windings. We constructed the synchronous machine adding the harmonic windings. In this paper, the expressions and the experimental results on the generation of harmonic voltages by the synchronous machine are presented.

Solar Interior Currents Presumed by Solar Surface Magnetic Fields

  • Bogyeong Kim;Yu Yi
    • Journal of The Korean Astronomical Society
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    • v.56 no.2
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    • pp.187-194
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    • 2023
  • The remote sensing technique of measuring the magnetic field was applied first to sunspots by Hale (1908). Later Babcock (1961) showed that the solar surface magnetic field on a global scale is a dipole in first-order approximation and that this dipole field reverses once every solar cycle. The Wilcox Solar Observatory (WSO) supplies the spherical harmonics coefficients of the solar corona magnetic field of each Carrington Rotation, calculated based on the remotely-sensed photospheric magnetic field of the solar surface. To infer the internal current system producing the global solar coronal magnetic field structure and evolution of the Sun, we calculate the multipole components of the solar magnetic field using the WSO data from 1976 to 2019. The prominent cycle components over the last 4 solar activity cycles are axis-symmetric fields of the dipole and octupole. This implies that the current inversion driving the solar magnetic field reversal originates from the equatorial region and spreads to the whole globe. Thus, a more accurate solar dynamo model must include an explanation of the origin and evolution of such solar internal current dynamics.

Flow Structure and Turbulence Characteristics in Meandering Channel (사행수로의 흐름구조 및 난류특성)

  • Seo, Il Won;Lee, Kyu Whan;Baek, Kyong Oh
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.5B
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    • pp.469-479
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    • 2006
  • In order to investigate characteristics of the primary flow and the secondary currents in meandering channels, the laboratory experiments were conducted in S-curved channels with angle of bend, $150^{\circ}$, and sinuosity of 1.52. The experimental conditions was decided varying average depth and velocity. Under these experimental conditions, spatial variations of the secondary currents in multiple bends were observed. The experimental results revealed that the distribution of primary flow in straight section is symmetric without respect to the experimental condition and the maximum velocity line of the primary flow occurs along the shortest path in experimental channel, supporting the result of previous works. The secondary currents in second bend became more developed than those in first bend. Particularly, the outer bank cell developed distinctively and the secondary current intensity was low at the straight section and high at the bends, periodically. Also, the secondary current intensity at the bends was as twice to three times as that at the straight section, and has its maximum value at the second bend. The turbulent flow characteristics of meandering channel was investigated with turbulent intensity of the primary flow and Reynolds shear stress. It was observed that the turbulent intensity is increasing when the velocity deviation of the primary flow is large whereas Reynolds shear stress increases when both the velocity deviation of the primary flow and the secondary current are large.

Structure and Variation of the Keum River Plume in Summer (하계 금강 Plume의 구조와 변동)

  • 이상호;최현용
    • 한국해양학회지
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    • v.30 no.2
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    • pp.125-137
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    • 1995
  • CTD, light transmission and tidal current data obtained off the Keum estuary in August, 1991 and 1992 were analyzed to look into the plume movement and the vertical structure of the plume changing with tidal currents. When the river plume was developed by a localized torrential downpour, the initial plume showed a surface lens of low salinity in the section south of the Yeon-Do. The axis of surface lens moved with tidal currents which flows mainly northeastward and southwestward tn the study area and the excursion of the lens axis reached 7 km. The plume during the ebb period showed a symmetric lens structure of low salinity which extends vertically to 3 m below the surface. During the flood period the plume deepened to 6 m below the surface in its northen side forming a sharp salinity front, which results in an asymmetric lens. We suggest that the salinity front with deepened plume moved to the north repeatedly, resulting in temperature increase and salinity decrease in the northern region off the estuary. When the river discharged continuously the large volume over 20 days, the plume forming surface lens extended to the Sybidongpa-Do and deflected to the north.

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