• Title/Summary/Keyword: Constant current

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Prediction of gate oxide breakdwon under constant current stresses (정전류 스트레스 하에서 게이트 산화막의 항복 특성 예측)

  • 정태식;최우영;이상돈;윤재석;김재영;김봉렬
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.33A no.7
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    • pp.162-170
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    • 1996
  • A breakdown model of gate oxides under constant current stresses is proposed. This model directly relates the oxide lifetime to the stress current density, and includes statistical nature of oxide breakdown using the concept of "effective oxide thinning". It is shown tha this model can reliably predict the TDDB characteristics for any current stress levels and oxide areas.

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A Protection Algorithm for DC Railway Systems Considering Train Starting (기동방식을 고려한 DC급전계통 보호알고리즘)

  • Kwon Y. J.;Choi D. M.;Kang S. H.;Han M. S.;Lee J. K.
    • Proceedings of the KIEE Conference
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    • summer
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    • pp.307-309
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    • 2004
  • A DC railway system has low feeder voltage, The remote fault current can be smaller than the current of load starting. So it is important to discriminate between the small fault current and the train starting current. The train starting current increases step by step but the fault current increases all at once. So the type of $\bigtriangleup I\;relay(50F)$ was developed using the different characteristics between the load starting current and the fault current. As for the train starting current, the time constant of train current at each step is much smaller than that of the fault current. To detect faults in U railway systems, an algorithm that is independent of train starting current. This algorithm use the time constant calculated by the method of least squares is presented in this paper.

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The Properties of Na-Ca Exchange Current in Single Atrial Cells of ,The Rabbit (토끼 단일 심방근 세포에서 Na-Ca 교환전류의 특성에 관한 연구)

  • Youm, Wook;Ho, Won-Kyung;Suh, Kyung-Phill
    • Journal of Chest Surgery
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    • v.22 no.4
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    • pp.548-561
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    • 1989
  • In single atrial cells isolated from the rabbit the properties of inward current of Na-Ca exchange were investigated using the whole cell voltage clamp technique. The current was recorded during repolarization following brief 2 ms depolarizing pulse to +40 mV from a holding potential of * 70 mV. Followings are the results obtained: 1. When stimulated every 30 seconds, the inward currents were activated and reached peak values 6-12 ms after the beginning of depolarizing pulse. The mean current amplitude was 342 pA/cell. 2. The current decayed spontaneously from the peak activation and the time course of the relaxation showed two different phases fast and slow phase. The time constants were 10-18 ms and 60-140 ms, respectively. 3. The recovery of inward current was tested by paired pulse of various intervals. The peak current recovered exponentially with time constant of 140 ms and 1 p M isoprenaline accelerated the recovery process. 4. Relaxation time course was also affected by pulse interval and time constant of the fast phase was reduced almost linearly according to the decrease of pulse interval between 30 sec and 1 sec. 5. The peak activation was increased in magnitude by long prepulse stimulation, 5 p M Bay K, 1 p M isoprenaline or internal and external application of c-AMP. 6. The relaxation time constant of the fast phase was prolonged by 5 p M Bay K or c-AMP, and shortened by isoprenaline. However the time course of the slow relaxation phase was not so much changed. From the above results, it could be concluded that increase of the calcium current by Bay K or c-AMP results in the potentiation and prolongation of intracellular calcium transient, and the facilitation of Ca uptake by SR might be a mechanism of shortening the time constant of current relaxation by short interval stimulation or isoprenaline.

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A Protection Scheme for DC Railway Systems (DC철도 급전계통 보호시스템 구성)

  • Kwon, Y.J.;Kang, S.H.;Oh, K.H.;Lee, J.K.;Lee, M.H.
    • Proceedings of the KIEE Conference
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    • 2003.11a
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    • pp.91-94
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    • 2003
  • A DC railway system has low feeder voltage, The fault current can be smaller than the current of load starting. So it is important to discriminate between the small fault current and the load starting current. The load starting current increases step by step but the fault current increases all at once. So the type of ${\Delta}I$ relay(50F) was developed using the different characteristics between the load starting current and the fault current. As for the load starting current, the time constant of load current at each step is much smaller than that of the fault current. First, to detect faults in DC railway systems, an algorithm using the time constant calculated by the method of least squares is presented in this paper. Secondly, to compose a protection scheme for DC railway systems is presented in this paper.

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Experimental Characteristics Examination of a Hybrid-Type Supercapacitor (하이브리드형 슈퍼커패시터의 실험적 특성 규명)

  • Jeong, Kyuwon;Shin, Jaeyoul
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.25 no.4
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    • pp.307-311
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    • 2016
  • Several types of supercapacitors have been developed for energy storage systems. Among them, the hybrid type has advantages such as a large capacitance per weight compared with the electric double-layer capacitator type. In this study, constant current charging and discharging tests were conducted for recently developed hybrid-type supercapacitors. Based on the experimental results, the capacitance and equivalent series resistance were obtained. The capacitance was larger than the designed capacitance at a low current but became small at a high current. In addition, the capacitance depended on the cell voltage. These results can be used to design an energy storage system.

Novel Soft Starting Algorithm of Single Phase Induction Motors by Using PWM Inverter

  • Kim, Hae-Jin;Hwang, Seon-Hwan;Kim, Jang-Mok
    • Journal of Power Electronics
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    • v.18 no.6
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    • pp.1720-1728
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    • 2018
  • This paper proposes a novel soft starting algorithm by using PWM inverter technique to control an amplitude of the motor starting current at a single-phase induction motor (SPIM). Traditional SPIM starting methods such as a Split-Phase, Capacitor-Start, Permanent-Split Capacitor (PSC), Capacitor-Start Capacitor-Run (CSCR), basically cannot control the magnitude of starting current due to the fixed system structures. Therefore, in this paper, a soft starting algorithm based on a proportional resonant (PR) control with a variable and constant frequency is proposed to reduce the inrush current and starting up time. In addition, a transition algorithm for operation modes is devised to generate a constant voltage and constant frequency (CVCF). The validity and effectiveness of the proposed soft starting method and transition algorithm are verified through experimental results.

A Modeling and Analysis of Electric Railway System Using Constant Power Model (정전력모델을 이용한 전기철도 시스템의 회로 모델링 및 해석기법)

  • 홍재승;김주락;오광해;창상훈;김정훈
    • Proceedings of the KSR Conference
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    • 2000.05a
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    • pp.116-122
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    • 2000
  • This paper presents a simulation method with constant power model for the train load. In power system simulation loads could be modeled as a constant power, constant current, constant Impedance or a function of voltage and frequency. At this time, however, representing a train load as the function is difficult because of the lack of data. Therefore as a first step, simulation method with a constant power model fer a train is studied, and the test result is compared with the simulation result using the constant Impedance model.

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A New Protection Algorithm for DC Railway Systems (새로운 직류급전계통 보호 알고리즘)

  • Kwon V.J.;Kang S.H.;Hyun S.H.;Han M.S.;Lee J.K.
    • Proceedings of the KSR Conference
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    • 2004.06a
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    • pp.1280-1285
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    • 2004
  • ADC railway system has low feeder voltage, The fault current can be smaller than the current of load starting. So it is important to discriminate between the small fault current and the load starting current. The load starting current increases step by step but the fault current increases all at once. As for the load starting current, the time constant of load current at each step is much smaller than that of the fault current. First, to detect faults in DC railway systems, an algorithm using the time constant calculated by the method of least squares is presented in this paper.

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A Study on the Transient Characteristics in 765kV Untransposed Transmission Systems (765kV 비연가 송전계통 과도 특성에 관한 고찰)

  • 안용진;강상희
    • The Transactions of the Korean Institute of Electrical Engineers A
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    • v.53 no.7
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    • pp.397-404
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    • 2004
  • This paper describes a study of transient characteristics in 765kV untransposed transmission lines. As the 765(kV) system can carry bulk power, some severe fault on the system nay cause large system disturbance. The large shunt capacitance and small resistance of 765kv transmission line make various difficulties for its protection. These problems including current difference between sending and receiving terminals on normal power flow, low order harmonic current component in fault current and current transformer saturation due to the long DC time constant of the circuit etc. must be investigated and solved. The analysis of transient characteristics at sending terminal has been carried out for the single phase to ground fault and 3-phase short fault, etc. The load current, charging current in normal condition and line flows, fault current, THD(Total Harmonic Distortion) of harmonics, time constants have been analysed for the 765kV untransposed transmission line systems.

Study of Multi-Step Current Lead (다단 전류도입선 해석)

  • Moon, J.S.;Seol, S.Y.
    • Proceedings of the KSME Conference
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    • 2000.04b
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    • pp.379-384
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    • 2000
  • High-Tc superconducting current leads with multi-step and continually varied cross-sectional area are studied to reduce heat leak into cryostat and material use. Assuming conduction-cooled lead the cross-sectional area is reduced along the heat flow direction according to the increase of critical current density which increases with decreasing temperature. In this study, we also analyze the multi-step cross-sectional area High-Tc current leads. The multi-st데 current leads changes the cross-sectional area to have constant safety-factor at changed section. The heat leak into cryostat, total voume, safety-factor and the temperature profiles are compared to those of the constant safety-factor current leads. The developed methods are applied to the Bi-2223 superconductor sheathed with Ag-Au alloy.

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