• Title/Summary/Keyword: On-current

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A New Overlap Current Restraining Method for Current-source Rectifier

  • Qin, Haihong;Liu, Qing;Zhang, Ying;Zhang, Xin;Wang, Dan
    • Journal of Power Electronics
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    • v.18 no.2
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    • pp.615-626
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    • 2018
  • To ensure a DC current path and avoid large voltage overshoot of the DC-link inductor, alternating PWM pulses in the current-source rectifier should be supplemented by overlap time, which generates an overlap current and causes input current distortion. In this study, the influence of overlap time is illustrated by comparing the AC-side current before and after overlap time is added. The overlap current distribution caused by overlap time is discussed under different modulation carriers, including triangle carrier, positive-going carrier, and negative-going carrier. The quantitative relationship between the extra harmonics of the AC-side current and overlap time is based on the Fourier analysis. Based on the commutation analysis, a new carrier modulation scheme that can restrain overlap current is proposed. A 3 kW prototype is established to verify the effectiveness of the influence of overlap time and the proposed restraining modulation scheme.

Analysis on Current Limiting Characteristics of a Superconducting Fault Current Limiter (SFCL) with a Peak Currnt Limiting Function (피크전류제한 기능을 갖는 초전도한류기의 전류제한 특성분석)

  • Han, Tae-Hee;Lim, Sung-Hun
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.24 no.1
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    • pp.47-51
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    • 2011
  • The superconducting fault current limiter (SFCL) with a peak current limiting function according to the initial fault current with the different amplitudes was suggested. The proposed SFCL, which consists of two limiting components, causes only the first superconducting element among two limiting components to be quenched in case that the initial fault current with the lower peak amplitude happens. On the other hand, the initial fault current with the higher peak amplitude makes both the superconducting elements of two limiting components to be quenched, which contributes to the peak current limiting function of the SFCL. To confirm the fault current limiting operation of the proposed SFCL, the short-circuit tests of the SFCL according to the fault angle were carried out and its effective fault current limiting operations could be discussed.

Modified Current Differential Relay for $Y-{\Delta}$ Transformer Protection ($Y-{\Delta}$ 변압기 보호용 수정 전류차동 계전기)

  • Jin, En-Shu;Kang, Yong-Cheol
    • The Transactions of the Korean Institute of Electrical Engineers A
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    • v.55 no.3
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    • pp.95-101
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    • 2006
  • This paper proposes a modified current differential relay for $Y-{\Delta}$ transformer protection. The relay uses the same restraining current as a conventional relay, but the differential current is modified to compensate for the effects of the exciting current. A method to estimate the circulating component of the delta winding current is proposed. To cope with the remanent flux, before saturation, the core-loss current is calculated and used to modify the measured differential current. When the core then enters saturation, the initial value of the flux is obtained by inserting the modified differential current at the start of saturation into the magnetization cure. Thereafter, the core flux is then derived and used in conjunction with the magnetization curve to calculate the magnetizing current. A modified differential current is then derived that compensates for the core-loss and magnetizing currents. The performance of the proposed differential relay was compared against a conventional differential relay. Test results indicate that the modified relay remained stable during severe magnetic inrush and over-excitation, because the exciting current was successfully compensated. This paper concludes by implementing the relay on a hardware platform based on a digital signal processor. The relay does not require additional restraining signal and thus cause time delay of the relay.

Effect of current waveform on drop transfer in pulsed gas metal arc welding (Pulsed GMAW 의 전류 파형이 금속이행에 미치는 영향)

  • Hammad, Muhammad A.;Yoo, Choong-D.
    • Proceedings of the KWS Conference
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    • 2009.11a
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    • pp.48-48
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    • 2009
  • Conventionally in pulsed gas metal arc welding (GMAW-P), drop transfer is analyzed with simplest square pulse waveform. While the pulse current is described by four parameters (peak current magnitude and time plus base current magnitude and time), it deviates the real pulse shape. Real pulse can be better idealized by the trapezoidal pulse waveform described by two additional parameters, i.e., current rise and fall rate (dI/dt). Power source response rate is described by these parameters. In this work, the effect of these parameters on drop transfer is predicted by the force displacement model (FDM). While peak current has significant effects on drop detachment, drop transfer is also influenced by the current rise rate. Predictions indicate that the current rise rate can have considerable effects on the size of the detached drop if other pulse parameters are kept constant. FDM is applied to determine peak time for one drop one pulse condition (ODOP) when rests of the pulse parameters are given. The predicted range of ODOP shows good agreement with experimental data.

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Property and Surface Morphology of Copper Foil on the Current Density (구리 박막의 표면형상과 물성에 대한 전류밀도 영향)

  • Woo, Tae-Gyu;Park, Il-Song;Jung, Kwang-Hee;Seol, Kyeong-Won
    • Korean Journal of Materials Research
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    • v.20 no.10
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    • pp.555-558
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    • 2010
  • This study examined the effect of current density on the surface morphology and physical properties of copper plated on a polyimide (PI) film. The morphology, crystal structure, and electric characteristics of the electrodeposited copper foil were examined by scanning electron microscopy, X-ray diffraction, and a four-point probe, respectively. The surface roughness, crystal growth orientation and resistivity was controlled using current density. Large particles were observed on the surface of the copper layer electroplated onto a current density of 25 mA/$cm^2$. However, a uniform surface and lower resistivity were obtained with a current density of 10 mA/$cm^2$. One of the important properties of FCCL is the flexibility of the copper foil. High flexibility of FCCL was obtained at a low current density rather than a high current density. Moreover, a reasonable current density is 20 mA/$cm^2$ considering the productivity and mechanical properties of copper foil.

Investigation on the inductive and resistive fault current limiting HTS power cable

  • Lee, Sangyoon;Choi, Jongho;Kim, Dongmin;Kwon, Yonghyun;Kim, Seokho;Sim, Kideok;Cho, Jeonwook
    • Progress in Superconductivity and Cryogenics
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    • v.16 no.2
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    • pp.59-63
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    • 2014
  • HTS power cable bypass the fault current through the former to protect superconducting tapes. On the other hand, the fault current limiting (FCL) power cable can be considered to mitigate the fault current using its increased inductance and resistance. Using the increased resistance of the cable is similar to the conventional resistive fault current limiter. In case of HTS power cable, the magnetic field of HTS power cable is mostly shielded by the induced current on the shield layer during normal operation. However, quench occurs at the shield layer and its current is kept below its critical current at the fault condition. Consequently, the magnetic field starts to spread out and it generates additional inductive impedance of the cable. The inductive impedance can be enhanced more by installing materials of high magnetic susceptibility around the HTS power cable. It is a concept of SFCL power cable. In this paper, a sample SFCL power cable is suggested and experimental results are presented to investigate the effect of iron cover on the impedance generation. The tests results are analyzed to verify the generation of the inductive and resistive impedance. The analysis results suggest the possible applications of the SFCL power cable to reduce the fault current in a real grid.

Analysis of Tidal Current for Cheonsu Bay Using Heaps Model (Heaps 모델을 이용한 천수만 해역의 조류해석)

  • 박영기
    • Journal of Environmental Science International
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    • v.4 no.2
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    • pp.245-251
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    • 1995
  • Generally, It is Introduced to well-known other models without considering tidal current of the field. The paper presents field measurements and numerical model solving velocity field of Cheonsu Bay by two-dimensional tidal model. It was proved that this scheme is easy to handle complex topography. Computed results is represented characteristics of tidal current for Cheonsu Bay. The results of the study can be summarized as follows ; 1. Tide form number has 0.21 value. Tidal range estimated 630.3 cm on spring, 454.1 cm on mean and 277.9 cm on neap, respectively 2. Tidal current has semi-diurnal form. Distance of traveling observed 16.6 km on flood and 15.5 km on ebb. 3. Tidal velocity showed reversing current. It was found that tidal velocity above 100 cm/sec is about 20 %. 4. Computed results are in good agreement with the observed data. Applying the algorithm to Cheonsu Bay, velocity fields and dry bank phenomena are simulated well in spite of complex topography. 5. An advanced study on the effects of open boundary conditions should be continuously performed.

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Analysis on Current Distribution of Four-Layer HTSC Power Transmission Cable with a Shield Layer

  • Lim Sung-Hun
    • Journal of Electrical Engineering and Technology
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    • v.1 no.3
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    • pp.308-312
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    • 2006
  • The inductance difference between conducting layers of high-Tc superconducting (HTSC) power transmission cable causes the current sharing of each conducting layer to be unequal, which decreases the current transmission capacity of HTSC power cable. Therefore, the design for even current sharing in HTSC power transmission cable is required. In this paper, we investigated the current distribution of HTSC power cable with a shield layer dependent on the pitch length and the winding direction of each layer. To analyze the effect of the shield layer on the current sharing of the conducting layers of HTSC power cable, the current distribution of HTSC power cable without a shield layer was compared with the case of HTSC power cable with a shield layer. It could be found through the analysis from the computer simulations that the shield layer of HTSC power cable could be contributed to the improvement of current distribution of conducting layers at the specific pitch length and the winding direction of conducting layer. The result and discussion for the current distribution calculated for HTSC power transmission cable with a shield layer were presented and compared with the cable without a shield layer.

Measurement and Estimation of Dynamic Resistance of the Human Body Using Body Current at Low-Voltage Levels (저전압에서의 통전전류를 이용한 인체의 동저항 측정 및 예측)

  • 김두현;강동규;김상철
    • Journal of the Korean Society of Safety
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    • v.16 no.1
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    • pp.37-42
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    • 2001
  • The severity of electric shock is entirely dependent on body resistance. When the human body becomes a part of electric circuit, the body resistance is given as a function of shock scenario. Factors which consist of applied voltage, shock duration, body current path and contact area, etc.. The body resistance is defined as the voltage applied to subjects divided by the body current. To secure safety of the subjects, the experiment is conducted on 10 subjects, the body current is limited to 4mA. And only three factors under many shock scenario conditions are used to determine the body resistance. The three factors are the applied voltage, the current pathway and the contact area. The object of this work is to estimate the dynamic resistance of the human body as a function of applied voltage using the body current at low-voltage levels. The data of the body current at low-voltage levels are extrapolated to high-voltage levels using two analytic functions with specified constants calculated by numerical method. Also we can provide permissible body voltage for various copper electrodes on the basis of the data determined with the dynamic resistance and the body current.

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Studies on the Mackerel Purse Seine Operating in the Sea Area of Cheju Island - 2 . Model Experiment ob the Deformation of Net in Two Layer Current (제주도 주변 해역 고등어 포착망의 연구 - 2 . 이중조에 있어서 망의 변형에 관한 모형실험 -)

  • 박정식
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.22 no.4
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    • pp.32-40
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    • 1986
  • A model experiment of purse seine by the circulating water tank was carried out on the changes of net shape and the tension of purseline under operation in two layer current. In the circular tank, the two layer current was made by cutting off the current of upper layer and producing the bottom current by the equipment shown in Fig. 1. The model experiment of purse sein was made on a reduced scale 1 :400, and the experiment was carried out according to the Tauti's model law. When the bottom current of O. 5 knot flows to lower part of three-eighths of net, following results are derived. The depth of sinkerline reached only about 80% of that of no current set. The horizontal shift of sinker line caused by the bottom current is maximized in tight set. The enclosed area by the floatIine immediately after the completion of set net is 61. 5% in tight set, 50. 0 % in loose set and 54. 1 % in lateral set of those in the case of no current. In the first half period of pursing, the tension of the purseline is enhenced by the bottom current and the pattern of increasing is irregular in the tension curves.

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