• Transactions on Electrical and Electronic Materials
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• 제14권5호
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• pp.235-241
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• 2013

A low power CMOS control circuit is applied in an integrated DC-DC buck converter. The integrated converter is composed of a feedback control circuit and power block with 0.35 ${\mu}m$ CMOS process. A current-sensing circuit is integrated with the sense-FET method in the control circuit. In the current-sensing circuit, a current-mirror is used for a voltage follower in order to reduce power consumption with a smaller chip-size. The N-channel MOS acts as a switching device in the current-sensing circuit where the sensing FET is in parallel with the power MOSFET. The amplifier and comparator are designed to obtain a high gain and a fast transient time. The converter offers well-controlled output and accurately sensed inductor current. Simulation work shows that the current-sensing circuit is operated with an accuracy of higher than 90% and the transient time of the error amplifier is controlled within $75{\mu}sec$. The sensing current is in the range of a few hundred ${\mu}A$ at a frequency of 0.6~2 MHz and an input voltage of 3~5 V. The output voltage is obtained as expected with the ripple ratio within 1%.

• 조명전기설비학회논문지
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• 제28권10호
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• pp.56-62
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• 2014

When fault currents contain decaying DC offset, the peak value of the fault current in the first cycle of the fault period is higher than the fault current during the steady-state period. To reduce the asymmetric fault current, this paper proposes an operation scheme using the series connection of two hybrid type Superconducting Fault Current Limiters (SFCLs) : an auxiliary SFCL and a main SFCL. The proposed method calculates the fault angle by comparing the zero-crossing time with fault detection time. According to the fault angle calculated, an auxiliary SFCL operates to reduce an asymmetric fault current during half a cycle after fault occurrence. After this process, the fault current is limited by a main SFCL. To confirm the usefulness of the proposed method, case studies using Electro-Magnetic Transients Program (EMTP)/Alternative Transient Program (ATP) Draw are perfomed.

• 대한전기학회논문지
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• 제40권1호
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• pp.24-30
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• 1991

This paper deals with the analysis of the transient characteristics of a superconducting a.c. generator(SCG) using Finite Element Method. Since the magnetic field induced by the field current and the armature currents are not sinusoidally distributed in a generator, the conventional equivalent circuit method, in general, uses the fundamental component only and is done in frequency domain. But the finite element analysis makes it possible to analyze the transient magnetic field distribution and the electrical characteristics of the double shields of SCG in time domain.

• 전자공학회논문지D
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• 제34D권12호
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• pp.31-38
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• 1997

A new CAD-compatible non-quasi-static (NQS) MOS transient model is presented. A new type of weighted residual method, the collcoatin method, is adopted to obtian an approximate ordinary differntial equation from the continuity eqation. Contrasting to the conventional NQS models, the new model can directly include the variatin of the depletion charge and the derived transient current sare expressed with only physically meaningful variables. The new model predicts transient behaviors reasonably well in the calculation including cutoff regions where the depletion charge rapidly changes.

• 조명전기설비학회논문지
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• 제27권12호
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• pp.81-86
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• 2013

An electric potential rise of the grounding electrode developed by the lightning stroke currents should be calculated for the purpose of effective protection of electrical and electronic equipment. In this paper, the electromagnetic model was applied to calculate the harmonic impedance of grounding electrode. Also the empirical equation related to the permittivity and resistivity of soil was used. The lightning current waveforms, which are expressed by the Heidler's equation, were used in order to calculate accurately transient electric potential rises. The transient voltage was obtained by using the simulated harmonic impedance and the lightning current in frequency domain. Finally, the transient voltages of horizontal grounding electrode(10m) under lightning stroke currents were calculated by IFFT(Inverse Fast Fourier Transform).

• 동력기계공학회지
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• 제14권2호
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• pp.40-47
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• 2010

This paper proposes a fault detection system to detect the strip rupture in six-high stand Cold Rolling Mills based on transient current signal of an electrical motor. For this work, signal smoothing technique is used to highlight precise feature between normal and fault condition. Subtracting the smoothed signal from the original signal gives the residuals that contains the information related to the normal or faulty condition. Using residual signal, discrete wavelet transform is performed and acquire the signal presenting fault feature well. Also, feature extraction and classification are executed by using PCA, KPCA and SVM. The actual data is acquired from POSCO for validating the proposed method.

• 한국수소및신에너지학회논문집
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• 제14권3호
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• pp.195-206
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• 2003

Polymer electrolyte membrane fuel cells(PEMFC) are very interesting power source due to high power density, simple construction and operation at low temperature. But they have problems such as high cost, improvement of performance and effect of temperature. This problems can be approached using mathematical models which are useful tools for analysis and optimization of fuel cell performance and for heat and water management, in this paper, transient model consists of various energy terms associated with fuel cell operation using the mass and energy balance equation. And water transfer in the membrane is composed of back diffusion and electro-osmotic drag. The temperature calculated by transient model approximately agreed with the temperature measured by experiment in constant current condition.

• 조명전기설비학회논문지
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• 제29권1호
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• pp.57-63
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• 2015

The incidence of fires caused by electrical factors has increased with the growth in domestic electrical consumption. According to the national fire data system of national emergency management agency, electrical fires accounted for 20% of all domestic fires in the last 10 years. Electrical fires are mainly caused by short circuit, leakage current, defect in an electrical equipment, over load, utility fault, etc. The fault current can be several times larger than the nominal current, thereby exceeding the rated current of cable. Consequently, the cable conductor, typically copper wire, heats up to a temperature that ignites surrounding combustibles. This paper describes the transient characteristics of the 0.6/1kV, TFR-8 cable have been investigated, and analyzed under the over current conditions for reduce the risk of electrical fire by experimental and FEM analysis. The experimental and FEM(Finite Element Method) analysis results of temperature and resistance variation according to the over current in copper wires were analyzed. The experimental results coincide well with the FEM analysis.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.2
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• pp.1146-1149
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• 2004

A new developed impulse current test system(100kV, 250kJ)is presented, which can carry out all impulse current and performance tests on surge arrester sections with rated voltage up to 12kV according to IEC 60099-4(2001). The maximum achievable peak value is 200kA for the impulse current $4/10{\mu}s$ and 60kA for the $30/80{\mu}s$ and $8/20{\mu}s$. The long duration current impulse is realized from class 1 to class 5. The digital transient recorder(4 channels 60MS/S 10bit) is used for measuring AC voltage, impulse current, reference voltage and leakage current. The complex control, measuring, evaluation and data storage system is controlled by one industrial PC system.

• 조명전기설비학회논문지
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• 제22권12호
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• pp.157-163
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• 2008

다상 교호 컨버터에서 인덕턴스가 불일치 할 때 첨두전류 제어기를 사용하는 경우에 각 상의 평균 전류는 동일하지 않다. 본 논문에서는 각 상의 인덕턴스가 불일치한 경우에 첨두전류 모드에서 평균전류가 동일해지는 전류분배 제어기를 제안한다 제어기는 과도상태에서도 전류의 평형이 잘 이루어질 수 있도록 설계한다. 제안된 방법을 2상과 4상 교호 승압컨버터에 적용시켰으며, 실험 결과를 통해 인덕턴스가 불일치한 경우에도 첨두전류 모드에서 전류평형이 잘 이루어짐을 보인다.