• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.4
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• pp.94-99
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• 2003

A strong need to improve the quality of electric power is increased because of increasing use of the sensitive and small-sized electronic devices. The transient overvoltages on low-voltage AC power distribution systems are induced by direct or indirect lightning return strokes, and they can cause damage and/or malfunction of the utility systems for home automation, office automation and factory automation as well as medical equipment. The behaviors of lightning overvoltages transferred through the transformer to the low voltage AC power distribution systems were experimentally investigated using a Marx generator. The surge voltages in low-voltage ac power systems are rarely limited by the application of the surge arrester to the primary side of distribution transformer and a custom service ground.

• Journal of Power Electronics
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• v.18 no.4
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• pp.1015-1026
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• 2018

A family of dual-DC-input (DI) dual-buck inverters (DBIs) is proposed by employing a DI switching cell as the input of traditional DBIs. Three power ports, i.e. a low voltage DC input port, a high voltage DC input port and an AC output port, are provided by the proposed DI-DBIs. A low voltage DC source, whose voltage is lower than the peak amplitude of the AC side voltage, can be directly connected to the DI-DBI. This supplies power to the AC side in single-stage power conversion. When compared with traditional DBI-based two-stage DC/AC power systems, the conversion stages are reduced, and the power rating and power losses of the front-end Boost converter of the DI-DBI are reduced. In addition, five voltage-levels are generated with the help of the two DC input ports, which is a benefit in terms of reducing the voltage stresses and switching losses of switches. The topology derivation method, operation principles, modulation strategy and characteristics of the proposed inverter are analyzed in-depth. Experimental results are provided to verify the effectiveness and feasibility of the proposed DI-DBIs.

• Journal of Electrical Engineering and Technology
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• v.9 no.1
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• pp.280-285
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• 2014

In order to evaluate the insulation deterioration in the stator windings of five gas turbine generators(137 MVA, 13.8 kV) which has been operated for more than 13 years, diagnostic test and AC dielectric breakdown test were performed at phases A, B and C. These tests included measurements of AC current, dissipation factor, partial discharge (PD) magnitude and capacitance. ${\Delta}I$ and ${\Delta}tan{\delta}$ in all three phases (A, B and C) of No. 1 generator stator windings showed that they were in good condition but PD magnitude indicated marginally serviceable and bad level to the insulation condition. Overall analysis of the results suggested that the generator stator windings were indicated serious insulation deterioration and patterns of the PD in all three phases were analyzed to be internal, slot and spark discharges. After the diagnostic test, an AC overvoltage test was performed by gradually increasing the voltage applied to the generator stator windings until electrical insulation failure occurred, in order to determine the breakdown voltage. The breakdown voltage at phases A, B and C of No. 1 generator stator windings failed at 28.0 kV, 17.9 kV, and 21.3 kV, respectively. The breakdown voltage was lower than that expected for good-quality windings (28.6 kV) in a 13.8kV class generator. In the AC dielectric breakdown and diagnostic tests, there was a strong correlation between the breakdown voltage and the voltage at which charging current increases abruptly ($P_{i1}$, $P_{i2}$).

• Journal of Power Electronics
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• v.16 no.6
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• pp.2294-2305
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• 2016

The introduction of a high-voltage direct-current (HVDC) system based on a modular multilevel converter (MMC) for wind farm integration has stimulated studies on methods to control this type of converter. This research article focuses on the control of the AC voltage and circulating current for a wind-farm-side MMC (WFS-MMC). After theoretical analysis, emotional learning (EL) controllers are proposed for the controls. The EL controllers are derived from the learning mechanisms of the amygdala and orbitofrontal cortex which make the WFS-MMC insensitive to variance in system parameters, power change, and fault in the grid. The d-axis and q-axis currents are respectively considered for the d-axis and q-axis voltage controls to improve the performance of AC voltage control. The practicability of the proposed control is verified under various conditions with a point-to-point MMC-HVDC system. Simulation results show that the proposed method is superior to the traditional proportional-integral controller.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.395-398
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• 1999

In ac PDP(plasma Display Panel), the discharge characteristics is very important to display clear images. In this paper, we have studied the measurement of voltage transfer curves which show the discharge characteristics in AC PDP. The change of the effective wall capacitance during a discharge is also studied. These depend on lateral spreading of charge distribution and the strength of the discharge. As a parameter of the frequency, we observed the effects of the frequency in voltage transfer curves and in effective wall capacitance changes. As frequency increases, minimum sustain voltage and firing voltage decrease. In upper region of gap voltage the chance of the effective wall capacitance is independent of frequency.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.371-373
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• 2002

High current density Bi-2223 tapes have recently become commercially available. The ac loss is an important issue in the design of high-T$_{c}$ superconducting power cables. In such complicated devices, special caution is required in the placing of voltage leads for measuring the in-phase voltage. In this paper, the ac losses for different contacts and arrangements of voltage leads have been experimentally investigated in a single layer model cable and discussed.d.

• Proceedings of the KIEE Conference
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• 2008.10b
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• pp.460-461
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• 2008

A new AC-PDP driving method was proposed to reduce the address period. The overlapped scan method can reduce the address period. However, this method has a narrow address voltage margin compared with conventional scan method in this paper, Slope overlapped scan method is presented. The proposed new overlapped scan method allows wider address voltage margin than conventional overlapped scan method.

• Proceedings of the KIEE Conference
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• 1999.07f
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• pp.2804-2806
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• 1999

This paper presents a voltage regulator for an AC power supply. It is designed to have the band Pass filter characteristic for the system to be free from DC-offset or sub-frequency fluctuation in the output voltage wave

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.02a
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• pp.210-212
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• 2003

High current density Bi-2223 tapes have recently become commercially available. The ac loss is an important issue in the design of high-T$_{c}$ superconducting power cables. In such complicated devices, special caution is required in the placing of voltage leads for measuring the in-phase voltage. In this paper, the ac losses for different contacts and arrangements of voltage leads have been experimentally investigated in a single layer model cable and discussed.d.

• Proceedings of the KIEE Conference
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• 2001.07a
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• pp.346-348
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• 2001

This paper analyze the interference problems, especially AC corrosion when the gas pipeline is buried with power cable in the same submarine tunnel. This paper present the results of the study about AC corrosion, limitation of safety voltage, modeling of power cables, gas pipeline and grounding systems, analysis of induction voltage according to various circumstance, soil resistivity, length of tunnel. and so on.