• 대한전기학회논문지:전력기술부문A
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• 제48권3호
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• pp.226-233
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• 1999

Protective relay for transformer operates in general by comparing with the differential current and the restraint current. These kinds of currents are changed on magnitude and phasor during the fault according to winding type and vector group. This paper presents the differential and restraint currents and operational principle of differential protective relay for two-winding and three-winding transformer with graphical mode. It is developed using MATLAB for and educational purpose on engineer related in power system and protection in university and power utility including large factory.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2002년도 추계학술대회 논문집
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• pp.121-124
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• 2002

The conventional three-level high frequency phase-shifted dc/dc converter has a disadvantage that a circulating current flows through transformer and switching devices during the freewheeling interval. Due In this circulating current and RMS current stress, conduction losses of transformer and switching devices increases. To alleviate these problems, we propose an improved three-level Zero Voltage and Zero Current Switching (ZVZCS) dc/dc converter using a tapped inductor, a snubber capacitor and two snubber diodes attached at the secondary side of transformer The proposed ZVZCS converter is verified on a 7kW, 30kHz experimental prototype.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 B
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• pp.1304-1306
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• 2004

Recently, the study for development of system having affinity for environment is on investigation. This issue is also applicable to transportation system. This paper suggested the inductive power transformer used for the road/railway applied to contactless power transfer system. The two secondary windings, large gaped magnetic structure and horizontal alignment between primary and secondary coil for that transformer approach a process for improvement of contactless power transfer system performance.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제53권8호
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• pp.420-424
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• 2004

This paper presents experimental data from model windings with different arrangement of coil in order to provide information to design a 22.9kV class HTS transformer. Before experiment, the composite insulation of two different type of HTS transformers are investigated. The first basic of investigation is a breakdown characteristic of liquid nitrogen and flashover characteristic on the GFRP surface under ac and impulse, The second investigation is insulation design, manufacture and test of model windings. These include a AC withstand voltage test of 50 kV rms and a lighting impulse test of 150 kV at peak.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 전력전자학술대회 논문집
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• pp.689-693
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• 2001

The conventional three-level high frequency phase-shifted dc/dc converter has a disadvantage that a circulating current flows through transformer and switching devices during the freewheeling interval. Due to this circulating current and RMS current stress, conduction losses of transformer and switching devices increases. To alleviate these problems, we propose an improved three-level Zero Voltage and Zero Current Switching (ZVZCS) dc/dc converter using a tapped inductor, a snubber capacitor and two snubber diodes attached at the secondary side of transformer. The proposed ZVZCS converter is verified on a 10 kW, 30kHz experimental prototype.

• 전기학회논문지P
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• 제57권4호
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• pp.437-443
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• 2008

We have developed an evaluation technique for both ratio error and phase displacement of current transformer (CT) comparator by using the precise standard capacitors and resistors. By applying this technique to equivalent circuit of CT comparator evaluation system, we can obtain the calculated and measured ratio errors (or phase displacements) in the CT comparator. Thus we can evaluate ratio errors and phase displacement of CT comparator by comparing the calculated and measured ratio errors (or phase displacements). The method was applied to CT comparator under test with the ratio errors and phase displacement ranges of $0{\sim}{\pm}10%$ and $0{\sim}{\pm}7.5$ crad, respectively. Finally we have compared the ratio error and phase displacement of the CT comparator obtained in this method with specifications of two companies.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.244-245
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• 2005

Electrical insulation is one of the most important parts in a high voltage apparatus. Traditionally mineral oils and synthetic esters have been widely used as dielectric coolants for power transformers. Recently, researchers are interested in the environmental friendly vegetable oil from environmental viewpoint. This paper reports on the synthesis and characterization of soybean based ester oils. Two different types of soybean based transformer oils, named as methyl ester and isopropyl ester were synthesized. The synthesis of these esters was achieved by transesterification reactions of soybean oil and alcohol in the presence of catalyst. The GC and NMR spectroscopic analysis of the esters have been performed. The thermal stability of the esters was determined by thermal gravimetric analysis(TGA).

• International journal of advanced smart convergence
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• 제13권2호
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• pp.195-204
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• 2024

In this paper, we investigate the comparative performance of two leading object detection architectures, YOLOv7 and Detection Transformer (DETR), across varying levels of data augmentation using CycleGAN. Our experiments focus on chest scan images within the context of biomedical informatics, specifically targeting the detection of abnormalities. The study reveals that YOLOv7 consistently outperforms DETR across all levels of augmented data, maintaining better performance even with 75% augmented data. Additionally, YOLOv7 demonstrates significantly faster convergence, requiring approximately 30 epochs compared to DETR's 300 epochs. These findings underscore the superiority of YOLOv7 for object detection tasks, especially in scenarios with limited data and when rapid convergence is essential. Our results provide valuable insights for researchers and practitioners in the field of computer vision, highlighting the effectiveness of YOLOv7 and the importance of data augmentation in improving model performance and efficiency.

• 전력전자학회논문지
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• 제4권4호
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• pp.384-394
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• 1999

This paper deals with a fixed frequency full-bridge inverter type DC-DC high-power converter with high frequency high voltage(HFHV) transformer-coupled stage, which operates under quasi-resonant ZVS transition priciple in spite of a wide PWM-based voltage regulation processing and largely-changed load conditions. This multi-resonant(MR) converter topology is composed of a series capacitor-connected parallel resonant tank which makes the most of parasitic circuit reactive components of HFHV transformer and two additional quasi-resonant pole circuits incorporated into the bridge legs. The soft-switching operation and practical efficacy of this new converter circuit using the latest IGBTs are actually ascertained through 50kV trially-produced converter system operating using 20kHz/30kHz high voltage(HV) transformers which is applied for driving the diagnostic HV X-ray tube load in medical equipments. It is proved from a practical point of view that the switching losses of IGBTs and their electrical dynamic stresses relating to EMI noise can be considerably reduced under a high frequency(HF) switching-based phase-shift PWM control process for a load setting requirements.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.388-391
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• 1996

The conventional high frequency phase-shifted full bridge DC-DC converter has a disadavantage that a circulating current flows through transformer and switching devices during the freewheeling interval Due to this circulating current, RMS current stress, conduction losses of transformer and switching devices are increased. To alleviate this problem, this study provides a novel circulating current free type high frequency soft switching phase-shifted full bridge DC-DC converter which applies the energy recovery snubber(ERS) attached at the secondary side of transformer. The ERS adopted in this study is consisted of three fast recovery diode($Ds_1$, $Ds_2$, $Ds_3$), two resonant capacitor($Cs_1$, $Cs_2$) and a small resonant inductor [(Lr) : It can be ignored because the transformer leakage inductance(Ll) is able to use in stead of inserting the resonant inductor(Lr)]