• 대한전기학회논문지:전력기술부문A
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• 제54권1호
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• pp.1-7
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• 2005

This paper proposes a novel UPQC(unified power quality conditioner) based on H-bridge modules, isolated through single-phase multi-winding transformers. The dynamic performance of proposed system was analyzed by simulation with PSCAD/EMTDC, assuming that the UPQC is connected with the 22.9kV distribution line. The proposed system can be directly connected to the transmission line without series injection transformers. It has flexibility in expanding the operation voltage by increasing the number of H-bridge modules and can compensate reactive power, harmonics, voltage sag and swell, voltage unbalance. The proposing UPQC has the ultimate capability of improving power quality at the point of installation on power distribution systems.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제54권9호
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• pp.422-430
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• 2005

This paper describes experimental analysis of UPFC, which is composed of cascaded H-bridge modules and single-phase multi-winding transformers for isolation. The operational characteristic was analyzed through experimental works with a scaled model, and simulation results with PSCAD/EMTDC. The UPFC proposed in this paper can be directly connected to the transmission line without series injection transformers. It has flexibility to expand the operation voltage by increasing the number of H-bridge modules. The analysis results can be utilized to design the actual WFC system applicable for the transmission system.

• 대한전기학회논문지:전력기술부문A
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• 제48권4호
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• pp.358-364
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• 1999

The auxiliary transformers or start-up/stand-by transformer(s) are installed against the start-up and shut-down of generator and emergency status in fossil power plant. The on-site power supply configuration using these transformers must be determined, considering configuration requirements, site characteristics, reliability and availability severely because it is remarkably important for safety and ecfonomy of plant. The auxiliary or start-up/stand-by power supply configuration has been determined considering only safety requirements and construction cost until now in Korea. This paper presents general theorems for the reliability estimation and proposes 2-unit based 4 alternatives for the start-up power supply stystem of 500㎿ standardized fossil power plant. The reliability and unavailability of equipment, system and configuration are determined using minimal cut-set methodology. The optimized plan of 4 alternatives is determined based on this ultimate reliability and unavailability.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 춘계학술대회 논문집 전기설비전문위원
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• pp.166-168
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• 2007

The DGA (Dissolved Gases Analysis) technique has been widely using for fault diagnosis of the power transformers. This technique has a high reliability than other techniques. KEPCO (Korea Electric Power Cooperation) has been using DGA technique since KEPCO established the criteria of DGA in 1985. In this paper, we introduce the DGA criteria of KEPCO and analyze the result of DGA. Also we introduce the cases of thoroughgoing inspection of the power transformers caused by DGA and compare the judgment of DGA with the result of throughgoing inspection.

• Journal of Electrical Engineering and Technology
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• 제12권3호
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• pp.1245-1249
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• 2017

Recently, unusual transformer failures have been reported in 25kV power systems connected with a VCB and transformer. In this study, performance of the protection system, dielectric strength of the transformers, characteristics of switching surges and resonance phenomena were analysed and assessed. All investigations regarding the insulation breakdown of the transformers were carried out by simulations, laboratory tests, factory tests and on-site measurements in order to thoroughly investigate the root causes. Furthermore, experimental methods for investigating the resonance phenomenon were derived and tests were conducted applying the derived method to recreate the phenomenon in the transformer. It is found that resonance between the transformer and switching surge generated by closing a VCB can initiate the breakdown of internal windings of a transformer.

• Journal of Electrical Engineering and Technology
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• 제13권1호
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• pp.78-88
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• 2018

The liberalization of electricity market and environmental concerns are the major driving forces for the development of Distributed Generation (DG). The mode of grid-connected wind power generation is becoming popular and has matured as a reliable DG technology. The voltage generated by the wind generator is stepped up to the higher voltage by the transformers before connecting to the grid. Operating algorithm of the differential relays for transformer protection used in the wind farms need to be modified to take care of the dynamic nature of fault current caused by the intermittent nature of the wind power. An algorithm for the differential relay is proposed in which dual slope characteristics are adjusted with varying fault level situation according to the wind generator in service as well as with the wind speed. A case study conducted for a typical wind farm shows that the proposed method avoids mal-operation of the differential relay in varying wind power conditions.

• Journal of Electrical Engineering and Technology
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• 제13권4호
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• pp.1623-1630
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• 2018

Normally, various auxiliary loads are installed along with the main load in industrial applications. Usually, load transformers are used to convey such types of auxiliary loads. The transformers become energized when the loads are turned-on, consequently, high amplitude of inrush current appears at the output of the uninterrupted power supply (UPS) system. To mitigate these high current amplitudes, this manuscript suggests a three-phase line-interactive UPS system to counter the inrush current during the turning-on of the auxiliary load transformer while powering the main load by using a current controlled inverter. Experimental results of a laboratory-sized prototype are provided in the support of the proposed UPS system for validation.

• 조명전기설비학회논문지
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• 제30권3호
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• pp.106-112
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• 2016

The high-voltage pulse generator consists of transformers of fundamental wave and harmonic waves, and shunt capacitors. The pulse has the fundamental wave and the harmonic waves that have been as a series circuit by the transformers to make high voltage pulse. This paper shows that pulse generator circuit is analyzed by using transformer equivalent circuits with the effect of load and simulated in time domain using Matlab program. The output voltage of pulse were obtained to 2.5kHz, 2.0kV. In high voltage circuit, capacitors are related to frequency band pass characteristics. Also, it is shown that the voltage of output pulse increases according to the growth of load.

• 전력전자학회논문지
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• 제10권1호
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• pp.95-101
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• 2005

본 연구에서는 H-Bridge 인버터와 변압기 조합에 의한 다중레벨 인버터로 구성함에 있어 스위칭 소자수를 저감하기 위해 각 H-Bridge 인버터의 한 암을 공통으로 사용할 수 있는 전력회로를 제안한다. 또한 각 인버터에 연결된 변압기의 이용률을 동일하게 할 수 있는 스위칭 방식의 제안으로 각 변압기의 용량을 동일하게 하였다. 제안된 전력회로 및 제어신호의 타당성을 입증하기 위해 프로토 타입 인버터에 대하여 실험을 행하였다

• Journal of Power Electronics
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• 제4권2호
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• pp.112-116
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• 2004

The pulsed power systems have been widely used many other countries and their new applications have been developed by many researchers, such as E/P(Electrostatic Precipitator) to remove the industrial dust, DeNOx/DeSOx power systems, ozone generators and power sources of the laser beam, etc. In this paper, we studied the cascading technique as a new technology consisted of two pulse transformers and obtained their experimental data and results. To obtain the high pulsed voltage adopted cascading technique, we designed our compact pulse generator and tested by adjusting the value of the load resistors to obtain high pulsed voltage with steep rising time and duration time. We explained their experimental results that obtained by adopting cascading technique. Also, we compared theoretical value with measured value obtained by using the cascading method.