• 한국전기전자재료학회논문지
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• 제23권10호
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• pp.809-813
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• 2010

Frequency domain measurement of propagation loss for ultra high frequency (UHF) partial discharge in the winding of power transformer using a spectrum analyzer and pulse generator is presented. We compared the performance of the method using a network analyzer with and without a winding. Using a network analyzer simplifies the measurement and offers better dynamic range and frequency range. It also provides precise propagation loss within the winding in frequency domain at UHF range. We applied this method to measure UHF propagation loss of transformer mock-up, modeled 154 kV 20 MVA power in KEPCO substation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 A
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• pp.498-499
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• 2006

Oil-filled transformer technology has been around more than 100 years. The principle of operation in the same today as it has been for the previous decades. But all transformers have their life so it is important to know their useful life and the time for replacement. This paper will address this issue and provide the distribution transformer oil aging test results. Distribution transformer and laboratory specimens were externally heated to their respective maximum temperatures. Sample of oil and paper were removed at convenient intervals for testing. We believe that the results of this study will show the possibility of assessing the life of transformers.

• 전력전자학회논문지
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• 제17권6호
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• pp.539-545
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• 2012

Due to merits cost and efficiency, the transformer-less type photovoltaic (PV) inverters have been popularized in the solar market. However, the leakage current flowing through a parasitic capacitor between PV array and ground can cause adverse effect in the transformer-less PV system. In this paper, a bi-directional PV inverter with high efficiency and low noise is proposed for the PV system with an energy storage device. The proposed inverter is a transformer-less type and performs the bi-directional power control between dc sources and grid with high efficiency. In addition, the proposed inverter can suppress the leakage current and obtain low noise characteristic. Finally, 3-kW prototype was implemented to confirm validity of the proposed inverter.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 추계학술대회 논문집 Vol.18
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• pp.151-152
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• 2005

Both $Al_2O_3$ and AlN nanopowders with diameters from ${\mu}m$ to mm were bead-milled and surface-modified by stabilizing agent. The size of bead-milled nanoparticles compared with the primary powder was effectively decreased and was dependent on milling time and bead size. The results of dispersion stability analysis indicated that chemical bonding between nanoparticles and surfactant is more effective than chemical adsorption to prepare the stable transformer oils containing nanoparticles. In this study, the thermal conductivity of the transformer oils containing nanoparticles was measured by transient hot-wire and laser flash methods.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 추계학술대회 논문집 학회본부 C
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• pp.613-615
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• 2000

We explained the present and future tendency in the electric machinery research and development status. Being started WTO system and in the Infinite competitiveness, we hope that this paper will be helpful to strengthen competitiveness of our electric machinery industry.

• 전기학회논문지
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• 제59권12호
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• pp.2125-2130
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• 2010

The neutral section on electric railway system is significant sector in order to prevent short circuit of two electric powers. However, while electric trains pass the neutral section, those speed is decreased and the accident of AC electric traction system and the electric train would be occurred. So the countermeasures are urgently needed. The automatic power switching technology system that is current being research and development is system to improve these problems. Because main object of this system is power change using static switch in the neutral section, it's expected to cause a variety of transients. Especially, onboard transformer inrush current for electric railway train can be occurred more than rated current according to switching time. Therefore, the analysis and improvement are needed to ensure the stability of this system. In this paper, we analyze the operating characteristics of the automatic power switching technology system. Especially, it reviews inrush current according to the closing phase angle. And we propose control plan of inrush current considering the case that voltage is maintained due to counter electromotive force and regenerative braking operation of electric railway train. Finally, the proposed control scheme was reviewed using the transient analysis program.

• KEPCO Journal on Electric Power and Energy
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• 제8권1호
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• pp.5-7
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• 2022

KEPCO's plan is undergoing a trial operation to replace the open-loop section with ring main units configuration where underground distribution lines are installed, by linking the multi-way circuit breakers auto (MCA) on the power side of each pad-mounted transformer. However, ring main units application mentioned above may cause the ripple effects, when implementing the configuration without a study of protection coordination. Because ring main units with classical pre-set protection devices contribution in fault condition didn't consider yet. For the reliable ring main units operation, it is necessary to resolve several protection issues such as the protection coordination with substation side, prevention of the transformer inrush current. These issues can radically deteriorate the distribution system reliability Hence, it is essential to design proper protection coordination to reduce these types of problems. This paper presents a scheme of ring main units' configuration and MCA's settings of time-current curves to preserve the performance of protection coordination among the switchgears considering constraints, e.g. prevention of the ripple effects (on the branch section when a transformer failure occurs and the mainline when a branch line failure occurs). It was confirmed that the propagation of the failure for each interrupter segment could be minimized by applying the proposed TCC and the interrupter settings for the MCAs (branch, transformer). Further, it was verified that the undetected area of the distribution automation system (DAS) could be supplemented by having the MCA configurated ring main units operate first, instead of the internal protection equipment in the transformer such as the fuse, STP when a transformer failure occurs.

• 전기학회논문지
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• 제63권3호
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• pp.414-417
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• 2014

At present, the demand for electric power increases, the electric power system is complicated. The size of the line-to-ground fault and the line-to-line fault occurred with complication of electric power system continue to increase, therefore several issues are raised. To address these issues effectively, the superconducting fault current limiter (SFCL) has been proposed, this study is ongoing. In this paper, we applied the SFCL in three-phase transformer and comparative analysis of the electric power burden to the SFCL. The superconductor is combined to the third winding of transformers in connection structure. In case of a third line-to-line fault, we did comparative analysis of the electric power burden to the SFCL based on the turn ratio of transformer third winding. In this case, we could confirm as the third turn ratio increased, electric power impressed to the superconducting element increased.

• 전기학회논문지
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• 제66권7호
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• pp.1007-1016
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• 2017

This paper aims to analyze the safety evaluation of the existing transformer for the 0.85 millions of public rental apartments as EVs(Electric Vehicles) increase in order to overcome the environment pollution issue and maintain sustainable development. It is analyzed that the 56.4% capacity of power transformer could secure as EV charging infrastructure, based on the analysis of respective utilization patterns of the housing and power transformer. The acceptable number of EVs is 0.04~0.06 per household from the spare capacity of the power transformer. It is analyzed that EV stock is prospected less than 0.03 per household in 2030, considering the condition of the public rental apartments residents and the growth rate of EVs according to practical scenario. The power demand for EVs is within the allowable capacity range of the power transformer, so the research shows that there is no problem in the stability of the existing transformer until 2030.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.219-220
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• 2013

The phenomenology of liquid breakdown has been an area of interest for many years but is still not fully understood. Moreover, it was known that the behavior of magnetic nanoparticles in transformer oil could affect the dielectric breakdown voltage positively or negatively. In this study, we have imaged the magnetic nanoparticles in a transformer oil in-situ using an optical microscopic set-up and a microchannel according to the electric and magnetic fields applied. And we have calculated numerically dielectrophoresis and magnetophoresis forces, which must be the driving mechanisms to move magnetic nanoparticles in the fluid. It was found that when the electric field is applied the magnetic nanoparticles in the fluid experience an electrical force directed toward the place of maximum electric field strength. And when the external magnetic field is applied, the magnetic nanoparticles form long chains oriented along the direction of the field.