• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.766-767
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• 2007

현재 국내 원자력 발전소내의 노후화된 GCB 차단기를 VCB로 교체할 경우, 관련한 기술적 규정들이 확립되지 않아, 이에 대한 기술적 평가가 요구되었다. 본 연구에서는 원자력 발전소 주요 전동기의 기동 및 차단시에 발생하는 개폐서지를 측정하여 발생된 서지의 크기를 분석하고 EMTP 시뮬레이션 방법을 통하여 교체 시 기술 기준을 제안하고 적정성을 검증하였다.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.77-78
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• 2007

국제규격에 따라 VCB(vacuum circuit breaker), ACB(air circuit breaker), 등과 같은 전력기기들의 기계적 동작 시험 시, 시험전후의 개폐시간, 개폐속도, 동작코일전류크기, 등과 같은 특성을 측정하고 이들의 변화정도를 평가하여 시험결과를 판단한다. 그러나 시험 중에는 이러한 동작특성들을 측정하지 않기 때문에, 시험 중에 실패하는 경우, 원인 규명에 많은 어려움이 따른다. 이러한 문제를 해결하기 위해, LS산전 PT&T(Power Testing & Technology Institutes)는 시험전후뿐만 아니라 전체시험횟수 동안 동작특성을 측정하고, 이들의 변화추이를 분석할 수 있는 시스템을 구축하고, 관련 소프트웨어를 개발하였다. 본 논문에서는 개발 내용과 결과를 소개하고자 한다.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.1001-1003
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• 1993

Steep-fronted surges associated with motor witching cause relatively large turn-to-turn winding stress. In order to calculate the surge level at the motor terminals, equivalent circuits consist of three parts with power sources, load cable and motor constants. This paper presents switching surges phenomena occurred in a high voltgae induction motor witching by EMTP.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.911-912
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• 2007

영구자석형 조작기(PMA)의 단점을 보완한 고전압 차단기용 전자석 조작기인 EMFA는 긴 스트로크를 가지는 차단기에도 사용이 가능하며, 특히 진공 차단기(VCB)용 조작기를 비롯하여, 가스 차단기(GCB)에 적용한 모델도 이미 개발되었다. 다양한 모델에 대한 설계 및 연구가 추가적으로 진행되고 있으나, 아직 설계 방법이 정형화되어 있지 않아 모델에 따라 그 형상이 달라지는 경우가 많다. 이러한 점을 개선하기 위해, 본 논문에서 EMFA의 설계 변수를 변화시켜 가며 나타나는 특성을 홀딩력과 자속밀도를 통해 분석하였다. 나아가 이를 바탕으로 설계 방법의 정형화에 대한 실마리를 제공하고자 한다. 해석에는 2차원 유한요소법을 이용하였고, 설계 변수는 조작기의 초기상태를 기준으로 설정하였다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.9
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• pp.52-59
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• 2014

The aims of this paper are to characterize the transient overvoltages(TOVs) and to evaluate the risk occurring at 22.9kV consumer's substation. The measurements of lightning- and switching-caused TOVs were made during Mar. 2013 and Feb. 2014. As a consequence, 47 events of TOVs were recorded and 4 of them were higher than the input voltage envelope(IVE) of the information technology industry council(ITI) curve. The measured TOVs are characterized by longer front times and longer durations compared to the $1.2/50{\mu}s$ standard impulse voltage waveform, and some of them represent bipolar waves with lower oscillation frequencies. It suggests that the test of non-standard impulse voltage waveforms is needed for effective risk assessments of power apparatus. Lightning- and switching-caused TOVs exceeding IVE of ITI curve are induced at the secondary of 22.9kV potential transformer(PT). We may, therefore, conclude that the surge protection devices should be applied at the secondary of PT and the surge absorbers should be installed at the primary of VCB or PT. The results presented in this paper could be useful to design the reasonable insulation coordination for 22.9kV consumer's substation.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.7
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• pp.439-451
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• 2020

This study focused on researching the factors affecting retail banking efficiency of Vietcombank branches in the Mekong-Delta region. By collecting data from financial statements from 15 branches of VCB in the Mekong-Delta Region between 2015 and 2018, the paper applies DEA estimation to measure the effectiveness of retail banking activities and uses the Tobit regression model to identify factors affecting retail banking efficiency. The results demonstrate that the retail banking efficiency of branches averaged 52.5% during the period. The rating result shows the branches in An Giang, Can Tho, Dong Thap, Kien Giang, Long An, Phu Quoc and Tra Noc rank at the top technical efficiency. In group of medium efficiency, there are branches in Soc Trang, Tien Giang and Vinh Long. In the category of the poor efficiency are the branches in Bac Lieu, Ben Tre, Ca Mau, Chau Doc and Tra Vinh. The results also show that bank scale-related factors, capital adequacy, credit quality, time specific and region impact significantly the retail banking efficiency. The research not, only contributes to enriching the empirical research method but also is significant for the management activities in business developing strategies, improving the operational efficiency of Vietcombank in the region.

• Proceedings of the KIEE Conference
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• 2000.11c
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• pp.543-546
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• 2000

본 논문에서는, 모의 진공차단기 내에서의 구리 증기입자의 공간적 및 시간적 밀도분포를 레이저유기형광법 (LIF)에 의해 계측하였다. 레이저 트리거 방전에 의해 생성된 어블레이션(ablation) 플라즈마에서의 구리입자를 324.75nm의 Nd:YAG 레이저를 이용하여 여기시키고, 이때 여기준위에서 기저준위로 천이할 때의 형광신호(510.55nm)를 분광기 및 광전자증배관을 이용하여 계측하였다. 음극점으로부터 넓은 각도를 가지고 전자가 튀어나오며, 넓은 범위에 걸쳐 전자나 이온이 존재하는 것을 알 수 있었다. 또한 음극으로부터 8mm ( x=0, y=8mm 진 위치에서 가장 강한 신호와, 2mm ( x=0, y=2mm 가장 약한 신호를 얻을 수 있었다.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1603-1605
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• 1994

Recently, Gas Circuit Breakers are rapidly replacing Vacuum Circuit Breakers in the medium voltage switchgear. This is due to the improved performance of - GCB in interrupting capability, price, weight, size etc., while the countermeasure to suppress the switching surges of VCB has not been satisfactory. Intensive research works on the GCB have been conducted in the world widely since 1980. Nowadays it is well known that the thermal expansion type GCB can provide- better performance than puffer type in the distribution power system. KERI has conducted researches in the GCB rated at 25.8kV 25kA with Jinkwang Co. using the thermal expantion principle since 1993. In this paper, the calculated results of electric and magnetic fields for the model GCB are presented and analyzed. The effect of permanent magnet used to improve the interruption capabilty at the low current level is also investigated. The design parameters for the interrupter inspected through the short-circuit tests conducted at high power laboratory of KERI.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.10
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• pp.630-635
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• 2015

A vacuum Interrupter (VI), a core part that composes the breaking part of medium-voltage vacuum circuit breaker (VCB), has the excellent insulation performance and arc-extinguishing capability. $SF_6$ gas had been used for the external insulation of VIs since the dielectric strength of $SF_6$ gas is superior to that of other insulation gases. However, because of environmental problems related with global warming, a solid-insulated technology was recently researched. The functionally graded material (FGM), as changing spatially the distribution of the relative permittivity inside an insulator, can reduce the electric field stress at the specific region. Especially, the external insulation performance of the VI with the molded FGM insulator is greatly improved as compared with that of the existing VI or the VI with a new external shield. In this paper, the effectiveness of this FGM insulator is verified by the numerical simulation.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.9
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• pp.111-119
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• 2008

As the penetration of distributed generation systems is recently high, there have been metering errors, trips of protective devices in KEPCO distribution systems including an occurrence of false fault-indicator in distribution automation system. The cause of malfunctions was the reverse-power-flow phenomenon due to transformer wiring types. By the effect of the reverse-power-flow, each of phase's fundamental currents was added by about 3 times on the neutral line. A new method based on the analysis of the reverse-power-flow is proposed in this paper. Fault currents on each section were analyzed by the proposed method, and the effect of types of transformer wiring was examined experimentally. In order to reduce the malfunctions due to the reverse-power-flow, controlling the zero-sequence impedance of transformer was designed and verified by using PSCAD/EMTDC software.