• 대한전기학회논문지:전력기술부문A
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• 제50권4호
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• pp.157-165
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• 2001

The two criteria to identify the disturbances of the power transformer has been reported in this paper. They have been derived through EMTP simulations of internal faults, inrush and overexcitation for the model of 154/22.9[kV], 40[MVA], Y-Y three-phase power transformer. We propose the crisp algorithm which uses two criteria. A series of test results clearly indicate that the method can identify not only an internal fault but also the other transients. The average of relay operation times is about 7.2[ms]. The proposed algorithm immunes to the transient state.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 추계학술대회 논문집 전기설비전문위원
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• pp.83-88
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• 2004

As the electric system is getting larger to meet the increasing demand for electric power, the rating of power apparatus is becoming inevitably higher in its working voltage and larger in its capacity. According to KEPCO reports, power transformers in the KEPCO system have undergone troubles such as winding short insulation breakdowns every year since 1981. the cause of this troubles were high one line grounding fault currents in KEPCO systems that had direct grounding systems. KEPCO has installed the NGR(neutral grounding reactor) to lower this fault current and reduced winding short insulation breakdowns in power transformers. But when a circuit breaker opened a no load bus, some trips of circuit breakers for protecting transformer have occurred by mal-operation of 59GT(overvoltage ground relay) that detect disconnection of NGR. Therefore, in this paper, we analyzed the cause and examined the effect of time delav circuit to prevent wrong operation of 59GT.

• 대한전기학회논문지:전력기술부문A
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• 제55권6호
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• pp.221-226
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• 2006

The current flowing though a power line is measured by a current transformer (CT). Since a CT is a kind of transformer, saturation of magnetic flux in the core may occur when a large primary current flows. This saturation makes the secondary current of a CT distorted and causes problems in the protection point of view. Because of the current distortion, a protection relay cannot collect the correct information showing how the primary power system changed. Consequently, the current distortion may cause the mal-operation or operation time delay of protective relay. In this paper, an algorithm based on AR model and LSQ is proposed to compensate the saturated CT secondary currents. Various test results indicate that the proposed algorithm can accurately compensate a severely distorted secondary current and is not affected by remanence.

• 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.

• 한국초전도ㆍ저온공학회논문지
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• 제7권1호
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• pp.37-41
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• 2005

This paper describes the construction scheme of new distribution system using HTS(High Temperature Superconducting) power equipments such as cable, transformer and FCL(fault current limiter). At present, one of the most serious problems in distribution power system, especially for metropolitan complex city, is to obtain the ROW for cable line routes, space for downtown substations and satisfy the environmental protection caused by NIMBY phenomena. Unfortunately, it is expected that this situation will get more and more worse. As the HTS technology to apply in power system Is developed, HTS cable utilizing mass-capacity characteristic can be a useful countermeasure to overcome this problem. This paper describes the application methodology of 22.9kV HTS cable with low-voltage, mass-capacity characteristics replacing the 154kV conventional cable. By applying 22.9kV HTS cable, the HTS transformer with higher capacity for the reduction of space and transformer numbers of downtown substation is necessary. Also, if the leakage Impedance of HTS transformer is same as or lower than that of conventional transformer, the fault current of 22.9kV bus will increase because the HTS transformer capacity is larger than that of the conventional transformer. This means the parallel application of HTS-FCL to reduce the fault current in addition to the HTS cable and transformer can be necessary. With the basic construction scheme of new distribution system, this paper describes the future study points to realize this new distribution system using HTS equipments.

• 조명전기설비학회논문지
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• 제17권1호
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• pp.17-24
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• 2003

본 논문에서는 네온 변압기의 효율을 높이기 위하여 주 자속과 누설 자속의 흐름을 분석하고, 이에 따른 압연 방향과 주 자속과의 방향을 최대한 일치 시켜서 자속에 의한 손실을 최소화 하고 역율을 향상시킨 고효율의 네온관용 변압기를 제시 하였다. 그리고 정격 부하시, 단락시 및 무부하시의 각각의 자속 분포를 해석하고 이를 응용하여 부하측 이상 발생시 즉시 전원이 차단될 수 있는 전자식 차단 장치를 개발부착 하였다. 즉 네온관의 파손이나 누전으로 인한 화재나 인체 감전의 위험을 사전에 방지 할 수 있는 전자식 보호 기능을 내장한 자체 진단형의 무방향성 코어의 압연 방향성을 고려한 고효율의 네온관용 변압기를 구현하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 학술대회 논문집 전문대학교육위원
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• pp.122-127
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• 2005

This paper proposes a prototype IED hardware design and it's real-time experimental results. To evaluate performance of the IED, the study is well constructed power system model including power transformer utilizing the EMTP software and the testing is made through simulation of various cases. The relaying that is well constructed using DSP chip and RISC CPU etc. has been developed and the prototype IED has been verified through on-line testing by LabVIEW simulator. The results show that an advanced relaying based prototype IED never mis-operated.

• KIEE International Transactions on Power Engineering
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• 제11A권4호
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• pp.9-14
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• 2001

This paper reports a set of digital time-domain simulation studies conducted on 154 kV wound Potential Transformer(PT) int he 154 kV Gas Insulated Substation(GIS). The Electro-Magnetic Transient Program(EMTP) is used to develop the PT model and conduct the transient studies. The accuracy of the PT model is verified through comparison of the EMTP simulation results with those obtained from the field test results. The investigations shows that the developed model can accurately predict PT transient resonance, especially, the phenomenon of ferroresonance. The model is developed not only to determine impact of transients on PT response but also to design ferroresonance suppressor devices of PT. And it can also be used to predict PT transient response on power system monitoring and protection scheme.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 A
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• pp.298-299
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• 2006

This paper analyzes operation sensitivity of a relay, a blind spot of differential protection relaying, and how to protect the blind spot in protective relying of $3{\Phi}$ Y-Delta transformer consisting of three $1{\Phi}$ transformers which Korean pumped storage power plants have been using. Each different protective relayings must be adopted because there are differences between $3{\Phi}$ trans-former and $3{\Phi}$ transformer consisting of three $1{\Phi}$ trans formers. Also, in the system using high resistance grounding for fault current restriction of delta side, protection for delta side faults have to be considered properly.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 B
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• pp.695-696
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• 2006

The inrush current of transformer cause saturation effects of recovery voltage for short-circuit power testing. the inrush current depends on the residual flux of the transformer core. when inrush current occurs, it is contains a d.c. component and the high harmonic content of the current are of importance to relay protection of testing circuit. this paper describes of decrease method of inrush current for high power short-circuit testing transformer.