• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.2
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• pp.425-431
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• 2011

The harmonic distortion level may be significant in electric propulsion systems, as the main loads usually are variable speed propulsion/thruster drives. Distortion of currents and supply voltage waveforms may lead to: Increased power dissipation(losses) in equipment connected to the network, such as generators, motors, transformers, cables, etc., from the harmonic currents, may cause overheating and deterioration of the insulation, and reduced life time of the equipment. In this paper introduced the canceling method of harmonic currents by a multipulse drive with phase shifting transformer. The simulation results indicated a good speed response to the middle speed range of electric propulsion motor. And also, THD(total harmonic distortion) and torque ripple could be reduced in comparing the 12-pulse drive with 6-pulse drive.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.13 no.6
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• pp.562-567
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• 2020

In this paper, this is a study on the correction of protection relays to monitor temporary power facilities for storage tanks especially transformers to block and protect faults such as insulation breakdown. When an abnormality such as a short circuit or a ground fault occurs in the power system, it is important to detect this quickly cut off the device and equipment in which the fault occurred and separate it from the power system to correct the protection relay so that it does not interfere with power supply. In addition the fault current calculation that accurately applies the fault type and the cause of the fault for protection cooperation will be the most important factor in the correction of the protection relay. For protection coordination a study was conducted on the method of coordination for protection of power facility protection for storage tanks such as over current relay, ground over current relay, under voltage relay, and ground over voltage relay applied to temporary.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.3
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• pp.213-221
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• 2004

In recent years, since more and more diode rectifiers with smoothing dc capacitor are used in electronic equipments, household appliances and ac drives, harmonics generated by these loads have become a major issue. In addition, 3-phase 4-wire system is widely employed in distributing electric energy to several office building and manufacturing plants. This systems show excessive currents in the neutral. These neutral currents are fundamentally third harmonic, and their presence is tied to wiring failure, elevating of neutral potentials, transformer overheating, etc. In response to the concerns, this paper proposes a series active power filter scheme based on direct compensating voltage extraction method and the advantage of this control algorithm is direct extraction of compensation voltage reference without multiplying gain. Therefore, the calculation of the compensation voltage reference will becom much simpler than other control algorithm. To verify the effectiveness of the proposed algorithm, a prototype active power filter is built and some experiments are carried out.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.3 no.4
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• pp.887-893
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• 1999

The characteristics of ozone generator targeted for air or water sterilizing in the vessel utilizing the surface corona discharge between the electrodes on the ceramic substrate was investigated by using the frequency control method. The frequency control was achieved by controlling the degree of resonance between the secondary winding inductance of transformer and the electrode capacitance of ceramic discharge plate, and the range of control was found to be 5 times of discharge current. This frequency control method showed the efficiency of 28 mP ozone generation and the stability within 3.4 % when the input voltage was varied within 40% range. The frequency control method is regarded to be more efficient way of corona discharge control compared to the conventional on/off control or voltage control methods.

• 전기의세계
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• v.59 no.9
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• pp.39-45
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• 2010

최근 배전계통에 연계되고 있는 태양광, 풍력발전 등과 같은 신 에너지전원의 용량은 점차 증가하고 있는 상황이지만, 설치자(신 에너지전원 소유자)의 보호방식은 기존 방식을 고수하고 있는 실정으로 신 에너지전원의 역 조류에 의해 설치자의 보호기기(자동화기기 포함)의 오 부 동작 발생 가능성이 커지고 있다. 따라서 본 논문에서는 신 에너지전원이 배전계통에 연계되어 운전되는 경우에 발생 가능한 보호협조의 문제점을 분석하고 이에 대한 대책 방안을 제시한다. 신 에너지전원의 역 조류에 의한 배전계통의 보호협조에 대한 문제점은 크게 3가지로 분류할 수 있는데, 신 에너지전원의 사고전류공급에 의한 보호기기의 정격차단용량(12.5KA)의 상회 가능성과 신 에너지전원의 연계로 인한 임피던스 병렬화로 사고전류의 감소로 발생할 수 있는 분류효과에 의한 보호기기의 부 동작, 연계용변압기의 결선방식에 의한 보호기기의 오동작으로 나눌 수 있다. 여기서는 이에 대한 문제점을 대칭좌표법을 이용하여 구체적으로 해석하고, 이에 대한 최적 운용방안을 제시한다.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.2013-2014
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• 2008

6.6KV 고전압 위험으로 접지계기용변압기(GPT)와 영상변류기(ZCT)의 2차측에 전압 전류 시험 유입방식으로는 해당 지락보호계전기의 정.부동작이 정확한지 검증이 되지 않아 안전사고 발생의 우려성이 존재하고 있었으며, 이의 해결을 위하여 6.6KV 고압측에 인공지락시험을 통하여 국내외 일부 계전기의 동작 전압 전류 극성이 사양과 상이한 것을 발견하여 실계통에 합당하도록 시정함과 동시에 감전시 인체 저항을 감안한 지락보호계전기(OVGR, SGR) 정정값을 도출하여 인명을 보호하게 하기 위한 지락보호계전 시스템에 대한 연구이다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.8
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• pp.499-504
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• 2016

In this paper, we analyzed the operational characteristics of the fault current limiting according to the amplitude of the fault current for the transformer type superconducting fault current limiter (SFCL). If the fault current happens, the superconducting element connected to the secondary coil is occurred quench and the fault current is limited. When the larger fault current occurs, the superconducting element connected to the third coil is occurred additional quench and the peak fault current is limited. We found that the fault current can be more effectively controlled through the analysis of the fault current limiting and the short-circuit tests.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.8
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• pp.1479-1484
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• 2009

The introduction of the large transformer due to the large power demand has increased the fault current in power distribution system. The increased fault current can exceed the cut-off ratings of the circuit breaker. As the methods to solve this problem, the superconducting fault current limiter(SFCL) has been notified. However, the limited fault current by SFCL affects the operational characteristics of the protective device such as overcurrent relay. Therefore, the selection of the proper impedance for the SFCL is required to keep overcurrent relay's protective coordination with the SFCL when a large transformer is introduced into the distribution system. In this paper, the SFCL's impedance for protective coordination was investigates in that a large transformer is introduced.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.9
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• pp.500-506
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• 2004

This paper proposes a modified current differential relay for transformer protection unaffected by the remanent flux. The relay uses the same restraining current as a conventional relay, but the differential current is modified to compensate for the effects of the exciting current. To cope with the remanent flux, before saturation, the relay calculates the core-loss current and uses it to modify the measured differential current. When the core then enters saturation, the initial value of the flux is obtained by inserting the modified differential current at the start of saturation into the magnetization cure. Thereafter, the actual core flux is then derived and used in conjunction with the magnetization curve to calculate the magnetizing current. A modified differential current is then derived that compensates for the core-loss and magnetizing currents. The performance of the proposed differential relay was compared against a conventional differential relay. Results indicate that the modified relay remained stable during severe magnetic inrush and over-excitation because the exciting current was successfully compensated. This paper concludes by implementing the relay on a hardware platform based on a digital signal processor. The relay discriminates magnetic inrush and over-excitation from an internal fault and is not affected by the level of remanent flux.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.12
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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.