• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2003년도 High Temperature Superconductivity Vol.XIII
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• pp.65-65
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• 2003

• 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.

• Journal of international Conference on Electrical Machines and Systems
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• 제3권3호
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• pp.331-338
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• 2014

When large penetration of the distributed generators (DGs) such as photovoltaic (PV) systems is growing up in grid system, it is important to quickly prevent islanding caused by power system fault to ensure electrical safety. We propose a novel active method for islanding prevention by harmonic injection synchronized with the exciting current harmonics of the pole transformer to avoid mutual interference between active signals. We confirm the validity of the proposed method by performing the basic tests of islanding by using a current source superimposed the harmonic active signal. Further, we carry out the simulation using PSCAD/EMTDC, and verify the fast islanding detection.

• KIEE International Transactions on Power Engineering
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• 제5A권1호
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• pp.1-8
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• 2005

During magnetic inrush or over-excitation, saturation of the core in a transformer draws a significant exciting current, which can cause malfunction of a current-differential relay. This paper proposes a modified-current-differential relay for transformer protection. The relay calculates the core-loss current from the induced voltage and the core-loss resistance as well as the magnetizing current from the core flux and the magnetization curve. Finally, the relay obtains the modified differential current by subtracting the core-loss and the magnetizing currents from the conventional differential current. A comparative study of the conventional differential relay with harmonic blocking is presented. The proposed relay not only discriminates magnetic inrush and over-excitation from an internal fault, but also improves the relay speed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 추계학술대회 논문집 전력기술부문
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• pp.249-251
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• 2001

The two fuzzy criteria to distinguish the internal fault from the inrush for the power transformer protection have been identified. They are based on the terminal voltage, fundamental and second harmonic component of differential current. A systemetic way to determine the associated fuzzy membership function is also proposed.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2007년도 추계학술대회 논문집
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• pp.275-278
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• 2007

Dissolved gases analysis (DGA) is one of the most useful techniques to detect incipient faults in power transformers. Criteria interpreting DGA result is the most important. Because of difference of operation environment, construction type, oil volume, and etc, the interpretative criteria of DGA at KEPCO must be different with other standard like IEC-60599, Rogers and Doernenburg. In this paper, we collected the DGA data of the normal condition transformers and the incipient fault transformer to suggest the most appropriate criteria. Using these data, this paper suggests appropriate condition classification algorithm. Suggested algorithm can help to detect incipient fault earlier without unnecessary sampling.

• 전기전자학회논문지
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• 제24권1호
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• pp.354-359
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• 2020

전력용 변압기의 결함을 검출하고, 고장을 예방하기 위해 유중가스분석 방법이 정기적으로 수행되고 있다. 유중가스분석방법에 의해 변압기 내부의 과열 또는 방전 현상의 발생은 확인할 수 있지만 결함 부위는 내부점검에 의하여 판별하여야 한다. 하지만, 권선 또는 철심 결함은 내부점검으로 확인할 수 없어 DGA만으로는 조치방안을 수립하기가 불가능하다. 본 논문에서는 변압기 내부점검 보고서를 바탕으로 내부 결함 모드를 분석하여 제시하고, DGA에 의한 판별법을 고려하여 내부 결함을 예측할 수 있도록 하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 추계학술대회 논문집 전력기술부문
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• pp.9-11
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• 2008

A protection current transformer (CT) has been widely used for protection devices. When a fault occurs, a CT should provide the faithful reproduction of the primary fault current. However, a CT may saturates due to the magnitude of fault current, dc component primary time constant and the remanent flux of the iron core, and the secondary current of a CT is distorted. The distorted current can cause mal-operation or the operating time delay of a protection relay. This paper provides a modeling of CT saturation using EMTP-RV. The performance of the proposed CT saturation modeling was investigated under various fault conditions varying the fault distance, fault inception angle, and remanent flux of the iron core. The results indicate that the proposed EMTP-RV modeling can operate correctly, and the reasons for CT saturation are verified by EMTP-RV simulations.

• KIEE International Transactions on Power Engineering
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• 제3A권4호
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• pp.181-190
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• 2003

This paper presents the design of a fuzzy power system stabilizer (FPSS) using an adaptive evolutionary algorithm (AEA). AEA consists of genetic algorithm (GA) for a global search capability and evolution strategy (ES) for a local search in an adaptive manner when the present generation evolves into the next generation. AEA is used to optimize the membership functions and scaling factors of the FPSS. To evaluate the usefulness of the FPSS, we applied it to a single-machine infinite bus system (SIBS) and a power system simulator at the Korea Electrotechnology Research Institute. The FPSS displays better control performance than the conventional power system stabilizer (CPSS) for a three-phase fault in heavy load, which is used when tuning FPSS. To show the robustness of the FPSS, it is applied with disturbances such as change of mechanical torque and three-phase fault in nominal and heavy load, etc. The FPSS also demonstrates better robustness than the CPSS. Experimental results indicate that the FPSS has good system damping under various disturbances such as one-line to ground faults, line parameter changes, transformer tap changes, etc.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 C
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• pp.1056-1058
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• 1998

Voltage dips caused by transmission system faults are usually of a short duration. High speed relaying and breaker operation will typically limit the disturbance to 0.1 seconds. Most motor controllers obtain their control power directly from the bus by means of a control transformer. Under this condition, a voltage dip can cause the contactor to drop out. disconnecting the motor from the line. The rapid re-energizing of the controller is in effect a fast reclosure which may result in motor damage. The time delay re-energizing of controller will result in a greater loss of speed and possibly loss of stability. Other means of controller can be used to prevent the motor from being disconnected from line during the fault. This can be accomplished by DC power controller or mechanically latched controller. This paper demonstrates that DC power controller or mechanically latched type controller to prevent the motor from being disconnected from line during the fault is, the most effective in minimizing speed reduction, transient motor current, transient motor torque and transient shaft torque by EMTP calculation.