• 정보와 통신
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• 제11권4호
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• pp.62-70
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• 1994

본고는 교환기의 기본구조를 변경하지 않고 프레임릴레이를 통하여 ISDN(Intergrated services digital network) 교환기에 물리적으로 적용 가능한 LAN(Local area network) 인터페이스 기술에 대하여 서술하였다. 프레임릴레이의 구현을 위해 기존 X.25 서비스와의 상호접속 방안이 매우 중요한데 이를 위해서는 X.75 및 I.122를 배경으로 하는 상호적인 방안이 고려되어야 한다. 프레임릴레이 서비스에 필요한 특징 및 트로토콜, 브릿지 상호접속 및 ISDN 노드에 사용되어 프레임 수행을 위한 프레임핸들러의 설계방법에 이어, 프레임릴레이를 통한 LAN과 ISDN간 상호접속 메카니즘에 대해 각각 서술하였다. 그리고 프레임릴레이를 통하여 LAN을 위한 고속 프레임릴레이 서비스를 구현한 주요국의 사례를 살펴보았다.

• Journal of Electrical Engineering and Technology
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• 제6권2호
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• pp.167-173
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• 2011

This paper presents a method for the development of the impedance locus to test the dynamic characteristics of protective relays. Specifically, using the proposed method, the impedance locus can comprise three impedance points, and the speed of impedance trajectory can be adjusted by frequency deviation. This paper is divided into two main sections. The first section deals with the configuration of impedance locus with voltage magnitude, total impedance magnitude, and impedance angle. The second section discusses the control of the locus speed with the means of the deviation between two frequencies. The proposed method is applied to two machine equivalent systems with offline simulation (i.e., PSCAD) and real-time simulation (i.e., real-time simulation environment) to demonstrate its effectiveness.

• Journal of Electrical Engineering and Technology
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• 제8권5호
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• pp.1002-1011
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• 2013

This paper proposes the new adaptive protection algorithm for inverse-time overcurrent relays (OCRs) to ensure their proper operating time and protective coordination. The application of the proposed algorithm requires digital protection relays with microcontroller and memory. The operating parameters of digital OCRs are adjusted based on the available data whenever system conditions (system with distributed generation (DG)) vary. Moreover, it can reduce the calculation time required to determine the operating parameters for achieving its purpose. To verify its effectiveness, several case studies are performed in time-domain simulation. The results show that the proposed adaptive protection algorithm can keep the proper operating time and provide the protective coordination time interval with fast response.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 A
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• pp.563-565
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• 2002

The designed frequency compensator is proposed to make the estimation of amplitude of fundamental frequency immune to frequency variation. The designed method which has a simple structure and low calculation burden is proper to apply digital protective relay. The results of experimental demonstrate that the frequency compensator has good performance to the estimation of amplitude of fundamental frequency against frequency variation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 춘계학술대회 논문집 전력기술부문
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• pp.38-41
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• 2001

This paper presents a digital current differential protection algorithm for a transformer in power system. This algorithm uses an FIR filter to improve the performance of the relay. This paper presents a practical method setting the operating slope of the relay and reduce ct mismatch. A series of EMTP simulation results have shown effectiveness of the algorithm under various type of transformers and conditions.

• 전자공학회논문지D
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• 제36D권4호
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• pp.8-17
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• 1999

본 논문에서는 디지틀 무선 전송장치의 공간 다이버시티 기술에 필수적인 IF 대역의 최대진폭 전력 결합기에 관한 이론적인 분석과 성능개선을 위한 방법을 다룬다. 결합기의 성능저하를 유발하는 위상검출기의 전압오차를 줄이는 방안으로 간단하고 특성이 우수한 위상 검출부의 검출전압에 대한 정규화를 제안하였다. 따라서 간단한 회로구성으로 노치(notch) 깊이 30dB 의 심각한 주파수 선택적 페이딩에 대해서도 결합기의 안정된 동작 및 성능개선을 확보할 수 있었다. 제안된 방법을 검증하기 위해 수치해석 및 64-QAM 변조방식의 디지틀 무선 전송장치와 연동한 signature 시험 결과를 제시 및 분석한다.

• 한국음향학회지
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• 제14권6호
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• pp.80-84
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• 1995

이동통신 방식에서 QPSK 신호를 사용하는 경우 신호전송의 실제상황에서 상승적형 주파수 판별기를 사용한 자동 주파수 제어부의 동작특성에 관한 새로운 해석을 하고 그 제어부의 주파수 지터를 계산하는 각종 분산식을 유도하였다. 그 방법은 먼저 개루프시의 판별기 출력성분과 각종 랜덤성분의 자기상관함수에대한 결과를 이용하여 전력 밀도 스펙트럼을 구한 후 폐루프 동작시의 주파수 지터를 계산하는 주파수 분산식을 구하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 추계학술대회 논문집 학회본부 A
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• pp.306-308
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• 1999

Recently, several developments of real-time simulators have been reported. But they are very high cost. And then they are difficult to apply for relay testing in small business. This paper presents the structure and performance of a new pc based, low cost, tester to digital protection relays. Fault transients are generated either by simulating signals using EMTP or by recorded fault signals.

• 대한전기학회논문지:전력기술부문A
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• 제48권7호
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• pp.855-862
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• 1999

A high speed digital distance relaying algorithm based on a least square error method is proposed. To obtain stable phasor values very quickly, first, a lowpass filter which has very short transient period and no overshoot is presented. Secondly, the least square error method having the data window of 3 samples is used by applying a FIR filter which removes the DC-offset component in current relaying signals. Test results show that the proposed distance relaying algorithm detects most of internal faults within a half cycle after faults in a 154[kV] overhead transmission line system.

• 전기학회논문지P
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• 제62권4호
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• pp.198-203
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• 2013

There are conditions that can be unbalanced three phase currents in a large generator by untransposed lines, unbalanced loads, unsymmetrical faults, and open phases. The unbalanced conditions can producing negative sequence components of current that induce two times frequence current in the surface of the rotor, the retaining rings, the slot wedges in the field windings. These rotor currents make the rotor rapidly overheat, so the rotor can cause substantial damage in a very short time. This paper presents the digital negative sequence relay algorithm for unbalanced protection in a generator. The proposed algorithm was tested by using collected current signals on PSCAD/EMTDC considering a hydro turbine based generator control system. It can be seen that the proposed relaying by negative sequence current is useful for detection of unbalanced state of large generator.