• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.760-761
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• 2011

Ground differential relay is used to provide fast, sensitive, and selective protection for the wye connected and grounded electrical power equipment such as generators, power transformers, and grounding transformers. The ground differential protection only protects the ground faults within the protection zone, so that it can't protect the line-to-line fault. This paper proposes the algorithm to provide the protection for the line-to-line fault through the ground differential protection. The proposed algorithm detects the line-to-line fault of transformer using the comparison between the positive and the negative current, when the ground differential relay dose not operate. The performance of the algorithm is verified using a PSCAD/EMTDC simulator under various case studies.

• Journal of information and communication convergence engineering
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• 제9권5호
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• pp.515-522
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• 2011

In this paper, we investigate cooperative diversity in a spectrum sharing environment where secondary users utilize primary users' spectrum only if the interference power received at the primary users is maintained below a predetermined level. The outage probability of a selective decode-and-forward (DF) based cooperative diversity scheme in the secondary network is derived to analyze the effects of spectrum sharing on cooperative diversity. Our analytical and simulation results show that the outage probability is saturated at a certain level of transmit power of secondary users due to interference regulation, and, hence, cooperative diversity gains are lost. Through asymptotic analysis, we also identify the critical value of transmit SNR beyond which the outage probability is saturated.

• 전기학회논문지
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• 제60권2호
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• pp.285-292
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• 2011

DC traction power system is operated ungrounded so that minimize the stray current. Because the stray current is still present, a rail potential is increased. The ground faults in the DC railway systems are usually detected by a potential relay(64P). Moreover, if the rail potential goes high in the ordinary operating state because of the traction load, the potential relay would be maloperated. A presented protective relaying algorithm that can identify exactly the faulted region and can distinguish a ground fault from the potential rising of the rail is presented in this paper. This paper presents simulation technique that is very similar to the real operation situation using PSCAD/EMTDC.

• 한국통신학회논문지
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• 제35권5C호
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• pp.487-494
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• 2010

본 논문은 OFDM (orthogonal frequency division multiplexing) 기반 이중-홉 다중 릴레이 시스템에서 상호정보를 최대로 하는 릴레이 선택 기법을 고려한다. 상기 시스템에서 DF (decode-and-forward) 릴레이를 적용할 때와 AF (amplify-and-forward) 릴레이를 적용할 때에 대해 각각 시스템 아웃티지 확률에 대한 하한과 제공 가능한 최대 다양성 차수를 유도하고 모의실험으로 아웃티지 용량을 제공한다. 성능 평가 결과 DF와 AF 방식 모두 아웃티지 확률 하한과 동일한 다양성 차수를 제공하지만, DF가 AF보다 아웃티지 확률 하한에 더 가깝고 더 큰 아웃티지 용량을 제공함을 볼 수 있다. 또한, 플랫 페이딩과 달리 주파수 선택성 채널에서는 다중 경로 수가 증가하거나 릴레이 선택의 후보 릴레이 수가 증가할수록 AF에 대한 DF 방식의 성능 이득이 더욱 커짐을 볼 수 있다. 따라서, OFDM 기반 다중 릴레이 시스템에서는 성능 면에서 AF 릴레이보다는 DF 릴레이가 유리함을 알 수 있다.