• 전기학회논문지
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• 제56권4호
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• pp.677-682
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• 2007

In the distribution system, Change of system happens frequently. However, most of the relays are operated manually by a person or not changed when system changed. So, when fault happened, a case that relaydoes not act rapidly happens. Also, in current power system, digital relays are used because of digitization of relay. Digital relay has very many advantages than existing analog relay. One of these advantages is that communication is available and easily can make characteristic curve. If specific values are sent to a relay by communication, A relay can make suitable characteristic curve according to the value. In this paper, by using voltages and currents measured by relay, state of CB(Circuit Breaker) and these relays, SCADA(Supervisory Control And Data Acquisition) system that control and correct characteristic curve of overcurrent relay at system change by using HMI(Human Machine Interface) is proposed.

• Journal of Communications and Networks
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• 제15권1호
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• pp.45-53
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• 2013

Multi-hop cellular networks (MCNs), which reduce the transmit power, mitigate the inter-cell interference, and improve the system performance, have been widely studied nowadays. The relay selection scheme is a key technique that achieves these advantages, and inappropriate relay selection causes frequent relay switchings, which deteriorates the overall performance. In this study, we analyze the conditions for relay switching in MCNs and obtain the expressions for the relay switching rate and relay activation time. Two mobile-based relay selection schemes are proposed on the basis of this analysis. These schemes select the relay node with the longest relay activation time and minimal relay switching rate through mobility prediction of the mobile node requiring relay and available relay nodes. We compare the system performances via simulation and analyze the impact of various parameters on the system performance. The results show that the two proposed schemes can obtain a lower relay switching rate and longer relay activation time when there is no reduction in the system throughput as compared with the existing schemes.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제54권9호
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• pp.437-443
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• 2005

This paper deals with an experimental study for Klippon reiay in Cheju-Heanam HVDC system Klippon relay was troubled many times for years, and Klippon relay's fault caused the HVDC system trip. So for several years, these reasons of Klippon relay fault were investigated. The malfunction of Klippon relay in Cheju-Haenam HVDC system has been caused by the incoming of random surge(current source and voltage source). This paper has stu야ed the theoretic리 analysis and experimental study of Klippon relay, and the solutions against the problems were suggested according to their causes. Among the problems, grounding problem was removed by one-point earth connection and by modification of grounding circuit. The effects of inrush current was removed by inserting the blocking diodes by series in Klippon relay circuits. Finally, The over-voltage induced on Klippon relay, by a relay excitation coil, was removed by inserting a free-wheeling diode in Parallel with the excitation coil.

• 한국통신학회논문지
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• 제34권3B호
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• pp.304-310
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• 2009

본 논문에서는 OFDMA 기반 relay 시스템에서 사용자에게 VoIP 서비스를 제공할 경우, relay station (RS)의 capability에 따른 시스템의 성능 차이를 분석하였다. Relay 시스템은, relay의 스케줄링 수행 여부에 따라 mid-capability (MC)와 high-capability (HC) relay를 적용한 시스템으로 구분할 수 있다. HC relay를 적용한 시스템의 경우, base station (BS) 뿐만 아니라 RS도 직접 스케줄링을 수행한다. 반면에 MC relay를 적용한 시스템의 경우, 각 RS로부터 mobile station (MS) 들의 수신 SINR, 발생 traffic양 등의 정보를 BS에서 수집하여, BS가 단독으로 스케줄링을 수행한다. 이 경우 MS의 정보 수집 및 RS로의 스케줄링 정보 전달을 위해 control 오버헤드는 커지지만, BS가 모든 MS에 대한 정보를 알고 있으므로 효율적인 자원 할당 및 스케줄링이 가능하다. 따라서 RS의 capability에 따라 전체 시스템의 성능이 달라질 수 있고, 이에 대한 분석이 필요하다. 본 논문에서는 모의 실험을 통해 VoIP traffic 환경에서 RS의 capability에 따른 평균 packet delay, good packet ratio, cell goodput 등을 도출하였다. 선정한 VoIP 성능 지표에 의하면, MC relay를 적용한 시스템이 HC relay를 적용한 시스템에 비해 성능이 우수함을 확인하였다.

• ETRI Journal
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• 제32권2호
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• pp.230-240
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• 2010

The IEEE802.16j standard uses non-transparent relay stations to extend coverage. There are two types of non-transparent relay modes, that is, the time-division transmit and receive (TTR) relay mode which can operate with one of two types of frame structures, a single-frame and multiframe structure, and the simultaneous transmit and receive (STR) relay mode. In this paper, we analyze the relay performance of TTR and STR relay modes in IEEE 802.16j MMR system. We also propose a fair resource allocation scheme for the downlink relay frame. Numerical results show that relay performance of the TTR with a single-frame or a multiframe structure and that of the STR relay modes are almost the same in a two-hop system. However, in a three-hop system, the TTR mode with a single-frame structure outperforms other relay modes.

• 한국산업정보학회논문지
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• 제14권4호
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• pp.8-15
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• 2009

초고속 접속을 위한 차세대 광대역 무선 이동 통신 기술의 하나로서, 중계기를 활용한 다중 입출력 기술이 유력하게 연구되고 있다. 본 논문에서는 채널 선택적 중계기 기반의 다중 입출력 전송 시스템을 제안한다. 중계기와 단말기 사이의 채널 상태에 따라 선택적으로 부채널을 사용함으로써 수신 성능을 크게 향상시킬 수 있다. 실험 결과를 통해, 제안된 중계기 기반 시스템의 성능이 기존의 시스템 성능보다 우수한 특성을 나타냄을 확인하였다.

• International Journal of Internet, Broadcasting and Communication
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• 제15권3호
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• pp.14-23
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• 2023

The cooperative communication systems using MIMO(multiple input multiple-output) relay are known as one of the most promising techniques to improve the performance and coverage of wireless communication systems. In this paper, we propose the cooperative communication systems using the relay with multi-antennas and DSTC(distributed space time coding) for decode-and-forward protocol. As using DSTC for DF(decode-and-forward), we can minimize the risk of error propagation at the wireless system using relay system. Also, the MIMO channel cab be formed by multi-antenna and DSTC at the MS(mobile station)-RS(relay station) and at the RS-BS(base station).Therefore, obtaining truly constructive the MIMO diversity and cooperative diversity gain from the proposed approach, the performance of system can be more improved than one of conventional system (relay with single antenna, no relay). The improvement in bit error rate is investigated through numerical analysis of the cooperative communication system with the proposed approach.

• 산업경영시스템학회지
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• 제13권22호
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• pp.59-64
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• 1990

This paper is aimed to study the standby redundant system with the relay of parallel structure, by making use of the character of standby system, which reliability is higher than parallel system's if the relay has higher reliability than a certain level. By assigning the low-priced relay to the subsystem, this method increases the relay reliability, optimizes the standby redundant system reliability without violating the restrictions, and consequently reduces the cost.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 A
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• pp.510-512
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• 2005

This paper introduces the development of automatic system for estimation of digital relay performance. We have developed an automatic estimation system "HRV2004(Himap Relay function Verifier 2004)" for digital relay in 2004 and it has been verified in the field for one years. This paper describes the development details and field experience of HRV2004. HRV2004 can perform a series of jobs required for the relay testing in one environment and could handle most of all models of protective relay currently produced by Hyundai Heavy Industries. The functionality of this program consists of GUI of relay setting for beginner, fault record analysis and relay performance estimation. The core of this system is an automatic reporting of estimation test. If user is only click a button for relay estimation and one will received testing report to deliver customer. Additional benefit is fast response than the manual estimation. For example, the manual estimation takes spending 6 hours but this system is about 15 minutes.

• 대한전기학회논문지:전력기술부문A
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• 제50권9호
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• pp.411-416
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• 2001

Distance relay is the most widely used in transmission line protection because it is applicable not only as main protection but also as back-up protection. However, the protection range of the distance relay is always fixed in the unchangeable operating range while the power system varies, and therefore the distance relay is the device that is the highly influenced by the power system changes. In this regard, this paper describes an approach to minimize the mal-operation of the distance relay due to the power system changes through changing protection range of the distance relay into optimal condition in response to the load variation and power system condition. Also mal-function of the distance repay in case of high resistance ground faults could be minimized through modeling the protection range into quadratic function.