• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.56 no.4
• /
• pp.677-682
• /
• 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
• /
• v.15 no.1
• /
• pp.45-53
• /
• 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.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.54 no.9
• /
• pp.437-443
• /
• 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.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.3B
• /
• pp.304-310
• /
• 2009

In this paper, we evaluate the performance of VoIP in OFDMA-based relay systems with various capabilities of relays. We classify relays according to capability as "mid-capability (MC)" and "high-capability (HC)" relay. In system with HC relays, not only base station (BS) but also relay station (RS) performs scheduling at its ova whereas only BS performs scheduling in system with MC relays using the information reported by MS (i.e. the received signal-to-interference-plus-noise ratio (SINR) of mobile station (HS), the amount of MS traffic, etc). In system with MC relays, the controling overhead of BS is larger than that of system with HC relays. However, since BS has all MS information, efficient resource allocation and scheduling is possible. We derived the "average packet delay," "good packet ratio," and "cell goodput" in a VoIP environment. The simulation results demonstrate that the system with MC relays has better VoIP performance over that with HC relays.

• ETRI Journal
• /
• v.32 no.2
• /
• pp.230-240
• /
• 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.

• Journal of Korea Society of Industrial Information Systems
• /
• v.14 no.4
• /
• pp.8-15
• /
• 2009

Relay-assisted multi-input multi-output (MIMO) technique has become a promising candidate for next generation broadband wireless communications for high speed access. In this paper, we propose channel selective relay-based MIMO transmission system. The performance of relay-based system can be improved by using the subcarriers selectively based on the channel condition between relay and mobile station. Simulation results show that the proposed relay-based system considerably outperforms the conventional relay-based system.

• International Journal of Internet, Broadcasting and Communication
• /
• v.15 no.3
• /
• pp.14-23
• /
• 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.

• Journal of Korean Society of Industrial and Systems Engineering
• /
• v.13 no.22
• /
• pp.59-64
• /
• 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.

• Proceedings of the KIEE Conference
• /
• 2005.07a
• /
• pp.510-512
• /
• 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.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.50 no.9
• /
• pp.411-416
• /
• 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.