• 제목/요약/키워드: relays

검색결과 558건 처리시간 0.026초

New Coordination Approach to Minimize the Number of Re-adjusted Relays When Adding DGs in Interconnected Power Systems

  • Ibrahim, Doaa Khalil;El Zahab, Essam El Din Abo;Aziz Mostafa, Saadoun Abd El
    • Journal of Electrical Engineering and Technology
    • /
    • 제12권2호
    • /
    • pp.502-512
    • /
    • 2017
  • The presence of DGs in power system networks tends to negatively affect the protective relays coordination. The proposed method introduces an approach to minimize the numbers of relays that acquire new settings on contrary to their original settings (case without DG), to achieve relays coordination in case of adding DG, since relays coordination with minimum number of relays of re-adjusted settings represents economical target, especially in networks containing mixture of electromechanical and adaptive digital relays. The scheme decides the possible minimum number of re-adjusted relays and their locations in an optimum manner to achieve proper relays coordination in case of adding DGs. The proposed approach is divided into two successive phases; the first phase is stopped when the first relays coordination solution is achieved. The second phase increases the possibility to keep higher number of relays at their original settings than that obtained in first phase through achieving multi solutions of relays coordination. The proposed approach is implemented and effectively tested on the well-known IEEE-39 bus test system.

Optimal Relays for Cooperative ARQ Protocol Based on Threshold of Distance

  • 단디쉬엔;공형윤
    • 한국통신학회논문지
    • /
    • 제33권4B호
    • /
    • pp.215-223
    • /
    • 2008
  • Retransmission signals from relays to destination when the destination fails to decode received signal from the source in Automatic Repeat Request (ARQ) protocol make the destination receive signals more reliably. With using omni -direction antenna in the practical system, in communication range of both the source antenna and the destination antenna, there are some relays that can be used to transmit signal to the destination. However, using all relays to transmit signal consume power and bandwidth. In this paper, we propose a new protocol in which the best relays are chosen based on threshold of distance from the source to the relay and the relay to the destination when the relays use decode- and forward (DF) protocol. Simulation results prove the efficiency of the protocol when we compare using only the best relays with using all relays to transmit signal to the destination.

열 모델을 이용한 전동기 보호성능 개선 (Improving Motor Protection Using Thermal Model)

  • 장중구
    • 전기학회논문지
    • /
    • 제64권3호
    • /
    • pp.473-479
    • /
    • 2015
  • Thermal relays are sometimes used instead of long time overcurrent relays for motor protection. But, it is difficult for any relay design engineer to adequately approximate motor heating curves which represent the average of a difficult-to-define thermal zone. Thermal relays frequently may not provide sufficient protection on heavy overloads. Digital multifunction relays are microprocessor-based devices. These relays offer highly reliable and advanced protection of motors. If a situation can be mathematically described, the microprocessor in a digital relay can be programmed to tackle that problem. Today's motor protection is accomplished with digital protective relays. Digital relays offer additional, highly important features to complement protection. The best way to prevent short in motor is to not overheat and degrade the insulation.

On Deploying Relays for Connected Indoor Sensor Networks

  • Zhu, Yanmin;Xue, Cuiyao;Cai, Haibin;Yu, Jiadi;Ni, Lei;Li, Minglu;Li, Bo
    • Journal of Communications and Networks
    • /
    • 제16권3호
    • /
    • pp.335-343
    • /
    • 2014
  • This paper considers the crucial problem of deploying wireless relays for achieving a connected wireless sensor network in indoor environments, an important aspect related to the management of the sensor network. Several algorithms have been proposed for ensuring full sensing coverage and network connectivity. These algorithms are not applicable to indoor environments because of the complexity of indoor environments, in which a radio signal can be dramatically degraded by obstacles such as walls. We first prove theoretically that the indoor relay placement problem is NP-hard. We then predict the radio coverage of a given relay deployment in indoor environments. We consider two practical scenarios; wire-connected relays and radio-connected relays. For the network with wire-connected relays, we propose an efficient greedy algorithm to compute the deployment locations of relays for achieving the required coverage percentage. This algorithm is proved to provide a $H_n$ factor approximation to the theoretical optimum, where $H_n=1+{\frac{1}{2}}+{\cdots}+{\frac{1}{n}}={\ln}(n)+1$, and n is the number of all grid points. In the network with radio-connected relays, relays have to be connected in an ad hoc mode. We then propose an algorithm based on the previous algorithm for ensuring the connectivity of relays. Experimental results demonstrate that the proposed algorithms achieve better performance than baseline algorithms.

Combined Relay Selection and Cooperative Beamforming for Physical Layer Security

  • Kim, Jun-Su;Ikhlef, Aissa;Schober, Robert
    • Journal of Communications and Networks
    • /
    • 제14권4호
    • /
    • pp.364-373
    • /
    • 2012
  • In this paper, we propose combined relay selection and cooperative beamforming schemes for physical layer security. Generally, high operational complexity is required for cooperative beamforming withmultiple relays because of the required information exchange and synchronization among the relays. On the other hand, while it is desirable to reduce the number of relays participating in cooperative beamforming because of the associated complexity problem, doing so may degrade the coding gain of cooperative beamforming. Hence, we propose combined relay selection and cooperative beamforming schemes, where only two of the available relays are selected for beamforming and data transmission. The proposed schemes introduce a selection gain which partially compensates for the decrease in coding gain due to limiting the number of participating relays to two. Both the cases where full and only partial channel state information are available for relay selection and cooperative beamforming are considered. Analytical and simulation results for the proposed schemes show improved secrecy capacities compared to existing physical layer security schemes employing cooperative relays.

배전계통의 고장계산 및 보호계전기 협조에 관한 연구 (A study on Fault Calculation and Coordination of Relays in Distribution System)

  • 김준연;남해곤;김태성
    • 대한전기학회:학술대회논문집
    • /
    • 대한전기학회 1993년도 정기총회 및 추계학술대회 논문집 학회본부
    • /
    • pp.16-18
    • /
    • 1993
  • Recently, the scale of distribution system is being enlarged by increasing power demand. When system fault occurs, fault currents and damage power facilities increase, so system stability decreases. Effective prevention of system from fault extention becomes influential as a subject in distribution system operation. In this study, exact settings of relays are obtained from program for fault calculation and coordination of relays in distribution system. In order to make smooth coordination between relays even when power system conditions vary, operation time and sensitivity of relays are optimized. As a result, reliability of distribution system is increased with rapid and exact operation of relays when fault occurs.

  • PDF

송전계통 보호계전기 보호협조 평가 시스템 (A Software System for Evaluation Setting and Coordination of Protective Relays in Power Transmission System)

  • 최면송;이승재;민병운;조필성
    • 대한전기학회논문지:전력기술부문A
    • /
    • 제51권10호
    • /
    • pp.518-524
    • /
    • 2002
  • A software system that has functions of setting and coordination checking of protective relays in power transmission system has been developed. The developed system utilizes database system to store the setting values of protective relays, power system parameters, checks the relay operation and evaluates coordination of relays in real Power system or test system. The fault data to simulates a fault to evaluate the coordination of relays is generated by PSS/E and EMTP. A universal logic generator module is added to adopt the variation of each relay's trip logic. The proposed system has been verified through many tests in the case study, and proved to be very powerful in inspecting the setting values and coordination of relays.

Adjustable Multiple Relay Selection Based on Steady-State Mean Square Joint Error for Cooperative Communication

  • Liu, Zhiyong;Zhang, Qinyu;Mu, Liwei
    • KSII Transactions on Internet and Information Systems (TIIS)
    • /
    • 제10권9호
    • /
    • pp.4326-4341
    • /
    • 2016
  • In this paper, an adjustable multiple relay selection (MRS) scheme for cooperative communication with amplify-and-forward (AF) relay under frequency selective channels is proposed. In the proposed scheme, the relays are ordered firstly by the steady-state mean square error (MSE), then the relays are sequentially selected out from N relays and the number of cooperating relays is adjusted dynamically according to the steady-state mean square joint error (MSJE). The aim of this work is to dynamically estimate the optimum number No of cooperating relays. Optimum means the minimum number of cooperating relays, No, achieving the minimum level of steady-state MSJE. Numerical results verify the analyses and show that the scheme can adaptively adjust the number of cooperating relays, and outperform conventional relay selection schemes. Hence, the proposed scheme provides better tradeoff between BER performance and spectral efficiency and to save more energy in cooperative wireless networks.

OFDMA 기반 Relay 시스템에서 Relay의 Capability에 따른 VoIP 성능 분석 (Effect of Relay Capability on VoIP Performance in OFDMA based Relay Systems)

  • 안성보;최호영;홍대형;임재찬
    • 한국통신학회논문지
    • /
    • 제34권3B호
    • /
    • pp.304-310
    • /
    • 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.

릴레이 수명 연장 방법에 의한 HID램프용 디밍 자기식 안정기의 구현 (The realization of the Dimmable Magnetic Ballast for HID Lamps by the Life Time Extension Method of the Relays)

  • 정광현;이현진;박종연
    • 전기학회논문지
    • /
    • 제58권3호
    • /
    • pp.516-522
    • /
    • 2009
  • The dimmable magnetic ballast which applies the variable inductor needs a switching process for the dimming process, and it consists of mechanical relays because of costs and reliabilities. However, it is hard to operate with correct timing in mechanical relay, so relays reduce their own life time in inductive applications. Moreover this creates a destructive problem at the switching process. The life time reduction of relays means the life time reduction of the ballast. Thus, in this paper, we described the problem at the witching process in the dimmable magnetic ballast with a variable inductor, which consists of relays and the soft AC switching method in order to solve the problems. As result, we achieved the improvement of the life time and reliability of the ballast.