• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.40 no.12
• /
• pp.2317-2323
• /
• 2015

In this paper, we analyze the performance of dual-hop amplify-and-forward (AF) relaying in cooperative networks with partial relay selection. An AF relay gain considered in this paper includes channel-noise-assisted relay gain. Leveraging a received signal-to-noise ratio (SNR) model, we derive exact closed-form expressions for the probability density function (pdf) and cumulative distribution function (cdf) of the end-to-end SNR. Moreover, an exact closed-form expression of the ergodic capacity for dual-hop AF relaying with channel-noise-assisted relay gain and partial relay selection is investigated. The analytical results shown in this paper are confirmed by Monte-Carlo simulations.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.62 no.1
• /
• pp.12-17
• /
• 2013

Fault currents are expressed as a combination of harmonic components and exponentially decaying DC offset components, during the occurrence of fault in power system. The DC offset components are included, when the voltage phase angle of fault inception is closer to $0^{\circ}$ or $180^{\circ}$. The digital protection relay should be detected quickly and accurately during the faults, despite of the distortions of relaying signal by these components. It is very important to implement the robust protection algorithm, that is not affected by DC offset and harmonic components, because most relaying algorithms extract the fundamental frequency component from distorted relaying signal. So, In order to high performance in relaying, advanced DC offset removal filter is required. In this paper, a new DC offset removal filter, which is no need to preset a time constant of power system and accurately estimate the DC offset components with one cycle of data, is proposed, and compared with the other filter. In order to verify performance of the filter, we used collecting the current signals after synchronous machine modeling by ATPDraw5.7p4 software. The results of simulation, the proposed DC offset removal filter do not need any prior information, the phase delay and gain error were not occurred.

• Proceedings of the KIEE Conference
• /
• 2000.07a
• /
• pp.194-196
• /
• 2000

This paper presents a new digital relaying algorithm for protection of a two winding power transformer. The proposed algorithm calculates mutual flux linkages of primary and secondary windings from the currents and voltages of primary and secondary windings. The mutual flux linkage ratio of primary and secondary windings is equal to the turn ratio in case of the steady state and magnetic inrush. On the other hand, the ratio is different from the turn ratio in case of internal winding faults. The algorithm does not require B-H curve. The results of various tests are satisfactory.

• Journal of Information Processing Systems
• /
• v.14 no.5
• /
• pp.1272-1285
• /
• 2018

The paper presents a novel embedded multifunctional media sever (EMMS) for mobile devices to receive various media programs. Being different from other contemporary system research, the paper mainly studies how to design a reception solution for terrestrial digital television (DTV) on mobile devices and how to enable mobile devices can receive DTV program, enjoy video-on-demand (VOD), achieve video surveillance and relay Internet video program via local Wi-Fi simultaneously. In the system design, we integrate broadcasting-terrestrial DTV tuner, streaming media re-transmission system, VOD disk, video camera and access interface to the Internet into EMMS, which can either receive terrestrial DTV radio signals and demodulate out digital transport stream (TS), or can read streaming media bit-stream from VOD disk, surveillance camera or access interface to the Internet. The experimental results show the proposed system is stable and quality-efficient. Comparing with the other systems, the proposed system has the least packet loss rate and response time.

• Proceedings of the KIEE Conference
• /
• 1996.07b
• /
• pp.664-667
• /
• 1996

The role of protective relaying system is important in the power system stability and reliability. Conventional relaying schemes have had many problems that adaptiveness for delicate variance of objective power systems is poor, and so on. In these days, in order to overcome the weaknesses, the studies to application of artificial intelligent scheme are required. In this paper, as the preceding research for development of intelligent protective relays, we tried to select the most suitable digital filter using comparison of frequency response and performance of wanted frequency component extraction etc.

• 전기의세계
• /
• v.35 no.2
• /
• pp.95-99
• /
• 1986

전력계통의 보호계전기는 1901년 electromechanical type의 과전류 계전기가 사용되기 시작된 이후 전력계통의 대형화에 따른 계전기의 고속화 및 고성능화의 필요성을 충족시키기 위하여 꾸준히 발전되어 왔다. 성능면에서 우수한 트랜지스터형 계전기의 활용은 물론, 1969년에는 소형 컴퓨터를 이용한 전력계통의 보호계전기법이 발표되었고 1974년부터는 마이크로 프로세서의 등장으로 종래의 Analog계전기의 단점을 보강하고 계전기의 고성능화, 고신뢰도는 물론 장치의 축소화와 경제성 면에서도 향상된 digital계전기의 발달이 더욱 활발하게 되었다. 여기서는 이와 같은 추세로 발달되고 있는 digital 계전기의 구조 및 특성을 간략히 기술하고 전력계통 보호를 위한 앨고리즘의 연구동향에 대하여 살펴보기로 한다.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.59 no.8
• /
• pp.1360-1365
• /
• 2010

In this paper, we propose a distance relaying algorithm using a Discrete Fourier Transform (DFT)-based modified phasor estimation method to eliminate the adverse influence of exponentially decaying DC offsets. Most distance relays are based on estimating phasors of the voltage and current signals. A DFT is generally used to calculate the phasor of the fundamental frequency component in digital protective relays. However, the output of the DFT contains an error due to exponentially decaying DC offsets. For this reason, distance relays have a tendency to over-reach or under-reach in the presence of DC offset components in a fault current. Therefore, the decaying DC components should be taken into consideration when calculating the phasor of the fundamental frequency component of a relaying signal. The error due to DC offsets in a DFT is calculated and eliminated using the outputs of an even-sample-set DFT and an odd-sample-set DFT, so that the phasor of the fundamental component can be accurately estimated. The performance of the proposed algorithm is evaluated for a-phase to ground faults on a 345 kV, 50 km, simple overhead transmission line. The Electromagnetic Transient Program (EMTP) is used to generate fault signals. The evaluation results indicate that adopting the proposed algorithm in distance relays can effectively suppress the adverse influence of DC offsets.

• Journal of Communications and Networks
• /
• v.18 no.3
• /
• pp.364-374
• /
• 2016

With vast amounts of spectrum available in the millimeter wave (mmWave) band, small cells at mmWave frequencies densely deployed underlying the conventional homogeneous macrocell network have gained considerable interest from academia, industry, and standards bodies. Due to high propagation loss at higher frequencies, mmWave communications are inherently directional, and concurrent transmissions (spatial reuse) under low inter-link interference can be enabled to significantly improve network capacity. On the other hand, mmWave links are easily blocked by obstacles such as human body and furniture. In this paper, we develop a multi-hop relaying transmission (MHRT) scheme to steer blocked flows around obstacles by establishing multi-hop relay paths. In MHRT, a relay path selection algorithm is proposed to establish relay paths for blocked flows for better use of concurrent transmissions. After relay path selection, we use a multi-hop transmission scheduling algorithm to compute near-optimal schedules by fully exploiting the spatial reuse. Through extensive simulations under various traffic patterns and channel conditions, we demonstrate MHRT achieves superior performance in terms of network throughput and connection robustness compared with other existing protocols, especially under serious blockage conditions. The performance ofMHRT with different hop limitations is also simulated and analyzed for a better choice of the maximum hop number in practice.

• Proceedings of the KIEE Conference
• /
• 1995.07b
• /
• pp.584-587
• /
• 1995

Recent development in the digital relay technology has introduced the adaptive relaying system which adopts the relays to the current operating states. This paper proposes the hierarchical digital protection system whose design has been based on 154 kV S/S. Applying the newest communication networking, the system provides the new protection capabilities improving the system reliability and speed.

• Proceedings of the KIEE Conference
• /
• 2001.11b
• /
• pp.246-248
• /
• 2001

In this paper, the fault analysis program that is convenient to analyse fault records of a digital relay and to set a digital relay is described. The key feature of this fault analysis program is as follows. - analysing fault records stored in a local PC and/or a digital relay - analysing events - setting a digital relay. This program is for a digital bus protection relay using a conventional variable percentage current differential relaying algorithm. So this program adds a function analysing the characteristic of each variable percentage current differential function and the connection state of the transmission lines at double-bus system.