• Journal of Communications and Networks
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• 제13권1호
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• pp.32-42
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• 2011

Frequency reuse among relay stations (RSs) in a down-link access zone is widely adopted for throughput enhancement in IEEE 802.16j relay networks. Since the areas covered by the RSs or the base station (BS) may overlap, some mobile stations (MSs) at the border between two neighboring transmitting stations (RS or BS) using an identical frequency band may suffer severe interference or outage. This co-channel interference within the cell degrades the quality of service (QoS) fairness among the MSs as well as the system throughput. Exclusive use of a frequency band division (orthogonal resource allocation) among RSs can solve this problem but would cause degradation of the system throughput. We observe a trade-off between system throughput and QoS fairness in the previously reported schemes based on frequency reuse. In this paper, we propose a new frequency reuse scheme that achieves high system throughput with a high fairness level in QoS, positioning our scheme far above the trade-off curve formed by previous schemes. We claim that our scheme is beneficial for applications in which a high QoS level is required even for the MSs at the border. Exploiting the features of a directional antenna in the BS, we create a new zone in the frame structure. In the new zone, the RSs can serve the subordinate MSs at the border and prone to interference. In a 3-RS topology, where the RSs are located at points $120^{\circ}$ apart from one another, the throughput and Jain fairness index are 10.64 Mbps and 0.62, respectively. On the other hand, the throughput for the previously reported overlapped and orthogonal allocation schemes is 8.22 Mbps (fairness: 0.48) and 3.99 Mbps (fairness: 0.80), respectively. For a 6-RS topology, our scheme achieves a throughput of 18.38 Mbps with a fairness of 0.68; however, previous schemes with frequency reuse factors of 1, 2, 3, and 6 achieve a throughput of 15.24 Mbps (fairness: 0.53), 12.42 Mbps (fairness: 0.71),8.84 Mbps (fairness: 0.88), and 4.57 Mbps (fairness: 0.88), respectively.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.29-30
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• 2008

This paper defines a concept of "protectability" for the performance evaluation of distance relay considering its sensitivity and selectivity. The paper starts from the probabilistic modeling of the errors, and based on this model, a detailed explanation of protectability calculation for each zone of the distance relay is presented. An effect of the Weighting Rate and the Measurement Deviation on the protectability evaluation is also given. By considering this effect, the optimization of relay setting can be realized. The proposed method is applied to a typical model system to show its effectiveness.

• 대한전자공학회논문지TC
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• 제44권9호
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• pp.17-24
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• 2007

본 논문에서는 멀티 홉 OFDMA 시스템에서 relay간 무선자원을 효율적으로 재사용하기 위한 방법으로 sub-cell reuse partitioning 기법을 제안한다. 셀 내에서 relay 들에 주파수 자원을 더 많이 재사용을 할수록 사용 가능한 자원이 늘어나 셀 용량을 증가시킬 수 있다. 하지만 이 경우 자원이 재사용되면서 동시에 발생되는 간섭이 많아져 Relay Station(RS) sub-cell edge에서 SINR 성능이 나빠질 수 있으며 결과적으로 fairness 성능을 나쁘게 만들 수 있다. 본 논문에서는 throughput 및 fairness 성능을 모두 좋게 만들기 위해 RS sub-cell을 내부와 외부로 나누어 내부에서는 재사용을 더 많이 하고, 외부에서는 재사용을 덜 적용하는 sub-cell reuse partitioning 기법을 제안하였다. 제안한 기법의 성능을 분석하기 위하여 모의실험을 구성하였다. Fairness 분석을 위하여 reuse partitioning과 함께 적용할 수 있는 스케줄링 알고리즘도 구현하였다. 도출된 성능 결과를 분석하여 sub-cell reuse partitioning 기법을 적용하여 throughput 성능과 fairness 성능을 함께 개선할 수 있음을 확인하였다. 특히, 스케줄링을 fairness 성능을 개선하는 방향으로 적용할 때, sub-cell reuse partitioning 기법을 적용하여 얻어지는 throughput 성능의 개선 효과가 더 크게 됨을 확인하였다.

• 전기학회논문지
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• 제60권1호
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• pp.43-49
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• 2011

A distance relay scheme is commonly used for backup protection. This scheme, called a step distance protection, is comprised of 3 steps for graded zones having different operating time. As for the conventional step distance protection scheme, Zone 2 can exceed the ordinary coverage excessively in case of a transformer protection relay especially. In this case, there can be overlapped protection area from a backup protection relay and, therefore, malfunctions can occur when any fault occurs in the overlapped protection area. Distance relays and overcurrent relays are used for backup protection generally, and both relays have normally this problem, the maloperation, caused by a fault in the overlapped protection area. Corresponding to an IEEE standard, this problem can be solved with the modification of the operating time. On the other hand, in Korea, zones are modified to cope with this problem in some specific conditions. These two methods may not be obvious to handle this problem correctly because these methods, modifying the common rules, can cause another coordination problem. To overcome this problem clearly, this paper describes an improved backup protection coordination scheme using an IEC 61850-based distance relay for transformer backup protection. IEC 61850-based IED(Intelligent Electronic Device) and the network system based on the kernel 2.6 LINUX are realized to verify the proposed method. And laboratory tests to estimate the communication time show that the proposed coordination method is reliable enough for the improved backup protection scheme.

• Journal of Electrical Engineering and Technology
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• 제8권5호
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• pp.1029-1039
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• 2013

To avoid undesirable disconnection of healthy wind generators (WGs) or a wind power plant, a WG protection relay should discriminate among faults, so that it can operate instantaneously for WG, connected feeder or connection bus faults, it can operate after a delay for inter-tie or grid faults, and it can avoid operating for parallel WG or adjacent feeder faults. A WG protection relay based on the positive- and negative-sequence fault components is proposed in the paper. At stage 1, the proposed relay uses the magnitude of the positive-sequence component in the fault current to distinguish faults requiring non-operation response from those requiring instantaneous or delayed operation responses. At stage 2, the fault type is first determined using the relationships between the positive- and negative-sequence fault components. Then, the relay differentiates between instantaneous operation and delayed operation based on the magnitude of the positive-sequence fault component. Various fault scenarios involving changes in position and type of fault and faulted phases are used to verify the performance of the relay. This paper concludes by implementing the relay on a hardware platform based on a digital signal processor. Results indicate that the relay can successfully distinguish the need for instantaneous, delayed, or non-operation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 A
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• pp.212-214
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• 2000

The distance relay technique used for transmission line protection operates overreach and underreach to the self protection region because the power system becomes complex and fault conditions are different. To solve these problems, this paper describes new technique to set the reliable self protection lesion. The trip region of the quadrilateral distance relay is set by training of multi layer recurrent elman network. The proposed network is able to reach the trip zone for the fault impedance, fault initial angle and source impedance variance correctly.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2015년도 제46회 하계학술대회
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• pp.1617-1618
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• 2015

This paper analyzed catenary impedance characteristics of relays installed in substation and sectioning post to protect power feeding circuit in the extended power feeding conditions. For this, we modelled AT feeding system using PSCAD/EMTDC and calculated catenary impedance. The relay installed in substation calculated catenary impedance of the extended power feeding area adding catenary impedance of self protection zone. But, the relay installed in sectioning post calculated catenary impedance of the only protection area. Therefore, we confirmed that the more reliable protection way can be utilized using the relay installed in sectioning post.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 A
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• pp.305-307
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• 2003

This paper presents an apparent impedance calculation procedure for distance relaying of transmission line involving FACTS (Flexible AC Transmission System) devices, particularly the UPFC (Unified Power Flow Controller), between Kangjin and Jangheung in Korea. With the changes of UPFC's parameters, the measurement and protective range (trip boundaries) of the adaptive distance relay can also be changed. So, it is the most important part in the field of system protection to analyze the operating characteristic of relaying system. The presence of UPFC significantly affects the trip boundaries which are also adversely affected by fault resistance combined with remote end infeed. This paper presents the apparent impedance calculations and the distance relay setting characteristics for faults involving the UPFC in the KEPCO system.

• 전기학회논문지
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• 제64권3호
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• pp.473-479
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• 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.

• 대한전기학회논문지:전력기술부문A
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• 제53권4호
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• pp.221-226
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• 2004

Power system has recently used Double-circuit Line and Multi-circuit Line in the industrial development. This has an advantage of system stability and reliability, but the complexity of the system has a disadvantage that makes it difficult to protect the power line. Double-circuit Line has two operation conditions in the Single-circuit operation and Double-circuit operation, so it has mutual impedance. To make it possible for the remaining single-line to operate independently while there is a fault with first line or when maintenance is needed, a trip region for the single-circuit operation should be set in order to set the relay trip region. An optimal trip region for each operation, a different operational conditions for the relay setting should be calculated. In this paper, trip regions of each operation condition have been compared by considering mutual impedance and fault resistance that led to the calculation of fault impedance. Also, as we know that one of the advantages in the distance relay is the back-up protection, we calculated the trip region(Zone-2) in consideration of the mutual impedance.