• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.210-212
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• 2003

Conventional PDC relaying with 2nd harmonic restraint makes some doubt in reliability. It can contain second harmonic component to a large extent even during internal fault, and shows a tendency of relative reduction because of the advancement of transformer's core material. It is, therefore, necessary to develop a new algorithm as well as a new technique for the effective and accurate discrimination. This paper deals with advanced algorithm, fuzzy logic based relaying by using flux differential, and a new fault detection criterion logic scheme by using wavelet transform. To comparative analysis of proposed techniques, the paper constructs power system model including power transformer, utilizing the EMTP, and collects data through simulation of various internal faults and magnetizing inrush.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.1
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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 the Earthquake Engineering Society of Korea
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• v.2 no.3
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• pp.37-49
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• 1998

Research and a, pp.ication of earthquake protection system in Taiwan have become very active since about ten years ago. Many passive isolators, etc., have been studied extensively. These studies have resulted in a few practical a, pp.ications and proposals of two draft design provisions for seismic isolation design of bridges and buildings. In addition to the pass control, analytical studies on active semi-active control have also been very active and the experimental studies have scheduled in the near future. This paper summarise the progress on recent research and a, pp.ication of earthquake protection systems in Taiwan. The emphases are given to the control systems that have been a, pp.ied in practical a, pp.ications.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.63 no.4
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• pp.368-372
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• 2014

The most widely used scheme for detecting loss of excitation on generator is used to sense apparent impedance from generator terminals. This paper presents loss of excitation algorithm using DFT filter based negative offset mho elements for generator field protection. It's algorithm includes two negative mho characteristics looking in the generator. The generator control system was modeled by PSCAD/EMTDC software, and then the proposed algorithm was tested by the collecting relaying signals from selected the generator model. From simulation results, the loss of excitation algorithm can be used to field protection for generator.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.1
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• pp.36-42
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• 2011

This paper mainly proposes the protective coordination scheme of the microgrid system. The microgrid protection is identical to the conventional protection system separating the normal part and contingency part to reduce damage when the contingency occur at power cables, facilities. But they are different in the protection type. The conventional protection system only considers unidirectional current. However the microgrid protection should be considered not only unidirectional current but also backfeed current because various microsources and loads are installed in the microgrid system. In case the contingency occurs in microsource, when microgrid is interconnected to grid, the protection system should be configured to not separate microgrid from grid before the microsource is isolated to microgrid. And in case of fault occur in power system, the microsources should not isolated to microgrid before the static switch at PCC is tripped to separate from power system. Considering these characteristic of microgird, this paper proposes the protective coordination scheme of microgrid and implemented the on-line real time monitoring system. Especially in case the microgrid is connected to low voltage distribution system with 220/380V voltage level, the proposed protection method with power IT technology can solve the problems when the existing protective devices only applied to the microgrid system.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.65 no.2
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• pp.122-129
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• 2016

Current differential protection relaying with second harmonic restraint is the main protection for large capacity power transformer. PSCAD simulation program is widely used for modeling of dynamic varying transients phenomena. This paper deals with a power transformer model and transients analysis using PSCAD software to develop IED for power transformer. Simulation was carried out using a three phase 40MVA, 154/22.9kV, 60Hz, two-winding transformer with Y-Y connection used in actual fields. The paper analyzed transformer magnetizing inrush, external fault, and internal fault conditions with this model in the time domain. In addition, we performed an analysis in the frequency domain using FFT during several conditions.

• Proceedings of the KIEE Conference
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• 2005.07a
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• pp.286-288
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• 2005

This paper proposes a digital simulator using NI DAQ Device and GO s/w by LabVIEW for IED of power transformer protection. The performance of the digital simulator has been verified through WatATP 99 simulation data.

• Proceedings of the KIEE Conference
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• 2006.11a
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• pp.135-137
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• 2006

변전소 보호, 제어, 감시와 자동화 능력을 선진화하면서 송변전설비 건설, 보수, 운영 및 관리비용을 확실하게 줄이기 위한 계획과 노력이 진행 중이다. 그러나 통신기술이 변화할 때 마다 새로운 통신 표준을 채용하거나 변전소 자동화시스템을 전체 교체하는 것은 바람직하지 않다. 따라서 IEC61850통합으로 기능과 변전소 데이터를 생성과 서버제공, SCADA, 보호응용, 상태 감시의 IED 광역보호 장치 통을 고려해 본다.

• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.240-241
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• 2006

Islanding operations of DG usually occur when power supply from the main utility is interrupted due to several reasons but the DG keeps supplying power into the distribution networks. These kinds of islanding conditions cause negative impacts on protection, operation, and management of distribution systems. Therefore, it is necessary to effectively detect the islanding conditions and swiftly disconnect DG from distribution network. This paper proposes the islanding detection algorithm for DG using the change of the voltage unbalance and the output power of DG. The proposed method effectively combines the conventional parameters for detecting the islanding conditions. The proposed methods were verified using the radial distribution network of IEEE 34 bus.

• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.266-267
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• 2006

A coupling capacitor voltage transformer (CCVT) is used in extra high voltage and ultra high voltage transmission systems to obtain the standard low voltage signal for protection and measurement. To obtain the high accuracy at the power system frequency, a tuning reactor is connected between a capacitor and a voltage transformer (VT). Thus, no distortion of the secondary voltage is generated when no fault occurs. However, when a fault occurs, the secondary voltage of the CCVT has some errors due to the transient components resulting from the fault. This paper proposes an algorithm for compensating the secondary voltage of the CCVT in the time domain. With the values of the secondary voltage of the CCVT, the secondary and the primary currents are obtained; then the voltage across the capacitor and the tuning reactoris calculated and then added to the measured secondary voltage. The proposed algorithm includes the effect of the non-linear characteristic of the VT and the influence of the ferro-resonance suppression circuit. Test results indicate that the algorithm can successfully compensate the distorted secondary voltage of the CCVT irrespective of the fault distance, the fault inception angle and the fault impedance.