• Proceedings of the KIEE Conference
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• 1999.07c
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• pp.1410-1412
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• 1999

Protective relay for transformer operates in general by comparing with the differential current and the restraint current. These kinds of currents are changed on magnitude and phasor during the fault according to winding type and vector group. This paper presents the differential and restraint currents and operational principle of differential protective relay for two-winding and three-winding transformer with graphical model. It is developed using MATLAB for an educational purpose on engineer related in power system and protection in university and power utility including large factory.

• Proceedings of the KIEE Conference
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• 2001.11b
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• pp.216-218
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• 2001

The transformer role is very important in power system operation and control; also its price is very expensive. Therefore many kinds of the efforts for transformer protection have been executed. So for as, current differential relay(87) has been mainly used for transformer protection. But current differential relaying method has several troubles as followings. Differential current can be occurred by transformers inrush current between winding1 and winding2 of transformer when transformer is initially energized. Also harmonic restrained element used in current differential relaying method is one of the causes of relays mal-operation because recently harmonics in power system gradually increase by power switching devices(SVC, FACTS, DSC, etc). Therefore many kinds of effort have been executed to solve the trouble of current differential relay and one of them is method using ratio of increment of flux linkages(RIFL) of the primary and secondary windings. This paper introduces a novel protective relay for power transformers using RIFL of the primary and secondary windings. Novel protective relay successfully discriminates between transformer internal faults and normal operation conditions including inrush and this paper includes real time test results using RTDS(Real Time Digital Simulator) for novel protective relay. A novel protective relay was designed using the TMS320C32 digital signal processor and consisted of DSP module. A/D converter module, DI/DO module, MMI interface module and LCD display module and developed by Xelpower co., Ltd.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.3
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• pp.445-450
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• 2020

Cooperative networks provides the benefits of performance improvements and capacity increment when the source node transmits signal to the destination node using several relay nodes. In this paper, we consider the cooperative network where the transmission scheme between the source node and relay node use conventional binary signaling, whereas the transmission scheme between thee relay node and destination node adopt the differential space time coding signaling. We analyze the performance of the system depending on the modulation scheme, i.e., coherent and differential modulation, at the source-relay links. The performance depending on the relay location is also compared by considering modulation scheme and the number of relay node.

• Proceedings of the KIEE Conference
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• 2002.07a
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• pp.229-231
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• 2002

The digital current differential relaying scheme is widely used for primary protection of 765(kV) power transformer. The current differential relay pickup the internal fault at the threshold which is set at 30% of rating current. Margin of 30% include current transformer error 5%, relay error 5%, on load tap changer error 7% and margin factor 140% obtained from the field experience. In this paper transformer protection relay and relay setting rule of high voltage power system are discussed. And we verify the correctness of relay setting rule with current differential relay using Matlab simulation.

• IEIE Transactions on Smart Processing and Computing
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• v.4 no.6
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• pp.443-449
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• 2015

This paper considers the physical layer security problem for a two-way vehicle-to-vehicle network, where the two source vehicles can only exchange information through an untrusted relay vehicle. The relay vehicle helps the two-way transmission but also acts as a potential eavesdropper. Each vehicle has a random velocity. By exploiting the random carrier frequency offsets (CFOs) caused by random motions, a secure double-differential two-way relay scheme is proposed. While achieving successful two-way transmission for the source vehicles, the proposed scheme guarantees a high decoding error floor at the untrusted relay vehicle. Average symbol error rate (SER) performance for the source vehicles and the untrusted relay vehicle is analyzed. Simulation results are provided to verify the proposed scheme.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.78-88
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• 2018

The liberalization of electricity market and environmental concerns are the major driving forces for the development of Distributed Generation (DG). The mode of grid-connected wind power generation is becoming popular and has matured as a reliable DG technology. The voltage generated by the wind generator is stepped up to the higher voltage by the transformers before connecting to the grid. Operating algorithm of the differential relays for transformer protection used in the wind farms need to be modified to take care of the dynamic nature of fault current caused by the intermittent nature of the wind power. An algorithm for the differential relay is proposed in which dual slope characteristics are adjusted with varying fault level situation according to the wind generator in service as well as with the wind speed. A case study conducted for a typical wind farm shows that the proposed method avoids mal-operation of the differential relay in varying wind power conditions.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.1
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• pp.29-37
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• 2018

Inrush current and fault current in a transformer need to be distinguished from one another. In order to do this, KEPCO uses a 2nd harmonic restraint/block method. We use two setting values for 2nd harmonic restraint; 15% and 10%. We also apply per-phase blocking method among various harmonic restraint methods. If the transformer is located at the radial system, we adjust 10% in the 2nd harmonic restraint, but this method is not enough to prevent mal-operations of the current differential relay and let us spend more time to change setting value again as the power system changes. In this paper, a more reasonable setting value for a 2nd harmonic blocking scheme in KEPCO is proposed. To present a proposed method, the fault data of the current differential relays which have occurred since 2009 are analyzed. To evaluate the performance of the proposed method, the results of the RTDS test for the current differential relay of the transformer by KEPCO are analyzed.

• The Journal of the Korea institute of electronic communication sciences
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• v.11 no.1
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• pp.17-22
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• 2016

In relay networks, relay nodes amplify or demodulate/remodulate the received signal from the transmitter, and transmit that signal to the receiver. The received signals from several relays are combined and used for demodulation at the receiver, which enhances the performance of the overall system. Partially differential modulation scheme which uses coherent modulation at the relay and non-coherent modulation scheme at the receiver is adopted for modulation scheme. We analyze the performance of systems depending on various energy allocations of source and relays given the total energy in relay networks.

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

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.505-506
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• 2007

A ratio differential relay using 80C196KC microprocessor was developed in this paper. The internal faults, external faults and inrush were simulated by EMTP. The performance of developed relay was verified with software and hardware simulation.