• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.28 no.6
• /
• pp.99-105
• /
• 2014

Power transformers are applied throughout the power system to connect systems of different voltage to one another. Since a ratio differential relay offers high sensitivity in detection of internal faults in power transformers, it is widely used in the main protection system. The use of nonlinear devices such as rectifiers and other devices utilizing solid state switching have been increased in industry during recent years. For nonlinear loads, the load current is not proportional to the instantaneous voltage. This situation creates harmonic distortion on the system. The harmonic could differential relay misoperation if not recognized. This paper aims at analyzing and probing into the influences of harmonics on a ratio differential relay for power transformer protection.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.62 no.7
• /
• pp.925-930
• /
• 2013

The fault current of the power transmission system is greater than that of the power distribution system. Therefore, the introduction of superconducting fault current limiter (SFCL) is more needed to reduce the increased fault current. The trigger-type SFCL consists of the high-temperature superconducting element (HTSC), the current limiting reactor (CLR) and the circuit breaker (CB). The trigger-type SFCL can be used to supplement the disadvantages of the resistive-type SFCL. The operation characteristics of the current ratio differential relay which is usually applied to the protection device of the power transmission system are expected to be affected under fault conditions and the applicability of the trigger-type SFCL. In this paper, we analyzed the operating characteristics, by the fault conditions, between the current ratio differential relay for line protection and the trigger-type SFCL in the power transmission system through the PSCAD/EMTDC simulation.

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

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

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

• Proceedings of the KIEE Conference
• /
• 2001.11b
• /
• pp.216-218
• /
• 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 Korean Institute of Communications and Information Sciences
• /
• v.35 no.1A
• /
• pp.1-9
• /
• 2010

This paper offers performance analysis of selection decode and forward (DF) networks with differential modulation/demodulation for an arbitrary number of relays in independent but not identically distributed Rayleigh fading channels. We have shown that the selection DF protocol with differential modulation can achieve full diversity in both independent identically distributed (i.i.d.) and independent but not identically distributed (i.n.d.) Rayleigh fading channels, and the performance loss due to using non-coherent detection is not substantial. Furthermore, we study the impact of combining techniques on the performance of the system by comparing a system that uses selection combining (SC) to one that uses maximum ratio combining (MRC). Simulations are performed and show that they match exactly with analytic ones in high SNR regime.

• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2013.06a
• /
• pp.104-105
• /
• 2013

차등 시공간 블록 코드 시스템은 다이버시티 이득을 송신단에서 파일럿 삽입이 필요 없이 얻을 수 있는 기술로 주목되고 있다. 특히, 협력 네트워크 시스템에서 서비스 영역을 확장하기 위하여 중계기를 사용하게 되는데 자연스럽게 채널 추정 기법을 고려하지 않은 방법들이 연구 되었다. 본 논문은 차등 준 시공간 블록 코드를 이용한 협력 전송 네트워크에서 ML(Maximum Likelihood) 기반의 준 최적 신호 결합 기법을 제시한다. 모의실험 결과를 통해 제안된 수신 결합 기법은 높은 신호 대 잡음비 환경에서 기존에 널리 사용되는 MRC (Maximum Ratio Combining) 기법보다 5dB이상의 이득을 얻는 것을 보여준다.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.57 no.2
• /
• pp.102-108
• /
• 2008

AC generator plays an important role of power system. The large AC generator fault may lead to large impacts or perturbations in power system. And then the protection of a generator has very important role in maintaining stability in a power system. In present, the DFT(discrete Fourier transform) based RDR(ratio differential relay) had been widely applied to a internal fault of a generator stator winding. But DFT has a serious drawback. In the course of transforming a target signal to frequency domain, time information is lost. DWT uses a time-scale region. This paper proposes an advanced fault detection algorithm using DWT(discrete Wavelet transform) to enhance the drawback of conventional DFT based relaying. To evaluate the performance of the proposed relaying, we used the test data which were sampled with 720 [Hz] per cycle and obtained from ATP(alternative transient program) simulation. And we made a comparative study of conventional DFT based RDR and the proposed relaying.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.57 no.4
• /
• pp.377-382
• /
• 2008

For stator winding protection of AC generator, KCL(Kirchhoff's Current Law) is widely applied. Actually a CRDR(Current Ratio Differential Relay) based on DFT(Discrete Fourier Transform) has been used for protecting generator. It has been pointed out that defects can occur during the process of transforming a time domain signal into a frequency domain one which can lead to loss of time domain information. Wavelets techniques are proposed for the analysis of power system transients. This paper introduces an algorithm to choose a suitable Mother Wave1et for generator stator fault detection. For optimal selection, we analyzed db(Daubechies), sym(Symlets), and coif(Coiflects) of Mother Wavelet. And we compared with performance of the choice algorithm using detail coefficients energy and RMS(root mean square) error. It can be improved the reliability of the conventional DFT based CRDR. The feasibility and effectiveness of the proposed scheme is proved with simulation using collected data obtained from ATP (Alternative Transient Program) package.