• Proceedings of the KIEE Conference
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• 2008.11a
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• pp.12-15
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• 2008

A distance relay has been widely used for transmission line protection. The distance relay detects a fault based on the calculated impedance i.e. the ratio of the voltage to the current measured from a current transformer (CT) and a coupling capacitor voltage transformer (CCVT), respectively. When a fault occurs and a CT saturates due to the magnitude of fault current, dc component, primary time constant, and the remanent flux of the iron core, the secondary current of a CT is distorted On the other hand, non-fundamental components generated during a fault can increase the error of a CCVT, particularly when a fault distance is short. The distortion of the current and voltage can cause mal-operation or the operating time delay of a distance relay. This paper describes the response of a distance relay considering the errors of a CT and a CCVT. The results indicate that the severe distortion of a CT and a CCVT have noticeable effect to a distance relay.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.4
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• pp.313-319
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• 2019

Induction motors connected with a three-phase AC system may malfunction due to reverse phase or open phase faults. Conventional overcurrent relays and overheating relays are used to prevent such accidents; however, their drawbacks include a low response speed and false operation. Therefore, in this study, a digital relay for the reverse-open phase was designed and fabricated. This relay can detect the reverse phase and open phase faults and send a trigger signal to the control circuit. The proposed relay was developed based on a microcontroller. The detection times of the reverse phase and open phase were verified as 320ms and 80ms, respectively. Compared with conventional relays that only protect the motor from one type of fault, the proposed relay can detect both, reverse phase and open phase faults. In addition, the fault detection, identification criterion, and trigger signal patterns can be modified by programming according to the requirements of users.

• Progress in Superconductivity and Cryogenics
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• v.11 no.3
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• pp.35-39
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• 2009

The study for a protective relay system is one of the important technical issues on the power system application of Superconducting Fault Current Limiter (SFCL). We used Real Time Digital Simulator(RTDS) to study the true interaction of the protection system with the power system. RTDS modeling of SFCL is necessary to the detailed protective relay tests. In this paper, we developed an analysis model using RTDS for studying the transient behavior of 22.9kV SFCL and carried out closed-loop testing of protective relays in distribution power system with the developed SFCL model. The SFCL model has the operation mechanism of 22.9kV hybrid SFCL being developed by LSIS and KEPRI in Korea. The parameters of the model are based on the test data of the real SFCL. Power system planners and operators can solve the expected problems in power system application of SFCL using protective relay testing results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.11 s.102
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• pp.1138-1146
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• 2005

This paper makes a study of a formulation of net filter discrimination(NFD) and its computation for analyzing adjacent channel interference and suggests a systematic algorithm for calculating protection ratios of co-channel and adjacent channel applicable to frequency coordination in the fixed radio relay networks. It is shown that adjacent channel protection ratio can be derived from two factors: One is NFD depending upon receiver filter characteristic as well as transmitter spectrum mask and the other is co-channel protection ratio given by a function of fade margin, modulation scheme, and allowable interference. Actually to show the computing procedure from transmitter spectrum mask and receiver filter characteristic, NFD has been obtained for channel bandwidth of 29.65 and 40 MHz at 6.2 and 6.7 GHz band, respectively. According to the results, NFDs at the first adjacent channel of 29.65 and 40 MHz provide 27.4 and 28.9 dB, respectively. From these data, adjacent channel protection ratios corresponding to each channel bandwidth yield 47.5 and 46.3 dB for a given 64-QAM and 60 km. The proposed method gives some merits of an easy calculation, systematic extension, and applying the same concept to frequency coordination in millimeter radio relay networks.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.6
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• pp.1129-1138
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• 2019

Since substations are structurally complex due to the concentration of protection coordination facilities with substation facilities for long distance power transmission, it is difficult to design a protection coordination system to minimize the spreading effect of the fault when a fault occurs on transmission line or distribution line. Therefore, in this paper, the bus configuration and the basic logic of protection coordination that have a major influence on the reliability of substation power supply were analyzed, and the substation protection coordination logic to detect internal and external faults was developed based on EMTP-RV. As the basic logic of substation protection coordination, the percent differential protection relay logic for substation internal fault detection and the overload protection relay logic for inference of external failure were modeled. Finally, the 154kV substation including the protection coordination logic was modeled using EMTP-RV, and the effectiveness of the protection coordination design methodology was confirmed through the several fault simulation cases based on EMTP-RV.

• Journal of Electrical Engineering and Technology
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• v.3 no.1
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• pp.29-35
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• 2008

With long time setting, zone 3 impedance relays are considered insensitive to power swings, and their operation condition during power swings is seldom analyzed. Instead of ti me-consuming simulation to the swing loci, their operation condition is directly quantified by polynominal functions in this paper to find the critical swing angle and frequency for relay operation under different relay settings and system parameters. It is found: (1) the swing loci are more densely populated inside than outside of the protection region, which corresponds to long residence time and possible relay operations; (2) the relays may be sensitive to load encroac hments and stable power swings with different relay settings and system parameters; (3) the critical swing frequency may be in the range of low-frequency power swings.

• Proceedings of the KIEE Conference
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• 2000.07a
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• pp.191-193
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• 2000

In this paper, being different from traditional methods, we design digital protective relay which can be applied to power management and control systems of not only small and medium but also a large scale plants. The digital protective relay was designed with DSP CPU(TMS320C31) to protect and measure more quickly and precisely. We will present test result which it performed according to the standards of Korea Electrical Manufactures Cooperative to prove the faculties of digital protective relay. The test result on the basis of KEMC1120 and IEC60255, show that the operation time error of the digital motor protection relay is improved within ${\pm}5%$.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.55 no.4
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• pp.183-189
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• 2006

In this work, the digital simulator for testing of digital protective relay is presented. The proposed simulator software has EMTP simulation data file conversion, sequence waveform generation, user define simulation data generation, communication engine, data analysis engine and measurements function etc. The simulator hardware is designed using 32bit floating point DSP architecture to achieve flexibility and high speed operation. This simulator is tested to evaluate the performance of relay simulator by using a output data of simulation model on EMTP.

• Proceedings of the KIEE Conference
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• 1998.07c
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• pp.902-904
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• 1998

When the faults occur in power systems, the protective relay plays a roles of protecting power systems. It is important that the protective relay have high selectiveity and sencitivity performance in power system by correct setting the relays. This paper proposed a testing methods if the reliability of digital relay as simulating the response of relay at faults in the real power system operation environment.

• Proceedings of the KIEE Conference
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• 1998.07c
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• pp.946-948
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• 1998

The distance relay is very important for transmission line protection. A quadrilateral zone shape is used mainly for a modern digital distance relay. The shape of quadrilateral is vendor specific. At the stage of design, the shape is determined considering all possible types of faults and diverse configurations of system. Also this type relay must be designed to avoid the operation by a sound phase at single-Phase-to-ground fault, by a sound phase at two-phase-to-ground fault. The effect of a source impedance and a load impedance is another important factor to design. In this paper, a reliable zone shape which is appropriate for the KEPCO's transmission system is provided.