• Proceedings of the KIEE Conference
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• 1997.07e
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• pp.1871-1873
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• 1997

The conventional current transformers are often take faults and out of order that for detect to over current of electric power lines because electromagnetic interference. But, it is possible to implement protection relay of high reliability using optical magnetic field sensor which are immunity and small size. The optical magnetic field sensor is possible to rapidly detect to over current and recover when electric power line have fault. And it is not necessary to make with capacitance of electric power lines as optical magnetic field sensor is have linearity from 0 to about 20kA. In this study, we designed and constructed compensative feedback circuit in order to minimize of optical power intensity variation with environ- mental variations(temperature, drive current) of light source. And this system have highest optical advantages and reliability.

• Proceedings of the KIEE Conference
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• 1997.07c
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• pp.1003-1005
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• 1997

To evaluate the quality of a system or its ability to perform a required function, it is necessary to quantify the reliability of that system. The reliability techniques are based on the concept of expected failure rate and average-outage-duration method. For each load point, the expected failure rate, average outage duration and average annual outage time are evaluated. This paper deals with the reliability evaluation for distribution system including the protection relay system. In evaluating the reliability, it suggests a method for the analysis of protective system reliability, that provides a probabilistic measure of the success of the protective apparatus to perform its intended function. The analysis shows the dependency of success on the reliability of many components, and the way this reliability may be enhanced by redundancy.

• International Journal of Control, Automation, and Systems
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• v.4 no.3
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• pp.365-371
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• 2006

This paper presents an algorithm based on a combination of Discrete Wavelet Transforms and neural networks for detection and classification of internal faults in a two-winding three-phase transformer. Fault conditions of the transformer are simulated using ATP/EMTP in order to obtain current signals. The training process for the neural network and fault diagnosis decision are implemented using toolboxes on MATLAB/Simulink. Various cases and fault types based on Thailand electricity transmission and distribution systems are studied to verify the validity of the algorithm. It is found that the proposed method gives a satisfactory accuracy, and will be particularly useful in a development of a modern differential relay for a transformer protection scheme.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.63 no.4
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• pp.312-316
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• 2014

In this paper, a voltage sag is analyzed in case of superconducting fault current limiter (SFCL) installed in power distribution system where replaces the main power transformer to large one to meet the power demand. First, the power system is configurated to analyze the operation characteristics of the protective relay with replacement of the main transformer and application of the SFCL. Next, the method to meet the protection coordination is analyzed with large transformer using PSCAD/EMTDC. Finally, the bus voltage is investigated according to the impedance of both main transformer and SFCL in case that the SFCL is applied into feeder.

• Proceedings of the KIEE Conference
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• 1998.07c
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• pp.1231-1234
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• 1998

Design & Operation of power system for meeting increase of electric power demand is becoming more difficult and complex. One of reasons is increase of fault current. As one of the most effective methods for suppressing the fault current, installation of SFCL is expected. This paper describes a method of fault analyses of power system with SFCLs, and also discusses determination of specification of SFCLs, effects of limiting the fault current due to SFCLs by use of the model system of two - bus electric power system with parallel circuit model transmission line. Also, describes the definition of six specific parameters of SFCL for power system application & a proposal of design method of specific parameter of a resistance type SFCL in overhead transmission lines considering operation of protective relays.

• Proceedings of the KIEE Conference
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• 2003.07a
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• pp.323-325
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• 2003

A current differential relay may maloperate for external faults with CT saturation and requires an additional method to cope with the problem. This paper proposes a current differential relaying algorithm for transmission line protection using an advanced compensation algorithm of the secondary current of CTs. The compensation algorithm is unaffected by a remanent flux. The proposed algorithm does not need an additional method for CT saturation and thus can achieve high stability for an external fault.

• Proceedings of the KSR Conference
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• 2003.05a
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• pp.493-498
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• 2003

Harmonic current originating from electric locomotives can be magnified due to the impedance characteristics of power supply circuit and bring about various problems. That is, electromagnetic interference with communication lines, operational trouble in signaling, overheat and/or vibration in power capacitor, mis-operation in protection relay and so on. Therefore, the exact assessment of the harmonic current flow must be undertaken at design and planning stage for the electric traction systems. For these reasons, this study propose a new approach to model and to analyse traction power feeding system focused on system response to current and voltage harmonic(PART I ). Measurements of harmonics are also performed for railway power supply systems under normal operation. Spectrum and distortion analyses in measurement data are variously described in PART II

• Proceedings of the KSR Conference
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• 2003.05a
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• pp.499-504
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• 2003

Harmonic current originating from electric locomotives can be magnified due to the impedance characteristics of power supply circuit and bring about various problems. That is, electromagnetic interference with communication lines, operational trouble in signaling, overheat and/or vibration in power capacitor, mis-operation in protection relay and so on. Therefore, the exact assessment of the harmonic current flow must be undertaken at design and planning stage for the electric traction systems. For these reasons, this study propose a new approach to model and to analyse traction power feeding system focused on system response to current and voltage harmonic(PART I ). Measurements of harmonics are also performed for railway power supply systems under normal operation. Spectrum and distortion analyses in measurement data are variously described in PART II

• Proceedings of the KSR Conference
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• 2006.11b
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• pp.878-884
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• 2006

Grounding fault and short of the DC power supply systems are detected and protected by high-speed circuit breaker, linked breaking device, ground relay and fault selective device, all of which are installed and operated in substaions. however, there have been many cases in which the protective devices did not detect grounding of of the over head catenary systems on concrete support for an extended period of time. Such cases often cause severe damages to the supports with high grounding resistances. If grounding accidents occur repetitively, the earth current and the rise of earth potential can damage not only passenger and staff but also electric facilities and equipment, necessitating high cost and endeavor to restore. The following study points out various problems that can be occurred occur as a result of high impedance grounding accident, and proposes a new system which can protect and intercept them.

• Journal of Electrical Engineering and Technology
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• v.2 no.1
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• pp.19-28
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• 2007

The paper discussed various techniques for islanding detection and described in detail the working principles of ROCOF and vector shift relays. A simulator was used to investigate why the stability of both types of relays maybe affected by network and load switching, short-circuit faults and in the case of a ROCOF relay the loss of bulk generation or the tripping of a transmission feeder. Finally, to enhance the reliability of Loss of Mains protection, a new islanding detection technique based on a GPS synchronized phasor measurement system was proposed.