• The Transactions of the Korean Institute of Electrical Engineers A
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• v.51 no.9
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• pp.460-466
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• 2002

A reliable fault phase selection algorithm plays a very important role in transmission line protection, Particularly in Extra High Voltage (EHV) networks. The conventional fault phase selection algorithm used the phase difference between positive and negative sequence current excluding load current. But, it is difficult to pick out only fault current since we can not know when a fault occurs and select the fault phase in weak-infeed conditions that dominate zero-sequence current in phase current. The proposed algorithm can select the accurately fault phase using the sum of unit vectors which are calculated by positive-sequence voltage and negative-sequence voltage.

• Proceedings of the KIEE Conference
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• 2001.07a
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• pp.22-24
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• 2001

This paper presents a fault phase selection algorithm for transmission line protection by means of the symmetrical components. Accurate fault phase selection is necessary for collect functioning of transmission line relaying, particularly in Extra High Voltage (EHV) networks. The conventional phase selection algorithm used the phase difference between positive and negative sequence current excluding load current. But, it is difficult to abstract only fault current since we can not know the time which a fault occurs. The proposed algorithm can select the accurately fault phase using fault current contained pre-fault current.

• Proceedings of the KIEE Conference
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• 2001.11b
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• pp.124-126
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• 2001

A reliable fault type identification (phase selection) plays a very important role in transmission line protection, particularly in Extra High Voltage(EHV) networks. The conventional fault type identification algorithm used the phase difference between positive and negative sequence current excluding load current. But, it is difficult to pick out only fault current since we can not know when a fault occurs and identify the fault type in weak-infeed conditions that dominate zero-sequence current in phase current. The proposed algorithm can identify the accurately fault type using the sum of unit vectors which are calculated by positive-sequence votage and negative-sequence voltage.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.2
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• pp.114-120
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• 2003

According to the use of distribution automation systems, the function to find or to search a fault phase is necessary for automatic switches in a distribution substation. In this paper, two algorithms are developed to fine the fault circuit and the fault phase for the automatic switches in substation with ungrounded power system. One is the fault circuit searching method using the zero sequence voltage at the bus and zero sequence current of circuit current and the other is to find the fault phase using the line voltage and zero sequence current. The developed algorithms are tested in the case study simulations. An ungrounded power system is modeled by EMTP as a case study system. The developed algorithms are tested in the case study simulations and each shows correct results.

• Journal of Electrical Engineering and Technology
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• v.9 no.4
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• pp.1401-1410
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• 2014

This paper presents a modified adaptive fading EKF (AFEKF) for sensor fault detection and isolation in the satellite. Also, the fault detection and isolation (FDI) scheme is developed in three phases. In the first phase, the AFEKF is modified to increase sensor fault detection performance. The sensor fault detection and sensor selection method are proposed. In the second phase, the IMM filer with scalar penalty is designed to detect wherever actuator faults occur. In the third phase of the FDI scheme, the sub-IMM filter is designed to identify the fault type which is either the total or partial fault. An important feature of the proposed FDI scheme can decrease the number of filters for detecting sensor fault. Also, the proposed scheme can classify fault detection and isolation as well as fault type identification.

• Journal of Power Electronics
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• v.15 no.4
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• pp.974-986
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• 2015

A novel inverter fault-tolerant control scheme is proposed to drive brushless DC motor. A fault-tolerant inverter and its three fault-tolerant schemes (i.e., phase A fault-tolerant, phase B fault-tolerant, and phase C fault-tolerant) are analyzed. Eight voltage vectors are summarized and a voltage vector selection table is used in the control scheme to improve the midpoint current of the split capacitors. A stator flux observer is proposed. The observer can improve flux estimation, which does not require any speed adaptation mechanism and is immune to speed estimation error. Global stability of the flux observer is guaranteed by the Lyapunov stability analysis. A novel stator resistance estimator is incorporated into the sensorless drive to compensate for the effects of stator resistance variation. DC offset effects are mitigated by introducing an integral component in the observer gains. Finally, a control system based on the control scheme is established. Simulation and experiment results show that the method is correct and feasible.

• Journal of the Korean Society of Safety
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• v.30 no.1
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• pp.28-33
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• 2015

Three phase heaters in 7 buildings of 2 sites were examined for precise diagnosis. The sample size was 626. Precise examinations of current and the heater wiring status revealed contact failures and arcs in equipments that had CUF larger than 10%. Contact failures and arcs may cause electrical fire. Therefore, the correlation between the CUF and the imperfections in heater equipment and its wiring was analyzed for three phase heaters. In addition, the protection devices used for detection of heater imperfections were found to be unsuitable for the purpose. Current status of the protection devices was analyzed, and suggestions for improvements were made for new standards of the protection device selection.

• Journal of Power Electronics
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• v.15 no.3
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• pp.796-805
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• 2015

New direct and indirect current control methods for a fault-tolerant active power filter topology are presented in this paper. Since a three-phase four-switch topology has a phase bridge current which cannot be directly controlled, a hysteresis control method in the α-β plane which controls the three-phase current in the two-phase stationary coordinate system is proposed. The improved SVPWM algorithm is able to eliminate the operation of the trigonometric functions in the traditional algorithm by rotating the α-β coordinates and alternating the sequence of the output vectors, which in turn simplifies the algorithm and reduces the switching frequency. The selection of the DC-side reference voltage and DC-side capacitor equalization strategy are also discussed. Simulation and experiments demonstrate that the proposed control method is correct and feasible.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.31-32
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• 2007

In this paper, a fault section detection method is proposed for ungrounded system in the case of a single line-to-ground fault. A conventional method is used for faulted feeder selection according to the angular relationship between zero-sequence currents of the feeders and zero-sequence voltage of the system. Fault section detection is based on the comparison of phase angle of zero-sequence current. Proposed method has been testified in a demo system by Matlab/Simulink simulations. Based on Distribution Automation System(DAS), Feeder Remote Terminal Unit(FRTU) is used to collect those necessary data, at present a demo system is under developing using Manufacturing Message Specification (MMS) in IEC61850 standard.

• Journal of the Korean Institute of Intelligent Systems
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• v.14 no.5
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• pp.642-647
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• 2004

The relations of fuzzy entropy, distance measure, and similarity measure are discussed in this paper. For the purpose of reliable signal selection, the fuzzy entropy is proposed by a distance measure. Properness of the proposed entropy is verified by the definition of the entropy measure. Fourier and Wavelet transform are applied to the stator current signal to obtain the fault features of an induction motor. Membership functions for 3-phase currents are obtained by the Bootstrap method and Central Limit Theorem. Finally, the proposed entropy is applied to measure the fault signal of an induction machine, and the fuzzy entropy values of phase currents are illustrated.