• Proceedings of the KIEE Conference
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• 1999.07c
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• pp.1139-1141
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• 1999

A variable percentage current differential relaying algorithm is widely used for bus protection. However, it may maloperate in case of high-impedance internal faults and external faults with CT saturation and thus additional method to cope with CT saturation is necessary. This paper proposes a percentage current differential relaying algorithm for bus protection using a compensating algorithm of secondary current of CTs. As the proposed method compensates the distorted secondary currents of CTs it can improves the sensitivity of relays in a large current region and does not need any additional method for CT saturation.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.8
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• pp.1115-1127
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• 2010

Several methods have been applied to detect winding faults (turn-to-turn short). The representative approaches have been focusing on current signals. The current signal can give important information to extract features and to detect faults. In this study, current sensors were installed to measure signals for fault detection of BLDC motors. Therefore, it is necessary to select proper feature extraction methods among the popular methods that use current signals.

• Proceedings of the KIEE Conference
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• 2001.11b
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• pp.115-117
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• 2001

A percentage current differential relaying algorithm is widely used for bus protection. However, it may maloperate external faults with CT saturation. This paper proposes a percentage current differential relaying algorithm for bus protection using CT saturation detecting algorithm. The CT saturation detecting algorithm uses difference of secondary current of CT and detects CT saturation. The proposed method distinguishes percentage differential relay operation caused by faults from percentage differential relay operation caused by CT saturations.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.62 no.4
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• pp.198-203
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• 2013

There are conditions that can be unbalanced three phase currents in a large generator by untransposed lines, unbalanced loads, unsymmetrical faults, and open phases. The unbalanced conditions can producing negative sequence components of current that induce two times frequence current in the surface of the rotor, the retaining rings, the slot wedges in the field windings. These rotor currents make the rotor rapidly overheat, so the rotor can cause substantial damage in a very short time. This paper presents the digital negative sequence relay algorithm for unbalanced protection in a generator. The proposed algorithm was tested by using collected current signals on PSCAD/EMTDC considering a hydro turbine based generator control system. It can be seen that the proposed relaying by negative sequence current is useful for detection of unbalanced state of large generator.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.4
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• pp.8-17
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• 2010

In this paper, a fault tolerant control against sensor faults of electric parking brake (EPB) is proposed. Fault tolerant control method of EPB system is strongly demanded since sensor faults can endanger a driver's safety. In this paper, a clamp force estimation method is presented using motor's armature current and angular velocity. Clamp force estimation method is applied for fault detection method with parity equations. The goal of the detection method is to detect and identify faults in encoder, current sensor, force sensor, and parking cable. And a switching logic for fault tolerant control against the three sensor faults is suggested. Experimental results show that the proposed force estimation method satisfies the specifications of EPB system. The effectiveness of the fault detection method is validated with experimental results. Although a single sensor fault happens, EPB system with the proposed fault detection method does not develop into a failure on subsystem or system level.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.39-40
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• 2007

The analysis of fault current limiting characteristics according to variation of fault current level in the integrated three-phase flux-lock type superconducting fault current limiter (SFCL), which consisted of three-phase flux-lock reactor wound on an iron core with the same turn's ratio between coil 1 and coil 2 for each single phase, was performed. To analyze the current limiting characteristics of this integrated three-phase flux-lock type SFCL, the short circuit experiments was carried out the various three-phase faults such as the single line-to-ground fault, the double line-to-ground fault, the triple line-to-ground fault. From the experimental results, the fault current limiting characteristic was improved according to increase of fault current level.

• Proceedings of the KIEE Conference
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• 1997.07b
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• pp.542-544
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• 1997

The analysis of distribution line faults is essential to the proper protections in the power system. A high impedance fault does not make enough current to cause conventional protective devices. In this paper, Fractal dimensions are estimated for distinction between normal status and fault status in the power system. Application of the concepts of the fractal geometry to analyze chaotic properties of high impedance fault current was described. In addition, to analyze variation of fault current and normal current on phase plane, embedding state variables are reconstructed from 1 dimensional time series.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 1999.02a
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• pp.101-105
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• 1999

We have performed an EMTDC simulation for the current limiting effects of a superconducting fault current limiter (SFCL). The fault currents in the 154 kV transmission line between the Gaepo and Sungnam substations increased up to 54kA and 60kA during the line-to-line and three phase faults, respectively. The SFCL with 100 $\Omega$ of impedance after quench limited the currents to less than 17 kA within a half cycle. This limited current is well below the upper limit of a circuit breaker, suggesting that the impedance of the SFCL in the transmission line is sufficient.

• Proceedings of the KIEE Conference
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• summer
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• pp.473-475
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• 2004

During ground faults in power system, large current and raised potential appear at nearby places. This paper presents an analytical procedure of the ground fault current for the towers of a transmission line(154kV) and distribution line(22.9kV) of an arbitrary number of spans during ground faults. In order to economically and securely protect against undesired consequences, it is necessary to evaluate as precisely as possible the value and distribution of the ground fault current.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.11
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• pp.1091-1100
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• 2004

This paper presents an approach for the monitoring and detection of faults in induction machine by using data fusion technique and Dempster-Shafer theory Features are extracted from motor stator current and vibration signals. Neural network is trained and Hosted by the selected features of the measured data. The fusion of classification results from vibration and current classifiers increases the diagnostic accuracy. The efficiency of the proposed system is demonstrated by detecting motor electric and mechanical faults originated from the induction motors. The results of the test confirm that the proposed system has potential for real time application.