• Progress in Superconductivity
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• v.6 no.1
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• pp.46-51
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• 2004

We fabricated a resistive type superconducting fault current limiter (SFCL) of 3-phase $6.6 kV_{rms}$ / rating, based on YBCO thin films grown on sapphire substrates with a diameter off inch. Each element of the SFCL was designed to have the rated voltage of $600 V_{rms}$ $/35A_{rms}$. The elements produced a single phase with 8${\times}$6 components connected in series and parallel. In addition, a NiCr shunt resistor of 23 $\Omega$ was connected in parallel to each of them for simultaneous quenches between the elements. Prior to investigating the performance of the 3 phase SFCL, we examined the quench characteristics for 8 elements connected in series. For all elements, simultaneous quenches and equal voltage distribution within 10% deviation from the average were obtained. Based on these results, performance of the SFCL for single line-to-ground faults was investigated. The SFCL successfully limited the fault current of $10 kA_{ rms}$ below 816 $A_{peak}$ within 0.12 msec right after the fault occurred. During the quench process, average temperature of all components did not exceed 250 K, and the SFCL was totally safe during the whole operation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.4
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• pp.737-746
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• 2009

In this study, we have developed one chip system IC for preventing the overload, detecting an abnormal conditions, and controlling the fire prevention in the intelligent home appliances. For the purpose, a circuit detectable an electric leak for preventing an electric shock, and a circuit detectable arc that has effect directly on the fire are designed. The circuits designed on every block are verified by comparing simulation with bread-boarding using a standard transistors. The system IC is fabricated by using 34 V 2 metal $1.5{\mu}m$ bipolar transistor process from evaluation results. The electrical performances of IC application circuits and the system IC equipped on PCB board are evaluated. It is confirmed that the system IC is well operated for arc and ground fault(GF) signal.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1529-1532
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• 2007

Failure Mode, Effects, and Criticality Analysis (FMECA) is an extension of FMEA which includes a criticality analysis. The criticality analysis is used to chart the probability of failure modes against the severity of their consequences. The result highlights failure modes with relatively high probability and severity of consequences, allowing remedial effort to be directed where it will produce the greatest value. However, there are several limitations. Measuring severity of failure consequences is subjective and linguistic. Since The result of FMECA only gives qualitative and quantitative informations, it should be re-analysed to prioritize critical units. Fuzzy set theory has been introduced by Lotfi A. Zadeh (1965). It has extended the classical set theory dramatically. Based on fuzzy set theory, fuzzy logic has been developed employing human reasoning process. IF-THEN fuzzy rule based assessment approach can model the expert's decision logic appropriately. Fault tree analysis (FTA) is one of most common fault modeling techniques. It is widely used in many fields practically. In this paper, a simple fault tree analysis is proposed to measure the severity of components. Fuzzy rule based assessment method interprets linguistic variables for determination of critical unit priorities. An rail-way transforming system is analysed to describe the proposed method.

• Journal of the Korea Computer Industry Society
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• v.3 no.7
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• pp.837-844
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• 2002

In general, software test is carried out to detect or repair errors in system during software development process. Namely, we can evaluate software reliability through collecting and removing the faults detected in testing phase. Software reliability growth model evaluates reliability of software mathematically. Many kinds of software reliability growth modeling which modeling the processes of detecting, revising and removing the faults detected in testing phase have been proposed in many ways. and, it is assumed that almost of these modeling have one typed detect and show the uniformed detection rate. In this study, significance levels of the faults detected in test phase are classified according to how they can affect on the whole system and then the fault detection capability of them is applied. From this point of view, We here by propose a software reliability growth model with faults detection capability according considering fault significance levels and apply some fault data to this proposed model and finally verify its validity by comparing and estimating with the existing modeling.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.3
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• pp.268-273
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• 2009

The roller bearings play an important role not only sustain radial or axial load of system, but carry out a rotatory movement as a various operating conditions. They happen that incipient faults which were caused by excessive load, manufacturing or assembling process's errors and many other reasons are created. The bearing faults make noise and vibration by a continuous collision of rotatory components, which can lower the quality and stability of auto-transmission. Therefore, it is important to detect the early fault as soon as possible. This paper presents a detecting method for the improvement in quality by developing the program which can be used to analyze and predict the vibrational characteristics caused by roller bearing faults. We completed development of the inspection system of vibration by applying the most efficient detecting methods and verified the system's reliability through experiments.

• Nuclear Engineering and Technology
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• v.33 no.1
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• pp.1-11
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• 2001

In contrast with conventional fieldbus researches which are focused merely on real-time performance, this study aims to evaluate the real-time performance of the communication system including fault-tolerant mechanisms Maintaining performance in presence of recoverable faults is very important in case that the communication network is applied to a highly reliable system such as next generation Nuclear. Power. Plant (NPP). If the tie characteristics meet the requirements of the system, the faults will be recovered by fieldbus recovery mechanisms and the system will be safe. If the time characteristics can not meet the requirements, the faults in the fieldbus can propagate to the system failure. In this study, for the purpose of investigating the time characteristics of fieldbus, the recoverable faults are classified and then the formulas that represent delays including recovery mechanisms are developed. In order to validate the proposed approach, we have developed a simulation model that represents the Korea Next Generation Reactor (KNGR) NSSS Process Control System (NPCS). The results of the simulation show us the reasonable delay characteristics of the fault cases with recovery mechanisms. Using the simulation results and the system requirements, we also can calculate the failure propagation probability from fieldbus to outer system.

• Journal of the Korean Society for Railway
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• v.11 no.6
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• pp.530-535
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• 2008

After train fire accident in Daegue, many research on train fire safety improvement have been carrying out. Since many alternative fire safety measures can be applied in our railway system, the effect of the each safety measure must be quantified prior to the safety investment. In order to estimate the effects of each safety measure quantitatively, fault trees and event trees are constructed in this study. Results can be applied for cost-benefit analysis or sensitivity analysis for safety measures in risk assessment process.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.20 no.5
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• pp.49-57
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• 2010

The fault cryptanalysis is a physical attack in which the key stored inside of the device can be extracted by occurring some faults when the device performs cryptographic algorithm. Since the international signature standard DSA(Digital Signature Algorithm) was known to be vulnerable to some fault analysis attacks, many researchers have been investigating the countermeasure to prevent these attacks. In this paper we propose a new countermeasure to compute DSA signature that has its immunity in the presence of faults. Since additional computational overhead of our proposal is only an inverse operation in signature process, the proposed DSA scheme can be implemented more efficiently compared to previous countermeasures.

• Progress in Superconductivity and Cryogenics
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• v.8 no.2
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• pp.43-45
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• 2006

Recently, the resistive Fault Current Limiter (SFCL) made with Coated Conductor (CC) has been researched with an advanced capability in CC. Current limiting elements must be connected in series in order to fabricate the resistive SFCL having large capacity. By the way, unless the applied voltage in the SFCL is distributed to the elements when the fault occurred, those elements will be critically damaged. Thus simultaneous quench of the elements is an important factor to design the resistive SFCL. In this paper, simultaneous quench characteristics of current limiting module by using BSCCO 2223 were researched before manufacturing the resistive SFCL by using CC. At the first fault stage, the elements generated the resistance at the same time. However, the unequal voltage is applied to the each element in process of time. The method is suggested to solve the problem of the unequal distribution. These experimental results will play an important part in developing for the resistive SFCL by using CC.

• Journal of Power Electronics
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• v.17 no.4
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• pp.1014-1026
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• 2017

The traditional fault diagnosis method for photovoltaic (PV) inverters has a difficult time meeting the requirements of the current complex systems. Its main weakness lies in the study of nonlinear systems. In addition, its diagnosis time is long and its accuracy is low. To solve these problems, a hidden Markov model (HMM) is used that has unique advantages in terms of its training model and its recognition for diagnosing faults. However, the initial value of the HMM has a great influence on the model, and it is possible to achieve a local minimum in the training process. Therefore, a genetic algorithm is used to optimize the initial value and to achieve global optimization. In this paper, the HMM is combined with a genetic algorithm (GHMM) for PV inverter fault diagnosis. First Matlab is used to implement the genetic algorithm and to determine the optimal HMM initial value. Then a Baum-Welch algorithm is used for iterative training. Finally, a Viterbi algorithm is used for fault identification. Experimental results show that the correct PV inverter fault recognition rate by the HMM is about 10% higher than that of traditional methods. Using the GHMM, the correct recognition rate is further increased by approximately 13%, and the diagnosis time is greatly reduced. Therefore, the GHMM is faster and more accurate in diagnosing PV inverter faults.