• Journal of Power Electronics
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• v.16 no.6
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• pp.2258-2271
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• 2016

In this paper, some crucial performance characteristics related to the operational reliability of the post-fault Pulse Width Modulated (PWM) rectifiers, such as line current harmonic distortion, Common Mode Voltage (CMV), and current stress on the capacitors, are fully investigated. The aforementioned performance characteristics of post-fault rectifiers are highly dependent on the utilized space vector modulation (SVM) schemes, which are also examined. Detailed analyses of the three most commonly used SVM schemes for post-fault PWM rectifiers are provided, revealing the major differences in terms of the zero vector synthesis approaches. To compare the performances of the three SVM schemes, the operating principles of a post-fault rectifier are presented with various SVM schemes. Using analytical and numerical methods in the time domain, the performances of the line current distortion, common mode voltage and capacitor current are evaluated and compared for each SVM scheme. The proposed analysis demonstrates that the zero vector synthesis approaches of the considered methods have significant impacts on the performance characteristics of rectifiers. In addition, the advantages and disadvantages of the proposed SVM schemes are discussed. The experimental results verify the effectiveness and validity of the proposed analysis.

• Progress in Superconductivity and Cryogenics
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• v.10 no.1
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• pp.42-47
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• 2008

In this paper, the fault current limiting characteristics for the superconducting fault current limiter(SFCL) using magnetic coupling between two coils were investigated. The SFCL consists of a high-$T_c$ superconducting(HTSC) element and two coils. This SFCL has different characteristics that depend on the connection form, the winding direction and the inductance ratio of two coils. The impedance and the operational current of the SFCL can be adjusted higher or lower than the resistance and the critical current of HTSC element. Therefore, the SFCL can change the amplitude of the limited fault current. To confirm it, the HTSC element was modeled and the fault current limiting characteristics of the SFCL were analysed through computer simulation. It was obtained from the analysis that the connection form and the winding direction of two coils of the SFCL were the important design parameters.

• Tunnel and Underground Space
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• v.29 no.6
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• pp.394-406
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• 2019

Difficult ground conditions (e.g., fault zone and mixed grounds) are highly probable to appear in subsea and urban tunnels because of the shallow working depth and alluvial characteristics. TBM usually experienced decrease of penetration rate and increase of downtime when it meets these difficult ground conditions. The problems are usually caused by the adverse geological conditions, and it is preferable to determine the optimal operational parameters of TBM based on the previous operational data obtained while excavating a preceding tunnel. This study carried out for efficient TBM excavation in fault zone and mixed grounds. TBM excavation data from the tunnel site in Singapore and the characteristics of the TBM excavation data was analyzed. The key operational parameters (i.e., thrust, torque, and RPM), penetration rate, and downtime were highly influenced by the presence of fault zones and mixed grounds, and the features was discussed. It is expected that the results and main discussions will be useful information for future tunneling projects in similar geological conditions.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.2
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• pp.278-283
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• 2013

With the increasing power demands, size of the fault current in electrical grids is steadily increasing, and it exceeds the breaking capacity of circuit breakers. To effectively cope with these problems, a high-speed interrupter was suggested. The high-speed interrupter provides fault current with a bypass to a fault current limiter in case of accidents and consequently, fault current can be restricted. In this study, behavioral characteristics of high-speed interrupter were analyzed by accident types occurred in a distribution system. When accidents occurred, a and b contact of the high-speed interrupter were turned-off and then, turned-on. Accordingly, fault current flowed to the circuit connected to a current limiting element, and the fault current limiter restricted fault current to within a half-cycle. Nevertheless, the behavior of the high-speed interrupter was slowed down by a switching surge. As a result, fault current was confirmed to be restricted not to within the anticipated half-cycle, but to after a half-cycle. Moreover, the behavioral characteristics of the high-speed interrupter changed not only by accident types, but by behaviors of R, S, and T phases. This was due to the errors in stroke lengths of the high-speed interrupters, which resulted in a slight time discrepancy among three interrupters. In addition, the switching behaviors of the b and a contact were confirmed not to have coincided due to the switching surge; b contact behaved first and a contact followed. because of this, accuracy of stroke length and switching surges through the solenoid suction increases may be necessary to resolve.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.6
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• pp.271-277
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• 2003

It is important to control layer current distributions of coaxial multi-layer HTS cables, because a homogeneous layer current distribution decreases AC loss and can supply the largest operational current. We have extended the theory that treat the operational current more than the critical current by considering V-I nonlinear characteristics of HTS tapes including flux flow resistance and contacting resistance between the cable and terminals. It is important to investigate the current distribution under the condition of operational current more than the critical current of cable, because the cable has experiences of fault current. In order to verify the extended theory, we have fabricated a two layers cable with the same twisting layer pitch. It was observed that almost all the operational current less than the critical current flowed on the outer layer because of its lower inductance. In case of operational current more than critical currents of layers, the flux flow resistances affect strongly current waveform and thereby the currents of layers were determined by the flux flow resistances. And we investigated breakdown characteristics in $LN_{2}$/paper composite insulation system for the application to a HTS cable. In this experiment, we got some information out of that the electrical characteristics of the insulation materials depends on the condition of butt gap.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.2
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• pp.300-304
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• 2017

Due to the introduction of various types of dispersed generations (DGs) with larger capacity in a power distribution system, the short-circuit current is expected to be increased, which more requires for the effective fault current limiting methods. As one of the promising countermeasures, the superconducting fault current limiter (SFCL) has been noticed. However, the decreased fault current by SFCL affects the operation of the overcurrent relay (OCR), representative protective device in a power distribution system. In this paper, the operation of the overcurrent relay due to the application of a SFCL in a power distribution system with DG linked by its bus line was analysed through the short-circuit tests. To analyze the effect of the SFCL application in a power distribution system with DG, the experimental simulated circuits were designed and the short-circuit tests for the power distributed system assembled with the DG, the OCR and the SFCL were carried out. Through the analysis on the short-circuit tests, the application of the SFCL in a power distribution system with DG could be confirmed to be contributed to the operational improvement of overcurrent relay.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.8
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• pp.3779-3784
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• 2012

Real-time process monitoring and diagnosis of industrial processes is one of important operational tasks for quality and safety reasons. The objective of fault diagnosis or identification is to find process variables responsible for causing a specific fault in the process. This helps process operators to investigate root causes more effectively. This work assesses the applicability of combining a nonlinear statistical technique of kernel Fisher discriminant analysis with a preprocessing method as a tool of on-line fault identification. To compare its performance to existing linear principal component analysis (PCA) identification scheme, a case study on a benchmark process was performed to show that the fault identification scheme produced more reliable diagnosis results than linear method.

• Journal of Advanced Research in Ocean Engineering
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• v.3 no.3
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• pp.125-135
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• 2017

The paper considers the practical application of the FMEA(Failure Mode and Effect Analysis) method to assess the operational reliability of the LNG(Liquefied Natural Gas) transfer system, which is a potential problem for the connection between the LNG FPSO and LNG carrier. Hazard Identification (HAZID) and Hazard operability (HAZOP) are applied to identify the risks and hazards during the operation of LNG transfer system. The approach is performed for the FMEA to assess the reliability based on the detection of defects typical to LNG transfer system. FTA and FMEA associated with a probabilistic risk database to the operation scenarios are applied to assess the risk. After providing an outline of the safety assessment procedure for the operational problems of system, safety assessment example is presented, providing details on the fault tree of operational accident, safety assessment, and risk measures.

• Proceedings of the KIEE Conference
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• 2002.11b
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• pp.134-136
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• 2002

In April of 2000, the Korea Power Exchange(KPX) was introduced into Korea electricity market. The purpose of this paper is to describe how the system operator indicates operational risks between the transmission planning and the supply and demand growth to make the market "work" and manage the power system in real time. This paper describes the experiences of kpx about the indication of operational risks including, for example, contingency analysis, voltage profile and fault capacity of three-phase short current.

• Progress in Superconductivity and Cryogenics
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• v.5 no.1
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• pp.103-106
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• 2003

The short circuit current problem is one of the operational problems that need to be solved by power system engineers in Korea. It is an important issue in the Seoul metropolitan area especially because of highly meshed configuration. Currently, it is regulated by changing 154 kV system configuration from loop connection to radial system, by splitting of the bus where load balance can be achieved, and by upgrading circuit breaker rating. A development project for 154 kV/2 KA SFCL application to 154 kV transmission system after 2010 is proceeding. In this paper, a feasibility study of superconducting fault current limiter (SFCL) is carried out in Seoul metropolitan area to find out the effects of its application and feasibility. This study shows that it can reduce fault current considerably, and as it can minimize the upgrading of circuit breaker rating, the economic potential of SFCL is evaluated positively.