• Proceedings of the KSR Conference
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• 2008.11b
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• pp.196-201
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• 2008

In DC traction systems, a part of feedback current returning through rails becomes leakage current, illumination on a metal laid underground results from the leakage current to ground. To prevent the leakage current on rails, feedback rails almost have insulated with the ground. Insulation between rails and the ground causes that the earth method changes a isolated method in DC traction systems. the rail potential rise results in the isolated method. the rail potential rise causes an electric shock when a person touches the ground and rolling stock. To decrease the rail potential rise and leakage current, there are methods for reducing the feedback resistance and current of rails, increasing the leakage resistance, decreasing the distance between substations. But it are necessary to forecast and analyze the rail potential and amplitude of leakage current. In this paper, we modeled DC traction systems and feedback circuit to simulate the rail potential and amplitude of leakage current using PSCAD/EMTDC that is power analysis program, forecasted the rail potential and amplitude of leakage current about changing various parameters in the electric circuit. By using the simulation model, we easily will forecast the rail potential and amplitude of leakage current in case of a level of basic design and maintenance in electric railway systems, valuably use basic data in case of system selection.

• Journal of Biomedical Engineering Research
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• v.15 no.2
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• pp.135-142
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• 1994

This paper presents average method to detect Visual-Transient Evoked Potential from the human scalp electric potential measured by the ElectroEncephaloGram. To confirm the validity of average method, the average-process is performed with both stimulated and no-stimulated potentials respectively, and both results are compared. The specific waveform, which is visual-transient evoked potential, is produced only in the case of stimulated potential. It was found that a dc-drift, due to instrumentation errors and other noises, can produce significant changes in the evoked-potential waveform. This can be removed with a high-pass filter (cut-off frequency=0.5Hz).

• KEPCO Journal on Electric Power and Energy
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• v.6 no.4
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• pp.419-425
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• 2020

DC distribution system has been evaluated as an excellent one in comparison with existing AC distribution network because it needs fewer power conversion stages and the full capacity of the equipment can be used without consideration for power factor. Recently, research and development on the implementation of DC distribution networks have been progressed globally based on the rapid advancement in power-electronics technology, and the technological developments from the viewpoint of infrastructure are also in progress. However, to configure a distribution network which is a distribution line for DC, more accurate and rapid introduction of analysis technology is needed for the monitoring, control and operation of the system, which ensure the system run flexible and efficiently. However, in case of a bipolar DC distribution network, there are two buses acting as slack buses, so the Jacobian matrix cannot be configured. Without solving this problem, DC distribution network cannot be operated when the network is unbalanced. Therefore, this paper presented a comprehensive method of analysis with consideration of operating elements which are directly connected between neutral electric potential caused by the unbalanced of load in DC distribution network with bipolar structure.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1552-1553
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• 2011

The HVDC transformer which is one of the main equipments for HVDC(High Voltage Direct Current) electric power transmission systems is exposed to not only AC voltage but also the inflowing DC voltage which comes from the DC-AC converter systems. Therefore, the HVDC transformer insulation system is required to withstand the electric field stress under AC, DC and DC polarity reversal conditions. However the electric field distributions under those conditions are different because the AC electric field and DC electric field are governed by permittivity and conductivity, respectively. In this study, the changes of electric potential and electric field of conventional AC transformer insulation system under DC polarity reversal test condition were analyzed by FEM(Finite Element Method). The DC electric field stress was concentrated in the solid insulators while the AC electric field stress was concentrated in the mineral oil. In addition, the electric stress under that condition which is affected by the surface charge accumulation at the interfaces between insulators was evaluated. The stress in some parts could be higher than that of AC and DC condition, during polarity reversal test. The result of this study would be helpful for the HVDC transformer insulation system design.

• Progress in Superconductivity and Cryogenics
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• v.5 no.1
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• pp.56-59
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• 2003

As electric power systems grow to supply the increasing electric power demand short-circuit current tends to increase and impose a severe burden on circuit breakers and power system apparatuses. Thus, all electric equipment in a power system has to he designed to withstand the mechanical and thermal stresses of potential short-circuit currents. Among current limiting devices, Fault Current Limiter (FCL) is expected to reduce the short-circuit current. Especially, Superconducting Fault Current Limiters (SFCL) offer ideal performance: in normal operation the SFCL is in its superconducting state and has negligible impedance, in the event of a fault, the transition into the normal conducting state passively limits the current. The SFCL using high-temperature superconductors offers a positive resolution to controlling fault-current levels on utility distribution and transmission networks. This study contributes to the EMTDC based modeling and simulation method of DC Reactor type SFCL. Single and three phase faults in the utility system with DC reactor type SFCLs have been simulated using EMTDC in order to coordinate with other equipments, and the results are discussed in detail.

• Proceedings of the KIPE Conference
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• 2008.06a
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• pp.97-99
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• 2008

It is possible to suppress voltage drops, power loading fluctuations and regeneration power lapses for DC railway systems by applying an energy storage system. Recently the electric double layer capacitor (EDLC) of the rapid charge/discharge type has been developed and used in wide ranges. The on board energy storage system with supercapacitor for railway vehicles presented in this paper seems to be a reliable technical solution with an enormous energy saving potential. In this paper, an efficient charge and discharge control method of a bidirectional DC-DC converter using the supercapacitor is proposed.

• Proceedings of the KIEE Conference
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• 2007.10c
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• pp.217-219
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• 2007

With the wide spread of direct current(DC) electric railroads in Korea, the stray current or leakage currents from negative return rails become a pending problem to the safety of nearby underground Infrastructures. The most widely used mitigation method for this interference is the stray current drainage method, which connects the underground metallic structures to the rails with diodes (polarized drainage) or thyristor (forced drainage). This method, however, inherently possesses some drawbacks such as an increase of total leakage torrents from rails, expansion of interference zone, etc. In order to resolve these drawbacks, we developed a rapid potential-controled rectifier and applied to a depot area where stray current inference is very severe. The effect of this method was analyzed from the field tell data and we suggest this method can be an excellent alternative to the drainage-bond-based mitigation methods.

• Proceedings of the KIEE Conference
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• 1999.07a
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• pp.79-82
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• 1999

So far, The methods for identifying the parameters of some region or material have been developed. This paper describes a new method for electric resistivity reconstruction using multi-resolution property of wavelet. The outputs of the potential electrodes are computed using two dimensional FEM in the wave number space by Fourier transforming the governing equation. The resistance distribution in the region of interests, which makes the computed potential distribution coincide with the measured potential, is found by minimizing the objective function using an optimization method. Multi-resolution analysis introduced in this paper will be proved to be the proper method in the viewpoint of effectivity and time-consuming by the numerical results.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.4
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• pp.892-898
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• 2011

In DC electric railways, while an electric rail car is driving, a part of the working current returned to the substation through rails leaks into the ground. Such a stray current causes railway facilities and metal objects to corrode electrolytically. Therefore, change of stray current needs to be monitored constantly. But so far in domestic, the research on stray current measuring techniques and system adaption are insufficient. To estimate stray current, this paper addresses a method of monitoring the return current that is returned into the negative pole of the substation in real time.

• Journal of Power Electronics
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• v.18 no.2
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• pp.445-455
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• 2018

A novel algorithm is proposed to regulate the neutral point potential in neutral point clamped three-level inverters. Oscillations of the neutral point potential and an unbalanced dc-link voltage cause distortions of the output voltage. Large capacitors, which make the application costly and bulky, are needed to eliminate oscillations. Thus, the algorithm proposed in this paper utilizes the finite-control-set model predictive control and the multistage medium vector to solve these issues. The proposed strategy consists of a two-step prediction and a cost function to evaluate the selected multistage medium vector. Unlike the virtual vector method, the multistage medium vector is a mixture of the virtual vector and the original vector. In addition, its amplitude is variable. The neutral point current generated by it can be used to adjust the neutral point potential. When compared with the virtual vector method, the multistage medium vector contributes to decreasing the regulation time when the modulation index is high. The vectors are rearranged to cope with the variable switching frequency of the model predictive control. Simulation and experimental results verify the validity of the proposed strategy.