• Proceedings of the KIEE Conference
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• 1996.11a
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• pp.343-345
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• 1996

In the case of synchronous machines, certain power system disturbances cause current to assume negative values when no static converter is present. But the converter prevents negative current from flowing, so that overvoltages occur. The overvoltages can be effectively limited as crowbar circuit using GTO. The crowbar circuit with current limiting resistor absorbs energy when overvoltage comes from power system repeatedly. The newly proposed circuit is verified through simulation and experiment

• Proceedings of the KIEE Conference
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• 1994.11a
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• pp.153-155
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• 1994

This paper presents a new low loss snubber including the overvoltage snubber for three-level GTO inverters. The proposed snubber can not only minimizes the snubber loss and the number of components but also improve blocking voltage balancing problem between the inner and the outer GTOs.

• JOURNAL OF ELECTRICAL WORLD
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• no.4 s.88
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• pp.10-14
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• 1984

• Journal of the Korea Convergence Society
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• v.8 no.11
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• pp.287-292
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• 2017

The electrodeposition of Zn on the automotive parts has been adapted However, because Zn electrodeposit needs to increase thickness for corrosion protection, it has problem of destruction of electrodeposit Zn-based electrodeposit have teen studied for corrosion protection and decreasing electrodeposit thickness. Especially; Zn-Co electrodeposit have much attention In this study, the Composition of Zn-Co electrodeposit in various manufacturing condition such as temperature, current density and electrolyte content was investigated to understand effect of electrolysis condition on Co content of specimen. The results were explained by cathode overvoltage and diffusion coefficient. As the current density increases, the electrolyte temperature decreases, and as the electrolyte concentration decreases, the overvoltage of the cathode increases. As the overvoltage of the cathode increases, the concentration polarization becomes more important than the activation polarization. Concentration polarization is determined by the diffusion of the mass transfer in the diffusion layer. In a constant concentration polarization, a large amount of elements with a large diffusion coefficient is diffused. That is, as the overvoltage of the cathode increases, the Zn content having a large diffusion coefficient increases.

• Korean Journal of Materials Research
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• v.13 no.3
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• pp.160-168
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• 2003

The co-firing processes for the supported type planar solid oxide fuel cell were investigated. A flat cell of $7.7${\times}$10.8\textrm{cm}^2$ was fabricated successfully by the co-firing process, in which green films were co-sintered in the forms of two layers of anode/electrolyte or of three layers of anode/electrolyte/cathode with gas distributor. A co-fired cell of two layers yielded a power of 200 ㎽/$\textrm{cm}^2$ at 608 ㎷. Its performance loss was mainly due to iR drop in the anodic gas distributor, which was attributed to poor contact between anodic gas distributor and current collector. The performance in the co-fired cell of three layers was much lower than that of two layers, which resulted from the large iR drop and activation overvoltage at the cathodic side. In the co-fired cell of two layers, the impedance analysis indicated that the performance decay during cell operation is due to both anode overvoltage and iR drop at anode side. Also the electrode reaction of the co-fired two layers' cell is considered to be controlled by activation overvoltage within the low current of 50 ㎃.

• Journal of the Korean institute of surface engineering
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• v.46 no.3
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• pp.120-125
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• 2013

This investigation was to identify the electrochemical corrosion protection conditions to minimize the cavitation damage by generating hydrogen gas with the means of hydrogen overvoltage before the impact pressure of the cavity is transferred to the surface. The hybrid potentiostatic test method is designed to evaluate a complexed cavitation and electrochemical characteristic for ALBC3 alloy that is diverse and its broad applications fields in marine industry. The surface observation showed that neither the cavitation damage nor the electrochemical damage by the hydrogen gas generation occurred in the potential of -2.6 V under the cavitation environment. In the potentiostatic experiments under the cavitation environment, the cavities were reflected or cancelled out by the collision of the cavities with the hydrogen gas generated by the hydrogen overvoltage.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.761-767
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• 2001

In this paper, filtering techniques to reduce the adverse effects of motor leads on high-frequency PWM inverter fed AC motor drives will be examined. The filter was designed to keep the motor terminal from the cable surge impedance to reduce overvoltage reflections, ringing, and the dv/dt, di/dt. Therefore, filtering techniques are investigated to reduce the motor terminal overvoltage, ringing, and EMI noise in inverter fed ac motor drive systems. The output filter is used to limit the rate of the inverter output voltage and reduce EMI(common mode noise) to the motor. The performance of the output filter is evaluated through simulations (PSIM) and experiment on PWM inverter-fed ac motor drive(3phase, 3hp(2.2kw), input voltage 220/380V, induction motor). An experimental PWM drive system reduction of conducted EMI was implemented on an available TMS320C31 microprocessor control board. Finally, experimental results showed that the inverter output filter reduces more CM noise than the LPF(low pass filter) and reduce overvoltage and ringing at the motor terminal.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2009.10a
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• pp.339-341
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• 2009

Surge Protective Device(SPD) is installed by increasing information and communication equipments and home network equipments by individual home, and the amount of SPD used is increasing by revision industry regulations and strengthening equipotential grounding system. Parts of SPD installed in residential distribution board has ZnO varistor, voltage constraint type devices, but it is exposed to Temporary Overvoltage Characteristic. This thesis analyzes products through Thermal Stability test for SPD for general house and suggests the better method. As results of analysis, Gas Discharge Tube(GDT) to cut off from a leakage current and more than two kinds of safety devices to protect Thermal Runaway were needed.

• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.1
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• pp.99-104
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• 1999

The large scale industry needs high voltage converters. Therefore series connection of power semiconductor devices is necessary. It is important to prevent the overvoltage from being induced across a device above ratings by the proper voltage balancing in the field of IGBT series connection. In addition, the overvoltage induced by a stray inductance has to be limited in the high power circuit. This paper proposes a new gate control scheme which can balance the voltage properly and limit the overshoot by controlling the slope of collector voltage under the turn-off transient in the series connected IGBTs. The proposed gate control scheme which senses the collector voltage and controls the gate signal actively limits the overvoltage. The new series connected IGBT gate driver is made and its validity is verified by the experimental results in the series connected IGBT circuit.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.3
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• pp.331-337
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• 2014

The Korean distribution system consists of overhead ground wire (OHGW), phase conductors and neutral wire. Especially, OHGW is installed over the phase conductors to protect distribution system from the lightning surge. The flashover rate and the magnitude of lightning overvoltage on distribution system can be affected by grounding condition of OHGW such as grounding resistance and grounding interval. In this paper, we conduct an analysis of lightning overvoltage and flashover rate according to the grounding condition of OHGW. The distribution system and lightning surge are modeled by using ElectroMagnetic Transient Program (EMTP). Also, the Monte Carlo method is applied to consider random characteristics of lightning, and the flashover rate is calculated based on IEEE std. 1410. The simulations are performed by changing the grounding resistance and interval of OHGW and the simulation results are analyzed.