• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.2
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• pp.145-152
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• 2013

Electrolytic capacitors used for smoothing DC link voltage is one of the major root causes of fault in power electronic system. The aging of aluminum electrolytic capacitors is expressed by the increase of their equivalent series resistance (ESR) and the reduction of their capacitance. Thus, the proposed technique in this paper is to measure capacitance, by comparing energy loss of DC link capacitors with stator resistor in electric machine. Condition of DC link capacitors can be estimated from the capacitance decrease rate between initial and aged capacitors. The results show that the proposed technique provides an easy, widely applicable and simple low cost solution for detecting dc link capacitor degradation.

• Journal of Welding and Joining
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• v.26 no.4
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• pp.44-49
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• 2008

Generally, wear plate is steel plate having improved surface contact strength and impact strength by surface hardening which is welded using materials with good corrosion resistance, wear resistance and thermal resistance property. CFP GMAW(Compound Filler Plate Gas Metal Arc Welding) is the cladding method using GMAW with the CFP, which is bound with waterglass, on the substrate. It has advantages of reducing compound powder loss, uniform penetration, and preventing hardness decrease. To develope mass production technique of CFP GMAW process for production of high quality wear plate, the method for controling shallow penetration and increasing productivity is required. In this study, twin torch method applied to CFP GMAW process for increasing productivity. And the method was developed by controling penetration control, CFP dry time, gas formation flux and water glass concentration. As a result, applying twin torch method to CFP GMAW process was possible and high quality wide bead could be made without overlap joint.

• New & Renewable Energy
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• v.1 no.1 s.1
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• pp.37-43
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• 2005

High-efficiency silicon solar cells have potential applications on mobile electronics and electrical vehicles. The fabrication processes of the high efficiency cells necessitate com placated fabrication precesses and expensive materials. Ti/Pd/Ag metal contact has been used only for limited area In spite of good stability and low contact resistance because of Its expensive material cost and precesses. Screen printed contact formed by Ag paste causes a low fill factor and a high shading loss of commercial solar cells because of high contact resistance and a low aspect ratio. Low cost Ni/Cu metal contact has been formed by using a low cost electroless and electroplating. Nickel silicide formation at the interface enhances stability and reduces the contact resistance resulting In an energy conversion efficiency of $20.2\%\;on\;0.50{\Omega}cm$ FZ wafer. Tapered contact structure has been applied to large area solar cells with $6.7\times6.7cm^2$ in order to reduce power losses by the front contact The tapered front metal contact Is easily formed by the electroplating technique producing $45cm^2$ solar cells with an efficiency of $21.4\%$ on $21.4\%\;on\;2{\Omega}cm$ FZ wafer.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.262-265
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• 2003

During magnetic inrush or over-excitation saturation of the core in a transformer draws a large exciting current. This can cause mal-operation of a differential relay. This paper proposes a modified current differential relay for transformer protection. In order to cope with the remanent flux at the beginning. the start of saturation of the core is detected and the core flux at the instant is estimated by inserting the differential current into a magnetization curve. Then, this core flux value can be used to calculate the core flux. The proposed relay calculates the core-loss current from the induced voltage and the core-loss resistance; the relay calculates the magnetizing current from the core flux and the magnetization curve. Finally, the relay obtains the modified differential current by subtracting the core-loss current and the magnetizing current from the conventional differential current. The proposed technique not only discriminates magnetic inrush and over-excitation from an internal fault, but also improves the speed of the conventional relay.

• The Korean Journal of Pain
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• v.10 no.1
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• pp.73-76
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• 1997

Background : Epidural anesthesia is now accepted as a popular technique for pain relief and anesthesia. However, accidental dural puncture may occur during placement of the epidural needle. This study was undertaken to evaluate difference of the epidural depth between parturients and non-parturients. Method : Eighty non-parturients receiving epidural anesthesia were assigned to group I, and eighty parturients whose body weight had not yet increased over 15 kg from pregnancy were assigned to group II. With patients in lateral decubitus position, 18 guage Tuohy needle was punctured by approaching at $L_{3-4}$ interspace. Epidural space was identified using loss-of-resistance to air technique. Result : Epidural depth was 4.18 cm and 4.25 cm in group I and group II respectively. There was no significant statistical difference in body mass index(BMI) and ponderal index(PI) (p<0.05), nor in epidural depth between the two groups. Conclusion : Epidural needle need not be placed deeper in parturients than in nonparturients.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.565-572
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• 2009

In this study, corrosion resistance of palm oil fuel ash (POFA) concrete as a blended concrete is evaluated by using electrochemical technique. The POFA is an industrial byproduct obtained from fuel ash after extracting palm oil from palm-tree. In order to obtain basic material characteristics of the POFA concrete, tests on compressive strength, slump, weight loss, bleeding and expansion ratio were carried out the early-aged POFA concrete. On the other hand, durability characteristics, both chloride penetration and carbonation depth test, were also conducted. Finally, corrosion resistance were evaluated by applying electro-chemical artificial crack healing technique, and the tests on the impressed voltage characteristic, galvanic current and linear polarization resistance. From the experimental results, it was found that long-term strength, bleeding, lower slump ratio, expansion ratio, chloride penetration, carbonation and corrosion resistance were improved by using the POFA due to activated pozzolanic reaction. It can be also mentioned that POFA concrete has a potential to be used as a cementitious binder for green-recycling resources.

• Journal of the Korean Society for Heat Treatment
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• v.18 no.6
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• pp.369-374
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• 2005

Nitrogen ion implantation in Nimonic 80A using plasma immersion ion implantation (PIII) was investigated at a pulse voltage of -60 kV and ion dose of $3{\times}10^{17}{\sharp}/cm^2$, $6{\times}10^{17}{\sharp}/cm^2$, $12{\times}10^{17}{\sharp}/cm^2$. PIII is an effective technology to improve the surface hardness and wear resistance of materials. And also this technology is not limited by the shape and size of materials. PIII would be a promising technique in the future. Surface hardness and wear resistance of the $N^+$ ion implanted Nimonic 80A were increased with the increase in the incident ion dose. The surface hardness of the untreated Nimonic 80A is 420 Hv, the hardness of implanted Nimonic 80A is 1050 Hv at $N^+$ ion dose of $12{\times}10^{17}{\sharp}/cm^2$. The wear loss of the untreated is 82.5 mg, the wear loss of the implanted is 0.004g at $N^+$ ion dose of $12{\times}10^{17}{\sharp}/cm^2$. The $Cr_2N$ is detected on the surface of the implanted Nimonic 80A by XRD analysis.

• Journal of Electrical Engineering and Technology
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• v.9 no.6
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• pp.2042-2048
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• 2014

In medium voltage electrical distribution networks, reforming the loss reduction is important, and in line with this, the issue of system engineering and use of proper equipment Expansion of distribution systems results in higher system losses and poor voltage regulation. Therefore, an efficient and effective distribution system has become more important. So, proper selection of conductors in the distribution system is crucial as it determines the current density and the resistance of the line. Evaluation of aging conductors for losses and costs imposed in addition to the careful planning of technical and economic networks can be identified in the network design. In this paper the use of imperialist competitive algorithm; genetic algorithm; is proposed to optimal branch conductor selection and reconstruction in radial distribution systems planning. The objective is to minimize the overall cost of annual energy losses and depreciation on the cost of conductors to improve productivity given the maximum current carrying capacity and acceptable voltage levels. Simulations are carried out on 69-bus radial distribution network using genetic algorithm approaches to show the accuracy as well as the efficiency of the proposed solution technique.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.10
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• pp.1780-1785
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• 2016

This paper presents few case studies of state diagnosis of XLPE cables using very low frequency techniques. The power cables of 22.9kV which have installation fault were assessed using VLF technique in addition to other techniques like insulation resistance and DC voltage withstand test. From the experimental results, The dielectric loss($tan{\delta}$) values of degradation of the cable(joint, knife, needle) at $U_0$ were 5.839, 5.526 and 6.251, respectively and all values were "further study advised". VLF PD measurement was also found defective portion. These method was effective in defect to fault in the degradation of the cable. However, the breakdown did not occur in the degradation of the cable because of properties of XLPE insulation. Few case studies of using VLF $tan{\delta}$ diagnosis for fault are measured and analyzed. The $tan{\delta}$ values at $U_0$ were "further study advised" or "action required".

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.73.1-73.1
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• 2010

For the successful cold starting of a fuel cell engine, either internal of external heat supply must be made to overcome the formation of ice from water below the freezing point of water. In the present study, switchable vanadium oxide compounds as variable temperature-electrical resistance materials onto the surface of flat metallic bipolar plates have been prepared by a dip-coating technique via an aqueous sol-gel method. Subsequently, the chemical composition and micro-structure of the polycrystalline solid thin films were analyzed by X-ray diffraction, X-ray fluorescence spectroscopy, and field emission scanning electron microscopy. In addition, it was carefully measured electrical resistance hysteresis loop over a temperature range from $-20^{\circ}C$ to $80^{\circ}C$ using the four-point probe method. The experimental results revealed that the thin films was mainly composed of Karelianite $V_2O_3$ which acts as negative temperature coefficient materials. Also, it was found that thermal dissipation rate of the vanadium oxide thin films partially satisfy about 50% saving of the substantial amount of energy required for ice melting at $-20^{\circ}C$. Moreover, electrical resistances of the vanadium-based materials converge on an extremely small value similar to that of pure flat metallic bipolar plates at higher temperature, i.e. $T{\geq}40^{\circ}C$. As a consequence, experimental studies proved that it is possible to apply the variable temperature-electrical resistance material based on vanadium oxides for the cold starting enhancement of a fuel cell vehicle and minimize parasitic power loss and eliminate any necessity for external equipment for heat supply in freezing conditions.