• Electrical & Electronic Materials
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• v.10 no.3
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• pp.255-261
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• 1997

In this study, pore-containing barium titanate ceramics were prepared with different porosities and pore sizes, in order to better understand how porosity and pore size affect electrical breakdown of barium titanate ceramics. A granulated barium titanate powder was mixed with three grades of commercial polymer microspheres up to 11wt%. The electrical breakdown test was performed at two different temperatures of 30.deg. C(below Tc) and 150.deg. C(above Tc) for samples immersed in a silicon oil bath using a 60kV de power supply. Electrical breakdown strength of pore containing barium titanate ceramics with porosity lower than 10% decreased as pore size and porosity increased. However, above the 10% porosity region, electrical breakdown strength decreased as the pore connectivity increased. From the experimental results, an optimum electrical breakdown model is proposed in an attempt to explain the effect of pores.

• Journal of the Korean Ceramic Society
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• v.33 no.11
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• pp.1217-1222
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• 1996

Undoped barium titanate ceramic samples with high density were produced by using both high purity hydro-thermally synthesized and oxalate-derived powders. Sintering temperature was varied in the temperature range 128$0^{\circ}C$-140$0^{\circ}C$ to control the average grain sizes of the samples. Electrical breakdown test was performed at two different temperature with 3$0^{\circ}C$(below Tc) and 15$0^{\circ}C$ (above Tc) for samples immersed in silicon oil bath using 60kV dc power supply. From the experimental results at below and above Curie temperature the grain size and thickness dependence of electrical breakdown strength for BaTiO3 ceramics was presented and breakdown behavior was also studied.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.385-388
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• 1997

As the environmental regulations become stricter, new machining technologies are being developed which takes envi ronmenta 1 aspects into account . Since cut t ing oi I has some impact on environment. many researches are being carried out to minimize the use of cutting oi I. The methods for minimizing cutting oil usage includes the following techniques: I ) Cooling of tools and work piece. 2) Useage of compressed cooling air for the removal of chip. 3) Minimal useage of environment-friendly vegetable cutt:ngoiI for lubrication between chip and tools. Since the turning machine is continuous, tools are under constant thermal load and tool wear increases as the lubricative performance degrades. Also surface roughnesses have a direct influence on turning. In order to examine the characteristics of turningmachining, this work investigates experimentally the degree of tool wear and characteristics of surface roughness in relation to machining conditions, supply methods, and cooling methods.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.486-489
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• 2003

To reduce lateral force of traditional plunger type piston in the swash plate type hydraulic piston pumps and motors, we have proposed rod type piston with ball joint on both ends. We have studied the theoretical reaction force on two types of piston moving in the cylinder block bore. and made an experiment for the resistance force measurement on a reciprocating motion of plunger and rod type piston, changing the test condition such as swash plate angel and supply oil pressure and so on. As a result. a rod type piston has more smaller resistance force, about 29%. than a plunger type one.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.3
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• pp.106-112
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• 2000

Since the oil crisis, we have been concerned about the energy saving techniques of electric generating systems. As a part of the effort to save energy, automatic electric load sharing device was developed. Usually, ship's electric generating system consists of two or three sets of generator. And, electric generating system is operated as single or parallel operation mode according to the demanded electric power. Therefore, it is important to investigate generators operating mode for the supply of required electric power in the ship in order to decrease the operating cost. So, this paper suggests the method to solve the optimal electric load distribution problem by dynamic programming. And, this thesis indicates that the proposed method is superior to the lagrange multiplier's method in obtaining optimal load distribution solution in the ship's electric generating system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.399.1-399
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• 2002

This paper describes the fluttering characteristics of the upper pad in a tilting pad journal bearing(6-pad, LOP type) using a steam turbine. In order to investigate the phenomena of the pad fluttering experimentally, the absolute vibration of the upper pads, the relative vibration between the bearing and the shaft and the circumferential distribution of the film thickness are measured under the different values of oil supply flow rate, shaft speed and bearing load. (omitted)

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.597-603
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• 2005

The remediation of railroad contaminated soil is gaining wide attention, recently. In railroad field, modification of diesel supply field, equipment of roll pad, FRP panel, and iron pannel under diesel locomotive storages are used for the prevention of contamination expansions. However, cheap and efficient remediation technology has not been suggested yet. In this study, the contaminated ballast was remediated by blasting technology. Because the contaminants mainly resides on the surface of ballast, blasting these contaminants make it available to recycle the ballast. We carried out the remediation of oil-contaminated ballasts using the blasting technology, and we could remediate them nicely. This technology is expected to be used for the cheap and quick remediation of contaminated ballast.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.10a
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• pp.178-183
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• 2000

Electrorheological(ER) effect on the dispersive system of polarizable fine powder/dielectric oil has been investigated. The electrical and rheological properties of zeolite and starch based ER fluid were reported. The ER fluids were constructed by mixing zeolite and starch power with two different dielectric oils. Yield stress of the fluids were measured on the couette cell type rheometer as a function of electric fields, particle concetrations, and temperatures. The electric field is applied by high voltage DC power supply. The outer cup is connected to positive electrode(+) and the bob becomes ground(-). And the temperatures the viscosity(or shear stress) versus shear rates were measured. In this experiment shear rates were increased from 0 to $200s^{-1}$ in 2 minutes.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.12
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• pp.2342-2348
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• 2009

Even though underground transmission cable is an essential transmission method to supply stable power for downtown and population center, the interaction of electromagnetic force by fault current is very large comparing to overhead transmission line due to restricted installation space such as tunnel, and close consideration is required for it. This paper presents countermeasures to reduce and release the effect of electromagnetic force with rope binding and installation of spacer and describes its efficacy through three phase short-circuit test, which will be utilized as basic materials for improvement and development of cleat, hanger, etc. to reduce and release effect of electromagnetic force in the future.

• Proceedings of the KIEE Conference
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• 2007.04a
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• pp.346-348
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• 2007

Underground pipe is an instrument to transport rapidly and safely a lot of fluid like gas, oil, water supply and drain system. It acts like blood vessels of human body in a modern industry. As in this country, the pipe facilities have been constructing since 1970's. The pipes constructed for a long time ago are already starting to reveal the problem like corrosion and most of them are built underground. So for companies, the managing of the underground pipes is very hard because it needs high technology and a lot of money. So we made a new robot system to repair and maintain the pipes at a low price. This new robot is devised using pressing wall type to work inside 700${\sim}$900(mm) size pipe. And it has good carrying and working power.