• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.5B no.2
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• pp.103-110
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• 2005

Broken rotor bars in induction motors can be detected by monitoring any abnormality of the spectrum amplitudes at certain frequencies in the motor current spectrum. Broken rotor bar fault detection schemes should rely on multiple signatures in order to overcome or reduce the effect of any misinterpretation of the signatures that are obscured by factors such as measurement noises and different load conditions. Multiple Discriminant Analysis (MDA) and Artificial Neural Networks (ANN) provide appropriate environments to develop such fault detection schemes because of their multi-input processing capabilities. This paper describes two fault detection schemes for broken rotor bar fault detection with multiple signature processing, and demonstrates that multiple signature processing is more efficient than single signature processing.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1276-1281
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• 2004

Nowadays CFCs and HCFCs refrigerants are restricted because it cause depletion of ozone layer. Accordingly, this experiment apply the ammonia gas and not CFCs and HCFCs for refrigerant to study the performance characteristic from the superheat control and improve the energy efficiency from the high performance. The condensing pressure of refrigeration system is increased from 15.0bar to 16bar by 0.5bar and superheat temperature is increased from $0^{\circ}C$ to $10^{\circ}C$ by $1^{\circ}C$ at each condensing pressure. As the result of experiment, when the superheat temperature is $0^{\circ}C$ at each condensing pressure, the refrigeration system has the high performance.

• Architectural research
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• v.8 no.2
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• pp.37-42
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• 2006

Starting from the quadratic optimal control algorithm, this study obtains the relation of the performance index for constrained systems and Gauss's principle. And minimizing a function of the variation in kinetic energy at constrained and unconstrained states with respect to the velocity variation, the dynamic equation is derived and it is shown that the result compares with the generalized inverse method proposed by Udwadia and Kalaba. It is investigated that the responses of a 10-story building are constrained by the installation of a two-bar structure as an application to utilize the derived equations. The structural responses are affected by various factors like the length of each bar, damping, stiffness of the bar structure, and the junction positions of two structures. Under an assumption that the bars have the same mass density, this study determines the junction positions to minimize the total dynamic responses of the structure.

• The KSFM Journal of Fluid Machinery
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• v.7 no.4 s.25
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• pp.24-31
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• 2004

The aim of this study is to provide fundamental information for the development of Semi-Active Damper Using Magnetic fluid. To achieve the aim, the damping effect of magnetic fluid is investigated by experiments that the diameter of inner circular bar and the input amplitude were varied in the magnetic field generated by the permanent magnet and the electromagnet coil. From the study, the following conclusive remarks can be made. As the diameter of inner circular bar and input amplitude increase, the damping effect is improved. This is explained by the fact that as the contact area between inner circular bar and magnetic fluid increases, the increase of friction lowers kinematic energy. If the magnetic field is generated, the damping effect is improved. This is explained the assumption that as the intensity of magnetic fluid particle increases, there is virtual mass phenomenon.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.11
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• pp.1647-1650
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• 2017

Bus bars are used in place of cables because they can carry more electrical energy with the same volume of conductors. This paper deals with the electrical properties of ceramic coating material for busbars. A ceramic coated samples were prepared for the electrical properties test. There are two types of samples. One is a sample without degradation, and the other is a sample degraded for 30 days. Four electrical properties tests were carried out in accordance with domestic standards. Four electrical characteristics tests are AC dielectric breakdown, V-t, lighting impulse dielectric breakdown, and discharge arc. Both samples showed excellent electrical properties, and the ceramic coating material is very good insulating materials for bus bar.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.8
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• pp.756-761
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• 2004

Since the use of CFC and HCFC refrigerants are to be restricted due to the depletion of ozone layer, this experiment applies the NH$_3$ gas to study the performance characteristics from the superheat control for improving the energy efficiency. The experiments are carried out for the condensing pressure of refrigeration system from 14.5 bar to 16.0 bar by 0.5 bar and for superheat temperature from $0^{\circ}C$ to 1$0^{\circ}C$ by 1$^{\circ}C$ at each condensing pressure. As a result of experiment, when the superheat temperature is 1$^{\circ}C$ at each condensing pressure, the refrigeration system has the highest performance.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1334-1339
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• 2004

Nowadays CFCs and HCFCs refrigerants are restricted because it cause depletion of ozone layer. Accordingly, this experiment apply the $NH_3$ gas and not CFCs and HCFCs for refrigerant to study the performance characteristic from the superheat control and improve the energy efficiency from the high performance. The condensing pressure of refrigeration system is increased from 14.5bar to 16bar by 0.5bar and superheat temperature is increased from $0^{\circ}C$ to $10^{\circ}C$ by $1^{\circ}C$ at each condensing pressure. As the result of experiment, when the superheat temperature is $1^{\circ}C$ at each condensing pressure, the refrigeration system has the high performance.

• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.801-803
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• 2003

Faults in induction motors can be categorized into mechanical faults and electrical faults, and most mechanical faults result from inferiority or damage of the bearing, while most electrical faults derive from insulation faults of stator windings and rotor bar cracks. When a crack appears on the rotor bar, its efficiency decreases, which increases energy consumption and temperature, reducing the life span of the motor. This kind of fault can only be sensed by the protection relay after the condition has worsened to a certain degree, bringing massive economic loss. This paper will deal with the diagnosis method of rotor bar faults through the load current analysis method of the motor used during operation.

• Korean Chemical Engineering Research
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• v.56 no.6
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• pp.871-877
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• 2018

Storing the surplus energy from renewable energy resource is one of the challenges related to intermittent and fluctuating nature of renewable energy electricity production. $CO_2$ methanation is well known reaction that as a renewable energy storage system. $CO_2$ methanation requires a catalyst to be active at relatively low temperatures ($250-500^{\circ}C$) and selectivity towards methane. In this study, the catalytic performance test was conducted using a pressurized bubbling fluidized bed reactor (Diameter: 0.025 m and Height: 0.35 m) with $Ni/{\gamma}-Al_2O_3$ (Ni70%, and ${\gamma}-Al_2O_3$30%) catalyst. The range of the reaction conditions were $H_2/CO_2$ mole ratio range of 4.0-6.0, temperature of $300-420^{\circ}C$, pressure of 1-9 bar, and gas velocity ($U_0/U_{mf}$) of 1-5. As the $H_2/CO_2$ mole ratio, temperature and pressure increased, $CO_2$ conversion increases at the experimental temperature range. However, $CO_2$ conversion decreases with increasing gas velocity due to poor mixing characteristics in the fluidized bed. The maximum $CO_2$ conversion of 99.6% was obtained with the operating condition as follows; $H_2/CO_2$ ratio of 5, temperature of $400^{\circ}C$, pressure of 9 bar, and $U_0/U_{mf}$ of 1.4-3.

• Membrane and Water Treatment
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• v.15 no.2
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• pp.79-88
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• 2024

Modification of Polyvinylidene fluoride (PVDF) hollow fiber membranes (HFMs) characteristics and performance were investigated via post treatment using different oxidants. sodium hypochlorite (NaOCl), hydrogen peroxide (H₂O₂) and potassium persulfate (KPS). Fourier transform infrared (FTIR) and Proton nuclear magnetic resonance (¹H-NMR) results revealed no structural differences after post treatment. Cross-sectional micrographs show finger-like structures at the outer and inner walls of the HFMs and sponge-like structures in middle, where NaOCl and KPS post treated fibers exhibited a decrease in finger-like structures in addition to aggregates appearing on the surface, consequently leading to an increase in the surface roughness (Ra) from 48 nm to 52.8nm and 56 nm, respectively. Hydrogen peroxide post treatment only was observed to decrease the water contact angle from 98° to 81.4°. It was also observed that the elongation at break and the modulus deceased after NaOCl post treatment from 34.5 to 28.5% and from 19.3 Mpa to 16.6 Mpa, respectively. Moreover, pure water flux after H₂O₂ post treatment increased from 87.8 LMH/bar to 113 LMH/bar at 0.45 bar, while no changes were detected for the methylene blue dye rejection (74%) between raw and hydrogen peroxide post treated fibers at the same pressure. According to the findings hydrogen peroxide post treated PVDF HFMs have the most uniform surfaces, with almost no alterations in structural and mechanical properties or porosities with enhanced hydrophilicity and pure water flux maintaining appropriate rejection. Therefore, it is considered an efficient surface modifying agent for UF/NF membranes or low-pressure separators.