• 전기의세계
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• v.18 no.2
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• pp.7-14
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• 1969

From the first customer located right at the substation to the last customer at the end of the line, voltage must be held within close limits, so the voltage regulation is more important than the thermal limit. On a typical distribution system during the peak load period, the voltage drop may be serious enough to cause unsatisfactory operation of home appliances in the residential area, and present many problems to manufacturing industries, where the voltage must be maintained within close limits to insure smooth operation. Among all the factors contributing to voltage drop in the distribution system, the voltage drop in the distribution transformer may account for 30% of this figure. If we can eliminate this factor, the power companies can provide better quality electricity to more customers with the existing distribution facilities, thus saving on initial investment costs. Taking all these problems into consideration, the author undertook the design of a capacitive transformer which would give zero voltage drop at rated load and at 80% lagging power factor while incorporating overload features to withstand 400% overload for at least 100 seconds. The following are the results obtained through design, manufacture and test of an initial experimental transformer built with these specific purposes.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.6
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• pp.72-80
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• 2013

For the proper cooling of in-wheel motor, the cooling channel should have the characteristics which are low pressure drop and adequate cooling oil supply to motor part. In this study, the flow performance of cooling channel for in-wheel motor was evaluated and the shape of the channel was optimized. First, the pressure drop and flow distribution characteristics of the initial channel model were evaluated using numerical analysis. Also, by the result of analysis and design modification, 4 design parameters of the channel were selected. Second, using the Taguchi optimal method, the cooling channel was optimized. In the method, nine models with different levels of the design parameters were generated and the flow characteristics of each models was estimated. Base on the result, the main effect of the design parameters was founded and optimized model was obtained. For the optimized model, the pressure drop and oil flow rate were about 0.196 bar and 0.207 L/min, respectively. The pressure drop decreased by about 0.3 bar and the oil flow rate to the motor part increased by about 0.2 L/min compared to the initial model.

• Journal of Power Electronics
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• v.10 no.4
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• pp.396-404
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• 2010

This paper presents simple schemes used to estimate the initial rotor position and the d- and q-axis inductances for effective Maximum Torque per Ampere (MTPA) operation in a wind-power system using an IPMSM (Interior Permanent Magnet Synchronous Machine). An IPMSM essentially requires an exact coordinate transformation and accurate inductance values to use a reluctance torque caused by the saliency characteristic. In the proposed high-frequency voltage testing method, there is no voltage drop caused by the resistance and the electromotive force. The initial rotor position and the inductance can be measured through an analysis of the stator current without turning the rotor. The experimental results are presented in order to illustrate the feasibility of the proposed method.

• Journal of Power Electronics
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• v.13 no.1
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• pp.94-103
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• 2013

A capacitor deterioration of LCL-filter grid-connected PWM converters is progressed by the self-healing mechanism. It leads to the degradation of the filter performance and drop of power factor. Thus, it is required to diagnose fault-point of capacitors and determine the replacement time. Typically, the fault of capacitors is determined when the capacitance is reduced up to 80% from initial value. This paper proposes algorithm to the determine capacitor replacement time of an LCL filter. The algorithm takes the advantage of change of the response on the injected resonant frequency corresponding to 80% value from the initial capacitance. The results of the algorithm are demonstrated through simulations and experiments.

• Journal of Life Science
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• v.5 no.4
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• pp.155-161
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• 1995

The effects of substrate concentration, enzyme concentration, reaction temperature, and water content were investigated in intramolecular esterification. This study used cyclohexane as organic solvent, power lipase as enzyme, and benzyl alcohol and octanoic acid as substrate. The initial reaction rate was found to be proportional to enzyme concentration; followed Michaelis-Menten equation for octanoic acid; and was inhibited by benzyl alcohol . The observed initial reaction rate first increased, then decreased with increasing reaction temperature, giving rise to the maximum rate at 20$\circ$. The drop in the reaction rate at higher temperature was to partition equilibrium change of substrate between organic solvent and hydration layer of enzyme molecule in addition to the deactivation by enzyme denaturation. Water layer surrounding enzyme molecule seemed to activate in organic solvent and the realistic reaction was done in the water layer. In the enzymatic reaction in organic solvent, the initial reaction rate was influenced by partition quilibrium of substrate, so the optimum condition of substrate concentration, enzyme concentration, reaction temperature, and water content would give a good design tool.

• Journal of the Korean Solar Energy Society
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• v.28 no.4
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• pp.62-67
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• 2008

In this study, we analyze the electrical characteristics of amorphous silicon thin film photovoltaic module which are installed about 5 years ago. Four modules from PV system are extracted and measured the maximum power change ratio using solar simulator(Class A). Also, infrared camera is used to get thermal distribution characteristics of system. The external appearance change is compared with initial module by naked eye examination. Through this experiment, 31% maximum output power drop is observed. The detail description is specified as the following paper.

• Journal of Power System Engineering
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• v.1 no.1
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• pp.42-51
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• 1997

In this study, in order to investigate the influence of cam profile on the injection rate, the characteristics of injection in PLN (pump - line - nozzle) diesel injection system were simulated. Six types of the profile of fuel cam were used for simulation. The maximum injection pressure and maximum injection rate of initial and end phase were analyzed to demonstrate the characteristics of injection. The mathematical model of the injection system and the computation results were verified by experimental results. Simulation results showed that the maximum injection pressure, maximum injection rate, injection quantity and pressure drop in the end phase were proportional to the velocity of fuel cam during the effective stroke.

• Steel and Composite Structures
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• v.16 no.6
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• pp.703-718
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• 2014

The initial clamping forces of high strength bolts subjected to different faying surface conditions drop within 500 hours regardless of loading, any other external force or loosening of the nut. This study develops a mathematical model for relaxation confined to creep on a coated faying surface after initial clamping. The quantitative model for estimating relaxation was derived from a regression analysis for the relation between the creep strain of the coated surface and the elapsed time for 744 hours. This study establishes an expected model for estimating the relaxation of bolted joints with diverse coated surfaces. The candidate bolts are dacro-coated tension control bolts, ASTM A490 bolt, and plain tension control bolts. The test parameters were coating thickness, species of coating. As for 96, 128, 168, and $226{\mu}m$ thick inorganic zinc, when the coating thickness was increased, relaxation after the initial clamping rose to a much higher range from 10% to 18% due to creep of the coating. The amount of relaxation up to 7 days exceeded 85% of the entire relaxation. From this result, the equation for creep strain can be derived from a statistical regression analysis. Based on the acquired creep behavior, it is expected that the clamping force reflecting relaxation after the elapse of constant time can be calculated from the initial clamping force. The manufacturer's recommendation of inorganic zinc on faying surface as $75{\mu}m$, appears to be reasonable.

• Current Photovoltaic Research
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• v.5 no.1
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• pp.33-37
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• 2017

Today, photovoltaic power generation mostly uses Si crystalline solar cell modules. The most vulnerable part of the Si solar cell module is that the power generation decreases due to the temperature rise. But, it is widely used because of low installation cost. In the solar market, where Si crystalline solar cell modules are widely used. The CPV (Concentrated Photovoltaic) module appeared in the solar market. The CPV module reduces the manufacturing cost of the solar cell by using non-Si in the solar cell. Also, there is an advantage that a rise in temperature does not cause a drop in power generation. But this requires high technology to install and has a disadvantage that the initial installation cost is expensive compared to normal Si solar cell module. So that we built a testbed to see these characteristics. The testbed was used to measure the amount of power generation in a long-term outdoor environment and compared with the general Si solar cell module.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.2 no.3
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• pp.201-209
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• 2004

Important operation parameters and performance of a high temperature ceramic candle filter system were evaluated through a series of demonstration tests at a pilot-scale vitrification plant. At the initial period of each test, due to the growth of dust cake on the surface of ceramic candles, the pressure drop across the filter media increased sharply. After that it became stable to a certain range and varied continuously proportion to the face velocity of off-gas. On the contrary, at the initial period of each test, the permeability of filter element decreased rapidly and then it became stable. Back flushing of the filter system was effective under the back flushing air pressure range of 3∼5 bar. Based on the dust concentrations measured by iso-kinetic dust sampling at the inlet and outlet point of HTF, the dust collection efficiency of HTF evaluated. The result met the designed performance value of 99.9%. During the demonstration tests including a hundred hour long test, no specific failure or problem affecting the performance of HTF system were observed.