• Proceedings of the KSR Conference
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• 2003.10c
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• pp.623-627
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• 2003

Aging and failure of motor insulation depend on the stresses imposed on it. The insulation life time depends on the severity of the stresses. The electrical aging by transient surge is very important to traction motor in EMU(electric multiple unit). This paper presents the insulation characteristics of stator coil by transient surge from inverter. There are several nondestructive tests available for checking the condition of motor insulation, the probable extent of aging, and the rate of which aging is taking place. So the insulation characteristics of stator coil were each analyzed by measurement of leakage current, dielectric loss($tan{\delta}$), capacitance, polarization index(PI) and partial discharge. The method of diagnosis is able to analyze the aging condition and predict the life of the traction motor in EMU.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.8
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• pp.782-790
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• 2000

A numerical study has been conducted to characterize the transient pressure in a building water supply system with an air chamber by utilizing a commercial code that employs the method of characteristics. Some results produced for the purpose of verification in the study agree quite well with the previously reported. Several parameters are then varied. Among them are the valve closure time, the wave speed, the static pressure, the polytropic exponent, the air chamber volume, the inner diameter and the shape of orifice in the air chamber, etc, while the water temperature and velocity are kept constant at $20^P{circ}C $,/TEX> and 0.8 m/s, respectively, Results reported in this parametric study may be useful to understand the unsteady behavior of the system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.2
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• pp.175-182
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• 2007

The objective of the present study is to investigate the heat storage characteristics of a packed bed according to periodically oscillating flows. Experiments have been performed to measure transient temperature distributions in solid and fluid Phases of the porous media. A simplified analytical model has been developed with intra-particle and dispersion effects neglected, and non-dimensional parameters have been derived. The transient temperature distributions according to the simplified numerical model agree well with the experimental results. Heat storage efficiencies defined in two different ways are obtained for various time periods and face velocities.

• Proceedings of the KIEE Conference
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• 1998.11a
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• pp.103-105
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• 1998

This paper presents the compensated 2-D magnetic fields analysis of superconducting AC generator(SCG) by using efficient 2-D model. 3-D analysis is necessary for the accurate analysis because SCG has a large leakage flux owing to the air cored winding and end ring structure. However, in 3-D FEM, considering the movement of rotor is difficult, so efficient 2-D model which can compensate the leakage flux has been proposed and the movement of rotor is easily considered. The characteristics in transient state of SCG and the prime role of damper also have been evaluated.

• Journal of Mechanical Science and Technology
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• v.19 no.4
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• pp.1036-1043
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• 2005

Concentric annular heat pipes (CAHP) were fabricated and tested to investigate their thermal characteristics. The CAHPs were 25.4 mm in outer diameter and 200 mm in length. The inner surface of the heat pipes was covered with screen mesh wicks and they were connected by four bridge wicks to provide liquid return path. Three different heat pipes were fabricated to observe the effect of change in diameter ratios between 2.31 and 4.23 while using the same outer tube dimensions. The major concern of this study was the transient response as well as isothermal characteristics of the heat pipe outer surface, considering the application as uniform heating device. A better performance was achieved as the diameter ratio increased. For the thermal load of 180 W, the maximum temperature difference on the outer surface in the axial direction of CAHP was $2.3^{\circ}C$ while that of the copper block of the same outer dimension was $5.9^{\circ}C.$ The minimum thermal resistance of the CAHP was measured to be $0.004^{\circ}C/W.$ In regard to the transient response during start-up, the heat pipe showed almost no time lag to the heat source, while the copper block of the same outer dimensions exhibited about 25 min time lag.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.1 no.1
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• pp.46-54
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• 1989

The purpose of this study is to obtain the dynamic characteristics of an absorption refrigerator powered by solar energy by experiments. Since the absorption refrigerator power by solar energy should have the characteristics which is suitable for the intermittence and rarity of solar energy, not only the characteristics of the steady state operations but also the partial load and the transient operations should be considered. The minimum available temperature of the storage tank should be known, and the absorption refrigerator can be suitably selected for air-conditioning systems. In this study, the experimental data of the transient state for on-off and warming-up operations has been obtained. Also the experiments are performed which test the minimum available temperature of the storage tank. The results show that it takes 1 hour to get to the steady state of the absorption refrigerator, and the minimum available temperature of the storage tank is about $68^{\circ}C$, and show that in the partial load operations the performance of the absorption refrigerator is improved by applying the modified control method to on-off operations.

• Proceedings of the KIEE Conference
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• 1986.07a
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• pp.151-153
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• 1986

• Proceedings of the Korean Nuclear Society Conference
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• 1999.10a
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• pp.171.1-171
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• 1999

• Journal of Mechanical Science and Technology
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• v.16 no.6
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• pp.839-850
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• 2002

A performance simulation program for the turboprop engine (PT6A-62), which is the power plant of the first Korean indigenous basic trainer KT-1, was developed for performance prediction, development of an EHMS (Engine Health Monitoring System) and the flight simulator. Characteristics of components including compressors, turbines, power turbines and the constant speed propeller were required for the steady state and transient performance analysis with on and off design point analysis. In most cases, these were substituted for what scaled from similar engine components'characteristics with the scaling law. The developed program was evaluated with the performance data provided by the engine manufacturer and with analysis results of GASTURB program, which is well known for the performance simulation of gas turbines. Performance parameters such as mass flow rate, compressor pressure ratio, fuel flow rate, specific fuel consumption and turbine inlet temperature were discussed to evaluate validity of the developed program at various cases. The first case was the sea level static standard condition and other cases were considered with various altitudes, flight velocities and part loads with the range between idle and 105% rotational speed of the gas generator. In the transient analysis, the Continuity of Mass Flow Method was utilized under the condition that mass stored between components is ignored and the flow compatibility is satisfied, and the Modified Euler Method was used for integration of the surplus torque. The transient performance analysis for various fuel schedules was performed. When the fuel step increase was considered, the overshoot of the turbine inlet temperature occurred. However, in case of ramp increase of the fuel longer than step increase of the fuel, the overshoot of the turbine inlet temperature was effectively reduced.

• Aerospace Engineering and Technology
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• v.4 no.2
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• pp.142-152
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• 2005

There are two definite objects for developing the startup transient of liquid rocket engine. One is to achieve the repeatability of startup to ensure higher reliability, and the other is to reduce the time of the startup transient. Typically in the initial phase of engine development as we are currently opposing, it is hard to estimate engine startup time due to the lack of experiences. In this work, a startup transient analysis tool was developed with the introduction of the mathematical model for each component of pump-fed liquid rocket engine system. Startup transient was investigated for a 25 ton class gas generator cycle engine to find necessary time for reaching steady state from startup and this enabled to reveal dynamic characteristics of the engine.