• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.4 no.1
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• pp.6-17
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• 1975

For a periodic variation of the flue gas temperature the heat conduction through the Ondol floor was analysized. Also the heat loss to the ground was estimated. The floor thermal capacity, as a function of the floor thickness, has strong influence on the time lag of the temperature variation. It is an important design parameter for intermittent heating. Even for the steady periodic variation, there was significant heat loss to the ground below the Ondol floor.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.3
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• pp.247-252
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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.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.2
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• pp.201-207
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• 2015

Turbine-generator torsional response is caused by interaction between electrical transient air-gap torque and mechanical characteristics of turbine-generator shafts. If torsional shaft torque exceeds a certain threshold, the loss of fatigue life may occur and, in the end, it is possible to happen permanent shaft failure. Therefore, it is required to understand the torsional response for reliable operation and protection of turbine-generator shaft system. In this paper, we introduced multi-mass modeling method of turbine-generator shaft system using mechanical-electrical analogy and state-space equation to verify the transient torsional response based on ElectroMagnetic Transient Program (EMTP). These simple realization methods for turbine-generator shaft torsional response could be helpful to understand torsional interaction phenomena and develop the transient torque reduction countermeasures for turbine-generator shaft system.

• New & Renewable Energy
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• v.3 no.2 s.10
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• pp.24-30
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• 2007

The transient response of PEMFC (proton exchange membrane fuel cell) is important criteria in the application of PEM fuel cell to real automotive system. In this work, using a transparent unit PEM fuel cell, the transient response and cathode flooding during load change are investigated. The cell voltage is acquired according to the current density change($0.3Acm^2$ to $0.6A/cm^2$) under various stoichiometry conditions and different flooding intensities, Also the cathode gas channel images are obtained by CCD imaging system simultaneously. The different level of undershoots appeared at the moment of load changes under different cathode stoichiometries and flooding intensities. It takes about 1s that the product water comes up onto the flow channel so that oxygen supply is temporarily blocked which causes voltage loss in that "undershoot". The correlation of the dynamic behavior with stoichiometry and cathode flooding is induced from the results of these experiments.

• International Journal of Air-Conditioning and Refrigeration
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• v.10 no.4
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• pp.220-228
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• 2002

The cool-down performance after soaking is very important in an automotive air-conditioning system and is considered as a key design variable. Therefore, transient characteristics of each system component are essential to the preliminary design as well as steady-state performance. The objective of this study is to develop a computer simulation model and ostinato theoretically the transient performance of an automotive air-conditioning system. To do that, the mathematical modelling of each component, such as compressor, condenser, receiver/drier, expansion valve, and evaporator, is presented first of all. The basic balance equations about mass and energy are used in modelling. For detailed calculation, condenser and evaporator are divided into many sub-sections. Each sub-section is an elemental volume for modelling. In models of expansion valve and compressor, dynamic behaviors are not considered in this analysis, but the quasisteady state ones are just considered, such as the relation between mass flow rate and pressure drop in expansion device, polytropic process in compressor, etc. Also it is assumed that there are no heat loss and no pressure drop in discharge, liquid, and suction lines. The developed simulation model is validated by comparing with the laboratory test data of an automotive air-conditioning system. The overall time-tracing properties of each component agreed well with those of test data in this case.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.59 no.2
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• pp.206-211
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• 2010

Since high-speed train is a dynamic load in which electric power is externally supplied, contact loss between the catenary and pantograph occurs. This phenomena including vibrations generates frequently irregular arcs, which, in turn causes EMI. Thus it is very important to develop the approach to reduce arc phenomenon by contact loss, as speed of electric railway vehicle increases. In case of an electric railway vehicle using electrical power, compared with diesel rolling stock, Power Line Disturbance(PLD) such as harmonics, transient voltage and current, Electromagnetic Interference(EMI), and dummy signal injection etc usually occur. In this study, the dynamic characteristics of a contact wire and a pantograph suppling electrical power to high-speed train are investigated with an electrical response point. To implement power line disturbance induced by contact loss phenomenon for high speed train operation, a hardware simulator which considers contact loss between contact wire and pantograph as well as contact wire deviation is developed. It is confirmed by the experiments that contact loss effect is largely dependent on voltage conditions when the contact loss occurs. Also, a passive filter is designed to reduce power disturbance and the designed system is verified by experiment.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.788-789
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• 2008

This paper deals with the loss distribution analysis of 250 kW traction induction motor using a coupled transient finite element method (FEM) and Preisach modeling, which is presented to analyze the characteristics under the effect of saturation and hysteresisloss. The focus of this paper is the efficiency evaluation relative to hysteresis loss, copper loss, etc. on the basis of speed condition a 250 kW Traction Induction Motor. Computer simulation and experimental result for the efficiency using dynamometer show the propriety of the proposed method.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.63 no.2
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• pp.74-80
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• 2014

Generator protection device has to detects an internal fault conditions in generator and abnormal operating conditions must be due to the hazards. Loss of excitation may cause generator itself failure as well as serious operating problem in power system, and then requires an appropriate response of generator protection device. Details modeling of generator control system and analysis of transient states in generator are important for optimal operation in power plants. In addition, the fault simulation data are also used for testing the characteristics of IED. In this paper, the hydro generator control system using PSCAD/EMTDC, visual simulation for power systems, was modeled. The generator control system which is composed of generator, turbine, exciter, governor was implemented. The parameters of generator control system model were obtained from field power plant. Loss of excitation simulations were performed while varying the fixed load. Several signals analysis were also performed so as to analyze transients phenomena.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.160-160
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• 2019

Water is a limited source that needs to be properly managed and distributed to the ever-growing population of the world. Rapid urbanization and development have increased the overall water demand of the world drastically. However, there is loss of billions of liters of water every year due to leakages in water distribution systems. Such water loss means significant financial loss for the utilities as well. World bank estimates a loss of $14 billion annually from wasted water. To address these issues and for the development of efficient and reliable leakage management techniques, high efforts have been made by the researchers and engineers. Over the past decade, various techniques and technologies have been developed for leakage management and leak detection. These include ideas such as pressure management in water distribution networks, use of Advanced Metering Infrastructure, use of machine learning algorithms, etc. For leakage detection, techniques such as acoustic technique, and in recent yeats transient test-based techniques have become popular. Smart Water Grid uses two-way real time network monitoring by utilizing sensors and devices in the water distribution system. Hence, valuable real time data of the water distribution network can be collected. Best results and outcomes may be produced by proper utilization of the collected data in unison with advanced detection and management techniques. Long term reduction in Non Revenue Water can be achieved by detecting, localizing and repairing leakages as quickly and as efficiently as possible. However, there are still numerous challenges to be met and future research works to be conducted in this field.

• Journal of Energy Engineering
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• v.24 no.4
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• pp.175-182
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• 2015

A methodology to determine the most conservative initial condition based on random sampling of operation parameters is established, in which a best-estimate computer code is adopted to minimize the conservatism in code models. To validate the applicability of the suggested method, safety evaluation for a transient of loss of condenser vacuum in a pressurized water reactor is performed. One-hundred different initial conditions are generated by MOSAIQUE program automatically and the peak pressure for the most conservative case is determined from transient analyses. The safety margin obtained with the new approach is almost equivalent to the values determined with the existing methodologies. It is found that the time and human resources required for the safety evaluation could be reduced with the suggested approach.