• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.1
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• pp.65-70
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• 2006

This paper presents the transient behaviors of grounding system impedance against lightning impulse currents. The dynamic characteristics of the deeply driven ground rod and grounding grid subjected to the impulse current were investigated. The transient ground impedance strongly depends on the configuration and size of grounding electrodes and the shapes of impulse currents, and the inductance of grounding electrodes has a significant affect on the transient ground impedance of grounding system Also, the deeply-driven ground rod was effective to reduce the transient ground impedance in time domain of miceroseconds.

• Journal of the Korean Society of Safety
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• v.29 no.5
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• pp.54-59
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• 2014

The record type receivers that are operated in large industrial sites have strength in preventing fire. However, because of its long circuit lines and multiple detectors, the receivers are vulnerable to lightning, noise, and breakdown of equipments, resulting in malfunction. In case of malfunctioning of detection circuits of main protection areas, such as electrical room and server room, potential release of gaseous extinguisher agents may lead to property and life damage. In this paper, we present the results on the characteristics of the transponder that initiates the solenoid valves, with respect to various electromagnetic and lightning inflow conditions. Based on the measured data, we analyzed the systematic problems of the transponder. In order to prevent receiver malfunctions, a sequential circuit was configured with two additional transponders and a timer. The circuit was tested with a simulator with preference and delay circuit algorithms.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.886-889
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• 2001

Silicone rubber is being used for the housing material of outdoor high voltage insulators such as composite insulator, bushing, surge arrestor and cable terminator because of good tracking and erosion resistance, good hydrophobicity and recovery of hydrophobicity and chemical stability. But, the leakge current occurs on surface of the composite polymeric insulation materials when the insulator is used for a long time with severe contaminative condition and it can lead the contamination flashover. So the leakage current is important to estimate the condition of the silicone rubber surface. In this paper, aging characteristics of silicone rubber used for outdoor insulation have been hydrophobicity of silicone rubber in salt fog chamber with average leakage current monitoring for observing the transformation of surface degradation properties of silicone rubber with different ATH(alumina trihydrate, A1$_2$O$_3$$.$3H$_2$O) filler contents. The experimental results show that a higher peak leakage current and to raise a long time for tracking with increasing amount of ATH by the salt fog and heat recycle ageing.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.720-723
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• 2005

Ship motion is a complex controlled process with several hydrodynamic parameters that vary in wide ranges with respect to ship load condition, speed and surrounding conditions (such as wind, current, tide, etc.). Therefore, to effectively control ships in a designed track is always an important task for ship masters. This paper presents an effective adaptive autopilot ships that ensure the optimal accuracy, economy and stability characteristics. The PID control methodology is modified and parameters of a PID controller is designed to satisfy conditions for an optimal objective function that comprised by heading error, resistance and drift during changing course, and loss of surge velocity or fuel consumption. Designing of the controller for course changing process is based on the Model Reference Adaptive System (MRAS) control theory, while as designing of the automatic course keeping process is based on the Self Tuning Regulator (STR) control theory. Simulation (using MATLAB software) in various disturbance conditions shows that in comparison with conventional PID autopilots, the designed autopilot has several notable advantages: higher course turning speed, lower swing of ship bow even in strong waves and winds, high accuracy of course keeping, shorter time of rudder actions smaller times of changing rudder direction.

• Journal of Ocean Engineering and Technology
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• v.28 no.2
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• pp.102-110
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• 2014

This paper presents the results of an experimental and numerical study on the towing characteristics of a barge. A series of model tests were carried out at the Ocean Engineering Basin of KRISO. A model with a 1:50 scale ratio was constructed out of wood. First, force coefficient tests were performed in order to obtain the surge, sway, and yaw force coefficients of the barge. The focus was the effect of skeg on the force coefficients. The stability parameter was calculated from the force coefficients. Next, towing tests in calm sea were carried out with different towline lengths and towing speeds. The trajectories of the barge and the towline tensions were measured during the tests. The measured trajectories were compared with numerical simulation results using a cross-flow model. The towing stability of the barge in a calm sea is discussed in detail.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1724-1726
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• 2001

This paper deals with the characteristics of the potential rises of down-conductor due to lightning surge currents. Direct lightning strikes can cause high impulse currents to the lightning protection system(LPS) of a building. These high impulse currents have the front time as short as 1[${\mu}s$]. In this case, the induced voltages caused in a closed circuit inside the building can be very high and cause damage or submit people to electric hazard. So, the LPS has to be designed to ensure safety condition to person and acceptable levels of induced voltages to the electrical and electronic equipments. The results of the potential rises related to the bonding conditions between the grounding conductor and metal raceway and the type of down-conductors are introduced.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1282-1284
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• 1998

ZnO Varistor is an electronic ceramic device for controlling the surge voltage from low level to high. In this study, the puncture mechanism occurring in ZnO varistor is investigated, and the simulation for restraining the puncture by formulating the relation between the applied voltage and the increase of the inside temperature of grain is applied. In order to simulate the cause of the current localization which is the primary factor causing the puncture, the localization phenomenon and the temperature distribution induced by the localized current, the Voronoi network is applied, which can realize the structure of the practical varistor better than the established simple network. Using the current through each grain and the voltage applied to the grain boundary obtained from that simulation, the Joule heating energy is calculated and the phenomenon that the puncture occurs can be analyzed quantitatively by simulating the electric and thermal characteristics according to the externally applied pulsed voltage.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1146-1149
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• 2004

A new developed impulse current test system(100kV, 250kJ)is presented, which can carry out all impulse current and performance tests on surge arrester sections with rated voltage up to 12kV according to IEC 60099-4(2001). The maximum achievable peak value is 200kA for the impulse current $4/10{\mu}s$ and 60kA for the $30/80{\mu}s$ and $8/20{\mu}s$. The long duration current impulse is realized from class 1 to class 5. The digital transient recorder(4 channels 60MS/S 10bit) is used for measuring AC voltage, impulse current, reference voltage and leakage current. The complex control, measuring, evaluation and data storage system is controlled by one industrial PC system.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.23 no.58
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• pp.41-47
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• 2000

Global(mega) event has increased throughout the 1990s, with the biggest surge occurring in the Asia-Pacific region. Along with this upward trend, competition for more desirable tourists is also surging, so destinations cannot be complacent (Getz, 1997). Event is appearing as the powerful method in the fierce competition around the industry. International events like 99 Hanam Environment Expo have been held annually in Korea since 1991 in which the local government system started. The main roles of event are to enhance the image of communities and attract tourists (Kotler and Haider and Rein, 1993), to strengthen destination attractiveness as drawing power (Mill and Morrison, 1985), and so on. Focused on the destination image, the research (Sirakaya and Sheppard and McLellan, 1997) about the effect of perceived safety at a potential vacation destination showed that destination marketers, travel agents, and hospitality industry members should be concerned with improving their images when such images are negative with regard to safety. Event industry in Korea does not seriously recognize the importance of the safety management against accidents known for tarnishing the destination images. Moreover few safety standards or studies for event industry can be found. This paper investigated the safety factors considered by visitors of 99 Hanam Environment Expo and analyzed the correlation between the safety factors and the demographic characteristics of the visitors.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.17 no.1
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• pp.29-34
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• 1981

More recently, unsteady flow in small-diameter pipes plays a major role in liquid propellantrocket systems, hydraulic and pneumatic control system, and elsewhere. And it has shown that line dynamics can have a marked effect on the hydraulic system characteristics. In this paper, transfer function of hydraulic lines with an accumulator and an outlet orifice is' developed and compared with experimental data from frequency response tests at various airvolume(V.) and the location of accumulator(ld1t), so that their performance may be correctly and easily predicted and the design of the systems incorporating them improved. The obtained results are as follows: 1. The dynamic response of hydraulic lines may be analyzed more accurately by use of the viscous term(22) in unsteady laminar flow. 2. There was good agreement between the theoretical and experimental results of this investigation, and hydraulic systems with liines included an accumulator can be analyzed more accurately by use of the pressure transfer function given by eq. (16). 3. For the mitigation of surge in hydraulic lines, it is more effective that the location ofaccumulator is close to the pipe outlet side. 4. According to the gas volume of accumulator is increased(the sealing pressure is close tomean line pressure), the damping effect of pressure wave is improved.