• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.3
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• pp.74-80
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• 2004

If the withdrawal force of strand driven roll which is controlled with predetermined speed isn't distributed regularly in continuous casting process, mold level is changed cyclically and slab quality is not good. In this paper, both casting speed control and load sharing control algorithm of strand driven roll according to ratio which is set up by operator at same time is proposed. The proposed algorithm is to share the withdrawal force by following torque current of each driven roll as average torque current by changing speed reference of each driven roll motor. The load sharing control with anti-wind up for improvement transient state is adopted and the proposed algorithm is implemented in POSCO pilot caster.

• 한국태양에너지학회:학술대회논문집
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• 2009.11a
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• pp.291-296
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• 2009

This paper investigates the energy saving potentials of a dedicated outdoor air system (DOAS) applied to a highrise apartment building. As for a typical $132-m^2$ apartment unit, two different HVAC systems; centralized DOAS-Ceiling Radiant Cooling Panel and decentralized Energy Recovery Ventilator-Packaged Air Conditioner were installed. Transient behavior and control characteristics of each system were modeled numerically using a commercial equation solver program, and annual cooling coil load and heating load reduction potentials were compared. The research shows that DOAS-Ceiling Radiant Cooling Panel system can reduce the cooling coil load over 21% annually compared with the current Energy Recovery Ventilator-Packaged Air Conditioner pair. In addition, over 40% of annual ventilation heating load can be reduced by use of DOAS.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.4
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• pp.332-341
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• 2014

A cascaded H-bridge multi-level STATCOM(STATic synchronous COMpensator), which is composed of many cell inverters with independent dc-sources, generates inevitably dc-side voltage unbalance among phases when it compensates unbalanced load. It comes from the difference of flowing active power in each phase when this compensator makes negative-sequence current to eliminate the unbalance of source-side current. However, this unbalance can be controlled by injecting zero-sequence current which is decoupled with grid currents, so the compensator can work well during this balancing process. Both a feedback control algorithm, which produces zero-sequence current proportional to dc-side voltage unbalance within each phase, and a feedforward control algorithm, which makes zero-sequence current directly from the compensator's negative-sequence current, were proposed. The dc-side voltage of each phase can be controlled stably by these proposed algorithms in both steady-state and transient, so the compensator can have fast response to satisfy control performance under rapid changing load. These balancing controllers were implemented and verified via simulation and experiment.

• Nuclear Engineering and Technology
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• v.53 no.9
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• pp.3112-3121
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• 2021

One of the major factors affecting the life span of a Reactor Pressure Vessel (RPV) is the Pressurised Thermal Shock (PTS). PTS is a thermo-mechanical load on the RPV wall due to steep temperature gradients and structural load created by internal pressure of the fluid within the RPV. Safe operating life of a nuclear power plant is ensured by carrying out fracture analysis of the RPV against thermal shock. Carrying out fracture tests on RPV/large scale components is not always feasible. Hence, studies on laboratory level specimens are necessary to validate and supplement the prototype results. This paper aims to study the fracture behaviour of standard Compact Tension [C(T)] specimens, made of RPV steel 20MnMoNi55, subjected to thermal shock through experimental and numerical investigations. Fracture tests have been carried out on the C(T) specimens subjected to thermal transient load and tensile load to quantify the effect of thermal shock. Crack resistance curves are obtained from the fracture tests as per ASTM E1820 and compared with those obtained numerically using XFEM and a good agreement was found. A quantitative study on the crack tip plastic zone, computed using cohesive segment approach, from the numerical analyses justified the experimental crack initiation toughness.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.6
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• pp.95-104
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• 2003

The electric traction systems are quite differ from general power systems which is single-phase and heavy load. Therefore, there are inevitably power quality problems such as steady state or transient voltage drop, voltage imbalance and harmonic distortion. Among these problems, since steady-state volatge drop is the one of most important factor in electric power quality, many researches about on the compensation of volatge drop by using SVC(Static Var Compensator) and/or STACOM(Static Compensator) have been studied and proposed Also, it is expected that transient voltage drop(voltage sag) could affect the control and safety of high speed traction load. In this paper, voltage sag compensation of AT(Auto Transformer) feeding system are studied The detailed transient models of utility source, scott transformer, AT, and traction load are estabilished. The application of DVR(Dynamic Voltage Restorer) in electric traction system is proposed to compensate the voltage sag of traction network which is occured by the fault of utility source. It can be shown that application of the DVR in electric traction system is very useful to compensate the volatge sag from the result of related simulation works.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.4
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• pp.633-642
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• 2021

Growing demand for electricity, when combined with the need to limit carbon emissions, drives a huge increase in renewable energy industry. In the electric power system, electricity supply always needs to be balanced with electricity demand and network losses to maintain safe, dependable, and stable system operation. There are three broad challenges when it comes to a power system with a high penetration of renewable energy: transient stability, small signal stability, and frequency stability. Transient stability analyze the system response to disturbances such as the loss of generation, line-switching operations, faults, and sudden load changes in the first several seconds following the disturbance. Small signal stability refers to the system's ability to maintain synchronization between generators and steady voltages when it is subjected to small perturbations such as incremental changes in system load. Frequency stability refers to the ability of a power system to maintain steady frequency following a severe system upset resulting in significant imbalance between generation and load. In this paper, we discusses these stability using system simulation by renewable energy deployment plan, and also analyses the influence of the renewable energy sources to the grid stability.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.9
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• pp.851-857
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• 2015

In this paper, we estimate the time-dependent C(t) integrals under elastic-plastic-creep conditions. Finite-element (FE) transient creep analyses have been performed for single-edge-notched-bend (SEB) specimens. We investigate the effect of the initial plasticity on the transient creep by systematically varying the magnitude of the initial step load. We consider both the same stress exponent and different stress exponents in the power-law creep and plasticity to elastic-plastic-creep behavior. To estimate the C(t) integrals, we compare the FE analysis results with those obtained using formulas. In this paper, we propose a modified equation to predict the C(t) integrals for the case of creep exponents that are different from the plastic exponent.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.4
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• pp.415-422
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• 2016

When shock acceleration is applied to a mechanical system, it may cause malfunctioning and damage to the system. Hence, to prevent these problems when developing a gimbal structure system for observation reconnaissance, the MIL-STD-810G shock standard must be satisfied as a design specification. Rubber vibration isolators are generally assembled on the base of the system in order to reduce the shock transferred from the aircraft. It is difficult to analyze the transient behavior of the system accurately, because rubber has a nonlinear load-deformation curve. To treat the nonlinear characteristic of the rubber, bilinear approximation was introduced. Using this assumption, transient responses of the system under base shock acceleration were calculated by the finite element method. In addition, experiments with a true prototype were performed using the same conditions as the analytical model. Compared with experimental data, the proposed numerical method is useful for the transient analysis of gimbal structure systems, including rubber vibration isolators with nonlinear stiffness and damping.

• Journal of Korean Society of Steel Construction
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• v.12 no.3 s.46
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• pp.269-279
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• 2000

It is much expected that steel bridges, which have been damaged by increase of vehicle load and corrosion, need repair or strengthening. In this paper, the stress generated by repair welding under loading are analyzed by three dimensional elasto-plastic analyses. The longer and deeper repair weld line bocemes, the larger the magnitude of transient stress becomes. The magnitude of transient stress generated by repair welding under loading $({\sigma}_y/3,\;{\sigma}_a)$ is similar to summation of stresses generated by repair welding and loading. The longer repair weld line ratio(1/b) becomes, the larger the magnitude of transient stress generated by repair welding under loading bocomes. And, the longer repair weld line ratio(1/b) becomes, the larger the magnitude of in-plane displacement generated by repair welding under loading$({\sigma}_y/3,\;{\sigma}_a)$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.10
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• pp.1001-1010
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• 2015

This paper estimates the time-dependent crack-tip stress fields under elastic-plastic-creep conditions. We perform Finite-Element (FE) transient creep analyses for a Single-Edge-notched-Bend (SEB) specimen. We investigate the effect of the initial plasticity on the transient creep by systematically varying the magnitude of the initial step-load. We consider both the same stress exponent and different stress exponent in the power-law creep and plasticity to determine the elastic-plastic-creep behaviour. To estimation of the crack-tip stress fields, we compare FE analysis results with those obtained numerically formulas. In addition, we propose a new equation to predict the crack-tip stress fields when the creep exponent is different from the plastic exponent.