• Journal of Electrical Engineering and information Science
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• v.2 no.3
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• pp.71-76
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• 1997

A lot of experiments and analyses have been done to determine the aging mechanism of mica-epoxy composite material used for large generator stator windings in order to estimate remaining life of the generator for last decades. After degrading artificially the mica-epoxy composite material, the surface analysis is performed to analyze breakdown mechanism of insulation in air and hydrogen atmosphere; i) In the case of air atmosphere, it is observed that an aging propagation from conductor to core by partial discharge effect and the formation of cracks between layers is widely carbonized surface. ii) In case of hydrogen atmosphere, the partial discharge effect is reduced by the hydrogen pressure (4kg/$\textrm{cm}^2$). Potassium ions forming a sheet of mica is replaced by hydrogen ions, which can lead to microcracks. It is confirmed that the sizes of crack by SEM analysis are 10∼20[$\mu\textrm{m}$] in length under air, and 1∼5[$\mu\textrm{m}$] in diameter, 10∼50[$\mu\textrm{m}$] in length under hydrogen atmosphere respectively. The breakdown mechanism of sttor winding insulation materials which are composed of mica-epoxy is analyzed by the component of materials with EDS, SEM techniques. We concluded that the postassium ions of mica components are replaced by H\ulcorner, H$_3$O\ulcorner at boundary area of mica-epoxy and/or mica-mica. It is proposed that through these phenomena, the conductive layers of potassium enable creation of voids and cracks due to thermal, mechanical, electrical and environmental stresses.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.11
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• pp.1554-1560
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• 2017

Prepare a lose of 765kV transmission route in power system operation condition, there are some Special Protection Scheme(SPS)s in Korean power system. These SPS can make some preselected generators are tripped to avoid generator overspeed. Because of many of the new large power plants are installed to existing power generation sites due to the siting problem, the number of generator tripped by SPS should be increased. But that can be a cause of system frequency change under the Under Frequency Relay(UFR) 1st pickup level 59.0Hz. Therefore generation constraint should be considered until new transmission lines are installed. In this paper, we propose the ESS application for generation constraint mitigation by frequency damping control of ESS. To analysis an effect of ESS application, we use PSS/E dynamic simulation tool, CBEST model and controller model. The proposed ESS application is applied to the empirical Korean power system.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.8
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• pp.620-623
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• 2013

The carbon nanotube / poly-vinylidene fluoride (CNT/PVDF) composite films for the nano-generator devices were fabricated by spray coating method using the CNT/PVDF solution, which was prepared by adding PVDF pellets into the CNT dispersed N-Methyl-2-pyrroli-done (NMP) solution. The flexible CNT/PVDF composite films were investigated by the scanning electron microscopy, which revealed that the CNTs were uniformly dispersed in the PVDF matrix and thickness of the films was approximately $20{\mu}m$. Fourier transform infra-red spectra were used to investigate crystal structure of the as-spray-coated CNT/PVDF films, and we found that they revealed extremely large portion of the ${\beta}$ phase PVDF. The capacitance of the CNT/PVDF films increased by adding CNTs into the PVDF matrix, and finally saturated. However, the resistance didn't show any saturation effect in the CNT concentration range of 0~4 wt%. Finally, the resulting nano-generator devices revealed reasonable current output after given mechanical stress.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.8
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• pp.114-121
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• 2011

This paper, as the second part of the paper, dealt with the field test and test results to validate PSS(Power System Stabilizer) parameters which are previously tuned in Part 1 paper. In Part 1 of the paper, the selection of parameters such as lead-lag time constants for phase compensation and system gain was optimized by using linear & eigenvalue analyses and they were verified through the time-domain transient stability analysis. In part 2, the performance of PSS was finally verified by the generator's on-line field test. Through the comparisons of simulation results and measured data before and after tuning of the PSS, the models of generator and its controllers including AVR, Governor and PSS used in the simulation are verified and confirmed.

• New & Renewable Energy
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• v.8 no.4
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• pp.13-20
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• 2012

This paper describes a transformerless static synchronous campensator (STATCOM) system based on cascade H-bridge multilevel inverter with star configuration. It is designed not only for the dynamic and continuous compensation of the reactive power but also for the improvement of power quality of existing wind power plant. Especially, when the induction generator of wind turbine is directly connected to the grid, reactive power are occurred by exiting current. so a reactive power compensation system based on the cascade H-bridge multilevel STATCOM is proposed because the output power quality and controllability of reactive power are required by grid code in many different countries. Using various The proposed reactive power control strategy using a STATCOM is compared with the conventional scheme using fixed-size of capacitor bank through various simulation results.

• Wind and Structures
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• v.21 no.4
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• pp.443-460
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• 2015

In this paper, an integrator based method to estimate the effective wind speed in wind turbine systems is proposed. First, the aerodynamic torque was accurately estimated through a proportional gain based observer where the generator speed is the measured output of the system. The torque signal contains not only useful frequencies of the wind, but also high frequencies and the ones due to structural vibration. The useful information of the wind signal is low frequency. A spectral analysis permitted the determination of the useful frequencies. The high frequencies were then filtered before introducing the torque signal in the wind speed observer. The desired effective wind speed was extracted through an integrator based observer using the previously estimated aerodynamic torque. The strength of the method is to avoid numerical solutions used in literature of the wind speed estimation. The effectiveness of the proposed wind speed estimator and its use to control the generator speed has been tested under turbulent situations using the FAST software (Fatigue, Aerodynamics, Structures, and Turbulence), for large scale Megawatt turbine.

• Journal of Ocean Engineering and Technology
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• v.35 no.2
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• pp.150-160
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• 2021

To ensure the international competitiveness of the domestic offshore plant industry, a consensus has been formed regarding the requirement for large offshore basins for performing offshore plant performance verification. Accordingly, the Korea Research Institute of Ships & Ocean Engineering has built the world's largest deep ocean engineering basin (DOEB). The purpose of this study is to evaluate the characteristics of velocity distribution under various conditions of the DOEB. An independent measuring jig is designed and manufactured to measure the current velocities of many locations within a short time. The measurement jig is a 15-m-high triangular-truss structure, and the measurement sensors can move 15 m vertically through an electric motor-wire device. The current speed is measured under various impeller revolutions per minute and locations of the DOEB using the jig. The spatial distribution characteristics of the current velocity in the DOEB and the performance of the current generator are analyzed. The maximum speed is 0.56 m/s in the center of the DOEB water surface, thereby confirming sufficient current velocity distribution uniformity for model testing.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.68 no.1
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• pp.1-7
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• 2019

Due to the highly concentrated power plants integrated through the limited transmission lines in Korea, a Special Protection System(SPS) has been applied to stabilize the power systems by instantly tripping the pre-determined generators in a large-scaled power plant when a fault occurs on the drawing transmission lines. Moreover, power outputs of those generators are constrained to avoid any activation of Under Frequency Load Shedding(UFLS) even after those generators are tripped by SPS action. For this, this paper proposes a method for calculating the required capacity of Energy Storage System(ESS) expected to relieve the operating constraints to generators using its fast response for controlling power system frequency. The proposed method uses the generator acceleration energy to derive the stable condition during the SPS action. In addition, its effectiveness is verified by the case studies adopting actual SPS operations in Korean power systems.

• Journal of the Korean Society of Industry Convergence
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• v.24 no.4_2
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• pp.491-499
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• 2021

Batteries are widely used for energy storage, such as ESS(Energy Storage System), electric vehicles, electric aircraft, and electric powered ships. Among them, a submarine uses a high power battery for an energy storage. When the battery of a submarine is discharged, a diesel generator generates AC power, and then AC/DC power converter change AC power to DC power for charging the battery. Therefore, in order to lower the current capacity of the diesel generator, it is necessary to use an AC/DC converter with a high input power factor. And, a power converter with a large power capacity must have high stability because it can lead to a major accident when a failure occurs. However, the control algorithm using the traditional PI controller is difficult to satisfy stability and dynamic characteristics. In this paper, we design the high power AC/DC converter with high input power factor for battery charging systems. And, we propose a stable control algorithm. The validity of the proposed method is verified through simulation and experiments.

• Nuclear Engineering and Technology
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• v.54 no.5
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• pp.1570-1578
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• 2022

During a severe accident, steam generator (SG) tubes undergo rapid changes in the pressure and temperature. Therefore, an appropriate creep model to predict a short term creep damage is essential. In this paper, a novel creep model for Alloy 690 SG tube material was proposed. It is based on the theta (θ) projection method that can represent all three stages of the creep process. The original θ projection method poses a limitation owing to its inability to represent experimental creep curves for SG tube materials for a large strain rate in the tertiary creep region. Therefore, a new modified θ projection method is proposed; subsequently, a master curve for Alloy 690 SG material is also proposed to optimize the creep model parameters, θ_i (i = 1-5). To adapt the implicit creep scheme to the finite element code, a partial derivative of incremental creep with respect to the stress is necessary. Accordingly, creep model parameters with a strictly linear relationship with the stress and temperature were proposed. The effectiveness of the model was validated using a commercial finite element analysis software. The creep model can be applied to evaluate the creep rupture behavior of SG tubes in nuclear power plants.