• Journal of Power Electronics
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• v.16 no.3
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• pp.1163-1175
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• 2016

In recent years, microgrids have been the focus of considerable attention in distributed energy distribution. Microgrids contain a large number of power electronic devices that can potentially cause negative impedance instability. Harmonic impedance is an important tool to analyze stability and power quality of microgrids. Harmonic impedance can also be used in harmonic source localization. Precise measurement of microgrid impedance and analysis of system stability with impedances are essential to increase stability. In this study, we introduce a new square wave current injection method for impedance measurement and stability analysis. First, three stability criteria based on impedance parameters are presented. Then, we present a new impedance measurement method for microgrids based on square wave current injection. By injecting an unbalanced line-to-line current between two lines of the AC system, the method determines all impedance information in the traditional synchronous reference frame d-q model. Finally, the microgrid impedances of each part and the overall microgrid are calculated to verify the measurement results. In the experiments, a simulation model of a three-phase AC microgrid is developed using PSCAD, and the AC system harmonic impedance measuring device is developed.

• Journal of computational fluids engineering
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• v.14 no.2
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• pp.9-18
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• 2009

The cargo containment system (CCS) for ships carrying cryogenic fluid consists of at least two levels of barriers and insulation layers. It is because, even though there is a small amount of leak through the primary barrier, the liquid tight secondary barrier blocks further leakage of the cryogenic fluid. However, once the secondary barrier is damaged, it is highly possible that the leaked cryogenic fluid flows through the flat joint made of glass wool and reaches the inner hull of the ship. The primary objective of the present study is to investigate the influence of the damage extent in the secondary barrier on the amount of leaked cryogenic fluid reaching the inner hull and the temperature distribution there. Simulation results using a computational fluid dynamics tool were compared with the experimental data for the leaked cryogenic fluid flow and evaporation in the secondary insulation layer. The experimental and computational results suggest that, unless there is a massive leak, the cryogenic fluid mostly evaporates in the insulation layer and does not reach the inner hull in the state of liquid.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.7
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• pp.139-144
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• 2008

Micro electrochemical machining was investigated to machine micro internal features. This method uses a micro disk tool electrode and can easily machine micro features inside of a micro hole, which are very difficult to make by the conventional processes. In order to limit the machining area and localize the electrochemical dissolution, ultra short pulses were used as power source and a micro disk electrode with insulating layer on its surface was used as a tool electrode. By electrochemical process, internal features, such as groove array, were fabricated on the stainless steel plate.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.11a
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• pp.215-216
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• 2019

The following conclusions were reached through the research on the development of the required performance extraction tools for the application and utilization of various construction methods of lightweght dry wall. 1) Performance required for walls of apartment buildings can be divided into safety, habitation, durability and productivity. Among these, horizontal load resistance, shock resistance, anti-seismic performance, insulation, and acoustic characteristics are the main performance that correspond to dry walls. In addition, safety related to toxic gases and contaminants are required according to recent eco-friendly requirements. 2) To select a wall according to the required performance of an inner wall applied to an apartment, a map tool in the form of 2D matrices was constructed to enable the required performance to be applied, indicating that the wall location and wall material and its differentiating according to the old method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11b
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• pp.101-104
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• 2005

This study presents experimental results from the performance test of a scaled reverberation chamber for measurement of sound insulation of panels. Experimental investigations were conducted in various parameters such as tunneling effect source locations, and maximum sound transmission loss. It is evident that the tunneling effect which means the variation with specimen location on the test frame gives rise to more than 3 dB deviation. One of the objective of this study that compares measured results between a real reverberation chamber and a simplified test apparatus, by using a specimen of a sandwich panel. It shows qualitatively resonable agreement from which one can find a potential to provide a design tool.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.169-172
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• 1999

Recently, the wavelet transform has been a new and powerful tool for signal processing. It is more suitable specially for the feature extraction and detection of non-stationary signals than traditional methods such as, the Fourier Transform(FT), the Fast Fourier Transform(FFT) and the Least Square Method etc. because of the characteristic of the multi-scale analysis and time-frequency domain localization. The wavelet transform has been developed for the analysis of PD pulse signal to raise in the progress of insulation degradation. In this paper, the wavelet transform was applied to one foundational method for feature extraction. For the obtain experimental data, a computer-aided partial discharge measurement system with a single acoustic sensor was used. If we are applying to the neural network method the accumulated data through the extracted feature, it is expected that we can detect the PD pulse signal in the insulation materials on the on-line.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.2
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• pp.180-186
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• 2011

This paper describes a micro electrical discharge machining (MEDM) technique that uses an insulated tool in combination with ultrasonic vibration to drill micro holes. As the machining depth becomes deeper, the dispersion of debris and circulation of the dielectric fluid are difficult to occur. Consequently, machining becomes unstable in the machining region and unnecessary electrochemical dissolution and secondary discharge sparking occur at the tool side face. To reduce the amount of unnecessary side machining, an insulated tool was used. Ultrasonic vibration was applied to the MEDM work fluid to better remove debris. Through these methods, a $1000\;{\mu}m$ thick stainless steel plate was machined by using a $73\;{\mu}m$ diameter electrode. The diameters of the hole entrance and exit were $96\;{\mu}m$ and $88\;{\mu}m$, respectively. It took only 351s to completely drill one hole.

• Journal of the Korea Institute of Building Construction
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• v.24 no.4
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• pp.447-458
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• 2024

This study investigates the effectiveness of Building Information Modeling(BIM) software, specifically SketchUp and Revit, in reducing errors during quantity take-off(QTO) for complex building elements. While 3D modeling offers advantages, existing software may not fully account for manufacturing discrepancies, such as variations in concrete cover thickness and reinforcing bar radius. To address this limitation, this research proposes a BIM-based QTO method for high-insulation wall panels with intricate details. The method utilizes a BIM family library, focusing on key parameters like concrete cover thickness and inner radius of shear reinforcement. A case study compared the cross-sectional details of a wall panel modeled in Revit with the actual manufactured specimen. The analysis revealed a 12% reduction in modeled concrete cover thickness and a 1.27 times larger modeled inner radius of the shear bar compared to the real-world values. The proposed method incorporates these manufacturing variations into the Revit model of the high-insulation wall panel. Software like Navisworks facilitates the identification and correction of any material interferences arising from these adjustments. Furthermore, the method employs a unit wall concept(1m²) to account for the volume of various materials, including insulation and splice sleeves at joints. This allows for the identification of a similar existing family within the BIM library(e.g., "Double RC wall with embedded insulation") that reflects the actual material quantities used in the wall panel. By incorporating these manufacturing-induced variations, the proposed method offers a more accurate QTO process for complex high-insulation wall panels. The "Double RC wall with embedded insulation" family within the Revit program serves as a valuable tool for material quantity estimation in such scenarios.

• Journal of Electrical Engineering and Technology
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• v.9 no.5
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• pp.1686-1693
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• 2014

In this paper, oil-paper samples composed of transformer windings were used to investigate the insulation degradation process subjected to partial discharge (PD), with artificial defects inside to simulate the PD induced insulation degradation. To determine appropriate test voltages, the breakdown time obtained through a group of accelerated electrical degradation tests under high voltages was firstly fitted by two-parameter Weibull model to acquire the average breakdown time, which was then applied to establish the inverse power law life model to choose advisable test voltages. During the electrical degradation process, PD signals were synchronously detected by an ultra-high frequency (UHF) sensor from inception to breakdown. For PD analysis, the whole degradation process was divided into ten stages, and chaos theory was introduced to analyze the variation of three chaotic parameters with the development of electrical degradation, namely the largest Lyapunov exponent, correlation dimension and Komogorov entropy of PD amplitude time series. It is shown that deterministic chaos of PD is confirmed during the oil-paper degradation process, and the obtained results provide a new effective tool for the diagnosis of degradation of oil-paper insulation subjected to PD.

• Journal of the korean Society of Automotive Engineers
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• v.14 no.4
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• pp.68-78
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• 1992

Vibration and vibro-acoustic characteristics of body panels enclosing the vehicle interior cabin are tested and analyzed for effective application of sound proofing materials. A set of deadener and insulation packages are proposed based on the experimentally evaluated and categorized contributions of noise radiating panels. The suggested packages are applied to a prototype vehicle, and a refined acoustic quality is achieved. A systematic experimental procedure proposed in this study can be a good tool in tuning the acoustic quality of prototype vehicles within a limited development period.