• Journal of the Korean Wood Science and Technology
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• v.45 no.5
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• pp.511-518
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• 2017

In recent years, many interests and researches on the insulations required the multiple performances other than insulation performance. The purpose of this paper is to find the optimal ratio between wood fiber and rice-husks charcoal to develop a structural board with carbonized rice-husks. Based on these rice-husks charcoals, basic research was carried out to develop thermal insulation materials with structural performance, and the following conclusions were obtained. The MC of the board using the carbonized rice-husks was 3.2-4.1% and the density was 0.58-0.68, indicating the possibility of excellent structural material. The bending strength was 9.1-32.6 MPa in the length direction and 9.2-34.1 MPa in the width direction. It is possible to obtain the bending strength of the normally used MDF level and to find the possibility of development of the thermal insulation material having the structural performances.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.3
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• pp.24-32
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• 2011

[ $SF_6$ ]gas, which has an excellent dielectric strength and interruption performance, is used in various applications such as gas insulated switchgear (GIS) in substations. However, since $SF_6$ has a high global warming potential (GWP), it is necessary to find an eco-friendly alternative insulation gas. In order to examine the possibility of using alternative insulation gases for $SF_6$ in power distribution system equipment, the dielectric strength and physical phenomena of dry air in a quasi-uniform electric field are investigated experimentally in this paper. As a result, the breakdown voltages for positive polarity are higher than those for negative polarity under impulse voltage applications. The negative 50[%] flashover voltage, $V_{50}$ of dry air under conditions above 0.4[MPa] gas pressure, is higher than 150[kV], that is the basic impulse insulation level of distribution equipment. The $V_{50}$ increases linearly with increasing the gas pressure, regardless of the waveform and polarity of the applied impulse voltages. The voltage-time curves are dependent on the rise time of the impulse voltage and gas pressure. Furthermore, streamer discharge was observed through light emission images by an ICCD camera under impulse voltage applications.

• Journal of Electrical Engineering and Technology
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• v.10 no.3
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• pp.1124-1130
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• 2015

Moisture and high temperature are the most important factors that lead to the ageing of oil-paper insulation, but the research about space charge characteristics of oil-paper insulation does not take the combined effect of ambient temperature, moisture and thermal ageing into account. The pulsed electroacoustic (PEA) method was used to investigate the influence of moisture and temperature on space charge characteristics of oil paper at different ageing stages. The results showed that moisture could speed up formation of space charge in oil paper when water concentration was low, but the formation was restrained if the water concentration was high. At the beginning of thermal ageing, heterogeneous charge accumulation had predominance, but it gradually changed to homogeneous charge injection with ageing. It was believed that moisture concentration could speed up ageing and enhance charge accumulation on one hand, and accelerate or slow down the establishment speed of space charge on the other hand, therefore, charge accumulation type changed with ageing. The more seriously the oil-paper insulation was thermally aged, the deeper the trap energy level was, hence more space charge was trapped, which could be speeded up by increasing the ageing temperature, but the effect of ambient temperature did not fit the Arrhenius law.

• Journal of Electrical Engineering and Technology
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• v.13 no.2
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• pp.902-910
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• 2018

In recent times, development of nanofluid insulation for power transformers is a hot research topic. Many researchers reported the enhancement in dielectric characteristics of nano modified mineral oils. Considering the drawbacks of petroleum based mineral oil, it is necessary to understand the dielectric characteristics of nanofluids developed with natural ester based oils. Palm oil has better insulation characteristics comparable to mineral oil. However very few research reports is available in the area of nanofluids based on palm oil. Partial discharge (PD) is one of the major sources of insulation performance degradation of transformer oil. It is essential to understand the partial discharge(PD) characteristics by collecting huge data base of PD performance of nano modified palm oil which will increase its confidence level for power transformer application. Knowing these facts, in the present work, certain laboratory experiments have been performed on PD characteristics of nano $SiO_2$ modified palm oil at different electrode configurations. Influence of concentration of nano filler material on the PD characteristics is also studied. Partial discharge inception voltage, Phase resolved partial discharge (PRPD) pattern, PD signal time-frequency domain characteristics, PD signal equivalent timelength-bandwidth mapping, Weibull distribution statistical parameters of PRPD pattern, skewness, repetition rate and phase angle variations are evaluated at different test conditions. From the results of the experiments conducted, we came to understand that PD performance of palm oil is considerably enhanced with the addition of $nano-SiO_2$ filler at 0.01%wt and 0.05%wt concentration. Significant reduction in PD inception voltage, repetition rate, Weibull shape parameter and PD magnitude are noticed with addition of $SiO_2$ nanofillers in palm oil. These results will be useful for recommending nano modified palm oil for power transformer applications.

• Journal of the Korean Solar Energy Society
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• v.37 no.4
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• pp.35-47
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• 2017

Energy efficiency solutions are being pursued as a sustainable approach to reducing energy consumption and related gas emissions across various sectors of the economy. Vacuum Insulation Panel (VIP) is an energy efficient advanced insulation system that facilitates slim but high-performance insulation, based on a porous core material evacuated and encapsulated in a barrier envelope. Although VIP has been applied in buildings for over a decade, it wasn't until recently that efforts have been initiated to propose and adopt a global standard on characterization and testing of VIP. One of the issues regarding VIP is its durability and aging due to pressure and moisture dependent increase of the initial low thermal conductivity with time; more so in building applications. In this paper, the aging of commercially available VIP was investigated experimentally; thermal conductivity was tested in accordance with ISO 8302 standard (guarded hot box method) and long-term durability was estimated based on a non-linear pressure-humidity dependent equation based on study of IEA/ECBCS Annex 39, with the aim of assessing durability of VIP for use in buildings. The center-of-panel thermal conductivity after 25 years based on initial 90% fractile with a confidence level of 90 % for the thermal conductivity (${\lambda}90/90$) ranged from 0.00726-0.00814 (W/m K) for silica core VIP. Significant differences between manufacturer-provided data and measurements of thermal conductivity and internal pressure were observed.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.5
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• pp.111-116
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• 2022

The causes of motor burnout include overload, phase loss, restraint, interlayer short circuit, winding ground fault, instantaneous overvoltage, and the rotor contacting the stator, leading to insulation breakdown, leading to breakdown or electrical accidents. Therefore, equipment failure causes not only loss due to cost required for equipment maintenance/repair, but also huge economic loss due to productivity decrease due to process stop because the process itself including the motor is stopped. The current level of technology for diagnosing motor failures uses vibration, heat, and power analysis methods, but there is a limit to analyzing the problems only after a considerable amount of time has passed according to the failure. Therefore, in this paper, a device and algorithm for measuring insulation resistance using DC AMP signal was applied to an industrial motor to solve this problem. And by following the insulation resistance state value, we propose a diagnosis of deterioration and failure of the motor that cannot be solved by the existing method.

• Journal of the Korean GEO-environmental Society
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• v.24 no.12
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• pp.61-67
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• 2023

Heat pipes located underground in urban areas and operated under high temperature and pressure conditions can cause large-scale human and economic damage if damaged. In order to predict damage in advance, damage and construction information of heat pipe are analyzed to derive independent variables that have a correlation with frequency of damage, and a simple regression analysis modified model using each variable is applied to the field. However, as the correlation between independent variables applied to the model increases, the independence between variables is harmed and the reliability of the model decreases. In this study, the independence of the pipe diameter, burial depth, insulation level of monitoring system, and disconnection or short circuit of the detection line, which are judged to be interrelated, was tested to derive a method for combining variables and setting categories necessary to apply to the frequency of damage estimation model. For the test of independence, the continuous variables pipe diameter and burial depth were each converted into three categories, insulation level of monitoring system was converted into two categories, and the categorical variable disconnection or short circuit of the detection line status was kept as two categories. As a result of the test of independence, p-value between pipe diameter and burial depth, level of monitoring system and disconnection or short circuit of the detection line was lower than the significance level (α = 0.05), indicating a large correlation between them. Therefore, the pipe diameter and burial depth were combined into one variable, and the categories of the combined variable were set to 9 considering the previously set categories. The insulation level of monitoring system and the disconnection or short circuit of the detection line were also combined into one variable. Since the insulation level is unreliable when the detection line status is disconnection or short circuit, the categories of the combined variable were set to 3.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.8
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• pp.1111-1116
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• 2011

Power distribution systems onboard vessels are typically configured without any live line connected to hulls for earthing purpose, where the line to hull voltages are affected and deformed depending on the impedances consisting of insulation resistances and distributed capacitances between power lines and hull. An insulation fault at power lines causes the line to hull voltages to increase to a higher level which brings more possibilities to electric shock and deterioration of insulation material. This study focuses on how to configure a module which enables to continuously monitor the voltages between power line and hull based on the vector diagram by analyzing the neutral point of 3 phase voltages and the algorithm for plotting method on the PC monitors.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.9
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• pp.1518-1523
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• 2016

In this study, in order to understand the degradation characteristics of oil-paper insulation for power transformers and OF cables, tan delta was measured using cable model specimens with long-term accelerated thermal and electrical aging. In addition, to find out the degradation level due to the accelerated aging, tensile strengths of aged papers were measured. As a result, tan ${\delta}$ showed the characteristics of slight decrease at the first stage and then increase with the aging time, which could be analyzed due to the evaporation of remaining moisture and the change of aging rate with time. Also, the trend of tensile strengths with aging temperature and time was appeared to be exponentially decreased and by use of these data equivalent calculated lifetimes and accelerated aging factors were derived for each aging temperatures. After then, tan ${\delta}$ was analyzed with the equivalent operating years. For all different aging temperatures, the aged data were very well fit to the equivalent operating years and it is shown that tan ${\delta}$ was increased with the decrease of tensile strength.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.59 no.2
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• pp.197-201
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• 2010

$SF_6$ gas would be used in power transformer, GIS (Gas insulated switchgear) and so on because of its electrically superior insulation and chemically stable structure. Recently, the reduction of $SF_6$ is required to avoid global warming and the researches on the dilution of $SF_6$ with other gases have been carried out. $SF_6$ mixture gases with $N_2$ and $C_xF_y$ have drawn attention to the synergy effect. However, in order to understand the mechanism of the synergy effect, it is important to analyze and evaluate properties of mixture gases quantitatively. In this paper, we investigated the mechanism of synergy effect from electron collision processes and electron energy distribution by solving Boltzmann equation with propagator method. Three kinds of gases for dilution of $SF_6$ ($SF_6/N_2$, $SF_6/CF$4 and $SF_6/C_4F_8$) are considered in this simulation. On the properties of $SF_6/N_2$ mixture gas, the variation of reduced electric field was shown highly within 0%~40% mixtures of $SF_6$. And the more low-level electron energy has been distributed, the higher insulation capability has appeared.