• Fire Science and Engineering
• /
• v.14 no.1
• /
• pp.1-7
• /
• 2000

Internal insulators give rise to partial discharge(PD), which cause local breakdown and even entire insulation breakdown. Treeing due to PD is one of the main causes of breakdown of the insulating materials and reduction of the insulation life. Therefore the necessity for establishing a method to diagnose the aging of insulation materials and to predict the breakdown of insulation has become important. From this viewpoint, we have studied on Electric Field dependence of tree shape in Low Density Polyethylene about treeing phenomena occurring on the high electrical field. As the result, under the reasoning that the growing of tree supposing when the inner part of tree is either dielectrec or conductor has the intermediate characteristics between dielectrec and conductor, theoretically investicated results well according with the experimental results.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.11a
• /
• pp.239-242
• /
• 2003

자동차 점화장치는 전원으로부터 공급된 낮은 전압을 점화코일을 통하여 연소실의 혼합기를 연소시키기에 충분한 고전압을 발생시키는 장치이며, 점화장치의 핵심은 점화코일이다. 이 점화코일은 절연성능이 우수한 절연재료가 사용되지만 고전압의 발생으로 점화코일 내부에서 일어나는 전기적 열화로 인해 누설전류가 흐르게 되어 전기적 고장을 초래할 수 있다. 이로 인하여 절연재료의 수명은 단축되며, 또한 점화코일에 전류가 흐름으로써 코일 내부에서 발생하는 온도변화에 따른 절연열화로 점화코일의 성능이 저하될 수 있다. 따라서 본 연구에서는 점화코일에 사용되고 있는 절연재료에 전압이 인가될 때 발생할 수 있는 비파괴검사의 일종인 부분방전 측정을 통하여 전압변화에 따른 에폭시 성형 점화코일의 위상각($\Phi$) - 방전전하량(q) - 발생빈도수(n)의 특성 변화를 조사하고 분석함으로써 점화코일의 수명을 예측하여 자동차 점화장치의 성능진단과 정보제공을 자동차 전기장치의 발전에 도움이 될 것을 기대하며, 온도상승에 따른 점화코일의 부분방전 특성을 실험하고 분석하였다.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.18 no.1
• /
• pp.93-99
• /
• 2005

Up to date, the life extension of industrial plant structures has been strongly required in the field of iron-manufacturing company, atomic or power generation company and so on. Fault monitoring, maintenance of aging structural components, safety assessment and residual life prediction may be recognized as typical and/or practical methods in terms of life extension methods. Based on the construction of damage scenario, precise analysis method and development of the risk or reliability assessment, a number of studies have been carried out in this viewpoint. In conjunction with the finite element analysis technique, a practical procedure for the safety assessment of iron-manufacturing plant structures was developed in this paper with a particular interest in furnace. By virtue of the detailed finite element analyses for blust furnace under an operational condition, the validity of the proposed procedure for safety assessment was presented.

• Journal of Advanced Navigation Technology
• /
• v.20 no.6
• /
• pp.511-518
• /
• 2016

RAPCON non only controls landing/take-off procedures but also approaching air traffics within 60-70 NM range of air force base. This paper, first of all, tries to research the failure rate per operation hours, mean time between failure (MTBF) of RAPCON according to six blocks such as interrogator, receiver, power unit, display unit, data process unit and antenna. In addition, this paper estimates the maintenance cost over next 10 months based on 50 monthly maintenance cost data. Considering the maintenance cost data from RAPCON which has been used over designed service life span, it is no doubt the forecasted data proved the monthly cost would go up incrementally during the rest of economic life of the facility. Such research result is also proven to be the same with the result of bathtub curve data during operating life.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.18 no.2
• /
• pp.108-116
• /
• 2014

The proper stress history measurement should be conducted in order to examine the accurate cause of fatigue cracks or the fatigue safety in the steel bridge. Only one strain gauge is generally installed in the field for the stress history examination because of the field circumstances, economic feasibility, workability, and so on. However, this method may not consider the actual size of the specific structure, the gauge length, and the affect of stress concentration in the welded joint. In addition, it is difficult to apply for the stress analysis. Therefore, this study suggests improvements that are a great number of gauge installations, the gauge location adjustment, and the use of the minimum length gauge. It is drived the correlative equation of strain for the distance between the welding toe and the strain gauge installation, and compare correlative equation with equation of IIW. Also, this study could estimate the remaining life and fatigue damage of bridge in service by selecting the suitable stress category. In conclusion, it is possible to understand the member which is high in the fatigue cracks, and the quantitative relations between the welding toe and the strain gauge installation distances. The proposed approach in this study can make an more accurate fatigue damage and a remaining life prediction so that the improved method should be applied in measuring the strain of bridges from now on.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.23 no.2
• /
• pp.75-83
• /
• 2019

In this study, to propose the deterioration curves of urethane, ceramic, polysiloxane and fluorocarbon coating for the steel bridge, an accelerated corrosion tests were carried out. The each coating system wes applied on the top of the specimens, and circular initial defects were introduced with different diameters with 0.5, 1.0, 3.0, 5.0 mm. An accelerated corrosion test condition was used to simulate severe corrosive environment depending on ISO 20340. The deterioration curve of each coating type was evaluated based on deteriorated area from the circular defects. In order to evaluate the coating service life of installed steel bridge using deterioration curve, the acceleration coefficient was calculated at correlation between ISO 20340 and corrosivity categories by ISO 9223 based on field corrosion rate. From test results, the propagation rate of coating deterioration area was different to diameter of circular defects. In case of urethane coating, the coating service lifes of 3% deterioration area was evaluated in 31.8, 15.8, 9.9 and 3.9 years with C2, C3, C4 and C5 category.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.28 no.1
• /
• pp.39-45
• /
• 2024

Seismic safety of expansion joints for piping systems has been underscored by water pipe ruptures and leaks resulting from the Gyeongju and Pohang earthquakes. Metal bellows in piping systems are applied to prevent damage from earthquakes and road subsidence in soft ground. Designed with a series of corrugated segments called convolutions, metal bellows exhibit flexibility to accommodate displacements. Several studies have examined variations in convolution shapes and layers based on the intended performance to be evaluated. Nonetheless, the research on the seismic performance of complex bellows having multiple corrugation heights is limited. In this study, monotonic loading tests, cyclic loading tests, and fatigue tests were conducted to evaluate the shear performance in seismic conditions, of metal bellows with variable convolution heights. Single- and triple-layer bellows were considered for the experimentation. The results reveal that triple-layer bellows exhibit larger maximum deformation and fatigue life than single-layer bellows. However, the high stiffness of triple-layer bellows in resisting internal pressure poses certain disadvantages. The convolutions are less flexible at lower displacements and experience leakage at a rate related to the variable height of the convolutions in certain conditions. At lower deformation rates, the fatigue life is rated higher as the number of layers increase. It converges to a similar fatigue life at higher deformation rates.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.15 no.3
• /
• pp.142-154
• /
• 2011

This study predicted the probability of corrosion initiation of reinforced concrete tunnel boxes structures using the Monte Carlo Simulation. For the inner wall and outer wall in the tunnel boxes, exposed to airborne chloride ion and seawater directly respectively, statistical values of parameters like diffusion coefficient D, surface chloride content $C_s$, cover depth c, and the chloride threshold level $C_{lim}$ were examined from experiment or literature review. Their average values accounted for $3.77{\times}10^{-12}m^2/s$, 3.0% by weight of cement, 94.7mm and 45.5mm for outer wall and inner wall, respectively, and 0.69% by weight of cement for D, $C_s$, c, and $C_{lim}$, respectively. With these parametric values, the distribution of chloride contents at rebar with time and the probability of corrosion initiation of the tunnel boxes, inner wall and outer wall, was examined by considering time dependency of chloride transport. From the examination, the histogram of chloride contents at rebar is closer to a gamma distribution, and the mean value increases with time, while the coefficient of variance decreases with time. It was found that the probability of corrosion initiation and the time to corrosion were dependent on the time dependency of chloride transport. Time independent model predicted time to corrosion initiation of inner wall and outer wall as 8 and 12 years, respectively, while 178 and 283 years of time to corrosion was calculated by time dependent model for inner wall and outer wall, respectively. For time independent model, the probability of corrosion at 100 years of exposure for inner wall and outer wall was ranged 59.5 and 95.5%, respectively, while time dependent model indicated 2.9 and 0.2% of the probability corrosion, respectively. Finally, impact of $C_{lim}$, including values specified in current codes, on the probability of corrosion initiation and corrosion free life is discussed.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.11
• /
• pp.145-150
• /
• 2017

In this study, among the various types of plant equipment, valves, which are susceptible to water hammer, were selected as the diagnosis target. In order to effectively measure the vibration, an accelerometer was adapted for use in this difficult environment. The results showed that the maximum peak-to-peak vibration displacement caused by the action of water hammer on the valve was 21.40 mm, which would affect the structural stability of the valve and pipe. Meanwhile, the measured data was applied to the HIL simulator to verify the reproduction of the vibration. In the future, field data will be applied to the HIL simulator for the purpose of assessing the fatigue, durability and expected residual life of the plant equipment.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.9 no.12
• /
• pp.1397-1404
• /
• 2014

Grab cranes are used for multi-purpose when the sand and soil are deposited into harbor wharf or the undersea construction is performed. Among the components of crane grab, the wire drum and disc brake pad are key expendables and have disadvantages that lot of heat is generated and very expensive when replacing them. In this study, the thermal image analysis for the disc brake, which works with wire drum of the crane is suggested. The suggested system performs the pad thermal diagnosis through the thermal image using the characteristics that the disc and pad surface temperatures are distributed abnormally before the brake failure and the disc pad damage. Therefore, the damage by the failure can be prevented by discovering the abnormality of the machine parts before failure and the life cycle of the pad and the cost can be extended and saved by operating the crane performing constant checkup for the overload.