• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.173-176
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• 1999

Crosslinked Decree is an important 7actor to determine dielectric property of crosslinked polyethylene(XLPE) used for the insulation material in Power cables. Recently, though it is necessary to investigate electrical properties according to crosslinked degree as a Part of the whose characterization of cable. it is not examined closely. In this study. crosslinked degree of samples were measured according to temperature and holding time of crosslinking. electrical tree characteristics of these characteristics of these samples were analyzed by crosslinked degree and applied temperature that was chanced from normal temperature to operating temperature of power cables. As a result. when the crosslinked degree was low, dielectric properties were decreased and influence of temperature was increased. but the crosslinked degrees were high, initiation voltages of treeing were increased and dielectric properties were improved. It is proved that the optimum crosslinked degree was one of most important factor for aging time and residual lifetime of Power cable.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.181-184
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• 2000

LDPE pelet is distilled to make 0.5 Wt% solutions and fabricated as LDPE thin film by dropping the solution onto glass substrate, and then annealed the film to be crystalline. The structure is observed as crystalline regions and non-crystalline regions. The crystalline region is exposed at radiation and as the result, there appeared degradation at the total region of the crystal structure. It is considered therefore that radiation exposure at the crystal structure is badly effected on insulation property and lifetime of materials.

• Electrical & Electronic Materials
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• v.11 no.11
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• pp.1-8
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• 1998

This paper presents an arificial neuro-fuzzy technique based prtial discharge (PD) pattern classifier to power system application. This may require a complicated analysis method employ -ing an experts system due to very complex progressing discharge form under exter-nal stress. After referring briefly to the developments of artificical neural network based PD measurements, the paper outlines how the introduction of new emerging technology has resulted in the design of a number of PD diagnostic systems for practical applicaton of residual lifetime prediction. The appropriate PD data base structure and selection of learning data size of PD pattern based on fractal dimentsional and 3-D PD-normalization, extraction of relevant characteristic fea-ture of PD recognition are discussed. Some practical aspects encountered with unknown stress in the neuro-fuzzy techniques based real time PD recognition are also addressed.

• International Journal of Safety
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• v.1 no.1
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• pp.36-42
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• 2002

This paper is aimed at predicting the life of rubber insulating gloves under normal operating stresses from relatively rapid test performed at higher stresses. Specimens of rubber insulating gloves are subject to multiple stress conditions, i.e. combined electrical and thermal stresses. Two modes of electrical stress, step voltage stress and constant voltage stress are used in specimen aging. There are two types of test for electrical stress in this experiment: the one is Breakdown Voltage (BDV) test under step voltage stress and thermal stress and the other is lifetime test under constant voltage stress and temperature stress. The ac breakdown voltage defined as the break-down point of insulation that leakage current excesses a limit value, l0mA in this experiment, is determined. Because the very high variability of aging data requires the application of statistical model, Weibull distribution is used to represent the failure times as the straight line on Weibull probability paper. Weibull parameters are deter-mined by three statistical methods i.e. maximum likelihood method, graphical method and least squares method, which employ SAS package, Weibull probability paper and FORTRAN, respectively. Two chosen models for predicting the life under simultaneous electrical and thermal stresses are inverse power model and exponential model. And the constants of life equation for multistress aging are calculated using numerical method, such as Gauss Jordan method etc.. The completion of life equation enables to estimate the life at normal stress based on the data collected from accelerated aging test. Also the comparison of the calculated lifetimes between the inverse power model and the exponential model is carried out. And the lifetimes calculated by three statistical methods with lower voltage than test voltage are compared. The results obtained from the suggested experimental method are presented and discussed.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.2
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• pp.273-278
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• 2015

In order to meet increasing power demands, electrical capacity of equipment for power transfers should become larger accordingly. The equipment used for producing and delivering high-voltage power is also required to operate with a high degree of reliability. The stable operation of power equipment is a necessity, not an option. The current through the power cable, the only device to deliver high power, generates a Joule heat, which causes a deteriorating process on the cable system. The XLPE cable is manufactured in such a manner that it can operate for 30 years at $90^{\circ}$, but there is no guarantee that each cable will reach its projected lifetime of 30 years. In this paper, we have measured the temperatures of nine power cables in operation, based on the theory of cable longevity. In order to study the relationship between temperature and longevity, we have devised a new set of equipment and installed it at Korea Western Power Co., Ltd. located in Taean.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.1
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• pp.227-232
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• 2016

As the demand for electric power increases, all devices operating in power stations and all devices adopted in order to deliver distant loads need to be operating in perfect condition at the level of reliability expected by consumers. In general, the lifetime of cables used in delivering high power is declared to be 30 years from the time of production. Deterioration (which is the worsening of electric properties) starts from the very moment of operation. In spite of the reduction in reliability caused by deterioration, the reality is that cables often operate at considerable risk of accidents because the reliability of operation has not been diagnosed. We have invented a device to diagnose the deterioration processes of high-voltage power cables. It has been installed and is currently operating at Korea Western Power Co., Ltd., located in Chungnam, Korea. In previously published papers we have shown graphs obtained by plotting insulation resistances versus time, through analyzing the data extracted from operating cables using the devices we have invented. In this paper, we verify that the previously plotted graphs agree with the life time index of Weibull distribution of probability.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.3
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• pp.169-173
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• 2015

This study is to predict the life exponent by measuring, over 7 years, the insulation resistance of high-voltage cables in 22 kV operation for 13 years. We found out the lifetime index in order to determine the time-dependent trend of deteriorating performance of power cables. The insulation resistances decreased according to elapsed time. We found that: the initial measurements of the cable systems were in agreement with the deterioration properties of the Arrhenius Law. By analyzing the life curve of the cable system, we also verified that the value of the life exponent (n) in the v-t characteristics defined by Weibull distribution has values from 10 to 11. When designing the cable system, the initial value of life exponent was chosen as 9 without any grounding. We have verified that the theoretical grounding based on the design safety of n=9 was actually the best one available. In the short term, we apply our research result to the diagnosis and evaluation of the power cables. In the long run, however, we plan to reduce the cost of the installation and management of cable systems in operation at power stations.

• Proceedings of the KIEE Conference
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• 1998.11c
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• pp.901-903
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• 1998

Crosslinked Degree is an important factor to determine dielectric property of crosslinked polyethylene(XLPE) used for the insulation material in power cables. Recently, though it is necessary to investigate electrical properties according to crosslinked degree as a part of the whole characterization of cable. it is not examined closely. In this study, crosslinked degree of samples were measured according to temperature and holding time of crosslinking, electrical tree characteristics of these samples were analyzed by crosslinked degree and applied temperature that was changed from normal temperature to operating temperature of power cables. As a result. when the crosslinked degree was low, dielectric properties were decreased and influence of temperature was increased. but the crosslinked degrees were high. initiation voltages of treeing were increased and dielectric properties were improved. It is proved that the optimum. crosslinked degree was one of most important factor for aging time and residual lifetime of power cable.

• Journal of Ocean Engineering and Technology
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• v.33 no.1
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• pp.85-91
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• 2019

In a cryogenic storage structure, the insulation system is in an environment in which fluid impact loads occur throughout the lifetime of the structure. In this study, we investigated the effect of repetitive impact loading on the mechanical performance of glass fiber-reinforced polyurethane foam. The repeated impact loading test was conducted in accordance with the required impact energy and the required number of repetitive impacts. The impact behavior of glass fiber-reinforced polyurethane foam was analyzed in terms of stress and displacement. After the impact test, the specimen was subjected to a compression test to evaluate its mechanical performance. We analyzed the critical impact energy that affected mechanical performance. For the impact conditions that were tested, the compressive strength and elastic modulus of the polyurethane foam can be degraded significantly.

• Journal of the Microelectronics and Packaging Society
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• v.12 no.2 s.35
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• pp.167-174
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• 2005

Smaller size and higher integration of electronic components make smaller gap between metal conducting layers in electronic package. Under harsh environmental conditions (high temperature/humidity), electronic component respond to applied voltages by electrochemically ionization of metal and metal filament formation, which lead to short failure and this phenomenon is termed electrochemical migration(ECM). In this work, printed circuit board(PCB) is used for determination of ECM characteristics. Copper leads of PCB are soldered by eutectic solder alloys. Insulation breakdown time is measured at $85^{\circ}C,\;85{\%}RH$. CAF is the main mechanism of ECM at PCB. Pb is more susceptible to CAF rather than Sn, which corresponds well to the corrosion resistance of solder materials in aqueous environment. Polarization tests in chloride or chloride-free solutions fur pure metal and eutectic solder alloys are performed to understand ECM characteristics. Lifetime results show well defined log-normal distribution which resulted in biased voltage factor(n=2) by voltage scaling. Details on migration mechanism and lifetime statistics will be presented and discussed.