• Journal of Electrical Engineering and Technology
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• v.11 no.3
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• pp.699-706
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• 2016

Partial discharges (PD) lead to the degradation of high voltage cables and accessories. PD activities occur due to the existence of impurities, voids, contaminants, defects and protrusions during the manufacture and installation of power cables. Commonly, insulation failures occur at cable joints and terminations, caused by inhomogeneous electric field distributions. In this work, a blend of natural rubber (NR) and linear low density polyethylene (LLDPE) was investigated, and the optimal formulation of the blend that could resist PD was discussed. The experiments were conducted under a constant high voltage stress test of 6.5 kV AC and the magnitude of partial discharge activities was recorded using the CIGRE method II. Pattern analysis of PD signals was performed along with the interpretation of morphological changes. The results showed that the addition of 10 wt% of NR and 5 wt% of Alumina Trihydrate (ATH) provided promising results in resisting PD activities. However, as the NR content increased, more micropores existed, thus resulting in increased PD activities within the samples.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.2
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• pp.119-126
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• 2002

The mica/epoxy composite used in generator(rated 22 kV and 500 MW) stator windings was aged at 180$\^{C}$ for up to 1000 hours in air and hydrogen. The degradation mechanism was investigated through the defect of evolution and microstructural analysis by performing SEM(Scanning Electron Microscope). As the thermal aging time increases, the number of voids per unit volume increases at the mica/epoxy interface of generator stator windings. The aged specimens in hydrogen showed retarded generation and growth of voids. Accelerated aging tests were conducted using the combination of thermal and electrical aging in air and hydrogen. The aging was carried out at a combined stress such as thermal aging at 110$\^{C}$, electrical aging at 5.5 kV/mm and frequencies 420 Hz in air, and electrical aging at 5.5 kV/mm and frequencies 420 Hz in hydrogen (pressure 4 kg/㎠). Thermal and electrical aging generates large voids at the mica/epoxy interface in air. Electrical aging in hydrogen also generates small voids, delaminations and cracks in mica tapes.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1957-1959
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• 2000

The PD measurement method is very useful to detect insulation degradation. Recently, the HFPD(High Frequency Partial Discharge) measurement testing is widely used in partial discharge measurement of HV machines because HFPD measurement testing receives less influence of external noise and has a merit of good sensitivity. Therefore it is very useful method compare to previous conventional PD testing method and effective diagnosis method in power transformer that requires in-service diagnosis. But partial discharges have very complex characteristics of discharge pattern so it is required continuous research to development of precise analysis method. In this study, simulated transformer is manufactured and HFPD occurred from simulated transformer is measured with broad band antenna and active-line RF measurement system in real time, the degradation grade of transformer is analyzed through produced patterns in simulated transformer according to applied voltages. Also the PD pattern which was measured with EMC analyzer and RF measurement system is compared.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.10
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• pp.553-558
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• 2000

This paper deals with change of contact angle, surface potential decay, surface resistivity and XPS of water-treated epoxy insulator. From the experimental results on the contact angle was reduced from $74^{\circ}$to $24^{\circ}$ due to the formation of polar hydroxyl groups on surface which was associated with intermolecular reaction between epoxy chains of three-dimensional network structure and water molecules. From the experimental results in the surface potential decay of water treated-samples, it was found that the accumulation of charge is decreased and the surface potential decay time is shortened by the interaction of polar hydroxyl groups induced on the treated surface as the increment of treatment time. The positive charging on the treated surface compared with negative charging is relatively lowered by the induction of polar hydroxyl groups. The surface resistivity was changed from $10^{15}[{\Omega}/cm^2$] to $10^{12}[{\Omega}/cm^2$] caused by water treatment. From XPS, it was found that the changes affected by the surface degradation of epoxy were caused by the generation of carboxyl groups through the chain decomposition and recombination with oxygen molecules in the air.

• KEPCO Journal on Electric Power and Energy
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• v.8 no.2
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• pp.73-77
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• 2022

Recently, as the number of years of operation has increased for more than 30 years, interest in evaluating the remaining life of major power facilities such as transformers and ultra-high voltage cables is increasing. In particular, the risk of failure is increasing because the underground transmission XLPE cable has been built since 1980 and has been operating in excess of 30 years of design life or close proximity. Therefore, it is necessary to develop an algorithm to evaluate the residual life of the XLPE cable considering the load to determine the risk of failure. Since load data is large amount of data, it is necessary to make the variable load information equivalent to the time unit first in order to calculate the remaining life of the system quickly. In overseas literature, transformers are reported to be standardized for variable load equivalent conversion formulas, but they have not been reported for ultra-high voltage cables. Therefore, in this paper, whether the equivalent conversion formula of a transformer can be applied to XLPE cables was reviewed through accelerated degradation tests under equivalent and variable temperature conditions, and considerations were studied when evaluating the remaining operating life of XLPE cables based on the experimental results.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.5
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• pp.643-648
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• 2013

In this study, degradation was observed by irradiating UV rays to the polymer insulators which have been widely used in outdoor electric power facilities. For an indoor accelerated UV test, 0.55 w/m2 of UV rays were applied using a xenon-arc method. A UV detection system with 65 ${\phi}mm$ in diameter, 100 mm in length and 1.0 of brightness (F/#) has been designed. Even though efflorescence on the surface of polymer insulators wasn't observed according to the accelerated UV test. UV rays were detected at around 50% and 40% of insulation breakdown in EPDM and silicone-type insulators respectively. As degradation continued because of an indoor accelerated UV test, breakdown voltage with which UV rays can be detected in an early stage decreased as well. A silicone polymer insulator would be severer than EPDM polymer insulator in terms of surface degradation because of UV strength against $V_m/V_{BD}$ was high in silicone polymer insulators. UV strength in silicone-type insulators increased at 1,000 $kJ/m^2$ because contact angle at the intial stage sharply decreased to from $113^{\circ}$ to $92.1^{\circ}$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.8
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• pp.501-507
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• 2015

In this paper, EPR (ethylene propylene rubber) insulation material was accelerated degradation test at $121^{\circ}C$, $136^{\circ}C$, $151^{\circ}C$, and experiment the typical EAB (elongation at break) at mechanical characteristics analysis. It is shown that the failure-time at the point of 50% of the initial value of Elongation rate to obtain the activation energy. The failure-time was shown each 5,219 hr, 3,165 hr, and 668 hr at three temperatures. In order to derive the activation energy, Arrhenius methodology was applied. Also, we got the Arrhenius plot from three accelerated temperatures. The activation energy values got 0.98 eV from EAB test. The experimental data were evaluated for estimating the probability density, and the suitable distribution by using statistical program MINITAB. It is shown that EAB data by the acceleration thermal degradation is most suitable for the Weibull distribution.

• Fire Science and Engineering
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• v.32 no.2
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• pp.48-56
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• 2018

This paper reports the results of a study on the over-current characteristics of IV insulated wire sheath according to accelerated degradation. In order to examine the degradation of a IV insulated wire sheath through insulation, acceleration degradation experiments were performed using the Arrhenius equation of acceleration life test models; test samples with equivalent lives of 0, 10, 20, 30 and 40 years were prepared. Then allowed currents with over-current of 100%~500% were introduced to measure the times of first generation of smokes and carbonization in the wire sheath, and it was found that the times of first generation of smokes and carbonization in the wire sheath decreased as the equivalent life increased. In more detail, when 270% over-current is applied, the electrical fire risk of equivalent life of 40 years increased by approximately 3.2 times based on equivalent life of 0 years. Also, when the over-current was 255% and 260%, carbonization occurred only in the equivalent life of 40 years, and the fire risk according to the accelerated degradation was increased dramatically. In addition, FT-IR and SEM analyzes were used to confirm the characteristics and surface changes of IV insulated wire sheath according to the equivalent life.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1608-1610
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• 1999

To find effective diagnostic method for Transmission OF cables, various characterizations were carried such as DGA (dissolved gas analysis), water contents, total acidity and AC breakdown voltage. It was found that the result was varied by sampling and container. The results from those characterization method showed the present condition and history very well and could be used to estimate the degree of degradation of cables.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1982-1984
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• 2004

Stator coil of rotating machinery has shown different characteristics according to impregnated with coil or not. And this is major determinant of equipment's life. In this paper, PD characteristics is studied as a classification scheme between two specimens. Processing of the coil impregnation is very important thing because that influences on thermal and electrical characteristics of the coil. And then PD is occurring at the coil and causing insulation degradation. For processing statistical processing, PD data acquired from PD detector using PDASDA(partial discharge acquisition, storage and display system). And also these statistical distribution and parameter are applied to classify PD sources by neural networks. As a result of, Neural Networks have a good discrimination rate for classification PD sources.