• Proceedings of the KIEE Conference
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• 1989.07a
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• pp.380-382
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• 1989

Dielectric breakdown strength (Eb) of thin Poly(Vinylidene Fluoride ; PVDF) film is studied in the temperature range between 4.2 K and 400 K. The results of this study can be summerized as follows. 1) Temperature dependence of dielectric breakdown strength (Eb) can be devided into high and low temperature regions. The critical temperature (Tc) at which two regions are devided depends on applied voltage. 2) Dielectric breakdown strength (Eb) by pulse voltage is higher than that by DC voltage. Especially this difference is remarkable at low temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.10a
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• pp.64-67
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• 2000

In this study, the DC dielectric breakdown of polyethylene used for clothing material of cable was experimented and then its data were simulated by Weibull distribution probability. The dielectric breakdown characteristics in polyethylene were examined and various effects of the DC dielectric breakdown on polyethylene were also discussed.

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2349-2351
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• 1999

In this paper, the variable absorption rates and DC dielectric breakdown strength of epoxy composites were measured at boiling absorption condition in order to observe the influences of moisture in out door use. Also, in order to improve withstand voltage properties at moisture absorbtion condition. IPN (interpenetrating polymer network) method which had been already reported, was introduced and the influence was investigated. As a result, it was confirmed that the moisture absorption rate was increased and DC dielectric breakdown strength was degraded with boiling time and filler content increasing. On the other hand, it was confirmed that moisture absorption rate and DC dielectric breakdown strength degrading rate were lowered by the improvement of adhesion strength In IPN specimens.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.529-531
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• 1999

In this Paper, the variable dielectric breakdown strengths of epoxy composites were investigated at belling absorption condition in order to observe the influences of moisture in out door use. Also. in order to improve withstand voltage properties at moisture absorbtion condition, IPN(interpenetrating polymer network) method was Introduced and the Influence was investigated. As Adding filler(SiO$_2$) classified by o(phr), 50(phr) and 100[phr] to two kinds of matrix resin, six kinds of specimens were manufactured. As a result, it was confirmed that dielectric breakdown strength wer degraded with boiling time and filer content increasing. But, it was confirmed that dielectric breakdown strength degrading rate were lowered by the Improvement of adhesion strength in IPN specimens.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.65-68
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• 2000

Polyethylene, has long history and is widely used, was researched due to good electrical properties by many authors. But PE under stress has the critical defects of space charge accumulation and tree growth, so various methods such as catalyst, additives and blend to improve these problems have been execute, of which we selected blending method. As in our previous papers we investigated electrical conduction, dielectric and AC dielectric breakdown characteristics, we did DC dielectric breakdown characteristics in this paper. We selected pure LLDPE, pure EVA and LLDPE films mixed with EVA as specimens, which were mixed with the weight percentages of 50, 60, 70 and 80[wt%] to be thin film. DC applying voltage speed was 500[V/sec]. The relation between dielectric breakdown characteristics and the variations of super structure due to mixing was investigated, and especially trap level at amorphous region, threshold energy increment of conductive electron at free volume were considered.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.08a
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• pp.64-68
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• 2002

According to the increasing power demand for the future construction of many underground cables will be required. However, construction of new ducts for power cables will be more difficult. Therefore, research work for realizing the high temperature superconducting(HTS) cable has advanced, where the development of electrical insulating system at cryogenic temperature is one of the major researches. For an electrical insulation design of HTS cable, it is important to understand not only breakdown but also partial discharge and dielectric loss($tan{\delta}$) in liquid nitrogen/paper composite insulation system. In this paper, we investigated breakdown characteristics in liquid nitrogen/paper composite insulation system for the application to HTS cable. And, we studied the breakdown characteristics of the multi-layer and butt gap of the insulation papers in liquid nitrogen. Also, we measured dielectric loss($tan{\delta}$) of the mini-model Cable made of TERLAM IPP.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.6
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• pp.583-589
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• 2011

The dielectric breakdown of bone-like materials subject to purely electric fields is investigated. In general, these materials consist of some layers with stronger dielectric strength and others with weaker dielectric strength in a parallel staggered pattern. The growth of the conductive channel is impeded during penetration of the weaker layer in the bone-like material because the electric-field concentration is relieved. The electric-field distribution around the head of the tubular channel is obtained from finite element analysis. The dielectric strength of the bone-like material is evaluated using the J integral, and some parameters affecting the dielectric strength are determined. It is shown that the J-integral values are reduced with an increase in the breakdown area in the weaker layer. It is also found that the ratio of the permittivity of the weaker layer to that of the stronger layer can strongly affect the dielectric breakdown.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.605-608
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• 2001

With the intention of investigating the breakdown properties of oil-immersed transformer oils in temperature range of 20∼100[$^{\circ}C$], we are made researches AC breakdown in the gap of 500∼2,500[$\mu\textrm{m}$]. The classification for the physical properties of oil for oil-immersed transformer by FTH and $^1$H-NMR experiments was confirmed to type of mineral oils. As the dependance of breakdown properties due to electrode gap length variation, breakdown voltage was found increasing according to the increase of gap, while dielectric strength was decreasing. As a result the characteristics for AC breakdown, It goes to prove that the breakdown voltage was increased to 90[$^{\circ}C$] but decreased over 90[$^{\circ}C$] in the temperature range. Also, breakdown voltage was found increasing in the increase of gap and the rising of temperature according to Weibull distribution.

• Progress in Superconductivity and Cryogenics
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• v.13 no.3
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• pp.5-9
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• 2011

DC high-temperature superconducting(HTS) cable system has attracted a great deal of interest from the view point of low loss, dense structure and large capacity. A HTS cable system is made of cable and termination. The insulating materials and insulation technology must be solved for the long life, reliability and compact of cable system. In this paper, we will report on the dielectric breakdown characteristics of insulating materials for HTS cable and termination. The AC, DC and lightning impulse breakdown strength of laminated polypropylene paper(PPLP) and glass fiber reinforced plastic(GFRP) have been measured under nitrogen pressures in the range of 0.l-0.4MPa. PPLP and GFRP are found to have a significantly higher DC breakdown strength. Also, DC surface flashover voltage of negative polarity is slightly higher than that of positive polarity in GFRP.

• Journal of Electrical Engineering and Technology
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• v.9 no.1
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• pp.280-285
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• 2014

In order to evaluate the insulation deterioration in the stator windings of five gas turbine generators(137 MVA, 13.8 kV) which has been operated for more than 13 years, diagnostic test and AC dielectric breakdown test were performed at phases A, B and C. These tests included measurements of AC current, dissipation factor, partial discharge (PD) magnitude and capacitance. ${\Delta}I$ and ${\Delta}tan{\delta}$ in all three phases (A, B and C) of No. 1 generator stator windings showed that they were in good condition but PD magnitude indicated marginally serviceable and bad level to the insulation condition. Overall analysis of the results suggested that the generator stator windings were indicated serious insulation deterioration and patterns of the PD in all three phases were analyzed to be internal, slot and spark discharges. After the diagnostic test, an AC overvoltage test was performed by gradually increasing the voltage applied to the generator stator windings until electrical insulation failure occurred, in order to determine the breakdown voltage. The breakdown voltage at phases A, B and C of No. 1 generator stator windings failed at 28.0 kV, 17.9 kV, and 21.3 kV, respectively. The breakdown voltage was lower than that expected for good-quality windings (28.6 kV) in a 13.8kV class generator. In the AC dielectric breakdown and diagnostic tests, there was a strong correlation between the breakdown voltage and the voltage at which charging current increases abruptly ($P_{i1}$, $P_{i2}$).