• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.9
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• pp.1159-1164
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• 2018

Vacuum circuit breakers(VCB) are widely used for current interruption of high-voltage inductive loads such as induction motors. This VCB can be chopped off before the current zero due to its high arc-extinguishing capability. One of the outstanding features of VCB is that it can cut off high frequency re-ignition current more than other circuit breakers. If the transient recovery voltage generated in the arc extinguishing is higher than the dielectric strength of the circuit breaker, a re-ignition phenomenon occurs. The surge voltage of the re-ignition is very high in magnitude and the steepness of the waveform is so severe that it can act as a high electrical stress on the winding. If the high frequency current of one phase affects the other two phases when the re-ignition occurs, it may cause a high surge voltage due to the virtual current chopping. If the magnitude of the voltage allowed in the motor winding is high or the waveform level is too severe, it may lead to insulation breakdown. Therefore, it is necessary to reduce the voltage to within a certain range. In this study, we briefly explain the various phenomena at the time of interruption, analyzed the magnitude of the dielectric strength and the transient recovery voltage at the simultaneous three-phase interruption that can give the greatest influence to the inductive load, proposed a method to reduce the impact.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1679-1681
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• 2004

Class-F and B resin-rich type insulating tapes are generally used for the ground wall insulations of respective air-cooled and water-cooled stator windings in larger turbine generators. In this paper, their electrical properties coupled with aging times in higher temperature than designed one in normal condition were experimentally investigated and the results of two comparative tests were presented on the existing class-F resin-rich type tape and a developed one after curing. The resin-rich tapes currently used arc composed of six and a half 3-layer sheets that arc structured with mica paper, the top and bottom supports of it respectively, and the epoxy resin to bind them tightly. The results for breakdown voltage and strength on the cured specimens were presented, which were composed of the unaged, the aged accelerated for one, two, and three thousand hours at 180 $^{\circ}C$. The surface and volume resistivities on them were measured and the results are also presented to make a comparative test for the initial electrical characteristics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.224-224
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• 2009

본 연구는 여러종류의 에폭시 나노콤포지트의 절연파괴 강도에 대한 와이블 특성을 연구하였다. 여러 종류 나노콤포지트는 나노입자 형상의 변화 즉, 층상실리케이트(Layered Silicate)와 구상 입자(SiO2)의 충진함량변화를 통한 절연파괴특성을 연구하였다. 나노+마이크로입자에대한 두 개의 체적비를 통한 멀티-나노복합물을 구현하였고, 그 절연파괴 특성의 결과와 기계적특성으로 굴곡강도특성을 Weibull Plot을 통하여 분석하였다. 순수한 나노콤포지트보다 멀티나노콤포지트가 기계적특성에서 월등하게 나타내었고, 절연파괴강도역시 형상파리미터가 대단히 큰 결과를 얻었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05e
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• pp.53-56
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• 2003

In this paper we investigated electrical properties for epoxy resin with improved mechanical property, elastomer epoxy. Investigated electrical properties are permittivity, tan $\delta$ and breakdown voltage strength(BDV). Permittivity and tan $\delta$ have dependancy on additive Quantity in general purpose epoxy resin. In particularly, those have very high values at low frequency and high temperature according to increasing component of elastomer. In case of BDV test, those materials have only a little difference due to increasing elastomer components. But in case of high quantities of elastomer, BDV has a difference. These results are represented that elastomer epoxy resin despite superior mechanical property needs many carefully thought as application electrical insulation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.295-295
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• 2008

Water tree experiments were done for several types of cross-linked polyethylenes. Test method is followed by ASTM D6097. Polyethylene is divided for four subgroup. First One is chemically cross-linked general XLPE, and second one is chemically cross-linked tree-retardant XLPE, and the third one is silane cross-linked polyethylene made by monosil process, and the last one is silane cross-linked polythylene made by copolymer. Tree retardant XLPE shows the shortest water tree length. Cahemcally cross-linked general XLPE shows the longest water tree length. Silane cross-linked polyethylene by copolymer is similar to tree retardant XLPE and similar breakdown strength. So silane cross-linked XLPE by copolymer could be used for the the medium voltage cable which should have tree retardant characteristics.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.10
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• pp.1800-1808
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• 2003

This work deals with the electrical conductivity of dielectric on output parameters such as metal removal rate and surface roughness value of a carbon steel(SM25C) and sintered carbides cut by wire-electrical discharge machining(W-EDM). Dielectric has several functions like insulation, ionization, cooling, the removal of waste metal particles. The presence of minute particles(gap debris) in spark gap contaminates and lowers the breakdown strength of dielectric. And it is considered that too much debris in spark gap is generally believed to be the cause of arcing. Experimental results show that increases of cobalt amount in carbides affects the metal removal rate and worsens the surface quality as a greater quantity of solidified metal deposits on the eroded surface. Lower electrical conductivity of the dielectric results in a lower metal removal rate because the gap between wire electrode and workpiece reduced. Especially, the surface characteristics of rough-cut workpiece and wire electrode were analyzed too. Debris were analyzed also through scanning electron microscopy(SEM) and surface roughness tester. Micro cracks and some of electrode material are found on the workpiece surface by energy dispersive spectrometer(EDS).

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.6
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• pp.15-21
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• 2006

This work deals with the electrical conductivity of dielectric on output parameters such as metal removal rate and surface roughness value of a carbon steel(SM25C) and sintered carbides cut by wire electrical discharge machining (WEDM). Dielectric has several functions like insulation, ionization, cooling, the removal of waste metal particles. The presence of minute metal particles(debris) in spark gap contaminates and lowers the breakdown strength of dielectric. And it is considered that too much debris in spark gap is generally believed to be the cause of arcing. Experimental results show that increases of cobalt amount in carbides affects the metal removal rate and worsens the surface quality as a greater quantity of solidified metal deposits on the eroded surface. Lower electrical conductivity of the dielectric results in a lower metal removal rate because the gap between wire electrode and workpiece reduced. Especially, the surface characteristics of rough-cut workpiece and wire electrode were analyzed too. Debris were analyzed also through scanning electron microscopy(SEM) and surface roughness tester. Micro cracks and some of electrode material are found on the workpiece surface by energy dispersive spectrometer(EDS).

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.226-229
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• 2003

Following the successful development of practical high temperature superconducting (HTS) wires, there has been renewed activity in the development of superconducting power equipments. HTS equipments must be operated in the coolant, such as liquid nitrogen (L$N_2$) or cooled by cooler, such as GM-cryocooler to maintain the temperature below critical temperature. In this paper, dielectric strength of some insulating materials, such as epoxy, teflon, and glass fiber reinforced plastic (GFRP) in L$N_2$was measured. Surface breakdown voltage of GFRP which is basic property in design of HTS solenoid coil was measured. Epoxy is a goof insulating material but it is fragile at cryogenic temperature. The multi-layer insulating method of current lead is suggested to compensate this fragile property. It consists of teflon tape layer and epoxy layer fixed with texture. Based on these measurements, the 6.6㎸ class HTS magnet for DC reactor type high-T$_{c}$ superconducting fault current limiter (SFCL) was successfully fabricated and tested.d.

• Advances in materials Research
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• v.1 no.1
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• pp.93-107
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• 2012

Epoxy resin is widely used in high voltage apparatus as insulation. Fillers are often added to epoxy resin to enhance its mechanical, thermal and chemical properties. The addition of fillers can deteriorate electrical performance. With the new development in nanotechnology, it has been widely anticipated that the combination of nanoparticles with traditional resin systems may create nanocomposite materials with enhanced electrical, thermal and mechanical properties. In the present paper we have carried out a comparative study on dielectric properties, space charge and dielectric breakdown behavior of epoxy resin/nanocomposites with nano-fillers of $SiO_2$ and $Al_2O_3$. The epoxy resin (LY556), commonly used in power apparatus was used to investigate the dielectric behavior of epoxy resin/nanocomposites with different filler concentrations. The epoxy resin/nanocomposite thin film samples were prepared and tests were carried out to measure their dielectric permittivity and tan delta value in a frequency range of 1 Hz - 1 MHz. The space charge behaviors were also observed by using the pulse electroacoustic (PEA) technique. In addition, traditional epoxy resin/microcomposites were also prepared and tested and the test results were compared with those obtained from epoxy resin/nanocomposites.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2004.05a
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• pp.502-505
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• 2004

The purpose of this experiment is to modify diagnosis criterion of isothermal relaxation current(IRC) measurement equipment which is using for distribution cable diagnosis. We're using this system for several years in the field instead of DC leakage current measurement and lots of cables were replaced. But we have to investigate on the reliability of this equipment for our cables because we didn't carried out condition assessment of extracted cables after field diagnosis by this equipment. It is important thing for cable maintenance. If the replacement criterion is improper we can not prevent failures or will waste budget on account of replacement of the sound cables. In this papar we selected field installed cables and injected silicone fluid to the cables for insulation rehabilitation. In order to prove reliability of the diagnosis equipment we compared diagnosis results and AC breakdown strength according to operating time after silicone treatment. This is the results of the field test for 1 year.