• Title, Summary, Keyword: Dielectric liquids

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A Study on Pulse Dielectric Breakdown of Cryogenic Liquids (극저온 액체의 펄스 절연파괴에 관한 연구)

  • Choo, Young-Bae;Ryu, Kyung-Woo;Kim, Sang-Hyun
    • Proceedings of the KIEE Conference
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    • pp.477-479
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    • 1987
  • An understanding of dielectric breakdown characteristics in cryogenic liquids is of importance in the development of various cryogenic and superconducting electrical equipments. This investigation describes measurements of pulse breakdown voltage, polarity effect, conditioning effect and time lag characteristics of cryogenic liquids.

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Hydrodynamic Modeling for Discharge Analysis in a Dielectric Medium with the Finite Element Method under Lightning Impulse

  • Lee, Ho-Young;Lee, Se-Hee
    • Journal of Electrical Engineering and Technology
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    • v.6 no.3
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    • pp.397-401
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    • 2011
  • The response of lightning impulse voltage was explored in dielectric liquids employing hydrodynamic modeling with three charge carriers using the finite element method. To understand the physical behavior of discharge phenomena in dielectric liquids, the response of step voltage has been extensively studied recently using numerical techniques. That of lightning impulse voltage, however, has rarely been investigated in technical literature. Therefore, in this paper, we tested impulse response with a tip-sphere electrode which is explained in IEC standard #60897 in detail. Electric field-dependent molecular ionization is a common term for the breakdown process, so two ionization factors were tested and compared for selecting a suitable coefficient with the lightning impulse voltage. To stabilize our numerical setup, the artificial diffusion technique was adopted, and finer mesh segmentation was generated along with the axial axis. We found that the velocity from the numerical result agrees with that from the experimental result on lightning impulse breakdown testing in the literature.

The Dependence of Temperature and Frequency for the Dissipation Factor in Liquid Dielectrics (액체절연체(실리콘유) 유전정접의 온도및 주파수의존성)

  • 이돈희;소병문;이수원;김왕곤;홍진웅
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.85-89
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    • 1993
  • Silicone oil exhibits the properies of both organic and inorganic substances and, thus, it has many superior properties such as higher thermal resistance and lower thermal oxidation level when compared to other dielectric liquids. In order to investigate the dielectric characteristics, dielectric liquids of viscosity 1 [cSt] is chosen as the specimen and experiment is performed in the temperature range of 20∼65 [$^{\circ}C$] and frequency range of 30∼1${\times}$10$\^$6/ [Hz] respectively. As a result, the observed linear decrease in dissipation factor at the frequency range below 3 [kHz] is due to the influence of frequency, whereas the increase in dissipation factor at higher frequency range is contributed by electrode's resistance. At a fixed frequency of 30 [kHz], increasing temperature results in higher peak value and wide width of the absorption curve. This is due to the increase in dipole and viscosity. As temperature increases, dipole moment is decreased from 0.98 to 0.64 [debye]. The activation energy which causes the relaxation and loss of dielectric is obtained about 15 [kcal/mole].

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Development of a Cross Capacitor Electrode for Measurements of Liquids Dielectric Constants (액체의 유전상수 정밀측정용 크로스 커패시터 전극 개발)

  • ;;;YU. p. Semenov
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.675-678
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    • 2000
  • Using the principle of the cross capacitor, a precise system for measuring the electric constants of liquids has been developed. The four electrodes of the cross capacitor were formed around fused-silica tube by plating a gold film. The effect of a non-uniform tube wall ok the measured permittivity was investigated As the individual characteristics of the tubes were determined to be constant, the pure dielectric constants extracted from any effect of the fused-silica material could be precisely derived with uncertainty of less than ${\pm}$ 0.02∼0.05 %.

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Characteristics of Dielectric Breakdown in Liquid Nitrogen (액체질소의 절연파괴특성)

  • 추영배;류경우;류강식;김상현
    • The Transactions of the Korean Institute of Electrical Engineers
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    • v.37 no.12
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    • pp.872-878
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    • 1988
  • During the past few years, a great deal of attention has been directed to the application of superconductivity to the electrical systems such as superconducting power transmission lines, superconducting magnet energy storage and so on. Yet in order to develop the practical model of these electrical equiqments utilizing suprconductivety and other phenomena at cryogenic temperautre, it is necessary to know the dielectric behaviour of insulating materials at cryogenic temperature in view of reliability, safety and economy of these machines. Investigation of dielectric properties of cryogenic liquids is very important due to the dual role of those as the dielectric and cooling medium. In this study, we investigated results measured over several kinds of dielectric characteristics of liquid nitrogen taking into consideration for application of high Tc superconductor. Dependence of breakdown voltage of gap width, polarity and pressure is reported in this paper and time delay characteristics of breakdown is also the subject of this discussion.

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Formulation of the Sucrose-Free Simulant Human Tissue for SAR Measurement at CDMA Mobile Band

  • Gimm, Yoon-Myoung
    • Journal of electromagnetic engineering and science
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    • v.7 no.2
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    • pp.53-58
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    • 2007
  • A general method to formulate the tissue-equivalent liquids for SAR measurement is proposed to make sucrose-free brain tissue applicable at 835 MHz as an example We suggest the tissue composition can be determined by measuring the dielectric constants and conductivities with the DI water and salt addition variation to the pre-manufactured auxiliary liquid of DGBE and TritonX-100 The manufactured liquid satisfies the specified electrical parameters of international standard at 835 MHz.

Degradation Diagnosis of Transformer Insulating Oils with Terahertz Time-Domain Spectroscopy

  • Kang, Seung Beom;Kim, Won-Seok;Chung, Dong Chul;Joung, Jong Man;Kwak, Min Hwan
    • Journal of the Korean Physical Society
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    • v.71 no.12
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    • pp.986-992
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    • 2017
  • We report the frequency-dependent complex optical constants, refractive index and absorption, and complex dielectric properties over the frequency range from 0.2 to 3.0 THz for aged power transformer mineral insulating oils. These results have been obtained using terahertz time-domain spectroscopy (THz-TDS) and demonstrate the double-Debye relaxation behavior of the mineral insulating oil. The measured complex optical and dielectric characteristics can be important benchmarks for liquid molecular dynamics and theoretical studies of insulating oils. Due to clear differences in THz responses of aged mineral insulating oils, THz-TDS can be used as a novel on-site diagnostic technique to monitor the insulation condition in aged power transformers and may be valuable alternative to characterize other developing eco-friendly insulating oils and industrial liquids.

Dry Electrical Discharge Machining for Deburring Drilled Holes in CFRP Composite

  • Islam, Md. Mofizul;Li, Chang Ping;Ko, Tae Jo
    • International Journal of Precision Engineering and Manufacturing-Green Technology
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    • v.4 no.2
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    • pp.149-154
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    • 2017
  • Dry electric discharge machining (EDM) is an evolving technology that uses gas as a dielectric instead of liquids like oil or deionized water. Dry EDM reduces machining costs and environmental hazards. Most studies on dry EDM deal with steel as the workpiece. Hence, this study investigates a dry EDM technique for the removal of burrs in drilled holes in CFRP composites. Oxygen and air was used as the dielectric medium, and the results were compared with a previous study on oil EDM. The material removal rate increased significantly with the capacitance, voltage, and gas pressure in both dry EDM and oil EDM. Positive tool polarity produced a higher material removal rate (MRR) than negative polarity in both cases. Compared to conventional oil EDM, using oxygen as a dielectric showed nearly three times better MRR, and that with air was two times better. Moreover, in dry EDM using oxygen as dielectric exhibited better performance than using air as dielectric. This study revealed that the dry EDM is more effective than that of oil EDM as a deburring technology.

Finite Element Analysis for Dielectric Liquid Discharge under Lightning Impulse Considering Two-Phase Flow (절연유체 내 2상유동을 고려한 뇌임펄스 응답 유한요소해석)

  • Lee, Ho-Young;Lee, Jong-Chul;Chang, Yong-Moo;Lee, Se-Hee
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.60 no.11
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    • pp.2097-2102
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    • 2011
  • Discharge analysis technique for dielectric liquid was presented by using the Finite Element Analysis (FEA) under a lightning impulse incorporating two-phase flow phenomena which described gas and liquid phases in discharge space. Until now, the response of step voltage has been extensively explored, but that of lightning impulse voltage was rarely viewed in the literature. We, therefore, developed an analyzing technique for dielectric liquid in a tip-sphere electrode stressed by a high electric field. To capture the bubble phase, the Heaviside function was introduced mathematically and the material functions for the ionization, dissociation, recombination, and attachment were defined in liquid and bubble, respectively. By using this numerical setup, the molecular dissociation and ionization mechanisms were tested under low and high electric fields resulted from the lightning impulse voltage of 1.2/50 ${\mu}s$. To verify our numerical results, the velocity of electric field wave was measured and compared to the previous experimental results which can be viewed in many papers. Those results had good agreement with each other.

An experimental study for boiling heat transfer enhancement under electric fields (전기장하에서의 비등 열전달 촉진에 관한 실험적 연구)

  • O, Si-Deok;Gwak, Ho-Yeong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.7
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    • pp.2298-2314
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    • 1996
  • Electric field effect on boiling of refrigerants R11, R113, and FC72 has been investigated experimentally. One purpose of the experimental investigation is to determine the effects of the electrode arrangements on electrohydrodynamic boiling of the above mentioned liquids. The test equipment employed in the experiment consists of a shell and tube heat exchanger with six or six and twelve rows of electrode wires around the tube. It has been found that the applied voltage promotes the boiling heat transfer coefficient except FC72. Boiling heat transfer enhancement obtained is about 230% for R11, 280% for R113. It has also been observed that bubbles detached from the tube aggregate at the place where the electrical gradient force balances with the buoyancy one. These aggregated bubbles force to decrease the boiling heat transfer coefficient as well as to reduce the voltage needed to the dielectric breakdown.