• Title, Summary, Keyword: Dielectric liquid

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Ferro-nematics and their outlook

  • West, John L.;Jakli, A.;Glushchenko, Anatoliy;Reznikov, Yuri
    • 한국정보디스플레이학회:학술대회논문집
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    • pp.287-288
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    • 2004
  • We report on the development of ferronematic liquid crystals, new materials that consist of a dilute suspension of ferroelectric particles in a nematic liquid crystal host. The particles share their ferroelectric properties with the nematic liquid crystal and impose a spontaneous dielectric polarization of about 10 nC/$cm^2$ to the entire medium, typical for many ferroelectric liquid crystals. As expected, these new materials have enhanced dielectric anisotropy and are sensitive to the sign of an applied electric field. The potential of their use in a number of devices are discussed.

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Electrohydrodynamic Analysis of Dielectric Guide Flow Due to Surface Charge Density Effects in Breakdown Region

  • Lee, Ho-Young;Kang, In Man;Lee, Se-Hee
    • Journal of Electrical Engineering and Technology
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    • v.10 no.2
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    • pp.647-652
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    • 2015
  • A fully coupled finite element analysis (FEA) technique was developed for analyzing the discharge phenomena and dielectric liquid flow while considering surface charge density effects in dielectric flow guidance. In addition, the simulated speed of surface charge propagation was compared and verified with the experimental results shown in the literature. Recently, electrohydrodynamics (EHD) techniques have been widely applied to enhance the cooling performance of electromagnetic systems by utilizing gaseous or liquid media. The main advantage of EHD techniques is the non-contact and low-noise nature of smart control using an electric field. In some cases, flow can be achieved using only a main electric field source. The driving sources in EHD flow are ionization in the breakdown region and ionic dissociation in the sub-breakdown region. Dielectric guidance can be used to enhance the speed of discharge propagation and fluidic flow along the direction of the electric field. To analyze this EHD phenomenon, in this study, the fully coupled FEA was composed of Poisson's equation for an electric field, charge continuity equations in the form of the Nernst-Planck equation for ions, and the Navier-Stokes equation for an incompressible fluidic flow. To develop a generalized numerical technique for various EHD phenomena that considers fluidic flow effects including dielectric flow guidance, we examined the surface charge accumulation on a dielectric surface and ionization, dissociation, and recombination effects.

Simple Technique for Measurement of Complex Permittivity and Detection of Small Permittivity Change Using Partially Open Cavity

  • Park, Sangbok;Chung, Young-Seek;Cheon, Changyul
    • Journal of Electrical Engineering and Technology
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    • v.9 no.1
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    • pp.268-272
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    • 2014
  • This letter presents a measurement methodology of the complex permittivity of liquid using a partially open cavity in narrow band. The partially open cavity (POC) can measure dielectric small changes caused by the temperature variation of the liquid inside the cavity as well. Using the resonance frequency and unloaded quality factor of the proposed POC, the complex permittivity is evaluated. The apertures on the walls of the cavity are designed to circulate the liquid inside to outside of the POC and located at the corner area of the cavity to minimize the disturbance of field distribution at the dominant mode. The results measured by the proposed POC were compared with those by the conventional open-ended probe and Cole-Cole equation. The POC showed better performance in measuring small dielectric constant changes than the open-ended probe.

Analysis of Partial Discharge Characteristics at Cryogenic Temperature below 77K (77K 이하 극저온 상에서의 부분방전 특성 분석)

  • Lee, Sang-Hwa;Kim, Bok-Yeol;Shin, Woo-Ju;Lee, Bang-Wook;Koo, Ja-Yoon
    • Proceedings of the KIEE Conference
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    • pp.1562-1563
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    • 2011
  • Partial discharge measurement is one of the effective diagnostic techniques to predict abnormal high voltage dielectric insulation conditions of the electric equipments. Recently partial discharge diagnostic techniques were also utilized to evaluate the cryogenic dielectric insulation of high temperature superconducting electric equipment in liquid nitrogen. Generally, liquid nitrogen at 77 K is used used as the cryogenic and dielectric media for many high temperature superconducting high voltage applications. When a quench in the superconductor occurs, bubbles are generated which can affect the dielectric properties of the liquid nitrogen. So in order to reduce the bubble formation, subcooled nitrogen was also employed for this purpose. In this work, investigation of partial discharge characteristics of subcooled liquid nitrogen were conducted in order to clarify the retardation of partial discharge initiation voltage according to the different subcooling temperature of liquid nitrogen. And also the relation of partial discharge phenomena and the activities of bubbles were analyzed. It was observed that PD inception voltages shows rather different characteristics according to the decrease of subcooling temperature and the activities of bubbles were strongly influenced by temperature of the subcooled liquid nitrogen.

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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.

Dielectric Properties of Liquid Crystalline Polymer (고분자액정의 유전특성)

  • Kang, Dae-Ha;Lee, Jae-Hoon;Park, Sang-Ho;Choi, Phil-Soo
    • Proceedings of the KIEE Conference
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    • pp.1266-1267
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    • 2008
  • Liquid crystalline polymer BB-3(1-methyl) takes two kinds of glass phases which are liquid crystalline glass and liquid glass below the glass temperature. This study is aimed to analyze the phase transitions of those samples with variation of temperature. For the analyzing temperature dispersion of dielectric constants was measured and the results were analyzed.

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Warm-up and Cool-down Characteristics of Cryogenic Insulation Materials in Liquid Nitrogen (액체질소에서의 극저온 절연매질의 Warm-up/Cool-down 특성)

  • Lee, Sang-Hwa;Shin, Woo-Ju;Khan, Umer Amir;Oh, Seok-Ho;Sung, Jae-Kyu;Lee, Bang-Wook
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.119-119
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    • 2010
  • Among the various factors influencing the service life of the electric equipment, the performance of dielectric insulation materials has an important role to determine their whole service life. In order to determine the degradation of insulating materials immersed in extremely low temperature media such as liquid nitrogen, the abrupt temperature change from cryogenic to normal room temperature should be considered. But the assessments of low-temperature aging test method for the dielectric materials immersed in liquid nitrogen considering these conditions were not fully reported. Therefore, for the fundamental step to establish the suitable degradation test methods for cryogenic dielectric materials, we focused on the evaluation of ageing test methods for dielectric materials exposed to low temperature environments considering thermal shock by cool-down and warm up test.

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Effect of the Surface Dielectric Layer on the Electro-Optical Performances of Liquid Crystal Devices

  • Park, Jae-Hong;Jung, Min-Sik;Lee, Sin-Doo
    • 한국정보디스플레이학회:학술대회논문집
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    • pp.543-546
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    • 2003
  • We studied the dielectric layer effect on the electro-optical (EO) properties of liquid crystal (LC) devices together with numerical simulations. Recently, it has been reported that the surface dielectric layer affects significantly the EO performances of LC microlens arrays and wide-viewing LC displays. it is found that the operation voltage of the LC device decreases with increasing the dielectric constant or with decreasing the thickness of the dielectric polymer layer. The experimental data agree well with theoretical results predicted in a simple dielectric model within the continuum formalism.

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The effect of splay elastic constant on the transmittance of fringe-field switching using a liquid crystal with positive dielectric anisotropy (유전율 이방성이 양인 액정을 사용한 FFS 모드에서의 스플레이 탄성상수에 따른 투과율 연구)

  • Kim, Tae-Hyun;Lee, Ji-Youn;Lee, Seung-Hee
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.518-519
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    • 2005
  • We have studied the transmittance of fringe-filed switching(FFS) using a liquid crystal with positive dielectric anisotropy. Generally, FFS having positive dielectric anisotropy has less transmittance than FFS using negative dielectric anisotropy. FFS mode transmittance depends on horizontal director deformation, however fringe filed is composed of vertical and horizontal field. Vertical field in the middle of electrode suppresses the transmittance of FFS mode, especially when we use positive one. So, it is important to prevent the LC director from the effect of vertical field. We changed the splay elastic constant and checked the transmittance. The transmittance of FFS having positive dielectric anisotropy was improved. Less tilted LC directors improve the transmittance of FFS using positive dielectric anisotropy. We can improve the transmittance by using LC which have high splay elastic constant when another LC properties are equal.

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A Study on the Dielectric Characteristics of Insulation Gases for a Sub-cooled Liquid Nitrogen System (이용률을 이용한 과냉질소 냉각시스템용 절연가스의 절연특성에 관한 연구)

  • Kang, Hyoung-Ku;Ko, Tae-Kuk
    • Progress in Superconductivity and Cryogenics
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    • v.12 no.1
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    • pp.52-55
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    • 2010
  • A sub-cooled liquid nitrogen system is known as a promising method to develop high voltage superconducting apparatuses such as superconducting fault current limiters (SFCLs) and superconducting cables. To develop a high voltage superconducting machine adopting the sub-cooled liquid nitrogen system with a constant pressure. injecting a non-condensable gas is indispensable. In this study. the dielectric characteristics of insulation gases are investigated and analyzed by using electric utilization factors ($\xi$). It is found that the maximum electric field at sparkover that occurs with 50 % probability. $E_{MAX.50%}$ exponentially decreases as the S increases. This means that the $E_{MAX.50%}$ at sparkover can be estimated with the $E_{MAX.50%}$