• Transactions on Electrical and Electronic Materials
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• v.10 no.3
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• pp.80-84
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• 2009

The microstructure, voltage-current, capacitance-voltage, and dielectric characteristics of CCT doped Zn/Pr-based varistors were investigated at different sintering temperatures. As the sintering temperature increased, the average grain size increased from 4.3 to 5.1 ${\mu}m$ and the sintered density was saturated at 5.81 g $cm^{-3}$. As the sintering temperature increased, the breakdown field decreased from 7,532 to 5,882 V $cm^{-1}$ and the nonlinear coefficient decreased from 46 to 34. As the sintering temperature increased, the donor density, density of interface states, and barrier height decreased in the range of (9.06-7.24)${\times}10^{17}\;cm^{-3}$, (3.05-2.56)${\times}10^{12}\;cm^{-2}$, and 1.1-0.95 eV, respectively. The dielectric constant exhibited relatively low value in the range of 529.1-610.3, whereas the $tan{\delta}$ exhibited a high value in the range of 0.0910-0.1053.

• Proceedings of the KSR Conference
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• 2003.10c
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• pp.606-610
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• 2003

The 200 class insulation system which adopted to traction motor have excellent dielectric strength but weaken to thermal stress therefore deterioration phenomena analysis according to thermal stress is necessary. Accelerated thermal aging tests have been used to determine thermal reliability of stator coils used as traction motor in electric multiple unit. The conventional aging test is carried on according to IEC 60034-18-31 and IEEE Std. 275-1992. Variation in insulation resistance, P.I, capacitance, dielectric loss($tan{\delta}$) and partial discharge are measured during the aging cycle. Sample coils for traction motor were tested by accelerated aging test which composed of heat, vibration and moisture. Reliability and expected life were evaluated on the insulation system for traction motor.

• Proceedings of the KSR Conference
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• 2003.10c
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• pp.623-627
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• 2003

Aging and failure of motor insulation depend on the stresses imposed on it. The insulation life time depends on the severity of the stresses. The electrical aging by transient surge is very important to traction motor in EMU(electric multiple unit). This paper presents the insulation characteristics of stator coil by transient surge from inverter. There are several nondestructive tests available for checking the condition of motor insulation, the probable extent of aging, and the rate of which aging is taking place. So the insulation characteristics of stator coil were each analyzed by measurement of leakage current, dielectric loss($tan{\delta}$), capacitance, polarization index(PI) and partial discharge. The method of diagnosis is able to analyze the aging condition and predict the life of the traction motor in EMU.

• Journal of the Korean Ceramic Society
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• v.35 no.8
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• pp.836-842
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• 1998

In this experiment well-know additives for Mn-Zn ferrites CaO and {{{{ { SiO}_{2 } }} were added at various content and their effects on microstructures and magnetic properties with sintering atmosphere were examined. By adding up to 0.04wt% {{{{ { SiO}_{2 } }} and and 0.06wt% CaO the sintered density was increased and then decreased gra-dually. Higher sintered density and initial permeability were observed by adding both CaO and {{{{ { SiO}_{2 } }} than by adding CaO or {{{{ { SiO}_{2 } }} alone. Without any additives initial permeability and tan$\delta$/${\mu}$ decreased at 1000kHz as oxidation degree(${\gamma}$) increased.

• Proceedings of the KIEE Conference
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• summer
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• pp.1124-1126
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• 2004

The measurements were performed to assess the insulation deterioration condition of the stator winding of Dae-Cheong hydro-generator ${\sharp}2$ which had been in service after being constructed 1980. After repair of the stator winding insulation. we conducted insulation diagnostic tests which include resistance, polarization index(P. I). AC current, dissipation factor($Tan{\delta}$) and partial discharges ($Q_{max}$). The results of diagnostic tests were compared to the previous records. On the basis of these test results. this paper tried to present the importance of insulation repair for the generator stator winding.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.441-444
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• 2000

In this paper, dielectric properties of XLPE sheets of 22kV cable with semiconducting and water were investigated. The breakdown strength of XLPE under rod/needle electrode were measured at without oil. It is found that the dielectric properties such tan$\delta$ of XLPE sheet dependence on semiconducting and water layer and are decreased much lower increase with temperature. The breakdown strength and the electrode effect are obtained as a function of thickness, and a equation for the sheet thickness dependent breakdown strength is also discussion.

• Electrical & Electronic Materials
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• v.7 no.5
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• pp.369-375
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• 1994

In this study, ferroelectric thin films of PZT with different Zr/Ti ratio were prepared by sol-get processing and annealed by rapid thermal annealing at >$500^{\circ}C$>$-700^{\circ}C$ for 10 sec. -1 min. Structures of the annealed films were examined by X-ray diffraction and SEM. Thin films of PZT with perovskite structure have been obtained by annealing at >$600^{\circ}C$ or above and for 20 seconds or longer. Maximum remnant polarization of 10.24.mu.C/cm$^{2}$ and minimum coercive field of 20.06 kV/cm were obtained from the 56/44 and 65/35 Zr/Ti composition films, respectively. Dielectric constant, .epsilon.$_{r}$ of 500-1300 and dielectric loss, tan .delta., of 0.01-0.035 were obtained from the films.s.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.41 no.6
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• pp.640-651
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• 1992

This paper describes the electric properties of mica reinforced silicone composites with the parameter of curing condition of silicone resin, application amount of silane coupling agent to the mica paper and the mica wt% to the composite. Heat-resistant silicone resin and mica paper made of mica flakes are used to prepared the mica/silicone composite as matrix and filler, respectively. To improve the dielectric properties and interfacial adhesion between matrix and filler, silane coupling agent is applied on the mica paper. As for matrix, tan$\delta$ value of 30$0^{\circ}C$ heat-treated silicone resin is the lowest under 1%. The optimal wt% of coupling agent is 0.3% to the weight of mica paper. 80 wt% of mica as filler to the mica/silicone composite shows the best electric properties. And the mica reinforced silicone composite shows good high-frequency and mechanical tensile stress properties.

• Electrical & Electronic Materials
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• v.10 no.1
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• pp.45-53
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• 1997

The purpose of this paper is to evaluate FRP rod for aging, which exposed to salt water and pure at elevated temperature. Dielectric constant and tan .delta. on time and frequency domain were tested to observe how rapidly the FRP rod aged. Dielectric constants of FRP rods with treating time were slightly increased. That of FRP rods with frequency, However, showed strongly the effects of large relaxation time estimated from interfacial polarization a or ionic. It is obvious that absorbed water affects to dielectric and electric properties of FRP with increasing the treating time.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05a
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• pp.13-17
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• 2000

In EPDM/ATH/clay compounds, clay rich compounds show lower tensile strength due to lower cure state derived from acidic nature of clay filler. As the ATH is replaced by clay, dielectric properties such as $tan{\delta}$, dielectric constant and volume resistivity improve, Polar nature of ATH is responsible for the higher hot water ingress. The amount of charge in the EPDM/clay compounds increases with an increase of clay concentration.