Decrease Of Dielectric Strength Research Articles

Characterization of Encapsulants for High-Voltage High-Temperature Power Electronic Packaging

Seven encapsulants with operating temperature up to 250 °C are surveyed for possible use in high-temperature high-power planar packages. Processability is assessed by studying the flow fronts and the cured properties of the surveyed materials between paralleled plates. Material B failed in the flow test because it dried out in seconds. Materials A, C, and D failed the curability test because A and C showed volume shrinkage during curing, while D cracked after curing owing to its brittle nature. It is found that elastic materials that usually correspond to low glass transition temperatures (Tg) tend to perform better with regard to large-area planar-structure packages. Materials E-G are confirmed to be comparatively stable with respect to temperature, and both dielectric strength and dielectric permittivity decrease by about 40 and 30%, respectively, as the temperature is increased from 25 to 250 °C. The thermal aging test show that the materials harden during the aging process. Meanwhile, cracking starts in the material matrix. The dielectric strength of the sample drops by 60-70% to only around 10 kV/mm once cracking occurs.

초고압 SF6 가스 차단기 투입 시 아크접촉자 내전압 특성 연구

The non-controlled closing of High-voltage SF6 gas circuit breaker can cause transient current and overvoltage in the field. The controlled closing technology is an effective way to reduce transient current and voltage, prevent equipment failures, and improve power quality. For the development of controlled closing, it is obviously necessary to determine the withstand voltage between arc contacts of High-voltage SF6 gas circuit breaker in making operation. This paper focuses on decrease of pressure and density of SF6 gas that can affect withstand voltage between arc contacts in making operation. The dielectric strength between arc contacts could be improved by minimizing the decrement of pressure and density of SF6 gas obtained by simulation and test and moreover the rate of decrease of dielectric strength (RDDS) of arc contacts could be foreseen.

Statistical analysis of electrical breakdown behavior of polyimide following degrading processes

Polyimide (PI) tape has been widely used as electrical insulation for wires and cables due to its excellent balance of electrical, mechanical and thermal properties. However, insulation materials are exposed to various environmental degradation mechanisms during service, which can cause deterioration of their insulation properties. In this paper, the effects of thermal exposure and immersion in water on dielectric strength of Kapton <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> HN PI film are investigated statistically by two-parameter Weibull distribution analysis. The PI samples were heated at 475°C for 1 to 4 h, and at 450 to 480°C for 4 h, to study the influence of thermal exposure. Moreover, to explore the effect of moisture absorption, other PI samples were immersed in distilled water for up to 96 h at room temperature. After the degrading process, breakdown voltage and thickness were measured at 20 different points on each sample. The Weibull cumulative distribution function for each of the degraded samples was plotted, and compared with that of a sample dried by heating at 200°C for 1 h. Significant decreases in both the scale parameter and the shape parameter of the Weibull distribution, obtained through least-squares regression, are observed, indicating a statistical decrease in dielectric strength and a more dense dispersion of electrical weak points in PI. This observed deterioration of insulation capability of PI is attributed to chemical degradation and formation of ionic side groups during heating and immersion in water, respectively.

X-ray diffraction study of ferroelectric and antiferroelectric liquid crystal mixtures exhibiting de VriesSmA∗-SmC∗transitions

In this Rapid Communication, results on smectic layer thickness, using synchrotron radiation x-ray diffraction, for different mixtures of ferroelectric and antiferroelectric liquid crystals are given. We find that with an increased ferroelectric component in the mixtures, the layer shrinkage at the de Vries SmA∗-SmC∗ transition increases. This observation can be used to explain our previously observed behaviors [U. Manna, J.-K. Song, Yu. P. Panarin, A. Fukuda, and J. K. Vij, Phys. Rev. E 77, 041707 (2008)] that the soft-mode dielectric strength decreases, the Landau coefficient increases, and the Curie-Weiss temperature range decreases with increased ferroelectric component in the mixture exhibiting de Vries SmA∗-SmC∗ transition.

Effects of MgO on dielectric properties and electrical conductivity of ternary zinc magnesium phosphate glasses

Glasses with composition ( ZnO ) 30 ( MgO ) x ( P 2 O 5 ) 70 - x ( x = 5, 8, 13, 18 and 20 mol%) have been successfully prepared by the melt-quenching technique. The dielectric permittivity ( ε ′ ) and loss factor ( ε ″ ) were measured in the frequency range of 0.01 Hz to 1 MHz and in the temperature range of 303 to 573 K. From the results, there is evidence of dipolar relaxation occurring between 10 3 – 10 6 Hz , while at low frequencies, the spectrum is dominated by dc conduction which was manifested by the 1 / ω slope of the loss factor plot. The value of the relaxing frequency ( ω p ) plotted against 1 / T shows a single relaxation mechanism with an activation energy of 0.45 eV. The average value of the activation energy for dc conduction was much higher (1.25 eV) suggesting its diffusion movement had encountered more difficult steps than the small displacement changing dipoles. With increasing MgO concentration, the dielectric permittivity ( ε ′ ), dc conductivity ( σ dc ) and dielectric strength ( Δ ε ) decrease and these were attributed to some of the magnesium ions participated in the glass-forming positions as well as modifiers. At lower temperatures, the complex permittivity plots present a skewed arc with center point lying below the real axis which is a non-Debye characteristic. The empirical data were sufficiently fitted by using the Harviliak–Negami equation. The temperature dependent of the parameter α is discussed.

Effects of Confinement and Electric Field on the Dielectric Behavior of Smectic- Phase

Dielectric permittivity measurements are carried out to investigate the effects of confinement and electric field on a chiral smectic liquid crystal in the smectic- () phase for various cell thicknesses. The Sm-A* – transition temperature and the temperature range for which the phase is stable decrease with decreasing cell thickness. On reducing the cell thickness, the surface-induced mode appears, as a result of the influence of the cell substrates. This increases the dielectric strength of the phase. The distribution parameter of the relaxation process, α decreases significantly, and in the case of a thin cell, the decrease observed reflects a wide symmetric distribution of the relaxation process. On increasing the electric field, the dielectric strength decreases and the relaxation frequency increases in the phase. These are explained by the ‘helical fracture’ model, originally proposed for the Sm-C* phase.

반도체 장비용 Al2O3코팅 진공부품의 내부식성 평가 연구

반도체 장비용 진공코팅부품의 공정영향에 의한 내부식 성능 평가방법을 연구개발 하였다. 평가기준을 마련하기 위해 반도체 공정에서 교체된 코팅부품의 특성을 분석 평가하였다. 코팅부품의 성능을 정량적으로 측정하기 위하여 부품의 코팅막으로 많이 사용되고 있는 <TEX>$Al_2O_3$</TEX> 막의 건식부식실험을 실시하였고 표면모폴로지, 누설전류 및 내전압측정 등을 수행하였다. 실험결과 건식부식처리 후 샘플의 누설전류량이 증가하였고, 절연내력이 크게 줄어 전기적 특성이 하향된 결과를 보였으며, 표면 모폴로지의 경우 부식시간 증가에 따라 표면 손상정도가 증가하는 것을 확인 할 수 있었다. 부식공정에 의한 이들 특성 값 변화를 이용하여 코팅부품의 공정영향에 의한 성능평가 방법을 개발할 수 있었다. This study is concerned with the evaluation of the corrosion resistance of coated semiconductor equipment parts with various processes. To select the appropriate basis for evaluation, replacement parts were observed during the semiconductor manufacturing process. This study also ran a dry corrosion test using <TEX>$Al_2O_3$</TEX>, which is mostly used as a coating material. This test quantitatively measured the efficiency of coated parts. Surface morphology, leakage current and breakdown voltage were also evaluated. This study showed that a dry corrosion process led to the drop of electrical properties, for example, the leakage current increase and the dielectric strength decrease. The surface morphology test displayed that surface damage is largely dependent on the exposure time to corrosive environments. By using the values that changed during the corrosion process, it may be possible to contrive a method to evaluate the efficiency of coated parts with various processes.

The Estimation of the Dielectric Strength Decrease of the Solid-solid Interfaces by using the Applied Voltage to Breakdown Time Characteristics

In the complex insulation system that is used in extra high voltage(EHV) devices, according to the trend for electric power equipment of high capacity and reduction of its size, macro interfaces between two different bulk materials which affect the stability of insulation system exist inevitably. In this paper, the dielectric strength decrease of the macro interfaces between epoxy and ethylene propylene diene terpolymer(EPDM) was estimated by using the applied voltage to breakdown time characteristics. Firstly, the AC short time dielectric strength of specimens was measured at room temperature. Then, the breakdown time was measured under the applied constant voltage which is 70% of short time breakdown voltage. With these processes, the life exponent n was determined by inverse power law, and the long time breakdown voltage can be evaluated. The best condition of the interface was LOS(low viscosity(350 cSt) silicone oil spread specimen). When 30 years last on the specimens, the breakdown voltage was estimated 44% of the short time breakdown voltage.

Effect of physical aging on the Johari-Goldstein and α relaxations of D-sorbitol: A study by thermally stimulated depolarization currents

The relaxations in amorphous D-sorbitol have been studied by thermally stimulated depolarization currents during annealing at 255 K, which is 17 K below its calorimetric glass transition temperature Tg=272 K. As the glass structurally relaxes on aging, the features of the alpha relaxation and of the Johari-Goldstein (JG) relaxation change with time. For the alpha relaxation (i) the dielectric strength decreases; (ii) the activation energy decreases; and (iii) the relaxation time increases. For the JG relaxation the dielectric strength also decreases but with a different time dependence, and there is no evidence for any modification of the kinetic features of the mobility. The amplitude of response to aging is higher for the higher temperature motional components of the Johari-Goldstein relaxation compared with the lower temperature ones.

Dielectric breakdown strength in magnetic fluids

AbstractThe application of an external magnetic field on the magnetic fluids induces needle like structuralization of magnetic particles. The influence of this aggregation of magnetic particles in an external magnetic field H on the magneto‐dielectric behaviour and dielectric breakdown strength of a transformer oil based magnetic fluids was measured. The observed decrease of dielectric breakdown strength (for H = 0 and H ⟂ E vs. distance between electrodes is found to be in agreement with a theory of semi‐classical bond percolation for a non‐linear composite material. In situation when E ‖ H oscillations of dielectric breakdown strength were observed that are associated with a size effect probably.

550kVガス遮断器の閉極位相制御に関する検討

Optimal dosing target of 550kV gas circuit breaker (GCB) is investigated. In dosing operation of GCB, making voltage depends on dielectric and mechanical characteristics of GCB, therefore optimal closing target has to be determined by investigation of these characteristics. Optimal closing target and estimated making voltage are shown as functions of Rate of Decrease of Dielectric Strength (RDDS) and mechanical scattering of closing time of GCB. Closing characteristics of 2 break GCB are investigated considering a change of the dividing voltage of each pole. Synchronous closing of 550kV live tank GCB were tested with the optimum targets for minimum and maximum making voltage prospected by the functions. The EMC tests of the synchronous switching controller were also confirmed by switching test with 550kV circuit.

Soft Mode Dielectric Relaxation Under the Influence of Bias Electric Field of a Ferroelectric Liquid Crystal Mixture

Temperature dependent soft mode part of the complex dielectric constant has been measured as a function of bias electric field both in the smectic C* and smectic A* phases for a ferroelectrc liquid crystal (FLC) mixture. From the experimental data, soft mode relaxation frequency and dielectric strength have been determined both in smectic C* and smectic A* phases. In smectic A* phase, relaxation frequency and inverse of dielectric stmngth of the FLC mixture does not follow the Curie-Weiss law. The critical exponent for the studied FLC mixture is 1.43. Dielectric results shows a dependence of soft mode dielectric strength and relaxation frequency with bias field near the tmudion temperature in smectic A* phase to an extent of 1°C above the transition tanperature and above 1°C bias field does not have any effect on relaxation frequency and dielectric strength It is observed that relexation frequency increases with increasing bias field while the compounding dielectric strength decreases.

Dielectric Strength of Thin Oxide Grown Thermally Using Thin Amorphous Silicon

The dielectric strength of thin (16 nm) thermal oxide grown using thin amorphous Si is investigated in terms of preoxidation annealing, oxidation, and postoxidation annealing temperatures. Even when the gate area is large (25 mm2), many metal oxide semiconductor capacitors provided histograms of oxide dielectric strength displaying narrow distributions. Preoxidation annealing at temperatures above 950°C drastically reduces the dielectric breakdown to nearly 0 MV/cm. The dielectric strength increases or decreases according to the postoxidation annealing temperature, suggesting that this change in dielectric strength is associated with a reversible mechanism. The implantation of ions straight through defective oxide layers clearly improves dielectric strength from 0 to about 3 MV/cm, implying that an oxide defect has a definite structure, which is destroyed during ion implantation when the constituent atoms are randomly displaced.

Experimental and theoretical study of the influence of a bias electric field on the dielectric properties of the chiral smectic A* phase

Abstract The influence of a bias electric field on the temperature and frequency dependence of the soft mode part of the complex dielectric constant of the chiral smectic A* phase has been studied experimentally. It was found that only close to T S*CS*A does the bias field have any influence on the experimentally determined quantities. Here the relaxation frequency increased with increasing bias field, while the corresponding dielectric strength decreases. We also present a theoretical calculation of the influence of a bias field on the complex dielectric constant of the chiral smectic A* phase which, apart from minor details, is in accordance with the observed behaviour. Finally we discuss how the nature of the electroclinic effect can be correlated with the influence of the bias field on the smectic A* dielectric constant.

Correlation of physico-chemical, mechanical and electrical properties of ultraviolet-degraded poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET) films have been exposed to ultraviolet radiation. Changes in physico-chemical, mechanical and electrical properties which occur in the films were examined. It was found that the specific viscosity, tensile strength, elongation at break, relative dielectric constant and dielectric strength decrease, while the dielectric loss factor, density, optical density of the ir spectrum band which refers to the trans form of the PET molecule, as well as the quantity of carboxylic end groups, increase. Least squares analysis and function straightening methods were used for the interpretation of the experimental data. Correlating relationships between measured parameters were established using the same methods. Special attention was paid to the changes in the electrical properties of poly(ethylene terephthalate), because no data are available so far. Mathematical correlations with chemical and mechanical properties were established.

Dielectric-Withstand Levels of Some 735-kV Air-Blast Circuit Breakers Under Both Direct and Synthetic Out-of-Phase Interrupting Tests

Simulations with the transient network analyzer at IREQ have revealed that following a load-shedding operation on the James Bay 735-kV power system, severe out-of-phase overvoltages could appear across the interrupting circuit breakers. The simulation results show that overvoltages could reach 2000 kV, while the maximum breaking current is as low as 5 kA rms. Since these overvoltage values far exceed the IEC specifications (1500 kV), direct and synthetic out-of-phase interrupting tests were performed on two types of breaker: a conventional air-blast circuit breaker of the type already in service and a modern improved design of the same type. The aim of the test program was to qualify high-voltage circuit breakers for the James Bay power system. The paper focuses on the analysis of the test results and deals especially with the decrease in dielectric strength of the breaker with the time that elapses after current interruption.

The effects of photo-degradation on the electrical properties of poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET) films have been exposed to uvradiation. Electrical property changes which occur in the films were examined. It was found that the relative dielectric constant and the dielectric strength decrease, while the dielectric loss factor increases. The rate of change of these parameters slowed down as the irradiation time increased. The parameter changes are presented graphically as a function of irradiation time and empirical equations are established. These empirical equations were obtained as second or third order polynomials by the least squares analysis method. The method of function straightening gave simpler power or exponential functions. These empirical equations represent the relationships between the electrical parameters and the irradiation time to a limit of relative error of less than 10%.

Electric Breakdown and Conduction through Mylar Films

Dc breakdown studies on Mylar film show that defects cause a decrease in dielectric strength with decreasing film thickness at room temperature but not at −180°C. The breakdown at defects is associated with moisture content. Using self-healing electrodes to eliminate weak areas, a dc dielectric strength of 6 Mv/cm is found, independent of film thickness. Prebreakdown current measurements indicate ionic currents which are fairly uniform throughout a sample, and field emission currents localized at incipient breakdown points. Breakdown probably occurs as a result of local heating by field emission currents.

Deproteinized Rubber

Abstract FOR some years deproteinized rubber has been used by this company in the manufacture of rubber insulation, and the rate of consumption is increasing rapidly. This new and unique raw material is now also being manufactured for the Simplex Wire and Cable Company by The Goodyear Tire and Rubber Company on plantations in the Far East. The special virtue of deproteinized rubber is its low water absorption and the electrical stability which it imparts to vulcanized rubber compounds immersed in water. Electrical engineers are specifying such compounds for submarine, underground, and duct cables and all other insulation that may be exposed to water. The electrical properties of ordinary rubber insulation are impaired by increasing water absorption; the dielectric strength decreases, and the capacitance and leakance (or dielectric loss) increase. Power cables become useless when decreasing dielectric strength is insufficient to withstand operating voltage. Communication cables deteriorate rapidly by water absorption because their increasing capacitance and leakance prevent the practical transmission of signals long before dielectric strength is low enough to cause failure at the extremely low operating voltage of such cables.