Multimodal operation of a ferroresonant circuit with quintic nonlinearity

The multimodal operation (jump phenomenon) of a ferroresonant circuit of practical interest is analyzed using West's method of frequency-damping boundaries with a fifth-order approximation for the saturation curve of the nonlinear inductor. For given circuit parameters, the applied voltage range over which ferroresonance can occur is determined, and it is shown that this method gives more precise information than the incremental describing function method on the possibility that a certain applied voltage will produce the jump phenomenon.     

Ferroresonance Analysis in LCR Circuits Including Rapidly Solidified Alloy Cores

We report an experimental and modeling analysis of ferroresonance phenomena in a series inductance–capacitance–resistance circuit with a saturable inductor. The nonlinear reactor core is made of a nanocrystalline ribbon whose magnetic properties can be modified by suitable thermal treatments. This choice of core allows us to investigate the influence of the magnetization curve on the evolution of the ferroresonance phenomenon. We detected different ferroresonance modes experimentally and reproduced them by simulation. We gave particular attention to the longitudinally field-annealed alloy, whose magnetization characteristic is close to a step ideal curve; this feature enables us to analytically interpret the ferroresonance mechanism and predict the conditions that lead to a stated evolution of the phenomenon.      

Sensitivity studies on power transformer ferroresonance of a 400 kV double circuit

The ability to predict ferroresonance significantly relies on the accuracy of the transformer model and the power system's parameters. The accomplishment of a suitable simulation model allows the sensitivity studies to be performed to determine the degree of influence of various components and parameters of the ferroresonance phenomenon such as line length, point-on-wave switching and transformer core loss. The modelling work carried out in ATP (commercially available software) on a 1000 MVA 400/275/13 kV power transformer model is described and the simulation with field ferroresonance test recordings is verified. The maps that define the boundaries between safe and ferroresonant (fundamental, subharmonic, chaotic) regions as a function of system parameters are created through the sensitivity studies performed.     

Effects of the polarity of bias voltage on the electrical performance of the diamond film detectors

The effect of the polarity of the applied bias voltage on the electrical response and the charge collection efficiency of sandwich structural diamond film detectors under 5.5 MeV ²⁴¹Am alpha-particle irradiation is investigated. Results show that, under the alpha irradiation the detector applied with a negative bias voltage has a higher response current and a better signal-to-noise ratio than that applied with a positive bias voltage. A better energy resolution of about 25.0% is obtained for the detector applied with a negative bias voltage, and however 38.4% for that with a positive bias voltage. Raman scattering studies demonstrate that these changes with the polarity of the bias voltage may be attributed to the different structural imperfection distributions along the thickness direction of the diamond film.     

Study on multi-peak behavior of pulsed dielectric barrier discharges in atmospheric-pressure helium

In this work the multi-peak behavior of the dielectric barrier discharge excited by repetitive voltage pulses (pulsed DBD) in atmospheric-pressure helium has been systematically investigated, based on a one-dimensional fluid model. The effects of the parameters of the applied voltage pulse and dielectrics on the multi-peak behavior of the pulsed DBD have been analyzed in detail. The parameters of the applied voltage pulse include voltage growth rate, amplitude, pulse-width, and frequency. The parameters of dielectrics refer to relative permittivity and dielectric thickness. Under the given amplitude of the applied voltage pulse, the number of current pulses presents no monotonic decrease with increasing voltage growth rate, and the dependence of the amplitude of each current pulse on voltage growth rate is different. For a given voltage growth rate, the number of current pulses will increase with increasing applied voltage amplitude, but the amplitude of each current pulse does not vary. In addition, the increase of the pulse-width or the frequency can induce not only later appearance of current pulses and smaller amplitude of the last current pulse at the rising edge of the applied voltage pulse but also larger amplitude of the last current pulse at the falling edge of the applied voltage pulse. Also, the decrease of relative permittivity of the dielectric or the increase of dielectric thickness results in smaller discharge current density and shorter time of charging dielectrics, which may increase the number of current pulses.     

Magnetic core model

The paper presents a nonlinear electric circuit to describe the behaviour of magnetic cores in low-frequency applications. A method of hysteresis modelling is proposed, which is able to reproduce minor loops and remanent flux. Classic eddy-current losses and anomalous losses are represented by a linear resistor and a non linear resistor, respectively. The obtained results are compared with those calculated by the models of Hodgdon and Preisach. Comparisons with experimental results are also accomplished. This model is useful for transformer transient phenomena studies, such as inrush currents and ferroresonance     

An unsymmetrical mode of ferroresonance

Earlier studies of ferroresonance note the existence of unsymmetrical modes of operation of series circuits with square-loop reactors. Here the observation of stable second harmonics in a series ferroresonant circuit with a reactor having very nonsquare-loop core material is noted; these harmonics produce unsymmetrical circuit waveforms. Circuit behavior is described, and a qualitative explanation is offered. An approximate solution of the nonlinear circuit equations using the method of reversion of series shows good correlation with the experimental waveforms. From the analysis, the necessary condition for this mode of circuit operation is shown to be the presence of a constant component of flux in the circuit. Potential application of the circuit as a logic element is suggested.     

Characteristics of a.c. electroluminescence in thin film ZnS : Mn display devices

Thin film electroluminescence (TFEL) displays are complex optoelectronic devices with challenging material requirement. The electrical characteristics of ZnS : Mn alternating current thin film electroluminescent devices grown by electron beam evaporation are assessed as function of voltage frequency and Mn concentration. The threshold voltage increases with increasing frequency of the applied voltage and saturation value of electroluminescence (EL) brightness increases linearly with the frequency of applied voltage. The EL brightness increases linearly with the frequency of the applied voltage. The EL brightness was found optimum for a particular activator concentration. A model is proposed and an expression is derived for the EL brightness, which is able to explain the dependence of the EL brightness on different parameters.     

Insights into the power law relationships that describe mass deposition rates during electrospinning

This work explores how in electrospinning, mass deposition rate and electric current relate to applied voltage and electrode separation, factors giving a range of applied electric fields. Mass deposition rate was measured by quantifying the rate of dry fibre deposited over time. Electric current was measured using a current feedback from the high voltage supply. The deposition of fibre was observed to occur at a constant rate for deposition times of up to 30 min. Both the mass deposition rate and electric current were found to vary with the applied voltage according to a power law. The relationship between the electric current and mass deposition rate was found to be linear for all combinations of applied voltage and electrode separation. This means that for all combinations of applied voltage and electrode separation, hence for all applied electric field conditions, there is a constant charge density of 96.1 C/kg for poly(vinyl alcohol).     

On the statistical aspects of threshold switching in thin polymer films

Threshold switching was observed under voltage pulse excitation in thin (2000– 8200 Å) polymer films. For a given applied voltage V (greater than the threshold) the sequence of switching events stops after a given time; new switchings are possible if the applied voltage is increased. Data on the statistical distribution of the number of events in a given switching sequence versus applied voltage amplitude suggest the existence of two independent gaussian phenomena. We assume these to be related to weak spots and to true bulk phenomena of the films during switching.     

超薄覆铜箔层压板耐电压检测技术

在超薄覆铜板的测试项目中引入耐电压测试,设计了一套符合覆铜板特点的耐电压测试装置,借由这套装置开展了对耐电压测试条件和影响因素的研究。通过应用试验发现:直流电压下耐电压失效多发生于升电压阶段,升电压速率是影响直流耐电压测试的关键条件;交流电压下耐电压失效与电压保持时间紧密关联;可以利用交流电压下的漏电电流,量化衡量超薄覆铜板的绝缘能力;树脂含量、绝缘厚度、基材杂质、基材空洞、环境湿度、铜箔粗糙度都是覆铜板耐电压能力的影响因素。     

光纤电压互感器蝇电光晶体对测量精度的影响

光纤电压互感器中电光晶体ＢＧＯ（Ｂｉ４Ｇｅ３Ｏ１２）的缺陷,杂质及内部残余应力引起自然双折射,降低仪器的电压测量精度。从理论上分析了晶体在不同方向应力时不同通光方向上的双折射,又从热光效应的原理出发,推导出调制度的变化与温度、电压之间的定量关系,得出调制深度对温度的变化率与调制度本身成正比、与外施电压成正比的结论。因此为提高仪器的温度稳定性,保证必要的灵敏度,必须使施加到电光晶体上的电压合理。ＢＧ     

一种基于TN型液晶的自控光阀

对TN(扭曲向列)型液晶的透光率测量实验表明,在外加电压的作用下TN型液晶可以吸收入射光线,并且在外加电压连续改变时,对入射光的透光率将呈现连续非线性变化。根据此特性,利用数字电路来控制加到液晶电极上的电压,就得到了一种空间光调制器──自控光阀。自控光阀能控制通过光阀的光强,使之趋于设定值。     

外电场作用下熔渣对MgO-C耐火材料的侵蚀行为

以高温炉渣为电解质,工业MgO-C砖为阴极,钼丝为阳极,研究外电场作用下耐火材料在炉渣中的腐蚀行为。研究结果表明,在CaO-SiO_2-Al_2O_3渣系中,单质硅的析出电位约为-6.1V;在CaO-SiO_2-Fe_2O_3渣系中,单质铁的析出电位约为-1.25V,硅的析出电位为-5.85V。当外加电压小于炉渣分解压时,电压趋使炉渣中离子(Fe~(2+),SiO_4~(2-))定向移动,阴极附近熔渣粘度不断增加,熔渣在耐火材料中扩散速度下降,导致炉渣渗透深度减小。当外加电压高于炉渣分解压时,电压加速炉渣的电化学分解,单质Si和Fe的析出是诱发熔渣组成发生偏移的驱动力,加速高熔点沉积层的形成,而高熔点沉积层有效阻断炉渣与耐火材料直接接触,导致渗透深度显著下降。高熔点沉积层组成与熔渣组成密切相关,在CaO-SiO_2-Al_2O_3渣系中主要由Ca_2SiO_4组成,在CaO-SiO_2-Al_2O_3-MgO渣系中主要由MgAl_2O_4组成。     

压电纤维复合材料桨叶的动力学建模

建立了压电纤维复合材料桨叶的非线性动力学模型。在此基础上,研究了压电纤维铺层对复合材料桨叶固有频率和桨叶扭转运动阻尼特性的影响。计算结果表明：桨叶扭转角变化量随着压电纤维施加电压的增加而增大;当电压为1000 V时,桨尖扭转角变化量大约为2°。压电纤维铺层对桨叶固有频率几乎没有影响,其存在不会改变原设计复合材料桨叶的频率分布。当压电纤维铺设方向与桨叶展向成45°时,其对桨叶扭转方向的阻尼特性有着很大的影响;采用适当的电压控制,可以明显增加扭转方向的阻尼。     

工业用巨型磁控溅射靶电源反馈控制的研究

磁控溅射技术在薄膜制备领域的应用十分广泛，而溅射靶电流的稳定性极大的影响溅射镀膜的膜层质量。本文对于工业用巨型磁控溅射靶电流的不稳定因素进行了分析，设计并实现了靶电压的反馈控制系统，大大改善靶电压与反应气体流量之间的迟滞回线，增强了靶电压的可控制性，并在实际生产中得到成功应用。     

Ab initio calculation of stable structures of a Na atomic chain under bias voltages

The stable geometries of a three-atom Na chain connected to two semi-infinite jellium electrodes are studied under bias voltages by performing ab initio force calculations within the density functional theory. At a low bias voltage of 0.01 V, the stable geometry is found to be symmetric, while it becomes asymmetric for higher bias voltages. The displacements of Na atoms in the chain are proportional to the applied bias voltages up to 1 V, while their behavior changes drastically above 1 V. These results can be understood from the behavior of charges induced by the applied voltage. It is also found that the structural relaxation due to the bias voltage also affects the potential drop along the chain and the current—voltage characteristics of the chain.     

Interferometric determination of the quadratic electro-optic coefficient of nitrobenzene

An interferometric method that was used to measure the electro-optic s(11) coefficient of nitrobenzene is presented. The method uses a Mach-Zehnder interferometer arrangement that produces a finite fringe interferogram. A nitrobenzene Kerr cell is placed in one arm of the interferometer and a pulsed high voltage is applied to the two rectangular electrodes. The voltage application causes the fringe image to shift in time, and this fringe shift is measured by a streak camera that streaks the fringe image across a slit. The streak start time is chosen before the application of the voltage pulse and ends after the voltage pulse has been applied. Thus continuous observation of the event is possible. By accurately measuring the fringe shifts the electro-optic s(11) coefficient can be determined. The experimental arrangement is described, and the results obtained are discussed.     

Ab initio calculation of stable structures of a Na atomic chain under bias voltages

The stable geometries of a three-atom Na chain connected to two semi-infinite jellium electrodes are studied under bias voltages by performing ab initio force calculations within the density functional theory. At a low bias voltage of 0.01 V, the stable geometry is found to be symmetric, while it becomes asymmetric for higher bias voltages. The displacements of Na atoms in the chain are proportional to the applied bias voltages up to 1 V, while their behavior changes drastically above 1 V. These results can be understood from the behavior of charges induced by the applied voltage. It is also found that the structural relaxation due to the bias voltage also affects the potential drop along the chain and the current–voltage characteristics of the chain.     

Mécanisme d'émission électronique dans les structures mim et propagation des électrons dans les métaux

The distribution of electrons emitted by MIM structures has been measured by recording an electron image on a photographic plate. Electrons are emitted into vacuum by “formed” structures when a negative voltage is applied to the outer metal films.The escape depth of the electrons emitted by “unformed” structures does not depend on the applied voltage. We conclude that the energy distribution of the electrons injected into the outer electrode does not depend on the applied voltage.