基于多导体传输线理论的脉冲变压器锥形绕组电压分布数值分析

 为了研究脉冲变压器锥形绕组在脉冲电压作用下的电压分布特性,采用多导体传输线方法,根据实际脉冲变压器锥形绕组的结构,建立了电气参数有限元简化计算模型及等效多导体传输线分析数学模型,以此模型计算了锥形绕组在脉冲电压激励下匝间的电压分布。计算结果表明,此模型可对脉冲变压器锥形绕组的电压分布进行有效计算,对绕组匝间绝缘设计有一定的参考意义。     

110kV冷绝缘高温超导电缆本体绝缘设计

对国内第一根基于YBCO涂层导体的110kV冷绝缘高温超导(CD HTS)电缆本体绝缘进行了设计。根据冷绝缘HTS电缆的结构特点,通过分析不同绝缘材料的介电特性,应用电场有限元数值分析模型和理论模型,计算了超导电缆本体电场分布,研究了超导电缆主绝缘厚度与局部放电起始场强的定量化关系,最后给出了110kV冷绝缘HTS电缆主绝缘材料与厚度的设计方案。     

具有L型源极场板的双槽绝缘体上硅高压器件新结构

为了提高小尺寸绝缘体上硅(SOI)器件的击穿电压,同时降低器件比导通电阻,提出了一种具有L型源极场板的双槽SOI高压器件新结构.该结构具有如下特征:首先,采用了槽栅结构,使电流纵向传导面积加宽,降低了器件的比导通电阻;其次,在漂移区引入了Si O2槽型介质层,该介质层的高电场使器件的击穿电压显著提高;第三,在槽型介质层中引入了L型源极场板,该场板调制了漂移区电场,使优化漂移区掺杂浓度大幅增加,降低了器件的比导通电阻.二维数值仿真结果表明:与传统SOI结构相比,在相同器件尺寸时,新结构的击穿电压提高了151%,比导通电阻降低了20%;在相同击穿电压时,比导通电阻降低了80%.与相同器件尺寸的双槽SOI结构相比,新结构保持了双槽SOI结构的高击穿电压特性,同时,比导通电阻降低了26%.     

New solutions for charge distribution on conductor surface

In the paper, a problem of electrostatics for charge distribution on a conductor surface is analytically solved for three new particular cases of conducting surfaces with complicated shape and specified value of electrostatic potential. The exact analytical expressions for surface charge density for the bodies are obtained. All the solutions are represented in a clear view of 3D graphs. It is shown that the proposed method of electrostatic problem for conductors allows to obtain infinitely many numerical solutions for the problem but only several special cases can be solved analytically.     

Optimization of field grading for a 1000 KV wide-band voltage divider

An HVDC reference voltage divider has been designed for high accuracy and wide-band measurements up to 1000 kV. To maintain wide-band characteristics, field distribution must be optimized in order to minimize the response time of the divider. To compensate the stray capacitance, a capacitive path that surrounds the resistive reference divider is added to function as a shield. Optimal capacitance values producing a matched distribution are obtained using 3D FEM simulations. Factors affecting the performance of the divider are assessed by simulating multiple scenarios representing different practical considerations in real-life applications.     

脉冲变压器锥形高压绕组电压分布实验研究

 对脉冲变压器锥形高压绕组进行了脉宽为1 μs,500 ns及100 ns三种不同脉宽的单脉冲实验,研究了不同输入条件下绕组中的电压分布特性,比较了空心、加内铁芯和加内外铁芯三种不同结构绕组中的对地电压及匝间电压的分布曲线。实验结果表明：在高频冲击电压条件下,脉冲变压器锥形高压绕组中的电压呈现非线性分布且存在明显的振荡过程,导致绕组首端的电压梯度增大,伴随脉宽减小电压波形发生明显畸变,冲击电压以波的形式在绕组中传播,从而引起匝间电压按照正弦规律起伏变化,匝间电压的极值通常出现在绕组首末端,加入铁芯有助于抑制电压谐振但同时增大了匝间电压。     

Effect of dimension on charge order domain in Ruddlesden-Popper manganites

The charge order (CO) domains of dimensionally controlled manganites Pr_1−xCa_xMnO₃ and Pr_1−xCa_1+xMnO₄ (x=0.5, 0.6 and 0.67), which have three-dimensional (3D) and two-dimensional (2D) Mn-O networks, respectively, have been studied by transmission electron microscopy (TEM). Although the electron diffraction data show similar dependences of the modulation wave vector on hole doping x, there are distinctive differences between the 3D and 2D systems in terms of the CO domain sizes. In the 2D system, the TEM images show that the domain size is almost constant irrespective of hole doping x. On the other hand, in the 3D system, the domain size of the incommensurate CO for x=0.6 is much smaller than those of the commensurate CO for x=0.5 and 0.67. Namely, in the 3D system, the CO states are strongly influenced by the incommensurability for the parent lattice. This difference indicates that the dimension of the Mn-O network plays a crucial role in the CO domain and suggests that the electron-lattice coupling of the 3D system is stronger than that of the 2D system.     

Electron states scattering off line edges on the surface of topological insulator

We study the local density of states （LDOS） for electrons scattering off the line edge of an atomic step defect on the surface of a three-dimensional （3D） topological insulator （TI） and the line edge of a finite 3D TI, where the front surface and side surface meet with different Fermi velocities, respectively. By using a S-function potential to model the edges, we find that the bound states existed along the step line edge significantly contribute to the LDOS near the edge, but do not modify the exponential behavior away from it. In addition, the power-law decaying behavior for LDOS oscillation away from the step is understood from the spin rotation for surface states scattering off the step defect with magnitude depending on the strength of the potential. Furthermore, the electron refraction and total reflection analogous to optics occurred at the line edge where two surfaces meet with different Fermi velocities, which leads to the LDOS decaying behavior in the greater Fermi velocity side similar to that for a step line edge. However, in the smaller velocity side the LDOS shows a different decaying behavior as x-1/2, and the wavevector of LDOS oscillation is no longer equal to the diameter of the constant energy contour of surface band, but is sensitively dependent on the ratio of the two Fermi velocities. These effects may be verified by STM measurement with high precision.     

强流二极管绝缘体滑闪监测及其影响

 以闪光二号加速器为研究平台, 建立了微分环阵列和Rogowski线圈同时监测二极管电流的方法,监测了二极管绝缘体表面的滑闪现象。根据电流探头测量结果的差异,分析了绝缘体滑闪对电子束流参数的影响。二极管绝缘体出现滑闪,位置附近的微分环波形严重畸变,其它位置的微分环和Rogowski线圈测量结果基本一致。采用距离滑闪位置较远的微分环结果处理二极管束流参数,相对于不出现滑闪时的结果,束流强度和总能量没有明显的变化。绝缘体滑闪沿面局部放电,能量损失较小,尚未对电子束流造成较大影响。     

高灵敏度绝缘子电晕放电检测系统研究

绝缘子是电力系统中非常重要的一类电气设备,由于电、热、机械力、污秽的积累等环境因素的作用会使其绝缘性能出现劣化和下降,可能使得绝缘子的表面形成放电,甚至会发生沿面闪络,危害了电力系统的安全。在此基础上提出基于日盲紫外线精确测试紫外线强度的方法,研制了基于日盲紫外线检测技术的绝缘子电晕放电检测装置,通过不同劣化程度和不同污秽条件的盘行悬式瓷绝缘子的实际测试,验证了该装置通过日盲紫外线强度的监测能够定性判断绝缘子的劣化程度和污秽程度,为输电线路绝缘子实时状态监测提供依据。     

带电线电场中导体球上的特定电荷分布

研究了带电导体球在带电直线电场中的电荷分布问题,并计算了两种特定情况下导体球表面的电荷密度.     

强流二极管绝缘体滑闪监测及其影响

以闪光二号加速器为研究平台, 建立了微分环阵列和Rogowski线圈同时监测二极管电流的方法,监测了二极管绝缘体表面的滑闪现象。根据电流探头测量结果的差异,分析了绝缘体滑闪对电子束流参数的影响。二极管绝缘体出现滑闪,位置附近的微分环波形严重畸变,其它位置的微分环和Rogowski线圈测量结果基本一致。采用距离滑闪位置较远的微分环结果处理二极管束流参数,相对于不出现滑闪时的结果,束流强度和总能量没有明显的变化。绝缘体滑闪沿面局部放电,能量损失较小,尚未对电子束流造成较大影响。     

Effects of an implant on temperature distribution in tissue during ultrasound diathermy

The effects of an implant on temperature distribution in a tissue-mimicking hydrogel phantom during the application of therapeutic ultrasound were investigated. In vitro experiments were conducted to compare the influences of plastic and metal implants on ultrasound diathermy and to calibrate parameters in finite element simulation models. The temperature histories and characteristics of the opaque (denatured) areas in the hydrogel phantoms predicted by the numerical simulations show good correlation with those observed in the in vitro experiments. This study provides an insight into the temperature profile in the vicinity of an implant by therapeutic ultrasound heating typically used for physiotherapy. A parametric study was conducted through numerical simulations to investigate the effects of several factors, such as implant material type, ultrasound operation frequency, implant thickness and tissue thickness on the temperature distribution in the hydrogel phantom. The results indicate that the implant material type and implant thickness are the main parameters influencing the temperature distribution. In addition, once the implant material and ultrasound operation frequency are chosen, an optimal implant thickness can be obtained so as to avoid overheating injuries in tissue.     

不同排列下高温超导带材交流损耗的仿真计算

交流损耗的数值计算对于高温超导带材具有重要的现实意义。应用有限元软件模拟仿真超导体部分计算求出不同排列下的交流损耗,与实验结果以及Norris公式的计算结果相比较,得到的仿真结果符合较好。结果说明圆筒形的排列能够有效地减少交流损耗。     

The influence of the Dresselhaus spin--orbit coupling on the tunnelling magnetoresistance in ferromagnet/ insulator /semiconductor/ insulator /ferromagnet tunnel junctions

This paper investigates the effect of Dresselhaus spin--orbit coupling on the spin-transport properties of ferromagnet/insulator/semiconductor/insulator/ferromagnet double-barrier structures. The influence of the thickness of the insulator between the ferromagnet and the semiconductor on the polarization is also considered. The obtained results indicate that (i) the polarization can be enhanced by reducing the insulator layers at zero temperature, and (ii) the tunnelling magnetoresistance inversion can be illustrated by the influence of the Dresselhaus spin--orbit coupling effect in the double-barrier structure. Due to the Dresselhaus spin--orbit coupling effect, the tunnelling magnetoresistance inversion occurs when the energy of a localized state in the barrier matches the Fermi energy E_F of the ferromagnetic electrodes.     

核电荷分布对类氢原子基态能量计算的影响

在高斯型核电荷分布模型中,分别采用基于B样条的Notre Dame和Dual-Kinetic-Balance基组求解类氢体系的Dirac方程。通过对所得的基态能量和点电荷分布模型的结果以及实验测量值进行比较,发现核电荷分布效应对结果具有重要影响,其相对修正随原子序数Z的增加而逐渐显著。当Z=100时,相对修正能达到10^−3。并在近核区域给出了两种模型下计算的波函数。当Z增加时,波函数的差别也逐渐明显。不同于其他将B样条应用于电子与原子核的长程相互作用计算的工作,此工作成功地将B 样条方法推广到了短程相互作用的研究。     

核电荷分布对类氢原子基态能量计算的影响

在高斯型核电荷分布模型中,分别采用基于B样条的Notre Dame和Dual-Kinetic-Balance基组求解类氢体系的Dirac方程。通过对所得的基态能量和点电荷分布模型的结果以及实验测量值进行比较,发现核电荷分布效应对结果具有重要影响,其相对修正随原子序数Z的增加而逐渐显著。当Z=100时,相对修正能达到10^−3。并在近核区域给出了两种模型下计算的波函数。当Z增加时,波函数的差别也逐渐明显。不同于其他将B样条应用于电子与原子核的长程相互作用计算的工作,此工作成功地将B 样条方法推广到了短程相互作用的研究。     

Electric field and the charge distribution on the surface of an insulator in a vacuum

The free charge steady-state distribution over the insulator surface that arises in a strong electric field in a vacuum can be found by solving the boundary-value problem for the electrostatic field strength if the angle between the field vector and vacuum-insulator interface is given. A general solution to this boundary-value problem is derived for the case of an in-plane field and rectilinear interfaces. Laws of charge and field formation that follow from the solution obtained are considered. Formulas for the electric field strength and charge density in terms of elementary functions are obtained for a number of particular cases. Power-type expressions for the electric field and a critical angle between the electrode and insulator surface that describe the field behavior and charge distribution near the vacuum-insulator-electrode contact are derived.     

Empirical estimation of the equilibrium charge distribution of heavy ions in solid and gaseous media

Based on the analysis of experimental data on equilibrium charge distributions of ions in gases and solid media, the analytical parameterization of the charge distribution width as a function of the average ion charge and nuclear charges of the ion and the target atom and that of the asymmetry as a function of the average ion charge are obtained. The proposed relations are applicable in a broad energy interval and describe the existing experimental data satisfactorily.     

电荷耦合效应对高耐压沟槽栅极超势垒整流器击穿电压的影响

通过沟槽结构和可调节的电子势垒,沟槽栅极超势垒整流器可以更为有效地实现通态压降和反向漏电流之间的良好折衷.在高压应用时,电荷耦合效应对于提高该器件的反向承压能力起到了关键作用.本文通过理论模型与器件模拟结果,分析了沟槽深度、栅氧厚度和台面宽度等关键参数对电荷耦合作用下二维电场分布的影响,归纳出了提高该器件击穿电压的思路与方法,为器件设计提供了有意义的指导.在此基础上,提出了阶梯栅氧结构,该结构在维持几乎相同击穿电压的同时,使正向导通压降降低51.49%.