全工况仿真平台在电气工程教学中的应用

各类非对称接地故障在中压配电网中是非常普遍的,因此在电气工程教学过程中对于lOkV配电网故障的产生、过程、危害以及防治等进行研究和授课具有十分重要的现实意义。本文使用电力系统仿真工具PSCAD／EMTDC构建了10kV配电网的全工况仿真平台,并建立了并行仿真环境,在此基础上可开展对中性点不同的接地方式、四类不同消弧线圈...     

力学性能预测模型及其控制的研究

首先介绍神经网络建模特点,利用神经网络建立起由工艺参数预测力学性能的质量模型,及根据力学性能要求优化工艺参数的逆质量控制模型, 预测效果图显示该模型的预测精度较高.然后,利用质量预测模型分析卷取温度对屈服强度的影响,并利用自校正PID（proportion integral differentiation）控制实现力学性能的控制,仿真结果证明该方法的有效性.     

10kV电机定子线圈防晕结构改进

本文探讨了 1 0kV级电机定子线圈防晕结构改进 ,有利于解决线圈电晕问题 ,提高线圈质量和使用寿命。     

The Mechanics of Feeding Bulk Solids in a Rotary Dryer

Based on an industrial case study, the performance of a rotary dryer employed in a mineral processing plant was investigated. The loads on the rotating elements of the dryer are analyzed with a view to ascertaining possible causes of failure. The particular type of dryer comprises a steam-heated drying unit composed of a central hollow drum and a number of parallel sets of circular heating tubes attached to the drum via radial header tubes. The drying unit rotates inside a stationary vessel containing the moist mineral ore. Blades attached by welds to the outer circular heating tubes assist in the circulation and transport of the ore through the dryer. However, in the actual dryer, the blade angles were less than optimal for good feed of material through the drying unit, and their welded attachments were a source of high levels of concentrated stress. While the close spacing between parallel sets of circular heating tubes is beneficial for heat transfer for the drying process, the close spacing leads to material buildup problems impeding the material feed. Influence of the variation of blade angle on feeding performance was investigated, and the various loads acting on the tubes and blades were analyzed.     

Experimental Investigation of Local Heat Transfer and Skin Friction in Tube Coils

Local heat transfer and skin friction around the tube perimeter of coils were studied in airflow. The heat transfer experiments were performed with two different coils D/d = 23 and 15.6, and skin friction experiments were performed with three different coils D/d = 25, 13.3 and 6.67 In the wide range of Re number from 4×103 till 105 . Variation of the local heat transfer around the perimeter and along the tube was defined. The behavior of the shear stresses at the wall and of the flow modes were studied. Investigations of the heat transfer indicated that with the increase of D/d the difference between heat transfer in the initial thermal section and the stabilized heat transfer increases. Investigations of the shear stress and its fluctuations indicated that, in large-curvature coils, the transition from laminar-vortex flow to turbulent flow around the tube perimeter takes place at different values of Re. In the region of the external generatrix of the bend, the transition occurs at smaller Re, whereas a     

A first characterization of the quench detection system for ITER

The purpose of this paper is to assess the expected response of conventional and non-conventional quench detection sensors proposed for the ITER coils, and to be tested in the QUELL experiment in SULTAN. The assessment is based on simulation of thermohydraulic transients in the ITER coils for various operating conditions, and a tentative definition of the transfer functions of each sensor concept. It is shown that, for the investigated conditions, the co-wound voltage taps are more accurate than hydraulic systems and conventional voltage balance methods. The additional complication associated with the insertion of taps in the conductor is well offset by the low sensitivity to external disturbances.     

交联聚合物溶液与聚合物溶液的特性差异

采用光学显微摄影、动态光散射和核孔膜过滤等方法，研究了低浓度部分水解聚丙烯酰胺(HPAM)与柠檬酸铝(AlCit)形成的交联聚合物溶液(LPS)中交联聚合物线团(LPC)的形态、尺寸、变形性等特性。结果表明，LPC与聚合物线团(PC)相比，在形态、尺寸、变形性能等方面存在明显差异。干燥后的LPS样品中，LPC为球形，PC的形状不清晰。低于某一临界质量浓度(0．200～0．300g／1)时，LPC尺寸略小于PC；高于此浓度后，LPC的尺寸始终大于PC。HPAM／AlCit交联体系的临界质量浓度(0．280g／1)略高于聚合物溶液的临界交叠质量浓度(0．250g／1)。由于分子内的交联作用，与PC相比，LPC的剪切变形能力和水化变形能力有限，LPC较强的抗剪切变形特性使其具有特殊的封堵多孔介质的能力。     

An efficient birdcage resonator at 2.5 MHz using a novel multilayer self-capacitance construction technique

The birdcage resonator, well appreciated for its high signal-to-noise ratio and its magnetic field uniformity characteristics, operates efficiently in mid- to high-field MRI systems but, unfortunately not for low-field (<0.4 T) applications. The inherently low inductance of the birdcage architecture is the main obstacle to achieving low-frequency resonance because of the need to use very high-value capacitors for the tuning. Small-case-size, high-value ceramic capacitors are known to have high dissipation factors which when used in the fabrication of RF coils could result in poor efficiency. To overcome this limitation, a novel technique known as multilayer self-capacitance (MLSC) construction has been developed and a prototype 2.5-MHz bird-cage resonator of length 25 cm and diameter 20 cm has been built. The technique involves the modification of the leg sections of the conductors constituting the bird cage into integrated capacitors using very low-loss materials as dielectrics. The observed unloaded Q-factor was 267 using the MLSC construction, and when loaded with a 16-cm-diameter bottle of 0.45% saline, its Q dropped to 246, The RF field uniformity plots have demonstrated that the MLSC technique has no adverse effects on the magnetic field homogeneity of the bird-cage resonator.     

EBT reactor magnetics and particle confinement

Optimization of the vacuum magnetic field of an ELMO Bumpy Torus (EBT) reactor is investigated. Several methods of improving reactor volume utilization and single particle confinement are analyzed. These include the use of (a) a large number of sectors and/or a large mirror ratio, (b) high field Nb₃Sn or Nb₃Sn/NbTi hybrid mirror coils, (c) split-wedge mirror coils, (d) axis-encircling aspect ratio enhancement (ARE) coils, and (e) recently developed field symmetrizing (SYM) coils. Of these, particle drift orbit and three-dimensional tensor pressure equilibrium calculations show that the use of SYM coils in conjunction with high field mirror magnets offers the most promise of good plasma performance in reactors that are smaller (by up to 50%) than previous reference designs that did not employ supplementary coils. Aspect ratio enhancement coils also offer an attractive alternative for improved confinement, but they do not have many of the advantages of SYM coils, particularly for reactor applications. Split-wedge mirror coils improve volume utilization and trapped particle confinement, but they do not enhance the confinement of transitional and passing particles. High field magnets improve confinement by permitting a larger mirror ratio and a larger plasma radius by virtue of their smaller cross-sectional area and higher current density. The relative merits of each magnetics configuration are discussed, including the effects on single particle confinement, reactor volume utilization, materials requirements, engineering design considerations, and reactor assembly, maintenance, and accessibility.     

HRB400热轧带肋钢筋延伸率偏低原因分析

采用金相、扫描电镜能谱分析和氮氧含量检测等手段,对40规格的HRB400热轧带肋钢筋延伸率偏低的原因进行分析,得出钢筋氮氧含量、夹杂物含量高是主要原因,因此,应采用提高钢筋的纯净度、加强生产过程控制、及时进行操作调整等措施解决这一问题。