电动机常见故障与处理方法

大部分电机属于老式电动机,使用年限较长,电机烧毁的事故常有发生,而且呈上升趋势,无法长期可靠运行,严重影响着生产、生活的安全。通过作者多年积累的电机维护、维修的经验,针对一些电动机最常见的绕组故障、机械故障以及相应判断、处理做以简单介绍。     

A new method for estimating initial rotor phase of self‐excited hybrid‐field synchronous motors

This paper proposes a new method for properly estimating the rotor initial phase (i.e., the position) of the newly emerging self‐excited hybrid‐field synchronous motors (SelE‐HFSMs), which have the rotor held by both a permanent magnet and a diode‐shorted held winding. The proposed method injects a spatially rotating high‐frequency voltage and detects the rotor phase directly by evaluating the norm of the associated current. The method is very simple, but has a high degree of usability. 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(3): 49–58, 2010; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.21027     

Transition Temperature of Bi_2Sr_2CaCu_2O_(8+x) Superconducting Films Prepared from Commercial Precursors

This paper have made a systematic study of the superconducting Bi-2212 phase transition temperature, which has a transition temperature (Tc) around 80-93 K, and depends on precise control of synthesis conditions, mainly including heat treatment parameters, oxygen partial pressure, and annealing temperature. Partial melting of the sample during preparation helps to raise its Tc. To elucidate the origin of this strong effect, the samples were heated with different melting process. The rapid changes in Tc valu...     

液相法合成氢化铝钠的研究

以NaH和AlCl3为主要原料,通过改变实验条件,探索研究液相法合成NaAlH4的合成条件。实验表明,在不加入任何催化剂的情况下无法实现NaAlH4的合成,在以NaAlH4、三乙基铝等物质为催化剂的条件下,虽有少量的产物生成,但是反应不明显,且产物中存在大量的非晶态物质。即便在高温高压下反应亦难以进行,大量的化合物均以非晶态形式存在。     

基于正交双通道算法的相位差测量

工频信号相位差测量技术目前已经很成熟,但是,用传统测量方法对音频或更高频率信号相位差进行高精度测量还有一定困难。文章提出了正交双通道算法实现无理论误差的信号相位差测量。     

采用一种优化编码方法的光学相关器在目标识别中的应用

VanderLugt相关器在纪录目标图形的傅里叶变换复振幅谱时,通常需要引入一个离轴的参考光波来纪录复振幅信息.本文利用计算机制匹配滤波器,对四级迂回相位编码方法进行了优化,事先生成不同目标的匹配滤波器进行目标识别,从而大大简化了实验方案,保证了VanderLugt相关器工作的实时性.实验结果显示了该方法的可行性.     

星载合成孔径雷达二维闪烁相位误差校正方法研究

分析了电离层闪烁效应对低频段星载合成孔径雷达(Synthetic Aperture Radar, SAR)方位向分辨率的影响, 并基于二维相位屏方法生成了距离向空变的闪烁相位误差.传统的相位梯度自聚焦(Phase Gradient Autofocus, PGA)方法难以适用于二维空变相位误差校正, 而本文基于闪烁相位误差在距离向具有连续性的特点, 在一定规则基础上将整幅图像划分为若干个子孔径, 对每个子孔径图像利用PGA方法进行相位误差估计, 再将得到的各子孔径相位误差进行插值运算, 从而得到整幅图像的闪烁相位误差.仿真结果表明:相比于传统PGA方法, 子孔径PGA方法可以有效解决二维空变闪烁相位误差对图像方位向分辨率的影响, 校正后的图像得到很好的恢复, 方位向分辨率明显提高.     

Characterization of germanium implanted Si1−xGex layer

Characterization of a Si_1−xGe_x layer formed by high-dose germanium implantation and subsequent solid phase epitaxy is reported. Properties of this layer are obtained from electrical measurements on diodes and transistors fabricated in this layer. Results are compared with those of the silicon control devices. It was observed that the germanium implantation created considerable defects that are difficult to eliminate with annealing. These defects result in boron deactivation in the p-type regions of the devices, giving rise to larger resistance. Optimization of the device structure and fabrication process is discussed.     

T(z) diagram and optical energy gap values of Cd1−zMnzGa2Se4 alloys

The T(z) diagram of the system Cd_1−zMn_zGa₂Se₄ was obtained from x-ray diffraction and differential thermal analysis measurements. It was found that at lower temperatures, a single phase solid solution occurs across the whole compositional range and values of lattice parameters were determined as a function of z. At higher temperatures, an order-disorder transition occurs, in the range 0 < z < 0.6 to a partially ordered tetragonal structure and for 0.6 < z < 1. 0 to a disordered defect zinc-blende structure. In the T(z) diagram, both the ordering boundary and the solidus curve appear to show discontinuities at z = 0.6, corresponding to the change in the disordered phase. It is suggested that the symmetries of the terminal compounds are different one from the other. Optical absorption measurements were made at 300 K to show the variation of the direct optical energy gap E_o with z, and again the values appear to divide into two parts below the above z = 0.6.