线路电流差动保护自适应CT变比的方法

提出了一种仅整定本侧CT变比的方法,保护传送及接收的不是电流二次采样值,而是由二次采样值根据本侧CT变比处理后得到的一次电流值,技术关键是传输一次电流值不能溢出。解决了两侧同一套保护定值不一致的问题,方便了运行及管理。该方法已应用于基于32位DSP的WXH-803数字式光纤电流差动保护。

母差保护TA断线原因分析及处理

母差保护装置TA断线报警原因有很多,很多时候并不是真正的TA断线,但往往会对运行、检修人员造成误解,本文针对母差保护装置"TA断线"原因和处理方法进行了简要分析。

Variability of leaf functional traits of invasive tree Rhus typhina L. in North China

Functional traits, specifically leaf functional traits, are core-topics to explore importance to the invasion success of invasive plant species. This study aims to address the differences in leaf functional traits and their corresponding variability of the invasive tree staghorn sumac Rhus typhina L. with different invasion success, including lower and higher invasion success, in two climatic regions in North China, including a warm temperate region and a cold temperate region. No significant differences were found for leaf functional traits of staghorn sumac across different invasion success. However, the variability of leaf chlorophyll and nitrogen concentrations of staghorn sumac under higher invasion success were approximately 66.023% and 68.615% higher than those under lower invasion success, respectively. The leaf chlorophyll and nitrogen concentrations of staghorn sumac in the warm temperate region were approximately 18.432% and 16.337% higher than those in cold temperate region, respectively. The variability of specific leaf area of staghorn sumac in warm temperate region was approximately 59.802% higher than that in cold temperate region. Accordingly, leaf chlorophyll and N concentrations as well as specific leaf area of staghorn sumac and their corresponding variability may play an essential role in shaping ecological success of studied invader along a climatic gradient.

Analysis of strain variation in cross shear zone of plate during snake hot rolling

In order to study the distribution of equivalent and shear strain of aluminum alloy plate during snake hot rolling, several coupled thermo-mechanical finite element models(FEM) are established. Effects of speed ratio and offset distance on strain distribution of the plate are analyzed. The length of cross shear zone is defined to have a better understanding of the deformation characteristic in cross shear zone, which is the essential difference from symmetrical rolling in deformation zone. The results show that the equivalent strain and shear strain of lower part both increase with the increase of speed ratio, while the upper part decreases; the equivalent strain through the whole thickness decreases with ascending offset distance, while the shear strain of lower part increases. The length of cross shear zone quickly increases with ascending speed ratio and slightly decreases with ascending offset distance. The "positive" and "negative" cross shear zones are formed with the increase of speed ratio and offset distance, respectively. The value of the sensitivity coefficient of speed ratio is an order of magnitude bigger than the offset distance. However, the shear strain at center point increases with the ascending speed ratio and offset distance for different mechanism. As speed ratio increases, the asymmetry of the distribution of equivalent is becoming larger and the shear strain is generated in the same direction in cross shear zone. The FEM results agree well with experimental results.

Natural frequency of tapered high pier considering pile-soil interaction

In seismic design of tapered high pier, the analysis of natural vibration frequency is of great importance. According to the engineering features of tapered high pier in mountainous area, a vibration calculation model was set up considering the tapered pier characteristics and pile-soil interaction. Based on Southwell frequency composition theory, it consists of elastic deformation of bridge pier and the rigid deformation of group piles, which are respectively solved by the finite-element method and energy method, and then the natural frequency is derived. The comparison between the measured and calculated results shows that the calculation errors with and without considering pile-soil interaction are 4.9% and 14.7%, respectively. Additionally, the main parameters (pier height, section variation coefficient and lateral foundation horizontal proportional coefficient) affecting natural frequency were investigated. The result shows that natural frequency ascends with the increase of the lateral foundation horizontal proportional coefficient; and it is quite necessary to consider the pile-soil interaction in natural frequency calculation of tapered high pier.

Geometry-dependent springback behaviors of thin-walled tube upon cold bending

As one kind of key lightweight components with enormous quantities and diversities, the bent tubular parts have attracted in- creasing applications in aerospace, automobile, etc. Thus, how the inevitable springback behaves under different bending specifications should be fully addressed to efficiently achieve the precision forming of various bent tubes. Taking the medium strength thin-walled 6061-T4 Al-alloy tube as the objective, via the deformation theory of plasticity, explicit/implicit FE method and experimental approaches, we explored and clarified the nonlinear springback rules of the tubes and corresponding mechanisms in universal rotary draw bending regarding angular springback and radius growth by deliberately changing the tube diameter D and wall thickness t. The geometry dependent springback behaviors of thin-walled tube upon cold bending are thus revealed: 1) With the increasing of D, the tangent tensile strain increases and the proportional coefficient decreases, which causes the angular springback to decrease, while the radius springback increases due to the larger bending radius. 2) With the increasing of t, the tangent tensile strain decreases and the proportional coefficient increases, resulting in the increase of both angular springback and radius springback. 3) Under the same D/t, the angular springback varies little, while the radius springback increases with the larger diameter D. 4) The D/t can be used as a reasonable nondimensional index to evaluate the springback angle; as to the radius growth, the individual effects of the D and t should be considered. 5) The verification of the above results was conducted by experiments and analytical analysis.