基于同步挤压小波变换的配电网单相高阻接地故障选线

为提高配电网单相接地故障选线的成功率,提出了一种基于同步挤压小波变换的配电网单相高阻接地故障选线新方法。该算法首先通过同步挤压小波变换方法确定各馈线的最大时频脊线,计算最大时频脊线下的挤压能量和挤压相角。在此基础上,通过闵可夫斯基距离来表征每条线路的故障特征,并以此特征区别接地与非接地馈线。仿真实验结果显示,该选线算法受故障位置,过渡电阻,初始角度,馈线结构等因素的影响较小,能够准确地识别故障线路。对比其他已知算法,该算法对电流信号的处理精度更高,能更好适应复杂的配电网系统。

Effects of second phases on mechanical properties and martensitic transformations of ECAPed TiNi and Ti-Mo based shape memory alloys

TiNi and Ti-based shape memory alloys were processed by equal channel angular pressing （ECAP） at 673-773 K along Bc route to obtain ultrafine grains for increasing the strength of parent phase and improving the functional properties. The effects of both thermodynamically stable and metastable second phases on the mechanical properties and martensitic transformations of these alloys were investigated. It is found that thermodynamically stable Ti2Ni phase has no effect on martensitic transformation and superelasticity of Ti-rich TiNi alloy, thermodynamically stable α phase is harmful for ductility of Ti-Mo-Nb-V-Al alloy, but metastable Ti3Ni4 phase is effective for R phase transformation, martensitic transformation and superelasticity of Ni-rich TiNi alloy. The mechanisms of the second phases on the martensitic transformations and mechanical properties were discussed.

Effect of annealing temperature on martensitic transformation of Ti_(49.2)Ni_(50.8) alloy processed by equal channel angular pressing

The effect of annealing temperature on the martensitic transformation of a Ti49.2Ni50.8 alloy processed by equal channel angular pressing （ECAP） was investigated by X-ray diffraction （XRD）, transmission electron microscopy （TEM） and differential scanning calorimetry （DSC）. The as-ECAP processed and subsequently annealed Ti49.2Ni50.8 alloys consist of B2 parent phase, Ti4Ni2O phase and B19′ martensite at room temperature. Upon cooling, all samples show B2→R→B19′ two-stage transformation. Upon heating, when the annealing temperature is less than 400℃, the samples show B19′→R→B2 two-stage transformation; when the annealing temperature is higher than 500 ℃, the samples show B19′→B2 single-stage transformation. The B2-R transformation is characterized by wide interval due to the dislocations introduced during ECAP.

Corrosion properties of ECAP-processed Mg-Al-Ca-Mn alloys with separate Al2Ca and Mg2Ca phases

To investigate the effect of separate Al_(2)Ca and Mg_(2)Ca phases on the corrosion properties of Mg−Al−Ca−Mn alloys,OM,SEM,immersion and electrochemical tests were conducted on the as-cast and ECAP Al_(2)Ca-containing(2Ca)and Mg_(2)Ca-containing(4Ca)alloys.At the beginning of corrosion,the two as-cast alloys are corroded slowly compared with ECAP alloys.With prolonging the corrosion time,the corrosion of ECAP alloys becomes slighter than that of as-cast alloys,which is mainly ascribed to the dispersion and refinement of the second phase in ECAP alloys.Moreover,the corrosion degree of 2Ca alloys is always slighter than that of 4Ca alloys,suggesting that Al_(2)Ca phase is more beneficial to the enhancement of corrosion resistance of Mg−Al−Ca−Mn based alloys than Mg_(2)Ca phase.Finally,based on the examinations of corrosion surface and electrochemical testing results,different corrosion mechanisms caused by the distributions and morphology of Al_(2)Ca and Mg_(2)Ca phases are discussed.

Evolution of TiNi precipitates in TiNi alloy during equal channel angular pressing

The evolution of Ti3Ni4 precipitates in Ti49.2Ni50.8 alloy during equal channel angular pressing(ECAP) and intermediate annealing was investigated by transmission electron microscopy. The solution-treated Ti49.2Ni50.8 alloy was aged at 450 ℃ for 10 to 60 min to obtain Ti3Ni4 precipitates ranging from 37 to 75 nm. After ECAP at 450 ℃ for one pass, Ti3Ni4 precipitates introduced by aging for 10 and 30 min totally dissolve into the matrix;however, those produced by aging for 60 min become smaller. The critical size of Ti3Ni4 precipitates to totally dissolve into matrix is determined to be in the range of 37-68 nm. The dislocation density of ECAP-processed samples depends on the initial size of Ti3Ni4 precipitates after aging. With increasing the duration of initial aging from 10 to 60 min, the dislocation density firstly increases and then decreases.