Binary polymer blend of ArPTU/PI with advanced comprehensive dielectric properties and ultra-high thermally stability

Flexible high-temperature polymeric dielectrics with advanced dielectric properties are urgently demanded in various applications. In this work, series of polymer blend films were prepared from aromatic polythiourea (ArPTU) and polyimide (PI). The experimental results revealed that the blend films were properly engineered to achieve higher breakdown strength, greater dielectric constant, and larger energy density than pure PI film. For instance, the optimum property was obtained from the blend film with 10 wt% ArPTU, exhibiting prominent dielectric properties (K = 4.52, E_b = 443 MV/m), enhanced energy density (4.00 J/cm³) as well as excellent heat resistance (T_g = 419°C). In addition, stable dielectric properties at broad temperature range from −50 to 250°C were also acquired. It is deduced that the good compatibility from ArPTU and PI with similar polarity are responsible for the improved properties. The superior comprehensive properties which combine the advantages of ArPTU and PI suggest the potential applications of ArPTU/PI blend film in high-temperature dielectric areas.     

Effect of modified layered double hydroxide on the flammability of intumescent flame retardant PP nanocomposites

The dodecyl sulfate intercalated CaMgAl-hydrotalcites (layered double hydroxides [LDHs]) were successfully prepared by co-precipitation method, and characterized by X-ray diffraction analysis, infrared spectroscopy (Fourier transform infrared spectra [FT-IR]), thermogravimetry (TG-DTA), scanning electron microscope, and Brunner−Emmet−Teller (BET). The prepared LDHs were added to the intumescent flame retardant (IFR) polypropylene (PP) nanocomposites, and the limiting oxygen index method (LOI), vertical combustion method (UL-94), cone calorimetry (CCT), and other test methods were used to study its thermal stability and combustion performance. The results showed that when the flame retardant was composed of 23 wt% IFR and 2 wt% O-SDS-LDHs, the LOI value of the material was increased to 31.5%, reaching the V-0 level, and the flame retardant performance was significantly improved. The results also showed that there was a significant synergistic effect between IFR and O-SDS-LDHs, which could improve the thermal stability and graphitization degree of PP nanocomposites. In addition, the peak heat release rate, total heat release, and total smoke production of the PP/IFR/O-SDS-LDHs system were 177 kW/m², 101 MJ/m², and 15.4 m², respectively, which were 82.2%, 51.0%, and 23.0% lower than those of pure PP, respectively. These improvements could be attributed to the presence of dense and continuous char layer formed by the synergistic effect.     

Study on performances of graphite-filled polypropylene/polyamide 6 composites manufactured by fused deposition modeling

The application and development of 3D printing technology are greatly restricted due to the poor performance and single-function of the manufactured products. Therefore, it is still an important topic to develop 3D printing products with excellent performance and multi-functions. In this study, a novel graphite-filled polypropylene/polyamide 6 composite was successfully prepared using fused deposition modeling (FDM, one of the most popular 3D printing technologies). The effects of graphite on printing quality, melt-crystallization behavior and thermal stability of the composites were studied. In addition, the influence of different printing arrangements on the electrical conductivity and mechanical properties of the composite were also studied, and the existing performance regulation mechanisms were deeply explored through the microscopic morphology characterization (graphite sheet orientation and void distribution) and force analysis. This work demonstrates that components with specific performance requirements can be tuned and manufactured using FDM, which further expands the application and development of 3D printing technology in the field of functional composite materials.     

牵引变电所群贯通供电系统负序补偿模型及控制策略

针对牵引变电所群贯通供电系统存在的三相电压不平衡问题,提出一种基于三相变压器与静止无功发生器(SVG)的负序集中补偿方案及控制策略.首先,根据牵引变压器的功率变换关系及不同的负荷情况,推导了2种模式下补偿装置对牵引负荷的补偿功率通用表达式.根据中国的电能质量标准,提出了以负序满意补偿为目标的双限值补偿方案,方案包括了模式选择方法、SVG容量配置方法及SVG运行方法.根据补偿方案,设计了带有模式判别的SVG双闭环补偿控制策略.然后,采用牵引变电所实测数据对补偿方案进行验证,证明了方案具有良好的补偿效果,与全补偿方案相比,所提方案需要的装置容量更小.最后,通过仿真证明了控制策略对负序补偿的有效性和较快的响应速度.     

基于下垂曲线截距调整的直流微电网自适应虚拟惯性控制

为了改善直流微电网的电压稳定性和动态性能,降低控制系统的复杂性,提出一种基于下垂曲线截距调整的直流微电网自适应虚拟惯性控制(AVIC)方法.在反正切函数中嵌套幂函数,根据电压和电压变化率的动态变化调整下垂曲线的截距,以控制换流器快速释放或吸收功率,从而为直流微网提供惯性支持.建立含AVIC的四端直流微电网小信号模型,并通过根轨迹分析揭示主要控制参数对系统稳定性的影响规律.最后,通过硬件在环仿真验证了所提方法的有效性.     

基于一种新型牵引补偿变压器的牵引变电群贯通供电系统负序补偿

针对牵引变电所群贯通供电系统负序补偿问题,该文提出基于一种新型牵引补偿变压器与静止无功发生器的负序补偿方案和控制策略.研究牵引补偿变压器的拓扑结构和负序补偿方案,根据无功补偿单元的数目将补偿方案分为补偿模式Ⅰ、Ⅱ和Ⅲ.从牵引负荷电流有功分量和无功分量角度出发,分别定义负序和无功的约束因子,基于变压器磁动势平衡方程、端口接线方程和对称分量法等构建不同补偿模式下的负序与无功综合补偿数学模型.定义最大无功功率补偿量,将其作为确定补偿方案的依据.提出适用于负序补偿方案的电压和电流双闭环控制策略,通过仿真验证了补偿方案及控制策略的正确性和有效性.基于牵引变电所实测数据分析补偿方案的确定方法,结果表明,合适的补偿方案可以降低补偿装置容量.     

环保型罐式多断口真空断路器均压配置研究

环保型罐式多断口真空断路器是未来高压真空断路器的发展趋势之一,但目前对罐式多断口真空断路器的均压配置问题研究不足.该文建立罐式多断口真空断路器三维电场模型,对比分析了罐式与传统柱式真空断路器的结构电压、电场分布和等效电容参数的差异,发现罐式结构对地杂散电容增大造成其电压分布更加不均匀.研究了罐式多断口真空断路器的单边、双边、三边和圆筒状的不同均压电容配置结构对断口间电压分布、罐体内部电场强度的影响规律.研究表明:不同均压配置结构的断口间均压效果由优到差依次为圆筒状、单边、三边、双边,圆筒状均压配置金属连接件处最大电场强度为3kV/mm,远小于其他方式的15～20kV/mm,该研究为罐式多断口真空断路器均压配置提供了参考依据.     

基于电压和电流特征的双馈风电变流器功率器件开路故障综合诊断

变流器功率器件开路故障监测与识别对提高双馈风电系统智能运维至关重要.针对现有基于变流器电压或电流单一特征以及固定阈值的方法难以同时实现功率器件故障诊断监测与识别问题,该文提出一种基于变流器直流母线电压的故障监测与基于转子电流故障识别的综合诊断方法.首先,理论分析变流器功率器件开路故障对直流母线电压的影响,基于累积和(CUSUM)算法,提出基于直流母线电压特征的故障监测方法;其次,针对转子输出电流非平稳特性和阈值固定问题,提出基于归一化输出电流平均值和绝对平均值为故障特征量及自适应阈值的故障识别方法;最后,仿真模拟不同功率器件先后开路,验证所提方法的有效性,以风速随机及电网电压跌落为场景验证所提方法的鲁棒性.同时,以功率器件典型开路故障实验数据验证仿真分析的准确性.仿真与实验结果表明,所提方法能准确实现变流器功率器件开路故障诊断.     

基于改进完全局部二值模式火焰特征提取的 转炉炼钢终点碳含量预测

转炉炼钢火焰图像特征的准确提取是预测终点碳含量的关键,针对于火焰图像相似性高进而难以区分碳含量相近的火焰图像,导致无法准确精准预测碳含量的问题,提出一种改进完全局部二值模式(improved complete local binary pattern,ICLBP)的彩色纹理特征提取方法,用于提取不同碳含量下更具区分性的炉口火焰图像特征并进行终点碳含量的预测.首先,在不同颜色通道下采用局部相位量化(local phase quantization,LPQ)提取图像相位信息,与CLBP提取的图像幅值信息组合成融合特征ICLBP_MP,以增强CLBP算法结构的鲁棒性;然后,通过改进的颜色信息加权策略对其进行加权,以增强火焰图像的颜色对比度信息;最后,使用K近邻回归模型对碳含量进行预测.实验结果表明,碳含量预测在0.02％误差范围内的准确率为83.9％.     

30Cr2MoV钢渗氮行为研究

将新型渗氮钢30Cr2MoV和传统38CrMoAl钢在不同温度下进行不同时间的气体渗氮,利用公式ξn=K0·e-Q/RTτ计算了氮在两种材料中扩散的激活能,并讨论了30Cr2MoV钢具有较强渗氮能力的原因.