Anomalous thermal expansion of Gd₂Fe_15.5Cr_1.5 compound

The structure and magnetic properties of Gd2Fe15.5Cr1.5 compound were investigated by means of X-ray diffraction and magnetization measurements.The Gd2Fe15.5Cr1.5 compound had a rhombohedral Th2Zn17-type structure.The Curie temperature of Gd2Fe15.5Cr1.5 compound was about 570 K.This value was about 60 K higher than that of the mother compound Gd2Fe17.Negative thermal expansion was found in Gd2Fe15.5Cr1.5 compound in a broad temperature range 294-572 K by X-ray dilatometry.The coefficient of the average thermal expansion was =-3.87×10-6 K-1 in 294-512 K,and-1.58×10-5 in 512-572 K.The magnetostriction deformations from 294 to 532 K were calculated by means of the differences between the experimental values of the lattice parameters and corresponding values extrapolated from the paramagnetic range.The result showed that the spontaneous volume magnetostrictive deformation ωS decreased linearly from 4.73×10-3 to 0.11×10-3 with the temperature increasing from 294 to 532 K.The analysis showed that the ωS mainly came from the contribution of the spontaneous linear magnetostrictive λc along the c axis.     

高压电器的高耐候性涂装新工艺

采用中温磷化后涂低毒快干环氧底漆,然后涂THP—27磷酸锌特种防锈底漆,再涂B89—2丙烯酸耐侯磁漆的方法,能使高压电器产品的涂装质量得到提高.     

考虑无功源容量约束的无功分区方法

无功分区是大规模电网提高无功电压管理的鲁棒性和灵活性的重要措施。虽然,基于复杂网络社团结构的方法为无功分区这个NP难题的求解提供了便捷高效的算法,但是这类方法未能有效处理无功源的容量约束,因此分区结果存在与无功电压控制需求不够一致的问题。为此,本文首先建立无功源平抑受控节点无功变化的控制灵敏度矩阵;之后结合无功源控制容量约束和无功源耦合程度给出了预分区方法,避免初始分区过大超过无功源控制能力的情况;继而,建立以无功传输效率为权重的加权模块度指标,以量化无功分区平衡的程度,避免在分区内出现远距离的无功输送通道。最后,在某省级实际电网规划方案中验证了该方法的有效性。算例表明,本文提出的无功分区结果更加合理,并有利于指导我国实际电网未来的无功源规划与建设。     

考虑电力系统规划的OPA模型及自组织临界特性分析

为便于对电网连锁故障进行研究,介绍了与电网升级演化的触发息息相关的电力系统发展诊断指标,在此基础上提出一种改进OPA模型。该模型在慢动态环节加入电网规划的作用,模拟负荷变化、发电厂新建扩容、变电站新建扩容、输电线路新建改造等较长时间尺度上的电网演化升级过程;在快动态环节充分考虑调度、继电保护等在连锁故障过程中采取的措施及发挥的作用,模拟由于线路开断或短路、发电机退出运行等故障引发的连锁故障。利用所提模型对河南开封商丘地区220 kV及以上主干电网进行仿真测试,在长时间尺度上模拟电网演化升级的过程,同时统计不同升级触发阈值下的故障规模分布,从而求得系统临界状态所对应的触发阈值。仿真结果表明,文中所提的考虑电力系统规划的OPA模型能够较好地模拟电网生长演化,反映连锁故障产生和传播的过程,对未来的电网建设及大停电的整体预防有一定指导意义。