多功能监控远距离转发报警系统

设计了一种多功能门窗监控远距离转发报警系统,该系统硬件由门磁触发的自动多路发射部分和数码显示现场地址的无线接收报警部分组成,发射与接收均采用270 MHz无线电编码传输技术,采用PT2262/PT2272编译码芯片,工作稳定、可靠,适合仓库、住宅、商场、银行、医院等需要防盗、防火、防煤气泄漏的场合使用.     

220 kV主变零序电流互感器接法简析

电力系统中,电压为220kV及以上的变压器应设置反映接地故障的带方向的零序电流保护,其中,零序电流可取自中性点TA二次,也可取自本侧TA二次三相零线(中性线)上的电流,或由本侧TA二次三相电流自产。在微机型保护装置中,零序电流大多是自产,这样有利于确定功率方向元件动作方向的正确性。     

The positive correlation of the strain hysteresis of textured PMN–24%PT ceramics with domain wall damping

High strain hysteresis is a stumbling block for the application of piezoelectric ceramics. This research affords a new insight into the origin of the ultra-low strain hysteresis of textured 76%Pb(Mg_1/3Nb_2/3)O₃–24%PbTiO₃ ceramics (PMN–24%PT). Highly textured PMN–24%PT ceramic system with some doping was successfully fabricated. This system shows unipolar strain curve approximately matching a straight line. The maximum hysteresis falls in 7%–11%. Compared to other representative piezoceramic system, current PMN–24%PT textured ceramics possess the least strain hysteresis. In addition, Mn²⁺ substitution for Nb⁵⁺ can inhibit domain wall mobility. The positive correlation between the ultra-low strain hysteresis and the domain wall damping is demonstrated by experiment and finite element simulation. In a conclusion, this work can enhance the understanding of strain hysteresis and contribute to high-precision piezoelectric actuators.     

基于激光阵列传感的层析成像系统研究

基于光学层析成像的基本原理 ,主要介绍激光阵列传感层析成像系统设计思想、光学布置、激励、接收单元结构、敏感场特性及系统实现方法 ,并给出系统的部分仿真和实验结果。     

线路保护中PT断线判据的分析和改进

PT断线作为电力系统中一种常见的故障,能否及时有效地进行判别,是继电保护装置正确动作的前提条件。针对PT断线的特点,在对不同厂家的判据进行了分析后,结合一次现场实例,指出了目前判据中存在的不足之处,给出了一种PT断线的实用判据。根据该判据开发的线路保护装置已经在现场投入使用,证明了该判据的工程实用价值。