Abstract
By analyzing the working principle of Current protection at present, a novel intelligent Current protection system is developed based on PLC. This system have a number of protective features, such as short circuit protection, over-current protection, open phase protection and so on. The operation condition and fault parameters of system can be displayed through touch screen liquid crystal display device.
Firstly, the development and present situation, importance and necessity are introduced, function specifications, controlling principle and technical requirement of Current protection system are put forward.
Secondly, according to safe condition circuit is designed; analyzed the fault character and protection principle of Grid current, action parameters are established; the program design method is plot, and compiled function module subprogram. Especially more attention is paid to design philosophy, operation principle, hardware block diagram and software flow chart of system.
Finally, the interference source and features of interference single exit in industrious production environment are discussed; anti-interference measures of hardware and software are set down to eliminate interference single in this paper.
This measurement and control system adopted PLC as control core, applied new protective theory and large scale integrated circuit, so its property is stable and action is reliable.
Key Words: programmable logic controller; Current protection;touch screen measurement ;over-load protection;open phase protection
目录
1 绪 论 5
1.1 电网电流继电保护的发展与现状 5
1.2 PLC的发展与应用 6
1.3 研究基于PLC的电网电流保护系统的意义 8
1.4 本文的研究内容 8
2 电流保护系统总体设计 10
2.1 CPU及扩展模块的选择 10
2.2 测控系统框图 11
3 测控系统硬件电路设计 13
3.2 外部参数设定电路 13
3.2.1 BCD 拨码盘 13
3.2.2 BCD码与PLC的接口: 14
3.4 过载保护设计 16
3.4.1 过载保护的原理 16
3.4.2 过载保护时限的确定 18
3.4.3 过载保护硬件电路 20
3.5 断相保护设计 20
3.5.1 断相运行电流 21
3.5.2 断相保护的硬件设计 23
4 测控系统的软件设计 25
4.1 系统的软件结构 26
4.2 监控程序模块设计 27
4.3 功能模块程序设计 27
4.3.1 额定参数读取模块 27
4.3.2 额定参数计算模块 29
4.3.3 模拟信号的采样处理 31
4.3.4 电流保护功能模块 32
5 测控系统的抗干扰设计 34
5.1 微机系统的干扰渠道及抗干扰措施 34
5.2 印刷电路板及电路的抗干扰设计 36
5.3 PLC的抗干扰设计 38
5.4 软件的抗干扰设计 39
结论 43
参考文献 44