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摘要：电力系统在运行中，相与相之间或相与地（或中性线）之间发生非正常连接（即短路）时而流过非常大的电流。其电流值远大于额定电流，并取决于短路点距电源的电气距离。大容量电力系统中，短路电流可达数万安。这会对电力系统的正常运行造成严重影响和后果，我们基于此要做系统保护。三段式过电流保护是最为典型的电力线路电流保护，它包括瞬时电流速断保护，限时电流速断保护和定时限电流速断保护。基于 PLC 的三段式过流保护可用于验证计算机保护动作逻辑修改的方便性，同时兼具直观性。PLC 的电气梯形图语言直观，编程简单，容易上手。PLC 的功能强大，具有控制、计数、定时、定位、运算、通讯等多种功能。这给基于PLC的三段式过电流保护设计提供了良好的平台。65370
本设计用 PLC 实现电力线路继电保护的相关实验，以设计性实验为主要内容。能够完成实验的选型、设计等环节。其特点是硬件结构简单，编程容易，有利于现场调试，接近工程现场。
毕业论文关键词：三段式过电流，PLC系统，继电保护
Abstract:Power system in operation and between phase and phase or phase and the ground (or neutral) occur abnormal connection (i.e. short circuit) sometimes through very large current. The current is greater than the rated current, the electrical distance and depends on the short circuit power supply point. The large capacity power system, short-circuit current of up to several million. This will cause serious consequences and influence the normal operation of the power system, we have to do this based on system protection.Three segment type over current protection is the most typical power line current protection, which includes instantaneous current quick break protection, limited current quick break protection and timing and limiting current quick break protection. PLC is based on over current protection can be used to verify the computer relay protection logic modification of convenience, while both intuitive. PLC electric ladder diagram language programming is simple, intuitive, easy to use. PLC is powerful, has the function of controlling, counting, timing, location, operation, communication etc.. This provides good platform for the design of three phase current protection based on PLC.
The relay protection of power line using PLC to implement the design, to design experiments the main content. To complete the experiment selection, design etc.. Its characteristics are simple hardware structure, easy programming, and help the field debugging, close to the project site.
Keywords: three over current, PLC system, relay protection
目录
1 绪论 4
1.1研究背景 4
1.2设计的主要内容 4
2 三段式过电流保护 5
2.1 三段式过电流保护的基本原理 5
2.2 继电保护的原理整定计算 5
2.2.1 电流Ⅰ段保护（无时限电流速断保护） 5
2.2.2 电流Ⅱ段保护（带时限电流速断保护） 6
2.2.3 电流Ⅲ段保护（定时限过电流保护） 6
3 PLC技术简介 8
3.1 PLC的技术概述 8
3.2 PLC的基本结构 8
3.3 PLC的工作原理 9
3.4 PLC的功能特点 9