直流系统接地检测电路设计

直流系统接地检测电路设计

摘要

目前在我国电力系统中运行的直流接地检测装置，多是通过整定平衡电阻桥的门限来进行接地检测的，但其具有整定值不准确、不灵活、接地电压（接地电阻）无法检测等缺点；还有的是通过在母线或支线上加入交流信号来实现检测的，但这种检测方式精度很难保证，而且还会对直流系统造成影响。

本检测电路的工作原理是首先由漏电流传感器检测出母线各支路的进线与出线之间的电流差，然后经过A/D转换生成单片机能够识别处理的数字信号，再由单片机判断出是否有接地状态，若有则计算出接地电阻和接地电压。本设计采用了高精度漏电流传感器和单片机控制技术；并使用了汉字化液晶显示屏人机界面，可方便直观地了解系统运行状态；又通过键盘设定母线电压上下限报警值及母线接地电阻的报警值，以适应对各种特殊功能的要求；还应用了扩展I/O口和数据选择芯片来实现多路检测数据输入。当直流系统的某条支路发生接地故障时，本电路可迅速查出接地极性、路号、阻值和母线段号，同时由日历时钟芯片DS12887提供接地时间，通过面板红色指示灯及音响报警。

关键词：接地检测，漏电流传感器，单片机，液晶显示屏

The Circuit Design of The Direct-current Grounding Detection System

Abstract

At present, in the domestic electric power system, most of the direct-current grounding detector work by setting up the threshold of the balance resistor bridge. But this way has its disadvan tages, for instance, it can’t make the adjusted value correct, hasn’t agility and can’t check the grounding voltage (earth resistance) and so on. And some of the direct-current grounding detector work by joining the alternating-current signal in the busbar or the branch. But this way is hard to guarantee the precision and can affect the direct-current system.

This detecting circuit’s principle is to check the current difference between the input line and output line of each brand of busbar by the drain current sensor at first, and then through A/D converter, generate digital signal that can be distinguished and tackled by single-chip microcomputer, finally the single-chip microcomputer judges whether there’s the grounding state, and if the state is being, then calculates the earth resistance and the grounding voltage. This design adopts drain current sensor of high accuracy and the controlling technique of the single-chip microcomputer, and also adopts the man-machine interface of the Chinese-character LCD display to observe the working state of the system conveniently and visually, it can set up the maximum and minimum alarming value of the busbar resistance and voltage to fit all kinds of special function’s requirements. The system can finish multi-way detecting data inputs by adopting patulous I/O port and data selector chip. When there are faults in a certain spur track of the direct-current system, the circuit can find out the earthed pole, the mark of the spur track, the resistance and the mark of busbar section quickly, at the same time, can provide the time of the grounding by calendar clock chip DS12887, and alarm by the panel red LED and sounder.

Keywords:ground detection, drain current sensor, single-chip microcomputer, LCD

目录

摘要......................................................................................................................................... I Abstract ..................................................................................................................................... II 1 绪论. (1)

1.1 引言 (1)

1.2 工作原理 (1)

1.2.1 电路特点 (1)

1.2.2 主要功能 (2)

1.3 设计思路 (2)

2 硬件电路设计 (4)

2.1 系统结构 (4)

2.2 信号采集电路 (5)

2.2.1 电压信号采集 (6)

2.2.2 电流信号采集 (6)

2.2.3 接地电阻阻值判断 (7)

2.3 单片机电路 (9)

2.3.1 89C51简介 (9)

2.3.2 可编程外围并行接口8255 (10)

2.4 键盘电路 (11)

2.5 液晶显示电路 (11)

2.5.1 T6963C的介绍 (11)

2.5.2 T6963C指令集 (11)

3 软件设计 (13)

3.1 主程序设计 (13)

3.2 液晶显示子程序 (13)