针对矿热炉通常功率因数较低，无功功率高，导致电网效率降低，供电能力下降，经济效益受到影响的现状。本文研制了一种基于MCGS触摸屏和PLC的矿热炉二次侧低压无功补偿监测系统。该系统能根据炉子的实时用电情况自动补偿各相无功功率，增加变压器输出功率，抬高电极电位，提高产品的产量与品质。 　　本文阐述了无功补偿的基本原理，比较各种无功补偿、提高功率因数方案的优缺点，分析现有无功补偿设计系统，在此基础上，最后综合实际矿热炉自身的情况，设计了一套自动分析现场环境从而控制电容器合理投切的监控系统，提出了动态投切电容以提高其平均寿命的控制方法。 　　本监测系统使用PLC和MCGS触摸屏组成监控系统，其中电网一次侧电量数据由智能综合电量变送器来采集监测数据，二次侧短网三相数据则由智能电测仪表分别采集，PLC通过RS485与一次侧的电参数、温度等智能仪表通信并直接控制投切电容，将数据计算处理发送给触摸屏。触摸屏通过RS232与PLC通讯，分别读取变压器一、二次侧的电网数据并显示，并自动加载控制策略，给PLC设置合理参数，记录工作状态。并且PLC通过RS485总线监测矿热炉连接电极的铜管导线温度，若温度高于设定报警值，则按电容平均寿命要求依次切断电容，设置了多种保护电路，并给出报警信号给操作人员用于排除故障。 　　本设计为解决了以往无功补偿系统控制策略的不足，在延长电容寿命方面采取了循环投切电容；根据不同产品和材料特性设计了三种自动控制策略，使得参数调节更加合理，提高了设备的使用寿命和补偿效率；在通信链路上使用RS232和RS485的电气隔离措施，有效解决了设备因交流接地而引起的损毁现象发生。 　　该设备在四川汶川电石提炼厂、云南文山、河南等运行使用，设备运行稳定，后期维护便利。有效的提高了功率因数，平衡三相炉况，增加了产量，每年为企业节约近百万元费用。

The Submerged Arc Furnace has low power factor,but reactive power is high.That let to decrease of efficiency for power supply and affected the economic benefit.Contraposingthis High energy-consuming equipment ,Development of automatic controlling system for low-voltage reactive compensation based on PLC and MCGS touch screen.This system can achieve the automatic control of Reactive Compensation on the situation, improve transformer output power,improve electrode potential position and the product quality was assured. 　　　 The subject was elaborated low voltage reactive power compensation principle.Then it compares the advantages and disadvantages of the existing reactive power compensation devices.Finally,developed a test control system of low voltage reactive power compensation basis on submerged arc furnace itself situation, proposed a throw-cut of the capacitor method for raise capacitor life span. 　　　 This system is comprised of two designed parts，such as the MCGS touch-screen upper computer system and PLC lower computer system,the transformer primary side power network data collection come from PDM,and the secondary distribution network data collection come from intelligent voltmeter,PLC using RS485 bus for collected these data.Using these data,PLC can throw-cut capacitor by automatic control policy.These also transmit for HIM by using RS232.The MCGS HIM can display the primary side power and the secondary distribution network data.At same time,PLC will loading automatic control system real-timely,setting parameters and recording the task data.PLC also can monitoring cooling water temperature of the copper pipe wire based on RS485 bus,if the temperature is too high, the capacitor will cut in turn and trigger off emergency situation for operation staff. 　　　 In order to solve reactive compensation system insufficient ,the capacitor can check in or out by cyclically policy for raise capacitor life span;According to the different material properties and product design three throw-cut policy,it can adjust parameters reasonable and raise equipment life span;Using RS232、RS485 at link layer，it can solved the equipment caused by ac earth damage effectively.At present,this system apply to many company,such as sichuan wenchuan calcium carbide refinery, wenshan in yunnan, henan and so on.The results show that this controlling system enhancing power factor, balance three phases power and increase production quantity.Enterprises will save money nearly one million each year.