The Design Of The Control System Of Low-veltage Reactive Power COmpensation Based On PLC For The Smelting Electric Furnance

In order to improve work efficiency of smelting electric furnace and the quality of powersupply, a kind of intelligent power monitoring and controlling system of reactive-powercompensationbased on PLC is developed. System, used PLC as the host, can complete themonitoring and controlling hundreds of capacitor of the reactive compensation automatically.Through the on-site touch-screen and the remote monitoring PC, it also can modify theswitching parameters online , real-time display and store each parameter of the grid.The subject is comprised of four designed parts,such as the remote monitoring PC ,on-site touch-screen , PLC and the system control cabinet.The remote monitoring PC, used virtual instrument named LabWindows/CVI asdevelopment platform, can display and store each parameter of the grid, draw the curves ofthe corresponding ones, modify the switching parameters, and monitor the capacitance whichis connected or cut. Upper and Lower data communication is using RS485 bus, and followingthe MODBUS protocol, which enhances the monitor's versatility in the industry.Touch-screen, which is used controlling on-site through the RS232 bus, can completethese functions, such as real-time display each parameter of the grid, connect or cut thecapacitance, and modify the switching parameters. It facilitates the engineering staff on-sitedebugging and controlling the system.The main achievement of lower computer program of PLC is communicating with PDMin transformer primary side and three voltmeters in transformer secondary side, collectingeach parameter of the both sides of the transformer, and uploading these parameters to thehost computer via the serial port for analysis and display. At the same time, it also receives thecontrol signal from the host computer to complete the action of connecting or cutting thecapacitance. When the host computer is damaged, PLC can work independently, which is improving the reliability of the system.The design of system control cabinet contains two aspects, which is the pattern ofinstruments'arrangement and the way of system's line connection. It is from hardware toensure the stable operation of the system.According to the above designs, after many trials and delivered to users for six months,the results show that the monitoring and controlling system meets the design requirements,and operates stably.