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Magnesium Oxide in electric arc furnace control system
Abstract: This paper introduces the application of UniMAT PLC in the control system of Magnesium Oxide smelting electric arc furnace. Electric arc furnace converts electric energy into heat energy, directly heating or melting magnesium carbonate ore, and separating qualified magnesium oxide materials. The stability and anti-interference ability of UniMAT PLC system have been fully verified in the field of electric arc furnace equipment in smelting industry, which provides a solid foundation for improving the stability of smelting process.
Key words: electric arc furnace, UniMAT PLC, automatic control, anti-interference
China's electric arc furnace smelting process has been lagging behind before the 1980s. After decades of development, the smelting process and control performance gradually catch up with the international level. Especially in magnesium oxide smelting, UniMAT PLC system has been affirmed by the equipment manufacturing customers, realizing automatic control, reducing manual workload and equipment damage and economic losses caused by manual misoperation.
2 working principle
Electric arc furnace smelting is a kind of low voltage and high current working mode. Electric energy is injected into graphite electrode, and an arc is formed between electrode and ore. The arc temperature is as high as 3000 C, which can effectively melt magnesium carbonate ore. The electric arc furnace mainly consists of electric arc furnace transformer, graphite electrode, lifting arm, moving furnace body, frequency conversion motor, control system and so on. Graphite electrodes are fixed on the lifting arm respectively, and the distance between graphite electrodes and ore is adjusted by the forward and reverse drive of frequency conversion motor, thus realizing the current control, ensuring the three-phase current balance and realizing the automatic control. Figure 1 describes the main components of the electric arc furnace.
3.Control system composition
In the uniMAT PLCsystem, can can can can can can can can can can can can can can can can can can can can can can can can can can can can can can can can can can can can can can can can can be the UniMAT PLC system configuration to the tab, 2.
UniMAT CPU226 has 24DI and 16DO; extensible 7 IO modules; integrates 2 communication ports, all supporting PPI communication; program storage space is 20K, user data storage space is 10K; uses FLASH technology to maintain power-down for a long time, without battery support, can save data for up to 10 years; special AES iterative encryption algorithm, protection Intellectual property rights.
4 control process
The core idea of the control system is to control the distance between graphite electrode and ore material, so as to control the current. The key node is the accuracy and stability of current and voltage signal acquisition. In order to achieve the above purposes, EM231 analog input module is selected to collect A, B, C three-phase current and voltage, and EM232 analog output module is used to provide - 10V to 10V voltage signals for inverter operation. The CPU processes the signals collected by EM231 and EM232, and realizes the automatic operation of the equipment according to the preset program. Figure 2 describes the corresponding functions of each PLC module of the control system. (forwarding password: UniMAT UN200 series PLC)
Fig. 2 function of PLC module
The system can realize two automatic and manual control modes. In automatic operation, the CPU collects feedback signals such as voltage and current and compares them with current settings, calculates them, and adjusts the analog voltage output to control the motor's forward and backward running frequency. During manual operation, the positive and negative frequencies of the motor are adjusted by operating the buttons on the control panel. Manual operation takes precedence over automatic operation when abnormal equipment occurs.
The system has the functions of fault alarm, failure shutdown and so on. When the equipment fails, there is a sound photoelectric alarm function, prompting the operator to respond, if there are serious faults such as current overrun, motor blockage, equipment automatic shutdown.
5 concluding remarks
The industrial control environment of the equipment is abominable, with transformers up to 20000KVA or more; graphite electrodes and materials directly produce high temperature arc; 3-phase 4-wire power supply system; complex electromagnetic environment, the CPU and module stability and anti-interference ability have higher requirements. Through verification, the UniMAT PLC module passed the harsh environment test.