The Valve Effect of an Electric ARC and Problems in Controlling Electric-ARC Furnaces

Abstract

The reasons for the existence of constant components of current and voltage in electric-arc furnaces are examined. It is noted that the accuracy with which the constant component of arc voltage is evaluated is strongly affected by the method used to sample the voltage signal. Results are presented from experimental studies of characteristics of the electric arc on a laboratory unit. It is shown that the magnitude of the constant component of the voltage on the electrodes depends on the constant component of the electrodes' current. A method is described for determining the constant component of the arc voltage based on values of the constant components of electrodes' current, voltage, and resistance. It is shown that it is best to use the method of dynamic volt-ampere characteristics for real-time monitoring of the parameters of the valve effect. Here, the quantity chosen as the controlled parameter is not the constant component of the arc voltage but the difference in its steady-state values. Keywords: electric-arc steelmaking furnaces, valve effect of an electric arc, alternating current, electrical characteristics, constant components of current and voltage, monitoring and control.In recent years, the trend in the automation of EAF steelmaking has been to move away from the use of automated equipment in favor of automated control of the production process. The world's leading manufacturers of metallurgical furnaces and control systems -in particular, SMS Demag -supply the Russian market with units that can produce steel in the fully automated regime. However, despite the many advantages of automated process control -including those that stem from the removal of subjectivity from the control process -in the Russian metallurgical industry these control systems have encountered problems in connection with the inconsistent and sometimes poor quality of the raw materials that are used.The modern high-power EAFs being acquired by Russian companies have automated control systems (ACSs) provided with closed-source software designed to operate the furnaces on high-quality scrap metal and fl uxes. The operation of these furnaces on Russian raw materials requires fl exible regulation of the main process parameters. The fact that the operating regimes cannot be modifi ed makes it impossible to take full advantage of the opportunity to minimize the consumption of energy and other resources and attain the high performance indices typically seen for the same furnaces abroad.On the other hand, the overwhelming majority of EAFs that are in operation in Russia are of small (from 1.5 tons) or moderate (15-25 tons) capacity, and the level of automated control over the operation of most of these furnaces is

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