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

Literature data on measurements of slag temperature in EAFs and ladle-furnaces are examined together with the author's own such measurements. Known recommendations on improving the foamability of the slag are also discussed. Results are presented from studies of technological features of "good" and "poor" slag-foaming regimes in a high-power electric-arc furnace.There have been reports that the temperature of the slag cover in high-power electric-arc furnaces used to make steel sometimes exceeds the temperature of the metal itself [1][2][3]. Values of slag temperature measured at different points in the cover at the end of the melting period and values of the temperature of the molten metal measured throughout the heat are within the range 1650-1800°C [1,3]. It has also been reported that the formation of a slag cover whose thickness is greater than the length of the electric arc creates a closed circuit inside the slag, this circuit by-passing both the metal and the arc. Thus, the temperature of the slag can rise to 1800°C, regardless of the metal's temperature [2]. The process that unfolds in the cover therefore becomes similar to the electroslag process, complete with high temperatures (1700-1800°C) in the slag bath.In addition, the source of the high temperatures may not be related to the arcs. A "hot spot" -a reaction zone where the metal bath undergoes intensive oxidation and which releases heat that may not be fully transferred to the volume of the metal -is created in the region where the oxygen jet comes into contact with the bath [4,5]. The surface of the melt inside the reaction zone is heated to the boiling point of iron, since excess heat that may not be transferred deep into the bath is expended on the vaporization of iron and oxides [4,5]. The temperature of the surfaces of the hot spots can be estimated based on the evaporation point of the components of the slag and metal (2500-3500°C) [6][7][8]. Since the hot spots are in a layer of foaming slag or in the immediate vicinity of the layer, this may not have any effect on its temperature. A temperature that is determined by an automated probe and is taken as the average temperature of the semifi nished product probably cannot truly be considered the average temperature of the slag cover or even an effective value of that temperature.It is obviously incorrect to analyze slag-foaming processes within a temperature range that is in fact not characteristic of foaming slags.We compared experimental results from measurements of the temperatures of the metal and slag during a heat against literature data [1, 3] on the temperatures of metal and foamed slag in a high-power electric-arc furnace (Fig. 1). Our measurements confi rmed the known fact that the slag is heated to temperatures higher than the metal and they indicated that the temperature of the slag in the region above the location where the temperature of the semifi nished product is traditionally measured is roughly 70° higher than the temperature of the semifi nished product and ranges from 1650 ...

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