Study About the Possibility of Electrodes Motion Control in the EAF Based on Adaptive Impedance Control Manuela Panoiu * , Caius Panoiu * and Sorin Deaconu * * Polytechnic University of Timisoara/Electrical Engineering and Industrial Informatics Department, Hunedoara, Romania, e-mail: m.panoiu@fih.upt.ro , c.panoiu@fih.upt.ro , sorin.deaconu@fih.upt.ro Abstract—The paper presents a study about the possibility of adaptive process control in three phased electric arc furnace. The method is based on the electrodes motion control. The control principle is depending on impedance of the electric arc. The method proposed use a data acquisition board whose input signals are taken from electric arc. These signals allow the calculation of electric arc impedance. Using a numeric computer, it can be commands the control of electrodes position independently on each one of three phases. We propose to use a static frequency converter on each phase to control the electrodes motion Keywords— Adaptive control, motion control, power factor correction. I. INTRODUCTION An electrical arc furnace (EAF) changes the electrical power into thermal energy by electric arc in melting the raw materials in the furnace. During the arc furnace operation, the random property of arc melting process and the control system are the main reasons of the electrical and thermal dynamics. That will cause serious power quality problems to the supply system [1], [2], [3], [4], [5], [6], [7]. Nowadays, AC-Electric Arc Furnaces (EAF) is typically designed to melt a batch of scrap into liquid metal within 1-3 hours [8]. Therefore the installed power reaches up to 1 MW/t. Melting down the scrap bunch and superheating it is a high dynamic process. The AC arc furnace has a non-linear current-voltage characteristic. Therefore it acts as a source of disturbance in the grid from which it is supplied. It emits both harmonics and interharmonics and generates voltage unbalances, voltage dips and voltage fluctuations. Another disadvantage in the EAF is caused by the variations in the line voltage leading to flicker, which can be observed due to the luminosity fluctuation of incandescent lamps. However, one of the most substantial disadvantages of arc furnace is caused by the reactive power due to the non- linearity of the electric arc [9], [10]. The significant values of the reactive power cause important losses of active power, therefore the efficiency are affected [1], [2], [5], [6], and [11]. The closed-up loop control is not optimized at many furnaces; the run of voltage is very dynamic. With a more optimized control closed-loop it should be possible to enhance the energy input and consequently the productivity. For improving the functioning regime by power factor correction it is possible to make an adaptive impedance control. The proposed solution is based on some measurements made on an industrial Plant in Romania, Hunedoara where a 100t, 100 MVA UHP EAF are in function. II. THE ELECTRICAL PARAMETERS OF THE EAF Figure 1 shows the physical model of the electric arc furnace [8]. In this particular EAF model, there are three electrodes that are moved vertically up and down with hydraulic actuators. Each of these electrodes has a diameter of roughly 1.5 m, weighs approximately 40 tons and is 1 to 2 stories tall. The ore is melted with a huge power surge from the electrodes. The actual product is denser than the scrap and thus falls to the bottom of the furnace creating the matte. Above the matte lies the slag where the electrode tips are dipped. The tremendous heat created by these electrodes causes the ore to liquefy and separate. Thereupon more raw materials are placed in the furnace and the process repeats itself. Fig. 1 The physical model of the Electric Arc Furnace A. Arcing Arcing is a phenomenon that occurs when the electrodes are moved above the slag. As the electrode approaches the slag, current begins to jump from the electrode to the slag, creating electric arcs. Depending on the magnitude of the input voltages of electrodes, the arcing distance can vary. Usually, arcing occurs in the region within centimeters of the slag (approximately 10 – 15 cm). Therefore, the EAF model must take into account the instances when x1, x2, x3 are negative (i.e. the electrodes are suspended above the slag), like in fig 1. scrap slag -ve X +ve X