Melting stage diagnostic in different types of electric arc furnaces based on the analysis of the harmonic composition of the electric arc current

The authors of the paper carried out experiments to study the harmonic composition of current for electric arc steel-making furnaces of different classes and power range operating at different steel-making enterprises of Russia. This made it possible to carry out the analysis of changes in the higher harmonics of current of electric steel-making furnaces, find out regularities of changes of certain harmonic components and to determine the average and maximum levels of harmonics for electric arc furnaces of each type. The research group also made the comparative analysis of the rate of change in the total effective values of even and odd harmonic components, which made it possible to find an important regularity that the rate of even harmonic weakening in the electric arc furnace is several times higher than that of odd harmonics. Thus the authors proved the applicability of the root-square-mean value of current of even harmonics for the purpose of diagnostics of heat stages in an arc steelmaking furnace using the conventional manufacturing process. This principle formed the basis of the structure of the new control system of electrical mode of the furnace and this new control system makes use of the diagnostic technique of the heat stage by the harmonic composition of the signal of electric arc current.