Papaika Y. Rational modes of electro-consumption of electric resistance furnaces

It is known that electric resistance furnaces are 90 per cent of heat-treatment machinery of machine-building enterprises. Today tendency of new generation of electric furnaces use takes place to improve quality of heating operation. But together with advantages of modern electric furnaces with thyristor controllers this brings up the question if these electric installations have electromagnetic compatibility with mains as it may have negative influence on other workshop using equipment. Mathematical model to computate parameters of voltage unbalance has been developed while studying unbalanced conditions of electrotechnical plants performance. Among other things it concerns electric resistance furnaces. The model is a system of equations on equivalent circuits of network taking into consideration technologic operating conditions of furnaces. Joint solution of the systems as for currents and voltages of positive sequence, reverse sequence and zero sequence helps to determine unbalance indices under any combination of mains-operated parameters and parameters of balanced load and unbalanced load. To make qualitative assessment of balancing effect of single-phase energizing conditions for furnaces it is necessary to determine limits of variation of unbalance indices under different combinations of mains-operated parameters and load-voltage characteristics. That's why it is expedient to use the mathematical model for parameter synthesis of optimum relations between general shop load and furnace load to remove unbalance. To generalize results obtained suppose that load within low voltage buses of workshop transformer is of balanced character, and furnace plant is a source of unbalance. Such an approach helps to determine unbalance falling at single-phase conditions of furnace.