CLOSED-LOOP POWER-CONTROL OF AN AC ELECTR IC-ARC FURNACE

The electrode position control used to date entails a rigid control st rategy in which there is no adjustment to the varying process conditio ns of the AC electric are furnace. As a result, it is possible only wi thin certain limits to achieve the goal of a uniform power input. The newly developed digital closed-loop power control system, by compariso n, operates on the basis of adaptive control parameters. Besides the e lectric current, the active power of the furnace is controlled by way of the voltage tap of the transformer. Accompanying controlled variabl es include the thermal losses. Moreover, the phase reactance is adapte d to the process requirements in each case by control of the reactor, which can be switched under load. The digital power control system has thus made it possible to increase the productivity of the featured fu rnace by up to 8%.