Analysis of interharmonics in DC arc furnace installations

This paper deals with interharmonic disturbances encountered during the operation of a DC arc furnace installation. The main cause of the flicker-like disturbances has been identified in a strong harmonic interaction between AC and DC sides of the thyristor converters. In order to analyze the effects of the various system parameters, the frequency response of the entire system has been derived. This approach allows the analysis of the harmonic amplification taking into account the line impedance, resonances introduced by harmonic filters, current regulator parameters, and the synchronizing procedure. Based on this analysis suitable provisions have been taken to mitigate the 125 Hz voltage distortion on a 50 Hz system. The frequency domain analysis has been verified by a time domain EMTP model of the system. Finally, measurements has been taken on the DC arc furnace installation using different control and filter parameters, which show the effectiveness of the adopted provisions.