Identification of electric power parameters of AC arc furnace low voltage system

Abstract

Electric AC arc furnaces used in steelmaking are nonlinear loads of large power. Due to chaotic nature of the electric arc and the melting process, such devices cause significant power quality problems in a supply network, mainly harmonics, inter-harmonics, unbalance, voltage dips and flickers. Limitation of this negative influence and optimization of the cast process is an important issue. In the paper there are presented results of identification of an AC arc furnace electric power parameters. We carried out digital measurements of voltages and currents in the furnace supply system during cast on the medium and low voltage sides of the furnace transformer. Next, we conducted frequency analysis and evaluation of the harmonics content in recorded waveforms at the secondary side of the furnace transformer. Computations were made using the fast Fourier transform (FFT) built-in in MATLAB. The waveforms of active power, current arc and THD indices during the melting process are presented. Furthermore, V-I characteristics of the AC electric arc, harmonics of voltages and currents as well as phasor diagrams for dominant harmonics at the melting and refining stages are shown. The conclusions and remarks concerning operation and development of a simulation model of an AC arc furnace are formulated.