Variation of load-carrying capacity indices of an AC Arc furnace network transformer

The paper deals with analysis of losses and load-carrying capacity indices for transformers in industrial power stations that supply nonlinear loads taking non-sinusoidal current. Waveforms of voltages and currents measured in an AC arc furnace system are presented. They are used to determine harmonic spectra of phase currents in the transformer´s secondary circuit and time variations of load-carrying capacity indices K, F_HL and i_max over a whole steel cast cycle. The dependencies of K and i_max on the harmonics content THD_I are presented for a representative steel cast cycle and their polynomial approximations are calculated.