Influence of the current control loops of DC arc furnaces on voltage fluctuations and harmonics in the HV power supply system

It is necessary, to an increasing extent, to take controllers and control loops into consideration in mathematical modelling and simulations for power quality studies. DC arc furnaces belong to those electric loads which network behaviour is essentially influenced by control processes. Rated at more than 100 MVA, these furnaces cause voltage fluctuations and harmonics in the HV power system. Based on experiences of onsite measurements at several plants, a mathematical furnace model was completed by implementing phase lock-loop and DC current control loops. The paper shows what influence is exerted to harmonics and flicker severity by the DC furnace current control. Case study calculations are compared to measurement results. It is shown that it is not sufficient to simplify or neglect the control loops in such cases.