Improvement of power quality in power supply systems of rolling mills using frequency converters with active rectifiers due to use of specialized passive filters

In recent years, the frequency converters (FC) with active rectifiers (AR) have become widespread due to their advantages. The advantages are the possibility of energy recovery in braking modes of electric drive and support of the set value of power factor at the input of AR. At the same time these converters have a significant disadvantage, that is the deterioration of voltage quality in the in-plant 6–35 kV power distribution network due to the imposition of high-frequency harmonics of the input voltage and current of AR on the resonant area of the supply network frequency response. This disadvantage can be eliminated by using special passive filters in the in-plant power networks. They ensure the shift of the main resonance of currents to a zone free from high-frequency harmonics of the FC with AR. It makes possible to reduce the harmonic distortion coefficient in the voltage sections of the main stepdown substation (MSS) of the enterprise. Processing of experimental data is carried out in the Matlab mathematical package with the Simulink application. Using income data of functioning metallurgical complex CherMK of PJSC “Severstal”, the authors carried out the analysis of voltage quality of 10 kV network using specialized passive filters and without them. The article presents the results of the study of the effectiveness of the use of specialized passive filters in the in-plant power supply system of the rolling complex operating at the CherMK of PJSC “Severstal”. The reasons of the deterioration of the voltage quality in the 10 kV distribution network are studied, and as a result, operational breakdown of the modes of sensitive electrical receivers. A complex mathematical model of the 10 kV network has been developed to study the way to improve the harmonic composition of voltage due to installation of specialized passive filters. This filter allows you to adjust the frequency characteristics of the 10 kV network, shift it to an area free of high-frequency harmonics generated by modern frequency converters with active rectifiers. Thus, the resonance of currents and voltages in 10 kV sections is eliminated. As a result, a significant improvement in the shape of the line voltage and a decrease in the harmonic distortion coefficient of voltage THDU = 75,2–91,2 % to values THDU = 0,49–1,4 % is observed. The main result of the research is the recommendation to use a specialized passive filter to eliminate the negative impact of the harmonic component of the current resonance. The research results can be used to design power supply systems of metallurgical enterprises that have powerful electric drives with active rectifiers.