Abstract
At present there is a tendency in the metallurgical industry to build mini-factories with a capacity of 1 to 2 million tons of steel per year. The largest supplier of technological equipment of such plants is the company Danieli (about 80% of the world's total). The main advantages of these factories are: combining ultra-compact sizes and high technologies with reduced in-vestment costs, extremely low cost of transformation, and also high ecological purity. That is why the demand for the construction of mini-plants is growing. In internal power supply systems of metallurgical mini-factories with an average produc-tion volume (1-2 million tons of steel per year) medium-voltage extended distribution networks of 6-35 kV are used. With a long length of cable lines, the total value of the distributed capacity of the cables can reach several microfarads. As a result of the interaction of an inductance of a network transformer and the capacitances of the cables in the frequency characteristic of the network, a resonance of the currents arises, the amplitude of which, with a large value of the cable capacity, can be located in the frequency range of higher harmonics generated by modern frequency converters with AR. In this case, there are strong high-frequency voltage distortions on the 10 kV BUS BARS, which can lead to the bread down of frequency converters due to errors in the operation of the control pulses forming units of power switches AR. For this reason, the actual task is to investigate various ways to eliminate resonances of current in the frequency characteristic of the power supply network, as well as strong distortions. The paper deals with investigations of the causes of high voltage distortions in the 10 kV grid of internal power supply of metallurgical enterprises, where powerful electric drives of rolling mill stands are built on the basis of multilevel frequency converters with active rectifiers installed. The processing of the experimental data was carried out in the Matlab - Simulink application, where the main coeffi-cients of the harmonic voltage components of the 10 kV network were calculated using by spectral analysis methods and developed signal processing algorithms. To study the methods of correcting the frequency response of a 10 kV network the mathematical modeling of the system of internal power supply was used. Currently, this problem is poorly understood and poorly covered in Russion and foreign literature. In this regard, the results of the research presented in the work have novelty, theoretical and practical significance. The main result of the research is the recommendation to eliminate current resonance by means the special connection R-L filter based on capucity banks and low inductance reactor with reactance about 100 ?H. The results of the research can be used in the design of power supply systems for industrial enterprises to implement the cor-rect choice of the configuration of medium voltage electrical networks, as well as in solving power quality problems at operating plants where strong high-frequency voltage distortions occur during the operation of powerful FC and AR
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