Abstract
Relevance. Static var compensators are critical elements of the power supply systems designed for high-power electric steel-making complexes comprising electric arc furnaces and ladle furnaces. Static var compensators help maintain the primary voltage of furnace transformers, due to which the design capacity of steel-making furnaces can be reached. They also ensure the specified power quality is reached in the point of common coupling of arc furnaces and other electrical loads. At present, one does not find, either in Russian or foreign literature, any guidelines on how to select the static var compensator components by rated power while accounting for asymmetric operation of different classes of electric arc furnaces. The existing techniques utilized by major manufacturers of compensators for electric arc furnaces in some cases can result in overrated power for the filtering and compensation circuit and the thyristor controlled reactors, which leads to increased price and operating costs due to high active power losses in the compensator elements. In this regard, it appears to be an important task to come up with a different approach to selecting the static var compensator by rated power based on the analysis of how the sequence components of the electric arc furnace currents tend to change at different process stages. Objectives: The objective is to come up with a better technique for deciding on the power of the static var compensator elements using experimental data characterising the change of the sequence components of currents, which would ensure accuracy of calculated compensator parameters without overestimating the unit’s rated power. Methods Applied: Arrays of instantaneous values of currents and voltages of electric arc furnaces of various power ratings and classes were used as the basic initial data for theoretical studies; the MATLAB software with the Simulink application was utilized for data processing; the above mentioned environment was used to analyse the real and imaginative parts of both positive and negative sequence currents of electric arc furnaces with the help of the symmetrical component method; some methods from the theory of probability and mathematical statistics were used to determine significant variation ranges of the furnace electrical parameters. Originality: The results of this research can be described as novel as this research provides the first-of-its-kind comprehensive analysis of asymmetric operation of electric arc furnaces of different classes; based on these studies, a new technique was developed for selecting the static var compensator by rated power, which, compared with other existing techniques, ensures high accuracy of calculated compensator parameters. Findings: Regularities have been established for varying sequence components of electric arc furnace currents; the authors demonstrate how the asymmetric operation can impact the target values of susceptances and total reactive power of the electric arc furnace compensator; statistical data have been obtained on the distribution of sequence components of currents for electric arc furnaces of different classes and power ratings; a new technique has been developed for selecting the power of the static var compensator for an electric arc furnace. Practical Relevance: The results obtained are of great theoretical relevance for electrical engineering of arc furnaces and can be useful for calculating the parameters of static var compensators operated as part of the power supply systems of steel-making complexes.
Keywords
Electric arc furnace, ladle furnace, static var compensator, reactive power compensation, electric power quality, asymmetrical arcing, high-order harmonic filtering, selecting the power of the static var compensator.
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