At present, semiconductor converters have found wide application in the electric power industry [6]. One of the most common semiconductor converters is a frequency converter, as it provides a three-phase voltage with adjustable frequency from a three-phase mains voltage. However, it, like other semiconductor converters, is the cause of the appearance of harmonics and, as a result, the non-sinusoidal shape of the voltage curve [1]. Harmonics are the cause of such negative effects in the electrical network as concomitant heating of the windings of motors, transformers, etc., false alarms in distribution networks, asymmetry in industrial networks with three-phase sources when harmonics occur in one phase, the occurrence of noise in communication networks, the influence on adjacent low-current and power cables due to the induced EMF, and also with the appearance of harmonics, there is a need to increase the cross section of neutral wires due to the summation of harmonics multiple of the 3rd in three-phase networks [3]. Therefore, the study of the harmonic components of the voltage is an urgent task. Subject of research: processes occurring in electrical networks with a frequency converter. Purpose of research: to identify the presence of harmonic voltage components in electrical networks with a frequency converter. Object of research: a research stand that simulates the operation of electrical networks with a frequency converter. Methods of research: in the process of performing research, scientific and technical generalization of literary sources on the initial prerequisites for research, methods of the theoretical foundations of electrical engineering and the theory of electrical networks, the method of analytical research, methods of system analysis were used. Experimental studies were carried out by a complex method using the Resurs-PKE device. Results of research he study: based on the studies carried out, it was shown that the frequency converter is a source of harmonic voltage components, while harmonics appear only in certain sections of the electrical circuit.
To date, there is a fairly large number of electrical equipment that is a source of asymmetric modes of operation in medium and low voltage electrical networks. This electrical equipment can create conductive low-frequency electromagnetic interference in electrical networks by the coefficient of voltage asymmetry in the reverse sequence. Studying the methodological basis of research on the theory of conductive low-frequency interference, it was found that when switching from one adjacent electrical network to another (for example, from a 0.4 kV network to a 10 kV network and vice versa) potential for conductive low-frequency interference decreases, i.e. the interference is partially suppressed by a certain amount. This amount is called the criterion determining the changes of the voltage asymmetry coefficient values in the reverse sequence in the transition of conductive low-frequency electromagnetic interference to the adjacent network. The purpose of this article is to develop a mathematical model for the study of network parameters affecting voltage asymmetry in the reverse sequence, which is reduced to a method for determining the value of the criterion for the effect of an asymmetric load on voltage distortion in a 10 kV network for recommendations for reducing voltage asymmetry. The article describes in detail the method of calculating this value and how it can be used to form recommendations for reducing voltage asymmetry. Scientific novelty of the study consists in the fact that an empirical mathematical model has been obtained that determines the criterion for the influence of an asymmetric load in a low-voltage network, the impact on which makes it possible to improve the electromagnetic situation in a 10 kV electrical network. This parameter can be taken into account when designing elements of electrical networks to determine the electromagnetic environment.
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