ANALYSIS OF SYMMETRICAL ELECTROMAGNETIC APPARATUS FOR THREE-PHASE ZERO-WIRE NETWORKS
Authors: Orlov Aleksandr I. , Karpov Il’ya A. , Sidorova Vera T. 
Published: December 2024

The most common problems of electricity quality in 0.4 kV power transmission lines are voltage deviations and voltage asymmetry, which are clearly manifested at the end sections of long lines with uneven distribution of consumers by phases. The technical means of solving these problems include devices for the uniform distribution of 1-phase consumers across the phases of a 3-phase network based on electromechanical relays, static semiconductor devices and electromagnetic devices.

The purpose of the article is to analyze the operation of a symmetrical electromagnetic apparatus consisting of one three-phase winding located on a common magnetic conductor. The scientific novelty consists in determining the operating conditions of a symmetrical electromagnetic apparatus, obtaining qualitative and quantitative characteristics of its operation.

The materials and methods. The object of the research is a static electromagnetic apparatus that exhibits properties of voltage and current symmetry when connected to a three-phase unbalanced electric network. The methods of theoretical electrical engineering are used, in particular, the method of symmetric components, including generally accepted methods of analyzing electromagnetic processes in electric machines, methods of mathematical and computer modeling, analysis and generalization. The accepted assumptions are: sinusoidal voltages and currents; the linearity of the magnetization curve of the magnetic core material and the absence of electrical and magnetic losses in the electromagnetic apparatus.

The results of the study. It is established that the effect of equalizing currents in the line and voltage symmetry when connecting an electromagnetic device containing one three-phase winding on a common magnetic circuit occurs in the case of simultaneous fulfillment of the conditions: a) the use of a three-phase magnetic circuit in which the zero-sequence magnetic flux cannot be closed in the magnetic circuit; b) connections of transformer windings according to a scheme that allows the flow of zero-sequence currents in linear conductors. The models of the 0.4 kV line with concentrated and distributed load are considered. It is shown that with an asymmetric load, the SEA currents acquire a component of zero sequence, and the linear currents are aligned compared to the load currents. The coefficient of voltage asymmetry of the zero sequence decreases practically to zero, the reverse sequence practically does not change. The effect of voltage symmetry when connecting the SEA occurs both before and after the place of its installation. A decrease in the total losses of electrical energy in the line due to the equalization of currents is demonstrated.

Conclusions. An electromagnetic device containing one three-phase winding on a common magnetic circuit has the effect of balancing the voltages and currents of a three-phase power line with a zero wire, if the design of the magnetic wire does not allow the possibility of closing the magnetic flux of zero sequence within its limits, and the winding connection circuit contains a neutral outlet connected to the zero wire of the network, through which zero-sequence currents can flow. The action of the considered electromagnetic apparatus manifests itself in equalizing the line currents in magnitude and, as a result, in reducing the total losses in it. The electromagnetic device symmetrizes the voltages before and after the place of its installation, the greatest effect is manifested when placing the proposed electromagnetic device at the end of the line or at the connection point of the most powerful consumer.