The paper dwells on the unified power quality indexes characterizing the\nphenomenon of voltage unbalance in three-phase systems. Voltage unbalance\nis one of the commonest occurrences in the town mains of 0.38 kV voltage.\nThe phenomenon describes as inequality of vector magnitude of phase voltage\nand shearing angle between them. Causes and consequences of the voltage\nunbalance in distribution networks have been considered. The algorithm,\nwhich allows switching one-phase load, has been developed as one of the methods\nof reducing the unbalance level. The algorithm is written in the function\nblock diagram programming language. For determining the duration and\nmagnitude of the unbalance level it is proposed to introduce the forecasting\nalgorithm. The necessary data for forecasting are accumulated in the course of\nthe algorithm based on the Function Block Diagram. The algorithm example\nis given for transforming substation of the urban electrical power supply system.\nThe results of the economic efficiency assessment of the algorithm implementation\nare shown in conclusion. The use of automatic switching of the\none-phase load for explored substation allows reducing energy losses (active\nelectric energy by 7.63%; reactive energy by 8.37%). It also allows improving\nsupply quality to a consumer. For explored substation the average zero-\nsequence unbalance factor has dropped from 3.59% to 2.13%, and the negative-\nsequence unbalance factor has dropped from 0.61% to 0.36%.
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