Study of short-circuit modes in a 0.4 kV electrical network for transformers with different circuits and winding connection groups

Currently, a lot of work is aimed at studying short-circuit modes in 0.4 kV electrical networks. At the same time, in most of them, only the values of the currents of emergency modes are investigated and the values of the symmetrical components of currents and voltages are not revealed. In this work, a study of the modes of symmetrical and asymmetric short circuits in an electrical network of 0.4 kV using the computer model «Project RZA» is implemented. The reliability of the model in comparison with the method of calculating short-circuit currents according to GOST 28249-93 is 2%. The prototype of the computer model of the 0.4 kV electrical network was a 1000-meter long radial power transmission line connected to a 250 kVA transformer and made using an uninsulated A-35 wire. The dependences of the distribution of currents and voltages of symmetrical components in the modes of asymmetric short circuits were revealed. The dependences of the current distribution on the sides of the high and low voltage of the power transformer for different circuits and groups of winding connections are established. It is noted that the most reliable electrical parameter that can be used to conclude that an emergency has occurred is the reverse voltage. The setpoint for this parameter, when installing automation equipment in a 0.4 kV electrical network for more than 50% of the total length of the line, can be assumed to be equal to 9% of the nominal phase voltage of the line.