Investigation of the mode of stable single-phase short circuit in a rural 0.4 kV electric network on a computer model

Currently, an urgent issue is the study of emergency modes of operation of electric networks in order to determine the operating parameters for using them as operating settings of technical devices introduced into electric networks to improve efficiency their functioning. The paper investigates the mode of a stable single-phase short circuit in a rural 0.4 kV electric network on a computer model including a power system, transformer, power transmission line, measuring units and an emergency mode simulation unit. During the study, the electrical parameters of currents and voltages from the high and low voltage of a 10/0.4 kV power transformer were determined, as well as the components of currents and voltages of the forward, reverse and zero sequences. It was found that the voltage of the forward sequence at the point of a short circuit, when it occurs from 0 to 1000 meters, decreases from 219 V to 141 V, the voltage of the reverse sequence increases from 23.1 V to 101 V, and the zero sequence decreases from 195 V to 40.2 V. In this case, the currents of the symmetrical components make up a third of the single-phase short-circuit current. In turn, the neutral current is equal to the single-phase short circuit current. The degree of asymmetry of phase voltages from the 10 kV side is 8% when the 0.4 kV network is closed at a distance of 25 meters from the transformer. In turn, when the short-circuit point is more than 675 meters away from the low voltage output of the power transformer, the phase voltages are symmetrical and the emergency mode in the low-voltage network does not affect the electrical parameters of the high voltage side.