Physical simulation of different types of two-phase short circuits in a rural 0.4 kV power supply network

Rural power supply networks feature two-phase and two-phase zero-conductor short-circuits in in case of crossed uninsulated wires or damaged insulated wires. It is practically impossible to detect the parameters of these modes, so they should be calculated. However, normative documents and literature sources do not provide dependencies to identify these modes along the entire length of the transmission line, including at the point of installation of sectionalizing devices. In order to determine the electrical parameters characteristic for the modes of two-phase and two-phase zero-conductor short circuits in rural 0.4 kV power supply networks, the authors used the method of physical simulation. The physical model of a rural power supply network contained a transformer TT-0.16-380/38 Y/Yn-0. The phase-to-phase voltage ratio was 38/22 V. The authors used a nichrome wire of the X20H80 alloy with a cross-section of 0.5 mm² and a resistance of 5.6 Ohm/m. The transformer neutral grounding resistance was taken as 4 Ohm, and that of 30 Ohm – for two repeated neutral wire grounding. As a result, it was found that in a two-phase short circuit in a 0.4 kV network, the currents in the damaged phases are equal, and the ratio of voltages on the undamaged and damaged phases was 1.3 to 1.9. In the case of a two-phase short circuit to the neutral conductor in one of the phases, the current value is equal to the algebraic sum of the neutral current and the current flowing in the other phase. At the same time, the voltage ratio of the undamaged phase to the damaged phases changes depending on the proximity to the fault point. The revealed dependencies can be used to identify these modes by microcontroller control units of sectionalizing devices, which will provide the network dispatcher with information about their occurrence and reduce the time for search and identification of the causes of damage.

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