Physical modeling of the reverse transformation mode in a rural 0.4/10 kV electric grid

RELEVANCE. Currently, there is a danger of supplying unauthorized voltage in rural electrical networks of 0.4 kV, which through reverse transformation at a transformer substation can be supplied to the 10 kV side. This can lead to fatal accidents among the staff of power grid organizations, or third parties. THE PURPOSE. Investigation of the reverse transformation mode in a rural 10/0.4 kV electric grid by means of physical modeling. METHODS. The study was conducted on a physical model of a 10/0.4 kV rural electric network using a single-phase lowpower transformer as a source of unauthorized voltage, which was connected to a low-voltage network at different distances from the model of a three-phase 10/0.4 kV transformer. In the experiments, electrical parameters were measured on the low and high voltage sides of the 10/0.4 kV transformer model. The obtained values, using similarity coefficients, were recalculated for a rural 10/0.4 kV electric grid powered by a 10/0.4 kV transformer with a capacity of 250 kVA. RESULTS. It was revealed that connecting a single-phase unauthorized voltage source to a 0.4 kV network, depending on its removal from a 10/0.4 kV transformer, leads to voltage values at the 0.4 kV output of the transformer from 11 V to 81 V (when approaching the beginning of the line departing from the transformer) in the phase to which the unauthorized voltage source is connected. On the 10 kilovolt side, the voltage varies from 234 V to 2579 V. The voltages of the other two phases on the 10 kV side range from 66 to 421 V, and on the 0.4 kV side – from 4.4 V to 22 V. CONCLUSION. The results obtained can be used as setpoints for triggering technical means of signaling and blocking reverse transformation, preventing reverse transformation in electric networks of 10/0.4 kV.

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