Study of Reverse Transformation Mode in 0.4/10 kV Electric Network on Physical Model

A current problem is the danger of unauthorized voltage appearance in 0.4 kV electrical networks, which can be supplied to the 10 kV side through reverse transformation at a transformer substation. The purpose of the current study is to investigate the mode of unauthorized voltage supply and the phenomenon of reverse transformation in 0.4/10 kV electrical network using physical modeling. The research was conducted on the physical model of 0.4/10 kV electrical network using a single-phase low-power transformer as a source of unauthorized voltage and connected to the low-voltage network at different distances from the model of three-phase 10/0.4 kV transformer. In the experiments, measurements of voltages, currents, powers, and power factors were carried out at the terminals of the unauthorized voltage source and on both LV and HV sides of 0.4/10 kV transformer model. The obtained values were recalculated using similarity coefficients for a 0.4/10 kV electrical network fed by a 10/0.4 kV transformer with a capacity of 250 kVA. The results of research showed that connecting a single-phase source of unauthorized voltage to a 0.4 kV network leads to 0.4 kV transformer terminal voltage values from 11 V to 81 V depending on the distance of the source from the 10/0.4 kV transformer. In this case, the voltage on the 10 kV side changes from 234 V to 2579 V.