Transient Regime Study for Voltages in the Secondary of the MV/LV Power Distribution Transformer at Faults in the MV Network

In this paper, the authors aim to analyze the transient voltages of $\mathbf{2 0} / \mathbf{0 . 4} \mathbf{~ k V}$ power transformers - with DZn5 connection - connected in a medium voltage (MV) line with radial feed, during a single-phase through-fault in the MV network, which shortly turns into a permanent fault. The records used for the analysis were obtained from a fault identification system installed in the MV network operated by the electricity distributor in the Oltenia region - Romania, using information from the equipment installed in the 0.4 kV distribution box of the transformer substations fed from the same MV line. The authors also make a comparative analysis of the voltage drops on each 0.4 kV phase and on each transformer substation, during the transient regime of the single-phase fault in the MV network. The MV network fault identification system is also briefly presented, as well as the advantages offered by such a system in the efficiency of the electricity distribution activity.