Analysis and Experiments Concerning Surges Transferred Between Power Transformer Windings Due to Lightning Impulse

Theoretical models, numerical simulations, and experimental tests for determining surges transferred between the windings of transformers subjected to lightning impulse are addressed. Considering the surges transmitted in the transformer windings have inductive and capacitive components, the proposed model is focused on five aspects: 1) voltage transmission by electromagnetic induction; 2) surge transferred in the transformer windings by capacitive coupling; 3) oscillating component of the voltage transferred between the windings; 4) voltage transferred between the primary and secondary windings; and 5) voltage transferred to the tertiary winding. The maximum transferred voltage is analytically determined. The simulation relies on the Math Script RT Module. Experimental tests were performed on two types of transformers. For the first one (type TTUS-ONAN, 50/67 MVA, 132/13.8/6.6 kV, Ynyn0d1 connection), the maximum voltage between the medium-voltage (MV) winding and ground, in case of a 200 V impulse applied to the high-voltage winding, is around 20.3 V; the voltage transferred to the tertiary winding reaches 8.1 V. For the second type (type TTUS-ONAN, 54/73 MVA, 110/15/6.6 kV, Ynyn0d1 connection), the voltage transferred to the MV winding reaches 21.1 V; the voltage transferred to the tertiary winding is 11.9 V. The laboratory tests validate the proposed analytical and simulation model.