Research for the Neutral Point Protection Measures of Voltage Transformer’s Secondary Windings

Experimental and simulation studies are carried out on the lightning transfer in the neutral point of the voltage transformer’s secondary winding and the potential difference between two points of ground network in the situations of lightning invasion, direct lightning stroke and power frequency grounding fault. The results show that the risetime of lightning surge wave has obvious influence on the over-voltage level of lightning transmission at the neutral point of the secondary winding, and the breadth values of the level for both the voltage-type and capacitance-type voltage transformer increase rapidly as the risetime of lightning suge wave decreases. The over-voltage level is limited greatly by an arrester, indicating that the ZnO arrester (MOA) can work well for protection against the over-voltage of the neutral point of the secondary winding, but it should be careful to choose suitable rating voltage of the arrester.