A Comparative Study on Propagation of Voltage Sag through Different Transformer Winding Connections

Propagation of voltage sag after occurrence of fault in power transformer may develop high inrush current and subsequently may lead to failure of the transformer. Transformer inrush current have high magnitude and contain undesirable harmonics which may lead to unwanted tripping of protective relays, reverberation in the system and mechanical strain in the winding. This paper studies the effect of voltage sag propagating in the transformer due to various symmetrical and asymmetrical faults in a chronological manner. Though various studies has been carried out to express the effect of propagation and mitigation of voltage sag, the unique study presented in this paper very precisely describes and compares the propagation of voltage sag through different transformer connections in a methodical way. For the purpose of analysis different types of actual transformer of North Eastern Regional Transmission System has been taken and the analysis has been performed with the help of SIMULINK by considering the occurrence of all the major faults. The study presented in this paper will help the utilities to choose the best and appropriate connection of transformer leading to reduction in failure of power transformer and ensuing total reliability of the system and prevention of loss of economy.