The Overvoltage Distribution across Transformer Windings in presence of Long Feeders

Abstract

This is a study presenting the impact of the long transmission lines or so-called feeders on the overvoltage distribution across power transformer windings. The overvoltage propagates along the power feeders until reaches a high voltage (HV) winding. The overvoltage is distributed across it. For the purpose of transient overvoltage evaluation, the HV winding model assumes distributed parameters. An equivalent circuit composed from series connected two-port elements substitutes the feeder. According to simulation results, the values of the line parameters play a significant role in determining the voltage across the HV winding. The strongly capacitive character of long feeders causes a larger voltage measured across the HV winding, compared to the line input. Moreover, the effective length of the transmission line is in direct correlation with the overvoltage amplitude across the HV winding. For this study, the model based upon lumped parameters and disk coils is suitable and provides appropriate information regarding the insulation requirements, as well. The signal, which emulated the commutation overvoltage, had a time variation closed to a step-up. All the numerical simulations from this paper have been performed running a software package called SYSEG (Symbolic State Equation Generation), prior developed by the authors.