On the use of the frequency domain in assessing resonant overvoltages during transformer energization.

Abstract

Resonant temporary overvoltages during transformer energization may result in damage to the transformer itself or surrounding equipment. These overvoltages are caused by the interplay between the transformer energization currents and the grid impedance. Current practice to assess the risk of transformer energization is by classifying grid scenarios into potentially problematic or non-problematic based on the magnitude of the grid impedance at frequencies coinciding with the grid harmonic frequencies. At the moment, this approach lacks a proof of validity. Therefore, this paper investigates the use of frequency domain characteristics, and more in general, linear analysis of the grid impedance, for assessing the risk associated with transformer energization. Findings show that the magnitude of the frequency domain grid impedance may not provide sufficient information for classifying problematic and non-problematic cases.