Voltage Distribution of Transformer Winding under the Fast Transient Pulse

Abstract

The fast transient pulse (FTP), mainly coming from the El component of the high-altitude electromagnetic pulse (HEMP) and the very fast transient overvoltage (VFTO), is a threat to the power system and its electrical infrastructures represented by power transformers. In order to study the voltage distribution of transformer windings under FTP, a circuit model of a two-winding transformer is built. Analytical method (AM) and finite-element method (FEM) are used and compared in the calculation of the electrical parameters for the model. An FTP waveform captured in a field test is used as input in this paper, and different kinds of voltage distribution are discussed using both time-domain and frequency-domain analysis. The simulation result shows that as the overvoltage propagates from the input end to the farther part of the winding, the input component begins to attenuate gradually and the natural frequency oscillation emerges and becomes larger. The maximum voltage near the tail of the winding becomes higher for that reason. The transfer function for the output voltage at the head-end of the HV grounding wire also shows a sheer increase near the natural frequency. This phenomenon should be taken into consideration in related insulation design or on-site test.