Determining Natural Resonant Frequencies of Large Power Transformer Windings

Abstract

Design, assembly process and preparation of windings for large power transformers are complex procedures. It is very important to recognize resonant frequencies of the windings during the design phase in order to avoid increase of vibrations, stresses or noise levels during normal operation of the transformer. Increased vibrations and stresses can occur when the frequency of the excitation is close to the natural resonant frequency of the system. In that case amplitudes will increase, and their values will depend, among other factor, also on the amount of damping present in the system. Therefore, in order to avoid very large amplitude of vibration at resonance, the natural frequency must be known. In this work analytical calculation of natural frequencies of high voltage and low voltage windings, is described. Additionally, numerical analysis (FEA) is performed in the software package Ansys. Analysis contains descriptions of geometry simplifications, boundary conditions, mesh validation and applied loads. Finally, results obtained with numerical analysis (FEA) are compared with analytical results.