PhD Thesis High Frequency Modeling of Power Transformers under Transients -by Kashif Imdad-Universidad Politécnica de Cataluña

LINK: https://www.tesisenred.net/bitstream/handle/10803/457774/TKI1de1.pdf?sequence=1&isAllowed=y

Abstract

This thesis presents the results related to high frequency modeling of power transformers. First, a 25kVA distribution transformer under lightning surges is tested in the laboratory and its high frequency model is proposed. The transfer function method is used to estimate its parameters. In the second part, an advanced high frequency model of a distribution transformer is introduced. In this research, the dual resonant frequency distribution transformer model introduced by Sabiha and the single resonant frequency distribution transformer model under lightning proposed by Piantini at unloaded conditions are investigated and a modified model is proposed that is capable to work on both, single and dual resonant frequencies. The simulated results of the model are validated with the results of Sabiha and Piantini that have been taken as reference. Simulations have shown that the results of the modified model, such as secondary effective transfer voltages, transferred impedances and transformer loading agree well with the previous models in both, the time and frequency domains. The achieved experimental and simulated objectives of this research are:  Methodology for determining the parameters of a power transformer.  High frequency modeling of a transformer in order to simulate its transient behavior under surges.  Modification of high frequency model for single and dual resonance frequency. The originality and methodology of this research are:  High frequency transformer model is derived by means of the transfer function method. In the literature, the transfer function method has been used in many applications such as the determination of the mechanical deformations or insulation failure of interturn windings of transformers. In this thesis, the parameters of the proposed model are estimated using the transfer function method.  Modification of high frequency model for single/dual resonance frequency using the transfer function method. The transfer function can also be used to determine the state of the transformer. The modification in the developed model using the proposed technique has been validated (by simulations).