Contribution to study and simulation of transients in power transformers

Abstract

This Phd thesis proposes a new model for the analysis of low frequency transients for transformer, with a modified equation to compute the flux-current saturation characteristic which represents the iron core inductance of the transformer. The model based on the V - I (voltage - current) no-load curves and uses the no-load reactive power losses. To validate the model, it was used to simulate the magnetizing no-load current in the steady state, as well as the transient inrush current at the network frequency. The experimental results presented in this thesis were obtained through a laboratory setup and a data acquisition system based on the dSPACE 1104 card. Moreover, a control technique to mitigate the transient inrush current in a transformer has been developed and applied experimentally in the laboratory and also in simulations. This control strategy was carried out taking into account the residual flux at the opening instant of the associated circuit breaker. In addition, for othe validations of the proposed technique, an applications have been made to mitigate the sympathetic inrush current (interaction phenomenon between two transformers, one is subject to the transient phenomenon and the other is already supplied) , and also the inrush current in a three-phase transformer, taking into account the phase shifting between the three phases.