A Coupled Thermal-Electromagnetic FEM Model to Characterize the Thermal Behavior of Power Transformers Damaged By Short Circuit Faults

This research work is an initiative to characterize the thermal behavior of power transformers in presence of winding short circuit faults as one of the most important causes of failures in power transformers. The paper contributes for this matter by accurately estimating the excessive power losses and temperature rise due to winding short circuit faults, through a circuit-magnetic-thermal FEM coupling method. The magnetic-circuit coupled FEM model of the faulty transformer allows the computation of the circulating current in the shorted turns, flux distribution in the transformer and the power dissipated by Joule effect in the shorted region of the winding. Once the local losses, required as heat sources for the thermal analysis, are calculated, a coupled electromagnetic-thermal FEM model of the transformer is developed to solve the transient heat flow equations and obtain the transient thermal characterization of the transformer damaged by short circuit faults. At each time step in the coupled transient FEM thermal model, a local linking of thermal and then steady state AC magnetic computations is carried out, as a means of better representation of the transformer dynamic thermal behavior. 