Análise de esforços eletromagnéticos em transformador submetido a um curto-circuito trifásico

Abstract

Transformers are essential equipment for electrical systems, when they are damaged or have some kind of failure their repair or even their replacement demands high financial costs. Many failures of this equipment occur due to the reduction of the insulation resistance of the windings, which can be caused by the vibrations produced by the electromechanical forces during its normal operation, that is, in permanent regime, by the electrochemical phenomena of the cooling liquid and also by the deformations of the windings caused by the high short-circuit currents. The action of protection systems, whose response time, as a rule, does not prevent transformers from being subjected to undesirable transient effects. However, a transformer is expected to support a certain number of short circuits during its operating time. In this context, it is important to use methodologies and techniques to try to understand and evaluate the electromechanical forces in transformers. In this perspective, the present work aims to investigate the types of failures that can occur in transformer windings as a result of radial and axial forces. Next, an analytical methodology is presented to calculate the forces and stresses in the windings of a three-phase transformer subjected to an asymmetric three-phase short circuit. Finally, the transformer will be modeled in the Finite Element Method Magnetics (FEMM) based on the finite element technique in order to compare it with the values obtained analytically.