Electromechanical Forces in Transformers Caused by Inrush Currents: An Analytical, Numerical and Experimental Approach
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Electromechanical Forces in Transformers Caused by Inrush Currents: An Analytical, Numerical and Experimental Approach R. Guimarães · A. C. Delaiba · J. C. Oliveira · E. Saraiva · A. J. J. Pereira Rosentino
Received: 23 July 2012 / Revised: 10 January 2013 / Accepted: 13 June 2013 / Published online: 21 August 2013 © Brazilian Society for Automatics–SBA 2013
Abstract Within the extensive range of reasons that cause internal faults in transformers, the axial and radial electromechanical forces produced by the inrush currents show themselves as noteworthy. In fact, such events may result in high levels of transient current, which may last for quite significant periods of time. Due to this effect, there exist a number of phenomena likely to manifest themselves. One such effect consists of the occurrence of electromechanical forces and their corresponding influences on the mechanical structure and lifetime of the equipment. In this sense, this article has as its objective the analysis of the electromechanical forces in transformers, through an analytical, numerical, and experimental approach. In order to examine and identify the qualitative and quantitative nature of the phenomenon, the studies are further corroborated through the use of the modeling technique using the averages of the finite element method in its 3D version. Finally, comparative analyses are made between the analytical and computational results with those derived from experimental tests, which showed the potential of the presented studies for the purpose of subsidizing projects and providing the design of the supporting mechanical structures of the transformer windings. Keywords Inrush current · Three-phase transformer · Radial forces · Axial forces · Finite elements method
R. Guimarães (B) · A. C. Delaiba · J. C. Oliveira · E. Saraiva · A. J. J. P. Rosentino Faculdade de Engenharia Elétrica (FEELT), Universidade Federal de Uberlândia (UFU), Av. João Naves de Ávila 2121, Campus Santa Mônica, CX 593, Uberlândia, MG CEP 38408-100, Brazil e-mail: [email protected]
1 Introduction Power transformers are essential components in electric systems and make up one of their most expensive components. When one of these pieces of equipment is damaged or presents some type of fault, the need to repair or substitute it becomes of the greatest urgency, therefore with this scenario at hand, along with the necessary financial resources, there is still the addition of other damages, such as the loss of invoicing, impacts on power quality performance indicators, among others to be taken into account. For information purposes, Bechara (2010) shows the conclusion of statistical research study carried out on 92 transformers of transmission, sub-transmission and distribution. The results show that 24 % of encountered faults were provoked by external short-circuits. The same research study show also that in sub-transmission transformers 75 % of the faults are presented in the windings and that transient shortcircuits are responsible for about 34 % of all cases.
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