This paper is focused on the investigation of transformers internal electromagnetic forces caused by external fault. The simulations are based on the finite elements method (FEM) to model a three-phase transformer and also to calculate the forces via traditional mechanical and electrical equations. Normal operation and symmetrical fault conditions are used for the estimation of internal radial and axial forces. This work, which leads to specific transformer performances, allows to verify the potentiality of the method used and also the physical consistence of the computational simulations. The results shown in this paper are flux distribution, losses and other information regarding the equipment operation. The FEM approach has shown to be a powerful tool on the estimation of mechanical stress within transformers and it can be quite useful at the design stage of such devices

The technology of power transformer modeling is studied in this paper and a switching strategy is proposed for controlling the phenomena associated with transformer inrush currents. A comprehensive time-domain program is developed to deal with these transients and a solution for obtaining the required residual fluxes is considered. The approach is computationally implemented and both the theoretical and the experimental investigations are carried out to highlight the method of application and its validation. The results emphasize the possibility of building devices that eliminate the well-known transformer inrush currents and their side effects

The purpose of this paper is to present two methodologies, one being analytic in nature and the other computational, both with the objective of producing a diagnostic of the electromagnetic forces, along with the electromechanical stresses which occur in transformers due to inrush and short circuit currents. To reach the desired outcome, a computational model was developed using the finite element method in its three-dimensional version. The computational package used was FLUX 3D. It should be noted that this platform permits the study of inter-relationships between the electrical, magnetic and mechanical magnitudes. The electromagnetic and electromechanical results obtained through these computational simulations will be analyzed side by side with those self-same magnitudes, which have had their origin drawn from analytical calculations or project values. It should also be noted that these studies can be used as a benchmark when reaching a management and/or technical decision as to the best time to preventatively repair and/or substitute a transformer. Lastly, it should be highlighted that the procedures investigated here in are based upon fundamentals which should be used to guide the project as well as the construction of the transformer, especially when concerning those points linked directly to the windings’ mechanical support structure.

Considering the guidelines contained in documents such as the IEEE Standard 519 and IEC 61000-3-6 that includes, among other indexes of power quality, the thematic of the harmonic distortion, the mentioned text refers to issues associated with definitions, measuring procedures, reference values, etc. Taking under consideration these determinations, and recognizing that the mitigating solutions for the adequacy of performance indexes involve significant financial costs, the proposition of finding ways to determine the responsibility for possible violations of pre-established limits for harmonic distortion arises. Among the proposals found to detect the contribution portions coming from the supplier and the customer, it is noteworthy that, in general, the methodologies based on principles use the frequency domain harmonized with the superposition of effects. Despite the simplicity of this procedure, it is emphasized that it relies on measuring information and on the previous knowledge of the equivalent harmonic impedances of the utility and customer, whose information are of difficult access. In this context, this paper is focused on a feasibility proposition to solve the above mentioned difficulties in obtaining the percentage of responsibility between the parties.

Short-term voltage variations (STVVs) are phenomena manifested as voltage sags, voltage swells, or interruptions lasting up to 1 minute. Despite their short duration, they greatly influence the operations of loads. In fact, residential, commercial, and industrial consumers can be strongly affected when facing supply discontinuities, loss of production, physical damages, and other issues. Under such circumstances, conflicts may arise between suppliers and consumers. Thus, a strategy that identifies whether the STVV phenomenon was produced upstream or downstream of a given point of common coupling between two agents interconnected by a transformer is proposed in this paper. The methodology is based on the transference mechanism of imbalance indicators through this connecting transformer. The current process is not about determining the physical location of the disturbance in the network but only about establishing the responsibility for the disturbance. The effectiveness of the process is determined through computational and experimental studies, for which typical electrical systems are employed. To this end, unbalanced STVVs are imposed on these systems, and the voltage and current imbalance levels on the primary and secondary sides of transformers are correlated to validate the proposal.

This paper aims at investigating electrical and mechanical performance of three-phase salient pole synchronous generator with unbalanced and non-linear loading. The time domain technique is employed to represent the three-phase synchronous generator. By studying the generator operation with non-ideal AC load conditions, the machine electrical and mechanical impacts caused by unbalances and harmonics are evaluated and discussed. Besides theoretical studies, experimental results obtained from a 2 kVA three-phase prototype were derived so as to validate the computational approach and conclusions. Finally, by using a real size generator of 25 MVA, more realistic results are computationally achieved and discussed