The conventional methods of parameter estimation in transformers, such as the open-circuit and short-circuit tests, are not always available, especially when the transformer is already in operation and its disconnection is impossible. Therefore, alternative (non-interruptive) methods of parameter estimation have become of great importance. In this work, no-interruption, transformer equivalent circuit parameter estimation is presented using the following metaheuristic optimization methods: the genetic algorithm (GA), particle swarm optimization (PSO) and the gravitational search algorithm (GSA). These algorithms provide a maximum average error of 12%, which is twice as better as results found in the literature for estimation of the equivalent circuit parameters in transformers at a frequency of 50 Hz. This demonstrates that the proposed GA, PSO and GSA metaheuristic optimization methods can be applied to estimate the equivalent circuit parameters of single-phase distribution and power transformers with a reasonable degree of accuracy.

In this article, the percentage of short-circuit impedance is calculated using the finite element method for a single-phase power autotransformer with tertiary winding. The autotransformer specifications are: 25 MVA, 230 kV, 60 Hz, three-legged core type. A detailed 3D model where mixed formulations in terms of scalar and vector potential and circuit coupling is used. This type of study is essential to design the autotransformer and guarantee the impedance value, and so the safety and operability of electrical power systems. To calculate the percentage of short-circuit impedance the voltage relationship between the short-circuit voltage and the nominal voltage is used. In addition, the magnetic energy storage technique is presented as another alternative to calculate this parameter. The results are validated with the data from the laboratory tests obtaining differences of less than 5%.

Designing and manufacturing transformers often involves variations in heights and thicknesses of windings. However, such geometric asymmetry introduces a significant impact on the magnitude of stray transformer losses. This study examines the effects of asymmetric coils on the generation of stray losses within core clamps and transformer tank walls. A model has been introduced to ascertain the dispersion magnetic field’s value at a specific distance from the coil. The analysis extends to characterising the dispersion magnetic field reaching the tank walls by using electromagnetic simulation by a finite element method. It explores strategies to diminish stray losses, including the placement of magnetic shunts as protective shields for the tank walls. It delves into the efficacy of employing a transformer shell-type configuration to mitigate the magnetic dispersion field. The findings revealed that achieving greater symmetry in transformer coils can minimise stray losses. Specifically, the incorporation of magnetic shunts has the potential to reduce additional losses by 40%, while the adoption of a shell-type configuration alone can lead to a 14% reduction. This work provides valuable insights into optimising transformer designs, contributes a user-friendly tool for estimating additional tank losses, thereby enhancing the knowledge base for transformer manufacturers.

Accurate prediction of the zero-sequence impedance ($Z_0$) of three-legged zigzag grounding transformers is essential for ground-fault protection and power-quality performance, yet manufacturer analytical estimations often have limited accuracy. This paper investigates how accurately $Z_0$ can be predicted using 3D finite element method (FEM) models based on the stored magnetic energy approach and how modeling the metallic tank and nonlinear core B–H behavior affects $Z_0$ relative to analytical calculations and laboratory measurements. Two 3D FEM models are developed for a three-legged zigzag grounding transformer, incorporating the nonlinear core characteristic; impedance boundary conditions are used to efficiently account for tank-induced currents while reducing computational cost. The FEM results are compared with laboratory tests and with the analytical method used by manufacturers. The proposed models achieve errors below 4% with respect to the nominal $Z_0$ and outperform the analytical approach. The contributions are a validated 3D FEM methodology that resolves zero-sequence flux paths under fault conditions and a practical modeling tool that improves grounding transformer design and ground-fault protection settings in modern power systems.

Las boquillas de un transformador de potencia generalmente representan el elemento con mayor riesgo de fallas en el dispositivo, esto se debe a los grandes esfuerzos dieléctricos a los que se somete. Estos aislantes se diseñan para reducir al máximo el campo eléctrico al que están expuestos, tanto en la superficie como en su interior. La contribución de este trabajo, resulta en el cálculo del campo eléctrico en una boquilla de tipo sólida, marca H-J, con el objetivo de identificar las zonas donde va a existir mayores concentraciones de estrés eléctrico, esto servirá de base para posteriores estudios de varios fenómenos que pueden causar el deterioro gradual del aislamiento, el más importante, las descargas parciales. Se realiza un resumen de la evolución de las boquillas, así como su clasificación según su tipo; se describe el desarrollo matemático para calcular las concentraciones de campo eléctrico y diferentes particularidades del software utilizado, COMSOL Multiphysics®. Se detallan las propiedades físicas y las especificaciones geométricas de la boquilla en estudio, se realiza una comparación entre los modelados en axisimétrico-2D y 3D, para observar diferentes comportamientos en la intensidad del campo eléctrico. La boquilla va a operar en un transformador de 115/34.5 kV, que entrega una potencia aparente máxima de 30 MVA, en el lado de baja tensión.