This paper presents a modified methodology for calculating static capacitance values between conductors with a circular cross-section. Two forms of coil's stacking were considered, perfectly in 90° and each layer embedded in the previous one. Finite element simulations were carried out to determine the capacitance values for a 5x5 array arrangement, taking into account the two stacking forms. It was observed that depending on the position of the turn in the coil, it could present different capacitances values for the adjacent turns. A comparison between the proposed and existing methods for over isolated conductors was performed as well. The proposed method displayed good agreement with simulation and experimental results. The gain of the proposed method can be even more appreciated when comparing results for over insulated conductors.

The internal temperatures and the ability to dissipate the heat from active part influence the windings’ insulation deterioration and determine how long power transformers are able to remain in operation. Due to the great importance of this equipment for the electrical system, studies to avoid failures and early aging are needed. This article presents an evaluation of thermal performance of power transformers and the optical fiber sensor positioning to temperature monitoring. For this, an experimental and numerical methodology is performed, comparing the measurements during the temperature rise test of single-phase prototype power transformer, under oil directed and air natural (ODAN) cooling system conditions equipped with 20 optical fiber sensors along its windings, to the obtained results of computational fluid dynamics (CFD) simulations performed in ANSYS Fluent software. It was verified that the punctual temperature measured by optical sensors may not accurately represent the critical temperatures along transformers’ windings, and the windings’ arrangements impact on oil flow and temperature distribution, as the number and positioning of block washers being necessary to be considered in previous studies for a better positioning of the sensors and temperature monitoring.

Electrical power systems are exposed to transient disturbances that change the voltage and current signals of the network, which can interrupt power and damage equipment. In high-frequency phenomena, it is essential to study the transient recovery voltage (TRV) to ensure the electrical insulation limits of circuit breakers are not violated, thus leading to a safe and reliable operation. Adequate models are crucial to achieving satisfactory results in the studies, according to the range of frequency of the transient being evaluated. This paper presents a comprehensive literature review of methods and models for studying electromagnetic transients, focusing on TRV requests imposed on circuit breakers, in addition to fault-clearing simulations on real system modeling. The analyses are fundamental both for the evaluation of the amplitude of the voltage signal and for its rate of rise. We also compare the reviewed models and techniques to provide a handy resource for researchers.

Electromagnetic forces can lead to the structural failure of power transformers due to extreme loading conditions, vibration, and/or fatigue. Therefore, studying the nature and the magnitude of these forces is a key task in the design and failure analysis of such important equipment. Keeping this issue in mind, this work aims at conducting a numerical analysis in order to evaluate the mechanical stresses and displacements of windings in power transformers due to the action of electromagnetic forces. With this purpose, a finite element model is developed considering electromagnetic and mechanical effects assuming short-circuit conditions. The study compares the cases employing copper and aluminum windings with header tap, in different temperatures. The model developed in this work is verified against analytical solutions. The numerical calculations allow for performing a detailed analysis in terms of the distribution of both displacements and stresses along the windings, which is of great relevance for identifying critical structural points and avoiding structural failure. Overall, the obtained results demonstrate that the finite element model is a useful tool for the structural design of power transformers that allow for investigating and optimizing key aspects before manufacturing.

Understand thermal, electrical and optics characteristics of Light Emitting Diodes (LEDs) is essential to achieve a good performance to the lighting system. This paper presents an optimized methodology for designing LED lighting systems. The objective is to provide the designers an optimal operation point taking into account thermal, electric and optical LED system characteristics. The proposed methodology brings the possibility to consider driver output current, heatsink size and LED junction temperature in the system design. A mathematical analysis is presented and experimental results validate the proposed methodology.