In this paper, a static and dynamic photoelectrothermal model including the impact of low-frequency current ripple on light-emitting diodes (LEDs) performance is proposed. The objective of this study is to evaluate the dynamical interaction among thermal, photometrical, and electrical properties of the LEDs when they are supplied by a dc constant current with a superposed low frequency sinusoidal ripple, which is the common case in offline LED drivers. Therefore, this paper presents both a model and experimental data for analyzing the LED photometrical behavior in terms of luminous flux, efficacy, flicker, and chromaticity. Three laboratory prototypes with different heat sinks and LED models have been tested. Experimental results are presented to evaluate the LED photometrical behavior under the aforementioned operating conditions and to validate the proposed modeling methodology.

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.

The knowledge about thermal, electrical, and photometrical characteristics of Light-Emitting Diodes (LEDs) is essential to achieve a good performance to the lighting system. This paper presents a methodology for designing LED systems. The main purpose is to provide an optimal operating point, considering the electrothermal design to achieve the maximum luminous flux for a given LED system. Based on two design routines, the proposed methodology brings the possibility to consider driver output current, heatsink size, and LED junction temperature in the system design. A mathematical analysis taking into account an LED electrothermal model is presented. Computational fluid dynamics simulation employing finite element method and experimental results validate the proposed methodology.

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.

This paper presents a new theoretical equivalent model (TEM) for organic light-emitting diodes (OLEDs). The parameters of TEM are identified using a simple characterization procedure based on auxiliary circuits and low-cost equipment. From this TEM, a method for intrinsic capacitance identification is proposed. This model is useful to simulate and analyze OLED devices considering dynamic and steady-state operation conditions. In addition, it provides guidelines for manufacturers and lighting designers to enhance the device performance and to design dedicated OLED drivers. In order to validate the proposal of this paper, four commercial OLEDs are tested, and the comparison between the theoretical and the experimental results is satisfactory.

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.