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In this work, two heuristic techniques used to reduce the number of simulations of lightning-induced voltages, which are required to assess the lightning performance of distribution lines according to the Monte Carlo methodology, are presented. The first uses the Rusck Formula to discard the events that do not cause damage to the line. The second is based on a multi-nonlinear regression of the previously simulated events. Both techniques were applied to estimate the flashover rate of straight and complex lines above flat ground with finite conductivities. As a result, between 80 \% to 90 \% of the total number of simulations were eliminated with a reduced error.

Abstract Small-scale hydroelectric plants, primarily run-of-the-river designs, are regularly subjected to hard particle wear and cavitation erosion due to the wide range of operating points. Depending on the severity of the operating conditions and erosion damage experienced by the machine throughout its service life, the operating companies of these facilities will be impacted. The impact will be technical, operational, logistical, and economic. A small-scale generation plant located in Amaime River in Colombia, is one such case, where severe wear occurs in the turbine components, with a consequent reduction of efficiency. In this study, the analysis of the erosion damage has been expanded and supplemented by computational fluid dynamics (CFD). From this approach, correlations between the wear rate and power output were obtained. Likewise and in conjunction with the computer estimates, a methodology to analyse the costs associated with wear based on historical data of operation was developed, creating a strategy of operation based on a stopping criterion that depends primarily on sediment concentration, turbinated flow, and wear level. The methodology optimizes the use of generators, which takes into consideration the revenue generation and the costs associated with operation and maintenance of pieces under conditions of intrinsic erosion wear in the facility.

Abstract In this paper, we explore the use of a frequency domain (FD) modeling and simulation approach to perform statistical studies of switching overvoltages (SSSOV) due to open-ended line energization, as an alternative to the use of time-domain (TD) EMTP-type tools. We analyze the potential advantages of such an approach in terms of accuracy and computational efficiency. We also utilize the FD approach to evaluate the effect of the type of network equivalent used when performing SSSOVs on open-ended lines as part of a network. Our results indicate that applying an FD method for SSSOVs requires substantially lower computer time than an EMTP-type tool to achieve accurate and meaningful statistical results. In addition, the use of constant-lumped-parameter Thevenin equivalents to approximate the rest of the network can result in a considerable deviation from the actual statistical switching behavior of a transmission system. Therefore, equivalents that preserve the rest of the grid's detailed frequency-dependent characteristics are critical for accurate statistical switching overvoltage studies.

Abstract This work introduces a generalized methodology for mathematical modelling and controller design of a single-phase cascaded H-bridge multilevel-converter comprising the connection of N H-bridges, which results in 2 N + 1 voltage levels. Towards this end, the average model of the converter is first transformed into a decoupled mathematical structure based on a new definition of state variables. Out of this, the control objectives, current tracking and voltage regulation, are decoupled from the voltage balance problem for such a general case of N H-bridges. To show the benefits of the proposed methodology, a shunt active power filter application has been considered in this paper, where the control objectives are the compensation of the power factor and harmonic distortion due to nonlinear loads, plus regulation and balance of all DC-bus voltages. In particular, this work focus on the balance issue, which leads to the design of N - 1 balance loops. A tuning strategy is also introduced to design the gains of the proposed control scheme, which are based on time scale separation and a desired closed-loop transient performance. The proposed generalized methodology is evaluated in a 7-level cascaded H-bridge converter both through simulations and experimentally.

We detect hints of determinism in an apparently stochastic corrosion problem. This experimental system has industrial relevance as it mimics the corrosion processes of pipelines transporting water, hydrocarbons, or other fuels to remote destinations. We subject this autonomous system to external periodic perturbations. Keeping the amplitude of the superimposed perturbations constant and varying the frequency, the system's response is analyzed. It reveals the presence of an optimal forcing frequency for which maximal response is achieved. These results are consistent with those for a deterministic system and indicate a classical resonance between the forcing signal and the autonomous dynamics. Numerical studies using a generic corrosion model are carried out to complement the experimental findings.

Abstract Solar refrigeration projects both national and international with sorption and other refrigeration systems have been developed in Mexico and other Latin American countries in the last 15 years. A review of the main projects, both for solar cooling and refrigeration and the results obtained are presented in this paper. A methodology where 19 solar technologies for cooling were identified is also presented. Although solar cooling is still not an economically viable technology, the advances made and the experience gained in the projects described and the improved systems envisaged, will make solar refrigeration systems play an important role in the future.

Abstract The effect of the injection of externally sourced carbon dioxide (CO2) on the stability of the flameless combustion regime was evaluated numerically and experimentally, taking temperature uniformity and pollution emissions (NO and CO) as criteria. The flameless combustion regime was studied in a lab-scale furnace fueled with natural gas (NG) at a thermal power of 20 kW based on the low heating value (LHV). The CO2 was injected into the lower part of the furnace to directly affect the reaction zone. Computational fluid dynamics (CFD) simulations were performed using the ansys-fluent software. The models used to describe the turbulence, the radiation heat transfer, and the turbulence–chemistry interaction were the standard k–ɛ model, discrete ordinate model (DOM), and eddy dissipation concept (EDC) model, respectively. The NG oxidation was described with a seven-step global reaction mechanism with the EDC model. Three excess air conditions were analyzed, 20%, 25%, and 30%, combined with various CO2 injection flows. At 30% excess air, the flame exhibited destabilization without any CO2 injection. Adding CO2 attenuates the destabilization because of the dilution effect. Increasing either the CO2 or excess air flow resulted in a considerable decrease in the global temperature of the process, consequently producing an increase in CO emissions and a decrease in NO emissions. Finally, for the conditions studied, increasing the mass flow of externally sourced CO2 did not destabilize the flameless combustion regimen. This result shows the potential of the implementation of flameless combustion in industrial processes where CO2 is releasing as a result of a reaction external to the combustion process, such as cement, ammonia, or lime production among others.

This paper presents a methodology for optimal multistage planning of Distributed Generation to improve the performance of the distribution system. The methodology considers the optimal placement and sizing of the distributed generation to minimize network losses using Particle Swarm Optimization algorithm for different scenarios and stages. If is necessary, in each stage an optimal placement and sizing were determinate, the solution proposed must not violate the limits of loading and voltage in the distribution system. The proposed methodology was implemented in a collaborative work between Python® and DIgSILENT PowerFactory®. The methodology was validated on a modified IEEE 13 test feeder in four scenarios, consider regional demand growth in the Colombian Caribbean Region. The results showed the effectiveness of the methodology with losses reduction approximately of 84.65% in scenario 2 and 29.78% in scenario 4. Moreover, the methodology improved the voltage profile with demand growth of 3.68% per stage.