Browsing by Autor "Maria F. Perez"

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Heuristic remedial actions in the reliability assessment of high voltage direct current networks
(Institute of Advanced Engineering and Science (IAES), 2021) Mario A. Ríos; Maria F. Perez
<p>Planning of high voltage direct current (HVDC) grids requires inclusion of reliability assessment of alternatives under study. This paper proposes a methodology to evaluate the adequacy of voltage source converter/VSC-HVDC networks. The methodology analyses the performance of the system using N-1 and N-2 contingencies in order to detect weaknesses in the DC network and evaluates two types of remedial actions to keep the entire system under the acceptable operating limits. The remedial actions are applied when a violation of these limits on the DC system occurs; those include topology changes in the network and adjustments of power settings of VSC converter stations. The CIGRE B4 DC grid test system is used for evaluating the reliability/adequacy performance by means of the proposed methodology in this paper. The proposed remedial actions are effective for all contingencies; then, numerical results are as expected. This work is useful for planning and operation of grids based on VSC-HVDC technology.</p>
Heuristic remedial actions in the reliability assessment of HVDC networks
(2021) Mario A. Ríos; Maria F. Perez
Planning of high voltage direct current (HVDC) grids requires inclusion of reliability assessment of alternatives under study. This paper proposes a methodology to evaluate the adequacy of VSC-HVDC networks. The methodology analyses the performance of the system using N-1 and N-2 contingencies in order to detect weaknesses in the DC network and evaluates two types of remedial actions to keep the entire system under the acceptable operating limits. The remedial actions are applied when a violation of these limits on the DC system occurs; those include topology changes in the network and adjustments of power settings of VSC converter stations. The CIGRE B4 DC grid test system is used for evaluating the reliability/adequacy performance by means of the proposed methodology in this paper. The proposed remedial actions are effective for all contingencies; then, numerical results are as expected. This work is useful for planning and operation of grids based on VSC-HVDC technology.
Influencia del ácido ascórbico en la adhesión sobre el esmalte blanqueado: estudio in vitro.
(2021) Maria F. Perez; J D Víctor Setién
The use of teeth whitening is associated with a decrease in restoration-tooth adhesive strength for up to three weeks afterits use. In order to find a solution to this problem, this study was carried out to evaluate the effectiveness of 10% ascorbic acid and to rapidly increase the adhesive strength. Sixty recently extracted caries-free bovine teeth were selected, resin discs 3 mm wide and 4 mm in diameter were made, they were divided into 4 groups, Group 1 (control), the conventional adhesive technique was applied, Group 2, 10% carbamide peroxide was applied for 12 days and the conventional adhesive technique was applied, Group 3, carbamide peroxide was applied for 12 days and the conventional adhesive technique was applied, Group 4, carbamide peroxide was applied for 12 days and the conventional adhesive technique was applied, Group 3, 10% carbamide peroxide was applied for 12 days, then ascorbic acid gel was applied for 10 minutes and the conventional adhesive technique was performed, Group 4, 10% carbamide peroxide was applied for 12 days and for 8 hours, ascorbic acid gel was applied and then the conventional adhesive technique was performed, all were subjected to a shear test in a universal testing machine. A one-factor ANOVA was performed with the p value preestablished at 0.05. Groups 1 and 4 obtained similar adhesive strength, while group 2 was the least resistant to the maximum load, obtaining a value of p <0.03 between groups. It is concluded that the use of 10% ascorbic acid for 8 hours after 10% carbamide peroxide reverses the low values of adhesive resistance caused by the free radicals remaining in the freshly bleached enamel.