Sharif Digital Repository

Calculating leakage inductances between windings of multi-winding traction transformers is one of the most important schemes in design procedure. In this paper, a new analytical method and finite element models have been introduced for electromagnetic modeling of traction transformers with four split windings. Using these methods, the leakage inductances between the split windings are calculated and the methods have been validated with the help of experimental data gathered from a typical 4000kVA cast-resin dry-type transformer. Some reformations are employed to improve the finite element results and effects of these reformations on accuracy of the models are studied. Employing the validated... 

Calculating leakage inductances between windings of multi-winding Traction transformers is one of the most important schemes in design procedure. In this paper, analytical and finite element methods (FEM) have been introduced for electromagnetic modeling of traction transformers with four pancake split windings. Using these models, the leakage inductances between the split windings are calculated and the models have been validated with the help of experimental data gathered from a typical 4000kVA cast-resin dry-type transformer. Some reformations are employed to improve the FEM results and effects of these reformations on accuracy of the model are studied. Employing the validated models, the... 

In this paper, some models have been introduced for dynamic thermal modeling of cast-resin transformers which are based on genetic algorithm. A typical 400kVA cast-resin transformer has been selected and the model parameters are estimated and validated with the help of experimental data extracted from different load cycles. The estimated models are used to generate a reliability model for cast-resin dry-type transformers and the effects of variation in load, ambient temperature and atmosphere conditions on the reliability of castresin transformer are illustrated. As it will be shown in this paper, the effects of working conditions on the life-time of insulation in dry-type transformers is... 

In this study, in order to compare effect of unidirectional compression and rolling on final microstructure of strain induced melt activated (SIMA) A356 aluminum alloy, rectangular samples with dimensions of 3cm×5cm in area and 1cm in thickness and cylindrical specimens with 2.5cm in diameter and 1cm in length, have been prepared for rolling and compressing processes, respectively. Then, these samples were plastically deformed at a same strain in ambient temperature. Afterward, the strained samples were cut into equal quarters. In the next stage, to produce globular microstructure, these specimens were partially remelted in 580°C for different times. Results obtained from light microscopy... 

A series of novel pseudopeptides contained coumarin skeleton were synthesized through the Ugi-four-component reaction. The 3-substituted coumarin-3-carboxamides were formed through reaction of benzaldehyde derivatives, anilines, coumarin-3- carboxylic acid and isocyanides with high yields and high bond-forming efficiency at room temperature. These novel amidated coumarins exhibit brilliant fluorescence in range of 535-547 nm in chloroform  

In this work, effective parameters of SIMA process to obtain non dendritic microstructure in A356 alloy were investigated. In addition, the effect of SIMA process on the evolution of morphology of silicon and intermetallic phases in this alloy was studied. Microstructure images obtained from optical microscopy and SEM observation showed that increase in plastic work up to 40% and then holding of samples in the semi solid state at temperature of 580°C, causes that primary dendritic structure changes to non dendritic, fine and globular structure, but optimum reheating time completely depended on initial thickness of samples. If all parameters of SIMA process are the same, the grain boundaries... 

The novel coumarin-3-carboxamides (=2-oxo-2H-1-benzopyran-3-carboxamides) 5a-5g containing lipophilic spacers were synthesized through the Ugi-four-component reaction (Scheme 1). The reactions of aromatic aldehydes 1, 4,4'-oxybis[benzenamine] or 4,4'-methylenebis[benzenamine] as diamine 2, coumarin-3-carboxylic acid (=2-oxo-2H-benzopyran-3-carboxylic acid; 3), and alkyl isocyanides 4 lead to the desired substituted coumarin-3-carboxamides 5a-5g at room temperature with high bond-forming efficiency. These novel coumarin derivatives exhibit brilliant fluorescence at 544 nm in CHCl 3  

Frequent air pollution episodes have been reported for Tehran, Iran, mainly because of critically high levels of fine particulate matter (PM2.5). The composition and sources of these particles are poorly known, so this study aims to identify the major components and heavy metals in PM2.5along with their seasonal trends and associated sources. 24-hour PM2.5samples were collected at a main residential station every 6 days for a full year from February 2014 to February 2015. The samples were analyzed for ions, organic carbon (including water-soluble and insoluble portions), elemental carbon (EC), and all detectable elements. The dominant mass components, which were determined by means of...