Identification of the Critical Characteristics of Different Types of Voltage Sags for Synchronous Machine Torque Oscillations

Abstract—This article investigates the effects of symmetrical and unsymmetrical voltage sags on an important characteristic of torque pulsation of synchronous machines. Voltage sags may cause high torque pulsations, which can damage the shaft or equipment connected to it. Duration, magnitude,and initial point-on-wave of the voltage sag are the major characteristics that can influence the synchronous motors torque transients. The effect of the characteristics on the severity of the transient torque is clarified parametrically, and the critical characteristics of each type of voltage sag are extracted. A theoretical analysis is first presented to determine the severest conditions. In this analysis, for each type of voltage sag, the stator flux trajectory in complex coordination is traced to monitor its variation during and after sag. By this method, the effects of different sag types can easily be compared during the sag and at the sag ending instant. To justify the theoretical analysis, simulations of a typical synchronous motor are carried out that confirm the theoretical analysis.     

Extraction of Fe(III), Zn(II), and Mn(II) Using a System with a Green Solvent for Trioctylmethylammonium Thiocyanate

Theoretical Foundations of Chemical Engineering - An environmentally friendly solvent, namely, polypropylene glycol 425, has been proposed for the extraction of metal ions from chloride solutions...     

Low-temperature bonding mortars

Several bonding mortars composed predominantly of Na₂O?B₂O₃?SiO₂ and Na₂O?Al₂O₃?SiO₂ were investigated. They serve to join refractories used in structures that operate cyclically at 900–1000°C, as in tunnel-kiln cars for the bisque firing of porcelain ware.     

Characterization of the Organic Matter of Humic Acids by Pyrolytic Gas Chromatography–Mass Spectrometry

The results of the pyrolytic analysis of products of the organic matter of Sphagnum fuscum, fuscum peat, and humic acids separated from peat with the use of pyrolysis–chromatography–mass spectrometry in the Rock-Eval version are presented. It was shown that Sphagnum fuscum and peat differed only slightly in the degrees of chemical transformation. Benzene, phenol, and their alkyl-substituted homologues predominated in the thermal desorption products of humic acids upon pyrolysis to 400°C. Acetic acid, monohydric phenols, syringol, and guaiacol, which are the basic compounds in the high-temperature fraction, were formed on the pyrolysis humic acids to 700°C from the carbohydrate, phenylpropionic, and guaiacylpropane structural fragments.     

Extraction of Pt(IV) and Pd(II) from Hydrochloric Acid Solutions Using Polypropylene Glycol 425

Theoretical Foundations of Chemical Engineering - An environmentally friendly extraction system based on polypropylene glycol 425 and sodium chloride for the extraction of Pt(IV) and Pd(II) from...     

Multifunctional coating MAI D5 intended for the protection of refractory materials

A thin-layer heterophase MAI D5 coating intended for the protection of carbon-containing composite materials (C-C-, C-SiC-, SiC-SiC-composite material) and refractory metal-based alloys against high-temperature gas corrosion and erosion is tested. The coating is formed from a specially developed Si-Ti-Mo-B-Y microcomposition powder material. A new approach to creating self-healing heterophase coatings is used. At operating temperatures, the structure and phase composition of the MAI D5 coating provides rapid self-healing of random defects on the coating surface and in the base material owing to the presence of a silicon-containing eutectic, which favors rapid recovery of a protective amorphous silica layer consumed during operation. Under operating conditions, the coating undergoes self-organization to form a multilayer system with a number of functional oxide micro-, submicro-, and nanolayers. Samples with the MAI D5 coating are subjected to combined tests on bench plants located at MAI and TsAGI under conditions emulating the re-entry of a hypersonic aircraft, when its surface temperature reaches 2400 K. Certification tests are performed in wind tunnels located at TsAGI during a simultaneous action of a hypersonic dissociated-air flow and mechanical loads. The protection of heat-loaded structural elements in space vehicles made of ultrahigh-temperature materials against high-temperature gas corrosion and erosion by the MAI D5 coating in hypersonic dissociated-air flows is shown to be efficient.     

Experimental study and thermodynamic analysis of phase equilibria in the silicon-rich part of the Si-Sr and Si-Ba systems

Using thermal and activation analysis techniques, we have constructed the liquidus curves in the primary crystallization fields of silicon in the Si-Sr and Si-Ba systems. The Sr and Ba solid solubilities in silicon have been determined using microhardness measurements, and have been shown to exhibit retrograde behavior. At 1573 K, the solubility of Sr in silicon is 1.15 at %, and that of Ba is 0.98 at %. The solidus and liquidus curves have been analyzed using thermodynamic modeling and the known thermodynamic properties of the melt and intermediate phases. We assume that the large deviations of the melts from ideal behavior are due to the formation of Zintl polyanions (or clathrates), and describe a model for the chemical structure of the silicon-rich melts.