Current Voltage Conditions Research Articles

Shaping the Structure and Properties of TiO2-ZnO Oxide Coatings Produced by Plasma Electrolytic Oxidation on Titanium Substrate.

The paper presents the results of preliminary research on the possibility of synthesizing ZnO-TiO2 mixed coatings by plasma electrochemical oxidation (PEO). The aim of the work was to synthesize TiO2-ZnO mixed coatings on a titanium substrate from an electrolyte containing ZnO nanoparticles (NPs) and to assess the parameters of PEO on the structure, chemical composition, and properties of the obtained oxide coatings. The PEO process was carried out under various current-voltage conditions using different signals: DC, DC pulse, and AC. In this work, optimal conditions for the PEO process were determined to obtain well-adhering oxide coatings with the highest possible content of ZnO. The structure and morphology of the resulting oxide coatings were investigated, and their chemical and phase composition was comprehensively examined (EDX, XRD, XPS, and GD-OES). In addition, their basic optical properties were assessed. It has been shown that in the PEO DC pulse process, it is possible to obtain oxide coatings characterized by a high degree of structure order, high ZnO content in the oxide coating (3.6 at.%, XPS), and prospective applications for photocatalytic purposes (3.12 eV).

Effects of autotransformer's stabilizing winding on current-voltage conditions during unsymmetrical faults

In this paper, model of three-phase autotransformer with stabilizing winding is developed in EMTP for short-circuit studies. Currents and voltages are determined inside transformer windings during unsymmetrical faults in the power system. Influence of delta connected stabilizing winding on current-voltage conditions is analysed. Results obtained by EMTP model are compared with the inductance matrix model of autotransformer developed in Matlab, consisting of winding self-inductances and corresponding mutual inductances between windings.

An Evaluation Method for Commutation Failure Caused by Waveform Distortion

Commutation failure is a key issue that affects the safe operation of HVDC transmission systems. Scholars at home and abroad have conducted research on the mechanism, evaluation indicators, and control strategies of commutation failure. However, most of the researches are aimed at the working conditions of commutation failure caused by a short-circuit fault on the AC side. There are few studies on the commutation failure caused by the harmonic injection on the AC side and the distortion of the AC bus voltage waveform. This paper clarifies the mechanism of commutation failure caused by waveform distortion, and proposes an index of harmonic commutation margin. On this basis, an evaluation method for commutation failure caused by waveform distortion is proposed. By predicting the commutation voltage-time area and optimization methods to assess whether the current voltage conditions have the risk of commutation failure. Finally, an electromagnetic transient simulation model is established on PSCAD/EMTDC, and the evaluation method in this chapter is verified by simulating the working conditions of the inverter side bus voltage waveform distortion. The results show its effectiveness in evaluating the commutation failure. The research provides a theoretical basis to the implementation of the control function and has broad engineering application prospects.

Electrochemical Synthesis of Cu-Cu2o-CNT/CNF Composite Coatings

The main scientific objective of performed studies was development of methodology for electrochemical synthesis of ternary composite materials in the Cu-Cu2O-CNT/CNF systems (CNT – carbon nanotubes, CNF – carbon nanofibers). Copper is the only metal that exhibits very high selectivity for electrochemical conversion of CO2 to ethylene (1). Ren et al. observed similar effect in case of p-type Cu2O (2). Reported effects allows on assumption that combination of both materials can be great solution in the frame of light supported electrochemical conversion of carbon dioxide to ethylene. Additionally application of carbon structures: CNT or CNF as charge transfer mediators can limit photodegradation of Cu2O, improving simultaneously its chemical stability (3) and catalytic activity as well as selectivity for electrochemical conversion of CO2 to ethylene (2). Presence of highly hydrophobic CNT/CNF phase in Cu matrix may significantly improve selectivity through limiting adsorption of polar water molecules favoring simultaneously adsorption of nonpolar CO2 molecules. Present studies describing optimization of electrochemical synthesis process towards synthesis of composite coatings of wide composition range. Synthesis conditions were investigated starting from thermodynamic analysis of the electrolyte. In next step, based on zeta potentials values stability of colloidal electrolyte containing carbon nanotubes was analyzed. Current-voltage conditions allowing on deposition of Cu with Cu2O with simultaneous incorporation of CNT/CNF structures were determined based on voltammetric and elctrogravimetric tests. Synthesized coatings were characterized towards their composition, structure and morphology. References Y. Kwon, Y. Lum, E. L. Clark, J. W. Ager and A. T. Bell, ChemElectroChem, 3, 1012 (2016).D. Ren, Y. Deng, A. D. Handoko, C. S. Chen, S. Malkhandi and B. S. Yeo, ACS Catalysis, 5, 2814 (2015).P. D. Tran, S. K. Batabyal, S. S. Pramana, J. Barber, L. H. Wong and S. C. J. Loo, Nanoscale, 4, 3875 (2012).