Influence Of Dc Current Research Articles

Changes in electrochemical properties of a heavy tungsten alloy during its processing under the influence of DC current in ammonia-alkali solutions

The method of linear voltammetry in the potentiodynamic mode was used to study the change in the anode behavior of a heavy tungsten VNZh alloy (in wt.%: 78.8 W; 15.2 Ni; 6.0 Fe), as well as the phase composition and morphology of its surface during its electrochemical dissolution under the influence of DC current. It was determined, that the phase composition of VNZh alloy surface is a solid solution of iron-nickel after tungsten dissolution from the surface of the alloy. It has been established, that in ammonia-alkali electrolytes the process of tungsten passing into solution does not stop after dissolution of the metal from the alloy surface, but continues both due to diffusion of the metal from the depth of the sample and the pits formation in the processed alloy.

Load Injected DC Current in Distribution Transformers: Investigation and Elimination

Due to heavy proliferation of power electronic and non-linear loads on a present day utility system, the DC current accumulated at the distribution transformer is significant. DC current shifts the operating point of the magnetization characteristic and hence causes the magnetizing current to exhibit severe asymmetry between positive and negative half cycles in magnitude and shape, owing to magnetic saturation. It affects the shape of input current and recreates a DC current at the input with magnitude even greater. This paper describes the work on influence of DC current on input current in a loaded transformer, and a system to divert DC current completely away from the transformer. Implementation was done with a specially designed current sensor and a fast responsive controlled current source. The later was implemented in power electronic with closed loop control. The work was challenging because measuring of small DC current superimposed with a large AC current was not straightforward, and also injecting a small DC current accurately against a large AC voltage was not straightforward. Both these challenges were successfully overcome and an extremely good DC current diversion system was developed. Details of the design and results of investigations are presented.

DC current effect on the magnetic phase and transport properties of polycrystalline La0.7Ca0.3MnO3

The influence of DC current on the resistivity and phase transition of polycrystalline La0.7Ca0.3MnO3 has been investigated. The specific heat measurement found that charge carriers and ferromagnetic spin-wave contributions were changed after applied DC current. Applying high electric fields leads to the formation of ferromagnetic regions. The resistivity drops abruptly once the percolating current path is established. As current through the sample disappears, the larger ferromagnetic (FM) clusters, however, remain and are frozen in giving a measurable contribution to the specific heat of the system. The larger clusters should give rise to the value of spin-wave stiffness constant (D), as it is expected to increase the strength of the ferromagnetic coupling. The metallic ferromagnetic regions would make the charge carrier delocalization and attribute to specific heat linear term γ.

Impact of electric currents on the insulator–metal phase transition in epitaxial thin films of La 1− xA xMnO 3 (A = Sr, Ca, and Ba)

The influence of dc currents with a high current density on the transport properties of epitaxial La 1− x A x MnO 3 (A = Sr, Ca, and Ba) thin films were studied. An application of a large current could lead to a remarkable reduction in the insulator–metal phase transition peak, demonstrating a significant electroresistance effect. After removing such currents the samples could completely return to its pristine state. Our experiments reveal that such an electroresistance should be a common feature for the perovskite manganites, rather than the results caused by the self-heating or self magnetic field. It may be ascribed to the two aspects: one is the strong interaction between carrier spins and localized spins in Mn ions, the other is the percolative mechanism of phase separation.