In this paper, a high sensitivity electrometer is adopted to measure DC conduction currents across the oil gap. The effect of morphology of electrode surface (3 dimensional roughness is approximately 0.03 mm) on conduction current is considered adequately, which is very lacking in the previous references. Based on the Fower-Nordheim theory, three stages will be clearly distinguished with the increase of the electric field strength. At low electric field stage (E<0.44 kV/mm), the current through the oil I is directly proportional to the electric field E, which meets the Ohm's law. Oil conductivity mainly depends on impurity ions with only low mobility. At medium electric field stage (0.44 kV/mm1.33 kV/mm), the obtained I-V 2 characteristics is linear, which can be explained by the space charge limited current. Moreover, main factors affecting the conduction current, including oil gap, electrode geometry and materials, polarity effect, temperature, hydrostatic pressure and moisture, have been analyzed and the causes are interpreted as well.Index Terms -Dielectric conduction mechanism, electrode geometry, morphology of electrode surface, hydrostatic pressure, moisture, polarity effect, temperature, transformer oil.

This work demonstrates a quasi‐distributed sensing method to obtain the accurate location and temperature value of hot‐spot by placing Fiber Bragg Grating sensors in the conductor wires of transformer's windings. The quasi‐distributed temperature measuring system can support the demodulation of up to 218 FBGs, and has the ability to obtain the temperature decay rates of windings, strips, iron cores, and top oil in a 35 kV/4000 kVA oil immersed power transformer through a temperature‐rise test. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:472–475, 2017

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The spinel Li4Ti5O12 (LTO) has been doped by Ca2+ via a solid-state reaction route, generating highly crystalline Li3.9Ca0.1Ti5O12 powders in order to improve the electrochemical performance as an anode. The structure changes, morphologies, and electrochemical properties of the resultant powders have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and cyclic voltammetry (CV), respectively. Crystal structure and composition were analyzed, and results were obtained with various tests of LTO. Electrochemical measurements revealed that Li3.9Ca0.1Ti5O12 anodes exhibit better rate capability, better cycling stability, and a higher specific capacity than pure LTO anodes.

This paper mainly discusses the mechanism for FRA method on bushing insulation detection. It builds several RC models of the bushing instruction in MA TLAB, as well as does some simulation work to observe the change of the FRA curve with different parameters. It also takes the influence of the valve wire into consider and get some useful conclusions. Simulation results show that the obvious indentation in the FRA curve will appear when the bushing has some insulation defects. The sum and change state of the indentation in FRA curve is related to the degree and relaxation polarization of the insulation defects of the bushing. It is found that the simulation and on-spot detection curves have tallies with each other, which verifies the feasibility of FRA method in this field.