Charge Carriers Relaxation Behavior of Cellulose Polymer Insulation Used in Oil Immersed Bushing

Cellulose insulation polymer material is widely used in oil immersed bushing. Moisture is one of the important reasons for the deterioration of cellulose polymer insulation, which seriously threatens the safe and stable operation of bushing. It is significant to study the polarization and depolarization behavior of oil-immersed cellulose polymer insulation with different moisture condition under higher voltage. Based on polarization/depolarization current method and charge difference method, the polarization/depolarization current, interfacial polarization current and electrical conductivity of cellulose polymer under different DC voltages and humidity were obtained. Based on molecular-dynamics simulation, the effect of moisture on cellulose polymer insulation was analyzed. The results show that the polarization and depolarization currents become larger with the increase in DC voltage and moisture. The higher applied voltage will accelerate the charge carrier motion. The ionization of water molecules will produce more charge carriers. Thus, high DC voltage and moisture content will increase the interface polarization current. Increased moisture content results in more charge carriers ionized by water molecules. In addition, the invasion of moisture will reduce the band width of cellulose polymer and enhance its electrostatic potential, so as to improve its overall electrical conductivity. This paper provides a reference for analyzing the polarization characteristics of charge carriers in cellulose polymer insulation.

Frequency dependence on polarization switching measurement in ferroelectric capacitors

Ferroelectric hysteresis loop measurement under high driving frequency generally faces great challenges. Parasitic factors in testing circuits such as leakage current and RC delay could result in abnormal hysteresis loops with erroneous remnant polarization (P r) and coercive field (E c). In this study, positive-up-negative-down (PUND) measurement under a wide frequency range was performed on a 10-nm thick Hf0.5Zr0.5O2 ferroelectric film. Detailed analysis on the leakage current and RC delay was conducted as the polarization switching occurs in the FE capacitor. After considering the time lag caused by RC delay, reasonable calibration of current response over the voltage pulse stimulus was employed in the integral of polarization current over time. In such a method, rational P–V loops measured at high frequencies (>1 MHz) was successfully achieved. This work provides a comprehensive understanding on the effect of parasitic factors on the polarization switching behavior of FE films.

Simulation and Modelling of Transient Electric Fields in HVDC Insulation Systems Based on Polarization Current Measurements

Simulating and modelling electric field dynamics in the insulation of medium- and high-voltage DC electrical systems is needed to support insulation design optimization and to evaluate the impact of voltage transients on ageing mechanisms and insulation reliability. In order to perform accurate simulations, appropriate physical models must be adopted for the insulating material properties, particularly conductivity, which drives the electric field in a steady-state condition and contributes to determining the field behavior during voltage and load transients. In order to model insulation conductivity, polarization, and conduction, mechanisms must be inferred through charging and discharging current measurements, generally performed at different values of electric field and temperatures in flat specimens of the material under study. In general, both mechanisms are present, but one of them may be predominant with respect to the other depending on type of material. In this paper, we showed that models based on predominant polarization mechanisms were suitable to describe impregnated paper, but not polymers used for HV and MV DC insulation. In the latter case, indeed, trapping–detrapping and conduction phenomena were predominant compared to polarization, thus conductivity models had to be considered, in addition to or as a replacement of the polarization model, in order to carry out proper electric field simulations.

On-site corrosion monitoring experience in concrete structures: potential improvements on the current-controlled polarization resistance method

The need for proactive maintenance of reinforced concrete structures with non-destructive testing (NDT) is less disputable today than ever. One of the most promising strategies in this regard is the in-situ measurement of the reinforcement corrosion rate. This study explored the reliability of modulated current confinement method (hereafter MCC) based on a review of in-situ measurements made with that technique in real-life structures over a 13-year period. The most prominent problems detected included defective confinement of the polarization current in low-resistivity environments and over-polarization of passive reinforcement. The findings, which showed enhancement of MCC reliability to depend on improving the electrochemical current regulation and control methodologies presently in place, are being applied to improve the design of the next generation of corrosion meters.

Synchrotron mechanism of X-ray and gamma-ray emissions in lightning and spark discharges

X-ray and γ-ray emissions observed in lightning and long sparks are usually connected with the bremsstrahlung of high-energy runaway electrons. Here, an alternative physical mechanism for producing X-ray and gamma-ray emissions caused by the polarization current and associated electromagnetic field moving with relativistic velocity along a curved discharge channel has been proposed. The existence of fast electromagnetic surface waves propagating along the lightning discharge channel at a speed close to the speed of light in vacuum is shown. The possibility of the production of microwave, X-ray and gamma-ray emissions by a polarization current pulse moving along a curved path via synchrotron radiation mechanism is pointed out. The existence of long tails in the power spectrum is shown, which explains observations of photon energies in the range of 10–100 MeV in the terrestrial gamma-ray flashes, as well as measured power spectrum of laboratory spark discharge.

Model-Based Analysis of Low Stoichiometry Operation in Proton Exchange Membrane Water Electrolysis

Proton exchange membrane water electrolysis cells are typically operated with high water flow rates in order to guarantee the feed supply for the reaction, the hydration of the ionomer phase and to homogenize the temperature distribution. However, the influence of low flow rates on the cell behavior and the cell performance cannot be fully explained. In this work, we developed a simple 1+1-dimensional mathematical model to analyze the cell polarization, current density distribution and the water flow paths inside a cell under low stoichiometry condition. The model analysis is in strong context to previous experimental findings on low water stoichiometry operations. The presented analysis shows that the low water stoichiometry can lead to dry-out at the outlet region of the anode channel, while a water splitting reaction is also present there. The simulation results show that the supply with water in this region is achieved by a net water transport from the cathode to the anode catalyst layer resulting in higher local proton resistances in the membrane and the anode catalyst layer.

Extraordinary and upper-hybrid waves in spin quantum magnetoplasmas with vacuum polarization effect

The propagation of extraordinary and upper-hybrid waves in spin quantum magnetoplasmas with vacuum polarization effect is investigated. Based on the quantum magnetohydrodynamics model including Bohm potential, arbitrary relativistic degeneracy pressure and spin force, and Maxwell's equations modified by the spin current and vacuum polarization current, the dispersion relations of extraordinary and upper-hybrid waves are derived. The analytical and numerical results show that quantum effects (Bohm potential, degeneracy pressure and spin magnetization energy) and the vacuum polarization effect modify the propagation of the extraordinary wave. Under the action of a strong magnetic field, the plasma frequency is obviously increased by the vacuum polarization effect.

Corrosion and mechanical behavior evaluation of in-situ synthesized Cu-TiB2 nanocomposite

In this paper, the synthesis of the copper matrix nanocomposite and the effect of adding TiB2 nanoparticles on the copper matrix was investigated. Three different amounts of TiB2 nanoparticles 5, 10, and 15 wt% were added and sintering was carried out at 900 oC for 4 hours under argon atmosphere. The phase formation of achieved nanocomposites was studied by X-ray diffractometer and the morphology of the synthesized samples was studied by field emission scanning electron microscopy and atomic force microscopy. The polarization and electrochemical impedance spectroscopy (EIS) at 3.5 wt% NaCl solution at room temperature was were carried out to evaluate the corrosion behavior of synthesized samples. Results show that adding the TiB2 nanoparticles decrease the corrosion resistance by the formation of galvanic couples, but the effect of amounts of porosities on the corrosion resistance is higher. It is revealed that the variation of the surface roughness is in direct relation to the value of polarization current density.