A novel high step-up DC-DC converter with a three-winding-coupled-inductor and an output capacitor in series is proposed in this study. By charging for two windings of dotted terminal connection in series by input source, the proposed converter can achieve a higher gain by using smaller turns ratios when the active switch is turned on. The passive clamping circuits are introduced for not only recycling leakage energy but also alleviating voltage spike on the main switch effectively. Meanwhile, the reverse-recovery problem of the diode is alleviated by the leakage inductor. Thus, the efficiency can be improved. In addition, output capacitors are in series to provide energy so that the volume of the output capacitor is reduced. The operating principle and steady-state analyses of the proposed converter are discussed in detail. Then, the performance of the proposed converter is compared with existing converters. Finally, a prototype circuit is built with a 40-V input voltage, 380-V output voltage, and 400-W output power to verify the performance of the proposed converter.

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Snow accumulates on the surface of insulator string, causing a decrease in its electrical performance, seriously threatening the reliable operation of the power grid. Most previous studies have focused on iced insulators; however, there is a lack of research on snow-covered insulators. In this paper, to reveal the influencing mechanism that snow has on the electrical characteristics of insulator string, based on an artificial snowing test in a chamber, the effects of equivalent salt deposit density, applied voltage type, and snow thickness on the flashover performance of snow-covered insulators are analyzed, and the flashover process is investigated. The results show that the relationship between the arc flashover gradient and the equivalent salt deposit density is a power function with a negative exponent, which is similar to that of polluted and ice-covered insulator strings. For the insulator strings with the same snow accretion, the direct current (DC) arc flashover gradient is lower than the alternating current (AC) arc flashover gradient. The relationship between arc flashover gradient and snow thickness is also a power function. The formation of a dry band during the flashover of snow-covered insulator string is similar to the flashover of the polluted insulator, and the arc propagation along the surface of the snow-covered insulator is similar to the flashover of the iced insulator.

An improved self-consistent, multi-component, and one-dimensional plasma model for simulating atmospheric pressure argon glow discharge is presented. In the model, both the plasma hydrodynamics model and chemical model are considered. The numerical simulation is carried out for parallel-plate geometry with a separation of 0.06 cm. The results show that Ar * plays a major role in the discharge, which is mainly produced by ground state excitation reaction. The electron temperature reaches its maximum in the cathode sheath but maintains a low value (0.23 eV) in bulk plasma. Elastic collision is the dominant volumetric electron energy loss in atmosphere argon glow discharge, which is negligible in low pressure argon glow discharge. The metastable step-wise ionization is the main mechanism for electron production to sustain the discharge. However, the highest contribution to electron production rate is ground state ionization reaction. The bremsstrahlung power density is related to electric voltage. With the increase of the electric voltage, the bremsstrahlung power density increases, namely, the strength of ultraviolet radiation spectrum enhances in the cathode sheath.

Investigating the corona mechanism plays a key role in enhancing the performance of electrical insulation systems. Numerical simulation offers a better understanding of the physical characteristics of air corona discharges. Using a two-dimensional axisymmetrical kinetics model, into which the photoionization effect is incorporated, the DC air corona discharge at atmosphere pressure is studied. The plasma model is based on a self-consistent, multi-component, and continuum description of the air discharge, which is comprised of 12 species and 22 reactions. The discharge voltage-current characteristic predicted by the model is found to be in quite good agreement with experimental measurements. The behavior of the electronic avalanche progress is also described. O + 2 and N + 2 are the dominant positive ions, and the values of O − and O − 2 densities are much smaller than that of the electron. The electron and positive ion have a low-density thin layer near the anode, which is a result of the surface reaction and absorption effect of the electrode. As time progresses, the electric field increases and extends along the cathode surface, whereas the cathode fall shrinks after the corona discharge hits the cathode; thus, in the cathode sheath, the electron temperature increases and the position of its peak approaches to the cathode. The present computational model contributes to the understanding of this physical mechanism, and suggests ways to improve the electrical insulation system.