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The winter in southern China is very cold,along with high humidity. Regional ice coating problem often appears in the long distance high voltage transmission lines,which may lead to serious power accidents such as tower collapse. A new direct current (DC) ice-melting device with series-parallel switching of rectifier bridge is studied to avoid widespread power outages. Based on the conventional 12-pulse DC ice-melting device,a new DC ice-melting topology is proposed through principle analysis,parameter design and simulation verification,and it simultaneously meet the high current demand for wire melting and the high voltage demand for ground wire melting. Compared with the conventional 12-pulse DC ice-melting device,the new DC ice-melting topology is able to select half-capacity transformer and half-current thyristor,which significantly reduces the equipment costs. Meanwhile,the harmonic current injected into the system decreases effectively when operating in high current output mode,so as to reduce the voltage distortion of the connected system. The new DC ice-melting device with the function of series-parallel switching of rectifier bridge is able to reduce the equipment costs and improve the system voltage quality when the DC ice-melting device is put into operation.

With the rapid development of the power grid， the overhigh short-circuit current becomes increasingly prominent， restricting the safe and stable power grid operation. Because of the shortcomings of the existing short-circuit current limiting methods， fast topology splitting and self-recovery current limiting scheme based on dynamic topology adjustment method in sectionalized connection mode is proposed. To meet the quickness of fault current limiting control system requirement， a control system architecture scheme based on FT3 communication is designed to increase data processing speed and reduce link transmission delay. A fast fault identification and phase control fault interruption method and its implementation scheme based on Kalman state estimation are proposed. Finally， the control system is verified by RTDS test. The results show that the short-circuit current limiting control scheme can quickly extract fault features and complete the splitting in the first cycle of short-circuit current to ensure the effectiveness of current limiting before conventional circuit breaker arcing.

Breaking capacity of circuit breakers can no longer meet the continuous rising demand of fault current in present new power systems. The phrase-controlled fault interruption technology based on zero crossing point prediction is an important solution. Zero crossing prediction method of fault current based on Bayesian estimation is studied in this paper. The fault current model through different processing strategies for the attenuation time constant of fault current is established， and three algorithms such as extended Kalman filter， standard Kalman filter and particle filter as well as their implementation are proposed. The prediction results of the algorithms through numerical simulation are compared and analyzed. The simulation analysis shows that the method of calculating attenuation time constant in advance and then using the standard Kalman filter for state estimation is superior in prediction time， accuracy and amount of calculation， and is suitable for the engineering practice of control and protection device.

To improve the application of molten salt method in carbon fibers (CFs) surface modification, the work explores the effect of the CFs-itself crystallinity on the formation and growth mechanism of TiC coating in the molten salt reaction. Three different types of CFs were used to prepare TiC coatings at 850°C, and the formation and growth mechanisms were studied. The results showed that CFs surface defects could preferentially initiate nucleation and cause inhomogeneity of TiC particles in the initial stage of TiC coating formation. The CFs surface with high crystallinity could obtain a finer and more uniform TiC coating because the growth rate of TiC particles is slower and the particles do not accumulate with each other during the coating growth. At the same time, the growth rate of TiC coating decreased with increasing CFs crystallinity during the TiC coating growth, which reason is that CFs with higher crystallinity require more activation energies of carbon atom counter diffusion. Therefore, the surface of CFs with higher crystallinity and fewer surface defects is easier to obtain a uniform and particle size TiC coating during the molten salt reaction. [ABSTRACT FROM AUTHOR]