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Cellulose insulating paper is widely used in the power industry for its good electrical insulating properties. Moisture sharply increases its conductivity, which directly leads to the weakening of insulation performance and greatly increases the risk of subsequent electric field distortion and insulation breakdown. This paper focuses on the microscopic mechanism of moisture changing the characteristics of charge transport in cellulose insulation and attempts to reveal the related conductivity mechanism. To achieve this purpose, microscopic and macroscopic perspectives are integrated and several simulation and experimental methods are utilized comprehensively. The molecular dynamics simulation results showed that most water molecules in damped cellulose were individually and uniformly adsorbed on the hydroxyl groups by hydrogen bond, and the quantum chemistry computation results showed that the lowest unoccupied molecular orbital more appeared on the water molecule and the corresponding density of state increased. Then, experimentally, it was confirmed that the trap energy level decreased by the thermally stimulated current method. On this basis, the promotion effect of moisture on charge transport is predicted and verified by polarization and depolarization current methods. As the moisture content increased, more charge carriers escaped from the trap by hopping and participated in long-range continuous charge motion. Therefore, after dampness, the current of cellulose insulating paper increased exponentially with the increase in electric field strength, which was consistent with the hopping conductivity mechanism. [ABSTRACT FROM AUTHOR]

Plasma bullet is the formation and propagation of a guided ionization wave (streamer), normally generated in atmospheric pressure plasma jet (APPJ). In most cases, only an ionization front produces in a dielectric tube. The present study shows that two or three ionization fronts can be generated in a single quartz tube by using a microwave coaxial resonator. The argon APPJ plumes with a maximum length of 170 mm can be driven by continuous microwaves or microwave pulses. When the input power is higher than 90 W, two or three ionization fronts propagate independently at first; thereafter, they confluence to form a central plasma jet plume. On the other hand, the plasma bullets move independently as the lower input power is applied. For pulsed microwave discharges, the discharge images captured by a fast camera show the ionization process in detail. Another interesting finding is that the strongest lightening plasma jet plumes always appear at the shrinking phase. Both the discharge images and electromagnetic simulations suggest that the confluence or independent propagation of plasma bullets is resonantly excited by the local enhanced electric fields, in terms of wave modes of traveling surface plasmon polaritons. [ABSTRACT FROM AUTHOR]