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This paper has the purpose to investigate the variation of electric field inside a HVDC cable insulation, and consequent potentiality of partial discharge inception in a defect upon load current variation. Simulations carried out by COMSOL Multiphysics show that load variations can incept partial discharges during cable operation at a constant voltage, depending on insulating material characteristics, defect size and location, and, in particular, the temperature and field dependence of electrical conductivity. Different values for temperature and field dependency of electrical conductivity, as well as of thermal conductivity and heat capacity are considered and their effect on the field distribution inside cavities near inner and outer semiconducting layer analyzed. For this purpose, a new analytical model to predict the behavior of PD amplitude and repetition rate from cable energization to steady state, including load variation, is introduced. The likelihood of PD inception during load transients, and not only voltage transients as previously demonstrated, poses further attention and constraints to HVDC cable design.

The Electro-Hydro-Dynamic (EHD) interaction induced in atmospheric-pressure air by a surface Dielectric Barrier Discharge (DBD) actuator has been experimentally investigated. Plasma Synthetic Jets Actuators (PSJAs) are DBD actuators able to induce an air stream, perpendicular to the actuator surface. These devices can be used in the aerodynamics field to prevent or induce flow separation, modify the laminar to turbulent transition inside the boundary layer, and stabilize or mix air flows. They can also be used to enhance indirect plasma treatment effects, increasing the reactive species delivery rate onto surfaces and liquids. This can play a major role in plasma processing and chemical kinetics modelling, where only diffusive mechanisms are often considered. This paper reports on the importance that different electrode geometries can have on the performance of different PSJAs. A series of DBD aerodynamic actuators designed to produce perpendicular jets have been fabricated on 2-layer printed circuit boards (PCBs). Linear and annular geometries have been considered, testing different upper electrode distances in the linear case and different diameters in the annular one. AC voltage supplied at 11.5 kV peak and 5 kHz frequency has been used. Lower electrodes were connected to ground and buried in epoxy resin to avoid undesired plasma generation on the lower actuator surface.Voltage and current measurements have been carried out to evaluate the active power delivered to the discharges. Schlieren imaging allowed to visualize the induced jets and gave an estimate of their evolution and geometry. Pitot tube measurements were performed to obtain the PSJAs' velocity profiles and to estimate the mechanical power delivered to the fluid.Optimal values of the inter-electrode distance and diameter have been found in order to maximize jet velocity, mechanical power or efficiency. Annular geometries are found to achieve the best performances.