Research On Prebreakdown In Naphthenic Base Liquid Dielectric Under Short-Pulsed Voltage

The exploration of liquid dielectrics discharge mechanism has been a hot research topic in the field of electrical insulation,mainly in order to improve and optimize the structure of insulation,make full use of the characteristics of liquid insulating medium.With the development of pulse power technology,insulating liquids are largely used in the generation,variation and transmission in high-power system,the study of the insulation breakdown property under short-pulsed voltage is important to the design of the new type of pulse power system.So the numerical simulation on prebreakdown process in naphthenic base liquid dielectric under short-pulsed voltage in this dissertation,discussioning the particles micro dynamic behaviors in the process of liquid dielectric prebreakdown and further understanding the liquid discharge from theory.For the purpose of studying the particles micro dynamic behaviors in the process of liquid discharge,we establish needle-sphere physical model and the corresponding mathematical model,then the governing equations that contain the charge continuity equations for positive ion,negative ion and electron,the thermal diffusion equation is included to denote the temperature variations and coupled with Poisson 's equation to describe the electric field,and the equations make a numerical simulation on prebreakdown process of naphthenic base liquid dielectric on electric field strength,space charge density,temperature variation and the formation and propagation process of streamer.The results show that greater applied voltage magnitudes form streamers with high velocity and larger radial radius under 0.1/2?s impulse wave;by increasing the applied voltage magnitude,the streamer velocity slowly increases until a critical voltage is reached,where an order of magnitude velocity increase is observed.Moreover,the propagation of streamer under 0.05/0.2?s and 0.01/0.1?s impulse waves are compared under the same peak voltage,short rise-times create large radius fast streamer.In addition,this dissertation details the liquid/solid surface flashover.The results indicate that liquid/solid surface flashover property is influenced by the solid permittivity.When the solid surface orientation is parallel to the axial electric field and the permittivity of solid is greater than liquid,the solid tends to attract the streamer and the surface accelerates streamer propagation due to the effects of polarization charge;when the permittivity of solid is less than liquid,streamer is rejected by the solid surface making the radius smaller and accelerating propagation along the axial direction,promoting the liquid dielectric discharge process.When the solid surface orientation is perpendicular to the axial electric field and the permittivity of solid is greater than liquid,the streamer quickly develops into the solid medium,and as the streamer contacts to the solid surface,due to the solid dielectric barrier function,the streamer travels along the solid surface to the radial development;when the permittivity of solid is less than liquid,because of the effects of surface polarization charge,slowing down the streamer velocity and discharge process.