Study On Numerical Analysis To Temperature And Model For Gas-liquid Two-phase Discharging Simulation Of Streamers In Natural Ester Based Insulating Oils

The temperature distribution of streamer channels in liquid dielectrics significantly influences the generation and dissipation of charged particles,but it is considerably challenging to measure the temperature distribution of the streamer.In response to the key issues,This work first studies the numerical method of resolving temperature distribution of streamer,then analyses the gas-liquid two-phase characteristics of streamer discharge in nature easter insulating oil,and further carried out numerical simulation research on streamer discharge of gas-liquid two-phase.The main content and results of this work are as follows: The main contents of this work are as follows:(1)The shadowgraph method based on diffuse reflection light optical path for imaging streamer discharge in natural ester insulating oil is studied.An improved method for the optical path of shadowgraph imaging the streamer discharge in oil is proposed to solve the incompatibility problem between a parallel light path and pyramid splitting camera.The diffuse reflection light source is used to improve the imaging performance,which significantly increases the quality of image data of streamer discharge in oil,and an improved shadowgraph measuring system for streamer discharge in oil is constructed.The acquirement of a large number of high-quality image data provides test technology that supports a better understanding of streamer behaviour and characteristics and revelation the mechanism of streamer propagation.(2)The analytic method of temperature distribution of streamer discharge channel in natural ester insulating oil is studied.By analyzing the streamer discharge shadowgraph imaging optical path,the relationship equations between the streamer discharge channel’s refractive index and the streamer image’s grayscale are derived,and the refractive index distribution of the streamer discharge channel is calculated by the finite difference method.The constitutive relations among the parameters such as grayscale,refractive index,temperature and molecular number density of the streamer discharge channel are obtained.The results show that the temperature rise significantly affects the reduction of the streamer refractive index compared with the increase of number densities among molecular dissociation and the electron and positive ion.(3)The mathematical model of ionization source term for gas-liquid two-phase streamer discharge is studied.The ratio of gaseous molecules of triglyceride dissociated production at different temperatures is analyzed by Reaxff reaction force field dynamic simulation.The relative proportion of gaseous molecules and the mass density of the streamer channel are obtained.Mathematical models respectively describe the variation of charged particles’ mobilities,field ionization rate and collision ionization rate of gasliquid two-phase streamer with temperature are established.The evolution characteristics of the luminescence channel of the gas-liquid two-phase streamer are analyzed.The photoionization source term of gas-liquid two-phase streamer discharge is constructed by the usage of Gaussian function.The results show that the fluctuation behaviour of the velocity of streamer is closely related to the mobility of charged particles and the critical temperature.The results show that the fluctuation behaviour of streamer velocity is closely related to the mobility of charged particles and the critical temperature of streamer gas phase.Photoionization promotes the rapid propagation of streamer along the axis of the needle plate electrode.The results demonstrate that the improved gas-liquid two-phase ionization source is reasonable.(4)Study on numerical simulation of gas-liquid two-phase streamer in natural ester insulating oils is carried out.Based on the traditional mathematical model of streamer,the numerical simulation model of gas-liquid streamer is established and studied by introducing the ionization term of gas-liquid two-phase.The streamer in natural ester insulating oil is simulated and the influence of temperature on streamer behaviour is studied by adjusting the ionization source term.The simulation and analysis results show that the gas-liquid two-phase streamer discharge model can simulate the evolution of streamer branches in oil,which can better reflect the measured image data of streamer discharge compared with the simulation results of the traditional model.Based on the above works,a method for analyzing the refractive index distribution of streamer channels in natural ester insulating oils is proposed.The relationship between refractive index and temperature of streamer channel is established.A mathematical model of ionization source and a numerical simulation model of gasliquid two-phase streamer channel are proposed and established.The numerical simulation of the branching behaviour of streamer in oil is realized,agreeing with the characteristics of streamer in oils.The work has scientific value for promoting the research of liquid dielectric discharge calculation and provides a numerical method for improving the electrical performance of natural ester insulated oil.