| Partial Discharge(PD)phenomena can not only indicate the insulation degradation of high-voltage electrical equipment,but also enhance defect severity and lead to premature failure of equipment.Therefore,by conducting research on the micro-mechanism of PD and constructing a simulation model,it improves our physical understanding and enables us to adjust any parameters freely so that the critical parameters and physical processes influencing PD behaviors can be identified.Moreover,from the perspective of analyzing the simulated PD pulse,a theoretical basis for a deeper research on electromagnetic propagation characteristics,noise reduction,and pattern recognition in PD detection is provided.In this dissertation a fluid dynamics model based on the drift-diffusion equations of charged species is utilized to simulate the microscopic process of PD.Firstly,the point discharge in a needle-plane geometry is modeled and simulated.As to the simulated Trichel pulse sequence,a detailed analysis of the charged particle number density and electric field intensity distribution of the four phases of each single pulse is performed;a comparison of the averaged current of the discharge current pulse sequence is made between numerical simulation and experiment,which evaluates the validity of the simulation model.Then,in order to understand the importance of coefficients used in the simulation model individually in terms of their impact on the characteristics of the pulses,the frequency,the DC current,and the rise time,a parametric study is carried out.In addition,considering the rising and falling edge of the PD pulse current being controlled by different physical processes,the data fitting method is used to abstract the segmented-function mathematical model from the point discharge current pulse signal obtained from the numerical simulation.The fitting results of a measured pulse signal verifies the validity of the mathematical model with Root Mean Squared Error larger than 94%.Finally,PD in air-filled spherical voids is studied by including photoionization reaction in the simulation model of point discharge,which is thought to be the major source for the production of seed electrons ahead of the cathode-directed streamers.The discharge mechanism consisting of an electron avalanche transitioning into a positive streamer is simulated and analyzed.Apart from that,an error analysis of the inception and residual electrical field between simulated values and theoretical ones is discussed. |
