| Composite insulators have been widely used in UHV transmission lines due to their advantages of light weight,high mechanical strength and anti-flashover performance.As the insulating material of the composite insulator is organic,it will deteriorate when its surface is subjected to continuous corona discharge,which may affect the performance of the insulator.Therefore,it is necessary to study the corona aging resistance of composite insulators.Most researchers have simulated the field aging conditions by the artificial accelerated aging test of composite insulators in the laboratory.In order to ensure the consistency of experimental conditions and the correspondence of various test results,higher requirements are put forward on the uniformity of the aged samples.The corona discharge electrode structure,parameters and others directly determine the development of the discharge process,thereby affecting the uniform aging of the sample surface.Therefore,based on the physical process of dielectric barrier corona discharge,a mathematical model of microscopic process of corona discharge was established considering plasma field and the electrostatic field coupling field with multi-field coupling software COMSOL.Through the simulation analysis of the development of microscopic discharge under different electrode layout and parameter,uniform aging electrode design was studied.The results can provide a theoretical basis for the design of artificial corona accelerated aging test electrodes and related standards.The COMSOL plasma field and the electrostatic field coupling field was used to simulate the design.Based on the theoretical basis of particle collision cross section,a mathematical model of corona discharge microscopic physicochemical process was established.By dielectric barrier discharge tests at different voltages and different frequencies,the relevant parameters of corona discharge were determined(voltage 10 k V,frequency 1k Hz),and the pin plate electrode simulation model was initially built.Through the simulation analysis of different pin plate electrode models,the development rules of electron density,average electron energy and space charge density with time and space were obtained.In the single-needle model,from the tip to the surface of silicone rubber,the electron density gathered in the middle region and showed a slight increase trend.As the voltage reversed,the electron density showed a downward trend.The average electron energy was the largest at the tip.On the silicone rubber surface charge accumulated.In the three-pin model,at the initial stage of the positive half-cycle of voltage,the needle electrodes on both sides enhanced the electrode of the middle needle,so that the electron density of the area to the middle needle rapidly increased.Latter,the electrode density of the two sides of the electrode gradually flattened with the middle needle electrode.In the negative half-cycle of the voltage,the electron density in the edge region of the silicone rubber was continuously increased,and the area of the needle electrode was slightly decreased.The last two were basically the same.Meanwhile,the influence of different time and distance between pins on the dielectric barrier corona discharge was studied and analyzed.When 1ms was selected as the reference time for the electrode design and analysis,a more uniform aging could be obtained when the distance between two pins was 6mm-10 mm.According to the result of the simulation,the distance between the needles and arrangement of the needles were properly adjusted to obtain a hexagonal structure in which the electrodes with the uniform aging of the silicone rubber are arranged with a distance of 8mm between the needles.According to the simulation results,the artificial corona accelerated aging test was carried out on the silicone rubber samples.The feasibility and effectiveness of the electrode were verified by Scanning electron microscopy,Fourier transform infrared spectroscopy,hydrophobicity test and flashover voltage test. |
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