Surface Charge Accumulation On Epoxy Based Nanocomposites Under Superposition Voltage And Its Influence On DC Flashover

Polymer based nanocomposites have drawn a lot of attention due to their excellent electrical insulating property,mechanical property and thermal property.Their broad application prospects in the UHVDC transmission system have been proposed.Surface charge accumulation on polymer material is an important reason for electric field distortion and flashover.To ensure the safety of the DC system,it is necessary to investigate the surface charge accumulation characteristics and its impact on the flashover.During the operation of the DC power system,the insulation material not only withstands the DC electric field,but also receives the lightning overvoltage and the impact of operating overvoltage.However,up to now,the research on the surface charge accumulation and flashover characteristics of insulating materials under DC-pulse superposed voltage is still very limited.In this paper,high voltage DC power supply and pulse generator designed by Marx generator principle have been employed,epoxy based nanoparticles were prepared as the test samples.Surface charge accumulation and DC flashover of the nanocomposites under superposed electric field were investigated,and the influence of voltage amplitude,charging time and content of nanoparticles on the charge accumulation and the flashover behavior have been analyzed.The main work is as follows:1.The EP/Al₂O₃ nanocomposites samples were prepared by using mechanical mixing method.Scanning electron microscopy?SEM?observation was employed to analyze the morphology of sample structure.For the purpose of determining the dispersion of nanoparticles in epoxy matrix,and relative permittivity of the composites with different contents of nanoparticles have been measured.The coupling circuit of high voltage DC power supply and microsecond pulse power supply was designed,and the surface charge measurement experiment system was established.2.A pair of plane to plane electrode structure was employed to investigate the charging and flashover.DC voltage and pulse superposed DC voltage were applied to the surface of sample,respectively.The voltage amplitude,voltage polarity,time of voltage application and nanoparticles content were considered to analyze the influence of different parameters on the amount of surface charge.The results showed that the applied voltage has a remarkable influence on surface charge accumulation.With the increase of the voltage,the accumulation of the charge becomes serious.Furthermore,the content of nanoparticles also sharply affected the surface charging behaviors.3.With the application of superposed voltage,the distribution of surface charge and DC flashover manner were investigated by taking voltage amplitude and polarity,the amount of accumulated charge,the nanoparticle content and the relative humidity into consideration.Obtained results showed that surface charge accumulation on the sample surface would reduce DC flashover voltage,and with the increase of the charging voltage,the flashover voltage tended to decrease significantly.When the relative humidity became increased,the DC flashover voltage of the sample decreased sharply.