This paper investigates mechanisms of the surface charge dissipation of silicone rubber (SiR) after dielectric barrier discharge (DBD) plasma treatments in an open air. Electrical and physicochemical properties of the untreated and plasma treated samples were evaluated by surface and volume conductivity, surface potential decay (SPD) measurements, Fourier transform infrared (FT-IR), and water contact angle tests. Results show that the surface conductivity of the plasma treated samples evidently increases with the treatment time. The samples with a longer DBD plasma treatment time enhance the SPD rate after the positive and negative corona charging. However, an abnormal surface potential variation is observed at the beginning of the SPD after the negative corona charging. It is found that the top-bottom surface plasma treatment can further accelerate the SPD of the samples compared with the untreated and single surface plasma treated samples. The physicochemical analysis shows that the concentration of polar groups is increased after the plasma treatment, and the water contact angle is consistently declined with the increase of the plasma treatment time. The calculated trap distribution illustrates that the hole trap energy and the electron trap density of the sample are decreased after the plasma treatments. This investigation attributes the measured SPD of the untreated sample and single surface treated samples to the electrical conduction along the sample surface, but the SPD of the top-bottom surfaces plasma treated samples is enhanced by the charge neutralization and transportation through the material bulk as well as the sample top surface conduction.

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Polymeric nanocomposite insulations are receiving the widespread attention of the electrical cable industry. This paper presents the electrical insulation performance of as‐received commercial 320 kV high‐voltage direct‐current (HVDC) cross‐linked polyethylene (XLPE)/MgO nanocomposite material with reference to the pure XLPE. The results of this commercial‐grade electrical insulation material are not reported hitherto. The scanning electron microscopy confirms the well‐dispersed nanofiller inside the polymer matrix. The DC electrical insulation performance is investigated by DC breakdown strength, space charge, DC electrical conductivity, and surface potential decay measurements. The test samples are subjected to the thermal aging at 135°C for 30 days. The un‐aged nanocomposite exhibits 20% higher DC breakdown strength, negligible hetero space charge accumulation, and the lower DC conductivity by one order than the un‐aged pure XLPE. Moreover, thermally aged nanocomposite shows more restraint to the deterioration of its properties. After the thermal aging, the DC breakdown strength decreased by 38% and 20% in the pure XLPE and its nanocomposite, respectively. Thermally aged nanocomposite shows negligible hetero charges and an increase in the DC conductivity by one order. However, the pure XLPE shows higher hetero charge accumulation and the increased DC conductivity by one order. In un‐aged XLPE nanocomposite higher crystallinity, higher deep trap density, and the lower carbonyl index are found to be the primary attributes of its improved performance. It is postulated that these significantly unchanged attributes can be the reason for the better anti‐thermal aging properties of the XLPE nanocomposite.

This paper presents an investigation on DC flashover voltage of silicone rubber (SiR) improved by dielectric barrier discharge (DBD) plasma treatments under ambient atmospheric pressure air. DC surface conductivity, surface potential decay (SPD), DC surface flashover voltage, partial discharge magnitude, Fourier transform infrared (FT-IR) spectrograms, and surface water contact angles are measured to analyze the influence of plasma treatment on the SiR. It is found that the speed of SPD increase consistently with the plasma modification time. The tendency of flashover voltage is increasing at first and then decreasing with the increased time of the plasma treatment. The magnitude and number of partial discharge pulses increase apparently with the increased plasma treatment time. Physicochemical measurements indicate that more amount of polar groups appear on surface after the DBD plasma modification, whereas the surface water contact angles decline continuously with the increased plasma modification time. However, the hydrophobicity is recovered after 30 d exposure in the air. It is demonstrated that the SPD is accelerated significantly due to the increased surface conductivities and density of shallow traps. However, the reduction of flashover voltage after longer time of the plasma treatment is attributed to the increased mobility of charge carriers on the sample surface.

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