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The free metal particles pollution has been a severe problem affecting the safety operation of gas insulated transmission lines (GIL) system and causes insulation failure. In this paper, a facile insulation film deposition method by using atmospheric pressure dielectric barrier discharge (AP-DBD) plasma was introduced. The SiOx film was deposited on copper surface to improve the lift-off voltage of metal particles. The film composition, surface morphology and film thickness based on the plasma deposition time were well studied. The results showed that deposited film was composed with Si- O-Si group, Si-OH group along with small amount of inorganic groups (CH2 and CH3). The oxidation degree and film thickness were enhanced when plasma treatment time was longer. The theoretical model of particle lift-off voltage was calculated before and after surface coating. After the electrode covered with SiOx insulation film, the lifting voltage of metal particles improved by about 38%, which agreed well with the prediction value. Our results proved that SiOx film deposited by AP-DBD was a very effective method for lift-off voltage improvement. [ABSTRACT FROM AUTHOR]

This work presents experimental results on different discharge modes for microsecond-pulse gliding discharges and their transition, and then analyzes the effect of the gap distance and flow rate on the discharge modes. The current amplitude, energy consumption per pulse and voltage range are used to reflect some discharge characteristics of discharge modes. The results show that there are three discharge modes for microsecond-pulse gliding discharges, i.e. the corona, diffuse and spark. Among the three modes, the values of the amplitude of the discharge current and the energy consumption per pulse for corona mode are lowest, then the diffuse mode and spark mode accordingly. When the gap spacing is smaller than 5 mm, there is no diffuse mode, and the corona discharges directly transit to spark discharges with the increase of the voltage. When the gap spacing is or more than 5 mm, the corona-diffuse-spark mode transition with the increase of the voltage is observed. The voltage range for diffuse discharge increases with the gap spacing. Moreover, when the flow rate increases, the ignition voltage for spark discharges increases, but the ignition voltage for diffuse discharges slightly changes, resulting in the voltage range for diffuse discharges increases. Therefore, diffuse mode is more likely to be obtained in a large gap with a relatively high flow rate. [ABSTRACT FROM AUTHOR]

Hydrophilic modification of polymethyl methacrylate (PMMA) surface is performed by atmospheric pressure plasma jet (APPJ) in Ar gas for improving the PMMA surface flashover performance in vacuum. In the experiments, APPJ is driven by a microsecond-duration pulsed generator, which has voltages of 0-30 kV, a rise time of 300 ns and a full width at half maximum of 2μs. Characteristics of the APPJ are analyzed according to its voltage and current waveform, discharge image and optical emission spectrum. Furthermore, surface properties of the PMMA surface before and after the treatment are characterized by water contact angle measurements and morphology observations. Results show that the main species of the plasma jet are composed of N2, Ar, OH, and O, among which such polar groups as OH and O enhance the hydrophilic property of the PMMA surface. The water contact angle decreases from 68° to a minimum value (16°) after the treatment. In addition, all the surface flashover voltages in vacuum for the PMMA samples treated by APPJ are higher than those for the untreated PMMA samples. [ABSTRACT FROM AUTHOR]

Gliding discharges can generate nonthermal plasma at atmospheric pressure. Therefore, they are widely used in plasma-assisted ignition and combustion. In this paper, the gliding discharge sustained by a resonant ac power supply was obtained with a pin-to-pin electrode geometry, and the characteristics of such discharge were investigated through its voltage–current and discharge images. Inceptive, nonstable, and stable stages involved in this gliding discharge were studied. Experimental results showed that the discharge was first ignited by a spark with a current peak of tens of amperes and soon turned into a stable stage, where the discharge respectively behaved in repetitive spark mode with a current peak of several amperes in a small gap and glowlike mode with a current peak of several microamperes in a relatively large gap spacing. Under a certain situation, a nonstable discharge was observed, which changed from a spark discharge to a glowlike discharge after some time. In addition, both the discharge stability and the breakdown voltage were influenced by the air flow. The discharge became unstable when the air flow exceeded 3 L/min. [ABSTRACT FROM PUBLISHER]

Pulsed power can provide instantaneously high power density to generate atmospheric nonthermal plasma in open air. In this paper, using two power supplies including a \(\mu \) s-pulse generator with a rise time of 300 ns and a pulsewidth of 5 \(\mu \) s and a ns-pulse generator of a rise time of 70 ns and a pulsewidth of 100 ns, pulsed gliding discharges are created with point-to-point electrodes in open air. Discharge images with these two generators under different flow rates are presented for a brief comparison of \(\mu \) s- and ns-pulse gliding discharges in air flow. [ABSTRACT FROM PUBLISHER]

Nanosecond pulsed discharges have various discharge modes, such as corona, diffuse discharge, spark or arc. A dense diffuse discharge is particularly desirable for various applications at atmospheric pressure. In this paper, a magnetic-compression pulse generator was used to produce repetitive positive nanosecond pulses for excitation of a diffuse discharge. The output pulse of the generator had a rise time of about 25 ns and a full width at half maximum of 40 ns. Electrical characteristics of the diffuse discharge were studied by measuring its voltage and current waveforms, as well as images of the discharge. The conduction current was calculated by the measured voltage and current, which was a true discharge current. The experimental results show that a stable diffuse discharge could be obtained at atmospheric pressure, and the conduction current was unipolar and had similar amplitude of several amperes under our experimental condition, which has the similar amplitude with the displacement current. Furthermore, the air gap spacing and pulse repetition frequency (PRF) affected the intensity and mode transition of the diffuse discharge. The conduction current increased with the PRF but decreased with the air gap spacing. Therefore, the diffuse discharge was likely available under some conditions of proper air gap, high PRF with positive pulse. [ABSTRACT FROM AUTHOR]