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This paper embodies the results of experimental studies of a dielectric barrier discharge low-temperature nonequilibrium plasma reactor that runs in air and nitrogen at atmospheric-pressure conceived for surface treatment applications. A homemade reactor, of typical plane-to-plane geometry with the dielectric covering the upper electrode which is stressed by a high voltage (40 kV, 3–20 kHz) is used. Electrical signals (current and voltage), optical emission spectroscopy records, and total light emission measured by photomultiplier have been analyzed and used to distinguish different plasma regimes which are studied for the treatment of a lignocellulosic material (sugarcane bagasse). In the filamentary discharge regime, the gas temperature of few tens of degree Celsius above the ambient one was determined, the electronic temperature of some electronvolts and electron density in the range of 1012–1013 cm−3 were estimated. Plasma treated pellets of sugarcane bagasse were analyzed by diffuse reflectance infrared Fourier transform spectrometry and the relative results obtained under filamentary discharge regime have shown significant degradation of the lignin macromolecule. It has been shown important modifications on the lignocellulosic material, namely, the plasma attacks drastically the lignin bonds. Strong modification of lignin was observed near wavenumber of 3400 cm−1, due to stretching vibrations of OH, and for the band 1114 cm−1 which is related to C=C and C=O stretching. Severe decrease of the band intensity 1596 cm−1, which due to C=C stretching and C=O, is also a result of the treatments done in this paper. [ABSTRACT FROM AUTHOR]

The three-electrode plasma reactor for the treatment of polluted gases combines a dielectric-barrier discharge with a remote third electrode, designed to enhance streamer propagation in a relatively large region. In this paper, experimental studies of the electrical magnitudes of the discharge for different electrode bias voltage configurations are presented. Also, the Laplacian electric field distribution in the interelectrode gap is calculated for each configuration. The degradation efficiency of NO in an N2 atmosphere for the different configurations is also reported. It is found that the discharge is generated only for that electrode bias configuration for which the external electric field promotes the streamer propagation across the electrode gap. Also, for a triggered discharge, the reactor efficiency for the removal of NO changes with the different electrode bias configurations. This result can be explained in terms of the electric field intensity. The configuration with higher external electric field improves the number of streamers propagating in the interelectrode gap so that more reactive species generated in the streamers are effectively entrained in the gas flow to be treated. [ABSTRACT FROM AUTHOR]

The audible noise (AN) production mechanism caused by corona discharge in ultrahigh voltage transmission lines is less understood. The study on sound pressure characteristic is necessary to obtain the inherent relation between AN and corona discharge. In this paper, the experimental research on single-point direct current (dc) corona discharge was evolved and the time-domain sound pressure waveform was obtained using capacitor microphone. The experiment results show that the dc corona discharge comprises multiple subsequent discharge pulses. The discharge voltage and the electrode polarity have a direct effect on the rising time and pulsed width of the single current pulse. The waveform of sound pressure produced by single discharge is a bipolar microsecond pulse, which lags behind the current pulse in time domain. The time delay is propagation time of sound signal from the discharge spot to the measurement spot. Based on the corona discharge characteristic in dc voltage, the experiment platform for nanosecond pulsed discharge was built to obtain the relation between discharge parameter and sound parameter. The characteristics of sound pressure in different discharge conditions were analyzed. The study results indicate that the sound pressure produced by pulsed discharge is similar with that produced by corona discharge. The experiment platform for pulsed discharge can be used to research the AN production mechanism by dc corona discharge. [ABSTRACT FROM AUTHOR]

As one of the most commonly used insulating mediums, in electrical discharge, sulfur hexafluoride (SF6) will decompose in the presence of water vapor and oxygen, producing various gaseous by-products. It is shown that the concentrations and production rates of SF6 gaseous decomposition by-products heavily depend on electrical field to gas density ratio (E/N) under corona discharge. Regarding the difficulty in measuring E and N, applied voltage and the SF6 pressure, are proposed in this paper to describe E and N, respectively. Several experiments of 50-Hz AC discharges were carried out under different applied voltages and different SF6 pressures using point-to-plane electrodes. The concentrations of SF6 gaseous by-products were measured by a gas chromatograph-mass spectrometer system (GS/MS). Experimental data show that the concentrations of SF6 gaseous by-products increase while the ratio (SOF2+SO2)/SO2F2 decreases, with increasing applied voltage. The concentrations decrease with increasing pressure of SF6. The formation mechanisms of SF6 gaseous by-products with the variations of applied voltage and the SF6 pressure are discussed, such as SO2F2, SOF2+SO2, CF4, and CO2 and so on. An experimental expression is derived which connects the SF6 pressure with the concentration of the decomposition by-products. [ABSTRACT FROM AUTHOR]

The primary mode of the pulsed positive streamer discharge in water has been studied by the shadowgraph imaging techniques utilizing an ultrahigh speed frame camera system. The propagation speed and the flare angle of the fan-shaped primary streamer were measured and their dependence on the water conductivity and the applied voltage were investigated. The initial propagation speed of the primary streamer is about 4–6 km/s and rapidly decreases to about 1.5 km/s. The water conductivity and the applied voltage have no significant influence on the propagation speed of the primary streamer. The flare angle of fan-shaped structure of the primary streamer ranges from 150° to 210°, and increases with increasing the applied voltage. In the voltage range 15 to 17 kV, the water conductivity has no significant influence on the flare angle of the fan-shaped structure, but as the applied voltage increases beyond 18 kV, the flare angle of the fan-shaped structure decreases with increasing the water conductivity. Based on the plasma discharge in a bubble and the fact that the radius of primary streamer is about 200–400 $\mu \text{m}$ , the primary streamer in water seems to be incepted by the positive ions at the head of the discharge filament generated in the microbubble, which penetrates into the water through spattering process and forms a gaseous trajectory in the bulk water. [ABSTRACT FROM AUTHOR]

In the present contribution, we analyze and quantify micro-discharge currents originating from rough electrode surfaces in HVDC gas insulated switchgear (GIS) applications. These currents can be significantly larger than those in the gas phase caused by natural ionization or those from bulk conduction in the solid insulators. They may thus dominate the charging of the insulator surface and are thus a key dimensioning criterion. Five different electrode systems with different, but clearly defined, roughness were designed. To quantify the amplitude of the micro discharge current as a function of the electrical field strength on the electrode surface, the consequence of these discharges in the form of accumulated charges on the surface of a PTFE sample was measured. The measurements were compared to simulation results from a model that uses the Townsend approximation for unipolar saturation ionic current, which is a widely used approximation in many areas of applications. As a main finding of our investigations, to avoid micro discharges, electrical field strengths of 7.1 kV/mm should not be exceeded in HVDC GIS design using typical industrial electrode roughness around 2 ?m and 0.5 MPa SF6. [ABSTRACT FROM AUTHOR]