Zhan Huamao

Homogeneous dielectric barrier discharge in air for surface treatment

Dielectric barrier discharges in atmospheric pressure gas, especially in air, are usually made of a large number of filamentary micro-discharges, which may cause the ununiformity of the surface treatment. In this paper, a new method to obtain a homogeneous dielectric barrier discharge in air is proposed. The homogeneous discharge, which is of a nature in between those of the filamentary discharge and the glow discharge, is very efficient as a means of modifying the hydrophilicity of textile or non-woven and does not cause any damage to the specimen. The homogenous discharge occurs by using of a cylinder-plane electrode geometry. The electrical characteristics of the cylinder-plane dielectric barrier discharge were compared with those of a parallel-plate dielectric barrier discharge and a metallic cylinder-dielectric plane discharge. Compared to the parallel-plane dielectric barrier discharge and the metallic cylinder-dielectric plane discharge, the distribution of the current and temperature of the homogeneous discharge gap is more uniform. It is proved experimentally that the homogeneous discharge in ambient air is a promising surface treatment method for textile and non-woven.

Spark model for 1100kV GIS disconnecting switch

In order to make the VFTO simulation more accurate, the spark characteristic of disconnecting switch and modeling is studied. The experimental circuit of the 1100kV GIS is simulated, and according to various computing resistance formulas of spark channels, the spark generated by disconnecting switch operation is modeled. The simulated voltage waveforms of the load side are compared with the measurement results. The simulated VFTO is obtained when different disconnecting switch spark models are adopted, with low-frequency oscillations of 200 kHz and 6 MHz, high-frequency of 36 MHz and 56 MHz, and the frequency range is basically consistent with the experimental results. The circuit oscillation frequency is mainly the same compared to different high-frequency decay rate with different spark models. The comparison shows that the simulated voltage waveforms of the load side match the experimental data better than others when Kushner model is adopted. However, the high-frequency attenuation rate of the simulated voltage at the load side is slower than that of the measuring voltage when Kushner model is used. Therefore, further developments in Kushner model are needed in order to reproduce with better accuracy the dynamic behavior of the disconnecting switch spark resistance.

Pre-ionization Methods for Atmospheric Pressure Discharge Controlled by Dielectric Barrier

Dielectric barrier discharge is one of the most usual methods for obtaining atmospheric pressure plasmas. It is proved theoretically that obtaining a uniform dielectric barrier discharge is strongly related to the concentration of seed electrons. Therefore, for producing enough electron concentration under a low electrical field and homogenize the discharge, some pre-ionization methods including accessorial impulse spark discharge, X rays, plasma jet have been employed. The pre-ionization effect of these methods on decreasing the applied voltage for the dielectric barrier discharge and homogenizing the discharge was investigated experimentally.

Study on the Disc Sensor Based on the Cavity Mold Theory

Ultra-high-frequency (UHF) sensor is the vital component of a partial discharge detection system and its coupling performance is affected by structural parameters. On the basis of the cavity model theory, this paper studied the influence of the disc electrode diameter, the thickness, the dielectric constant of the dielectric substrate, and the position of the coaxial connection on the performance of the disc-type UHF sensor with the application of the XFdtd software. The simplified finite-difference time-domain simulation model for the gigahertz transverse electromagnetic (GTEM) cell has been established, and the influence of the coaxial feed position on the performance of the disc-type UHF sensor is studied via the frequency domain effective heights in the simulation. The result shows that as the disc electrode diameter, the thickness, and the dielectric constant of the dielectric substrate increase, the working frequency band shifts toward the reducing direction. The position of the coaxial connection has an obvious effect on the resonant mode of sensor, too.

Effect of Space Charge on the Propagation Path of Air Gap Discharge

The existence of space charge may be addressed as one of the reasons that could cause shielding failure of transmission lines. In order to study the effect of space charge on discharge propagation path, a new experimental system, including mainly DC high voltage generator, impulse voltage generator as well as rod-plane electrode, has been established. The space charge was generated around the rod by means of pre-applying DC high voltage, and the air gap discharge experiments were conducted with and without pre-applying DC high voltage, respectively. Meanwhile, high speed cameras worked simultaneously from the front and lateral side to record the discharge propagation path so as to obtain the curvature. After statistical analysis, it is shown that the curvature increases in the middle and lower portions of the propagation path when the effect of space charge is taken into account.

Dielectric barrier discharge in nitrogen and argon

Summary form only given. Dielectric barrier discharges in air are generally streamer-like discharges, however, a homogeneous discharge, called atmospheric pressure glow discharge, may be obtained in some noble gases such as helium and argon. Dielectric barrier discharges in nitrogen and argon are studied experimentally to determine mechanisms controlling the transition from glow to streamer discharge. The influences of the applied voltage, the gas gap distance, the gas pressure and other factors on the discharge are investigated. The characteristics of the dielectric barrier discharge in nitrogen and argon are analyzed and compared. The aim of the paper is to study the experimental conditions of obtaining an atmospheric pressure glow discharge in nitrogen and argon. The possibility of obtaining an atmospheric pressure glow discharge in air is examined by increasing the proportion of air in nitrogen gradually. The waveforms of the applied voltage and discharge current under different experimental conditions are reported, which is helpful to describe the characteristics of the discharge and judge whether the discharge is a glow discharge or not

Effect of preionization on forming atmosphere glow discharges in air

There are some obstacles in obtaining atmosphere glow discharge plasma although the technology of low-pressure glow discharge plasma has been highly developed. Discharge stability decreases greatly as pressure increases, especially in air. As a way to produce high electron densities and lower the electric field for discharges, a preionization method is used to prevent the transition from glow to steamer-like discharge in air. It is found that the preionization can assist the starting of discharges and lower the electric field for discharging in air effectively. Under normal atmosphere conditions, the electric fields employed in the reactor decrease by about 25% when the preionization method is adopted. Some experimental conditions which effect the preionization are studied to test the validity and stability of the preionization method. Experimental results show that the preionization plays an important role in the atmosphere glow discharge in air and its effect varies with some factors such as gas flow and frequency of the power supply.