Chengyan Ren

Experimental study on conduction current of positive nanosecond-pulse diffuse discharge at atmospheric pressure

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.

Surface modification of polymethyl-methacrylate using atmospheric pressure argon plasma jets to improve surface flashover performance in vacuum

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.

A Gliding Discharge in Open Air Sustained by High-Voltage Resonant AC Power Supply

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.

X-ray emission from a nanosecond-pulse discharge in an inhomogeneous electric field at atmospheric pressure

This paper describes experimental studies of the dependence of the X-ray intensity on the anode material in nanosecond high-voltage discharges. The discharges were generated by two nanosecond-pulse generators in atmospheric air with a highly inhomogeneous electric field by a tube-plate gap. The output pulse of the first generator (repetitive pulse generator) has a rise time of about 15 ns and a full width at half maximum of 30–40 ns. The output of the second generator (single pulse generator) has a rise time of about 0.3 ns and a full width at half maximum of 1 ns. The electrical characteristics and the X-ray emission of nanosecond-pulse discharge in atmospheric air are studied by the measurement of voltage-current waveforms, discharge images, X-ray count and dose. Our experimental results showed that the anode material rarely affects electrical characteristics, but it can significantly affect the X-ray density. Comparing the density of X-rays, it was shown that the highest x-rays density occurred in the ...

Surface modification of epoxy using an atmospheric pressure dielectric barrier discharge to accelerate surface charge dissipation

In this paper, an atmospheric-pressure dielectric barrier discharge is used to modify the surface of the epoxy material and enhance the dissipation of surface charge to reduce the accumulation of surface charge. In the experiments, atmospheric-pressure air dielectric barrier discharge is driven by a microsecond pulse generator. Surface properties of epoxy before and after the plasma treatment are characterized by water contact angle, surface potential, and surface/volume conductivity measurements. Atomic force microscope and X-ray photoelectron spectroscopy are used to investigate the changes of the morphology and the chemical composition of the epoxy surface. Experimental results indicate that the surface of epoxy is etched by the plasma and the increase of the surface roughness enhances the surface insulation ability. The O radicals in plasma and the carbonyl groups formed on the surface make the surface charge trap shallower, change the epoxy surface composition then increase the surface conductivity and accelerate surface charge dissipation. When the epoxy is treated for an appropriate time, the epoxy surface insulation performance will be enhanced obviously and the surface charge dissipation will be accelerated.

Simulation of Partial Discharges in Single and Double Voids Using SIMULINK

Partial discharges (PD) in the insulation of power equipment have been a focal point in the field of electrical technology. Numerical simulation of PD is an important approach to knowing the PD mechanics. In this paper, the physical model of PD in voids was modified and the simulation circuit of PD in voids was built using Simulink. The simulations of the epoxy resin samples with a single void and double voids were investigated, respectively. The discharge voltage waveforms, discharge current waveforms, and the single discharge waveforms of voids were obtained by simulation. At the same time, we measured the PD pulse waveforms of epoxy resin samples in time-domain by an ultra-wideband PD measuring system. The test samples enclosing artificial voids have the same size as the simulation samples. The single discharge waveforms of a single void and double voids obtained by simulation are very similar to the measured ones in the same condition. Moreover, the different discharge rules between one void and two voids are found by simulation. The conformity of the simulation results and test ones indicates that the simulation model is effective and the simulation results are reliable

Investigation on the Time-Varying Inductance Gradient of Railgun

The inductance gradient of railgun is one of the key factors in the EM railgun launcher. Generally, people take it as a constant value during simulation, but in fact it is variable in firing. Better understanding of the inductance gradient during launching is helpful to the predicting of the armature transition velocity. To obtain the waveform of the time-varying inductance gradient, the experimental current waveform was analyzed with time-frequency analysis tools. Thus the frequency-time waveform (f-t waveform) of the load current was obtained. The 3-D railgun model was setup in Maxwell 3D modular of Ansoft Corporation. Frequency points of the f-t waveform corresponding with B-dot signals were input to the simulation model to calculate the corresponding inductance gradient and the time-varying inductance gradient was gained. It is indicated that the inductance gradient of the railgun is decreased rapidly before the load current reaches its peak value. The propelling force on the armature is calculated with the inductance gradient waveform and the load current waveform. The armatures mass will show pseudo increase at the rise of current and decrease rapidly when the armatures wings are soft enough.

Development of a phased array sparker

Most of the metallogenic belt of metal ores are in the orogenic belt, the surface and subsurface geological conditions are very complicated, the conventional seismic exploration techniques can not meet the requirements of the seismic exploration, such as dynamite source, vibrator, airgun and the sparker. A phased array sparker was developed for this potential application, which mainly consists of nine modular sparker, a programmable pulse generator and nine ground transducers which can be easily inserted into the ground. Each sparker includes an isolated diode, a capacitor with a stored energy of 500 J and a thyristor discharge switch. The programmable pulse generator was used to control the discharging time of each sparker. The transducer used to convert the electric energy into the seismic wave energy has a hermetical discharging chamber filled with salt solution. The preliminary tests were presented.

Experimental Study on Sound Characteristics Produced by DC Corona and Pulsed Discharges

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.

Polarity effect on corona discharge of needle-plane electrodes and audible noise under DC voltage

The corona discharge and audible noise in different polarities have different characteristics and rules. The experiment of sing point corona discharge under DC voltage was developed and the sound pressure produced by corona discharge was measured. The amplitude and pulse characteristics of needle-plane corona discharges were studied. The sound pressure in time domain was measured by capacitor microphone. The discharge current and sound pressure waveforms in different voltages and polarities were obtained. The research results indicate the DC corona discharges were composed of a series of pulsed discharges. The rising edge and pulse width of single discharge pulse have relation to discharge voltage and electrode polarity. The amplitude and pulse width of current pulse in positive corona discharge is higher than that in negative corona discharge. The corona discharge produces the sound pressure with a microsecond pulse lagging behind the single discharge pulse in their waveforms. The time delay between current pulse and sound pulse is mainly caused by sound propagation time from discharge spot to measurement spot. Whether there is sound pulse is mainly decided by the amplitude and pulse width of corona discharge current. The audible noise has positive correlation with the sound pressure. So the audible noise produced by positive corona discharge is higher than that produced by negative corona discharge. At the same time, the sound pressure has relation to the discharge repetitiveness. The research result provides the foundation to go deep into the audible noise mechanism of transmission lines.