V A Panov

Electrical breakdown voltage of transformer oil with gas bubbles

Electrical breakdown strength of liquid-gas micro bubble mixtures of transformer oil with sulfur hexafluoride and air for the case of quasi homogeneous gas inclusions distribution and 10% volumetric gas content was experimentally investigated. DC voltage up to 140 kV was applied to a 8 mm gap between hemispherical electrodes. It is shown that transformer oil bubbled with air leads to threshold breakdown voltage decrease by 34% and 19% when bubbled with sulfur hexafluoride. The stabilization effect of sulfur hexafluoride micro bubbles on the value of threshold breakdown voltage is observed.

Electrical breakdown of soil under nonlinear pulsed current spreading

Laboratory investigations on pulsed current spreading from spherical electrodes and evolution of electrical breakdown of silica sand with different water contents under a 15–20 kV voltage pulse were carried out. A sharp nonlinear decrease in the pulsed resistance of soil was observed when the current density exceeded a certain threshold value. Then ionization-overheating instability develops and leads to current contraction and plasma channel formation in the soil. The method for determination of the threshold electric field for ionization is proposed. Electrical discharge in wet sand was found to develop with a significant delay time for long discharge gaps similar to thermal breakdown.

Pulsed electrical discharge in conductive solution

Electrical discharge in a conductive solution of isopropyl alcohol in tap water (330 S cm−1) has been studied experimentally applying high voltage millisecond pulses (rise time ~0.4 , amplitude up to 15 kV, positive polarity) to a pin anode electrode. Dynamic current–voltage characteristics synchronized with high-speed images of the discharge were studied. The discharge was found to develop from high electric field region in the anode vicinity where initial conductive current with density ~100 A cm−2 results in fast heating and massive nucleation of vapor bubbles. Discharges in nucleated bubbles then produce a highly conductive plasma region and facilitate overheating instability development with subsequent formation of a thermally ionized plasma channel. The measured plasma channel propagation speed was 3–15 m s−1. A proposed thermal model of plasma channel development explains the low observed plasma channel propagation speed.

Nonlinear Impulse Current Spreading and Electrical Breakdown in Soil

The results of laboratory experiments on the impulse current spreading from the spherical electrodes and the breakdown occurring in quartz sand of various humidity at the impulse voltages of 20–40 kV are presented. It is shown that, at the current densities on the electrode above some critical value, a sharp nonlinear decrease of the impulse grounding resistance occurs, an ionization-superheating instability develops, and thus the current contraction takes place and a plasma channel in the soil occurs. A method is proposed to determine the critical strength of the ionization electric field. It was discovered that, at long discharge gaps in humid sand, the breakdown develops with a long time delay, similarly to thermal breakdown.

Supersonic plasmatron nozzle profiling with the real properties of high temperature working gas

The effects of real gases (excitation of vibrational degrees of freedom, dissociation and ionization) taken into account for supersonic nozzle profiling. The paper presents the method of the supersonic nozzle profiling for non-monotonic dependence of adiabatic index on temperature. The results of nozzle profile calculation for two sets of input parameters, based on independently determined specific heat for molecular nitrogen N2 and products of its thermal decomposition in the temperature range of 260–105 K and atmospheric pressure are presented. The experimental set-up based on proposed method of supersonic nozzle has been developed and manufactured. The gas velocity at different distances from the nozzle outlet has been measured. Results show the existence of the supersonic and transsonic flow regimes after the nozzle.

Evolution of electrical discharge channel in isopropyl alcohol solution

Evolution of the spark channel created by the high voltage pulse generator in 15% isopropyl alcohol solution in tap water was investigated experimentally. Fast camera images show the start of spark discharge channel with the anode region glowing, which is due to ionization-overheating instability near the surface of anode electrode. Measured propagation velocity is about 4 m/s and points to thermal process of channel evolution. Partial discharges in gas bubbles near the spark channel were observed. When the channel bridges the gap the cathode flash of lightning occurs which is much brighter than anode glowing and channel one. After destruction of the spark channel the cathode glowing stays for a longer period than anode one.

Overvoltage effect on electrical discharge type in medium-conductivity water in inhomogeneous pulsed electric field

The transition between thermal and streamer discharges has been observed experimentally in water solution with conductivity 100 μS/cm applying positive voltage pulses to pin-to-rod electrodes. The transition happens at five-fold pulse amplitude. Considering streamer propagation as an ionization wave helped to establish relation between the parameters governing transition from one to another discharge mechanism.

Limit charge of particulates at their ejection from plane electrode

Laboratory experiments on both metal and dielectric polarized solid particle levitation between plane electrodes at static electric field are performed. The dependence of particles charge on their mass is studied. The particle charge is found to increase with particle mass. The method to obtain extremely high electric charge on particles at atmospheric pressure is introduced. The maximum electric charge 2.8 × 107e is achieved in experiments with heavy metal particles.