The Research On The Characteristics Of Two-Phase Mixture Discharges Under Lightning Impulse Voltage

A two-phase mixture (TPM) is a mixture of gas and macroparticles of high concentration, and there has been significant interest in many technical applications and natural phenomena concerning two phase-mixture discharge (TPMD). As one type of important discharges, TPMD is a fundamental and important physical mechanism to better understand the basic problems associated with the physics of TPMD and lead to the optimal solution of engineering problems, as well as find out physical explanations for the natural phenomena concerning TPMD, but until now there is no widely accepted analysis for TPMD.In textual research, it follows a main line that focuses on the difference between gas discharge and TPMD. Experiment investigations concentrate on the characteristics of TPMD in non-uniform field, at atmospheric pressure, which are directly bound up with the electrical insulation, and effects of macroparticle sizes, dielectric constant, volume fraction of materials on TPMD are systematically studied in this work.TPMD under lightning impulse voltage is the only type of important discharge in this work. These TPMs include gas-liquid TPMs and gas-solid TPMs. Water is used to produce droplets suspended in the air as gas-liquid TPMs; solid materials are used to produce particles in the air as gas-solid TPMs. For experimental feasibility and easy analysis, macroparticles in a TPM are a single compound (excluding smoke) with one particle size distribution. Experimental facilities and methods are described in second chapter of this work. For quantitative analysis, the sizes and volume fractions of macroparticles in 21 kinds of TPMs are measured by PIV system, microscope, etc.Based on directly contrast the breakdown voltages and the percentages of the discharge path in TPMs with that in air, it reveals whether TPMs are suitable for the discharge development or not mainly depends on the macroparticle sizes, regardless of organic or inorganic materials, solid or liquid materials. When D< 0.01 mm, the percentage of the selection of TPMs is always smaller than 50%, and the break voltage in TPMs is greater than that in air; when D> 0.1 mm, the percentage is greater than 50%, and the break voltage in TPMs is smaller than that in air; when 0.01 mm< D< 0.1 mm, the percentage is smaller than 50% under positive LIs and the break voltage in TPMs is greater than that in air but above 50% under negative LIs and the break voltage in TPMs is smaller than that in air. The break voltage in TPMs and the percentage of the selection of TPMs vary with the relative dielectric constant and volume fraction of macroparticles in TPMs, but don't reverse the trends of the variation. Based on the experimental observation and electric field analysis, the diameter, dielectric constant and volume fraction of macroparticles are used to analyze the mechanism of macroparticle size effects on TPMD. Three factors should be considered in TPMD:(1) The seed electrons for the formation of avalanches in the streamer front or the electrons in avalanches are easily captured by macroparticles; (2) In the path of the streamer, the macroparticle removes charge from the streamer, slowing it and in some cases preventing the streamer from further propagation; (3) The maximum field value and the distorted field range around the macroparticles are incseasing with increasing the diameters of macroparticles. The factors in aggregate are changed with the different kinds of the diameters of macroparticles. Even if the dielectric constant and volume fraction of macroparticles are hold, the diameters reverse the variation of the selection percentage in TPMs. Therefore, whether TPMs are suitable for the discharge development or not mainly depends on the macroparticle sizes, regardless of organic or inorganic materials, solid or liquid materials.