Study on the effects of gas pressure on the liftoff of spherical particles under electric field

Abstract

The gas insulated switchgears are widely used in high voltage substation due to their advantages, such as smaller space requirement, less frequent requirement for maintenance, high operational reliability and safety. The failures in gas insulated switchgears due to the contamination of conducting particles are critical. This thesis studied the experiments on the lifting electric field of spherical particles under different gas types and pressures between parallel electrodes. The electrode gap was 10 mm. The various materials and sizes of spherical particles were used. The particle radius was 0.4, 0.68 and 1.19 mm for aluminum, 0. 5 mm for steel, and 1 mm for stainless steel spheres. We carried out the experiments under pressures of 0.5, 0.75, 1, 2 and 3 bar for the air, and 1 and 3 bar for a mixture of air/SF6 and air/N2. The proportion of gas mixtures was 1:1. The experimental results indicated that the particle liftoff depended on the pressure and the particle size for all gas media. The lifting electric field increased significantly with increasing the pressures and particle sizes. In addition, the lifting electric field of particle liftoff in the gas mixtures was smaller than that in the air under same pressure for each particle size. The difference in lifting electric field from positive and negative voltage was clear under 3 bar pressure or the particle of 0.4 mm radius in the air. However, the case of the gas mixtures indicated that the difference in the lifting electric field was significantly reduced. The difference between the electrostatic force and the gravitational force increased approximately by a linear relationship with the product of particle surface area and gas pressure. The force difference of the gas mixtures was smaller than that of the air.