| Electrical insulation performance of compressed gas insulated switchgear (GIS) and gas insulated transmission line (GITL) systems is adversely affected by metallic particle contaminants with a loss of up to 90% of the gas dielectric strength. Such particles play a crucial role in determining the system insulation integrity. However, the inside surface of GIS/GITL enclosures may be coated with a dielectric material to alleviate the adverse effect of contaminating metallic particles on insulation withstand.; In the present research, the control of metallic particles in compressed GIS/GITL by dielectric coating of the enclosure is studied both theoretically and experimentally. Particle dynamics, particle charge and lift-off field, and SF6 breakdown probability are the highlights of the research. The study shows that coating the enclosure would impede the charge a particle can acquire; hence, inhibit the particle movement and minimize the probability of insulation breakdown.; A theoretical model of particle movement is discussed, which is used to simulate the particle motion in coaxial systems under AC applied voltages. The effects of the applied voltage, gas pressure, and particle size are demonstrated. Meanwhile, the charging process of a particle with coated enclosure is considered under both conduction and microdischarge mechanisms. Lift-off fields are calculated accordingly. Calculation results show that a combination of the two mechanisms may contribute to the particle charging process. Based on the particle movement model and the concept of breakdown voltage profile, the calculation of SF 6 breakdown probability is introduced.; The present work focuses on wire particles in coaxial electrode systems with applied AC voltages. However, the theoretical models can be extended to other particle shapes and sizes, system configurations, and applied voltages. Experiments were conducted in order to study particle dynamics and measure lift-off fields. Results of laboratory experiments—conducted at Chalmers University—to verify the validity of computational models are presented. |
