Dielectric Behavior of Compact Design Three Phase Coated Gas Insulated Busduct with Metallic Particle Contamination
The use of a gaseous medium with higher dielectric strength like sulphur hexafluoride (SF6) instead of air helps in manifold reduction in the size of the sub-station component. Compact GIS systems are essentially three-phase common systems with more than one functional element in one enclosure. Metallic particles can be either free to move in the GIS or they may be tuck either to an energized electrode or to an insulator surface. If a metallic particle crosses the gap and comes into contact with the inner electrode or if a metallic particle adheres to the inner conductor, the particle will act as a protrusion on the surface of the electrode, and the voltage required for breakdown of the GIS will also cause a significant reduction of the breakdown voltage. One method of conducting particle control and deactivation is by coating the inner surface of the outer enclosure. To determine the particle trajectories in a three-phase common enclosure gas insulated busduct (GIB) an outer enclosure of diameter 500 mm and inner conductors of diameters 64 mm spaced equilaterally are considered. Aluminum, copper and silver particles were considered to be present on enclosure surface. Simulation of particle movement with reduced phase conductor is also carried out with a view to obtain optimum size of conductor for reliable operation by reducing the original diameter of the conductor from 64 mm to 54 mm in steps of 5 mm.
Dynamics of metallic particle contaminants in GIS with dielectric-coated electrodes
Electrical insulation performance of compressed gas insulated switchgear (GIS) and gas insulated transmission line (GITL) systems is adversely affected by metallic particle contaminants. Dielectric coatings applied to the inside surface of the outer enclosure of a coaxial GIS/GITL system improve the insulation performance in several ways. Coating has the effect of smoothing the electrode surface and reducing the prebreakdown current in the gas gap. Also, the electrostatic charge acquired by a particle is reduced and hence the range of its motion under an applied power frequency field is inhibited. The movement of such particles is complex and dependent on several parameters. In this paper the dynamics of wire particles in a coaxial system under AC voltage is studied when the inside surface of the outer enclosure of a coaxial GIS/GITL system is coated with a high resistance material. Suggestions for reducing the particle excursion in GIS/GITL systems are discussed.
New particle-control techniques for gas-insulated apparatus
The feasibilities of two new methods of controlling contaminating particles in gas-insulated apparatus have been experimentally investigated. The first method is to coat the particles with an insulating layer: for the first time it was found that (1) coatings can render harmless particles that would otherwise lower the withstand voltage by factors of 2 to 5 and (2) coatings can be formed on particles residing in the system. The second method, trapping particles in an insulating material, was found effective also, and suitable materials were compounded for different temperature ranges.