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.
Electric field effect on metallic particle contamination in a common enclosure gas insulated busduct
Sulphur hexaflouride (SF6) is generally found to be very sensitive to field perturbations such as those caused by conductor surface imperfections and by conducting particle contaminants. A study of CIGRE group suggests that 20% of failures in gas insulated substations (GIS) is due to the existence of various metallic contaminations in the form of loose particles. The presence of contamination can therefore be a problem with gas-insulated substations operating at high fields. If the effects of these particles could be eliminated, then this would improve the reliability of compressed gas insulated substation. It would also offer the possibility of operating at higher fields to affect a potential reduction in the GIS size with subsequent savings in the cost of manufacture and installation. The purpose of this paper is to develop techniques, which will formulate the basic equations that will govern the movement of metallic particles like aluminum and copper in a bus duct. The simulation considers the electric field effect on particle movement and the results have been presented and analyzed
A new method of near field analysis
The problem of the accurate determination of the total electromagnetic field produced by a current distribution on a circular disc type aperture is examined. For comparison of the near and Fresnel region solutions, an exact Maxwellian integral is used as the starting point. Aperture and space coordinates are separated by the use of Bessel function addition theorems, allowing the field to be expressed as a sum of terms containing radial and angular integrals. The radial integrals involve only the disc (aperture) distribution and coordinates while the angular integrals involve only the elevation angle. The distance from origin appears implicitly in the series coefficients. These integrals are suitable for high speed computations and have been evaluated for a number of cases. The results are compared with the small angle and general Fresnel formula values for various observation angles, distances from the aperture, and aperture distributions.